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Welding and NDT Management + Statutory and Regulatory Act

Board of Studies

Prof. H. N. Verma Prof. M. K. GhadoliyaVice- Chancellor Director, Jaipur National University, Jaipur School of Distance Education and Learning Jaipur National University, JaipurDr. Rajendra Takale Prof. and Head AcademicsSBPIM, Pune

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Subject Expert Panel

Prof. Milind M. Kulkarni Ashwini PanditProfessor, Sinhgad College of Engineering Subject Matter ExpertPune

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Content Review Panel

Tejaswini MulaySubject Matter Expert

___________________________________________________________________________________________Copyright ©

This book contains the course content for Welding and NDT Management + Statutory and Regulatory Act.

First Edition 2013

Printed byUniversal Training Solutions Private Limited

Address05th Floor, I-Space, Bavdhan, Pune 411021.

All rights reserved. This book or any portion thereof may not, in any form or by any means including electronic or mechanical or photocopying or recording, be reproduced or distributed or transmitted or stored in a retrieval system or be broadcasted or transmitted.

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I

Index

Content ...........................................................................................................................................................IIList of Figures .............................................................................................................................................VIIList of Tables ..................................................................................................................................................XAbbreviations ............................................................................................................................................... XICase Study ................................................................................................................................................. 163Bibliography .............................................................................................................................................. 168Self Assessment Answers ........................................................................................................................... 171Book at a Glance

II

Contents

Chapter I ....................................................................................................................................................... 1Introduction to Welding .............................................................................................................................. 1Aim ................................................................................................................................................................ 1Objectives ...................................................................................................................................................... 1Learning outcome .......................................................................................................................................... 11.1 Introduction - Shielded Metal Arc Welding (SMAW) ............................................................................. 2 1.1.1 Equipments used in Shielded Metal Arc Welding ................................................................... 21.2 Gas Metal Arc Welding (GMAW) ........................................................................................................... 3 1.2.1 Equipments Required for Gas Metal ARC Welding ................................................................ 41.3 Submerged Arc Welding (SAW) .............................................................................................................. 4 1.3.1 Equipments Required for Submerged ARC Welding .............................................................. 51.4 Gas Tungsten ARC Welding (GTAW) ..................................................................................................... 6 1.4.1 Equipments Required for Gas Tungsten Arc Welding ............................................................. 71.5 Welding of Stainless Steels ...................................................................................................................... 7 1.5.1 Problem Areas .......................................................................................................................... 8Summary ....................................................................................................................................................... 9References ..................................................................................................................................................... 9Recommended Reading ............................................................................................................................... 9Self Assessment ........................................................................................................................................... 10

Chapter II ................................................................................................................................................... 12Welding Procedure, Performance Qualification and Welding Variables ............................................. 12Aim .............................................................................................................................................................. 12Objectives .................................................................................................................................................... 12Learning outcome ........................................................................................................................................ 122.1 Welding Procedure and Performance Qualification ............................................................................... 132.2 Welding Variables .................................................................................................................................. 132.3 Joint Types ............................................................................................................................................. 14 2.3.1 Butt Joint ................................................................................................................................ 14 2.3.2 Corner and T – Joint .............................................................................................................. 14 2.3.3 Lap Joint ................................................................................................................................ 15 2.3.4 Edge Joint .............................................................................................................................. 152.4 Parts of Joints ......................................................................................................................................... 152.5 Edge Shapes ........................................................................................................................................... 182.6 Single Groove Weld Joints ..................................................................................................................... 192.7 Double Groove Weld Joints ................................................................................................................... 202.8 Types of Welds ....................................................................................................................................... 21 2.8.1 Groove Welds ......................................................................................................................... 22 2.8.2 Fillet Welds ............................................................................................................................ 23 2.8.3 Pipe Welds - Groove Welds ................................................................................................... 242.9 Parts of Weld .......................................................................................................................................... 262.10 Weld Sizes ............................................................................................................................................ 302.11 Complete Fusion .................................................................................................................................. 322.12 Incomplete Fusion ................................................................................................................................ 332.13 Fusion Welds ........................................................................................................................................ 34Summary ..................................................................................................................................................... 36References ................................................................................................................................................... 36Recommended Reading ............................................................................................................................. 36Self Assessment ........................................................................................................................................... 37

Chapter III .................................................................................................................................................. 39Pressure Welding and Cutting Methods .................................................................................................. 39Aim .............................................................................................................................................................. 39

III

Objectives .................................................................................................................................................... 39Learning outcome ........................................................................................................................................ 393.1 Pressure Welding Methods ..................................................................................................................... 403.2 Resistance Welding ................................................................................................................................ 40 3.2.1 Spot Welding .......................................................................................................................... 40 3.2.1.1 Important Parameters of Spot Welding .................................................................. 42 3.2.2 Seam Welding ........................................................................................................................ 42 3.2.3 Projection Welding ................................................................................................................. 43 3.2.4 Resistance Butt Welding ....................................................................................................... 44 3.2.5 Flash Welding ........................................................................................................................ 443.3 Friction Welding .................................................................................................................................... 45 3.3.1 Friction Surfacing .................................................................................................................. 45 3.3.2 Friction Stir Welding .............................................................................................................. 453.4 High Frequency Welding ....................................................................................................................... 473.5 Ultrasonic Welding ................................................................................................................................ 473.6 Diffusion Welding .................................................................................................................................. 473.7 Cutting Methods..................................................................................................................................... 473.8 Thermal Cutting ..................................................................................................................................... 47 3.8.1 Oxy-fuel Cutting .................................................................................................................... 47 3.8.2 Plasma Cutting ....................................................................................................................... 49 3.8.3 Laser Cutting .......................................................................................................................... 50 3.8.4 Water Jet Cutting .................................................................................................................... 503.9 Thermal Gouging ................................................................................................................................... 51 3.9.1 Oxy- fuel Gas Flame Gouging ............................................................................................... 51 3.9.2 Air Carbon Arc Gouging ........................................................................................................ 51 3.9.3 Manual Metal Arc Gouging ................................................................................................... 52 3.9.4 Plasma Arc Gouging .............................................................................................................. 523.10 Care and Storage of Electrodes ............................................................................................................ 52Summary ..................................................................................................................................................... 53References ................................................................................................................................................... 53Recommended Reading ............................................................................................................................. 54Self Assessment ........................................................................................................................................... 55

Chapter IV .................................................................................................................................................. 57Soldering, Brazing and Design of Welded Components ......................................................................... 57Aim .............................................................................................................................................................. 57Objectives .................................................................................................................................................... 57Learning outcome ........................................................................................................................................ 574.1 Introduction ............................................................................................................................................ 58 4.1.1 Types of Joints ....................................................................................................................... 584.2 Soft Soldering ........................................................................................................................................ 594.3 Brazing ................................................................................................................................................... 604.4 Braze Welding ........................................................................................................................................ 624.5 Arc Brazing ............................................................................................................................................ 624.6 Laser Beam Brazing ............................................................................................................................... 634.7 Symbolic Representation of Welds on Drawings .................................................................................. 63 4.7.1 Elementary Symbols and Supplementary Symbols ............................................................... 64 4.7.2 The Importance of the Reference Lines ................................................................................. 64 4.7.3 The Position of the Arrow Line ............................................................................................. 65 4.7.4 Complementary Symbols ....................................................................................................... 664.8 Design Consideration ............................................................................................................................. 67 4.8.1 Design to Transfer Local Forces ............................................................................................ 68 4.8.2 Design as Determined by the Type of Load ........................................................................... 69 4.8.2.1 Tensile Loads ........................................................................................................... 70 4.8.2.2 Compressive Loads ................................................................................................. 70

IV

4.8.2.3 Shear Loads ............................................................................................................. 70 4.8.2.4 Bending Loads ........................................................................................................ 70 4.8.2.5 Torsional loads ........................................................................................................ 71 4.8.3 Design to Resist Corrosion .................................................................................................... 71 4.8.4 Design for Production ............................................................................................................ 73Summary ..................................................................................................................................................... 74References ................................................................................................................................................... 74Recommended Reading ............................................................................................................................. 74Self Assessment ........................................................................................................................................... 75

Chapter V .................................................................................................................................................... 77Quality Assurance and Quality Management ......................................................................................... 77Aim .............................................................................................................................................................. 77Objectives .................................................................................................................................................... 77Learning outcome ........................................................................................................................................ 775.1 Introduction ............................................................................................................................................ 785.2 Quality Requirements for Welding (EN 729) ........................................................................................ 785.3 Welding Coordination (EN 719) ............................................................................................................ 795.4 Specification and Approval of Welding Procedures (EN 288) .............................................................. 81 5.4.1 General Rules (En 288 – 1) .................................................................................................... 81 5.4.2 Welding Procedures Specification (EN 288 – 2) ................................................................... 82 5.4.3 Welding Procedure Tests for Arc Welding of Steel (EN 288 -3) ........................................... 82 5.4.4 Welding Procedure Test for Arc Welding of Aluminium and its Alloys (EN 288 – 4) .......... 83Summary ..................................................................................................................................................... 86References ................................................................................................................................................... 86Recommended Reading ............................................................................................................................. 86Self Assessment ........................................................................................................................................... 87

Chapter VI .................................................................................................................................................. 89NDT Management ...................................................................................................................................... 89Aim .............................................................................................................................................................. 89Objectives .................................................................................................................................................... 89Learning outcome ........................................................................................................................................ 896.1 Introduction to Non-Destructive Testing ............................................................................................... 906.2 Radiography Testing (RT) ...................................................................................................................... 906.3 Ultrasonic Testing (UT) ......................................................................................................................... 956.4 Magnetic Particle Testing (MT) ............................................................................................................. 966.5 Liquid Penetrant Testing (PT) ............................................................................................................... 986.6 Leak Testing (LT) ................................................................................................................................. 1006.7 Visual Testing (VT) .............................................................................................................................. 1026.8 Discontinuities ..................................................................................................................................... 1036.9 Applications of NDT in Marine Environment ..................................................................................... 104 6.9.1 Methods of NDT used in Marine Applications .................................................................... 1046.10 Pressure Tests (Leak Test or LT) ........................................................................................................ 105Summary ................................................................................................................................................... 106References ................................................................................................................................................. 106Recommended Reading ........................................................................................................................... 106Self Assessment ......................................................................................................................................... 107

Chapter VII .............................................................................................................................................. 109The Petroleum Act, Petroleum Rules and the Indian Boilers Act ...................................................... 109Aim ............................................................................................................................................................ 109Objectives .................................................................................................................................................. 109Learning outcome ...................................................................................................................................... 1097.1 Introduction ...........................................................................................................................................110

V

7.2 Flammable Substance – Specific Precautions .......................................................................................1117.3 Extraction from Factory Rule (Maharashtra) 1963 ...............................................................................1127.4 Comments on The Indian Boilers Act, 1923 .........................................................................................113 7.4.1 Steam-pipes and Fittings .......................................................................................................114 7.4.2 Mechanical Tests ...................................................................................................................115 7.4.3 Method of Manufacture, Heat Treatment and Marking .......................................................1167.5 Flanges ..................................................................................................................................................117 7.5.1 Screwed on Flanges ..............................................................................................................118 7.5.2 Welded on Flanges ................................................................................................................1187.6 ASME Boiler and Pressure Vessel Code ...............................................................................................118 7.6.1 Code System .........................................................................................................................119 7.6.2 Issue Frequency ....................................................................................................................119 7.6.3 Applicability ..........................................................................................................................119 7.6.4 Code Interpretation ...............................................................................................................119 7.6.5 Code Cases ............................................................................................................................119 7.6.6 Salient Features of ASME Codes ......................................................................................... 1207.7 Erection Procedure for Field Erected Vertical Storage Tanks .............................................................. 120Summary ................................................................................................................................................... 122References ................................................................................................................................................. 122Recommended Reading ........................................................................................................................... 122Self Assessment ......................................................................................................................................... 123

Chapter VIII ............................................................................................................................................. 125Statutory and Regulatory Act ................................................................................................................. 125Aim ............................................................................................................................................................ 125Objectives .................................................................................................................................................. 125Learning outcome ...................................................................................................................................... 1258.1 Introduction to ASME Piping Codes ................................................................................................... 126 8.1.1 Pressure Piping Codes – B 31 .............................................................................................. 126 8.1.2 Code Revisions and Updating .............................................................................................. 1278.2 Review of Piping Fundamentals .......................................................................................................... 127 8.2.1 Butt Welded Fittings ............................................................................................................ 128 8.2.2 Socket Welded Fittings ........................................................................................................ 129 8.2.3 Flanged Fittings ................................................................................................................... 1298.3 Scope and Extent of ASME B 31.1 ...................................................................................................... 1308.4 Piping Engineering – Statutory/State and Local Body Regulations .................................................... 130 8.4.1 Chief Controller of Explosives (CCE or CCOE) ................................................................. 130 8.4.2 Static and Mobile Pressure Vessels Rules (SMPV Rules) ................................................... 131 8.4.3 Oil Industry Safety Directorate (OISD) Rules ..................................................................... 132 8.4.4 Indian Boiler Regulations (IBR) .......................................................................................... 132 8.4.5 Environmental and Pollution Control Regulations .............................................................. 132 8.4.6 The Chief Inspector of Factories (The State Inspector of Health and SAFETY) Regulations 133 8.4.7 State Industrial Development Corporation (SIDC) Rules .................................................. 133 8.4.8 Traffic Advisory Committee (TAC) and Loss Prevention Association (LPA) Rules ........... 134 8.4.9 Director General of Civil Aviation (DGCA) Rules .............................................................. 134 8.4.10 Indian Electrical Rules ....................................................................................................... 1358.5 Regulations Pertaining to Storage, Usage and Transportation of Hazardous Chemicals .................... 135 8.5.1 Hazardous Chemicals .......................................................................................................... 1368.6 Storage ................................................................................................................................................. 136 8.6.1 Solid Storage ........................................................................................................................ 136 8.6.2 Liquid Storage ...................................................................................................................... 136 8.6.3 Gas Storage .......................................................................................................................... 1378.7 Responsibility for Safety ...................................................................................................................... 1378.8 Preparation of Equipment .................................................................................................................... 138 8.8.1 Isolation of Equipments from Hazards ................................................................................ 138

VI

8.9 Preventive Maintenance ....................................................................................................................... 1388.10 Transportation .................................................................................................................................... 138Summary ................................................................................................................................................... 140References ................................................................................................................................................. 140Recommended Reading ........................................................................................................................... 140Self Assessment ......................................................................................................................................... 141

Chapter IX ................................................................................................................................................ 143Standard Symbols for Welding ............................................................................................................... 143Aim ............................................................................................................................................................ 143Objectives .................................................................................................................................................. 143Learning outcome ...................................................................................................................................... 1439.1 Introduction .......................................................................................................................................... 1449.2 General Provisions for Welding Symbols ............................................................................................ 145 9.2.1 Location Significance of Arrow ........................................................................................... 145 9.2.2 Location of Weld with Respect to Joint ............................................................................... 147 9.2.3 Orientation of Specific Weld Symbols................................................................................. 148 9.2.4 Break in Arrow ..................................................................................................................... 148 9.2.5 Combined Weld Symbols..................................................................................................... 149 9.2.6 Multiple Arrow Lines ........................................................................................................... 149 9.2.7 Multiple Reference Lines ..................................................................................................... 149 9.2.8 Field Weld Symbol............................................................................................................... 151 9.2.9 Extent of Welding Denoted by Symbols .............................................................................. 151 9.2.10 Weld-All-Around Symbol .................................................................................................. 152 9.2.11 Tail of the Welding Symbol ............................................................................................... 152 9.2.12 Contours Obtained by Welding .......................................................................................... 154 9.2.13 Finishing of Welds ............................................................................................................. 154 9.2.14 Melt-Through Symbol ....................................................................................................... 154 9.2.15 Melt-Through with Flange Welds ...................................................................................... 155 9.2.16 Method of Drawing Symbols ............................................................................................. 155 9.2.17 U.S. Customary and Metric Units ...................................................................................... 155 9.2.18 Weld Dimension Tolerance ................................................................................................ 155 9.2.19 Application of Arrow and Other Side Convention ............................................................. 155 9.2.20 Applications of Break in Arrow of Welding Symbol ......................................................... 156 9.2.21 Specification of Groove Weld Size Depth of Bevel Not Specified ................................... 157Summary ................................................................................................................................................... 159References ................................................................................................................................................. 159Recommended Reading ........................................................................................................................... 159Self Assessment ......................................................................................................................................... 160

VII

List of Figures

Fig. 1.1 Shielded metal arc welding ............................................................................................................... 2Fig. 1.2 SMAW equipment ............................................................................................................................ 3Fig. 1.3 Gas metal arc welding ...................................................................................................................... 3Fig. 1.4 GMAW equipment ............................................................................................................................ 4Fig. 1.5 Submerged arc welding .................................................................................................................... 5Fig. 1.6 Granular flux welding ....................................................................................................................... 6Fig. 1.7 Gas tungsten arc welding .................................................................................................................. 6Fig. 1.8 GTAW equipment ............................................................................................................................. 7Fig. 2.1 Root face and groove face (1) ......................................................................................................... 16Fig. 2.2 Root face and groove face (2) ......................................................................................................... 16Fig. 2.3 Root face and groove face (3) ......................................................................................................... 16Fig. 2.4 Root face and groove face (4) ......................................................................................................... 17Fig. 2.5 Bevel angle, depth of groove angle, groove radius and root opening (1) ....................................... 17Fig. 2.6 Bevel angle, depth of groove angle, groove radius and root opening (2) ....................................... 17Fig. 2.7 Bevel angle, depth of groove angle, groove radius and root opening (3) ....................................... 18Fig. 2.8 Single groove weld joints (1) .......................................................................................................... 19Fig. 2.9 Single groove weld joints (2) .......................................................................................................... 20Fig. 2.10 Single groove weld joints (3) ........................................................................................................ 20Fig. 2.11 Single groove weld joints (4) ........................................................................................................ 20Fig. 2.12 Double groove weld joints (1) ...................................................................................................... 20Fig. 2.13 Double groove weld joints (2) ...................................................................................................... 21Fig. 2.14 Double groove weld joints (3) ...................................................................................................... 21Fig. 2.15 Double groove weld joints (4) ...................................................................................................... 21Fig. 2.16 Welding position-groove welds (1) .............................................................................................. 23Fig. 2.17 Welding position-groove welds (2) .............................................................................................. 23Fig. 2.18 Welding position-fillet welds (1) .................................................................................................. 24Fig. 2.19 Welding position-fillet welds (2) .................................................................................................. 24Fig. 2.20 Welding position-pipe welds (1) ................................................................................................... 25Fig. 2.21 Welding position-pipe welds (2) ................................................................................................... 25Fig. 2.22 Welding position-pipe welds (3) ................................................................................................... 25Fig. 2.23 Welding position-pipe welds (4) ................................................................................................... 26Fig. 2.24 Parts of welds (1) .......................................................................................................................... 26Fig. 2.25 Parts of welds (2) .......................................................................................................................... 26Fig. 2.26 Parts of welds (3) .......................................................................................................................... 27Fig. 2.27 Parts of welds (4) .......................................................................................................................... 27Fig. 2.28 Parts of welds (5) .......................................................................................................................... 27Fig. 2.29 Parts of welds (6) .......................................................................................................................... 28Fig. 2.30 Parts of welds (7) .......................................................................................................................... 28Fig. 2.31 Parts of welds (8) .......................................................................................................................... 28Fig. 2.32 Parts of welds (9) .......................................................................................................................... 29Fig. 2.33 Parts of welds (10) ........................................................................................................................ 29Fig. 2.34 Parts of welds (11) ........................................................................................................................ 29Fig. 2.35 Parts of welds (12) ........................................................................................................................ 30Fig. 2.36 Convex fillet weld ........................................................................................................................ 30Fig. 2.37 Concave fillet weld ....................................................................................................................... 31Fig. 2.38 Fillet weld with incomplete fusion ............................................................................................... 31Fig. 2.39 T-joint with root opening .............................................................................................................. 32Fig. 2.40 Complete fusion (1) ...................................................................................................................... 32Fig. 2.41 Complete fusion (2) ...................................................................................................................... 32Fig. 2.42 Complete fusion (3) ...................................................................................................................... 33Fig. 2.43 Complete fusion (4) ...................................................................................................................... 33Fig. 2.44 Incomplete fusion (1) .................................................................................................................... 33Fig. 2.45 Incomplete fusion (2) .................................................................................................................... 34

VIII

Fig. 2.46 Incomplete fusion (3) .................................................................................................................... 34Fig. 2.47 Fusion welds (1) ........................................................................................................................... 34Fig. 2.48 Fusion welds (2) ........................................................................................................................... 35Fig. 2.49 Fusion welds – surfacing weld ..................................................................................................... 35Fig. 2.50 Fusion welds – resistance spot seam weld .................................................................................... 35Fig. 3.1 Five type of resistance welding ...................................................................................................... 40Fig. 3.2 The principle of spot welding ......................................................................................................... 41Fig. 3.3 Principle of Seam Welding ............................................................................................................. 43Fig. 3.4 Principle of projection welding ...................................................................................................... 43Fig. 3.5 Resistance butt welding .................................................................................................................. 44Fig. 3.6 Friction stir welding........................................................................................................................ 46Fig. 3.7 Typical cutting speeds for plasma cutting, oxy-fuel gas cutting and laser cutting ......................... 48Fig. 4.1 Butt overlap joints .......................................................................................................................... 58Fig. 4.2 Three times the thickness of the thinner part is a suitable lap length ............................................. 59Fig. 4.3 Different combinations of materials can result in the gap increasing or decreasing as the parts are raised to working temperature ......................................................... 59Fig. 4.4 Symbols used on welding drawings ............................................................................................... 63Fig. 4.5 Examples of elementary symbols ................................................................................................... 64Fig. 4.6 Supplementary symbols .................................................................................................................. 64Fig. 4.7 A T-joint with one fillet weld .......................................................................................................... 65Fig. 4.8 A cruciform joint with two fillet welds ........................................................................................... 65Fig. 4.9 Examples of symmetrical welds ..................................................................................................... 65Fig. 4.10 Position of the arrow line .............................................................................................................. 66Fig. 4.11 Complementary symbols .............................................................................................................. 66Fig. 4.12 Reference information .................................................................................................................. 66Fig. 4.13 Examples of change in stress flow ............................................................................................... 67Fig. 4.14 Schematic stress flow in various types of welded joints .............................................................. 67Fig. 4.15 Marked surfaces act like shells ..................................................................................................... 68Fig. 4.16 Beam with a hanger eye ................................................................................................................ 68Fig. 4.17 A hanger eye welded to the flange of a beam-poor design ........................................................... 69Fig. 4.18 Reinforcements transfer the load to the web of the beam ............................................................ 69Fig. 4.19 (a) shows a poor design, which has been improved as shown in (b). If the beam is subjected to horizontal forces, the attachment should be arranged as shown in (c) ....................................... 69Fig. 4.20 Bending stresses ........................................................................................................................... 70Fig. 4.21 (a) Torsion-resistant, closed (b) Low torsion-resistance, open ..................................................... 71Fig. 4.22 Centre of torsion (CT) for a number of sections. CG = Centre of Gravity .................................. 71Fig. 4.23 Designing to avoid corrosion ........................................................................................................ 72Fig. 4.24 Avoiding corrosion around welds ................................................................................................. 72Fig. 4.25 Designing for zinc-coating ........................................................................................................... 73Fig. 5.1 Standards that regulate quality requirements for welding structures ............................................. 78Fig. 6.1 Radiographic testing ....................................................................................................................... 93Fig. 6.2 Standard X8 ray tube and demonstration of geometric unsharpness .............................................. 94Fig. 6.3 Typical radiographic exposure arrangements for pipe welds ......................................................... 95Fig. 6.4 Penetrant testing method .............................................................................................................. 100Fig. 6.5 Indications of discontinuities ........................................................................................................ 103Fig. 6.6 Types of discontinuities ................................................................................................................ 104Fig. 9.1 Weld symbols ................................................................................................................................ 144Fig. 9.2 Standard location of elements of welding symbol ........................................................................ 145Fig. 9.3 Supplementary symbols ................................................................................................................ 145Fig. 9.4 General provisions ........................................................................................................................ 146Fig. 9.5 Location significance of arrow ..................................................................................................... 146Fig. 9.6 Arrow side..................................................................................................................................... 147Fig. 9.7 Other side ...................................................................................................................................... 147Fig. 9.8 Both sides ..................................................................................................................................... 148Fig. 9.9 Orientation or specific weld symbols ........................................................................................... 148

IX

Fig. 9.10 Break in arrow ............................................................................................................................ 148Fig. 9.11 Combined weld symbols ............................................................................................................. 149Fig. 9.12 Multiples arrows lines ................................................................................................................ 149Fig. 9.13 Sequence of operations ............................................................................................................... 150Fig. 9.14 Supplementary data .................................................................................................................... 150Fig. 9.15 Field weld and weld all-round symbol ....................................................................................... 151Fig. 9.16 Field weld symbol ...................................................................................................................... 151Fig. 9.17 Hidden members ......................................................................................................................... 152Fig. 9.18 Tail of the welding symbol ......................................................................................................... 152Fig. 9.19 References .................................................................................................................................. 153Fig. 9.20 Welding symbols designated typical .......................................................................................... 153Fig. 9.21 Designation of special types of welds ........................................................................................ 153Fig. 9.22 Omission of tail .......................................................................................................................... 153Fig. 9.23 R-rolling...................................................................................................................................... 154Fig. 9.24 Finishing method unspecified ..................................................................................................... 154Fig. 9.25 Weld dimension tolerance ........................................................................................................... 155Fig. 9.26 Arrow-side V-Groove weld symbol ............................................................................................ 155Fig. 9.27 Other-side V-Groove weld symbol ............................................................................................. 156Fig. 9.28 Both-sides V-Groove weld symbol ............................................................................................. 156Fig. 9.29 Arrow side................................................................................................................................... 156Fig. 9.30 Other side .................................................................................................................................... 157Fig. 9.31 Both sides ................................................................................................................................... 157Fig. 9.32 Specification of groove weld size depth of bevel not specified (1) ............................................ 157Fig. 9.33 Specification of groove weld size depth of bevel not specified (2) ............................................ 157Fig. 9.34 Specification of groove weld size depth of bevel not specified (3) ............................................ 158Fig. 9.35 Specification of groove weld size depth of bevel not specified (4) ............................................ 158Fig. 9.36 Specification of groove weld size depth of bevel not specified (5) ............................................ 158Fig. 9.37 Specification of groove weld size depth of bevel not specified (6) ............................................ 158

X

List of Tables

Table 2.1 Joint types .................................................................................................................................... 14Table 2.2 Edge shapes (1) ............................................................................................................................ 18Table 2.3 Edge shapes (2) ............................................................................................................................ 18Table 3.1 Examples of applications for a number of resistance welding methods ...................................... 45Table 4.1 List of combinations of normal types of solder ........................................................................... 60Table 4.2 Composition of common brazing filler metals............................................................................. 62Table 5.1 Requirement elements in EN 729 – 2 .......................................................................................... 79Table 5.2 Requirement elements in ISO 9001 in comparison with EN 729 – 2, – 3, – 4 ............................ 80Table 5.3 Numerical reference numbers of common fusion welding methods as given in ISO 4063 ......... 82Table 6.1 Equipments in magnetic particle testing ...................................................................................... 97Table 6.2 Techniques in magnetic particle testing ....................................................................................... 97Table 6.3 Techniques for visual testing ...................................................................................................... 102Table 7.1 Typical distances .........................................................................................................................110Table 7.2 Carbon Steels – Butt welded pipes .............................................................................................116Table 7.3 Maximum permissible working pressure and temperature .........................................................117

XI

Abbreviations

ANSI – American National Standards InstituteAWS – American Welding Society CCE / CCOE – Chief Controller of ExplosivesDGCA – Director General of Civil AviationDWDI – Double Wall Double ImageDWSI – Double Wall Single ImageERW – Electric Resistance WeldingETP – EffluentTreatmentPlantEWE – European Welding EngineerEWS – European Welding SpecialistEWT – European Welding TechnologistGIDC – Gujarat Industrial Development CorporationGMAW – Gas Metal Arc WeldingGTAW – Gas Tungsten ARC WeldingHSD – High speed dieselIBR – Indian Boiler RegulationsIP – Internal PressureLPA – Loss Prevention AssociationLPG – Liquid Petroleum GasLSHS – Low Sulphur High StockLT – Leak TestingMIDC – Maharashtra Industrial Development CorporationMT – Magnetic Particle TestingNDT – Non Destructive TestingNOD – Nominal Outside DiameterOISD – Oil Industry Safety DirectoratePQR – ProcedureQualificationRecordsPT – Liquid Penetrant TestingQW – QualificationofWeldersRT – Radiography TestingSAW – Submerged Arc WeldingSIDC – State Industrial Development CorporationSMAW – Shielded Metal Arc WeldingSMPV – Static and Mobile Pressure Vessels RulesSWSI – Single Wall Single ImageTAC – TrafficAdvisoryCommitteeTIG – Tungsten Inert GasUT – Ultrasonic TestingVT – Visual TestingWPAR – Welding Procedure Approval RecordsWPS – WeldingProcedureSpecificationsXS – Extra StrongXXS – Double Extra Strong

1

Chapter I

Introduction to Welding

Aim

The aim of this chapter is to:

introduce shield metal arc welding •

discuss gas metal arc welding •

describe the equipments required for gas metal arc welding•

Objectives

Objectives of this chapter are to:

explain submerged arc welding •

discuss the equipments required for gas tungsten arc welding•

elaborate gas tungsten arc welding •

Learning outcome

At the end of this chapter, you will be able to:

understand welding of stainless steels•

identify problem areas in welding of stainless steels•

comprehe• nd the equipments required for submerged arc welding


2

1.1 Introduction - Shielded Metal Arc Welding (SMAW)Shielded metal arc welding joins metals by heating with an electric arc between a covered metal electrode and the work piece. The melted electrode metal is transferred across the arc into the molten pool of base metals, becoming the depositedweldmetal.Aslagisformedfromtheelectrodecoatingandthebasemetalimpuritiesfloattothesurfaceand cover the deposit, protecting it from atmospheric contamination and controlling the cooling rate. Shielding of the weld comes from the breakdown or decomposition of the electrode covering. Quality welds require a protective shield from the harmful gases in the surrounding air. Filler metal comes from the electrode core wire and covering, which is made up of iron powder and alloying elements.

SMAW is sometimes referred to as ‘stick’ welding. It is the most widely used of all the processes we will talk about becauseofthesimplicityoftheequipment,highstrengthandqualityandthelowcost.Ithasmaximumflexibilityand welds most metals in a wide range of thicknesses. Welding with this process can be done almost anywhere and under extreme conditions.

It can be powered by gasoline or diesel if necessary. SMAW is used extensively in industrial fabrications, structural steel erections (buildings, bridges, etc.), box cars, trucks, dams and other commercial weldments.

Base Metal

Protective gas from electrode coating

Molten weld metal

Electrode coating

Electrode wire

Metal dropletSolidified

metal

ARC

Slag

Fig. 1.1 Shielded metal arc welding

1.1.1 Equipments used in Shielded Metal Arc Welding

The SMAW process is usually manually operated, but it can be automated with a machine or gravity ‘stick’ •feeder.Asshowninfig.1.2, thebasicequipmentconsistsofapowersource,cables,anelectrodeholder,aground clamp and the electrode.The power supply can be either alternating current, direct current electrode negative (straight polarity) or direct •current electrode positive (reverse polarity), depending on the job requirements. Direct current power supplies are often preferred because they are more versatile.TheelectrodeintheSMAWprocessservesseveralimportantfunctions.Itestablishesthearcandsuppliesfiller•metalforthewelddeposit.Thecoveringontheelectrode,knownastheflux,alsohasspecialcharacteristicsthat you should be aware of. Here is a list of some of these characteristics:

It provides a gas that shields the arc from atmospheric contamination. It provides scavengers, deoxidisers andfluxing agents to clean theweld and prevent excessive grain growth.It establishes the electrical characteristics of the electrode, meaning that the electrode covering determines

3

if ac or dc power supplies are to be used.It provides a blanket of slag that protects the metal while it is cooling and controls the cooling rate. It provides a way to add alloying elements to strengthen the weld.

CoveredelectrodesareclassifiedaccordingtospecificationsissuedbytheAmericanWeldingSociety.Commercial•specificationsforcoveredelectrodescanbefoundintheAWSASspecificationsseries.

Electrode holder Power

source

Electrode Electrode lead

Base metalWork lead

Fig. 1.2 SMAW equipment

1.2 Gas Metal Arc Welding (GMAW)GasmetalarcweldingorGMAW,usestheheatofanelectricarcbetweenacontinuously-fed,barefillermetal•electrode and the base metal. The heat melts the electrode end and the base metal surface to form the deposited weld metal.Shielding of the arc and the molten weld pool comes entirely from an externally supplied gas, which may be •inert, active or a mixture. This process is sometimes referred to as “MIG” welding. Figure below shows how this process works. Slag formed during SAW and SMAW processes does not form •withGMAW,asthereisnofluxused.However,aglass-likefilmofsilicaformsfromhighsiliconelectrodes,which must be treated like slag.

Solidifiedweld metal

Molten weld metal

Shielding gas

Metal droplets

Electrode Base metal

Nozzle

Fig. 1.3 Gas metal arc welding

GMAW is quite a versatile process. Major advantages include:•Higher deposition rates than SMAW reduction of smoke and fumes; high versatility Broad application ability that welds a wide range of thicknesses and metals


4

It can be by a semi-automatic machine or automatic method. In the semi-automatic method, the electrode is fed •automatically through a hand-held gun. The welder controls the inclination and distance of the gun from the work as well as the travel speed and manipulation of the arc. In the machine method, a welding operator monitors a mechanised travel operation for necessary adjustments. •In the automatic method, the entire operation is fully machine controlled. GMAW can also be used for surfacing applications. This means a metal is covered by another metal (applied •by welding) which has better corrosion, wear or hardness properties.

1.2.1 Equipments Required for Gas Metal ARC WeldingGas metal arc welding equipment consists of a welding gun, a power supply, a shielding gas supply and a wire-drive system. Fig below shows the basic equipment needed for the GMAW process.

Hand – held gun

Gas out

Gun control

Feed control

Wire spool

Shielding gas source

Voltage control

Power source

Fig. 1.4 GMAW equipment

1.3 Submerged Arc Welding (SAW)Submerged arc welding or SAW, joins metals by heating them with an electric arc or arcs between a bare metal •electrode (or electrodes) and the base metal. The arc is submerged in and shielded by a blanket of granular, fusiblematerialontheworkknownasflux.In the SAW process, you cannot see the arc between the electrode and the work piece, as it is hidden. The •electrode is not in contact with the work piece. The melted electrode metal is transferred across the arc into the moltenpoolofbasemetalsandflux,becomingthedepositedweldmetal.Thefluxthatmeltsclosetothearcintermixeswiththemoltenmetal,purifyingandfortifyingthemetal,same•aswhathappensintheSMAWprocess.Aslagisformedherefromthefluxandimpuritiesthatalsofloatonthesurface and cover the deposit, protecting it.An advantage of submerged arc welding is its deep penetration. Also, the high deposition rates of SAW reduce •the total heat input into a joint. Welds that would require multiple passes by shielded metal arc welding can be deposited in one pass by submerged arc welding. Fig. 1.5 shows this process. The welder or welding operator does not have to wear a helmet with this process, •but,sincehecannotseethroughtheflux,hemayhaveadifficulttimedirectingthearcifitgetsoff-track.Becausethearcishiddenfromviewandrequiresatrackingsystem,SAWhaslimitedflexibility.Butthisis•offset by several major advantages, such as:

High weld metal quality and strength. Extremely high deposition rate and travel speed.

5

Noarcflash-minimisingprotectionrequirements. Little, if any, smoke. Easily automated, reducing manipulative skill needs.

Direction of travel

Molten flux

ElectrodeFro fluxhopper

Granular fluxblanket


ARC Path

Base metal

Slag

Molten weld metal

Fig. 1.5 Submerged arc welding

SAW also welds a wide range of thicknesses and most of the steels, ferritic and austenitic, are welded by •SMAW.A major use of the SAW process is in the fabrication of heavy steel plate weldments, e. g., pressure vesse1s and •tanks, large diameter pipes, maintenance and repair, and, in ship-building, sub-assembly fabrication.

1.3.1 Equipments Required for Submerged ARC Welding

Weldingunderagranularfluxisasemi-automatic,machineorautomaticprocessinwhichelectrodefeedand•arc length are controlled by the wire feeder and power supply. Inautomaticwelding,atravelmechanismmoveseitherthetorchortheworkandnormallyafluxrecovery•systemre-circulatestheunfusedgranularflux.For machine and automatic welding, arc travel is either pre-aligned or guided by a spot lighter (or pointer) •directed onto the path. The machine method, in which a welding operator must monitor the operation, is the most popular. In the automatic method, a pushbutton operation, is second in popularity. The least used is the semi-automatic •method in which the welder guides the gun (welding head) by hand. In semi-automatic welding, the gun and its fluxhopperarepressedagainstthefacesoftheworktocontrolthelocationoftheweld.


