61769477 welding-inspection-cswip-gud

Welding Inspector

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Duties and Responsibilities

Section 1

Main Responsibilities 1.1

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• Code compliance

• Workmanship control

• Documentation control

Personal Attributes 1.1

Important qualities that good Inspectors are expected to have are:

•Honesty

•Integrity

•Knowledge

•Good communicator

•Physical fitness

•Good eyesight

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Standard for Visual Inspection 1.1

Basic Requirements

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BS EN 970 - Non-destructive examination of fusion

welds - Visual examination

Welding Inspection Personnel should:

• be familiar with relevant standards, rules and specifications

applicable to the fabrication work to be undertaken

• be informed about the welding procedures to be used

• have good vision (which should be checked every 12

months)

Welding Inspection 1.2

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Conditions for Visual Inspection (to BS EN 970)

Illumination:

• 350 lux minimum required

• (recommends 500 lux - normal shop or office lighting)

Vision Access:

• eye should be within 600mm of the surface

• viewing angle (line from eye to surface) to be not less than

30°

30°

600mm


Aids to Visual Inspection (to BS EN 970)

When access is restricted may use: • a mirrored boroscope• a fibre optic viewing system

Other aids:• welding gauges (for checking bevel angles, weld profile, fillet

sizing, undercut depth)• dedicated weld-gap gauges and linear misalignment (high-low)

gauges• straight edges and measuring tapes• magnifying lens (if magnification lens used it should have

magnification between X2 to X5)

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usually by

agreement}

Welding Inspectors Equipment 1.3

Measuring devices:

• flexible tape, steel rule

• Temperature indicating crayons

• Welding gauges

• Voltmeter

• Ammeter

• Magnifying glass

• Torch / flash light

• Gas flow-meter

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Welding Inspectors Gauges 1.3

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TWI Multi-purpose Welding Gauge Misalignment Gauges

Hi-Lo Gauge

Fillet Weld Gauges

G.A.L.

S.T.D.

10mm

16mm

L

G.A.L.

S.T.D.

10mm

16mm

01/4 1/2 3/4

IN

HI-

LO

S

ing

le P

urp

os

e W

eld

ing

Ga

ug

e

1

2

3

4

5

6

Welding Inspectors Equipment 1.3

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Tong Tester

AmmeterVoltmeter


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Stages of Visual Inspection (to BS EN 970)

Extent of examination and when required should be defined in

the application standard or by agreement between the

contracting parties

For high integrity fabrications inspection required throughout

the fabrication process:

Before welding

(Before assemble & After assembly)

During welding

After welding

Typical Duties of a Welding Inspector 1.5

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Before Welding

Preparation:

Familiarisation with relevant „documents‟…

• Application Standard/Code - for visual acceptance

requirements

• Drawings - item details and positions/tolerances etc

• Quality Control Procedures - for activities such as material

handling, documentation control, storage & issue of

welding consumables

• Quality Plan/Inspection & Test Plan/Inspection Checklist -

details of inspection requirements, inspection procedures

& records required


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Before Welding

Welding Procedures:

• are applicable to joints to be welded & approved

• are available to welders & inspectors

Welder Qualifications:

• list of available qualified welders related to WPS‟s

• certificates are valid and ‘in-date’


Before Welding

Equipment:

• all inspection equipment is in good condition & calibrated as necessary

• all safety requirements are understood & necessary equipment available

Materials:

• can be identified & related to test certificates, traceability !

• are of correct dimensions

• are in suitable condition (no damage/contamination)

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Before Welding

Consumables:

• in accordance with WPS’s

• are being controlled in accordance with Procedure

Weld Preparations:

• comply with WPS/drawing

• free from defects & contamination

Welding Equipment:

• in good order & calibrated as required by Procedure

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Before Welding

Fit-up

• complies with WPS

• Number / size of tack welds to Code / good workmanship

Pre-heat

• if specified

• minimum temperature complies with WPS

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During Welding

Weather conditions

• suitable if site / field welding

Welding Process(es)

• in accordance with WPS

Welder

• is approved to weld the joint

Pre-heat (if required)

• minimum temperature as specified by WPS

• maximum interpass temperature as WPS


During Welding

Welding consumables

• in accordance with WPS

• in suitable condition

• controlled issue and handling

Welding Parameters

• current, voltage & travel speed – as WPS

Root runs

• if possible, visually inspect root before single-sided welds are filled up

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During Welding

Inter-run cleaning

in accordance with an approved method (& back gouging) to good workmanship standard

Distortion control

• welding is balanced & over-welding is avoided

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After Welding

Weld Identification

• identified/numbered as required

• is marked with welder‟s identity

Visual Inspection

• ensure weld is suitable for all NDT

• visually inspect & „sentence‟ to Code requirements

Dimensional Survey

• ensure dimensions comply with Code/drawing

Other NDT

• ensure all NDT is completed & reports available


After Welding

Repairs

• monitor repairs to ensure compliance with Procedure, ensure NDT after repairs is completed

• PWHT

• monitor for compliance with Procedure

• check chart records confirm Procedure compliance

Pressure / Load Test

• ensure test equipment is suitably calibrated

• monitor to ensure compliance with Procedure

• ensure all records are available

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After Welding

Documentation

• ensure any modifications are on ‘as-built’ drawings

• ensure all required documents are available

• Collate / file documents for manufacturing records

• Sign all documentation and forward it to QC department.

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Summary of Duties

A Welding Inspector must:

• ObserveTo observe all relevant actions related to weld quality throughout production.