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Hand – held gun

Flux hopper

Electrode wire Wire

reel

Control system

Power source

Base metal

Auto – torch flux

Or

Fig. 1.6 Granular flux welding

1.4 Gas Tungsten ARC Welding (GTAW)Gas tungsten arc welding (GTAW), sometimes referred to as ‘TIG’ welding, joins metals by heating them with •an arc between a non-consumable tungsten electrode and the work piece. Shielding is obtained from an inert gas or inert gas mixture. Filler metal may be added; it is not transferred •across the arc, but is melted by the arc. The electrode that carries the current is a pure tungsten or tungsten alloy rod. Figure below shows how this process works.

Direction of Travel

Welding torch

Shielding gas

Tungsten electrode

Fillerrod

Base metal

Molten weld metal


ARC

Fig. 1.7 Gas tungsten arc welding

Thearcareaisprotectedfromatmosphericcontaminationbythegasshielding,whichflowsfromthenozzle•of the torch. The gas displaces the air, eliminating nitrogen, oxygen and hydrogen from contact with either the molten metal •or the hot tungsten electrode. There is little or no spatter and little or no smoke. The as welded bead is smooth anduniform,requiringlittlefinishing,ifany.

7

The GTAW process can be used to make high quality welds in almost all metals and alloys. There is no slag and •the process can be used in all positions. It also is the slowest of the non-mechanised processes.

1.4.1 Equipments Required for Gas Tungsten Arc Welding

Welding with a non-consumable tungsten electrode shielded with an inert gas is generally a manual process, •but may be mechanised or even automated. The equipment needed includes:

An electrode holder with gas passages and a nozzle to direct the shielding gas around the arc and a gripping mechanism to energise and hold a tungsten electrode.A supply of shielding gas. Aflowmeterandgaspressure-reducingregulator. A power source. A supply of cooling water if the electrode holder is water-cooled.

The power source for AC and DC gas tungsten arc welding is usually a drooping voltage type. In this type of •power supply, the shape of the volt-ampere curve is steep so that a change in arc length will not create a major change in current. Figure below illustrates the equipment needed for the gas tungsten arc welding process.The variables that have the most effect on this process are the electrical variables of current, voltage and power •source characteristics. They affect the amount, distribution and control of arc-produced heat and also play a role in arc stability and in the removal of refractory oxide from the surfaces of certain metals.The electric arc is produced by the current passing through the ionized inert shielding gas. The ionized atoms •loseelectrodesandareleftwithapositivecharge.Thepositivegasionsflowfromthepositivetothenegativepole of the arc.The electrons travel from the negative to the positive pole. The power expended in tile arc, expressed in electrical •units, is the product of the current passing through the arc and the voltage drop across the arc.

Filler metal

Inert gas

supplyPower source

Water drainBase metal

Work lead Electrode leadFoot pedal (Optional)

Gas

Torch

Fig. 1.8 GTAW equipment

1.5 Welding of Stainless SteelsThe three most popular processes for welding stainless steels are shielded metal arc, gas tungsten arc and gas •metal arc welding; however, almost all the welding processes can be used. Stainlesssteelsareslightlymoredifficulttoweldthanmildcarbonsteels.Thephysicalpropertiesofstainless•steel are different from mild steel and this makes it weld differently. These differences are:


8

Lower melting temperature. Lowercoefficientofthermalconductivity. Highercoefficientofthermalexpansion. Higher electrical resistance.

Theausteniticstainlesssteelshaveabout45%higherthermalcoefficientofexpansion,higherelectricalresistance•and lower thermal conductivity than mild carbon steels. High travel speed welding is recommended, which will reduce heat input, reduce carbide precipitation and •minimise distortion. The melting point of austenitic stainless steel is slightly lower than mild-carbon steel. Because of lower melting temperature and lower thermal conductivity, the welding current is usually lower. •The higher thermal expansion dictates that special precautions should be taken with regard to warpage and distortion. Tack welds should be twice as often as normal. Any of the distortion reducing techniques such as back-step •welding,skipweldingandwanderingsequenceshouldbeused.Onthinmaterials,itisverydifficulttocompletelyavoid buckling and distortion.

1.5.1 Problem Areas

The most serious problem when welding stainless steels is to avoid carbide precipitation. As mentioned previously, •this may occur when the material is held at a high temperature for a long period. Electrodescontainingextralowcarbon,indicatedbythesuffixL,shouldbeused.Mostelectrodesarestabilised•withcolumbiumortitanium.Thisalsohelpstoeliminatethecarbideprecipitationproblem.Thesearedefinitelyrequired when the weldment will be subjected to high temperature service.Another factor that affects the quality of austenitic weld joints is the control of ferrite content in the micro-•structure. Austenitic weld deposits may develop micro-cracks during welding if ferrite is not controlled. Thecompositionofthefillermetalshouldbeselectedbasedonthedepositcontainingasmallpercentageof•ferrite. The ferrite content should not become too high or else the weldment will have lower than desired impact strength. For low temperature service, the weld metal should have the ferrite in the range 4 to 10%. The ferrite content •of the weld deposit depends on the composition of the base metal as well as the composition of the deposited fillermetal.AspecialconstitutiondiagramforstainlesssteelweldmetalhasbeendesignedbySchaeferandmodifiedby•Delong.

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SummaryShielded metal arc welding joins metals by heating with an electric arc between a covered metal electrode and •the work piece. SMAW is sometimes referred to as ‘stick’ welding.The SMAW process is usually manually operated, but it can be automated with a machine or gravity ‘stick’ •feeder.The power supply can be either alternating current, direct current electrode negative (straight polarity) or direct •current electrode positive (reverse polarity), depending on the job requirements. Direct current power supplies are often preferred because they are more versatile.GMAW is quite a versatile process. Gas metal arc welding equipment consists of a welding gun, a power supply, •a shielding gas supply and a wire-drive system.In the SAW process, you cannot see the arc between the electrode and the work piece, as it is hidden. A major •use of the SAW process is in the fabrication of heavy steel plate weldments.Gas tungsten arc welding (GTAW), sometimes referred to as ‘TIG’ welding, joins metals by heating them with •an arc between a non-consumable tungsten electrode and the work piece. Welding with a non-consumable tungsten electrode shielded with an inert gas is generally a manual process, •but may be mechanised or even automated.The power source for AC and DC gas tungsten arc welding is usually a drooping voltage type.•The variables that have the most effect on this process are the electrical variables of current, voltage and power •source characteristics.

ReferencesIntroduction to Welding Technology• . [Online]. Available at: <http://www.newagepublishers.com/samplechapter/001469.pdf> [Accessed 7 June 2011].Introduction to Welding• . [Online]. Available at: <http://www.globalsecurity.org/military/library/policy/navy/nrtc/14250_ch3.pdf> [Accessed 7 June 2011].Gonzales. R. F., 1975. • Introduction to Welding,CanfieldPress.Ruth, K., 2004. • Welding Basics, Creative Publishing international.Learnhowtoweld. • How to arc weld: Arc welding, machines and basic setup [Video Online]. Available at: <http://www.youtube.com/watch?v=_nEjZMAizsM&playnext=1&list=PLB701A06F44CB92C4> [Accessed 12 July 2011].nptelhrd, IIT Roorkee, • Gas Metal Arc Welding [Video Online]. Available at: <http://www.youtube.com/watch?v=TRUoiMFsaoA> [Accessed 12 July 2011].

Recommended ReadingPratt. J. L., 1979. • Introduction to the Welding of Structural Steelwork, Steel Construction Institute.Haynes., J., 1995. • Welding Manual, 1st ed., Haynes Manuals.Finch, R., 1997. • Welder's Handbook: A Complete Guide to MIG, TIG, Arc & Oxyacetylene Welding, 2nd ed., HPBooks.


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Self Assessment

Which of the following is false?1. Shielded metal arc welding joins metals by heating with an electric arc between a covered metal electrode a. and the work piece.Shielding of the weld does not come from the breakdown or decomposition of the electrode covering.b. The melted electrode metal is transferred across the arc into the molten pool of base metals, becoming the c. deposited weld metal.Shielding of the weld comes from the breakdown or decomposition of the electrode covering.d.

What is referred to as ‘stick’ welding?2. SAWa. MIGb. SMAWc. GMAWd.

Which is the most widely used process?3. SMAWa. MIGb. SAWc. GMAWd.

Gas metal arc welding or ______________, uses the heat of an electric arc between a continuously-fed, bare 4. fillermetalelectrodeandthebasemetal.

SMAWa. MIGb. SAWc. GMAWd.

Which of the following is false?5. Shielded metal arc welding equipment consists of a welding gun, a power supply, a shielding gas supply a. and a wire-drive system.Submerged arc welding or SAW, joins metals by heating them with an electric arc or arcs between a bare b. metal electrode and the base metal.Gas metal arc welding equipment consists of a welding gun, a power supply, a shielding gas supply and a c. wire-drive system.The arc is submerged in and shielded by a blanket of granular, fusible material on the work known as d. flux.

Which of the following is false?6. The most serious problem when welding stainless steels is to avoid carbide precipitation.a. In the automatic method, a pushbutton operation is second in popularity.b. The melting point of austenitic stainless steel is slightly higher than mild-carbon steel.c. Thefluxthatmeltsclosetothearcintermixeswiththemoltenmetal,purifyingandfortifyingthemetal,d. same as what happens in the SMAW process.

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Which of the following is true?7. SAW also welds a wide range of thinness and most of the steels, ferritic and austenitic, are welded by a. SMAW.SAW also welds a wide range of thicknesses and most of the steels, ferritic and austenitic, are welded by b. SAW.SAW also welds a wide range of thicknesses and most of the steels, ferritic and austenitic, are welded by c. GMAW.SAW also welds a wide range of thicknesses and most of the steels, ferritic and austenitic, are welded by d. SMAW.

_____________underagranularfluxisasemi-automatic,machineorautomaticprocessinwhichelectrode8. feed and arc length are controlled by the wire feeder and power supply.

Weldinga. Shieldingb. Meltingc. Coolingd.

Gas tungsten arc welding (GTAW), sometimes referred to as _______________ welding, joins metals by heating 9. them with an arc between a non-consumable tungsten electrode and the work piece.

TIGa. MIGb. SWAGc. SMAWd.

What is obtained from an inert gas or inert gas mixture?10. Weldinga. Shieldingb. Meltingc. Coolingd.


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Chapter II

Welding Procedure, Performance Qualification and Welding Variables

Aim


introduceweldingprocedureandperformancequalification•

discussWeldingProcedureSpecification(WPS)indetail•

describeProcedureQualificationRecords(PQR)indetail•

Objectives

The objectives of this chapter are to:

explain welding variables•

specify different joints types and parts of joints•

elucidate edge shapes in brief•

Learning outcome


understand single and double groove weld joints•

identify different types and parts of weld•

comprehend • complete and incomplete fusion in detail

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2.1 Welding Procedure and Performance QualificationASMErelatestoqualificationofwelders,weldingoperators,brazersandbrazingoperatorsandtheproceduresthatthey employ in welding and brazing. It is divided into parts, part QW gives requirements for welding and part QB contains requirements for brazing.

Thepurposeofweldingprocedurespecifications(WPS)andprocedurequalificationrecords(PQR)istodeterminethat the weldment proposed for construction is capable of providing the required properties for its intended application.

WPS is intended to provide direction for the welder and lists the variables, both essential and non-essential and the acceptable ranges of these variables when using the WPS.

PQR lists what was used in qualifying the WPS and the test results. It is presumed that welder or welding operator performingtheweldingprocedurequalificationtestisaskilledworkmansothattheweldingprocedurequalificationtest establishes the properties of weldment and not the skill of the welder.

Thepurposeofperformancequalificationistodetermineifthewelderisabletodepositsoundmetalortheoperatoris able to operate welding equipment properly.

Part QW is divided into 4 articlesArticle I - Welding General Requirements•ArticleII-WeldingProcedureQualifications•ArticleIII-WeldingPerformanceQualifications•Article IV - Welding Data•

Beforeweproceed,letusfirstunderstandvarioustestpositionsingrooveweldsinplates,grooveweldsinpipesandfilletweldsinplates,etc.

1Gor1Fiscalledflatposition.•2G or 2F is called horizontal position.•3G or 3F is called vertical position.•4G or 4F is called overhead position.•Position 5G is only in welds in pipes. It is a position where the pipe axis is held horizontal and the circumferential •seam is welded without rotating. In a way it is a combination of 1G, 3G and 4G.Position 6G is also for the pipes, when the pipe axis is at 45° to the horizontal plate and the circumferential •seam is welded without rotating the pipe. It is a combination of all positions.

2.2 Welding VariablesWelding processes show essential variables, supplementary essential variables and non-essential variables for •proceduresqualificationandessentialvariablesforperformancequalification.Essential variables for procedure are those welding variables whose change will affect the mechanical properties •(other thannotch-toughness)of theweldment (example - change inp-number,fillermetal, electrode type,preheat, post heat, etc.). Supplementary essential variables for procedure are those welding variables whose change will affect the •notch toughness properties of weldment (example - uphill or downhill vertical welding, heat input, preheat or PWHT).Non-essential variables for procedure are those welding variables whose change will not affect the mechanical •properties of weldment (example - joint design, method of back gauging or cleaning, etc.). Essential variables for performance are those welding variables which will affect the ability of the welder to •deposit a sound weld (for example, position, deletion of backing F-number, etc.).


14

Changeinprocessisanessentialvariableforprocedureaswellasperformance.Beforeweproceed,letusfirst•understand the term P-number, A- number and F-number.All those materials are divided into various P-numbers depending on their nominal composition and further •divided intogroupsdependingon the typeof refinement/Min. specifiedUTS, etc.QW-422gives the fulldetails.Plain carbon steels, C- Si, Cr -Mn and C-Mn-Si are grouped as P1 materials and austenitic stainless steel as P-8 •material.Ferrousweldingconsumableareclassifiedundervariousa-numbersbasedontheirweldmetalchemicalcomposition and all welding electrodes and welding rods are grouped in different F- number depending on their AWSclassificationwhichisbasedontypeoffluxandchemicalcomposition.

2.3 Joint TypesWelds are made at the junction of the various pieces that make up the weldment. The junctions of parts, or joints, aredefinedasthelocationwheretwoormoremembersaretobejoined.Partsbeingjoinedtoproducetheweldmentmaybeintheformofrolledplate,sheet,shapes,pipes,castings,forgings,orbillets.Thefivebasictypesofweldingjoints are shown below.

Butt Joint Corner Joint T – Joint Lap Joint Edge Joint

Table 2.1 Joint types

2.3.1 Butt JointA Butt joint is used to join two members aligned in the same plane. Refer Table. 2.1. This joint is frequently used in plane, sheet metal and pipe work. A joint of this type may be either square or grooved.

Applicable welds:

Bevel-Groove• Flare-V-Groove•U-Groove• Edge- Flange•Flare-Bevel-Groove• J-Groove Braze•V-Groove• Square-Groove•

2.3.2 Corner and T – JointCorner and T – joints are used to join two members located at right angles to each other. In cross section, the corner joint forms an L-shape and the T – joint has the shape of the letter T. Various joint designs of both types have usage in many types of metal structures.

Applicable welds: for corner joint:

Fillet• Corner-Flange•Bevel-Groove• Edge-Flange•Flare-Bevel-Groove• Plug•Flare-V-Groove• Slot•J-Groove• Spot•Square-Groove• Seam•U-Groove• Projection•V-Groove• Braze•

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Applicable welds: for T – joint:

Fillet• Slot•Bevel-Groove• Spot•Flare-Bevel-Groove• Seam•J-Groove• Projection•Square-Groove• Braze•Plug•

2.3.3 Lap JointA lap joint, as the name implies, is made by lapping one piece of metal over another. This is one of the strongest typesofjointsavailable,however,formaximumjointefficiency,youshouldoverlapthemetalsaminimumofthreetimes the thickness of the thinnest member you are joining. Lap joints are commonly used with torch brazing and spot welding applications.

Applicable welds:

Fillet• Slot•Bevel-Groove• Spot•Flare-Bevel-Groove• Seam•J-Groove• Projection•Plug• Braze•

2.3.4 Edge JointAn edge joint is used to join the edges of two or more members lying in the same plane. In most cases, one of the membersisflanged,asintable2.1.Whilethistypeofjointhassomeapplicationsinplatework,itismorefrequentlyused in sheet metal work. An edge joint should only be used for joining metals ¼ inch or less in thickness that are subjected to heavy loads.

Applicable welds:

Bevel-Groove• V-Groove•Flare-Bevel-Groove• Edge•Flare-V-Groove• Corner-Flange•J-Groove• Edge-Flange•Square-Groove• Seam•U-Groove•

2.4 Parts of JointsThe root of a joint is that portion of the joint where the metals are closest to each other. The root may be a point, a line or an area, when viewed in cross section. A groove is an opening or space provided between the edges of the metal parts to be welded. The groove face is that surface of a metal part included in the groove. A given joint may have a root face or a root edge. The root face is the portion of the prepared edge of a part to be joined by a groove weld that has not been grooved. The root face has relatively small dimensions. The root edge is basically a root face of zero width.

The root of a joint, the bevel angle is the angle formed between the prepared edge of a member and a plane •perpendicular to the surface of the member.The Groove angle is the total angle of the groove between the parts to be joined.•The groove radius is the radius used to form the shape of J- or U- groove weld joint. It is used only for special •groove joint designs.


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The root opening refers to the separation between the parts to be joined at the root of the joint. It is sometimes •called the “root gap”.

Root Face and Groove Face

Fig. 2.1 Root face and groove face (1)





Groove Face

Groove Face


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Groove Face

Root Edge


Groove Angle Groove Angle

Depth of Bevel Depth of Bevel

Groove Radius

Root Opening

Bevel Angle

Bevel Angle

Fig. 2.5 Bevel angle, depth of groove angle, groove radius and root opening (1)

Groove Angle

Depth of Bevel (C) (D)

Bevel Angle

Bevel Angle

Bevel Angle



18

Groove Angle andBevel AngleRoot Opening

Groove Radius

Groove Angle

Bevel Angle


2.5 Edge Shapes

Square edge shape Single-bevel edge shape Double-bevel edge shape

Table 2.2 Edge shapes (1)

Single-J-Groove edge shape Flange edge shape Round edge shape

Table 2.3 Edge shapes (2)

Square edge shape

Applicable welds:

Double-Bevel-Groove• Single-J-Groove•Double-Bevel-Flare-Groove• Square-Groove•Double-J-Groove• Edge•Single-Bevel-Groove• Fillet•Single-Flare-Bevel-Groove• Braze•

Single-bevel edge shape

Applicable welds:

Single-Bevel-Groove•Braze•Single-V-Groove•

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Double-bevel edge shape

Applicable welds:Double-Bevel-Groove•Double-V-Groove•

Single-J-Groove edge shape

Applicable welds:Single-J-Groove•Single-V-Groove•

Flange edge shape

Applicable welds:Single-Flare-Bevel-Groove• Projection•Single-Flare-V-Groove• Seam•Edge• Spot•Fillet• Braze•

Round edge shape

Applicable welds:

Double-Flare-Bevel-Groove•Flare-V-Groove•Double•Braze•

2.6 Single Groove Weld JointsGroove welds are simply welds made in the groove between two members to be joined. The weld is adaptable to a variety of butt joints. Groove welds may be joined with one or more weld beads, depending on the thickness of the metal. If two or more beads are deposited in the groove, the weld is made with multiple-pass layers. As a rule, a multiple-pass layer is made with stringer beads in manual operations.

Single Square – Groove Weld Single Bevel – Groove Weld

Fig. 2.8 Single groove weld joints (1)


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Single V – Groove Weld Single V – Groove Weld with Backing


Single J – Groove Weld Single U – Groove Weld


Single Flare – Bevel Groove Weld Single Flare – V – Groove Weld


2.7 Double Groove Weld Joints

Double Square – Groove Weld Double Bevel – Groove Weld

Fig. 2.12 Double groove weld joints (1)

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Double V – Groove Weld Double J – Groove Weld


Double U – Groove Weld


Double Flare – Bevel – Groove Weld Double Flare – V – groove Weld


2.8 Types of WeldsNumerous welds can be applied to the various types of joints. While choosing joint geometry and weld types, you need to consider following aspects:

Accessibility to the joint for welding•Type of welding process being used•Suitability to the structural design•


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Cost of welding•

There are nine categories of welds associated with weld symbols:Groove welds•Fillet welds•Plug or Slot welds•Spot or Projection welds•Seam welds•Back or Backing welds•Surfacing welds•Flange welds•

2.8.1 Groove WeldsA groove weld is “a weld made in a groove between the work pieces”. There are eight types of groove welds:

Square-groove•Scarf•V-groove•Bevel-groove•U-groove•J-groove•Flare-v-groove•Flare-bevel-groove•

Theirnamesimplywhattheactualconfigurationslooklikewhenviewedinacrosssection.Singlegrooveweldsarewelded from only one side. Double groove welds are welded on both sides. Groove welds in many combinations areusedselection,influencedbyaccessibility,economyandadaptationtostructuraldesign.

Square and double square groove welds: • Square-groove welds are the most economical to use, but are limited by thickness of the members. Welds for one side are normally limited to a ¼ inch or less.V- and double V-groove welds: • With thicker material joint accessibility must be provided for welding to ensure weld soundness and strength.Bevel- and double-bevel-groove welds: • Bevel- and J-groovewelds aremoredifficult toweld thanV-orU-groove welds. Bevel welds are easier in horizontal.U-groove and double U-groove: • Welds in using J- and U-grooves can be used to minimise weld metal. These welds are very useful in thicker sections.J- and double-J-groove welds: • J-groovesaremoredifficulttoweldbecauseoftheoneverticalside(exceptinhorizontal). J- and U- are used when economic factors outweigh the cost of edge preparation.Flare-bevel and flare-groove welds: • Flare-bevelandflare-v-grooveweldsareusedinconnectionwithflangedor rounded member.

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Vertical

Horizontal

Flat position1G position

Horizontal position2G position

Weld axisWeld axis

30°

10°

60°

30°

Fig. 2.16 Welding position-groove welds (1)

Vertical

Vertical position3G position

Overhead position4G position

Weld axis (Vertical)

Weld axis

80°

80°

Fig. 2.17 Welding position-groove welds (2) 2.8.2 Fillet Welds

1F Flat position•2F Horizontal position•3F Vertical position•4F Overhead position•


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Vertical

Vertical

Flat Position1 F Position Horizontal Position

2 F Position

Weld axisWeld axis

30°

150°

0°

125°

Fig. 2.18 Welding position-fillet welds (1)

Vertical position3 F position

Overhead position4 F position

Weld axis (Vertical)

Vertical

Weld axis

125°

Fig. 2.19 Welding position-fillet welds (2)

2.8.3 Pipe Welds - Groove Welds

1G Horizontal rolled position•2G Vertical position•5GHorizontalfixedposition•6G Inclined position•6GR Inclined position with restriction ring•

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Horizontal Rolled Position1 G Position

15°

15°

Fig. 2.20 Welding position-pipe welds (1)

Vertical Position2 G Position

15°15°


Horizontal Fixed Position5 G Position

15°

15°



26

Inclined Position6 G Position

Inclined Position with Restriction Ring6 GR Position

Restriction Ring

Weld

45° - 5°


2.9 Parts of Weld

Face Reinforcement

Root Reinforcement

Weld Face

Weld Root

Fig. 2.24 Parts of welds (1)

Root Surface

Weld Root


27

Groove weld made before welding other side

Back Weld

Face Reinforcement

Root Reinforcement


Groove weld made after welding other side

Backing weld

Weld root


Weld RootFillet Weld

Weld Toe

Weld face



28

Spacer Strip


Heat Affected Zone

Weld Metal Area


Weld Root


29

Weld Root


Fillet Weld

Weld Root


Weld Root



30

Base MetalWeld Bead

A

B

Calculation of Dilution from Cross – sectional Area of Weld Bead

Dilution = B (100) A+B


2.10 Weld SizesThesizeofthefilletweldisdeterminedbythelegsofthetriangleshapewhichrepresentthelegsofthefillet.Awelded piece may have a different weld size on each side or they may be the same size. Sometimes a weld of unequal legsmayberequired.Ifnosizeisshownonthefilletweld,asizeforallfilletswillbegivenonthedrawingasanoteorspecification.

Actual Throat

Effective Throat

Convexity

Leg and Size

Theoretical Throat

Fig. 2.36 Convex fillet weld

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Concavity

Actual Throat and Effective Throat

Theoretical Throat

Leg

Leg

Size

Size

Fig. 2.37 Concave fillet weld

Actual Throat

Effective Throat

Leg and Size

Leg and Size

Incomplete Fusion

Theoretical Throat

Fig. 2.38 Fillet weld with incomplete fusion


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Actual Throat and Effective Throat

Root Opening

Leg

LegSize

Size

Theoretical Throat

Fig. 2.39 T-joint with root opening

2.11 Complete FusionIn welding, fusion which has occurred over the entire base- metal surfaces exposed for welding.

Fig. 2.40 Complete fusion (1)


33



2.12 Incomplete FusionIncomplete fusion can be a weld discontinuity where fusion did not necessarily occur between weld metallic and fusion confronts or adjoining weld beans. This absence regarding fusion may take place at any location inside weldjointandmayevenbepresentinsidefilletweldsand/orgroovewelds.Incompletefusioncouldbecausedbythe inability, during the welding method, to elevate the beds base material or earlier deposited weld metallic to its sheddingtemperature.Itisfrequentlyfoundononelegofyourfilletweldwhichiscausedbycompletelywrongwelding angle that enables for a disproportion of heat among both sides with the joint. It may also be due to failure to eliminate oxides or some other foreign material from the surface of the base material to that your deposited weld metallic must fuse.

Incomplete Fusion

Incomplete Fusion

Fig. 2.44 Incomplete fusion (1)


34

Incomplete Fusion

Incomplete Fusion

Fig. 2.45 Incomplete fusion (2)

Incomplete Fusion

Fig. 2.46 Incomplete fusion (3) 2.13 Fusion WeldsFusion welding is a group of processes that bond metal together by heating a portion of each piece above the melting pointandcausingthemtoflowtogether.

Depth of FusionFusion face

Weld Interface

Weld Interface

Fig. 2.47 Fusion welds (1)

35

Depth of Fusion

Weld Interface

Depth of Fusion

Fusion Face

Fig. 2.48 Fusion welds (2)

Depth of Fusion

Weld Interface Fusion face

Fig. 2.49 Fusion welds – surfacing weld

Weld Interface

Weld Interface

Depth of Fusion

Fusion Face

Paving Surface

Size

Fig. 2.50 Fusion welds – resistance spot seam weld


36

SummaryASMErelatestoqualificationofwelders,weldingoperators,brazersandbrazingoperatorsandtheprocedures•that they employ in welding and brazing.Thepurpose ofwelding procedure specifications (WPS) and procedure qualification records (PQR) is to•determine that the weldment proposed for construction is capable of providing the required properties for its intended application.Thepurposeofperformancequalificationistodetermineifthewelderisabletodepositsoundmetalorthe•operator is able to operate welding equipment properly.Position 5G is only in welds in pipes.•Welding processes show essential variables, supplementary essential variables and non-essential variables for •proceduresqualificationandessentialvariablesforperformancequalification.Supplementary essential variables for procedure are those welding variables whose change will affect the notch •toughness properties of weldmentCorner and T – joints are used to join two members located at right angles to each other.•A lap joint, as the name implies, is made by lapping one piece of metal over another.•An edge joint is used to join the edges of two or more members lying in the same plane.•The root of a joint is that portion of the joint where the metals are closest to each other.•A groove is an opening or space provided between the edges of the metal parts to be welded. The groove face •is that surface of a metal part included in the groove.Groove welds are simply welds made in the groove between two members to be joined.•Bevel-andJ-grooveweldsaremoredifficulttoweldthanV-orU-groovewelds.•Thesizeofthefilletweldisdeterminedbythelegsofthetriangleshapewhichrepresentthelegsofthefillet.•

ReferencesIntroduction to Welding Technology• . [Online]. Available at: <http://www.newagepublishers.com/samplechapter/001469.pdf> [Accessed 7 June 2011].Introduction to Welding• . [Online]. Available at: <http://www.globalsecurity.org/military/library/policy/navy/nrtc/14250_ch3.pdf> [Accessed 7 June 2011].Gonzales. R. F., 1975. • Introduction to Welding,CanfieldPress.Hicks, J., 1999. • Welded Joint Design, 3rd ed., Woodhead Publishing.nptelhrd. IIT Kharagpur, • Design of Welded Joints-I [Video Online]. Available at: <http://www.youtube.com/watch?v=7b1bd-lgra0> [Accessed 12 July 2011].nptelhrd. IIT Kharagpur, • Design of Welded Joints-II [Video Online]. Available at: <http://www.youtube.com/watch?v=LQpxTqHB_p8> [Accessed 12 July 2011].

Recommended ReadingMohler, R., 1983. • Practical Welding Technology, Industrial Press, Inc. Althouse, A.D., Turnquist, C.H., Bowditch, W.A., Bowditch, K.E., 2000. • Modern welding, Goodheart-Willcox Co. Jeffus, L.F., 1997. • Welding: principles and applications, 4th ed., Cengage Learning.

37

Self Assessment

Which of the following is false?1. Thepurposeofweldingprocedurespecificationsandprocedurequalificationrecordsistodeterminethata. the weldment proposed for construction is capable of providing the required properties for its intended application.WPS is intended to provide direction for the welder and lists the variables, both essential and non-essential b. and the acceptable ranges of these variables when using the WPS.PQR lists what was used in qualifying the WPS and the test results.c. WPS is intended to provide direction for the welder and lists the variables which are not essential and the d. acceptable ranges of these variables when using the WPS.

Which of the following is true?2. Thepurposeofperformancequalificationistodetermineifthewelderisabletodepositsoundmetalorthea. operator is able to operate welding equipment properly.Thepurposeofweldingprocedurespecificationsistodetermineifthewelderisabletodepositsoundmetalb. or the operator is able to operate welding equipment properly.Thepurposeofperformancequalificationistodetermineiftheoperatorsisabletodepositsoundmetalorc. the welder is able to operate welding equipment properly.Thepurposeofperformancequalificationisnottodetermineifthewelderisabletodepositsoundmetalord. the operator is able to operate welding equipment properly.

_____________ is also for the pipes, when the pipe axis is at 45° to the horizontal plate and the circumferential 3. seam is welded without rotating the pipe.

Position 5Ga. Position 3Gb. Position 6Gc. Position 2Gd.

What show essential variables, supplementary essential variables and non-essential variables for procedures 4. qualificationandessentialvariablesforperformancequalification?

Melting processesa. Welding processesb. Shielding processesc. Performancequalificationd.

Which of the following is false?5. Non-essential variables for procedure are those welding variables whose change will not affect the mechanical a. properties of weldment.Essential variables for performance are those welding variables which will affect the ability of the welder b. to deposit a sound weld.Change in process is an essential variable for procedure as well as performance.c. Essential variables for procedure are those welding variables whose change will affect the mechanical d. properties of weldment.


38

What is used to join two members aligned in the same plane?6. Butt jointa. Corner jointb. T – jointc. Lap jointd.

Corner and ____________ are used to join two members located at right angles to each other.7. butt jointa. corner jointb. T – jointc. lap jointd.

Which of the following is true?8. A T - joint is one of the strongest types of joints available.a. A lap joint is one of the strongest types of joints available.b. A butt joint is one of the strongest types of joints available.c. A edge joint is one of the strongest types of joints available.d.

A/An ______________ has some applications in plate work and is more frequently used in sheet metal work.9. butt jointa. corner jointb. edge jointc. lap jointd.

Bevel-and_____________aremoredifficulttoweldthanV-orU-groovewelds.10. J-groove weldsa. Square-Grooveb. Flare-V-Groovec. Edge-Flanged.

39

Chapter III

Pressure Welding and Cutting Methods

Aim


introduce pressure welding methods•

explain resistance welding in detail•

discuss spot welding and its important parameters•

examine different cutting methods•

Objectives


elaborate seam welding and projection welding•

explain them the meaning of resistance butt welding•

describeflashweldinginbrief•

Learning outcome


understand friction welding and its features in detail•

comprehend high frequency welding•

defineultrasonicweldinganddiffusionwelding•

get an o• verview of thermal cutting


40

3.1 Pressure Welding MethodsPressure welding can be carried out by many welding methods, the fact having in common that the surfaces of the joint are pressed or worked together. Smiths in traditional forges used forge welding, which involved heating the metalinafireuntilitwasplastic,thenitcouldbeforgedtogether.Thismeansthatforgedweldingcouldbeclassifiedamong methods of pressure welding. In some cases, the surfaces to be joined are heated to melting point, while in othermethodstheweldcanbemadewithoutsignificantheating.

3.2 Resistance WeldingResistance welding is one the oldest types of welding. Heat is generated by the passage of an electric current through the resistance formed by the contact between two metal surfaces. The current density is so high that a local pool of molten metal is formed, joining the two parts. The current is often in the range 1,000 – 100,000 A and the voltage in the range 1 – 30 V.

Resistanceweldingmethodsarecomparativelyfoundtobefast,efficientandlow-polluting.Nofillermaterialsarerequired. The drawbacks can be high capital cost and has limited range of applications. In principle, each machine can be used for only one type of welding.

Therearefivedifferenttypesofresistancewelding:

Spot welding

Seam welding

Projection welding

Resistance welding

Flash welding Five types

of resistance welding

Fig. 3.1 Five type of resistance welding

3.2.1 Spot Welding

It is the best known resistance welding method. It is used for joining thin sheet materials by overlap joints and •is widely used in the automotive industry. An ordinary private car can have up to 5,000 spot-welded joints.Incombinationwitharapidheatingtime,thehighcurrent,meansthatthethermalenergyinputisefficiently•used. Spot welding therefore has several advantages over other methods of welding sheet metal, such as:

Little deformation of the work piece, as the thermal energy is more or less restricted to the immediate vicinity of the weld.Very high rate of production for mechanised processes. Easy to automate with high consistency, therefore suitable for mass production.

41

Low energy requirement and little pollution. Fast resistance welding of 1 + 1 mm sheet. Nofillermaterialsrequired. Little special training required. Less environmental impact than when welding with an arc.

Two electrodes clamp the two sheets of metal together with a considerable force, while passing a high current •through the metal. Thermal energy is produced as the current passes the electrical contact resistance between the two sheets, is •given by:

Q = ∙R∙t

Where, Q = quality of thermal energy (Ws)I = current (A)R = the resistance across the weld (Ω)t = welding time duration (s)

Ir1

r2

r2r3

r1

P

Fig. 3.2 The principle of spot welding

The total resistance between the electrodes is made up of:

2 = 2 +

Where, = contact resistance between each electrodes and the work piece = the resistance through the metal of each of the pieces to be joined = the contact resistance between the two pieces of metal

The contact resistance between the electrodes and the work piece and particularly the contact resistance between •the two pieces of metal to be joined is considerably higher than the resistance of the conducting path through the metal. Minor unevenness in the surface of the metal means that the current is concentrated to a few contact points, •with the result that the heating is greatest at these points. Changing the clamping force can modify the contact resistance and thus also the heating.As welding starts, the contact resistances are very high. The initial passage of current breaks through the surface •layers, so that the contact resistances drop rapidly. Most of the heat formed at the contact between the electrodes and the work piece is conducted away through the water cooled electrodes.


42

However, this is not the case with the heat developed in the contact resistance between the two work piece sheets, •so the temperature here rises until the melting temperature of the metal is reached, while the surfaces continue to be pressed together by the clamping force, so that a weld nugget forms in the contact area.The electrodes need to be of a material with a high hardness, low electrical resistance and high thermal •conductivity. Cooling is decisive for their life. Wear and tear, together with deformation, increases the effective contact size of the electrodes, which reduces •the current density and, in due course, the strength of the welds produced. An electrode normally has a life of about 5,000 – 10,000 welds; when welding galvanised steel, this life is •reduced to about 500 – 2,000 welds. Tip dressing, using a special tool, restores the shape of the electrode tip.

3.2.1.1 Important Parameters of Spot WeldingThe spot welding process includes a number of variables that can be adjusted in order to achieve optimum welding performance. Tables of optimum values have been produced, but it is also necessary to optimise the process by trial and error.

Theweldingcurrentisthecurrentthatflowsthroughtheworkpiece.Ofalltheparameters,itishasthegreatest•effect on strength and quality of the weld, as the amount of heat produced is proportional to the square of the welding current. The welding current must therefore be carefully adjusted; too high a current results in a weld with poor strength, with too great a crater depression, spatter and some distortion. It also means that the electrodes are worn unnecessarily. Too low current, on the other hand, also produces a weld of limited strength, but this time with too small weld area.Squeeze time is the time needed to build up the clamping force. It varies with the thickness of the metal and •withtheclosenessofthefitandisalsoaffectedbythedesignoftheelectrodejaws.The clamping force is the force with which the electrodes press the sheets together (kN). It is important that this •should be carefully controlled, as too low clamping force results in a high contact resistance, accompanied by spatter and resulting in poor weld strength, while too high a force results in too small a weld, again with poor strength, but accompanied by unnecessary wear on the electrodes and too great crater depression.Weldingtimeisthetimeforwhichcurrentflowsthroughtheworkpieceandismeasuredincycles,i.e.,during•which alternating current passes through one cycle.Hold time is the time from when the current is interrupted until the clamping force can be released. The plates •mustbeheldtogetheruntiltheweldpoolhassolidified,sothatthejointcanbemovedortheelectrodescanmoved to the next welding position.The electrode area determines the size of the area through which the welding current passes. The electrode •diameter (d) is determined in relation to the thickness of the metal (t) from the following formula:

d=5∙

When welding high – strength steels, a factor of 5 in the formula can suitably be increased to about 6 – 8.•

3.2.2 Seam Welding

Seam welding is used in the same way as spot welding and operates on essentially the same principle. The •difference is that two wheel – shaped electrodes are used, rolling along (and usually feeding) the work piece.

43

Fig. 3.3 Principle of Seam Welding

Thetwowheelsshouldbeofthesamesize,inordertopreventthepartfrombeingdeflectedtowardsoneof•them.Theactualcontactprofilecanbedesignedinanumberofways,inordertosuittheshapeoftheparttobe welded. Thecurrentmayflowcontinuouslywhileweldingisbeingcarriedout,orintermittentlytoproduceaseriesof•spots, so closely positioned as to produce weld. An unavoidable problem of seam welding is that some of the current ‘leaks’ through the completed weld.As the electrode rollers rotate, they do not need to be lifted between each spot, as with spot welding. If the weld •does not have to be continuous, seam welding can be therefore used to position spots some regular distance from each other, which can be carried out quicker than ordinary spot welding.

3.2.3 Projection Welding

Projection welding is used to join two overlapping sheets of relatively thin metal just like seam welding and •spot welding. The process involves pressing a number of ‘dimples’ in one of the plates, welding the two plates together at •the same time.

Fig. 3.4 Principle of projection welding

This method can also be used for welding metal sheet to the ends of bars, rods or pipes, or for welding nuts to •sheets. Wire grids are also particularly suitable for projection welding.An advantage of the process, relative to spot welding, is that there is less wear and tear on the electrodes due •to the greater contact area.


44

3.2.4 Resistance Butt Welding

Resistance butt welding is used for end-to-end welding of rods or wires, for instance, for welding wire baskets, •shopping trolleys or wire racks for use in oven, etc., The ends of the material are pressed together and a current is passed through them. The temperature across the contact resistance becomes so high that the metal softens to a plastic state and the •two parts can be joined together.Butt welding can be used for welding steel, copper, aluminium and its alloys, as well as for gold, silver and •zinc. The maximum contact area is usually stated to be about 150 mm2. The upward limit is determined by the ability of the welding machine to ensure even distribution of the heat •across all parts of the joint. The lower limit is determined by the purely practical ability of handling the material, for instance for steel wire, the smallest size is generally regarded as being about 0.2 mm diameter.

Fig. 3.5 Resistance butt welding

3.2.5 Flash Welding

Likebuttwelding,flashweldingisamethodinwhichtheendsoftheworkpiecearepressedtogetherand•welded. It is used for welding thicker work pieces such as heavy anchor chain, rails and pipes.The process starts by preheating the components, by moving the parts forward and backward, in and out of contact •with each other a number of times, while current is passing, so that the contact points heat up and heat the body ofthemetalbehindthemwhenthetemperatureissufficientlyhigh,followedbythenextstageofflashing.Thepartsareslowlybroughttogetherandpressedfirmlyincontactwhichcausesrapidmeltingandgasification,•with spectacular ejection of molten material in a rain of sparks. The molten metal of the two surfaces joins and the process continues with application of forging pressure so •that molten material and any trapped oxides or contamination are pressed out of the joint into a surrounding collar or upset.

Item Welding methodSpot Projection Seam Flash

Stainless steel sinksWire meshes, storage trays, etcFurniture parts, chairs, tablesPipes, sleeves, nipplesTools, drillsLockerTops and bottoms of tanksVehicle bodiesDifferential casings

45

SilencersPipes and sections to be joined perpendicularlyRailsChainSubstantial girders

Table 3.1 Examples of applications for a number of resistance welding methods

3.3 Friction WeldingFriction welding does not involve complete melting of the joint surfaces. The surfaces are heated up and affected •in various ways by pressure and friction, with the welding process itself being somewhat similar to that of forge welding. The method has been used for more than 30 years. It is very suitable for certain applications, particularly where •at least one of the parts is rotationally symmetrical. Traditionally, the necessary friction has been generated by relative movement between the work piece parts; •although in recent years the technology has been further developed so that the necessary friction generating motion can be applied by an external tool.

3.3.1 Friction Surfacing

Using the friction welding principle it can be possible to clad surfaces. This involves a round bar of consumable •materials that is rotated while being pressed against and moved over the work piece surface. The process is suitable for welding different combinations of materials, such as, austenitic stainless steel, which •can be applied to ordinary carbon steel.Trialsofthismethodhavealsobeenusedformakingweldedjoints.Onemethodinvolvesapplyingfillermaterial•into a continuous joint between two sheets of not too thick material. If the material is thicker, holes can be drilled initwhichcanthenbefilledbyarotatingfillerbar.

3.3.2 Friction Stir Welding

Friction stir welding is an interesting development of earlier friction welding methods. The two parts of the •work piece are clamped in a butt joint against a solid support. Welding is carried out with a tool similar to a milling cutter, but with the difference that no metal is actually cut, •instead,thefrictionoftherotatingtoolagainsttheworkpieceissufficienttosoftenthemetalwithoutactuallymelting it. A collar on the tool prevents the softened metal from being displaced upwards, with the result that both the •underside and top of the joint are very smooth.A disadvantage is that a hole is left in the position in which tool travel stops. Welding speed is comparable with •that of other methods.Friction stir welding is particularly suitable for welding aluminium, for instance, for making longitudinal welds •along aluminium extrusions. It is also possible to use with certain other materials, such as copper, titanium, lead, zinc and magnesium. Trials •of welding plastics have also been carried out.The process uses a rotating tool, with a pin that penetrates almost completely through the work piece. The joint •is a gap – free butt joint and requires no special joint preparation. Theworkpiecemust,howeverbefirmlyclamped,ashighpressureisgeneratedasthetoolpasses.Thisalso•applies to the root face if full weld penetration is required. The method is similar to that of milling, except that no material is cur, instead, it is pressed past the rotating pin •andfillsthegapcompletelybehindit.


46

Frictionandthe‘stirring’effectraisethetemperaturesufficientlytosoftenthemetalwithoutmeltingit.The•shape of the rotating tool is designed so that it presses down the weld convexity so that it remains level with the original surface.

ProbeShouldered tool

Fig. 3.6 Friction stir welding

Materials thicker than about 25 mm are most often welded from both sides. The welding speed depends on the •thickness and type of material, for example, 15 mm aluminium can be welded at a longitudinal speed of about 180 mm/min, while 5 mm thick material can be welded at a linear speed of up to 3000 mm/min.Following are the special features of the method:•

The quality of the joint is good and reproducible. The root face can be so good that the weld is almost invisible, while the top is essentially smooth, but with a puddle surface effect left by the tool.With a low heat input, there is very little thermal stress or distortion. Mechanical properties are better preserved compared to arc welding. A hardness drop of just 10-20% has been measured.FSW may be used for alloys that are crack sensitive when they are welded with normal fusion welding processes.No visible radiation, noise or smoke generation. Nofillermaterialsrequired. Production rate is comparable with that of other methods. Goodprofitabilitydue tovery littleneedforpreparationorsubsequentprocessing.Noconsumptionof fillermaterials.Welding can be carried out in the same milling machine or multi – operation machine, using the same clamping as for other operations.The formation of a hole from the tool where it stops can be a disadvantage. The problem of producing an invisible termination has not been solved.Heavyandpowerfulfixturesareneededtokeepthepartsoftheworkpiecetogetherandpressedtothe backing plate.

47

3.4 High Frequency WeldingThis method could be regarded as a form of resistance welding, as the heat is created by resistive heating of a •current induced in the work piece. The use of a very high frequency, for example, 400 kHz, concentrates the current close to the surface of the material, known as skin effect, or in parts of the work piece close to a current carrying conductor, known as proximity effect. This provides a means by which heating can be restricted to, or concentrated in, those parts of the surfaces to •beweldedtogether,withthefinalweldbeingmadebypressingthepartstogether.Current can be supplied to the work piece by contact blocks or sliding shoes. The fast, concentrated heating •provides a high rate of welding, with low heat input and little conduction of heat to other parts. An interesting application is that of longitudinal seam welding of pipes, for which welding rates of 30–100 m/•mm can be achieved, depending on the thickness of the material and the power input.

3.5 Ultrasonic Welding

Ultrasonic welding bonds the work piece parts together by vibrating them against each other at high frequency •under pressure. To some extent, the equipment used for this is similar to that used for resistance welding, except that it is vibration, rather than electric current, that provides the energy input to the work piece.Ultrasonicweldingissuitableforthinsheet,filmsorwires.Partstobejoinedshouldpreferablybefairlysmall;•at least one of them, the one that will be made to vibrate should not be more than a few millimetres in size. While using this method to weld items in sensitive electronic equipment, it has a particular advantage that it •produces very little heat.A layer of oxide, or even of insulation, need not prevent a good connection. However, the surfaces should be •thoroughly degreased, as grease acts as a lubricant and degrades the quality.

3.6 Diffusion WeldingDiffusion welding is a method of joining surfaces to each other without melting and without deformation. •The process is carried out under vacuum or in a protective gas atmosphere, with the application of high pressure •andtemperatureoverarelativelylongperiodoftime.Providedthatthesurfacesareclean,flatandaccuratelymachined, large areas can be bonded in this way. A disc of tool steel, for example, with integral cooling passages, can be produced by welding a cover disc to •another disc in which the necessary channels have been machined.Diffusion welding can be used for many materials, including the joining of different types of metals and also •the bonding of metals to non-metals. However, results are often improved by incorporating an intermediate layer between the two outer different layers.

3.7 Cutting MethodsThermal cutting processes by gas, plasma or laser are often covered in conjunction with the corresponding welding methods. This is because almost the same equipment is used for both processes and because the methods are often also utilised together. It is then also appropriate to take the opportunity to cover competing methods, such as water jet cutting.

3.8 Thermal CuttingThermal cutting is used considerably in connection with the preparation of parts for welding. In addition to cutting plates, etc., it may also be necessary to prepare the joints by bevel-edging them. The quality and smoothness of the resulting cut surface are generally satisfactory for the purpose and the methods are easy to mechanise.

3.8.1 Oxy-fuel Cutting

Oxy-fuelcuttingusesaflammablegas,generallyacetyleneorpropane.Burningthegasinoxygen,ratherthan•justairproducesaflamewithahightemperature.


48

Theflamefirstpreheatstheworkpiece,whenasufficientlyhightemperaturehasreachedandajetofoxygen•produces the cut by actually burning the metal. This produces a metal oxide in the form of liquid slag, which is blown out of the joint by the jet of gas.•Theflamealsohelpstomaintaintheuppersurfaceoftheplateabovetheignitiontemperatureofthemetalwhile•cutting is in progress, although most of the necessary heat required for the cutting comes from combustion of the actual material being cut. For example, when cutting 25 mm steel, about 85% of the heat comes from combustion oftheiron.Inthinnermaterials,however,agreaterproportionoftheheatisappliedbytheflame.

EquipmentOxy-fuel cutting can be carried out either manually, using a cutting torch, or by machine, with a numerically – •controlled cutter head. In the same way as for gas welding, there are two main types of torch:

High – pressure torches Injector torches

The difference between welding torches and cutting torches is that the latter have a nozzle for the oxygen cutting •jet,generallyinthecentreoftheflamenozzle.

MaterialsForsuccessfulgascutting,thematerialtobecutmustfulfilcertainconditions.•

The oxide must have a melting point that is lower than the melting point of the metal itself. In the case of iron, the oxides melt at about 1400°C, which is lower than the 1530°C melting point of low – carbon iron. It is the melting temperature of the oxides that explains why stainless steel and aluminium are not suitable for gas cutting.The ignition temperature of the metal must be lower than its melting point. In the case of low – carbon steel, the ignition temperature is about 1050°C.Combustionofthemetalmustcreatesufficientheattomaintaincombustion.

From this, it follows that it is only low – alloy steels with a carbon content of up to about 0.3% that can be •cut in the usual way by oxygen burners. In such steel, thicknesses up to about 300 mm can be cut by oxy-fuel cutting. Wherequalityrequirementsinrespectofthefinishedcutarelessstringent,veryconsiderablethicknessescan•be cut, up to about 3000 mm. At the other end of the scale, below 25 mm, oxy-fuel cutting is in competition with plasma cutting, which gives a higher rate of cutting.

8

6

4

2

00 20 40 60 80 100

Laser cutting

Plasma cutting

Gas cutting

Plate thickness [mm]

Cut

ting

spee

d [m

/min

]

Fig. 3.7 Typical cutting speeds for plasma cutting, oxy-fuel gas cutting and laser cutting

49

Other methods of cutting are recommended for cutting stainless steel and cast iron. However, oxy-fuel cutting •can be used to cut these materials, with the use of appropriate additives.

GasesIngaswelding,acetylenehasspecialcharacteristics,burningwithan intenseflameandahighcombustion•velocity. This high combustion velocity can be a disadvantage or even a danger, in that the combustion front can migrate backwards, into the burner nozzle. Ontheotherhand,thehotcoreoftheflamemakesthegassuitableforcuttingthinnermaterials,whichcanbe•done with good productivity.Propaneburnswithaflamewithlowerheatconcentration.Thisthereforespreadstheheatmoreevenlyalong•the cut, which can be an advantage when cutting thicker materials.Hydrogen is not commonly used as a fuel gas, although interest in it has been aroused in recent years through •the ability to produce oxygen and hydrogen by hydrolysis of water. This involves the use of electrical energy to dissociate water into its elemental constituents, at a rate as needed for cutting. In terms of their thermal characteristics,hydrogenflamesaresimilartopropaneflames.Oxygenperformsthreedutiesinconnectionwithgascutting.Itproducestheheatingflamewiththefuelgas;•it burns the material to be cut and it blows the resulting slag out of the cut. The purity of the oxygen is very important for cutting speed: 99.3–99.7 % purity is common. A reduction of 0.5 •percentage points reduces the cutting speed by about 10 %.

3.8.2 Plasma Cutting

The hot concentrated jet produced by the plasma method, which has previously been described in connection •with welding, is very suitable for cutting. However, as opposed to gas cutting, which works primarily by burning the material using the oxygen in the cutting jet, plasma cutting works by melting the material and then blowing the molten material out of the cut by the pressure of the plasma jet. When used for cutting, the pressure of the plasma gas is higher than as used for welding and both smoke and •noise are generated, at least when cutting thicker plate. However, this can be considerably reduced by cutting the metal on a cutting table, with the metal itself under water.The range of applications is wide, although materials of particular interest for this process are such as stainless •steel, aluminium and copper, which cannot be cut by ordinary oxy-fuel gas cutting.

EquipmentA hand torch can be used for simpler jobs, although industrial production generally uses numerically controlled •cutting tables, with one or more cutting heads, approximately as for gas cutting. Noise, visual radiation/arc glare and smoke can be quite intensive, but can be considerably reduced if the metal •to be cut and the plasma nozzle are under water. The arc electrode is normally tungsten or tungsten with thorium oxide. However, the development of electrodes •containing hafnium or zirconium has made it possible also to use oxidising cutting gases, even to the extent of using ordinary air.The power unit has a constant current characteristic, as for TIG and plasma welding, but must be designed •for a much higher voltage. The operating voltage exceeds 100 V and the open – circuit voltage can exceed 200 V. Special measures must be taken to prevent the operator from coming into contact with these dangerous voltages.

Plasma gasesPure argon is sometimes used as the pilot gas, in order to ensure reliable ignition of the pilot arc. The cutting •gas needs to have good heat transfer properties which can be used:

Pure nitrogen Mixture of argon / hydrogen


50

Nitrogen / hydrogen Compressed

One way of increasing the cutting speed in low – alloy steel is to use an oxidising gas that provides an active •contribution by burning the metal, in the same way as with oxy-fuel gas cutting. The simplest and cheapest gas, of course, is ordinary compressed air. However, this imposes special requirement •in respect of the electrodes. As a tungsten electrode is attacked by oxygen, a well-cooled hafnium or zirconium electrodes must be used. It •must also be accepted that there will be somewhat higher costs for replacing the electrodes.

PropertiesPlasma cutting can be the best alternative, even for ordinary low – alloy steel. For thicknesses up to about 25 •mm, the rate of cutting can be considerably faster than that of oxy-fuel gas cutting, which also means that the size of the heat affected zone is reduced. On the other hand, the kerf width is about 1.5–2 times wider than that produced by gas cutting. In addition, the •surfaces are not completely parallel; the cut is slightly wider at the top.

3.8.3 Laser Cutting

A laser beam has excellent characteristics for cutting, in particular the precision of the cut is very good and •there is very little thermal effect. The method is best suited for relatively thin materials, where very high productivity is required. Many non-•metallic materials can also be cut by laser.

EquipmentThe laser light is generated by CO• 2 or Nd:YAG lasers. The laser itself is stationary and the beam of light is carried to the cutting head where it is focused by a lens. The cutting motion may be two – dimensional or three – dimensional; the Nd:YAG laser is preferable for three •– dimensional control, as it can provide higher output powers and the light can be conducted through glass fibres,withthecuttingheadcontrolledbyanindustrialrobot.

Cutting gasA cutting gas is supplied to the cutting head together with the focused laser beam, in order to:•

Assist in blowing molten and vaporised material out of the cut. Protect the lens from spatter Depending on the material being cut, the cutting gas can either protect the surfaces from oxidation, through the use of an inert gas or through the use of an oxidising gas, provide an input from combustion heat, thus improving cutting performance.

When cutting ordinary low – alloy steel, the use of oxygen can increase the cutting speed by 25 – 40% as •compared with the cutting speed using compressed air. High purity oxygen gives the highest cutting speed.

3.8.4 Water Jet Cutting

Water jets alone can be used for cutting soft or porous materials. When cutting metals or hard materials, such •as glass or stone, abrasive water jet cutting is used, with sand being an additive in the jet.The unique feature of water jet cutting is that there is no thermal effect on the material, thus eliminating any •thermal or mechanical stresses that could affect the results. This means that, although the cutting speed may be lower than that of certain competing methods, time can be •saved overall through elimination of the need for any subsequent treatment. The quality of the cut is good, when compared with the results produced by thermal methods. The method is •

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alsosuitableforcuttingmaterialsthatcanbedifficulttocutinanyotherway.

EquipmentAn electrically driven hydraulic oil pump produces an oil pressure of 150 – 200 bars. The oil then drives a high •pressure pump that produces a water pressure of up to 4000 bar. This pressure is converted in the jet to a very high velocity, of up to about 1000 m/s. The water jet nozzle is •subjected to very high wear and so therefore includes an insert which is generally made from industrial sapphire, to provide an operating life of about 100 h. The hole through the sapphire is usually about 0.1 – 0.3mm, producing a hair – thin jet and a cut which is almost •equally narrow. The cut produced by a abrasive cutting is somewhat wider, up to about 1.5 mm.A cutting table is generally used, with a numerically controlled cutting head, as for thermal cutting processes. •Industrial robots can also be used for three – dimensional cutting.

MaterialsMost materials can be cut by water jets. Using water alone, materials such as wood, paper, felt, foamed plastic, •etc., can be cut. Abrasive water jet cutting can deal with metals such as stainless steel, copper, aluminium and titanium or with •compositessuchasglassfibre–reinforcedplasticorhardmaterialssuchasglass,ceramicsandnaturalstone.

PropertiesWater jet cutting has generally been employed where other methods are unsuitable. •Metals can be cut at a rate of about 10 – 30 cm• 2/min, or somewhat more for soft metals. Thicknesses can be up to about 100 mm. Materials such as glass, plastic, rubber, stone, etc., can be cut at rates •of about 100 – 300 cm2/min.

3.9 Thermal GougingWeldingisoftenaccompaniedbyaneedtocutawaysurplusmaterial,insuchcases,gougingcanbemoreefficientthan grinding when repairing defects in welds or when cutting a groove to avoid weld defects when the work piece is to be turned over and the weld completed from the root side.

Several of the methods and particularly those that use an electrical arc, create considerable quantities of smoke, so that special ventilation should be provided when using them indoors. In addition, as gouging involves melting the material and blowing it away, the operator should protect himself and the surroundings.

3.9.1 Oxy- fuel Gas Flame Gouging

This method is basically based on the same technology as used for gas cutting. It uses a special nozzle, which •facilitates working along the work piece surface. It is suitable for use with carbon steel and low – alloy steels, in the same way as is gas cutting.•

3.9.2 Air Carbon Arc Gouging

This method also has gone under the name of arc air gouging or carbon arc gouging. It uses approximately the •same equipment as for welding with coated electrodes. The gouging electrode is a copper – plated carbon electrode, used in an electrode holder that has an outlet for •compressed air. The best power unit is one that can provide a high current and, if possible, also a high short – circuit current, •in order to maintain the correct arc force. The electrode is held at an angle to the work piece and together with a jet of compressed air, can remove metal •at a high rate.


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The carbon electrode should be connected to the positive pole of the power unit; special electrodes are available •for use with AC. Electrode diameter from 3 mm to 19 mm are used, depending on the current available and the desired rate of metal removal.

3.9.3 Manual Metal Arc Gouging

Manual metal arc gouging does not require any equipment other than that as used for welding with coated •electrodes. The electrode, however, is a special gouging electrode, with a thick coating, which produces a considerable quantity of gas. The arc is stuck in the usual manner and the electrode is then inclined at a considerable angle to the work, with •the tip pointing in the direction of travel. It produces a smooth groove, with a high rate of metal removal. Best performance is obtained by connecting the electrode to the negative pole or by using AC.•

3.9.4 Plasma Arc Gouging

Plasma arc gouging uses the same equipment and gases as for plasma cutting. The nozzle, however, may •incorporate a nozzle for shielding gas. It is held about 20 mm from the work piece, at an angle of about 45° to it and pointing in the direction of •travel. The angle can be changed to vary the width/depth relationship in the groove.•Benefitscomparedtoaircarbonarc:•

Less generation of fumes and gases and reduced noise level. Higher productivity and groove quality. No risk of carbon pick-up. Suitable also for non – ferrous metals.

3.10 Care and Storage of ElectrodesQuality of weld depends to a great extent on the condition of the electrode just before use. Utmost care is required in handling and storage of electrodes. Electrode coating should neither get damped nor be damaged or broken. Electrodes with damp coating will produce a violent arc, porosity and cracks in the joint. Electrodes with damaged coating will produce joints of poor mechanical properties.

Toavoiddamagetocoating,electrodesduringstorageshouldneitherbendnordeflect,andelectrodepacketsshouldnot be thrown or piled over each other. Electrodes should be stored in dry and well-ventilated store rooms. The main reasons behind electrodes get damaged mainly because of the reasons as described below:

Mechanical handling: • Electrodes get damaged because of rough handling. Rough handling results in breaking protective coating of electrodes. In absence of protective coating, weld will have defects like porosity, cracks.Absorption of moisture: • Electrode, particularly low hydrogen type, is very much hydroscopic. Electrodes start absorbing moisture when they are kept open to the atmosphere. This absorbed moisture results in defects 1ike blow holes and porosity.Deterioration due to ageing: • Electrodes kept for prolonged period may show white crystals (fur) on the electrode coating. This is due to chemical reaction between CO2inairandsodiumsilicateofflux.Thisdoesnothaveparticulareffectonthequalityofweld.Thisonlyindicatesheavyfluctuationsofhumidityandtemperatureinthe storage room.Rusting of electrodes: • Iron powder electrodes sometimes get rusted when kept in open air for a long time. All such electrodes should not be used and all such electrodes should be scraped.

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SummaryPressure welding can be carried out by many welding methods, the fact having in common that the surfaces of •the joint are pressed or worked together.Resistance welding is one the oldest types of welding. Heat is generated by the passage of an electric current •through the resistance formed by the contact between two metal surfaces.Spot welding is the best known resistance welding method.•Seam welding is used in the same way as spot welding and operates on essentially the same principle.•Projection welding is used to join two overlapping sheets of relatively thin metal just like seam welding and •spot welding.Resistance butt welding is used for end-to-end welding of rods or wires, for instance, for welding wire baskets, •shopping trolleys or wire racks for use in oven, etc.Flash welding is used for welding thicker work pieces such as heavy anchor chain, rails and pipes.•Friction welding does not involve complete melting of the joint surfaces.•A disadvantage of friction stir welding is that a hole is left in the position in which tool travel stops.•Ultrasonic welding bonds the work piece parts together by vibrating them against each other at high frequency •under pressure.Diffusion welding is a method of joining surfaces to each other without melting and without deformation.•Thermal cutting processes by gas, plasma or laser are often covered in conjunction with the corresponding •welding methods.Thermal cutting is used considerably in connection with the preparation of parts for welding.•The hot concentrated jet produced by the plasma method, is very suitable for cutting.•A laser beam has excellent characteristics for cutting, in particular the precision of the cut is very good and •there is very little thermal effect.Water jets alone can be used for cutting soft or porous materials.•Manual metal arc gouging does not require any equipment other than that as used for welding with coated •electrodes.Quality of weld depends to a great extent on the condition of the electrode just before use.•Electrodes get damaged because of rough handling. Rough handling results in breaking protective coating of •electrodes.Electrode, particularly low hydrogen type, is very much hydroscopic.•Electrodes kept for prolonged period may show white crystals on the electrode coating. This is due to chemical •reaction between CO2inairandsodiumsilicateofflux.

ReferencesIntroduction to Welding• . [Online]. Available at: <http://www.globalsecurity.org/military/library/policy/navy/nrtc/14250_ch3.pdf> [Accessed 7 June 2011].Welding Procedure• . [Online]. Available at: <http://www.roymech.co.uk/Useful_Tables/Manufacturing/Welding.html> [Accessed 13 June 2011].Gonzales, R. F., 1975. • Introduction to Welding,CanfieldPress.Geary, D., 1999. • Welding, 1st ed., McGraw – Hill Professional. Ultrasonic Welding• . [Video Online]. Available at: <http://www.youtube.com/watch?v=KPhHCDZ-VX0> [Accessed 13 June 2011].


54

AmericanGunsmith, • ATI Professional Welding Section 2B Cutting Pipe [Video Online]. Available at: <http://www.youtube.com/watch?v=88v5a3ZEevw&playnext=1&list=PL44F44B4BDF2EAD87> [Accessed 13 July 2011].

Recommended ReadingHouldcroft, P.T. and John, R., 2001. W• elding and Cutting: A Guide to Fusion Welding and Associated Cutting Process, Woodhead Publishing.Mohler, R., 1983. • Practical Welding Technology, Industrial Press, Inc. Galvery Jr., W.L., Marlow, F.B., 2007. • Welding Essentials, 2nd ed., Industrial Press, Inc.

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Self Assessment

Which of the following is false?1. Resistance welding is one the oldest types of welding.a. Resistanceweldingmethodsarecomparativelyfoundtobefast,efficientandlow-polluting.b. Minor unevenness in the surface of the metal means that the current is concentrated to a few contact points, c. with the result that the heating is greatest at these points.Minor unevenness in the surface of the metal means that the current is concentrated to a few contact points, d. with the result that the heating is lowest at these points.

What is used for joining thin sheet materials by overlap joints and is widely used in the automotive industry?2. Spot weldinga. Ultrasonic weldingb. High frequency weldingc. Friction stir weldingd.

Which of the following is false?3. The initial passage of current breaks through the surface layers, so that the contact resistances drop a. rapidly.The initial passage of current breaks through the surface layers, so that the contact resistances do not drop b. rapidly.Most of the heat formed at the contact between the electrodes and the work piece is conducted away through c. the water cooled electrodes.The electrodes need to be of a material with a high hardness, low electrical resistance and high thermal d. conductivity.

What includes a number of variables that can be adjusted in order to achieve optimum welding performance?4. Spot welding processa. Ultrasonic welding processb. High frequency welding processc. Friction stir welding processd.

______________ is used in the same way as spot welding and operates on essentially the same principle.5. Spot weldinga. Ultrasonic weldingb. Friction weldingc. Seam weldingd.

What is used to join two overlapping sheets of relatively thin metal just like seam welding and spot welding?6. Seam weldinga. Flash weldingb. Projection weldingc. Diffusion weldingd.


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Which of the following is true?7. Resistanceflashweldingisusedforend-to-endweldingofrodsorwires,forinstance,forweldingwirea. baskets, shopping trolleys or wire racks for use in oven, etc.Resistance butt welding is used for end-to-end welding of rods or wires, for instance, for welding wire b. baskets, shopping trolleys or wire racks for use in oven, etc.Resistance seam welding is used for end-to-end welding of rods or wires, for instance, for welding wire c. baskets, shopping trolleys or wire racks for use in oven, etc.Resistance friction welding is used for end-to-end welding of rods or wires, for instance, for welding wire d. baskets, shopping trolleys or wire racks for use in oven, etc.

______________ does not involve complete melting of the joint surfaces.8. Spot weldinga. Ultrasonic weldingb. High frequency weldingc. Friction weldingd.

What is particularly suitable for welding aluminium?9. Spot weldinga. Ultrasonic weldingb. High frequency weldingc. Friction stir weldingd.

Electrode, particularly low _____________ type, is very much hydroscopic.10. oxygena. carbonb. hydrogenc. cadmiumd.

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Chapter IV

Soldering, Brazing and Design of Welded Components

Aim


introduce the basics of soldering and brazing•

explain them the meaning of soft soldering•

examine the details involved in brazing•

Objectives


describe braze welding in brief•

explain arc welding in short•

definelaserbeamwelding•

Learning outcome


represent welds on drawings symbolically•

comprehend the design of welding components in detail•

understand th• e design for production in brief


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4.1 IntroductionBrazing and soldering are widely used in connection with mass production. They are important industrial methods of bonding metals. They have their given applications in connection with particular materials and components for which welding are unsuitable due to the considerably higher temperatures and limited abilities to bond different metals. Soldering and brazing are suitable bonding processes for joining ferrous metals to non-ferrous metals, and for bonding used in the manufacture products made of copper or copper alloys. Although the main application differs from those of welding, they can in many cases be fully acceptable alternatives to welding.

The processes are economic due to the lower working temperatures and to the fact that there is generally no need foranysubstantialchipping,grindingorcleaningofthejointasafinishingprocess.

Brazingorsolderinginvolvesheatingtheareatobejoinedtotheworkingtemperatureofthefillermetal,ortoasomewhat higher temperature. As the working temperature is always lower than the melting temperature of the base material, and generally very much lower, the base material will remain solid throughout the process. This is the maindifferenceinprinciplebetweensoldering/brazingandwelding.Afluxisgenerallyusedinorderchemicallyto remover oxides from the surfaces and to prevent new oxide layers forming during the heating process. If the surfacesaresufficientlyclean,themoltenfillermetalcanwetthemanddiffuseintothebasemetal.Thisproducesanalloy of the metal and the base material in a thin layer in the bond zones, thus producing an uninterrupted metallic bond in the form of the soldered or brazed joint. Thermodynamic processes result in both materials diffusing into each other; the elevated temperature of the process causes elements from the added metal to diffuse into the base material and vice versa.

The structure and composition of the bonding layer can be decisive for the strength of the joint, and so it is important tochooseafillermetalthatiscompatiblewiththebasematerial.

Thesolidifiedlayeroffillermetalinthejointmustbethinifthebeststrengthandfillpropertiesaretobeachieved,which means that the gap between the two pieces to be joined exceeds 0.5 mm only in exceptional cases. Narrow gapsdrawthemoltenmetalintothembycapillaryattraction,withthebestfillbeingobtainedwhenthegapisbetween0.05 mm and 0.25 mm. A brazing alloy with a narrow working temperature range normally penetrates better than one with a wider working temperature range.

4.1.1 Types of Joints

Brazing uses the same types of joints as welding does, i.e., the ordinary butt and overlap joints. The strength of •a brazed joint depends on various factors, including the area of the joint. The greater the area, the greater the forces that the joint can withstand.As it is not necessary, when preparing a brazed joint, for the joint to be manually accessible throughout its •length, geometry such as that of the butt overlap joint or similar can often be used. An overlap width equal to about three times the thickness of the thinner part should be aimed at, in order to •providesufficientstrengthofthejoint.

Fig. 4.1 Butt overlap joints

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t

3t

Fig. 4.2 Three times the thickness of the thinner part is a suitable lap length

A particular problem when making brazed joints is that of the previously mentioned gap width. When joining •dissimilar metals and / or different thicknesses, the width of the gap changes as a result of different rates of expansion of the metal as it is heated to the working temperature. A suitable gap width is normally obtained by placing the parts in contact with each other, without any additional •pressure.

Room temperature

Brass Iron Iron

IronIron

Brass

BrassBrass

Brazing temperature

Fig. 4.3 Different combinations of materials can result in the gap increasing or decreasing as the parts are raised to working temperature

4.2 Soft SolderingThe most commonly used solders for soft soldering are alloys of tin and lead, although a wide range of other •alloys is used to a lesser extent, often for special purposes. Refer table 4.1 for the list of combinations of normal types of solder.Solderisoftensuppliedintheformofwireorbars,generallywithfluxcores.•Fluxes are often weak acids or salts. As they are corrosive, their residues must be removed from the joint after •soldering. An alternative, which does not normally result in corrosion if traces are left, is the use of resins dissolved in an •organicsolvent.Therearealsoliquidandpastefluxes.Copper and its alloys are the materials that are most commonly joined using soft soldering. The solder is •normallyatin-leadalloy,andthefluxisanon-corrosiveoronlymildlycorrosiveflux.Similarfluxesarealsoused for soldering mild steel.


60

Stronglyactivefluxesmustbeusedforsoftsolderingofmaterialswithchemicallystableoxidefilms,suchas•aluminium or stainless steel, in order to remover the oxide and allow the solder to come into contact with a sufficientlycleanmetalsurface.To produce a satisfactory joint, stainless steel should be pickled immediately before soldering.•

Sn Pb Cd Bi Ag Sb Zn Cu Melting range, °C Application

99.9 Trace 232 Tinning (food tins)

63 37 183 Cu, steel, etc (the commonest solder)

60 40 183-18850 50 183-226 Brass, solder baths50 32 18 145 Heat-sensitive parts42 58 138

44.5 55.5 124

60 38 2 183-188 Electronic assemblies, corrosion-resistant

22 25 50 95-10712.5 25 12.5 50 70-7496.5 3.5 220 Cu pipes (HVAC work)95.5 3.8 0.7 217 Electronic items (lead-free)

97.5 2.5 305 Electrical work at high operating temperatures

95 5 233-240 Food industry (not copper)70 30 300-350 Al and Al alloys

Table 4.1 List of combinations of normal types of solder

Although much soft soldering is carried out manually, the process is also very suitable for mechanisation. In the •latter case, the gap between surfaces to be joined should be narrow, not more than 0.2 mm, in order to ensure that the molten solder can reach all parts by capillary attraction. The commonest joints for such processes are various types of overlap joints.Mechanised processes are used for such applications as the manufacture of circuit boards for electronic •products.

4.3 BrazingThe key factors in determining the quality of a brazed joint are the method of brazing the composition of the •brazingfillermetalandtheflux.Foruseasafillermaterial,ametaloralloymusthavealowermeltingpointthan the work piece material, and must be able to wet the work piece material. In addition, when molten, it must flowsufficientlyeasilytoenableitproperlytofillthejoint.Theresultingalloymustprovidethenecessarymechanicalandphysicalproperties,whilethefillermetalmust•notbevaporisedtoanysignificantextentduringtheheatingprocess,asthiscouldresultinpoorfusion.Metalsinthefollowinggroupsarethosemostcommonlyusedasbrazingfillermetals.Silverbrazingalloysconsistofalloysofsilver,copper,zincandsometimesalsocadmium.Theyfloweasily,•with low working temperatures of 600 - 800°C. They can be used with all heating methods, and for almost all materials except aluminium and magnesium alloys. However,duetothetoxicityofcadmium,fillermetalscontainingitmustnotbeusedunlessfullevacuationof•the brazing fumes is provided.

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Copperphosphorusfillermetalsarebasedonalloysofcopperandphosphorus,andmayalsocontainsilver.•They are used almost exclusively for brazing copper and copper alloys. As phosphorus reduces copper oxides, themetalisself-fluxing,andsonoadditionalfluxisnormallyneeded.Oxygenfreeelectrolyticcopperisusedforfurnacebrazing.Brasswhenusedasbrazingfillermetal,consists•mainly of copper and zinc, and may often include smaller quantities of tin and silicon. It is used for brazing materials such as mild steel.High temperature brazing materials consist of nickel based alloys and silver manganese alloys. They are used •for brazing components intended to operate at temperatures well above normal ambient temperatures, such as parts of gas turbines or steam turbines.Aluminiumanditsalloysarebrazedwithfillermetalsconsistingofaluminium-siliconalloysoraluminium-•silicon-copper alloys.Filler metals are available in various physical forms, such as wire, bar, strip, foil or granules; some bar forms •includefluxcoresorfluxcoating.Theycanofcoursealsobesuppliedinperformshapes,suchasrings,washers,etc.Joint surfaces must be carefully cleaned if the best bond quality is to be obtained. Oxides must also be reduced, •and oxide formation during heating must be prevented. One way of doing this is to make the joint in an air-free environment.However,brazingisgenerallycarriedoutinair,whichmeansthatself-fluxingfillermetalsoraseparatefluxmustbeused.Thefluxconsistsofamixtureofvariousmetallicsalts,andisappliedtothejointsurfacesasahigh-viscosity•liquid, as a paste or as a powder. Heating drives off the carrier, before the salts melt and react with the oxides onthejointsurfaces.Thechoiceoffluxdependsonthetypeofworkpiecematerialandthebrazingtemperatureofthefillermetal.Brazed joints are generally some form of overlap joint. To a lesser extent, joints may be of butt type, but should •be chamfered to improve the joint strength. The gap width should be in the range 0.05-0.5 mm and preferably 0.1-0.2 mm.

Brazing can be performed manually, mechanised or automated.

Type of alloy

Ag % Cu % Zn % Sn % Cd

% P % Mn % Ni % Al

% Si % Fe % Melting range °C

Work-ing

temper-ature

°C

Silver and cadmium -

free 55 21 22 2 630-660 650

45 27 25 3 640-680 67049 16 23 7.5 4.5 625-705 69049 27.5 20.5 2.5 0.5 670-690 69034 36 27 3 630-730 71044 30 26 680-740 73020 44.9 35 0.1 690-810 810

Silver cadmium

alloys40 19 21 20 595-630 610

Copper-Phosphorus

alloys5 89 6 650-810 715

2 91.8 6.2 650-810 71015 80 5 650-800 705


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92 8 710-740 85093 7 710-82094 6 710-850 850

High temperature

materials85 15 960-970 960

Bronze / Brass 48 41.8 10 0.2 880-910 900

60 39.7 0.1 0.2 885-900 90058 40 0.8 0.3 0.4 0.1 0.4 875-890 890

47.5 41.5 0.1 0.3 10 0.3 0.3 890-900 900Aluminium

alloys 4 86 10 520-586 550

87 13 575-582 580

Table 4.2 Composition of common brazing filler metals

4.4 Braze WeldingBrazingisreferredtoasbrazeweldingwhenusedtomakeVorXbuttjoints,orforfilletjoints,andisgenerally•performedmanuallywithgasflameheating.Thefillermetalmustberelativelyviscous,inordertoprovidethebestfillofthejoint.Varioustypesofbrassalloysandappropriatefluxesaregenerallyused.ReferTable4.2.Thisisnowadaysaless•commonly used process, but is employed to some extent for making joints in copper and copper alloy pipes, as well as for brazing bronze and cast iron.

4.5 Arc BrazingArcbrazingisthenamegiventobrazingmethodsbasedonarcweldingmethods.Themostinterestingfieldof•applications here seems to be automotive body components manufactured of zinc coated steel sheet. The reason for this is that conventional fusion welding often is subjected to different problems due to the burn-•off of the zinc coating and process instabilities such as pores and spatter. Brazing speed can often reach the double value compared to welding.In arc brazing heat input is reduced and there is less vaporisation of zinc. The advantages of changing brazing •fillermetalwiththelowmeltingtemperatureare:

Minimal amount of spatter Less post-treatment of the brazed seam Low heat input Low burn-off of the zinc coating

Filler material can be low alloy copper based aluminium bronze or tin bronze based.•MIG brazing involves replacing the electrodes in an MIG welding torch with an electrode made of a copper •basedbrazingfillermetal.Thepowerratingsaresetsothatthefillermetalmelts,buttheedgesofthejointareonly heated, and not melted, by the arc. The shielding gas used is pure argon or argon with a small amount of active gas that improves the arc stability. •It is common to use argon with up to 2 % CO2 as shielding gas. Pulsed MIG arc can be used to improve arc stability. MIG brazing allows a high joining rate. Brazing speeds up to 3 m/min can be achieved.TIGbrazingusesamechanisedfeedingofthebrazingfillerwire.Pureargonisusedasshieldinggas.•

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Plasma arc brazing uses a plasma torch combined with a wire feed of brazing metal. The plasma arc is more •stable and gives better brazing properties compared to MIG brazing. Generally argon is used both as plasma and shielding gas but small additions of other gases (He, H2) could be used to improve the brazing speed.

4.6 Laser Beam BrazingWhen joining thin sheets of steel laser beam brazing is an excellent alternative to the arc brazing technique. •Both, CO2 and Nd:TAG lasers are used but also high power diode lasers are becoming available. For brazing the focus of the beam does not need to be as precise as for welding. It has an advantage of being •able to increase the laser beam spot size by defocusing. Filler wire is supplied by a wire feeder but can also be pre-placed.Laser beam brazing cause very small heat affected zones. The seam becomes very smooth and before painting •allows a minimum of after treatment.

4.7 Symbolic Representation of Welds on DrawingsA welding symbol on a drawing consists of:

An arrow line (1)•One or two reference lines (2)•An elementary symbol (3)•Possible supplementary symbols•Dimensions of the weld•

1

2

3

Fig. 4.4 Symbols used on welding drawings


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Fig. 4.5 Examples of elementary symbols

4.7.1 Elementary Symbols and Supplementary Symbols

In general, the elementary symbol is similar in shape to that of the welded joint (i.e. before welding, indicating •howthemetalsheetsaretobepreparedforwelding).Examplesofelementarysymbolsareshowninfig.4.5.If the unbevelled edge exceeds 2 mm, the joint is a single-V butt joint with broad root faces (Y). If not, it is a single-V butt joint.Supplementary symbols may be used, in combination with the elementary symbols, see Fig. 4.6. Absence •ofsupplementarysymbolsmeansthattherearenospecificrequirementsinrespectoftheshapeoftheweldsurface.

Fig. 4.6 Supplementary symbols

4.7.2 The Importance of the Reference Lines

The position of the elementary symbol on the reference lines indicates on which side of the arrow line that the •weld is to be placed.

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The upper, solid line (which is recommended to be terminated by a tail showing that the representation refers to •IS0 2553) indicates a weld on the arrow side. In this case, the elementary symbol is placed on the solid line. The lower, interrupted line indicates a weld on the other side. In this case, the symbol ‘hangs’ below the •interrupted line.

Other side Other sideArrow side Arrow side

Weld on arrow side Weld on arrow side

Fig. 4.7 A T-joint with one fillet weld

Other side of joint A

Other side of joint A

Other side of joint B

Other side of joint B

Arrow side of joint A

Arrow side of joint A

Arrow side of joint B

Arrow side of joint B

Fig. 4.8 A cruciform joint with two fillet welds

The interrupted reference line is not used for fully symmetrical welds. Refer Fig. 4.9 for example.•

Fig. 4.9 Examples of symmetrical welds

4.7.3 The Position of the Arrow Line

Ingeneral,thereisnosignificanceinthepositionofthearrowlineinrelationtotheweld,exceptinthecaseof•single bevel butt welds and single-J butt welds where the arrow of the arrow line must point towards the plate that is prepared.


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Desired weldSymbol on drawing

Fig. 4.10 Position of the arrow line

4.7.4 Complementary Symbols

Whenaweldistobeappliedallthewayroundapart,thesymbolisacircleasshowninfig.4.11.Fieldorsite•weldsareshownbymeansofaflag.

a) Peripheral weld b) Field or site weld

Fig. 4.11 Complementary symbols

Further information can be given after the tail, in the following order:Process (e.g. in accordance with IS0 4063)•Acceptance level (e.g. in accordance with IS0 5817 and IS0 10042)•Working position (eg. in accordance with IS0 6947)•Filler metal (e.g. in accordance with IS0 544, IS0 2560, IS0 3-58 1)•

Thevariousitemsshouldbeseparatedbyslashes(I).Inaddition,referencecanbemadetospecificinstructions(e.g.aproceduresheet)usingasymbolinaclosedtail,asshowninthefigurebelow.

A1

Fig. 4.12 Reference information

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4.8 Design ConsiderationLoad and stress distribution

Whensubjectedtoaload,astressflowspreadthrough,andactson,thevariouspartsofthestructure.Changesin•thegeometryinterferewiththisstressflow,givingrisetostressconcentrations,asshowninthefigurebelow.These stress concentrations are of less importance in statically loaded structures. Although, strictly, some parts •of the material may be stressed to beyond their yield strength limit, this does not actually involve any safety risk, as parts of the material will simply yield and redistribute the stresses.

a) Consistent stressflow

b) Circular hole c) Notch d) Changed section

Fig. 4.13 Examples of change in stress flow

F FFσn=

A

AA

A

A

A

A

F

F

Fig. 4.14 Schematic stress flow in various types of welded joints

The situation is different, however, in structures subjected to fatigue loads. In such cases, the stress concentrations •are vital in determining the overall strength of the structure, so that care must be taken in the design to avoid stress concentrations. As far as welded joints are concerned, the welds themselves constitute a stress concentration, as shown in the •figurebelow.


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4.8.1 Design to Transfer Local Forces

A main rule of design is that parts should be arranged so that forces are transferred in the plane of the material, •and not perpendicular to it. If an applied force acts in the plane of the material, then the material is used to its maximum (resulting in •tensional, compressive or shearing stresses).

Force transferring sectionF

F

Fig. 4.15 Marked surfaces act like shells

If, instead, the load is applied perpendicularly to the plane of the sheet, it will act like a plate and be subjected •to bending, which in turn means that all of the material cannot be used to its maximum. Fig.4.16 shows the parts transferring the forces in an I-beam. It follows so that if a hanger eye is to be attached •toabeam,itshouldbedesignedasshowninthefigurebelow.

F F

Fig. 4.16 Beam with a hanger eye

Fig. 4.17 is an example of how not to design. If the hanger eye must be arranged perpendicular to the web of •thebeam,reinforcementscouldbeappliedasshowninfig.4.18,whichwilltransfertheloadtothewebofthebeam. Thiswillthenreplacetheundesirableloadonthebottomflangebyamorefavourableapplicationoftheforce•in the plane of the reinforcements.

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FF

Fig. 4.17 A hanger eye welded to the flange of a beam-poor design

FF

Fig. 4.18 Reinforcements transfer the load to the web of the beam

Fig. 4.19 shows a completely wrong position for positioning a hanger eye, giving rise to high bending stresses •intheweb.Italsoshowsabetterwayinwhichtheforcescanbetransferredintotheplaneoftheflanges.

F F F

F

a) b) c)

Fig. 4.19 (a) shows a poor design, which has been improved as shown in (b). If the beam is subjected to horizontal forces, the attachment should be arranged as shown in (c)

4.8.2 Design as Determined by the Type of LoadThe following order of priorities can be recommended for dealing with the various types of load encountered in a structure:

Tensile loads•Bending loads•


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Compressive loads•Torsional loads•Shear loads•

4.8.2.1 Tensile Loads

An excellent result will be achieved if it is possible to design the various elements of the structure such that •they are subjected mainly to tensile stresses. The entire cross section of the material then plays its part in carrying the load, thus utilising the material in the •optimum manner to produce light, cheap designs.

4.8.2.2 Compressive Loads

Arranging for the loads in the structure to be carried as compressive loads also makes good use of the material. •However, the strength of a slender structure can be reduced by the risk of buckling or other instability phenomena. The critical buckling load is independent of the strength of the material. This means that, when designing slender •structures in which the risk of buckling determines the load-carrying capacity, it does not help to choose an alternative material having higher structural strength.On the other hand, the modulus of elasticity of the material plays a decisive part in determining the load-carrying •capacity of slender structures. All structural steels have the same modulus of elasticity. In the case of slender structures that are welded and subjected to compressive loads, the longitudinal residual •compressive stresses acting on each side of the weld, also have a negative effect on the load-carrying capacity. In the case of cistern-like structures in particular, the true buckling stress is considerably lower compared to •theoretically calculate buckling stress.

4.8.2.3 Shear Loads

When part of a structure transfers the load by shearing, it acts as a shell, which is favourable. However, there •is a risk of shear buckling in the case of thin walled shells. The load-carrying capacity will then be reduced in a similar way as for buckling under compressive loading.•

4.8.2.4 Bending Loads

Ifitisnotpossibletoavoidhavingtotransfertheloadsbybendingthestructuralparts,thefirststepistoattempt•to place the material as far away from the centre of gravity of the cross section as possible. Figure below shows two cross sections having the same cross-sectional areas.

a) b)

Mb Mb

+σ+σ

-σ

-σ

Fig. 4.20 Bending stresses

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4.8.2.5 Torsional loads

It is particularly unfavourable to attempt to transfer torsional loads in open, thin-walled sections. Welded •structures are often of this type. If,instead,theopeningcanbeclosed,torsionalresistancewillbesubstantiallyincreased,asshowninthefigure•below.

a) b)

T T

Fig. 4.21 (a) Torsion-resistant, closed (b) Low torsion-resistance, open

Every cross section has a point - centre of torsion - to which an external force can be applied without imposing •torsional loads upon the section. Thefigurebelowshowsexamplesofthepositionofthecentreoftorsioninanumberofcommonsections.•

CG

CG CG CG

CG

CG

CT

CT

CT

CTCT

CT=CG CT=CG

CT

Fig. 4.22 Centre of torsion (CT) for a number of sections. CG = Centre of Gravity

4.8.3 Design to Resist Corrosion

Considerations can be made for corrosion at the design stage as follows:•Design the structure to avoid corrosion. Design the structure so that it is easy to apply corrosion protection, and •so that the corrosion protection can easily be maintained.Design the structure with an allowance for corrosion (rust allowance), i.e., so that some corrosion can occur •without risk of failure or leakage. It is important to avoid pockets and crannies in which dirt and water can collect,asshowninfig.4.23


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Drain hole

Fig. 4.23 Designing to avoid corrosion

Unsuitable shape Unsuitable shape Suitable shapeSuitable shape

Fig. 4.24 Avoiding corrosion around welds

If it is not possible to avoid areas where water can gather, drain holes of at least 20 mm diameter should be •provided in appropriate positions.Thestructureshouldbedesignedsothatnarrowgapsareavoided,asshownintheabovefigure.Usebuttwelds•instead of overlap welds.If overlap welds cannot be avoided, they must be applied all the way round the material, taking particular care •to avoid pores. Rustprotectioncanbeappliedbyhotzinc-coating.Enclosedvolumes,asshowninthefig.4.25,musthave•openings in order to prevent bursting effect when immersed in the solution of zinc.

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Usable Good

Fig. 4.25 Designing for zinc-coating

4.8.4 Design for ProductionProductcostscanbekeptdown,unnecessaryworkontheshopfloorcanbereducedandoverallqualitycanbeimproved if, right at the initial sketch stage, the designer carefully thinks through the production aspects of the design, and understands how the particular production process operates. Some general points are as follows:

Usestandardrolledorextrudedprofiles,orsteelcastings,asfaraspossible,whichwillminimisetheamount•of welding required.Welding can be reduced, and the number of parts kept down, by bending sheet materials.•Use rational welding methods, such as spot welding, arc welding, friction welding etc.•Consider the accessibility of parts to be welded (and accessibility for inspection and maintenance).•Try to position joints so that the required welding position is comfortable. Horizontal welding is preferable to •overhead welding.Chooseasuitablegroove,havingtheminimumfillermetalneededtomeetthenecessaryrequirementsinrespect•of quality, penetration requirements etc.Optimisethethroatthicknessoffilletwelds.Doublingthethroatthicknessrequiresfourtimesasmuchfiller•metal: welding distortions also increase with increasing throat thickness. In general, some degree of penetration canbeexpectedforfilletwelds,whichmeansthattheactualthroatwillbesomewhatthickerthanasshownonthe drawing.Use intermittent welding wherever possible.•Selectmaterialsfamiliartothemanufacturer.High-strengthmaterialscanbedifficulttohandleandwork.•Trytoavoidusingtoomanydifferentmaterialqualities,sheetthicknessesortypesofprofiles,inordertoavoid•any risk of mix-ups.Specify the geometry, quality classes, and inspection requirements etc. of welds unambiguously and in an •optimum manner, in order to keep down manufacturing costs.Special consideration may be required if production is automated. The weld, for example, must be positioned •accurately, and it may be necessary to provide greater space for the robot to reach the weld. Butt welds can be difficultifbackingisnotprovided.Permissibletolerancelevelsarereduced.Using symmetrical welds can reduce welding distortions.•Weldingismadeeasierifthepartsareself-locatingandself-fixing.•


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SummaryBrazing and soldering are widely used in connection with mass production and are important industrial methods •of bonding metals.Brazingorsolderinginvolvesheatingtheareatobejoinedtotheworkingtemperatureofthefillermetal,orto•a somewhat higher temperature.Brazing uses the same types of joints as welding does, i.e., the ordinary butt and overlap joints.•Fluxes are often weak acids or salts.•Copper and its alloys are the materials that are most commonly joined using soft soldering.•The key factors in determining the quality of a brazed joint are the method of brazing, the composition of the •brazingfillermetalandtheflux.High temperature brazing materials consist of nickel based alloys and silver manganese alloys.•BrazingisreferredtoasbrazeweldingwhenusedtomakeVorXbuttjoints,orforfilletjoints,andisgenerally•performedmanuallywithgasflameheating.Arc brazing is the name given to brazing methods based on arc welding methods.•MIG brazing involves replacing the electrodes in an MIG welding torch with an electrode made of a copper •basedbrazingfillermetal.When joining thin sheets of steel laser beam brazing is an excellent alternative to the arc brazing technique.•

ReferencesIntroduction to Welding• . [Online]. Available at: <http://www.globalsecurity.org/military/library/policy/navy/nrtc/14250_ch3.pdf> [Accessed 7 June 2011].Gonzales. R. F., 1975. • Introduction to Welding,CanfieldPress.Mouser,J.D.,1998.Weldingcodes,standards,andspecifications,McGraw-HillProfessional.•Brazing and Soldering• [Online]. Available at: <http://www.weldingengineer.com/1soldering.htm> [Accessed 13 June 2011].Soldering and Brazing Training• [Video Online]. Available at: <http://www.youtube.com/watch?v=Yjyy51PQ2cw> [Accessed 13 June 2011].Brazing, Soldering and TIG Welding• . [Video Online]. Available at: <http://www.youtube.com/watch?v=Yjyy51PQ2cw> [Accessed 13 June 2011].

Recommended ReadingStephens, J.J., Weil,K.S., 2006, Brazing and soldering, Proceedings of the 3• rd International Brazing and Soldering Conference, ASM International.Cain, T., 1985. Soldering and brazing, Workship Practice, Issue 9 of • Workshop practice series, Argus Books.Gregory, E.N., Armstrong, A.A., 2005. W• elding symbols on drawings, CRC Press.

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Self Assessment

Which of the following is false?1. Soldering and brazing are suitable bonding processes for joining ferrous metals to non-ferrous metals, and a. for bonding used in the manufacture products made of copper or copper alloys.Soldering and brazing are important industrial methods of bonding metals.b. Soldering and brazing have their given applications in connection with particular materials and components c. for which welding are unsuitable due to the considerably higher temperatures and limited abilities to bond different metals.Soldering and brazing have their given applications in connection with particular materials and components d. for which welding are unsuitable due to the considerably lower temperatures and limited abilities to bond different metals.

Which of the following is false?2. Brazingorsolderinginvolvesheatingtheareatobejoinedtotheworkingtemperatureofthefillermetal,a. or to a somewhat higher temperature.As the working temperature is always higher than the melting temperature of the base material, and generally b. very much higher, the base material will remain solid throughout the process.As the working temperature is always lower than the melting temperature of the base material, and generally c. very much lower, the base material will remain solid throughout the process.The structure and composition of the bonding layer can be decisive for the strength of the joint, and so it is d. importanttochooseafillermetalthatiscompatiblewiththebasematerial.

_____________ uses the same types of joints as welding does.3. Brazinga. Meltingb. Solderingc. Coolingd.

The strength of a brazed joint depends on various factors, including the _____________ of the joint.4. sizea. ratiob. structurec. aread.

Which of the following is true?5. The most commonly used solders for soft soldering are alloys of copper and lead.a. The most commonly used solders for soft soldering are alloys of tin.b. The most commonly used solders for soft soldering are alloys of tin and lead.c. The most commonly used solders for soft soldering are alloys of lead.d.


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Solder is often supplied in the form of wire or bars, generally with _____________.6. fluxcoresa. alloysb. metalsc. brazingd.

Which material is most commonly joined using soft soldering?7. Leada. Tinb. Copperc. Cadmiumd.

____________ brazing alloys consist of alloys of silver, copper, zinc and sometimes also cadmium.8. Cadmiuma. Silverb. Tinc. Leadd.

_______________ free electrolytic copper is used for furnace brazing.9. Hydrogena. Carbonb. Manganesec. Oxygend.

When part of a structure transfers the load by _____________, it acts as a shell, which is favourable.10. shearinga. bendingb. weldingc. brazingd.

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Chapter V

Quality Assurance and Quality Management

Aim


introduce quality assurance and quality management•

explain them the details of quality requirements for welding (EN 729)•

describe welding coordination (EN 719) in brief•

Objectives


elucidatethespecificationandapprovalofweldingprocedures(EN288)•

discuss welding procedure tests for arc welding of steel in detail•

determine the welding procedure test for arc welding of aluminium and its alloys•

Learning outcome


recallthegeneralrulesforthespecificationandapprovalofweldingprocedures•

understandweldingprocedurespecification(EN288–2)•

comprehen• d the documents of approved welding procedure tests


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5.1 IntroductionThe company performing the work needs to analyse quality requirements at the tendering stage in respect of welding structuresthataresetoutindirectives,regulations,standardsorcustomerspecifications,todecidewhethertheycanbefulfilledornot.Generallythisisassistedbysystematicmethodofworking.Forthis,companieswithISO9001/9002certificationhavedocumentedprocedures.ISO9001/9002issystemstandardsconcernedwithqualitysystems.Theydefineweldingasa specialprocess thatmustbeproperlycontrolled inorder toensure that thenecessaryqualityrequirementsarefulfilled.

ISO 9001 / 9002 Quality System

EN 729 Quality Requirements for Welding

EN 287Approval Testing of Welders

Certification

EN 288SpecificationandApprovalof

Welding Procedures

pWPS – WPAR – WPS

EN 719 Welding Coordination

Task and Responsibilities

Competence: Welding Engineer, EWE

Welding Technologist, EWTWelding Specialist, EWS

Fig. 5.1 Standards that regulate quality requirements for welding structures

5.2 Quality Requirements for Welding (EN 729)En 729 is a process standard for welding and describes how quality assurance of welding work can be ensured. •It consists of four different parts. EN 729 – 1, which is a guideline part, sets out the following application areas:•

AsguidanceforspecificationandestablishmentofthatpartofISO9001/9002concernedwiththemanagement of special processes.As guidance for determination of welding quality requirements in those cases where the quality system standards are not applicable.In connection with auditing assessment of welding quality in accordance with above two points.

The standard has three different quality requirement levels, relating to comprehensive requirements, standard •requirementsandelementaryrequirements,sothatthesupplier/customer/requirementspecifiercanchoosetherequirement level that is suitable for the welding work to be performed.En 729 – 2 is used for all three quality requirement levels when ISO 9001 or 9002 requirements apply. This •is because the requirements in EN 729 – 2 can be set at a suitable level for the particular structure concerned, depending on the effect of welding on the product safety and function. However, if ISO 9001/9002 requirements are not involved, then EN 729 is applied, as follows:•

EN 729 – 2 - Comprehensive quality requirements EN 729 – 3 - Standard quality requirements EN 729 – 3 - Elementary quality requirements

The next stage in the process is to select the particular elements from EN 729 – 2, - 3 or – 4 that are applicable •to the particular working area. The standard includes an appendix that provides assistance on this.

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EN729–4specifiesaminimumacceptablequalityrequirementlevel,fromwhichnoelementsmaybeaccepted.•If there are requirements in respect of general quality management systems, EN 729 – 2 must be chosen.

Requirement Element Heading number in the standard

Contract and design review 4Subcontracting 5Welders and other welding – related personnel 6Inspection / testing personnel 7Equipment 8Activities associated with welding 9Consumables 10Storage of parent materials 11Post – weld heat treatment 12Welding inspection / testing 13Non – conforming and corrective actions 14Calibration 15Identificationandtraceability 16Quality records 17

Table 5.1 Requirement elements in EN 729 – 2

The differences between EN 729 – 2 and EN 729 – 3 are slight and relate primarily to requirements in respect •of equipment maintenance, calibration and approval of WPS and batch inspections of electrodes. EN 729 – 1 includes an appendix that provides an overall description of the differences between the three levels •of the standard.Refer table 5.2, which shows the relationship between requirement elements in ISO 9001 and the corresponding •requirements in EN 729 – 2, - 3 and - 4.

5.3 Welding Coordination (EN 719)Weldingisaprocessthatrequiresmanagementandcoordinationinordertoensurethatthespecifiedquality•requirementscanbefulfilled.EN 719 describes the duties and responsibilities associated with such coordination and management of welding, •brieflysummarisedbelow.The extent of the coordination required depends on the company’s own requirements, requirements in applicable •standards and in the contract. The duties in connection with this coordination and management can be shared by a number of persons. However,itmustbedefined,e.g.,bydocumentsdescribingthedutiesofthepersonsconcerned.•

ISO 9001 EN 729 – 2 EN 729 – 3 EN 729 – 44.1.2 Organisation 6.1 6.14.1.2.2 Personnelandequipmentforverification 7.1 / 2 7.1 / 2 -4.3 Contract review 4.2 4.2 (4)4.4.5 Design review 4.3 4.3 (4)4.6 Purchasing 5 5 (5)4.8 Productidentificationandtraceability 16 (15) -4.9 Process control – Planning 9.1 (9.1) -

Process control – Instructions 9.2 / 4 (9.3) (8)Process control – welding procedure approval 9.3 9.2 -Process control – Workshop capacity 8.1 / 2 (8.1 / 2) -Process control – Equipment 8.3 / 4 (8.3) -


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Process control – Maintenance 8.5 (8.3) -Process control – Heat treatment 12 (12) -

4.10.2 Process control and testing 13.2 / 3 13.2 / 34.10.3 Final inspection and testing 13.4 13.44.10.4 Inspection and test reports 9.5 - -4.11 Calibration 15 - -4.12 Inspection and test status 13.5 13.5 -4.13 Non conformance products 14 (14) (11)4.14 Corrective actions 14 (14) (11)4.15.2 Handling 10.3 10.2 -4.15.3 Storage 11 11 -4.16 Quality documents 17 16 (12)4.18 Training 6.2 / 3 6.2 / 3 6

Table 5.2 Requirement elements in ISO 9001 in comparison with EN 729 – 2, – 3, – 4

( ) = Less extensive requirements- = No requirementsExamples of such duties include:

Specification Control / coordinate inspect / witness

Somebody must be appointed as the company’s authorised welding coordinator, authorised to issue approval •the necessary welding documents on behalf of the company. Of the activities listed in EN 729, the following can be linked to quality-related duties in accordance with EN •719:

Contract review Design review (in respect of feasibility of manufacture) Purchasing of base materials Selection of consumables Selection of subcontractors Production planning Selection of equipment Approval of welders Personnel for inspection / testing Performing the welding Inspection and testing Documentation

A suitable way of meeting the above requirements in connection with the manufacture of welded products is to •use checklists for the preparation of tenders and for production planning.

QualificationsWeldingcoordinatorsmustpossessthenecessaryqualificationsfortheirduties,intheformofgeneralandspecial•technical knowledge, coupled with experience from the welding industry. Under EN 719, technical knowledge can be divided into three levels: comprehensive, standard and •elementary.Examplesoftrainingandqualificationsthatareregardedasfulfillingtherequirementsinrespectoftechnical•

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knowledge are the following, as approved by the European Welding Federation (EWF):European Welding Engineer, EWE European Welding Technologist, EWT European Welding Specialist, EWS

5.4 Specification and Approval of Welding Procedures (EN 288)EN288,withAnnexeA1:1997,describesthespecificationsforandapprovalof,weldingproceduresforweldingmetallic materials. It consists of the following parts:

General rules for fusion welding.•Weldingprocedurespecificationsforarcwelding.•Welding procedure tests for arc welding of steels.•Welding procedure test for arc welding of aluminium and its alloys.•Approval by using approved welding consumables for arc welding.•Approval related to previous experience.•Approval by a standard welding procedure.•Approval by a pre-production weld test.•Welding procedure test for pipeline welding.•

5.4.1 General Rules (En 288 – 1)Application

Thissectionofthestandarddefinesgeneralrulesfordescriptionandqualificationofweldingprocedures.•It assumes that welding will be carried out using conventional welding methods, controlled by a welder or •weldingoperatorworkinginaccordancewithaweldingprocedurespecificationorweldingdatasheet.Thestandardapplieswhenqualificationofweldingproceduresiscalledfor,e.g.,incontracts,productstandards,•regulations or directives.

Specification of welding proceduresAllweldingoperationsmustbesufficientlyplannedbeforeproductionstarts.Thisincludesproducingwelding•procedurespecificationsforallweldedjoints,inaccordancewiththerequirementsofEN288-2andprovidingasmuchdetailasrequiredbythequalificationmethod.All important variables that could affect the properties of the welded joint must be included. Any permissible •variationsmustbespecified.Until theweldingprocedurespecificationhasbeenapprovedinaccordancewithEN288, it isclassifiedas•preliminary, pWPS.

ApprovalA welding procedure can be approved by one of the following alternatives:

previous experience of such welding•approved welding consumables•welding procedure test•standard welding procedure•pre-production test welding•

Annexe A of EN 288-1 sets out guidelines for application and selection of approval methods.


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5.4.2 Welding Procedures Specification (EN 288 – 2)

EN288-2 specifies the technical contents of thewelding procedure specification (WPS) for arcwelding•methods. Subject to agreement between the contracting parties, the standard may also be applied to other fusion welding •methods.A WPS must specify, in detail, how welding is to be performed. It must contain all important information relating •to the welding work, with indication of whether such factors can affect the metallurgy, mechanical properties or geometry of the welded joint.ThenomenclatureofweldingandalliedprocessesisspecifiedandnumberedinIS04063.Numbersdesignating•the most common welding methods are shown in the table 5.3. Model forms for WPS are given in the standard in the form of an appendix.

5.4.3 Welding Procedure Tests for Arc Welding of Steel (EN 288 -3)EN 288-3 sets out the conditions for welding approval procedures for the arc welding of steel and includes the welding methods in Table 16.3.

Welding Method ISO 4063 designation

Metal arc welding with covered electrode 111Flux cored metal – arc welding without gas shield 114Submerged arc welding 12MIG welding 131MAG – welding 135MAG–weldingwithfluxcoredwire 136TIG – welding 141Plasma arc welding 15Oxy – acetylene welding 311

Table 5.3 Numerical reference numbers of common fusion welding methods as given in ISO 4063

Other fusion welding methods can be included, subject to agreement between the parties.

Test piecesThestandardspecifiestheshapeandminimumdimensionsofstandardisedtestpiecestobeusedinconnection•withtheweldingprocedure.Thetestpiecesmustbesufficientlylargetoensurethatthereissufficientmaterialto conduct away the heat. When impact testing of the heat-affected zone is required, the test pieces must be marked with the rolling •direction.All welding of test pieces must be carried out in accordance with the preliminary WPS and under the same •conditions as can be expected in production. Working positions and angles of slope and rotation must be as specifiedinIS06947.Tack welding must be included in the test welds if it is to be used in production. Welding and testing must be •supervised by an examiner or examining body.

Examination and testingTesting consists of both non-destructive and destructive testing, as appropriate. They are as follows:

Visual perception•Radiographic or ultrasonic testing•Crack detection•

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Transverse tensile test•Transverse bend test•Impact testing•Hardness test•Macro and micro examination•

Thestandardspecifieshowthetestpiecesshallbepositioned.Retesting

If the welding procedure test pieces do not meet all the test requirements, the results cannot be approved. It is •permissible to perform a further procedure test.If any single test piece fails to meet the requirements due to geometrical defects, two new test pieces may be •selected for retesting. If either of them fails, then the entire WPS also fails.

Range of approvalAWPSthathasbeenqualifiedbyamanufacturerisvalidforweldinginworkshopsandatsitesunderthesame•technical management.WeldingproceduretestsformthebasisforqualificationofaWPS,ofwhichtheimportantvariablesliewithin•the approval range of the procedure test. Essential variables are as follows:

Base material•Material thicknesses•Welding method•Welding position•Type of joint•Consumables•Type of welding current•Heat input•Preheat temperature•Intermediate pass temperature•Post heat treatment•

Documents of approved welding procedure tests (WPAR):Records from welding and testing shall include all the information needed for approval. •Welding Procedure Approval Records (WPAR) must be signed by the examiner. Model forms of WPAR are •included in the standard.

Older welding procedure tests:Olderweldingproceduretests,carriedoutinaccordancewithnationalstandardsorspecifications,canbeapproved•providedthatthetechnicalrequirementsinEN288arefulfilledandthatthetestconditionscorrespondtotheproduction conditions that will be encountered. Use of these older welding procedure tests shall be agreed between the contracting parties.•

5.4.4 Welding Procedure Test for Arc Welding of Aluminium and its Alloys (EN 288 – 4)

In a similar manner to EN 288-3, EN 288-4 describes the conditions applicable to approval of welding procedures •to be used for arc welding of aluminium and its weldable alloys in accordance with IS0 2092 and 2107. These welding methods are MIG welding, TIG welding and plasma welding.Thestandard,whichfollowsthesameprinciplesasinEN288-3,specifieshowweldingistobeperformedand•what tests that are to be carried out.


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Important variables for the procedure test are the same as for steel, but with lesser differences in the validity •area. Note that welding position is an essential variable. Tensile testing employs a correction factor linked to the type of alloy of the base material and its delivered •conditions. Bend testing is carried out using a larger former diameter for the high-strength alloys than for untreated aluminium.

Use of approved welding consumables (EN 288-5)EN 288-1 allows welding procedures to be approved on the basis of their use of approved consumables. This •method is described in EN 288-5, which applies for repetitive welding operations and for work piece materials of which the structures and properties in the heat-affected zone do not degrade during operation.For steel, applicable welding methods are metal-arc welding, MIGMAG welding and TIG welding, while MIG •welding and TIG welding are approved for aluminium. The standard applies to carbon manganese steels and chrome nickel steels, as well as for pure aluminium and •non-heat-treatable aluminium alloys. Base material thicknesses are 3–40 mm.Approvalisgivenbyanexaminerorexaminingorganisation,basedontheworkpiecematerialspecificationin•accordance with an EN standard and description of approved consumables in accordance with the relevant EN standardsandaspecificpWPSinaccordancewithEN288-2.Approval is valid as long as the approved consumables continue to be used and is documented by means of the •examiner’s initials and dating on the pWPS concerned.

Approval related to previous experience (EN 288-6):Many workshops have considerable experience of the manufacture of welded structures involving third-party •inspection,withgoodoperatingexperienceofthefinishedproducts.Insuchcases,theweldingprocedurecanbe approved on the basis of reference to previous experience. EN 288-6 describes the conditions for this procedure and covers metal arc, submerged arc, MIGIMAG, TIG •and plasma welding.It must be possible to document an EN 288-2 pWPS based on previous experience by authentic tests or •investigationsthatshowthatthetechnicalspecificationrequirementsfortheproductarefulfilled.Twomethodsofdocumentationarespecified:

Documentation of testing (e.g., non-destructive or destructive testing, leak testing), together with a summary of welding production over a period of at least one year.Theperformancerecordsofweldsinoperationoverasuitableperiod(fiveyearscanbesuitable).

Range of approval is in accordance with EN 288-3 and 288-4 and continues to apply as long as manufacturing •is carried out in the prescribed manner. Approval is documented by the examiner initialling and dating the preliminary WPS, which is then kept by the •manufacturer.

Approval by a standard welding procedure (EN 288-7):EN 288-7 describes the conditions for approval and use of a standard welding procedure. These procedures are •restrictedtothematerialgroupsandworkpiecethicknessesspecifiedinEN288-7.A standard WPS must comply with the requirements in EN 288-2 and be approved by an examiner or examining •bodywho/thatverifies thatweldingand testingarecarriedout inaccordancewith the requirementsof thestandard. Organisations that have prepared approved standard welding procedures can then supply them as bases for other •companies various welding data sheets. The use of standard welding procedures, as of approved consumables or previous experience, can be limited by standards applicable to particular products or by requirements in contracts.

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The use of standard welding procedures requires the involvement of a welding coordinator in accordance with •EN719,coupledwitharequirementthatthecompany’squalitymanagementsystemmustfulfiltherequirementsof the applicable part of EN 729.Standardweldingproceduresarevalidaslongastheaboverequirementsarefulfilled.•

Approval by a pre-production weld test (EN 288-8):Welding procedures may be approved by pre-production weld tests if the shape and sizes of test pieces in •accordance with the standard do not represent the particular types of welded joints to be made. The conditions associated with this method of approval are set out in EN 288-8.The test pieces must comply with the applicable product standard, or be as agreed between the contracting •parties. A pWPS must be prepared before welding the test pieces, which must be carried out under conditions representative of the planned production.As far as possible, testing shall include the various requirements given in the standard. In general, the following •tests must be carried out:

visual inspection crack detection macro examination hardness test (depending on the material requirements)

In general, the validity range of approval is as set out in the applicable parts of EN 288, but restricted to the •type of joint used for the testing. Approval of the procedure remains valid as long as production conditions are the same as those used during •testing. As far as possible, WPAR must comply with EN 288-3 or 288-4.


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SummaryEn 729 is a process standard for welding and describes how quality assurance of welding work can be •ensured.En 729 – 2 is used for all three quality requirement levels when ISO 9001 or 9002 requirements apply.•EN729 – 4 specifies aminimumacceptable quality requirement level, fromwhich no elementsmay be•accepted.The differences between EN 729 – 2 and EN 729 – 3 are slight and relate primarily to requirements in respect •of equipment maintenance, calibration and approval of WPS and batch inspections of electrodes.EN 729 – 1 includes an appendix that provides an overall description of the differences between the three levels •of the standard.EN288-2 specifies the technical contents of thewelding procedure specification (WPS) for arcwelding•methods.ThenomenclatureofweldingandalliedprocessesisspecifiedandnumberedinIS04063.•Important variables for the procedure test are the same as for steel, but with lesser differences in the validity •area.Tensile testing employs a correction factor linked to the type of alloy of the base material and its delivered •conditions.EN 288-1 allows welding procedures to be approved on the basis of their use of approved consumables.•EN 288-7 describes the conditions for approval and use of a standard welding procedure.•

ReferencesQuality Management Principles• . Available at: <http://www.iso.org/iso/qmp> [Accessed 14 June 2011].Introduction to Welding• . Available at: <http://www.globalsecurity.org/military/library/policy/navy/nrtc/14250_ch3.pdf >. [Accessed 7 June 2011].Gonzales. R. F., 1975. • Introduction to Welding,CanfieldPress.Street, J.A.,1982.• Instrumentation for quality assurance in arc welding, The Welding Institute.WeldingProcessClassification• . [Video Online] Available at: <http://www.youtube.com/watch?v=oRpaof56noc> [Accessed 13 July 2011]. Weld Stresses Lecture• [Video Online] Available at: <http://www.youtube.com/watch?v=Nap_0fjCktY> [Accessed 13 July 2011].

Recommended ReadingBurgess, N.T., 1983. • Quality assurance of welded construction, Applied Science.International Institute of Welding, 1988. Guidelines for Quality Assurance in Welding Technology, Woodhead •Publishing.Blondeau, R., 2008. • Metallurgy and Mechanics of Welding, John Wiley and Sons.

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Self Assessment

_____________ is a process standard for welding and describes how quality assurance of welding work can 1. be ensured.

En 729a. En 729 – 1b. En 729 – 2c. En 729 – 4d.

What is used for all three quality requirement levels when ISO 9001 or 9002 requirements apply?2. En 729a. En 729 – 1b. En 729 – 2c. En 729 – 4d.

Whatspecifiesaminimumacceptablequalityrequirementlevel,fromwhichnoelementsmaybeaccepted?3. En 729a. En 729 – 1b. En 729 – 2c. En 729 – 4d.

_______________isaprocessthatrequiresmanagementandcoordinationinordertoensurethatthespecified4. qualityrequirementscanbefulfilled.

Solderinga. Weldingb. Brazingc. Meltingd.

Which of the following is false?5. EN 729 describes the duties and responsibilities associated with coordination and management of a. welding.EN 719 describes the duties and responsibilities associated with coordination and management of b. welding.Under EN 719, technical knowledge can be divided into three levels: comprehensive, standard and c. elementary.Annexe A of EN 288-1 sets out guidelines for application and selection of approval methods.d.

Which of the following is false?6. EN729,withAnnexeA1:1997,describesthespecificationsforandapprovalof,weldingproceduresfora. welding metallic materials.UntiltheweldingprocedurespecificationhasbeenapprovedinaccordancewithEN288,itisclassifiedasb. preliminary, pWPS.EN288-2specifiesthetechnicalcontentsoftheweldingprocedurespecification(WPS)forarcweldingc. methods.EN288,withAnnexeA1:1997,describesthespecificationsforandapprovalof,weldingproceduresford. welding metallic materials.


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All_____________operationsmustbesufficientlyplannedbeforeproductionstarts.7. solderinga. meltingb. weldingc. brazingd.

Which of the following is true?8. AWPARthathasbeenqualifiedbyamanufacturerisvalidforweldinginworkshopsandatsitesunderthea. same technical management.AWPSthathasbeenqualifiedbyamanufacturerisvalidforweldinginworkshopsandatsitesundertheb. same technical management.ApWPSthathasbeenqualifiedbyamanufacturerisvalidforweldinginworkshopsandatsitesunderthec. same technical management.AWPSthathasbeenqualifiedbyamanufacturerisnotvalidforweldinginworkshopsandatsitesunderd. the same technical management.

Weldingproceduretestsformthebasisforqualificationofa_____________,ofwhichtheimportantvariables9. lie within the approval range of the procedure test.

WPSa. WPARb. pWPSc. SAWd.

What must be signed by the examiner?10. WPSa. WPARb. pWPSc. SAWd.

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Chapter VI

NDT Management

Aim


introduce Non-destructive testing •

describe radiography testing in brief•

explain the applicable ASME codes and standards for radiography testing•

determine the applications of NDT in marine environment•

Objectives


elucidate ultrasonic testing in detail•

explain magnetic particle testing •

elaborate liquid penetrant testing•

Learning outcome


understand leak testing •

comprehend visual testing in brief •

examin• e the discontinuities


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6.1 Introduction to Non-Destructive TestingNon-destructive testing (NDT) is a method of examining the materials for internal as well as surface anomalies or discontinuities without destruction of the product or material.

AdvantagesTofulfilcode/standards/specificationrequirements.•It is a quality control and quality assurance tool.•It is used before and after fabrication (manufacturing).•It is used during fabrication (manufacturing) – (Used during online testing).•It is used during various testing service.•100 % examination of tests is possible in NDT.•NDT can be performed on metals as well as non – metals.•DuringNDTinternal/surfaceflawsaredetected.•

LimitationsMinimum two methods for complete examination of the product.•Trained,qualifiedandcertifiedpersonsareauthorisedtoconducttestsandinterpretandevaluatetestresults•(Level I, II and III) as per ASNT SNT – TC – I A.

MethodsRadiography Testing (RT)•Ultrasonic Testing (UT)•Magnetic Particle Testing (MT)•Penetrant Testing (PT)•Eddy Current Testing (ET)•Leak Testing (LT)•Thermal Infraredgraphy (TIR)•Neutron Radiography Testing (NRT)•Acoustic Emission Testing (AET)•Vibration Analysis (VA)•

Selection of NDT method depends on:Code/standards/specification/client’srequirements•Discontinuities - Type / Nature, Size & Orientation•Manufacturing process•Equipment available•Cost•

6.2 Radiography Testing (RT)[For internal discontinuities]Highly penetrating radiation like X-rays and gamma rays are used to penetrate the material and the image of the materialisrecordedonanX-rayfilmbytheprocessofionisationofSilverBromideemulsionontheX-rayfilmby ionising radiation (Shadow graph). A black and white image is obtained after chemically processing of exposed X-rayfilmtogetradiograph.

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The absorption of radiation depends on density, thickness of material and energy level of radiation. It is most widely used, one of the primary methods of NDT.For Radiography we need:

Source of Radiation (X – Ray / Gamma Rays)•Object (Welding, Casting, etc)•Recordingmedia(X–Rayfilm)•

AdvantagesRadiography testing can be used to examine all types of materials (metals / Non – metals).•It reveals internal nature of materials.•It reveals fabrication errors.•It reveals structural errors.•It reveals structural discontinuities.•It can be used on variety of materials•Film provides a permanent record.•Gamma radiography does not require electrical power.•

LimitationsRadiography testing is usually suited to having access to both sides of the welded joint.•It is a positive method for detecting porosity, inclusions, cracks, and voids in the interior of welds.•It has a crack and lacks fusion.•In radiography testing lamination detection is not possible.•X-ray and gamma radiation is invisible to the naked eye and can have serious heath and safety implications.•It is a slow and an expensive method.•Specially trained and authorised persons•It is very good for voluminous discontinuities’ (Porosity and Lack of penetration)•It is impracticable for complex objects.•

EquipmentPortable / Stationary•Portable: Amertest (tech – ops), Gammarid, Teletron, etc. (Imported / Indian)•Ir 192, Co – 60 Gamm ray Radioactive Isotoes•X – ray m / c – 160 Kv, 5 mA / 200 Kv, 5 mA / 300 Kv, 5 Ma•

Factorsaffectingthequalityofradiograph(sensitivity)arecontrastanddefinite.To qualify a radiograph for evaluation sensitivity and density variation must meet code requirements.

Penetration

Ir 192 isotope Steel – max. Penetration 75mmCo 60 Isotope Steel – max. Penetration 200mmX – ray 160 Kv Steel – max. Penetration 19mmX – ray 200 Kv Steel – max. Penetration 30mmX – ray 300 Kv Steel – max. Penetration 50mm


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Techniques

SWSI Single Wall Single ImageDWSI Double Wall Single ImageDWDI (Elliptical) Double Wall Double ImageDWDI (Superimposed) Double Wall Double ImageSWSI For plates, welds Flat components, Long seams, ‘C’ seamsDWSI For pipe joints (NOD > 3 ½ inches)DWDI For pipe joints (NOD > 3 ½ inches)DWDI Superimposed (NOD > 3 ½ inches)

(NOD: Nominal Outside Diameter)

Applicable ASME Codes/ASTM StandardsASME Sec V Article 2 – For Techniques•For Acceptance criteria•

ASME Sec VIII Div 1 (UV 51 – Full radiography and UW52 Spot radiography) ASME Sec I (PW51) ASMEB31.1 (136.4.5)

ASTM E-94 : Standard Guide for Radiographic Testing•ASTM E-142: Standard Method for Controlling Quality of Radiographic Testing•ASTM E- 1030 : Standard Test Method for Radiographic Examination of Metallic Castings.•

Acceptance -Rejection StandardAs Per ASME UW 51, PW 51 and B31.1, indication shown on the radiograph of weld and characterised as imperfections are unacceptable under the following conditions:

Any indication characterised as crack or zone of incomplete fusion or penetration.•Any other elongated indication on the radiograph which has length greater than•

1/4 inch for ‘t’ up to 3/4 inch 1/3 t for ‘t’ from 3/4 inch to 2 1/4 inch 3/4 inch for ‘t’ over 2 1/4 inch

Where‘t’ is equal to the thickness of the weld excluding any allowable reinforcement. For a butt weld joining two •members having different thicknesses at the weld, ‘t’ is the thinner of these two thicknesses. If a full penetration weldincludesafilletweld,thethicknessofthethroatofthefilletshallbeincludedin‘t’.Any group of aligned indications that have an aggregate length greater than ‘t’ in a length of 12t, except when •the distance between the successive imperfections exceeds 6L where ‘L’ is the length of the longest imperfection in the group.RoundedindicationsinexcessofthatspecifiedbytheacceptancestandardgiveninAppendix4.•

As per UW 52Welds in which indications are characterised as slag inclusions or cavities shall be unacceptable if the length •of any such indication is greater than 2/3 t where‘t’ is the thickness of the weld excluding any allowable reinforcement.For a butt weld joining two members having different thicknesses at the weld,‘t’ is the thinner of these two •thicknesses.Ifafullpenetrationweldincludesafilletweld,thethicknessofthethroatofthefilletshallbeincluded in‘t’.

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If several indications within the above limitations exist in line, the weld shall be judged acceptable if the sum of •the longest dimensions of all such indications is not more than‘t’ in a length 6t (or proportionately for radiographs shorter than 6t) and if the longest indications considered are separated by at least 3L of acceptable weld metal where L is the length of the longest indication. The maximum length of acceptable indications shal1 be 3/4 inch (19 mm). Any such indications shorter than •1/4 inch (6 mm) shall be acceptable for any plate thickness.Rounded indications are not a factor in the acceptability of welds not required to be fully radiographed.•

Radiation source

Specimen

Penetration and

absorption

Void

Film

Fig. 6.1 Radiographic testing


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Negative supply SourcePositive supply

Electron beam

Cooling

Anode

Filament Target Lead shield

F

a

Object

Film

U0

Glass envelop

Fig. 6.2 Standard X8 ray tube and demonstration of geometric unsharpness

Geometric unsharpness,

UG =

Source, is given by,

Umax =

Where,‘t’ is the specimen thickness. For good quality gamma radiographic work it is generally accepted that U should not be more than 0.25mm.

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Fig. 6.3 Typical radiographic exposure arrangements for pipe welds

6.3 Ultrasonic Testing (UT)(For Internal Discontinuities)Piezo – is an electric principle of ultrasound generation. Sound with frequency above 20 KHz is used to generate mechanicalvibrations in thematerialunder test.The transmittedultrasoundenergy is reflectedbackwhen thediscontinuity is encountered and is converted in the form of electronic pulse.

For ultrasonic testing we needSource of ultrasound generation - Transducer (Piezo – electric crystal)•Object to be tested•Electronic pulse display device: CRT•

AdvantagesUltrasonic testing is accessible only on one side of the welded joint.•Ultrasonic testing is highly sensitive.•Lamination discontinuities (Planner) can be detected•It is particular about thickness measurement.•It is applicable to almost all metals and non – metals.•It requires is a fast and less expensive method.•

End view

Source (Typical)

Side view

(A) (B)

(C) (D) (E)

(F)


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LimitationsIt has no permanent records.•Itisdifficultforcoarsegrainmaterials.•It is operator dependant (skill of operator)•

EquipmentPortable•Stationary•

ApplicationsIngots - Cracks, Piping•Rolled - Cracks, Piping•Forged - Cracks, Piping, Bursts•Welds - Cracks, lack of penetration, lack of Fusion, Slag inclusions•Cast - Cracks, Inclusions, Cavities•

MethodsUltrasonic testing involves two methods for testing. They are as follows:

Pulse Echo•Transmission•

TechniquesPulse echo contact beam – (A Scan) – Amplitude Vs. Distance•Pulse echo immersion – (A Scan, B Scan, C Scan)•

Applicable ASME Codes/ASTM StandardsASME Section V, Article 5 : For techniques•ASME Sec VIII Div 1 Appendix 12, ASME Sec I (PW 52), ASME B31.1 (136.4.6) : For Acceptance criteria•ASTM A388 : Standard Practice for Ultrasonic Examination of Heavy Steel Forgings•ASTMA435:StandardSpecificationforStraightBeamUltrasonicExaminationSteelPlates•ASTMA577:StandardSpecificationforUltrasonicAngleBeamExaminationofSteelPlates•ASTMA578:StandardSpecificationforStraightBeamUltrasonicExaminationofPlainandCladSteelPlates•for Special ApplicationsASTM A609 : Standard Practice for Castings, low Alloy and Martensitic Stainless Steel Ultrasonic •ExaminationASTM A745 : Standard, Practice for Ultrasonic Examination of Austenitic Steel Forgings•ASTM E213 : Standard Practice for U1trasonic Inspection of Metal Pipe and Tubing•

6.4 Magnetic Particle Testing (MT)[For Surface and sub – surface discontinuities]Ferromagneticmaterials aremagnetised to createmagneticflux.Themagneticflux leakage takes place at thediscontinuity location because of poles formation. When ferromagnetic media is applied on the surface of the material,themediagetsattractedatleakagefieldtoformavisualindicationofdiscontinuity.

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For magnetic particle testing we need:Source of magnetisation - Electromagnet•Object to be tested: ferro-magnetic•Ferromagnetic powder: wet / dry to form to form visual indication of discontinuity•

AdvantagesIt has surface and sub – surface (near surface) discontinuities.•It is a simple and easy method.•It has a medium speed and is less expensive.•It is highly sensitive.•

LimitationsIt is applicable only on ferromagnetic materials.•

Equipments

Prod. Type Portable and mobileHead shot StationaryCentral conductor StationaryYoke PortableCoil PortablePermanent magnet PortableBlacklightassembly(UVlight)forfluorescentpowder

Table 6.1 Equipments in magnetic particle testing

ApplicationsIngots - Porosity, Cracks•Welds - Cracks•Forgings - Laps, cracks, burst•Castings - Cracks, Hot tears, Cold shut•Rolled Bar - Seams, Stringers•

Techniques

AC Surface discontinuities

HWDC / FWDC Subsurface discontinuities

Circular Magnetisation: AC / HWDC / DC

Prod type (for welds and cast), Head shot (forged and cost articles), Central, conductor (hollow parts forged and cast)

Longitudinal magnetisation: AC / HWDC / DC

Yoke type – most portable (cast, weld, forged), Coil (forged and castings)

Table 6.2 Techniques in magnetic particle testing


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MethodsMagnetic Particle Testing (MT) is performed by two methods. They are as follows:

Visible•Fluorescent by:•

Continuous Magnetisation – Application of ferromagnetic media when current is ON. Residual Magnetisation – Application of ferromagnetic media after the current is OFF.

6.5 Liquid Penetrant Testing (PT) (For surface discontinuities)Liquid penetrant testing works on principles of capillary action. A coloured dye (Penetrant) is applied on the surface of the article, by capillary action the dye goes into the surface open discontinuities, excess surface dye is removed by a remover chemical (cleaner) after dwell time is over and then white developer is applied on the surface. The reverse capillary action aids the dye to come out on the surface from the discontinuity. The indication is visually seen in the background of the white developer.

ProcessPre-cleaning•Application of dye penetrant•Excess penetrant removal (After dwell time is over)•Application of developer•Interpolation and evaluation of indications (after dwell time is over)•Post cleaning•

Chlorine, Fluorine and Sulphur contents less than 1%. No intermixing of different groups is allowed.

AdvantagesApplicable on all metals and non – metals.•

LimitationsIt is applicable only for surface open discontinuities.•It is a slow and costly method.•To perform this method some skill is required.•Itisnotsuitableonhighlyporousmaterial(UnfiredCeramic)•

TechniquesVisibleandfluorescentdyepenetrant•Dry / wet developers•

MethodsFollowing are the two methods used for performing Liquid Penetrant Testing (PT)

Visible•Fluorescent•

Types of penetrant (Based on type of penetrant remover)Postemulsifiablepenetrant•Solvent removable penetrant•Water washable penetrant•

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Penetrant systems available: FluorescentPostemulsifiablepenetrant•Fluorescent solvent removable penetrant•Fluorescent water washable penetrant•Visiblepostemulsifiablepenetrant•Visible solvent removable penetrant•Visible water washable penetrant•

Developers available:Dry (Powder)•Wet•

Water soluble Water suspendible Solvent suspendible (non – aqueous)

Solvent removable visible penetrant with solvent suspendible developer most widely used.

ApplicationsIt is applicable for surface open discontinuities in,

Ingots•Welds•Castings•Forging•Rolled products•Non – metals•

Applicable ASME Codes /ASTM StandardsASME Sec V Article 6 : For Techniques•ASME Sec VIII Div 1 (Appendix 8)•ASME B31.1 (136.4.4)•ASTM E165 : Standard Test Method for Liquid Penetrant Examination•ASTM E1209 : Standard Test Method for Fluorescent Penetrant Examination using Water Washable Process•ASTM E1219 : Standard Test Method for Fluorescent Penetrant Examination using Solvent Removable •ProcessASTM E1220 : Standard Test Method for Visible Penetrant Examination using Solvent Removable Process•


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Penetrant applied to surface Time allocated for penetrant to sep into the opening

Surface penetrant removed Developer applied to draw pen-etrant out of opening

Specimen visually examined Post cleaning

Fig. 6.4 Penetrant testing method

6.6 Leak Testing (LT)[Through Discontinuities]Leak testing is the determination of the rate at which a liquid or gas will penetrate from a “tight” component or assembly to the outside or vice versa, as a result of a pressure differential between the two regions or of permeation of a somewhat extended barrier.

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TechniquesBubble test•Hydro test•Helium leak detector•Residual gas analyser•

Most precise and accurate method out of the three is the use of helium gas, being the lightest one.For leak testing we need:

Leak detector with all accessories •Test object •Gas cylinder with testing probe / sniffer probe•

AdvantagesIn this method any type of material (metal / non – metals) can be tested.•It is sensitivity and has a medium speed of testing.•It requires less skill.•

LimitationsIt is portable.•It can be detected only through discontinuities.•It is expensive.•It has no permanent records.•It cannot differentiate the discontinuities porosity / crack.•It cannot detect slag, side – wall fusion.•Testing is possible only in assembled condition.•

EquipmentFor bubble test: Compressor•Forhydrotest:Mechanicallyoperatedhydraulicpumpwithrelevantfittings•Heliumleakdetectorrotarypump(roughing)andotherrelevantfittingslikeflexiblemetallichose,etc•

ApplicationsIt is applicable in welding of metals.•Sealing joints of assemblies test:•

The leak testing is applicable to test the systems or assemblies, where high vacuum or ultra high vacuum is required.

Factors affecting speed of testingInner rough surface•Faultyortoomanyfittingsinassembly•

Applicable ASME Code/ASTM StandardsASME Sec. V Article 10 : For Technique•ASME B31.1 (137.0) : For Acceptance criteria•ASTM E432 : Standard Recommended Practice for the Selection of a Leak Testing Method•


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ASTME479:RecommendedGuideforpreparationofaLeakTestingSpecification•ASTM E1603 : Leakage Measurement using Mass-Spectrometer Leak Detector or Residual Gas Analyser in •the Hood MethodASTM E515 : Leaks using Bubble Emission Techniques•

6.7 Visual Testing (VT)[For surface discontinuities]Visual examination is performed by using the naked, alone or in conjunction with various magnifying devices, without changing, altering or destroying the materials involved.

AdvantagesIt requires low cost (except remote viewing).•Inspection is possible at any stage.•It requires a fast speed.•It is used for recording.•Applicable on all materials.•Both side accesses are not required in this method.•It is a safe method of testing.•

LimitationsIt is sensitive.•Less skill are required for testing.•It is applicable on only surface discontinuities•

Techniques

Direct Visual Examination Remote Visual Examination Translucent Visual Examination

Minimum light level shall be •50 foot candles

Parts are examined using •Boroscope, Fibroscope, Magnifiers,Weldgauges,etc

Parts are examined using •incandescentartificiallighting

Parts should be at maximum •24″fromeye

Part to be examined should be •at angle not less than 30 deg, to the surface

Table 6.3 Techniques for visual testing

Surface condition and preparationThe surface irregularities of weld ripples shall be removed by any suitable process at a suitable degree. •Surface cleaning agents such as solvents, paint removers, etchants, and water diluted acids/alkalis, soap solution, •etc. should be used.

EquipmentRulers•Magnifiers•

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Weld gauges•Callipers•Suitableincandescentbulb/flashlight/measuringtapes•White light meters•Microscope•Mirror•

RequirementsAn operator should have near vision of J1 level at least with one eye. He should have spent 25% time in one •NDT method and balance 75% time should have been spent on VT.

ApplicationsForging Defects - Bursts, Seam, laps, Porosity and Cracks•Casting Defects - Shrinkage, hot tear, cold shut, sand inclusions, porosity and cracks•WeldingDefects-Centrelinesolidificationcracks,HAZcracking,weldtoecracks,undercuts,porosity,pin•holes, lack of penetration, lack of fusion, burn through, mismatch.Pipes / Tubes - (Methods of Manufacturing: Sinking pilgering, drawing and extrusion) Die Marks, Slivers (line •of inclusion), Porosities (material defects opened out in drawing), Surface seams.

Tubes/PipesorTubularproductsmayrequireBoroscope/fibroscopeforremoteviewing.

6.8 DiscontinuitiesAll the discontinuities are not necessarily defects.•Discontinuities not meeting acceptance criteria are called defects.•

INDICATIONS

INTERPRETATIONS

NON RELEVANT RELEVANT

EVALUATION

ACCEPT REJECT (DETECT)

FALSE

Fig. 6.5 Indications of discontinuities


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TYPES OF DISCONTINUITIES

Inherent

Cast Wrought (Ingot) Welding Fatigue

Hot tearsCold shut

Non metallicInclusionBlow holes & porosityShrinkage piping

RollingForgingHeatTreatment etc.,

StressCorrosion – cracking

Processing Services

Fig. 6.6 Types of discontinuities

Processing discontinuitiesForging - Laps, Bursts•Rolling - Lamination, Stringers, Seams•Heat treatment - Cracks•Grinding - Cracks•Welding - Crater cracks (star, shaped, longitudinal, transverse),stress cracks, porosity, slag inclusion, Tungsten •inclusion, Lack of penetration, Lack of fusion, Undercuts, Excess penetration, Concavity.

6.9 Applications of NDT in Marine EnvironmentThe sight of a Lloyd’s Surveyor in his hard hat, tapping with his light hammer, looking for a hollow sound in •a casting or deck plating, suspected wasted, was common in the bygone days. That light hammer was one of the earliest tools for non-destructive testing of materials and it used audible sound •for gauging cavities or “un-sound” materials.Sonar used for soundings in shallow water is another NDT method commonly known to mariners. It uses •ultrasound (inaudible frequencies of sound for sensing depth of water to the bottom of the sea or the estuary.

6.9.1 Methods of NDT used in Marine Applications

Stern and tail shafting: • Thoroughly forged and normalised steel shafting - It is 100% ultrasonically tested, i.e., fully scanned, to ensure that there are no unacceptable defect indications. Its key ways are magnetic particle tested when new and at each special survey, to detect any fatigue cracks, particularly at sharp edges and corners.Hull plates, deck plates: • Comprehensive spot checks by UT are carried out for thickness gauging at every maintenance and special survey, to ensure wastage has not reached unacceptable proportions.Keel plates and above, up to bilge plates: • All weldments (generally butt welds) are fully radiographed (RT), with stringent acceptance criteria. Above the bilge line, butt welds are spot radiographed, with spots selected at random by the ship surveyor for quality assurance purposes, targeting gross defects.Anchors and chains: • These are magnetic particle tested (MT), at maker’s Works and thereafter proof load tested.

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Crankshafts, connecting rods and gudgeoned pins: • All these forgings are magnetic particle tested in as forged condition by prod method, and by head shots where possible, and after machining, by using AC Yoke method of MT, to avoid any sparking marks on the highly machined surfaces.

6.10 Pressure Tests (Leak Test or LT)Boilers, Air Receivers, Cylinder heads, Piston Crowns, Pipe Lines, Valves, Coolers land Condensers, Pump •casings are all subjected to hydrostatic or pneumatic pressure testis to look for leakages, if any. It’s common for a Surveyor to certify an equipment to be “sound and tight” after a successful test.•That brings us back to the word “sound”! Soundness is what all the tests on equipment and structure are supposed •to check and assure its user.


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SummaryNon-destructive testing is a method of examining the materials for internal as well as surface anomalies or •discontinuities without destruction of the product or material.AblackandwhiteimageisobtainedafterchemicallyprocessingofexposedX-rayfilmtogetradiograph.•The absorption of radiation depends on density, thickness of material and energy level of radiation.•Factorsaffectingthequalityofradiograph(sensitivity)arecontrastanddefinite.•Rounded indications are not a factor in the acceptability of welds not required to be fully radiographed.•Piezo – is an electric principle of ultrasound generation.•Ferromagneticmaterialsaremagnetisedtocreatemagneticflux.•Liquid penetrant testing works on principles of capillary action.•Visual examination is performed by using the naked, alone or in conjunction with various magnifying devices, •without changing, altering or destroying the materials involved.The surface irregularities of weld ripples shall be removed by any suitable process at a suitable degree.•Sonar used for soundings in shallow water is another NDT method commonly known to mariners. It uses •ultrasound.

ReferencesNDT Management• [Online]. Available at: <http://ndt-specialist.com/search/non-destructive-testing-ppt/> [Accessed 14 June 2011].Introduction to Welding Technology• [Online]. Available at: <http://www.newagepublishers.com/samplechapter/001469.pdf >. [Accessed 7 June 2011].NDT Management• [Online]. Available at: <http://www.authorstream.com/Presentation/pinkalone23-189642-non-destructive-final-education-ppt-powerpoint/>[Accessed14June2011].Ultrasound Non-Destructive Testing NDT of Composite Carbon Material• [Video Online]. Available at: <http://www.youtube.com/watch?v=TkH0LLpmx8c&feature=related> [Accessed 13 July 2011].Mix. P. E., 2005. • Introduction to Nondestructive Testing: A Training Guide, 2nd ed., Wiley – Interscience.Gonzales. R. F., 1975. • Introduction to Welding.CanfieldPress.

Recommended ReadingPaul. E., 2005. • Introduction to Non Destructive Testing: A Training Guide, 2nd ed., Wiley – Interscience.Ravi., 2009. • Non Destructive Testing Techniques. New Age Science.Hellier. C., 2001. • Handbook of Non-destructive Evaluation, 1st ed., McGraw-Hill Professional.

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Self Assessment

____________ is a method of examining the materials for internal as well as surface anomalies or discontinuities 1. without destruction of the product or material.

SAWa. TIGb. NDTc. MIGd.

Which of the following is false?2. Selection of NDT method depends ona. code.Selection of NDT method depends on standards.b. SelectionofNDTmethoddependsonspecification.c. Selection of NDT method does not depend on client’s requirements.d.

Which of the following is false?3. AblackandwhiteimageisobtainedafterchemicallyprocessingofexposedX-rayfilmtogetradiograph.a. The absorption of radiation depends on density, thickness of material and energy level of radiation.b. Radiography testing is most widely used and one of the secondary methods of NDT.c. Radiography testing is most widely used and one of the primary methods of NDT.d.

Factorsaffectingthequalityof____________arecontrastanddefinite.4. radiographa. solderingb. weldingc. brazingd.

Which of the following is true?5. Welds in which indications are characterised as slag inclusions or cavities shall be acceptable if the length a. of any such indication is greater than 2/3 t.Welds in which indications are characterised as slag inclusions or cavities shall be unacceptable if the length b. of any such indication is greater than 2/3 t.Welds in which indications are characterised as slag inclusions or cavities shall be unacceptable if the length c. of any such indication is less than 2/3 t.Welds in which indications are characterised as slag inclusions or cavities shall be unacceptable if the length d. of any such indication is greater than 3/2 t.

Rounded indications are not a factor in the acceptability of welds not required to be fully ______________.6. weldeda. solderedb. brazedc. radiographedd.


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Thetransmitted_____________energyisreflectedbackwhenthediscontinuityisencounteredandisconverted7. in the form of electronic pulse.

ultrasounda. kineticb. mechanicc. potentiald.

Which of the following is false?8. Ferromagneticmaterialsarenotmagnetisedtocreatemagneticflux.a. Themagneticfluxleakagetakesplaceatthediscontinuitylocationbecauseofpolesformation.b. The surface irregularities of weld ripples shall be removed by any suitable process at a suitable degree.c. Ferromagneticmaterialsaremagnetisedtocreatemagneticflux.d.

Which of the following is false?9. Whenferromagneticmediaisappliedonthesurfaceofthematerial,themediagetsattractedatleakagefielda. to form a visual indication of discontinuity.Sonar used for soundings in shallow water is another NDT method commonly known to mariners.b. All weldments (generally groove welds) are fully radiographed (R T), with stringent acceptance criteria.c. All weldments (generally butt welds) are fully radiographed (R T), with stringent acceptance criteria.d.

Which of the following is false?10. NDT works on principles of capillary action.a. The reverse capillary action aids the dye to come out on the surface from the discontinuity.b. Visual examination is performed by using the naked, alone or in conjunction with various magnifying devices, c. without changing, altering or destroying the materials involved.Discontinuities not meeting acceptance criteria are called defects.d.

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Chapter VII

The Petroleum Act, Petroleum Rules and the Indian Boilers Act

Aim


definepetroleumasperthePetroleumAct,1934•

discuss exemption limits of Petroleum Act, 1934•

explainflammablesubstanceandspecificprecautionsthatshouldbetaken•

Objectives


determine the extraction from Factory Rule, 1963•

elucidate the comments on The Indian Boilers Act, 1923•

discuss the application of act to economisers•

explaintheerectionprocedureforfielderectedverticalstoragetanks•

Learning outcome


enlistthefeaturesofsteampipesandfittings•

understandflangesindetail•

comprehend AS• ME boiler and pressure vessel code


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7.1 IntroductionAsper theAct, thedefinitionofPetroleum is – It is any liquidhydrocarbon,mixtureof hydrocarbonsor anyinflammablemixture(liquid,viscous/solidcontaininganyliquidhydrocarbon.)Classificationofpetroleumisbasedonflashpoint.

ClassA – flashpointlessthan23°C(LPG)•ClassB – flashpoint23°Cormorebutlessthan650C(HSD,Kerosene)•ClassC – flashpoint65°Cormorebutlessthan93°C.(FurnaceOil,LSHS,LSGR)flashpoint93°C•or more, not covered under Act.

Storage of any petroleum product covered under the Act requires storage licence. However, some quantities are exempted are given below:

Exemption limits:Class A - Not more than 30 lit (i.e. up to 30 lit)•Class B - Not more than 2500 lit and not more than 1000 lit in the container•Class C - Not more than 45kl (i.e. upto45 kl). Some relevant rules (R 120 means Rule 120 etc.)•R 120 - All enclosures surrounding above ground tanks to be properly drained, drain valve operation should •be possible from outside enclosure.R 121 - Installation to be protected by surrounding wall or fence at least 1.8m high•R 124 - For storage tank LID ratio should be not more than 1.5 or L = 20m. Whichever is less (e.g. 4000cub m •tank, dia-16m, ht-20 m).R 127 - All tanks should be provided with proper earthing connection, each tank should have at least 2 earthing •connections; resistance to earth for such connection should be not more than 7 ohms.R 131 - Plans of installation are to« submitted for prior approval.•R 138 - Minimum distance of 1.5 m to be maintained between tank wall and enclosure.•R167-(Major)storagetanktobeatleast90mawayfromboiler,furnace,stilletc.(Anysourceofopenflame),•However Furnace Oil lay tank can be installed in boiler house.R 168 - LPG (major) storage to be minimum 90m away from boiler furnace etc. Further, the same should be •minimum30mawayfromblendingorfillingofpetroleum.

TheRulesspecifydistancestobemaintainedbetweenstoragetankandboundaryfencingfillingpoint,electricmotor(coupled to pump) etc. These distances depend on type of petroleum and quantity stored.Sometypicaldistancesaregivenintable9.1below.Forspecificinstallationreferrules.Minimum distances to be maintained where Class A and Class B petroleum stored exceed 5 Kl or diameter of tank exceeds 9 m.

Storage Tank

Tank vehicle unloading area

FLP electric motor

Non FLP electric motor Boundary fencing

Class A 15 m 8 m 15 m 20 mClass B 15 m 8 m 15 m 15 mClass C x x x 4.5 m

Table 7.1 Typical distances

‘x’meansnospecific,stipulationundertherules.

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7.2 Flammable Substance – Specific Precautions

Prevent static charge build – up•Provide evaluation and inert purging connection for system start – up•Leadsafetyvalveoutlettoflareheader•Check requirement of inert purging connection in safety valve outlet line•

Following documents need to be submitted to factory inspector, extracts from factories act 1948 and Maharashtra factories rules 1963 and national building code:

Plot planThe plot plan to be preferably drawn to scale 1,500 or less (As per MIDC, GIDC requirements)•

Equipment layout plan:Elevation and necessary cross sections of various buildings drawn to scale 1:100 or less with following additional •information clearly marked up.

Aisles and passage ways to be marked up and width indicated. Minimum width to be 1m. Equipment close to the wall or column clear distance between equipment and wall / column to be marked. Minimum distance between any machine and wall / column should preferably be 1m.Formulti-storeybuildings,stairways/fireescapestairwaystobehighlighted,forno.andtypeofstairways, refer rule 70 given in the extracts below.For all power driven machinery, motor Kw to be marked up.

The above information should preferably be marked up on reproducible of equipment layout.•

While deciding equipment layout, following additional requirements to be taken into account:All workroom / buildings should be not more than 18 m wide with windows on both the outer (longer) walls. •Ifnot,provisionofefficientforceddraughtventilationwillbeinsisteduponinrespectofanysuchworkroom/ building and details of this viz., capacity of the forced draught fans, resultant air changes per hour proposed to be obtained should be furnished.Minimumheightfromthefloortotheroofofbuildingshouldbenotlessthan3.75m.•The height of all rooms for human habitation shall not be less than 2.75m measured from the surface of the •floortothelowestpointoftheceiling(bottomofslab).Incaseofair-conditionedrooms,aheightofnotlessthan2.4mmeasuredfromthesurfaceofthefloortothe•lowest point of air-conditioning duct or the false ceiling shall be provided ( as per national building code part III, Para. 8.2.1).Mezzaninefloor(anintermediatefloorbetweentwofloors,abovegroundlevel)shouldhaveminimumheight•of2.2mandarearestrictedto1/3oftheareaoftheflooronwhichitisconstructed.Themezzaninefloorshouldnotbesub-dividedintosmallercompartmentsandshouldbesoconstructedasnot•to interfere under any circumstance with the ventilation of the space over and under it. (As per National Building Code Part III, Para. 2.0 and 8.6).

Exit requirements (Extracts from National Building Code Part IV – Fore Protection)Everybuildingtobeprovidedwithexitssufficienttopermitsafeescapeofoccupantsincaseoffireorother•emergency. All exits shall be free of obstructions and shall be so arranged that they may be reached without passing through another occupied unit.An exit may be a doorway, corridor, and passage ways to an internal staircase or external staircase, or to a •veranda or terraces which have access to a street or the roof of a building. An exit may also include a horizontal exit leading to an adjoining building. Lifts and escalators are not considered as exits.


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Thereshallbenotlessthantwoexitsservingeveryfloor.Incasebothareinternalstairwaysatleastoneofthem•shall be an enclosed stairway.Every exit door way shall open into an enclosed stairway, a horizontal exit on a corridor or passageway providing •continuous and protected means of egress.No exit doorway shall be less than 1 m in width and 2 m in height. They shall open outwards, i.e., away from •the room but shall not obstruct the travel along any exit. No door when opened shall reduce the required width of stairway or landing to less than 90 cm.Exitdoorshallnotopenimmediatelyuponaflightofstairsalandingequaltoatleastthewidthofthefloorshall•beprovidedinthestairwayateachdoorway,theleveloflandingshallbesameasthatoftheflooritserves.Exit corridors and passageways shall be of width not less than the aggregate required width of exit doorways •leading from them in the direction of travel to the exterior. Where stairways discharge through corridors and passageways, the height of corridors and passageways shall be not less than 2.4 m.The minimum width of an internal staircase shall be 1m. The minimum width of treads shall be 25 cm for an •internalstaircase.Themaximumheightofrisershallbe19cmandtheyshallbelimitedto12perflight.Handrails shall be provided with a minimum height of 1m. The minimum width of horizontal exit shall be same as exit doorways.Fireescapestaircaseshallnotbetakenintoaccountincalculatingtheevacuationtimeofabuilding.Allfire•escapesshallbedirectlyconnectedtothegroundandentrancetofireescapeshallbeseparateandremotefromthe internal staircase. Fireescapestairsshallhavestraightflightnotlessthan75cmwidewith15cmtreadsandrisersnotmorethan•19cm.Thenumberofrisersshallbelimitedto16perflight.Handrailshallbeprovidedwithaminimumheightof 1m.Exitsshallbesolocated,thatthetraveldistanceonthefloorshallnotexceed30mforindustrialbuildingand•storage shed and 22.5m for a hazardous area. The travel distance to an exit from the dead end of a corridor shall not exceed half the above distance.Whenevermorethanoneexitisrequiredforanyroomspaceorfloorofabuilding,exitsshallbeplacedas•remote from each other as possible and shall be arranged to provide direct access in separate directions from any point in the area served.

7.3 Extraction from Factory Rule (Maharashtra) 1963Rule 3(1)An application for obtaining previous permission for the site on which the factory is to be situated and for the construction or extension of a factory shall be made to the Chief Inspector of Factories.Application for such permission shall be made in Form I which shall be accompanied by the following documents:

Aflowchartofthemanufacturingprocesssupplementedbyabriefdescriptionoftheprocessinitsvarious•stages.Plans in duplicate drawn to scale showing:•

The site of the factory and immediate surroundings including adjacent buildings and other structured roads, drains, etc.The plan, elevation and necessary cross-sections of the various buildings, indicating all relevant details relatingtonaturallightingventilationandmeansofescapeincaseoffire.Theplansshallalsoclearlyindicatethe position of the plant and machinery, aisles and passage ways.

Rule 70 - Means of Escape in Case of FireEveryfactoryshallbeprovidedwithadequatemeansofescapeincaseoffireforthepersonsemployedand•without prejudice to the generality of the foregoing.

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Each room of the factory building shall in relation to its size and number of persons employed in it be provided •withanadequatenumberofexitsforuseincaseoffirethoughtnotnecessaryconfinedtosuchuse,sopositionedthat each person will have a reasonably free and unobstructed passage from his work-place to an exit.Noexitintendedforuseincaseoffireshallbelessthan90cminwidthorlessthan195cminheight.•In the case of a factory building or part of factory building more than one storey and in which less than 20 •persons work at any one time, there shall be provided at least one substantial stairway permanently constructed either inside or outside the building and which affords direct and unimpeded access to ground level.In the case of a factory building or part of a factory building in which 20 or more persons work at a time above •thelevelofthegroundfloororwhereinexplosiveorhighlyinflammablematerialsareusedorstored,atleasttwo separate and substantial stairways permanently constructed either inside or outside the building and which afford direct and unimpeded access to ground level.Everystairwayinafactorywhichaffordsameansofescapeincaseoffireshallbeprovidedwithasubstantial•hand-rail which if the stairway has an open side shall be on that side and if the stairway has two open sides such hand-rail shall be provided on both sides.In the case of building constructed or converted for use as a factory after the date of the passing of the act, the •following additional requirements shall apply:

Atleastoneofthestairwaysprovidedshallbeoffire-resistingmaterials. Everyhoist-wayorlift-wayinsideafactorybuildingshallbecompletelyenclosedwithfire-resistingmaterials andallmeansofaccesstothehoistorlifeshallbefittedwithdoorsoffireresistingmaterials.Nofireescapestairshallbeconstructedatananglegreaterthan450fromthehorizontal. Thefireescapestairshallbewithin45malongthelineoftravelfromanypartofthefloorfromwhichit is meant to provide escape.No stairway shall be less than 90 cm in width.

7.4 Comments on The Indian Boilers Act, 1923Constitutionality of the Act

In order to sustain the presumption of constitutionality of a legislative measure the court can take into consideration •matters of common knowledge, matters of common report, the history of the times and also assume every state of facts which can be conceived existing at the time of the legislation. This rule has been well enunciated in R.K. Dalmia, S.R, Tendulkar and Mohd Hanif Quareshi. •The aforesaid cases focus that the courts must presume that the Legislature understands correctly appreciates •the needs of its own people and that its laws are directed to problems made manifest by experience.

Short title, Extent and CommencementThis Act may be called the Indian Boilers Act. 1923.•It extends to the whole of India 7 [except the State of Jammu and Kashmir]•ItshallcomeintoforceOilsuchdate8asthe9[CentralGovernment]may,bynotificationinthe10[official•Gazette], appoint.

Definitions of terms used in Act “accident” means an explosion of a boiler or steam-pipe or any damage to a boiler or steam-pipe which is •calculated to weaken the strength thereof so as to render it liable to explode; 1(aa) “Board” means the Central Boilers Board constituted under Sec. 27-A;)“boiler” means any closed vessel exceeding 2[22.75 litres] in capacity which is used expressly for generating •steamunderpressure3[***]andincludesanymountingorotherfittingattachedtosuchvesselwhichiswhollyor partly under pressure when steam is shill off.“Chief Inspector”, “Deputy Chief Inspector” and “Inspector” mean, respectively, a person appointed to be a •Chief Inspector a Deputy Chief Inspector and an Inspector under this Act ;]


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[(cc)“economiser”meansanypartofafeed-pipethatiswhollyorpartlyexposedtotheactionoffluegasesforthepurpose of recovery of waste heat;(ccc)“feed-pipe”meansanypipeorconnectedfittingwhollyorpartlyunderpressurethroughwhichfeed-waterpasses directly to a boiler and (which) does not form an integral part there of:]

“owner” includes any person using a boiler as agent of the owner thereof any person using a boiler which he •has hired or obtained on loan from the owner thereof.

CommentsThe word “owner” includes any person using a boiler of which he is the agent of the owner.•Itisnotcorrecttosaytl1atinviewofthespecialsignificanceattachedtothe“wordowner”asdefinedintheIndian•Boilers Act the directors can be prosecuted for contravention of the provisions of Sec. 6 (c) of the Act.7Theclearmeaningoftheword“boiler”isthatthedefiniteandclearobjectofacontrivanceshouldbetogenerate•steam under pressure. It is evident that the contrivance in question was designed for that very object and for no other. The use to which the steam was ultimately put is quite irrelevant to the issue.

Ins. by the Indian Boilers (Amendment) Act, 1937 (11 of 1937), Sec. 3 Section 21 of the Indian Boilers Act, 1960(18to1960)isreproducedbelow.“21.TemporarycontinuanceinofficeofmembersoftheexistingBoard-ThemembersoftheBoardholdingofficeassuchatthecommencementofthisActshallcontinuetoholdofficeuntiltheBoardisreconstitutedundertheprincipalAct,asamendedbythisActandonthere-constitutionoftheBoardshallceasetoholdofficeassuch.”

“prescribed” means prescribed by regulations or rules under this Act.•“steam-pipe” means any pipe through which steam passes from a boiler to a prime-mover or other user or both. •If:

The pressure at which steam passes through such pipe exceeds 3.5 kilogram per square centimetre above atmospheric pressure.Suchpipesexceeds254millimetresininternaldiameterandincludesineithercaseanyconnectedfitting of steam-pipe.

“structural alteration, adding or renewal” shall not be deemed to include any renewal or replacement of a petty •naturewhenthepartorfittingusedforreplacementisnotinferiorinstrengthefficiencyorotherwisetothereplacedpartorfitting.

Application of Act to Feed-pipesEvery reference in this Act [except where the word “steam-pipes” is used in CI.(f) of Sec. 2], to a steam pipe or •steam-pipes shall be deemed to include also a reference to a feed-pipe or feed-pipes respectively).

Application of Act to EconomisersEvery reference in this Act to a boiler or boilers (except in CI. (ccc) of Sec. 2,4 [***] 5[***] shall be deemed •to include also a reference to an economiser or economisers respectively.)

7.4.1 Steam-pipes and FittingsPipes

Steam pipes may be of carbon steel, cast steel, alloy steel and in some cause of copper. Steel pipes may be solid •drawn(coldorhotfinished),buttweldedorelectricresistancewelded.Copper pipes shall be solid drawn and no pipe made from electro-deposition of copper on a mandrill shall be •used for steam delivery.

MaterialWhere, however, material used is inconformity with the code of the country of manufacture and it is covered by •theseregulations,thepermissiblestressfiguresspecifiedinthecodeatdifferenttemperaturesmaybeaccepted

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inlieuoffigurescomputedfromthedatarequiredtobefurnishedunderRegulation350inanyofthefollowingcases:

WhereacertificateisfurnishedfromtheInspectingAuthoritytotheeffect that thesteelcomplieswith requirementsofthegradesteel(tobespecified)andthatthepermissiblestressfortheworkingconditionsas, allowed for in the code of the country of manufacture falls within the limits permissible under the regulations.Where the basis upon which these stresses have been arrived at is made available and such basis is not found to be such as to give rise to stresses higher U1an those permissible under the regulations.Where pipes have to be fabricated by longitudinal fusion butt electric arc welding of plates robed to shape, the limits prescribed for butt welded pipes in table 9.3, under Regulation 349 shall not apply.

The hydraulic test for pipes in maker’s premises may be dispensed with by the Inspecting Authority provided •these pipes arc fully tested by approved radiographic or ultrasonic techniques; but this dispensation shall not apply to pipes having an internal diameter greater than 600 mm. In the event of detection of any defect after conducting hydraulic test of these pipes at site, it shall be the •responsibility of the manufacturer to repair or replace the defective pipes. As may be deemed necessary by the Inspecting Authority.Electric fusion welded pipes in which the butts are fully radiographed or ultrasonically tested be hydraulically •tested in the shops, provided the system as a whole is hydraulically tested at site to be requisite test pressure in accordance with Regulation 374.In the case of fusion welded pipes test plates to present all welded scams shall be attached at each or longitudinal •seam and tested except that one test may represent a lot of pipes up to 60 metres in length and of the same grade of material and same thickness of the pipe subject to the same heat treatment.

Steel PipesThe pipes shall be made from steel made by an Open Hearth or Electric Process or by any of the Oxygen •Processes.3[***].Hotfinishedseamlesspipesmay,howeverbemadeofBessemerSteel.Bessemer Steel shall not be used for pressure exceeding 21 kg/cm2 (300 lbs/in2) or temperatures exceeding •2600C (50001). If the Bessemer process is used, the steel shall be made by a manufacturer approved by the Inspecting Authority.When used for temperatures exceeding 3990C (7500F) the steel shall be of non - segregated or fully skilled •type.Carbon and alloy steel pipes shall not be used for design temperatures exceeding those given in table 9.3.•For designed temperature over 4270C (8000F) special precaution shall be taken to ensure that the surface •condition of the pipe is suitable for these requirements.Thematerialsfromwhichseamlessandelectricresistanceweldedpipesaremadeshallconfirmtotheappropriate•specificationoftubes.Thematerialsfromwhichbutweldedpipesaretobemadeshallconformtotherequirementsof table 9.2, under Regulation 347.1[(c) * * * *].

7.4.2 Mechanical TestsCold Bend Test [for pipes over 102 mm (4 in.) nominal bore]

A strip not less than 38 mm. (1 ½ in.) wide cut circumferentially from one end of each selected pipe shall when •coldwithstand,withoutshowingeithercrackorflawbeingdoubledoverinthedirectionoforiginalcurvatureround a bar, the diameter of the bar being; for pipes up to and including 10 mm (3/8 in.) thick 3 times the thickness.

Bend Test on the WeldA strip not less than 38 mm (1 ½ in.) wide cut circumferentially from one end of each selected pipe with the •weldnearthemiddleofthestrip,shallwhencoldwithstand,withoutshowingeithercrackorflaw,beingdoubledover in the direction of original curvature round a bar, the diameter of the bar being equal to eight times the


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thickness of the test piece, the weld being placed at the point of maximum bending.In case where the outside diameter of the pipe is less than 8 times the wall thickness, the diameter of the former •shall be equal to 4 or 2/3 of the nominal bore of the pipe, whichever is less.

Additional TestShouldapipeselectedfortestingfailinanyoneormoreofthetestsspecifiedabove,twofurthertestsofthe•same kind may be made from the same or another pipe from the same batch.Should either of the-sc further tests fail, the pipes represented may be reheat treated and then re-tested.•If the repeal tests arc satisfactory, the pipes shall be accepted provided they comply with other requirements but •if failure again occurs, the pipes which the test pieces represent shall be rejected.

Kind of pipes

Ultimate tensile strength in Kg/ Sq Mm tons per

sq in

Minimum elongation percent

Sulphur percent

max

Phosphorus percent max

Not less than

Not more than

On 203 mm (8 in) On 51 mm (2 in)

6 mm (1/4″) thick and over

Less than 6 mm (1/4″) thick

6 mm (1/4″) thick and over

Less than 6 mm (1/4″) thick

Strips cut from the pipes clear of the welds and tested in their curved condition

35 (22) 44 (28) 20 18 32 30 0.06 0.06

Test lengths taken from finishedpipes (ends of pipes to be plugged for grips)

35 (22) 44 (28) 25 23 - -

Table 7.2 Carbon Steels – Butt welded pipes

7.4.3 Method of Manufacture, Heat Treatment and Marking

On completion of any work which involves heating, whether for hot bending of the pipe or for any other similar •purpose, the pipe shall be carefully annealed.Cold-drawn carbon pipes shall be carefully annealed throughout their lengths after the operation of drawing. •Cold-drawnseamlessalloysteelpipesshallbedeliveredinthenormalisedconditionandhot-finishedpipesrolled or hot-drawn condition or in the normalised condition.Markinginspectionandidentificationmarksshallbestampedonthefacesofpipesplainatendswhenflanges•arcfilledidentificationmarksshallbestampedontherimsofflanges.

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Material Method of manufacturing

Maximum permissible

working pressure

Maximum permissible temperatures Form

°C °F

Carbon steel *

Cold-drawn seamless No restriction 482 900

Straights bends or fittings

Hotfinishedseamless

Do 21 Kg / cm2 482 900 Do

Butt welded Max. Nominal bore allowable 102 mm. (4 in)]

(300 lb / sq.in.) 260 500 Do

Electric resist-ance welded No resistance 482 900 Do

Cast steel Castings No resistance 482 900Straights bends or fittings

Molybdenum steel

Cold drawn seamless and castings

No restriction 524 975 Do

Chromium molybdenum steel

Cold drawn seamless and hot finishedseamless

No restriction 621 1150 Do

Copper

Solid drawn up to and including 127 mm (5 in.) dia.

12.6 Kg / cm2

(180 lbs / sq. in)

Not allowed for superheated steam

Straights and bends

Table 7.3 Maximum permissible working pressure and temperature

7.5 FlangesFlanges of Carbon Steel Pipes

Thematerialforcarbonsteelflanges,whereforged,castorcutfromtheplates(excludingbranchesforged•integral with the pipes) shall be made of steel produced by an Open Hearth or Electric process or any of the Oxygen processes.Carbon steelflanges shall not be used for temperatures exceeding4540C (8500F).Flanges shall bemade•without a weld and shall be free from lamination or other defects; they may be secured by screwing, riveting or welding.Blankflangesshallbeofmildsteelorcaststeelandshallbenotlessthaninthicknessthantheflangestowhich•theyarcattached.ThematerialshallcomplywiththerequirementsspecifiedinrelevantregulationsofChapterII or Chapter V of these regulations.

Flanges of Alloy Steel PipesThematerialforalloysteelflangeswhereforged,castorcutfromplates(excludingbranchesforgedintegral•with the pipes) shall be made from the steel produced by an Open Hearth or Electric process. Flanges should be made without a weld and shall be free from lamination or other defects. The material of alloy •steelflangesshallcomplyinallrespectswiththerequirementsofRegulation234.


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Thematerialforflangesshallbesimilartothatofthepipestowhichtheyarctobeattached.Theflangesareto•be so designed that the total C.55 induced in them does not exceed the maximum permissible stress as may be determined by the criteria laid down under Regulation 271.Blankflangesofalloysteelshallbenotlessinthicknessthantheflangestowhichtheyaretobeattached.The•materialshallbesimilartothatoftheflanges.

Nun-Ferrous FlangesThematerial for non-ferrousflanges shall be of bronze.The chemical composition shall complywith the•requirements of sub-clause (iv) of Regulation 282 (a). Whenflangesareattachedtocopperpipesbybrazing,theyshallbesecuredinsuchadditionalway(i.e.by•rivetingorformingaconicalbareintheflange)sothattheresistancetowithdrawalfromtheflangedoesnotdepend wholly on the brazing.

7.5.1 Screwed on Flanges

Whereflangesaresecuredbyscrewingthescrewthreadonthepipesandintheflangesshallbearrangedtoend•atapointjustinsidethebackofbossoftheflange.Aftertheflangehasbeenscrewedonthepipeshallbeexpandedintotheflangebyarollerexpandedintothe•flangebyarollerexpander.Suchscrewedandexpandedflangesmaybeusedforsteamforamaximumworkingpressuresof31.5kg/cm2•(450 lbs/sq. in.) and a maximum temperature of 3990C (7500F) and for feed for a maximum pressure of 42 kg/cm2 (600 lbs./sq.in.).

7.5.2 Welded on Flanges

Whereflangesareweldedon,theweldingshallbedonebytheoxy-acetyleneormetalisprocessthelatterwith•covered electrodes which shall comply with Regulations 94 to 98.Theproportionoftheweldshallbeasindicatedinthefigurenos.28to34ofthefollowingtypes:•

WeldingNeckflange. ‘FaceandBack’welded-onflangeformetalarewelding. ‘Boreandback’welded-onflangeformetalarewelding.4.‘FaceandFillet’welded-onflangefarmetal are welding.‘BoreandFillet’welded-onflangeformetalarcwelding. ‘Slipon’welded-onflangeformetalarewelding. ‘Slipon’welded’-onbossedflangeforoxy-acetylenewelding.

Theflangeshallnotbeatightfitonthepipe.•Themaximumclearancebetweentheboreoftheflangeandtheoutsidediameterofthepipeshallbe3mm.(1/8•in~ at any point, and the sum of clearances diametrically opposite shall not exceed 5 mm. (3/16 in.)

7.6 ASME Boiler and Pressure Vessel Code

ASME Codes give stipulations and guidelines for the design. Materials, manufacture and testing of pressure •vessels. These are issued by the American Society of Mechanical Engineers, New York.Thecodeswerefirstissuedin1915.Sincethen,manychangeshavebeenmadeandnewsectionsaddedto•the code as need arose. It is a live code and is revised and updated periodically. It keeps pace with time and is responsive to its users.

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7.6.1 Code SystemIn its present from the ASME Code System is a follows:

Section I – P – Power Boilers•SectionII –S– Materialspecifications•Part A Ferrous materials•Part B Non Ferrous Materials•PartC Weldingrods,electrodes,fillermetals•Part D Material properties•Section III – N – Nuclear Power Plant Components•Section IV – H – Heating Boilers•Section V – T – Non destructive Examinations•Section VI Care and operation of Heating Boilers•Section VII Rules for care of Power Boilers•Section VIII UG Division 1 - Pressure Vessels•Division 2 - Alternative Rules (Pro Vessel)•Division 3 Rules for constructive of High Pressure Vessels•SectionIX –Q– WeldingandBrazingQualifications•Section X Fibre glass reinforced Plastic Pressure Vessels•Section XI Rules for in service inspection of Nuclear Power Plant Components•

7.6.2 Issue Frequency

ASME Issues completely new edition of all sections after three years on 1st of July of the year of issue. Latest •edition issued on: 1st July 1998. Addenda to the latest edition are issued on 1st July every year.

1998 Edition with 1998 Add. - 1st July 98 1999 Addenda - 1st July 99 2000 Addenda 1st July 2000

A fully revised edition incorporating all above addenda would be issued on 1st July 2000. Prior to July 1998, •all addenda were being issued on 31st December of every year.

7.6.3 Applicability

The editions and addenda become applicable after six months from date of issue. •Thus, 1st Jan. 2000, the construction of Pressure Vessels shall be as per 1998 edition and 1999 addenda. •However, for old contracts spilling over beyond 1st Jan 2000, the old applicable edition and addenda are •valid.

7.6.4 Code Interpretation

ASME issue written replies known as “Interpretations” to the inquiries concerning technical aspects of the •code. These are issued twice in a year (July and December) and are sent to “Edition - subscribers” as up-date •service.

7.6.5 Code Cases

Boiler and Pressure Vessels committee meets regular1y to consider proposed additions and revisions to the code. •At the same time it may formulate code cases to clarify ‘Intent’ of existing requirements.


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These are published as code case books. It is published along with new editions and supplements are automatically •sent to subscribers of code case book till new edition is published.

7.6.6 Salient Features of ASME Codes

Every ASME Code starts with specifying the scope of the code in terms of capacity, size and pressure and other •limitations if any. It also deals with and the battery limits and the areas of code jurisdictions.TheCodescategoriseandclassifyacceptablegradesformaterialsofconstructionforspecificapplicationscovered•by the codes. The codes also identify and categorise various methods of construction I fabrication.The codes specify the required N.O.T: and other inspections. They also specify the accept I reject criteria. •WhatismostimportantabouttheASMEcodeisthatitcoversavastfieldofmanufacturingactivitywithoutsermonising. They are user friendly, and keep pace with changing technologies. No wonder - the users and the manufactures world over have adopted the ASME codes whole heatedly. There •are more boiler and pressure vessels built under ASME codes than those under all other codes taken together.The participants are advised to refer the actual code clauses and extract information from the latest codes •applicable. ASME code is even evolving document and one has to refer to the latest applicable edition and. addenda. These notes will help in understanding the code, and should not be referred to as the “Code” it self.

7.7 Erection Procedure for Field Erected Vertical Storage TanksTank Foundations

Foundations made by others shall be checked for uniform slope and levels for our acceptance. Reference of •North and East markings or 00 orientations marking on the foundation has to be furnished by the client. Sump pit on the foundation must be given prior to the commencement of the Bottom laying. •

Base Plate LayingTheannularplateswillbelaidfirstandthenthesketchplatesandfullplateswillbelaidwithsequencesmentioned•in the drawing; minimum lap for any two plates will be 30 mm. Temporary tack welding will be done during the time of lying.•

Base Plate WeldingTheannularbuttjointswillbeweldedfirst.Subsequentlyeveryalternateshortseamwillbefittedandwelded•and at the same time nearest short seams will be freed from tack welds. Thesameprocedurewillberepeatedforlongseamweldingalso.Temporaryerectioncleatsandjigs/fixtures•will be used for lying and avoiding distortion during the time of welding.

Shell ErectionAfter grinding off the weld reinforcement on the top side of annular joints where the shell will rest and vacuum •box testing of this portion, erection of shell will commence subsequent to marking the circle to tank inner radius on the tank base. First shell course plates will be rested on the markings by providing small cleats on both sides of the shell plates •on the tank base. For maintaining the gap for the vertical joints, spacers will be inserted in between the two plate edges. After •tack welding the vertical joints, plumbing and gauging will be done prior to the welding of vertical joints. Temporary strong backs will be provided during the time of welding in order to check peaking of joints.•After completing the vertical welding from one side, the shell will be back chipped before weld is deposited •from the other side. Second shell course erection will then be done, and the second shell plates will be rested onthefirstshellcoursewiththehelpofspacersandwedges.Minimumtwonos.Of erection channels will be wedged per plate erected, with lower course of plate, for stability and safety.•Forthesecondcourseverticaljoints,fittingandweldingwillbedoneassaidforthefirstcourse.Aftercompleting•

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the vertical welding, horizontal joint set up and plumbing will be done prior to welding the same. Sequence of welding for the horizontal joints will be same as vertical welding.For outside welding on the shell, welder’s trolley will be used and for inside, scaffolding will be provided for •erection and welding purpose.In the same manner, subsequent shell courses will be erected and welded. To safeguard erected tank plates, •haywire supports will be provided from plates to the channels anchored in ground. Afterweldingthelasthorizontaljoint,thecurbanglewillbefittedandwelded.Shelltobottomjointcanbe•fittedbeforeorafterfittingthecurbangle.Afterweldingthecurbangle,finalplumbcheckwillbedoneinaccordancewiththedesigncodeandalsopeaking•and banding check for the shell joints will be done.Identificationmarksforwelderandweldjointshallbemarkedonthetankbyusingpaintormetallicmarker•simultaneouslyduringfitupandwelding.

Vacuum Box Test and RadiographyAfter all welding work on the tank base and shell vertical/horizontal joints, shell to bottom and curb angle to •shell joints are welded, the tank base butt/ lap joints will be vacuum box tested. Radiography of vertical/horizontal welds will proceed as erection and welding work progresses.•

Roof Structure and Roof Plate ErectionThe roof structures will then be erected and welded. After inspection of the same, the roof plates will be laid •maintaining a lap of 25 mm minimum. The sequence of welding of short and long seams for the roof plates will be the same as base plates. •After all seams are welded, the roof peripheral joint with the curb angle will be set up and welded.•

Tank AppurtenancesInstallationandweldingoftankfittings(onshellandroof)andstairwaywillthenbetakenupasperorientation•given in the drawings. The compensating pads given for openings shall be air tested for leakage as per design code.•

Tank CleaningAfter all erection and welding work is over, the tank interior shall be cleaned by removing and grinding off all •tacksandotherfixtures.The tank shell openings shall then be blanked off preparatory to hydro test.•

Tank TestingPrior to hydro test, foundation levels will be taken by the customer with reference to the bench mark. After •inspectionofthetankandgettingapprovalfromthecustomer,waterfillingintothetankwillcommence.24hourintervalshallbegivenafterfillingthewaterto¼full,½fulland%fullandcomparingoffoundation•levels will be done at the above mentioned intervals.Afterfillingthetankshelluptothetop,thetankwillbeallowedtosettlefor48hours.Priortodrainingthe•water,finallevelswillbetaken.Rooftestwillbedoneinaccordancewiththecodepriortodrainingthewater.Duringthetimeoffillingand•draining water, all roof openings will be kept open to avoid damage to the tank.


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SummaryPetroleumisanyliquidhydrocarbon,mixtureofhydrocarbonsoranyinflammablemixture(liquid,viscous/•solid containing any liquid hydrocarbon.)TherulesspecifydistancestobemaintainedbetweenstorageTankandboundaryfencingfillingpoint,electric•motor (coupled to pump) etc.The word “owner” includes any person using a boiler of which he is the agent of the owner.•Theclearmeaningoftheword“boiler”isthatthedefiniteandclearobjectofacontrivanceshouldbetogenerate•steam under pressure.“prescribed” means prescribed by regulations or rules under the Act.•Steam pipes may be of carbon steel, cast steel, alloy steel and in some cause of copper.•On completion of any work which involves heating, whether for hot bending of the pipe or for any other similar •purpose, the pipe shall be carefully annealed.Flanges should be made without a weld and shall be free from lamination or other defect.•Blankflangesofalloysteelshallbenotlessinthicknessthantheflangestowhichtheyaretobeattached.•Themaximumclearancebetweentheboreoftheflangeandtheoutsidediameterofthepipeshallbe3mm.•The editions and addenda become applicable after six months from date of issue.•ASME issue written replies known as “Interpretations” to the inquiries concerning technical aspects of the •code.The codes categorise and classify acceptable grades formaterials of construction for specific applications•covered by the codes.Radiography of vertical/horizontal welds will proceed as erection and welding work progresses. •

ReferencesPetroleum Act Petroleum Rules• [Online]. Available at: <http://peso.gov.in/Petroleum_Act.aspx> [Accessed 15 June 2011].Petroleum Act• [Online]. Available at: <http://www.alaviandassociates.com/documents/petroleum.pdf > [Accessed 15 June 2011].Kohan. A., 1997. • Boiler Operator’s Guide, 4th ed., McGraw – Hill Professional.

Recommended ReadingChattopadhyay. P., 2000. • Boiler Operations Questions and Answers, 2nd ed., McGraw-Hill Professional.Kumar. S., • Environmental Protection. Northern Book Centre.The Indian Boilers Act • [Online]. Available at: <http://dipp.nic.in/boiler/ibact.htm> [Accessed 15 June 2011].

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Self Assessment

An application for obtaining previous permission for the site on which the factory is to be situated and for the 1. construction or extension of a factory shall be made to the _______________.

Chief Inspector of Factoriesa. Ministry of Petroleum & Natural Gab. sSite ownerc. Chief Minister d.

Storage of any petroleum product covered under the Act requires ______________.2. plot plan a. equipment layout plan b. storage licencec. exit requirementd.

The______________specifydistancestobemaintainedbetweenstorageTankandboundaryfencingfilling3. point, electric motor etc.

plot plana. rulesb. licensesc. storaged.

The_____________tobemaintainedbetweenstoragetankandboundaryfencingfillingpoint,electricmotor4. (coupledtopump)specifiedbytherulesdependonthetypeofpetroleumandquantitystored.

ratioa. sizeb. shapec. distancesd.

Which of the following is true?5. Minimum distances to be maintained where Class A and Class B petroleum stored exceed 5 Kl or diameter a. of tank exceeds 8 m.Minimum distances to be maintained where Class A and Class B petroleum stored exceed 5 Kl or diameter b. of tank exceeds 7 m.Minimum distances to be maintained where Class A and Class B petroleum stored exceed 5 Kl or diameter c. of tank exceeds 9 m.Minimum distances to be maintained where Class A and Class B petroleum stored exceed 5 Kl or diameter d. of tank exceeds 3 m.

What should be drawn to scale 1,500 or less?6. Plot plana. Storage areab. Equipment layout planc. Distancesd.

http://petroleum.nic.in/


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Which of the following is false?7. Minimumheightfromthefloortotheroofofbuildingshouldbenotlessthan3.75m.a. The height of all rooms for human habitation shall not be less than 2.75m measured from the surface of the b. floortothelowestpointoftheceiling.Mezzaninefloorshouldhaveminimumheightof2.2mandarearestrictedto1/3oftheareaoftheflooronc. which it is constructed.Themezzaninefloorshouldbesub-dividedintosmallercompartments.d.

Which of the following is false?8. The minimum width of an internal staircase shall be 1m.a. The minimum width of treads shall be 25 cm for an external staircase.b. Themaximumheightofrisershallbe19cmandtheyshallbelimitedto12perflight.c. The minimum width of treads shall be 25 cm for an internal staircase.d.

The word ______________ includes any person using a boiler of which he is the agent of the owner.9. ownera. proprietor b. leaserc. possessord.

Which of the following is false?10. Theclearmeaningoftheword“boiler”isthatthedefiniteandclearobjectofacontrivanceshouldbetoa. generate steam under pressure.“prescribed” means prescribed by regulations or rules under this Act.b. “steam-pipe” means any pipe through which steam passes from a boiler to a prime-mover or other user or c. both.“owner” means prescribed by regulations or rules under this Act.d.

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Chapter VIII

Statutory and Regulatory Act

Aim


introduce ASME piping codes•

state the applicability of ASME piping codes•

determine code interpretation and code cases•

Objectives


elaborate the piping fundamentals•

explain the regulations pertaining to storage, usage and transportation of hazardous chemicals•

discuss storage, responsibility for safety and preparation of equipment •

Learning outcome


realise the scope and extent of ASME B 31.1•

understand piping engineering, statutory / state and local body regulations•

enlist salient feat• ures of ASME codes


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8.1 Introduction to ASME Piping CodesASME piping codes give stipulations and guidelines for the design, materials, manufacture and testing of pressure piping. These are issued by the American Society of Mechanical Engineers, New York. It is a LIVE code and is revised and updated periodically by issuing new editions and addenda. It keeps pace with time and is responsive to the questions from its users.

ApplicabilityThe editions and addenda become applicable after six months from date of issue. Thus, 1st Jan. 2000, the construction of piping shall be as per 1998 edition and 1999 addenda. However, for old contracts spilling over beyond 1st Jan 2000, the old applicable edition and addenda are valid till the completion of contract / up to start-up.

Code InterpretationASME issue written replies know as “Interpretations” to the inquiries concerning technical aspects of the code and are sent to “Edition - subscribers” as up-date service.

Code CasesASME committee meets regularly to consider proposed additions and revisions to the code. At the same time it may formulate code cases to clarify ‘Intent’ of existing requirements. These are published as code-cases. It is published along with new editions and supplements are automatically sent td subscribers of code case book till new edition is published.

Salient Features of ASME CodesEvery ASME code starts with specifying the scope of the code in terms of capacity, size and pressure and other •limitations if any. It also deals with and the battery limits and the areas of code jurisdictions.Thecodescategorise andclassify acceptablegrades formaterialsof construction, for specificapplications•covered by the codes. The codes also identify and categorise various methods of construction I fabrication.The codes specify the required N.D.T. and other inspections. They also specify I reject criteria.•ASME code is that they are user friendly and keep pace with changing technologies and new materials. Hence •the users and the manufactures over the world have adopted the ASME codes whole heartedly.The participants are advised to refer the actual code clauses and extract information from the latest codes •applicable. ASME code is even evolving document and one has to refer to the latest applicable edition and addenda. These notes will help in understandings the code and should not be referred to as the “Code” itself.•

8.1.1 Pressure Piping Codes – B 31

The ASME B31 Code for Pressure Piping consists of a number of individually published Sections. •RulesforeachSectionhavebeendevelopedconsideringtheneedforapplicationofspecificrequirementsfor•various types of pressure piping. Application considered for each Code Section includes:

B31.1 Power Piping: Piping typically found in electric power generating stations, in industrial and institutional plants, geothermal heating systems and central and district heating and cooling systems.B31.3 Process Piping: Pipingtypicallyfoundinpetroleumrefineries,chemical,pharmaceutical,textile,paper, semiconductor, arid cryogenic plants and related processing plants and terminals.B31.4 Pipeline: Transportation systems for liquid hydrocarbons and other liquids, transporting products which are predominately liquid between plants and terminals and within terminals, pumping and metering stations.B31.5 Refrigeration Piping: Piping for refrigerants and secondary coolants.B31.8 Gas Transportation and Distribution Piping Systems: Piping transporting products which are predominately gas between sources and terminals, including compressor, regulating and metering stations; and gas gathering pipelines.

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B31.9 Building Services Piping: Piping typically found in industrial, institutional, commercial and public buildings and in multi-unit residences, which does not require range of sizes, pressures and temperatures covered in B31 .1.B31.11 Slurry Transportation Piping Systems: Piping transporting aqueous slurries between plants and terminals and within terminals, pumping and regulating stations.

It is the owner’s responsibility to select the code section which almost nearly applies to a proposed piping •installation. Factors to be considered by the owner include: limitations of the code section; jurisdictional requirements; and the applicability of other codes and standards. All applicable requirements of the selected code section shall be met. For some installations, more than one •code section may apply to different parts of the installation.Thelatesteditionandaddendaissuedatleast6monthspriortotheoriginalcontractdateforthefirstphaseof•activity covering a piping system or systems shall be governing document for all design, materials, fabrication, erection, examination and testing for the piping until the completion of the work and initial operation.

8.1.2 Code Revisions and Updating

The 1998 edition of this code is issued on July 1, 1998. The next edition is scheduled for publication on July •1, 2001. The use of addenda allows revision made in response to public review comments or code committee actions. Eachaddendaisdesignatedbysmallletter(a,b,etc.)suffixedaftercodedesignation,ThusaddendatoB31.1•code (1998 edition) issued in 1999 will be “ASME B 31.1 a-1999”, addenda 2000 will be ASME 6 31.1 b-2000 and so on.ASME issues written replies to inquiries concerning interpretations of technical aspects of the code. The •interpretations are published in a separate publication in a separate supplement. Periodically certain actions of the ASME. B31 Committee will be published as cases. The cases are published in a separate supplement.Clauses in the code are not necessarily numbered consecutively. Such discontinuities result from following a •common outline, insofar as practicable, for all code sections. In this way, corresponding material is correspondingly numbered in most code sections, thus facilitating reference •by those who have occasion to use more than one Section.

8.2 Review of Piping FundamentalsA pipe or a tube is hollow longitudinal product. ‘A tube’ is general term used for hollow product having circular, •elliptical or square cross-section or for that matter cross section of any closed perimeter.Apipeistubularproductofcircularcross-sectionthathasspecificsizesandthicknessesgovernedbyparticular•dimensional standard. Tubes can be ordered for any OD or ID and thicknesses, pipes are ordered on basis of nominal sizes. Pipescanbeclassifiedbasedonmethodsofmanufactureorenduse.•

Methods of manufactureSeamless Pipes are manufactured by drawing or extrusion process. ERW pipes (Electric Resistance Welding •pipes) are formed from a strip which is longitudinally welded along its length. Welding may be by electric resistance, high frequency or induction welding. •ERW pipes can also be drawn for obtaining required dimensions and tolerances.•

Classification based on end use:Pressure pipes• are those which are subjected to motive pressure and system pressure and or temperatures. Fluid pressureingenerallyinternalpressureduetofluidbeingconveyedormaybeexternalpressure(e.g.jackedpiping) and are mainly used as plant piping.


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Line pipes• aremainlyusedforlongdistanceconveyingofthefluidsandaresubjectedtomotivepressures.These are generally not subjected to high temperatures.Structural pipes• are not used for conveyingfluids and therefore are not subjected to fluid pressures ortemperatures. They are used as structural components (e.g. handrails, columns, sleeves etc.) and are subjected to static loads only.

Pipes Dimensional StandardsThe standards for pipeline dimentions are:

DiametersPipes are designated by nominal size, starting from 1/8” nominal size and increasing in steps up to 36 inches. •For the nominal size up to and including 12”, there is one unique O.D. (different from nominal size) and 1.0 would vary depending on schedule number. For nominal sizes 14” and above, 0.0 is same as nominal size.

ThicknessPipe thicknesses are designated by schedule number (which determine internal pressure) or weight designation •like Std. (S), Extra Strong (XS) and Double Extra Strong (XXS).PipeschedulenumberSisdefinedas:Sch.No.S=1000P/S.•Where P = Internal Pressure (PSI) and S = Allowable tensile strength of material used. Common pipe schedules •are,

Sch 40 Sch 80 Sch 120 Sch 160

For larger pipe sizes intermediate schedule numbers (Sch 20, Sch 30, etc.) are also employed (Ref. pipe •dimension Chart).For carbon steel, pipe wall thickness tolerance is ± 12 1/2% i.e., pipe wall thickness can vary 12 1/2% from •thickness obtained from dimension chart.For stainless steels schedule numbers are designated by su-Tix S i.e; lOS, 40S, 80S etc.•

LengthPipes are manufactured in ‘random length’ which is 20’+ -2.5 and in double random length 40’ + - 5.0.•

Pipe FittingsPipefittingsarethecomponentswhichtietogetherpipelines,valvesandotherpartsofapipingsystem.They•are used in “making up” a pipe line. Fittingsmaycomeinscrewed,welded,soldered,orflangedvarietiesandareusedtochangethesizeoftheline•or its direction and to join together the various parts that make up a piping system.Themajorityofpipefittingsarespecifiedbythenominalpipesize,type,materialandthenameofthefitting.•Besidestheendconnectionsasabove(screwed,welded,soldered,flanged)itisalsopossibletoorderbellandspigotfittings,whichareusuallycastironandusedforlowpressureservice.Ingeneral,afittingisanycomponentinpipingsystemthatchangesitsdirection,altersitsfunction,orsimply•makesendconnections.Afittingisjoinedtothesystembybolting,weldingorscrewing,dependingonmanyvariables in the system.

8.2.1 Butt Welded Fittings

Weldedfittingsareusedprimarilyinsystemsmeanttobepermanent.Theyhavethesamewallthicknessasthe•mating pipe. Advantages of butt welded systems are the follows:

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They have a smooth inner surface and offer gradual direction change with minimum turbulence. They require less space for constructing and hanging the pipe system. They form leak-proof constructions. They are almost maintenance free. They have a higher temperature and pressure limit. They form a self-contained system. They are easy to insulate. They offer a uniform wall thickness through-out the system.

One of the major disadvantages of butt-welded systems is that, they are not easy to dismantle. Therefore, it is •oftenadvisabletoprovidethesystemwithenoughflangedjointssothatitcanbebrokendownatintervals.One of the main uses of the butt-welded system is for steam lines, which are usually in high temperature / high-•pressure service.

8.2.2 Socket Welded Fittings

Socketweldedfittingshavecertainadvantagesoverbutt-weldedfittings.Theyareeasiertouseonsmall-size•pipelines and the ends of the pipes need not be bevelled since the pipe end slips into the socket of the joint. Withsocketweldedfittingsthereisnodangeroftheweldprotrudingintothepipelineandrestrictingflowor•creating turbulence. Thus, the advantages of the socket welded system are:

The pipe does not need to be bevelled. No tack welding is necessary for alignment since joint and the pipe are self -aligning. Welded material cannot extend into the pipeline. It canbe used in place of threadedfittings, therefore, reducing the likelihoodof leaks,whichusually accompanytheuseofthreadedfittings.It is less expensive and easier to construct than other welded systems.

Oneofthemajordisadvantagesofthistypeoffittingisthepossibilityofamismatchinsidethefittingwhere•improperly aligned or mated parts may create a recess where corrosion could start.Socket-weldedfittingshavethesameinsidediameterasstandard(Schedule40),extrastrong(Schedule80)and•doubleextrastrong(Schedule160)pipe,depending.Ontheweightofthefittingandmatingpipe.Socket-weldedfittingsrarecoveredinASA816.11.Theyaredrilledtomatchtheinternaldiameterofschedule•40 or schedule 80 pipes.

8.2.3 Flanged Fittings

Flangedconnectionsarefoundonpipingsystemsthroughoutthepetrochemicalandpowergenerationfieldson•pipelinesthatareaminimumof2in(5.08cm)indiameter.Themajorityofflangedfittingsaremadeofcaststeel or cast iron.Flangedsteelfittingsareusedinplaceofcastironwherethesystemissubjectedtoshockorhigh-temperature/•high-pressuresituationswherethedangeroffireisprevalent,becausecastironhasatendencytocrackorrupture under certain stresses. Aflangemaybecastorforgedontotheendsofthefittingorvalveandboltedtoaconnectingflangewhichis•screwed or welded onto the pipeline, thereby providing a tight joint. An assortment of facings, ring joint grooves andconnectionsareavailableinflangevariations.Oneadvantageofflangedsystemsisthat,theyareeasilydismantledandassembled.Oneofthedisadvantages•is that they are considerably than an equally rated butt-welded system, because of the large amount of metal thatgointomakingupjointsandflanges.Moreover,flangedfittingsoccupyfarmorespace than thebutt-weldedorscrewedequivalents.Becauseof•thishigherweightload,aflangedsystembecomesfarmoreexpensivetosupportorhangfromtheexistingstructure.


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8.3 Scope and Extent of ASME B 31.1The code sets forth engineering requirements deemed necessary for safe design and construction of pressure •piping.Unlessagreementisspecificallymadebetweencontractingpartiestouseanotherissue,ortheregulatorybody having jurisdiction imposes the use of another issue, the latest edition and addenda issued at least 6 monthspriortotheoriginalcontractdateforthefirstphaseofactivitycoveringapipinginstallationshallbethe governing document for all design, materials, fabrication erection, examination and testing for the piping until the completion of the work and initial operation.Rules for this code section have been developed considering the needs for applications which include piping •typically found in electric power generating stations, in industrial and institutional, plants, geothermal heating systems and central and district heating and cooling systems.This code prescribes requirements for the design, materials, fabrication, erection, test and inspection of piping •systems .Power piping systems as covered by this code apply to all piping and their component parts. They include but are not limited to steam, water, oil, gas and air services.Thiscodecoversboilerexternalpipingasdefinedbelowforpowerboilersandhighpressurewaterboilersin•which steam or vapour is generated at a pressure of more than 15 psig [100kPa (gage)]; and high temperature water is generated at pressures exceeding 160 psig [1103kPa (gage)] and/or temperatures exceeding 2500C (1 200C).Boiler external piping shall be considered as piping which begins where the boiler terminates at:•

Thefirstcircumferentialjointsforweldingendconnections. Thefaceofthefirstflangeinboltedflangedconnections. Thefirstthreadedjointinthattypeofconnectionandwhichextendsuptoandincludingthevalve.

This code does not apply to the following:•Economizers, heaters, pressure vessels and components covered by Sections of the ASME Boiler and pressure vessel code.Building heating and distribution steam piping designed for 15psig or less, or hot water heating systems designed for 30 psig or less.Pipingforhydraulicorpneumatictoolsandtheircomponentsdownstreamofthefirstblockorstopvalve off the system distribution header.Piping for marine or other installations under federal control.

8.4 Piping Engineering – Statutory/State and Local Body RegulationsFollowing are various statutory/state and local body regulations related to piping engineering.

8.4.1 Chief Controller of Explosives (CCE or CCOE)

These are statutory rules and come under the purview of Chief Controller of Explosives based in Nagpur. This is •aCentralGovernmentAuthorityforwholeofIndia.Theregionalofficesof‘CCE’arelocatedineachregion.However,theseregionalofficesdonothaveauthoritytoapprovetheinstallations.Theycanonlybeconsulted•on matters relating to these regulations. The Authority for approval of the installations is vested only in the Chief Controller of Explosives (CCE) based in Nagpur.All liquid hydrocarbons (and some of the non-hydrocarbons as per the list available in the CCE’s Nagpur and •otherRegionalOffices)fallinginclassesA,B,&Carerequiredtobestoredaspertheserules.HencethestoragesfallingunderthepurviewoftheserulesmustbesegregatedfromotherflammableInonflammableliquids at the plot plan stage itself. This is a must from space allocation point of view also as the’ CCE’ storages require lot of space.ItisessentialtoconsulttheCCEauthorities,(eitherNagpurortheRegionaloffice)fornon-hydrocarbonsfalling•under purview of these rules.GenerallyCCEshallnotallowotherflammableliquidstobestoredalongwiththeliquidsunderCCEpurview.•However, there is a possibility that in some special cases he may allow this. Hence this aspect is needed to be

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discussed with CCE before the layouts are frozen. It should be kept in mind that reducing the number of storage installations always leads to space saving for the Client. Hence it is always preferable to try to club CCE and nonCCEflammablestorageswithCCE’spriorapprovalforthesame.The liquids coming under CCE purview can also be stored in underground tanks. There are no written rules •available from CCE for this type of installation. However, following are some of the conventions followed in such cases:

The underground edge to fence distance can be 2 to 3 metres. It is preferable to keep it 4.5 metres or more if the space allows.The CCE regulations for distances from the loading I unloading points to fence have to be allowed. The loading I unloading areas have to be located inside the protected area (fence). Brick I masonry enclosures and leakage detection systems are needed to be provided depending on nature of liquids.Freeaccessforfirefightingshouldbeavailableatleastonthreesidesoftheinstallation,withroads. The clear distance between the underground tanks shall be 1.0 m minimum. These storages are required to be located at certain minimum distances from other plant facilities, as per these regulations. The CCE shall not approve installations which are not located at such (applicable) minimum distance from other facilities.

Allfacilitiesinsidea‘Refinery’(crudeoilrefinery)fallunderthepurviewoftheserules,irrespectiveofwhether•theyarestoragesorprocessplants.HencealllayoutsforarefineryneedCCEapproval.Construction of these facilities is not allowed before drawings for the installation are approved by the CCE in •writing.The installation under these rules requires dyke walls around the tanks to curtain the liquids. The dyke capacities •shall be as per petroleum rules.

8.4.2 Static and Mobile Pressure Vessels Rules (SMPV Rules)

These are statutory rules and come under the purview of CCE based in Nagpur.•These rules state as to pressurised storages fall under its purview and how these storages are to be located.•It is essential to identify the storages falling under the purview of these rules are at the plot plan stage itself as •these storages generally require lot of space.GenerallytheCCEshallnotallowanyotherpressurisedfluidstobestoredalongwiththefluidsunderCCE•purview. However, there is a possibility that in certain special cases he may allow this. Hence this aspect is needed to be discussed with CCE before the layouts are frozen. It should be kept in mind that reducing the number of storage installations always leads to space saving for the •client. Hence, it is always preferable to try to club CCE and non- CCE storages with CCE’s prior approval for the same.Underground storage is not included just now in these rules. CCE should be consulted if any pressurised storage •tanks are required to be located underground.Freeaccessforfirefightingshouldbeavailableatleastonthreesidesoftheinstallationwithroads.•These storages are required to be located at certain minimum distances from other plant facilities, as per these •regulations.Construction of these facilities can be started only after the drawings for the installation are approved by the •CCE in writing.The loading/unloading compressors (if any) required for storage installation shall be located inside the protected •area (fence) with minimum 15 m distance (check with latest rules) between edge of bullet / sphere and edge of compressor house. The distance between compressor house and fence should be the same as the distance between loading / unloading •point and fence as per the petroleum rules.


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8.4.3 Oil Industry Safety Directorate (OISD) Rules

These rules are not statutory in nature and hence not mandatory. However, these have to be followed if required •by client.These rules cover process plants, utilities and of sites, all storages for all types of plants including LPG storage •/loading/unloadingandflammablestorages.The CCE has been considered including these rules in the petroleum rules (CCE rules).•For the choice between OISD rules and petroleum rules the client should be involved as the OISD rules are •generally more stringent and hence require more space for the storages. Hence unless made mandatory by CCE or Client, these rules should not be followed.For LPG installations it has become a general practice in India to follow the OISD rules. As the distance •requirements of these rules are generally more than the petroleum rules, there is no problem as far as CCE approvals are concerned.As per the conventional practice in the Oil Industry in India, OISD rules have to be followed for all crude oil •refinerylayouts.EventhoughOISDrulesareusedforlayoutsofhydrocarbonstorage/refinery,theinstallationapprovalshall•be by CCE only.

8.4.4 Indian Boiler Regulations (IBR)

These rules are statutory rules of the Central Government but the administration of the rules is at the state level •i.e., there is a separate IBR authority for each state located in its capital unlike CCE.Installations of all steam pipelines (coming under the purview of these rules) are required to be approved by •the IBR authorities of the state in which the same are located.The IBR equipment and IBR piping items manufactured in a particular state shall be approved by the IBR •authority of that state. The installation shall be approved by the IBR authority of the state in which the installation is located. All disputes in this regard have to be referred to the Central Boiler Board located in Delhi.Fabrication and installation of piping coming under purview of these rules shall not be started unless the •construction drawings and other documents are approved by the state IBR authority.

8.4.5 Environmental and Pollution Control Regulations

These rules are statutory in nature and hence have to be followed.•These are overlapping state and central Government regulations which control the following:•

The location of the plant. Acceptable level of pollutants in the atmosphere due to the plant. Theeffluenttreatmentandacceptablequalityofdischargeoftreatedeffluents. Impact on the surroundings of the plant.

To conform to these requirements, following norms shall be followed:•The liquideffluents shallbedischarged to theeffluentcollectionsystem leading toEffluentTreatment Plant(ETP).Noneoftheeffluentsshalleverbedischargedtostormwaterdrainsoranyothernaturaldrainchannels.The chimney height for boilers and incinerators shall be decided by the boiler incineration vendor to suit the requirements of State Pollution Board.Theheightofflareandthesafetyzonearounditshallbedecidedbyprocessdiscipline/processlicensoror theflaresuppliertosuittherequirementsofStatePollutionBoard.Thepilotpanelforflareshallbelocatedoutsidethesafetyzoneoftheflare. The effluent interceptors located either in the plant or storages shall be used only for the immiscible fluids.Theundergroundstoragesstoringfluidshazardoustohealth,groundwaterandenvironmentshallhavea

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dyke around the tanks to contain any leakages. Also these underground enclosures shall have provision for testing the presence of leakages in the dyke to facilitate prompt corrective action.Theaboveundergroundstorageswhichstorefluidshazardoustogroundwaterandhealthshallhaveconcrete paved/epoxycoatedfloors,drainingtosumpsinsidethedyke.Theprocessplantshandlingfluidshazardoustohealthshallbeopentypeandwellventilatedi.e.,theseshall never have walls as far as possible. These plants also shall never have enclosed staircases.

8.4.6 The Chief Inspector of Factories (The State Inspector of Health and SAFETY) Regulations

These rules are statutory in nature and hence mandatory.•These are ‘Factory Rules’ formulated and enforced by each state in the Indian Union. The review, inspection •and enforcement machinery of each state is separate and is called the Inspectorate of Health and Safety.This State Directorate ensures that the plant / factory buildings, equipment arrangements and plant general •environment are suitable for proper operations of the plants and good health and proper safety of operating personnel. These reviews and inspections are carried out as per the ‘State Factory Rules’.For each plant it is essential to obtain Factory Inspector’s approval for each non-plant building and all plant •buildings.Theopenairplantlayoutsandoperatingplatformsdonotrequirethisspecificapproval.However,theselayoutsalsomustconfirmtotheserulesasthesamemaybereviewedbythisinspectoratefor•proper equipment arrangements and ease of operations i.e., provision of proper operating passages and distances between the equipment.The most important of these rules are as follows:•

All the machinery must have 1.0 m wide (minimum 900 mm) clear distance between itself and any building columns / walls / other equipment or any such obstruction for easy operability, maintenance and safety.All the equipment shall have proper (1.0 m) passages / enough space around them for safe passage of operators, easy operation and maintenance.Thefloorheightsshallbefixedsuchthatminimumclearheadroomaspertherulesisavailable.However, forprocessplantsthisrulemaynotbefollowedasmanytimes,thefloorheightsaregovernedbytheprocessrequirements. These deviations for process plants are generally acceptable to the inspectorate.Drainagesystemsforproperdrainageofplanteffluentsshallbeincorporated. The sizes of canteen and rest room, number and size of toilets, primary health facilities and change rooms are as per these rules, based on number of workers per shift and total number of workers.Theplanthaspropersafetyarrangementslikefirefightingsystems.Forlargecomplexesaseparateoffice isrequiredforthefiresafetyofficer.The approval for all non-plant buildings is obtained by the client by submitting architectural drawings for these facilities. For plant building requiring these approvals, the equipment layout drawings and architectural drawings are submitted by the client to this authority. The staircase location/numbers/width and type (closed or open) have to be as per the state factory rules.

8.4.7 State Industrial Development Corporation (SIDC) Rules (OR Local Body (Gram Panchayat etc.) Rules)

These rules have been accorded the status of statutory rules by the Central Government and hence the same are •mandatory. All deviations to these must have prior written approvals from these bodies.These rules generally govern the following:•

The Green belt requirements around the plant within the plot. The distance of a plant from the adjacent highway, main road or human settlements. The requirements of free space in the plant area (i.e. ratio of free space to the built up space or FSI of the plot).The type of process plant which can be located in that particular area.


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Thefiresafetyprovisionsfortheplant. Relative locations of facilities with respect to the existing surrounding facilities e.g. the rules may not permit location of a new boiler just across the boundary near existing hazardous storage tanks of an existing facility.Drainagefacilitiesoftheplant.Therulesgenerallydonotpermitfillingofanexistingnaturaldrainage (nallah) existing on the plot. The diversion may be allowed but requires prior permission.The size of water storage inside the plant requires approval of the SIDC if the water is drawn from the SIDC main. The same is true for size and location of electrical sub-station inside the plant.Forplantsofcomplexeshavinghightrafficoftrucks/tankers,theserulesgenerallyrequireparkingspace to be provided inside the plant area. Use of the SIDC roads / highways or other roads for parking is not allowed.

8.4.8 Traffic Advisory Committee (TAC) and Loss Prevention Association (LPA) Rules

These rules are now called as Loss Prevention Association (LPA) rules.•These rules are non-statutory in nature.•Even though these rules are non-mandatory in nature it is essential to follow these strictly in the layout as the •insurance premium charged by the insurance companies for a particular plant depend on:

Approval of the plant layout by the LPA. Non-conformities with respect to these rules brought out by LPA after their review of plant layouts. Loading of premium as suggested by LPA to take care of the nonconformities which in their opinion lead to additional risk to plant facilities.

Not conforming to LPA rules leads to client having to pay additional premium every year to insure the plant. •Most of the times the additional loading of premium is avoidable if due care is taken in the layouts.There are different types of rules for different types of plants i.e., rules for petrochemical plants are different •than those for ordinary chemical plants.Theserulesrelatetodistancesbetweenvariousplantfacilitieslikeprocessplant,storages,flare,boilers/furnaces•etc.Alsotheserulesdefinethewaythecablesshouldberoutedintheplants.TheLPArulesforfirefightingsystemslaydowntheconditionsforapprovaloffirefightingsystemsforvarious•types of plants. These rules generally govern the following:

The distances at which hydrants are located from each other and from the edge of buildings / facilities. Fire pumps capacities. Numberoffirewaterpumps. Requirement of diesel engine driven pumps and electric motor driven pumps. Thecapacityoffirewaterreservoir. Thetypeofconstructionoffirewaterreservoir. Type of pump house and its location. Type and number of staircases required or the buildings. Control room location. Requirements of perfect party walls/blast proof walls.

TheLPAhasseveralregionalofficesinIndia.TheplantsinaparticularregioncanbeapprovedbytheLPAin•that particular region only.

8.4.9 Director General of Civil Aviation (DGCA) Rules

These rules are statutory in nature and hence mandatory.•These regulations shall apply when any structure in the plant exceeds 30 metres in height. Either illumination •and/or painting shall be provided on such structure as per these rules. All structures of height 120 M or more

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shall be provided with aviation light irrespective of the location of the plant.If the plant site is near an airport. It is mandatory to obtain DGCA’s prior approval for locating the plant in that •area.

8.4.10 Indian Electrical Rules

These rules are statutory in nature and hence mandatory.•Following are some of the requirements for layout of Electrical areas.•

Sub - station and switch gear rooms shall be as close as possible to electrical load centres. Direction of wind shall be taken into account while locating electrical equipment near cooling tower dusty areas etc.Electrical equipment shall be located relatively at higher level to avoid water clogging.

8.5 Regulations Pertaining to Storage, Usage and Transportation of Hazardous ChemicalsVariouschemicals,flammableliquidsandgasesareextremely,importanttoourmodernwayoflifeandconstituteamajorvolumeofpresentdaycommerce.Billionsofgallonsofhighly’flammableliquidsandhazardouschemicalsaremanufacturedandmarketedwithahighdegreeofsafety.Ontheotherhandmanyfiresleadingtoinjuryanddeathresultfromimproperstorageanduseofflammableliquids,especiallyinandaroundthehouseorinsmallbusinesspremises. The difference lies in realizing how hazardous the materials are and the application of safe procedures.

Factors determining severity of hazardsHow the chemical is used•Type of job operation (how the workers are exposed)•Work pattern•Duration of exposure•Exposed liquid surfaces•Evaporation rate•Patternofairflow•Operating temperature•Concentration of vapour in work, room•Ventilationefficiency•Housekeeping•

Chemical data sheetName•Properties•

Physical Chemical

Uses•Hazards•

Personal health Fire and explosion Control measures

Storage and handling•Personal protective equipment•

Toxicity


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T.L.V

Symptoms of poisoning•First aid•Waste disposal•

8.5.1 Hazardous ChemicalsChemicals can be divided into three classes:

Chemicals which in no way support or assist combustion these are silicates, carbonates, bicarbonates, phosphates, •chlorides, bromides, iodides, sulphates, sulphites, sulphides, thiosulphates, higher halogenated compounds.Chemicals which are themselves combustible these arc organic compounds like cellulose, sugars, proteins, •resins, petroleum, etc.Chemicals which produce oxygen for burning: In this group come nitrates, chlorates, perchlorates, permagnates, •chromates, dichromates and organic nitrates.

For reasons which can be understood, chemicals from group 2 must not come in contact with chemicals from group 3. While stocking chemicals in godowns it is necessary to know the incompatibles those which react exothermically with one another. Some of these incompatible chemicals are:

Acid chemicals vs. basic ones: e.g. free acids like hydrochloric, sulphuric, acetic acids or chemicals like potassium •bisulphate, against bases like ammonia, lime, soda, metal oxides, etc.Ammonium salts vs. basic oxides or carbonates: These will react, may be with tragic end.•Bleaching powder vs. turpentine: Bleaching powder liberates chlorine which reacts exothermically with •ammonia, ammonium carbonate or unsaturated organic substances like turpentine oil or linseed oil. This may beasourceoffire.

8.6 StorageDiscussed below are various norms for storage of solid, liquid and gas in.

8.6.1 Solid Storage

Planning storage arrangements for solids, both the nature and the form of the material should be taken into •account. Solid materials may enter or leave the plant in bags, drums or bulk carrier. These may be stored in their own containers, in hoppers or silts, or bulk piles, either indoors or outdoors.Flammability of the material must be established to determine the safe size and spacing of storage units and •thedesignbasisfortheelectricandfireprotectionsystems.Thepossibilityofspontaneouscombustion,eitherin bulk piles or piles of bags may limit the safe depth of storage. If stored in the open, these should be arranged in a number of separate piles with no point in each pile more •than 10ft, in height. Occasional temperature measurements of such piles may be required. Susceptibility to dust explosions will determine the grounding equipment that will be required.Bins for the, storage of pulverised material should be of non-combustible material and so located that radiation •from boilers, furnaces, steam pipes or other sources of heat cannot raise the temperature of the contents to a dangerous degree.Fine metallic powders can be pyrophoric and these should be stored in air tight containers. Oxidising agents •like chlorates can explode violently in contact with organic materials. Care should be taken to keep such materials in a segregated area. Metals like sodium, potassium, etc. react •violentlywithwatergivingrisetoflames.Thesematerialsmustbestoredawayfromwater.

8.6.2 Liquid Storage

Liquids are generally received or shipped in drums, carboys, tank cars or trucks or by pipeline. They may be •stored in their shipping containers or in ranks.

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Whiledealingwithflammableliquids,itshouldbekeptinmindthatitisthevapourfromtheevaporationof•the liquid rather than the liquid itself that burns or explodes when mixed with air in the presence of a source of ignition.AccordingtoPetroleumRules1976, inflammableliquidsartclassifiedinto threeclasses.Theseclassesare•dependingontheflashpointasgivenbelow:

Class A Flash point below 230C Class B Flash point not below 230C but below 650C Class C Flash point not below 650C but below 930C

Liquidswithflashpintsbelow320C(900F)areliabletogiveoffignitablevapoursatnormalambienttemperatures.•Suchliquidsmaybestoredinclosedcontainersandinlimitedquantitiesinroomsoffireresistingconstructionwhicharesituatedabovethegroundandisolatedfromthereminderbuildingbyfirewallsandselfclosingfiredoors.Largequantitiesofsuchliquidsshallbestoredinisolatedbuildingsoffireresistingconstructionorinoutdoor•storage tanks preferably underground. The rooms should not have openings covered with glass or transparent material which would allow the direct rays of the sun to pass.Sameprecautionsshouldbetakenforliquidswithflashpointsbetween32660C(901500F),particularlyin•tropical countries where the ambient temperatures arc likely to be high during summer months.Whenstoredinroom,itshouldbethoroughlyventilatedattheflooraswellasattheceilingleveltoremove•vapours which might accumulate from leaking containers. The room should be further provided with special trappedfloordrainagefacilitiesandexplosionreliefintheformofpressureopeningwindowsoraweakwall,providing 1sq.ft of venting for every 50ft. of room volume.Electrical,fittingsinareaswhereflammableliquidsandsolventarchandledandstoredshouldbeofflameproof•and vapour proof type. Adequate arrangements for quickly draining any spillage should be provided in all areas. However, attempts •shouldbemadetominimisetheliquidgoingintothesewer,asitsvapourmaycausefiresandexplosionsinlines.Whilestoringindrums,theseshouldnotbefilledfullywithliquid.About5ftspaceshouldbeleftforvapours.•Drums should be stored with bungs on top to avoid leakage of material. Theminimumdistancespecifiedforstoringhighlyflammableliquidsfromplantsis30ft,butfromresidential•area it should be 100 ft. The distance depends on the quantity and quality of the hazardous material being stored. The relevant authority for us is the Indian Explosives Act and Petroleum Act.

8.6.3 Gas Storage

Flammable gases should be stored separately from each other and from other goods. It should be borne in mind •thatnon-flammablegascylindersarealsocapableofexplodingifheated.Cylinders containing compressed gases may only be stored in the open if they are adequately protected against •excessive variation of temperature, direct rays of the sun, accumulation of snow or continuous dampness.When such cylinders are stored inside industrial establishments the storage spaces should be isolated from the •otherareasbyfireresistingandheatresistingwallsorpartitions.Compressedgasesshouldneverbestoredathighlyflammablesubstancesornearanysourceofheat.

8.7 Responsibility for SafetyThe operating department must be held responsible for emptying washout, steaming out, purging with inert gas •and other steps to make equipment safe before it is turned over for maintenance or repair work. Maintenance personnel has the responsibility of making sure proper blanking off of pipelines, ventilation and •testingforflammablevapoursatthetimeofactualstartingofmaintenanceorrepairwork.During shutdown and start ups special care must be taken to see that all lockout and tagging procedures are •followed closely for electrical work, for moving machinery and valves etc.


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8.8 Preparation of EquipmentPumping out and draining all the liquid from the container.•Thorough cleaning.•Samplingofall toproveabsenceoftoxicornoxiousvapourandpresenceofsufficientoxygen(at least16•percent volume).Men who enter vessels must be equipped with safety belts and life lines. For ease in lifting, belts should be •fittedhighunderarmpitsandnotaroundwaist.Airline apparatus supplying fresh air and PVC suit may be required in most of the cases.•The manhole should be of 22”; in extreme case 1lr’ opening may be allowed. Rope or chain ladders with rigid •rungs are to be provided for entry.

8.8.1 Isolation of Equipments from Hazards

All power driven devices such as agitators must be locked out at positive disconnect switches.•Blinding or positively segregating connected pipeline from all possible sources of hazardous liquid, gas or •steam. All the blinds which have been inserted must be listed so that these can be removed after the work is completed.Tagging and locking all related valves and switches. Each group of workers shall use their own tagging and •locking devices and shall they be responsible for removing them.

8.9 Preventive MaintenanceUnplanned maintenance is always carried out under sudden pressure causing accidents and injury due to some •shortcurstakentocompletethejobwithinashortspecifiedtime.With a view to avoid sudden breakdown and unscheduled down time, inspection, repair and replacement of •equipment must be carried out on an intelligently planned schedule. Apart from tremendous cost advantages, the advantages to safety are obvious as the trouble spot will be located •well in advance and exposure to emergency condition will be reduced to minimum.Preventive maintenance implies preventing emergency repairs; still some emergency does occur and we must •plan to take care of it well in advance and not after it happens. Planning should include emergency kit and personnel so that everyone knows who should do what, how and •with what, if the situation calls for.

8.10 TransportationThe movement of hazardous substances by any mode of transport presence, in general, is a greater risk of •accidental release than in a static installation. Some aspects of transport which need to be considered include:

Regulation Design Operation Hazards Emergency planning

Hazards presented by the transport of chemicals are:•Fire Explosion Toxic release Conventional toxic substances Ultra toxic substances

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The initiating factor in a transport accident may be:•Cargo Transporter Operations

Thecargomaycatchfire,explodeorcorrodethetank;thetransportermaybeinvolvedinacrashorderailment;•the operations such as charging and discharging may be wrongfully executed. Thus the events which can give rise to hazards particularly include:•

Container failure Accident impact Loading and unloading operation

Considering the hazards of uncontrolled release of chemicals into the environment, several international •organisations, particularly U.N. have produced detailed recommendations over the last two decades, for the safe transport of chemicals, which have provided the framework for new legislations introduced by various Governments in many countries.Some of the rules framed under the Explosives Act, 1884, Petroleum Act 1934, are Petroleum Rules 1976, •ExplosivesRules1983,StaticandMobi1ePressureVessels(Unfired)Rub1981,GasCylinderRules1981etc.cover most of the important factors coming under the preview of the above rules.The recent notification dated 30thDecember 1985of theStateTransport authority of theGovernment of•Maharashtraenumeratesspecificconditionsforadherencebypublicandprivatecarrierswhile transportinghazardous chemicals as under:

Speciallabelsornoticesshouldbeprominentlyaffixedonpackagesoronvehicles,bearingemblems,as specifiedbytheTransportCommissioner,MaharashtraState,Bombay,pictoriallyrepresentingtheparticulardangers arising out of the carriage of any hazardous chemical.Chemical names, descriptive names or prescribed “Correct technical names” should invariably be displayed on packages or vehicles carrying hazardous chemicals.The drivers of all road vehicles carrying hazardous chemicals must carry with them “Instructions in writing” relating to each class of dangerous substance or whether carried in packed form (i.e. in tins, drums, etc.) or in bulk road vehicles. Theinstructionsincludingfirstaidtreatmentandadvicefordealingwithfire,accident,spillageorleakage must be written in English, Hindi and Marathi and in the languages of the State of transit and destination. Theseinstructionsinwritingshouldbeobtainedfromthefire/chemicalcompany,whichpermitthehazardouschemicals to be transported.A summary of these instructions in writing in a card form to be called “Transport Emergency Card” (Term card) should also be carried by the driver in his cabin; The Term card should be provided by the Party / Supervisor / Chemical Company loading the said chemical.Special’ signs or plates denoting that dangerous goods are being conveyed should be displayed which will identify the substances and also reveal its hazardous properties and indicate what action should be taken in emergencies.

Itisimpliedfromtheabovenotificationthatone:hastobemuchmorecarefulaboutpackages,containersproper•labels, instructions as well as Term Cards etc. In addition the drivers and cleaners are to be trained to take care of emergencies and are to be provided with •firstaidkit,protectiveclothing,fireextinguishersneutralisingagentetc.The drivers must not park the vehicles carrying hazardous materials in thickly populated areas and should drive •away the leaking tanker/vehicle away from the populated area.


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SummaryASME piping codes give stipulations and guidelines for the design, materials, manufacture and testing of •pressure piping.Every ASME code starts with specifying the scope of the code in terms of capacity, size and pressure and other •limitations if any.Thecodescategorise andclassify acceptablegrades formaterialsof construction, for specificapplications•covered by the codes.The ASME B31 Code for Pressure Piping consists of a number of individually published Sections. Rules for •eachSectionhavebeendevelopedconsideringtheneedforapplicationofspecificrequirementsforvarioustypes of pressure piping.A pipe or a tube is hollow longitudinal product. ‘A tube’ is general term used for hollow product having circular, •elliptical or square cross-section or for that matter cross section of any closed perimeter.Pressure pipes are those which are subjected to motive pressure and system pressure and or temperatures. Pipes •are designated by nominal size, starting from 1/8” nominal size and increasing in steps up to 36 inches.Pipefittingsarethecomponentswhichtietogetherpipelines,valvesandotherpartsofapipingsystem.•Socketweldedfittingshavecertainadvantagesoverbutt-weldedfittings.Theyareeasiertouseonsmall-size•pipelines and the ends of the pipes need not be bevelled since the pipe end slips into the socket of the joint.Chemicals which in no way support or assist combustion these are silicates, carbonates, bicarbonates, phosphates, •chlorides, bromides, iodides, sulphates, sulphites, sulphides, thiosulphates, higher halogenated compounds.Planning storage arrangements for solids, both the nature and the form of the material should be taken into •account.Flammable gases should be stored separately from each other and from other goods. It should be borne in mind •thatnon-flammablegascylindersarealsocapableofexplodingifheated.The movement of hazardous substances by any mode of transport presence, in general, is a greater risk of •accidental release than in a static installation.

ReferencesA Piping Tutorial• [Online]. Available at: <http://www.pipingdesign.com/advice/umesh_piping_tutorial.pdf> [Accessed 15 June 2011].Piping Codes and Standards • [Online]. Available at: <http://www.ebookbyte.com/admin/upload/Mechanical%20Engineering/Piping%20Handbook%20Ch-A4%20%28www.eBookByte.com%29.pdf> [Accessed 15 June 2011].Pressure Vessels Fabrication• [Video Online]. Available at: <http://www.youtube.com/watch?v=bVTeIXLyqok> [Accessed 13 July 2011].Pressure Vessels Fabrication• [Video Online]. Available at: <http://www.youtube.com/watch?v=8Yqsh-aw968&feature=related> [Accessed 13 July 2011].Becht. C., 2009. • Process Piping: The Complete Guide to ASME B31.3, 3rd ed., ASME Press.Silowash. B., 2009. • Piping Systems Manual, 1st ed., McGraw – Hill Professional.

Recommended ReadingChuse. R., 1992. • PressureVessels:TheASMECodeSimplified, 7th ed., McGraw – Hill Professional. Wingate. J. A., 2007. • Applying the ASME Codes, 2nd ed., ASME Press.Ellenberger. P., 2010. • Piping and Pipeline Calculations Manual: Construction, Design Fabrication and Examination. Butterworth-Heinemann.

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Self Assessment

Which of the following is false?1. ASME issue written replies know as “Interpretations” to the inquiries concerning technical aspects of the a. code and are sent to “Edition - subscribers” as up-date service.ASME committee meets regularly to consider proposed additions and revisions to the code.b. The codes specify the required welding management and other inspections.c. The codes specify the required N.D.T. and other inspections.d.

_______________ is typically found in electric power generating stations, in industrial and institutional plants, 2. geothermal heating systems and central and district heating and cooling systems.

Power pipinga. Process pipingb. Pipelinec. Refrigeration pipingd.

______________ is typically found in industrial, institutional, commercial and public buildings.3. Power piping a. Building services pipingb. Pipelinec. Process pipingd.

Which of the following is false?4. A pipe is hollow longitudinal product.a. ‘A tube’ is general term used for hollow product having circular, elliptical or square cross-section or for that b. matter cross section of any closed perimeter.Pipescanbeclassifiedbasedonmethodsofmanufactureorenduse.c. Weldscanbeclassifiedbasedonmethodsofmanufactureorenduse.d.

______________ are manufactured by drawing or extrusion process.5. Seamless pipesa. ERW pipesb. Pressure pipes pipingc. Structural pipingd.

______________ are those which are subjected to motive pressure and system pressure and or temperatures.6. Seamless pipesa. ERW pipesb. Pressure pipes pipingc. Structural pipingd.


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Which of the following is true?7. Structuralpipes aremainlyused for longdistanceconveyingof thefluids andare subjected tomotivea. pressures.Line pipes are mainly used for long distance conveying of the fluids and are subjected to motive b. pressures.Seamless pipes aremainlyused for longdistance conveyingof thefluids and are subjected tomotivec. pressures.Pressure pipes aremainly used for long distance conveying of thefluids and are subjected tomotived. pressures.

Which of the following is false?8. Structuralpipes aremainlyused for longdistanceconveyingof thefluids andare subjected tomotivea. pressures.Pipes are designated by nominal size, starting from 1/8” nominal size and increasing in steps up to 36 b. inches.PipeschedulenumberSisdefinedas:Sch.No.S=1000P/S.c. For stainless steels schedule numbers are designated by su-Tix S i.e; lOS, 40S, 80S etc.d.

Pipefittingsarethecomponentswhichtietogetherpipelines,valvesandotherpartsofa______________.9. weld systema. piping systemb. NDTc. slurry transportation piping systemd.

Whathascertainadvantagesoverbutt-weldedfittings?10. Pipefittingsa. Weldfittingsb. Flangedfittingsc. Socketweldedfittingsd.

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Chapter IX

Standard Symbols for Welding

Aim


discuss the care and storage of electrodes•

elaborate general provisions for welding symbols•

highlighttheorientationofspecificweldsymbols•

Objectives


explain multiple reference lines•

describefieldweldsymbols•

illustrate weld all around symbols•

Learning outcome


identify the contours obtained by welding•

recognise various welding symbols•

comprehend weld dim• ension tolerance


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9.1 IntroductionThe weld symbol indicates the type of weld and, when used, is a part of the welding symbol.Weldsymbolsshallbeasshowninfigurebelow.Thesymbolsshallbedrawn“on”thereferenceline(forillustrativepurposes shown dashed).

The welding symbol consists of several elements. Only the reference line and arrow are required elements. Additional elementsmaybeincludedtoconveyspecificweldinginformation.

Alternatively,weldinginformationmaybeconveyedbyothermeanssuchasbydrawingnotesordetails,specifications,standards, codes or other drawings which eliminates the need to include the corresponding elements in the welding symbol.Allelements,whenused,shallhavespecificlocationswithintheweldingsymbolasshown.Mandatoryrequirements regarding each element in a welding symbol refer to the location of the element and should not be interpreted as a necessity to include the dement in every welding symbol.

GROOVE

SQUARE

FILLET PLUG SLOT STUDSPOT

ORPROJECTION

SEAMBACK

ORBACKING

SURFACING EDGE

SCARE V BEVEL U J FLARE-V FLARE-BEVEL

∅

∅

Fig. 9.1 Weld symbols

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(N)

S(E)

FA

T

RP

Finish symbol Groove angle included angle of countersink for plug weldsRootopeningdepthoffillingfor plug and slot welds

Length of weldPitch (centre to centre spacing) of welds

Field weld symbol

Weld around symbol

Number of spot seam stud, plug, slot or projection welds

Elements in this area remain as shown when tail and arrow are reversed

Reference line

Contour symbol

Groove weld size

Depth of bevel size or strength or certain welds

Specificationprocess or other reference

Tail (omitted when reference is not used)

Weld symbol Arrow connecting reference line to arrow side member of joint or arrow side of joint

Bot

hSi

des

Oth

er

Side

Arr

ow

side

Fig. 9.2 Standard location of elements of welding symbol

Weld All Around

Field Weld

Melt Through

Consum-able Insert (Square)

Backing or Spacing (Rectangle)

ContourFlush or

Flat Convex Concave

Fig. 9.3 Supplementary symbols

9.2 General Provisions for Welding SymbolsFollowing are general provisions regarding various symbols of welding.

9.2.1 Location Significance of ArrowInformation applicable to the arrow side of a joint shall be placed below the reference line. Information applicable to the other side of a joint shall be placed above the reference line.


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Other side

Other side

Other side

Other side

Other side

Other side

Arrow sideArrow side



Fig. 9.4 General provisions

Fillet, groove and flange weld symbols: • For these symbols, the arrow shall connect the welding symbol reference line to one side of the joint and this side shall be considered the arrow side of the joint. The side opposite the arrow side of the joint shall be considered the other side of the joint.Plug, slot, spot, projection and seam weld symbols: • For, these symbols, the arrow shall connect the welding symbol reference line to the outer surface of one of the joint members at the centre line of the desired weld. The member towards which the arrow points shall be considered the arrow side member. The other joint member shall be considered the other side member.Symbols with no side significance: • Someweldsymbolshavenoarrow-sideorother-sidesignificance,althoughsupplementarysymbolsusedinconjunctionwiththemmayhavesuchsignificance.

FW

RSEW

RSW

Fig. 9.5 Location significance of arrow

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9.2.2 Location of Weld with Respect to Joint

Arrow side: • Weldsonthearrowsideof thejointshallbespecifiedbyplacingtheweldsymbolbelowthereference line.

Fig. 9.6 Arrow side

Other side: • Weldsontheothersideofthejointshallbespecifiedbyplacingtheweldsymbolabovethereferenceline.

Fig. 9.7 Other side

Both sides: • Weldsonbothsidesofthejointshallbespecifiedbyplacingweldsymbolsbothbelowandabovethereferencelinedirectlyoppositeeachother.Staggeredintermittentfilletweldsaretheexception.


148

Fig. 9.8 Both sides

9.2.3 Orientation of Specific Weld SymbolsFillet bevel-groove, J-groove, flare-bevel-groove and corner-flangeweld symbols shall be drawnwith theperpendicular leg always to the left.

Fig. 9.9 Orientation or specific weld symbols

9.2.4 Break in ArrowWhenonlyonejointmemberistohaveabevel,J-grooveorflange,thearrowshallhaveabreakandpointtowardthatmember.Thearrowneednotbebrokenifitisobviouswhichmemberistohaveabevel,J-grooveorflange.Itshallnotbebrokenifthereisnopreferenceastowhichmemberistohaveabevel,J-grooveorflange.

Fig. 9.10 Break in arrow

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9.2.5 Combined Weld SymbolsFor joints requiring more than one weld type, a symbol shall be used to specify each weld.

Fig. 9.11 Combined weld symbols

9.2.6 Multiple Arrow LinesTwo or more arrows may be used with a single reference line to point to locations where identical welds are specified.

Fig. 9.12 Multiples arrows lines

9.2.7 Multiple Reference Lines

Sequence of operations: • Twoormorereferencelinesmaybeusedtoindicateasequenceofoperations.Thefirstoperationisspecifiedonthereferencelinenearestthearrow.Subsequentoperationsarespecifiedsequentiallyon other reference lines.


150

1st

1st

2nd

2nd

3nd

3nd Operation

Operation

Operation

Fig. 9.13 Sequence of operations

Supplementary data: • The tail of additional reference lines may be used to specify data supplementary to welding symbol information.

Process Data

(CO STD)

Data

Fig. 9.14 Supplementary data

Field weld and weld all-around symbols: • When required, the weld (or examine) all around symbol shall be placedatthejunctionofthearrowandreferencelineforeachoperationtowhichitisapplicable.Thefieldweldsymbol may also be applied to the same location.

151

UT

Fig. 9.15 Field weld and weld all-round symbol9.2.8 Field Weld SymbolFieldwelds(weldsnotmadeinashoporattheplaceofinitialconstruction)shallbespecifiedbyaddingthefieldweldsymbol.Theflagshallbeplacedatarightangleto,andoneithersideof,thereferencelineatthejunctionwith the arrow.

Fig. 9.16 Field weld symbol

9.2.9 Extent of Welding Denoted by Symbols

Weld continuity: • Unless otherwise indicated, welding symbols shall denote continuous welds.Changes in the direction of welding: • Symbols only apply between any changes in the direction of welding or to the extent of hatching or dimension lines, except when the weld-all-around symbol is used. Additional welding symbols or multiple arrows shall be used to specify the welds required for any changes in direction. When it is desirable to use multiple arrows on a welding symbol, the arrows shall originate from a single reference line or fromthefirstreferencelineinthecaseofamultiplereferencelinesymbol.Hidden members: • When the welding of a hidden member is the same as that of a visible member, it may be specifiedasshowninthefigure.Iftheweldingofahiddenmemberisdifferentfromthatofavisiblemember,specificinformationfortheweldingofbothshallbespecified.Ifneededforclarification,auxiliaryillustrationsor views shall be provided.


152

2 Angles

TypicalBothAngles

Fig. 9.17 Hidden membersWeld location specified: • Aweldwithalengthlessthantheavailablejointlength,whoselocationissignificant,shallhavethelocationspecifiedonthedrawing.Weld location not specified: • A weld with a length less than the available joint length and not critical regarding locationmaybespecifiedwithoutindicatingthelocation.

9.2.10 Weld-All-Around Symbol

Weld-all-around symbol: • A continuous weld whether single or combined type, extending around a series of connectedjointsmaybespecifiedbytheadditionoftheweld-all-aroundsymbolatthejunctionofthearrowand reference line. The series of joints may involve different directions and may lie in more than one plane.Circumferential welds: • Welds extending around the circumference of a pipe are excluded from the requirement regarding changes in direction and do not require the weld-all-around symbol to specify a continuous weld.

9.2.11 Tail of the Welding Symbol

Welding and allied process specification: • Theweldingandalliedprocesstobeusedmaybespecifiedbyplacingtheappropriateletterdesignationsinthetailoftheweldingsymbol.Anauxiliarysuffixmaybeused.

GTAW-AU

Fig. 9.18 Tail of the welding symbol

References: • Specifications,codesoranyotherapplicabledocumentsmaybespecifiedbyplacingthereferencein the tail of the welding symbol. Information contained in the referenced document need not be repeated in the welding symbol.

153

A-2

B3S

Fig. 9.19 References

Welding symbols designated typical: • Repetitions of identical welding symbols on a drawing may be avoided by designating a single welding symbol as typical and pointing the arrow to the representative joint. The user shall provide additional information to completely identify all applicable joints.

TYP-5Places

Fig. 9.20 Welding symbols designated typical

Designation of special types of welds: • When the basic weld symbols are inadequate to indicate the desired weld,theweldshallbespecifiedbyacrosssection,detail,orotherdatawithareferencetheretointhetailofthe welding symbol. This may be necessary for skewed joints.

DETA

SK NO 52

Fig. 9.21 Designation of special types of welds

Omission of tail: • When no references are required, the tail may be omitted from the welding symbol.

Fig. 9.22 Omission of tail

Drawing notes: • Drawing notes may be used to provide information pertaining to the welds. Such information need not be repeated in the welding symbols.


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9.2.12 Contours Obtained by WeldingWeldstobemadewithapproximatelyflush,flat,convexorconcavecontourswithouttheuseofmechanicalfinishingshallbespecifiedbyaddingtheflushorflat,convexorconcavecontoursymboltotheweldingsymbol.

9.2.13 Finishing of Welds

Contours obtained by finishing: • Weldstobemechanicallyfinishedapproximatelyflush,flat,convexorconcaveshallbespecifiedbyaddingtheappropriatecontoursymbolandthefinishingsymbol.Finishing methods: • Thefollowingfinishingsymbolsmaybeusedtospecifythemethodoffinishing,butnotthedegreeoffinish:

C – CHIPPING G – GRINDING H – HAMMERING M – MACHINING R – ROLLING

G

M

C

Fig. 9.23 R-rolling

Finishing method unspecified: • Weldstobefinishedapproximatelyflush,flat,convexorconcavewiththemethodunspecifiedshallbeindicatedbyaddingtheletter“U”totheappropriatecontoursymbol.

U

UFig. 9.24 Finishing method unspecified

9.2.14 Melt-Through SymbolThe melt-through symbol shall be used only when complete joint penetration plus visible root reinforcement is required in welds made from one side.

Melt-through symbol location: • The melt-through symbol shall be placed on the side of the reference line opposite the weld symbol.Melt-through dimensions: • Theheightofrootreinforcementmaybespecifiedbyplacingtherequireddimensiontotheleftofthemelt-throughsymbol.Theheightofrootreinforcementmaybeunspecified.

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9.2.15 Melt-Through with Flange Welds

Melt-through with edge-flange welds: • Edge-flangeweldsrequiringcompletejointpenetrationshallbespecifiedbytheedgeflangeweldsymbolwiththemelt-throughsymbolplacedontheoppositesideofthereferenceline.The same welding symbol is used for joints either detailed or not detailed on the drawing.Melt-through with corner-flange welds: • Corner-flangewelds requiring complete joint penetration shallbespecifiedbythecornerflangeweldsymbolwiththemelt-throughsymbolplacedontheoppositesideofthereferenceline.Abrokenarrowshallpointtothemembertobeflangedwherethejointdoesnotgivethisinformation.

9.2.16 Method of Drawing SymbolsSymbols may be drawn mechanically, electronically or freehand. Symbols intended to appear in publications or to beofhighprecisionshouldbedrawnwithdimensionsandproportionsgivenasperspecifications.

9.2.17 U.S. Customary and Metric UnitsThe same system that is the standard for the drawings shall be used on welding symbols. Dual units shall not be used on welding symbols. If it is desired to show conversions from metric to U.S, customary or vice versa, a table of conversions may be included on the drawing. For guidance in drafting standards, reference is made to ANSI Y14 Drafting Manual. For guidance on the use of metric (SI) units, reference is made to ANSI/AWS A1.1. Metric Practice Guide for the Welding Industry.

9.2.18 Weld Dimension ToleranceWhen a tolerance is applicable to a weld symbol dimension, it shall be shown in the tail of the welding symbol withreferencetothedimensiontowhichitappliesorthetoleranceshallbespecifiedbyadrawingnote,codeorspecification.

Fillet Leg + 1.8Tolerance – 0

SegmentLength + ¼Tolerance – ¼

1/4

2-6

Fig. 9.25 Weld dimension tolerance

9.2.19 Application of Arrow and Other Side Convention

Weld Cross Section Symbol

Fig. 9.26 Arrow-side V-Groove weld symbol


156


Fig. 9.27 Other-side V-Groove weld symbol


Fig. 9.28 Both-sides V-Groove weld symbol 9.2.20 Applications of Break in Arrow of Welding Symbol


Fig. 9.29 Arrow side

157


Fig. 9.30 Other side


Fig. 9.31 Both sides

9.2.21 Specification of Groove Weld Size Depth of Bevel Not Specified

½ (½)


Fig. 9.32 Specification of groove weld size depth of bevel not specified (1)

1 1/8

3/4

3/8

(3/8)(3/4)




158


½

½

(½)

(½)

1 1/4






3/4(3/4)



159

SummaryWeldsonbothsidesofthejointshallbespecifiedbyplacingweldsymbolsbothbelowandabovethereference•linedirectlyoppositeeachother.Staggeredintermittentfilletweldsaretheexception.Symbols only apply between any changes in the direction of welding or to the extent of hatching or dimension •lines, except when the weld-all-around symbol is used.Theweldingandalliedprocesstobeusedmaybespecifiedbyplacingtheappropriateletterdesignationsinthe•tailoftheweldingsymbol.Anauxiliarysuffixmaybeused.Specifications,codesoranyotherapplicabledocumentsmaybespecifiedbyplacingthereferenceinthetail•of the welding symbol.Edge-flangeweldsrequiringcompletejointpenetrationshallbespecifiedbytheedgeflangeweldsymbolwith•the melt-through symbol placed on the opposite side of the reference line.

ReferencesIntroduction to Welding Technology • [Online]. Available at: <http://www.newagepublishers.com/samplechapter/001469.pdf >. [Accessed 7 June 2011].Care and Storage of electrodes• [Online]. Available at: <http://www.welding-technology-machines.info/arc-welding-processes-and-equipments/care-and-storage-of-electrodes.htm> [Accessed 15 June 2011].How to Use an Arc Weld: Electrodes Care & Maintenance for Arc Welding Machine• [Video Online]. Available at: < http://www.youtube.com/watch?v=sPxELcKWobI> [Accessed 13 July 2011].Arc Welding Tips for Beginning Welders: Selecting an Electrode for Arc Welding• [Video Online]. Available at: < http://www.youtube.com/watch?v=LSe5WTYa-Ho&feature=relmfu> [Accessed 13 July 2011].Gonzales. R. F., 1975. • Introduction to Welding,CanfieldPress.Rampaul. H., 2002. • Pipe Welding Procedures, 2nd ed., Industrial Press.

Recommended ReadingHouldcroft. P. T., 1977. • Welding Process technology. Cambridge University Press.Jeffus. L., 2011. • Welding: Principles and Applications, 7th ed., Delmar Cengage Learning.The Lincoln Electric Company, 1973. The Procedure handbook of Arc Welding, 12• th ed.


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Self Assessment

Match the Following1.

Weld All AroundA. 1.

Field WeldB. 2.

Melt ThroughC. 3.

Consumable Insert (Square)D. 4.

A-3, B-2, C-4, D-1a. A-4, B-2, C-3, D-1b. A-3, B-4, C-1, D-2c. A-3, B-1, C-2, D-4d.

When a ____________is applicable to a weld symbol dimension, it shall be shown in the tail of the welding 2. symbolwithreferencetothedimensiontowhichitappliesorthetoleranceshallbespecifiedbyadrawingnote,codeorspecification.

complete joint penetrationa. sequence of operationsb. supplementary datac. toleranced.

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Match the following3.

SquareA. 1.

ScarfB. 2.

BevelC. 3.

Flare-BevelD. 4.

A-3, B-2, C-4, D-1a. A-1, B-2, C-3, D-4b. A-3, B-4, C-1, D-2c. A-4, B-1, C-2, D-3d.

Which of the following is false?4. Weldsonthearrowsideofthejointshallbespecifiedbyplacingtheweldsymbolbelowthereferencea. line.Weldson thebothsidesof the jointshallbespecifiedbyplacing theweldsymbolabove thereferenceb. line.Weldson theother sideof the joint shallbespecifiedbyplacing theweldsymbolabove the referencec. line.Weldsonbothsidesof the joint shallbespecifiedbyplacingweldsymbolsbothbelowandabove thed. reference line directly opposite each other.

Which of the following is true?5. Filletbevel-groove,J-groove,flare-bevel-grooveandcorner-flangeweldsymbolsshallbedrawnwiththea. perpendicular leg always to the right.Filletbevel-groove,J-groove,flare-bevel-grooveandcorner-flangeweldsymbolsshallbedrawnbelowb. with the perpendicular leg.Filletbevel-groove,J-groove,flare-bevel-grooveandcorner-flangeweldsymbolsshallbedrawnwiththec. perpendicular leg always to the left.Filletbevel-groove, J-groove,flare-bevel-grooveandcorner-flangeweldsymbolsshallbedrawnaboved. with the perpendicular leg.

Whatshouldbespecifiedbyaddingthefieldweldsymbol?6. Field weldsa. Circumferential weldsb. Electrodesc. Seam weldsd.


162

Which of the following is false?7. Aweldwithalengthlessthantheavailablejointlength,whoselocationissignificant,shallhavethelocationa. specifiedonthedrawing.Aweldwithalengthlessthantheavailablejointlengthandnotcriticalregardinglocationmaybespecifiedb. without indicating the location.Theweldingandalliedprocesstobeusedmaybespecifiedbyplacingtheappropriateletterdesignationsc. in the tail of the welding symbol.Aweldwitha lengthmore than theavailable joint length,whose location is significant, shallhave thed. locationspecifiedonthedrawing.

Which of the following is true?8. When references are required, the tail may be omitted from the welding symbol.a. When no references are required, the tail may be omitted from the welding symbol.b. When no references are required, the electrodes may be omitted from the welding symbol.c. When no references are required, the tail may not be omitted from the welding symbol.d.

The _____________ shall be placed on the side of the reference line opposite the weld symbol.9. melt-through symbola. seam weld symbolb. plug weld symbolc. spot weld symbold.

Which of the following is false?10. Theheightofrootreinforcementmaybespecifiedbyplacingtherequireddimensiontotheleftofthemelt-a. through symbol.Theheightofrootreinforcementmaybeunspecified.b. The melt-through symbol shall not be placed on the side of the reference line opposite the weld symbol.c. When a tolerance is applicable to a weld symbol dimension, it shall be shown in the tail of the welding d. symbol with reference to the dimension to which it applies.

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Case Study I

Meeting Customer’s Welding Flux DemandsInthiscasestudy,amanufacturerinvestigatescustomercomplaintsregardingweldingfluxusedtofabricateoil,gasand water pipelines, among other products. A Pareto chart and DOE help point the way to a solution.

SubmergedArcWelding(SAW)fluxhasmanyapplicationsinthefabricationofoil,gasandwaterpipelines;gascylinders; ship building; and surfacing of worn-out mining and material handling equipment. The following case study tracksaprojecttomeetcustomerdemandbyfine-tuningtheupperandlowercontrollimitsusedinmanufacturingthis welding consumable.

Problems with FluxThegranularceramicsubstanceknownasSAWfluxismanufacturedbymixingmineralandchemicalcomponentsin proprietary proportions and fusing the mixture in an electric furnace. The molten product is then quenched in water,driedinarotarykiln,andcrushedandsievedtoyieldagranularproduct.Thefinalproductissoldinsievemesh fractions, in a number of sizes.

The granular composition is physically added to cover the welding arc zone (hence the name submerged arc). It shieldstheweldarczonefromtheatmosphere,refinestheweldmetalandpeelsoffaftersolidification.

Thecompany in this case studywas approachedbyoneof itsflux-usingcustomerswith anunusualproblem.By speeding up the welding process and, in effect, increasing operating currents and voltages, the company was experiencing higher productivity. However, the productivity increase also resulted in a dramatic rise in weld defects. Uptothispoint,theyhadusedSAWfluxformorethan10yearswithverysatisfactoryresults.

A data collection team was sent immediately to the customer’s location to investigate. Through analysis, the team identifiedthemesh(particle)sizefractionofthefluxtobetherootcauseofthedefects.Whilethecompanyhadbeen supplying the customer with a product designated as mesh 8 x 48 (meaning 100 percent of the mixture would pass through a size-8 sieve, and 0 percent would pass through a size-48 sieve), the new optimal size fraction was mesh 18 x 30. This fraction had upper and lower control limits that were almost 50 percent stricter than what was being currently supplied.Fixing this problem meant eliminating 20 percent of the company’s currently sellable product. Because India is a very cost-sensitive market, price increases to make up for the loss was not an option. Thus, the company began a Lean Six Sigma initiative to reduce product variation to the new customer requirement and simultaneously reduce its operational costs drastically.

Completing the ProjectThe company set a project goal of reducing product variation to the customer-acceptable upper control limit of mesh 18 and lower control limit of mesh 30 within two months.TheLeanSixSigma team collected data from theflux creation process and plotted a Pareto chart ofwheredefectsoccurred.Theynotedwhenthefluxsizefractiondidnotconformtothenewcontrollimits.Ofthevariousmanufacturing process points – quenching, drying in the kiln, crushing and sieving – the largest number of defects (75 percent) was found in the crushing stage, with 15 percent taking place in the sieving stage.

Based on this information, the team decided on an action plan. They started by focusing on optimising the operation of the roller crusher and the sieve decks. Simultaneous 5S (sort, straighten, shine, standardize, sustain) and total productive maintenance (TPM) programs were initiated for both machinery stations to aid in continuous improvement. The programs included regularly scheduled vibration and alignment checks, and calibration of measurement tools.

Next, the team collected data by varying the operational parameters of the crusher, namely the revolutions per minute,thegapbetweenthecrushersandthefeedrate.TheyplottedthedatainaParetochartandfishbonediagramto help address the process limitations.


164

The team also carried out a design of experiments, varying the three parameters (roller gap, roller revolution speed and material feed rate). Through these trials they arrived at the ideal set of parameters. Line balancing, movement analysis and takt time studies also were undertaken to ensure a uniform production rate between work stations and breakdown-free production.

One example of the added process improvements based on the data-driven campaign is the placement of photo cells connected to warning buzzers to indicate non-conforming gaps between the crusher rollers. This poka-yoke, or failsafe, system ensured a properly calibrated machine at all times. The rollers themselves were surfaced with a special alloy and machined to ensure smooth, vibration-free operation.

Ultimately, through the strategic application of Lean Six Sigma protocols, the company experienced a more than 30 percent improvement in its bottom line.

About the author: Naddir Minoo Patel is a metallurgical engineer and was the general manager and chief executive ofSilicoProducts,wherehedirected theoperationsofasubmergedarcweldingfluxmanufacturingfacility inMumbai, India. He is now a process optimisation consultant based out of Calgary, Canada.

Source: Meeting Customer’s Welding Flux Demands. [Online] <http://www.isixsigma.com/index.php?option=com_k2&view=item&id=1455:case-study-meeting-customer%E2%80%99s-welding-flux-demands&Itemid=177> [Accessed 22 June 2011].

Questions:

What is the granular ceramic substance known as and how is it manufactured?1. AnswerThegranularceramicsubstanceisknownasSAWflux.Itismanufacturedbymixingmineralandchemicalcomponents in proprietary proportions and fusing the mixture in an electric furnace.

What the Lean Six Sigma team focused on? 2. AnswerThey started by focusing on optimising the operation of the roller crusher and the sieve decks

What where the defects noted by the Lean Six Sigma team on Pareto chart?3. AnswerLeanSixSigmanotedwhenthefluxsizefractiondidnotconformtothenewcontrollimits.Ofthevariousmanufacturing process points – quenching, drying in the kiln, crushing and sieving – the largest numbers of defects (75 percent) were found in the crushing stage, with 15 percent taking place in the sieving stage

165

Case Study II

Industrial Parts Service Inc., Woodstock, Ontario, Canada

Industrial Parts Service Inc. of Woodstock, Ontario, is saving $1,757 a year in energy costs because it bought energy-efficientarcweldingmachines.

The companyIndustrial Parts Service is a 20 employee shop that fabricates assemblies for original equipment manufacturers in the logging, agricultural and construction industries.

The problemIn welding, power is wasted when the welding power source is left running even though the operator is not welding. The operating factor, or number of hours the machine is actually used in a day, is much less than one would expect. Most welding processes will consume 10 to 15 lb. of welding wire per hour if operated continuously. Yet in the average shop, usage is generally less than 2 to 3 lb. per operator, for an overall duty cycle of about 20 percent. Theweldingpowersourceisidling80percentofthetime.Whenlookingatpowerefficienciesinwelding,theidlecurrent draw is more important than the draw when welding.

The solutionLately,many companies havebeenpurchasing inverter-typepower sources becauseof their energy efficiencywhen idling. Often the inverter brings additional features that may be of value, such as smaller size or improved arc characteristics. On the downside, inverters usually cost more up front.

IndustrialPartsServicefoundasolutionthatfititsrequirementswithoutcostingmore.ThecompanychosethePanasonicKF-350arcweldingpowersupplybecauseithasexcellentarccharacteristicsandisenergyefficient.The unit goes into hibernation six minutes after the last weld is completed, and it springs back to life the moment the welder touches the gun trigger switch. When idling, the unit consumes about 100 watts, compared with 1500 to 2000 watts for other machines.

The savingsWhen idling with “energy savings” turned on, the KF-350 consumes 100 VA. A competitive 450-amp machine with similarSCR(Silicon-ControlledRectifier)technologyconsumes1930VAwhenidling.

For Industrial Parts Service, electricity costs 10¢/kWh, including service charges. Based on a single shift (2000 hours/year) at a 20 percent duty cycle, the machine is idling for 1600 hours/year. For a welding machine that consumes 100 VA when idling rather than 1930 VA, the annual saving per machine is 2928 kWh, or $292.80. Industrial Parts Service has six Panasonic KF 350 machines in its shop, so the energy-saving hibernation feature saves about $1,757per year.

It’s satisfying to be able to save money without really doing anything other than making sure you buy energy-efficientequipmentattheoutset.Whenaddingneworreplacingexistingequipment,energyusageshouldbeoneof the chief considerations

Source: Business: Industrial. [Online]<http://oee.nrcan.gc.ca/industrial/equipment/arc-welding/case-study.cfm?attr=24> [Accessed 22 June 2011].

Questions:How was welding power wasted?1. WhatsolutiondidtheIndustrialPartsServicefind?2. How did the inverter help them in saving power?3.


166

Case Study III

Non Destructive TestingA process plant contained two stainless steel vessels which had been operating for 21 years. The contents of the vesselswereflammable,mildlytoxicandcontained500ppmofchlorides.Thevesselswereoperatedfromfullvacuum up to 15 psi for 20 cycles per day. They contained an agitator which was used in part of the process. Both vessels had been hydraulically tested to 70 psi when new but had not been subjected to a test since.

The company philosophy was ‘Leak before break’ but they didn’t think that stainless steel would break. No leak detection equipment had been installed and reliance was placed on plant operators noticing the smell or observing drips.

The plant owners hired a Competent Person from a large insurance company who produced the Written Scheme of Examination (WSE) for the vessels. There was no evidence of shared decision making between the plant owner and the insurance company. A generic WSE was put into use. This followed SAFED guidelines on periodicity of inspectionwhichwasspecifiedas:

External visual examination supplemented by a hammer test every 2 years.

Was this suitable?The combination of stainless steel and chlorides immediately raises concerns regarding the possibility of stress corrosion cracking. Whilst the cracks were likely to initiate on the inner surface an external examination could detect thepresenceofthroughwallcracks.However,stresscorrosioncrackscanbeverytightanddifficulttoseewiththenakedeye.Thehammertestoffersnobenefit-whoknowswhatagoodvesselshouldsoundlike!

During a thorough examination of one of the vessels the Competent Person called for a small welded repair to an external weld and for this to be followed by a hydraulic test. The vessel developed leaks at 40 psi. Further investigation of the vessel found thousands of through wall cracks. The vessel had not leaked in service because the contents were too viscous to pass through the tight stress corrosion cracks.

ThecompetentpersonmodifiedtheWSEforthe2ndvessel:Yearly examination instead of 2 yearly.•Addition of internal examination from the access way.•Addition of internal dye penetrant examination using red dye on 10% of welds.•

Was this suitable?The Internal inspection would be carried out from the small access way with agitator still in place.The failed vessel had shown most through wall cracks in base. This region could not be inspected on the second vessel from the access way.

Inspection of 10% of welds.Thefailedvesselshowedthroughcracksonparentplateandmostwelds.Therewasnojustificationforlimitingtheinspection to welds only and for just inspecting 10% of them.

Dye Penetrant Inspection using red dye.Withthecrackingontheinternalsurfacetherewasachancethatthecracksmayhavebeenfilledwithproductandif this had been the case dye penetrant inspection would not have been effective.

Stress corrosion cracking can be tight and if so the dye penetrant indications would not reveal the defects. Fluorescent dyesgiveahighersensitivityandwouldgivemuchbetterresultsintheconfined,darkspaceofthevessel.

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Regulation 9 of The Pressure Systems Safety Regulations 2000 requires that a competent person examines those partsofthepressuresystemincludedintheschemeofexaminationwithintheintervalsspecifiedinthescheme.The actions above raise the question of how competent was the competent person? Did they understand the damage mechanisms and the detection requirements?

The competent person, who was independent from the plant owner, did not involve their company NDT expert in amendingtheWSE.Whentheexpertwasfinallyconsultedtheyestimatedthattheprobabilityofdetection,usingthe method stated, was less than 30%. In limiting the inspection to just 10% of the welds then the overall probability of detecting a crack in a weld was just 3%. This is unacceptably low. A probability of detection of only 50% may be acceptable for a regularly applied, non-critical inspection whilst for a highly critical inspection the probability of detection would need to be up near 95%.

However,theexaminationofthesecondvesseldidfindtwoincidencesofstresscorrosioncracking(SCC):onearound the access way nozzle and a star crack in the plate. The nozzle was repaired by welding and the vessel was hydraulically tested to 60 psi. The star crack was to be monitored at the next inspection in a year’s time. No further review of WSE was performed and the vessel was put back into service. The Competent person who put the vessel back into service was not the regular surveyor for the site and it raises the question of whether they fully understood the process.

When the poor inspection and quick return to service was questioned the following excuses were offered:The client needed the vessel back as quickly as possible.•We worked day and night for 2 days.•We have never seen this problem before.•We follow SAFed guidelines.•There is no better way to inspect this type of vessel.•

ConclusionsTheclientplacedahighdependencyonthecompetentpersontosatisfythe‘sufficient’aspectoftheWSE.•The Competent Person may not have understood the process.•When part of a large company, the Competent Person system relies on the surveyor feeding back information •toHeadOfficewhichtheywillnotbeabletodoiftheylackunderstanding.The client imposed time pressures on the Competent Person.•The Competent Person had access to experts in various disciplines but these were not used.•The initial WSE was poorly thought out.•ThefinalWSEwasevenmorepoorlythoughtout.•No attempt was made to estimate critical crack sizes or growth rates and the NDT selected did not have a •capability for measuring defect through wall size.

Finally,justbecausealeadingcompetentpersoncertifiestheWSEitdoesnotmeanthatitissufficient:theWSEshould be scrutinised and the contents challenged wherever there is doubt on their suitability.

Questions:According to you, what led to the leakage in two stainless steel containers?1. Howfluorescentdyeswould2. help in revealing the defect?In few steps explain how you would conduct the survey in the above case.3.


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Recommended Reading

Althous• e, A.D., Turnquist, C.H., Bowditch, W.A., Bowditch, K.E., 2000. Modern welding, Goodheart-Willcox Co. Blondea• u, R., 2008. Metallurgy and Mechanics of Welding, John Wiley and Sons.Burgess, N.T., 1983. • Quality assurance of welded construction, Applied Science.Cain, T., 1985. Soldering and brazing• , Workship Practice, Issue 9 of Workshop practice series, Argus Books.Chattopadhyay. P., 2000. • Boiler Operations Questions and Answers, 2nd ed., McGraw-Hill Professional.Chuse. R., 1992. • PressureVessels:TheASMECodeSimplified, 7th ed., McGraw – Hill Professional. Ellenberger. P., 2010. • Piping and Pipeline Calculations Manual: Construction, Design Fabrication and Examination. Butterworth-Heinemann.Finch, R., 1997. Welder’s Handbook: A Complete Guide to MIG, TIG, Arc & Oxyacetylene Welding, 2• nd ed., HPBooks. Galvery Jr• ., W.L., Marlow, F.B., 2007. Welding Essentials, 2nd ed., Industrial Press, Inc.Gregor• y, E.N., Armstrong, A.A., 2005. Welding symbols on drawings, CRC Press.Haynes., J., 1995. • Welding Manual, 1st ed., Haynes Manuals.Hellier. C., 2001. • Handbook of Non-destructive Evaluation, 1st ed., McGraw-Hill Professional. Houldcrof• t, P.T. and John, R., 2001. Welding and Cutting: A Guide to Fusion Welding and Associated Cutting

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http://www.google.co.in/search?tbo=p&tbm=bks&q=inauthor:%22William+A.+Bowditch%22

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Self Assessment Answers

Chapter Ib1. c2. a3. d4. a5. c6. d7. a8. a9. b10.

Chapter IId1. a2. c3. b4. d5. a6. c7. b8. c9. a10.

Chapter IIId1. a2. b3. a4. d5. c6. b7. d8. d9. c10.

Chapter IVd1. b2. a3. d4. c5. d6. c7. b8. d9. a10.


172

Chapter Va1. c2. d3. b4. a5. a6. c7. b8. a9. b10.

Chapter VIc1. d2. c3. a4. b5. d6. a7. a8. c9. a10.

Chapter VIIa1. c2. b3. d4. c5. a6. d7. b8. a9. d10.

Chapter VIIIc1. a2. b3. d4. a5. c6. b7. a8. b9. d10.

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Chapter IXa1. d2. c3. b4. c5. a6. d7. b8. a9. c10.