• RecordTo record, or log all production inspection points relevant to quality, including a final report showing all identified imperfections

• CompareTo compare all recorded information with the acceptance criteria and any other relevant clauses in the applied application standard

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It is the duty of a Welding Inspector to ensure all the welding and

associated actions are carried out in accordance with the

specification and any applicable procedures.

Welding Inspector

Terms & Definitions

Section 2

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Welding Terminology & Definitions 2.1

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What is a Weld?

• A localised coalescence of metals or non-metals produced

either by heating the materials to the welding temperature,

with or without the application of pressure, or by the

application of pressure alone (AWS)

• A permanent union between materials caused by heat, and

or pressure (BS499)

• An Autogenous weld:

A weld made with out the use of a filler material and can

only be made by TIG or Oxy-Gas Welding

Welding Terminology & Definitions 2.1

What is a Joint?

• The junction of members or the edges of members that are to be joined or have been joined (AWS)

• A configuration of members (BS499)

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Joint Terminology 2.2

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Edge Open & Closed Corner Lap

Tee ButtCruciform

Welded Butt Joints 2.2

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A_________Welded butt jointButt

A_________Welded butt jointFillet

A____________Welded butt jointCompound

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Welded Tee Joints 2.2

A_________Welded T jointFillet

A_________Welded T jointButt

A____________Welded T jointCompound

Weld Terminology 2.3

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Compound weld

Fillet weldButt weld

Edge weld

Spot weld

Plug weld

Butt Preparations – Sizes 2.4

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Full Penetration Butt Weld

Partial Penetration Butt Weld

Design Throat

Thickness

Design Throat

Thickness

Actual Throat

Thickness

Actual Throat

Thickness

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Weld Zone Terminology 2.5

Weld Boundary

C

A B

D

Heat Affected Zone

Root

Weld metal

A, B, C & D = Weld Toes

Face

Weld Zone Terminology 2.5

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Excess Root Penetration

ExcessCap heightor Weld Reinforcement

Weld cap width

Design

Throat

Thickness

Actual Throat

Thickness

Heat Affected Zone (HAZ) 2.5

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tempered zone

grain growth zone

recrystallised zone

partially transformed zone

Maximum

Temperature

solid-liquid Boundarysolid

weld

metal

unaffected base

material

Joint Preparation Terminology 2.7

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Included angle

Root Gap

Root Face

Angle of

bevel

Root FaceRoot Gap

Included angle

Root

Radius

Single-V Butt Single-U Butt

Joint Preparation Terminology 2.8 & 2.9

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Root Gap

Root Face Root FaceRoot Gap

Root

Radius

Single Bevel Butt Single-J Butt

Angle of bevel Angle of bevel

Land

Single Sided Butt Preparations 2.10

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Single Bevel Single Vee

Single-J Single-U

Single sided preparations are normally made on thinner materials, or

when access form both sides is restricted

Double Sided Butt Preparations 2.11

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Double sided preparations are normally made on thicker materials, or

when access form both sides is unrestricted

-VeeDouble-BevelDouble

- JDouble - UDouble

Weld Preparation

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Terminology & Typical Dimensions: V-Joints

bevel angle

root face

root gap

included angle

Typical Dimensions

bevel angle 30 to 35°

root face ~1.5 to ~2.5mm

root gap ~2 to ~4mm

Butt Weld - Toe Blend

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6 mm

80

Poor Weld Toe Blend Angle

Improved Weld Toe Blend

Angle

20

3 mm

•Most codes quote the weld

toes shall blend smoothly

•This statement is not

quantitative and therefore

open to individual

interpretation

•The higher the toe blend

angle the greater the

amount of stress

concentration

•The toe blend angle ideally

should be between 20o-30o

Fillet Weld Features 2.13

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Design

Throat

Vertical

Leg

Length

Horizontal leg

Length

Excess

Weld

Metal

Fillet Weld Throat Thickness 2.13

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ba

b = Actual Throat Thickness

a = Design Throat Thickness

Deep Penetration Fillet Weld Features 2.13

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ba

b = Actual Throat Thickness

a = Design Throat Thickness

Fillet Weld Sizes 2.14

Calculating Throat Thickness from a known Leg Length:

Design Throat Thickness = Leg Length x 0.7

Question: The Leg length is 14mm.

What is the Design Throat?

Answer: 14mm x 0.7 = 10mm Throat Thickness

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Calculating Leg Length from a known Design ThroatThickness:

Leg Length = Design Throat Thickness x 1.4

Question: The Design Throat is 10mm.

What is the Leg length?

Answer: 10mm x 1.4 = 14mm Leg Length

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Features to Consider 2 2.14

Importance of Fillet Weld Leg Length Size

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Approximately the same weld volume in both Fillet

Welds, but the effective throat thickness has been

altered, reducing considerably the strength of weld B

2mm

(b)

4mm

8mm

(a)

4mm


Importance of Fillet weld leg length Size

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Area = 4 x 4 =

8mm2

2

Area = 6 x 6 =

18mm2

2

The c.s.a. of (b) is over double the area of (a) without the extra

excess weld metal being added

4mm 6mm

(a) (b)

4mm 6mm

(a) (b)

Excess

Excess

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Fillet Weld Profiles 2.15

Mitre Fillet Convex Fillet

Concave Fillet

A concave profile

is preferred for

joints subjected to

fatigue loading

Fillet welds - Shape

EFFECTIVE THROAT THICKNESS

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“s” = Effective throat thickness

sa

“a” = Nominal throat thickness

Deep penetration fillet welds from high heat

input welding process MAG, FCAW & SAW etc

Fillet Features to Consider 2.15

Welding Positions 2.17

PA 1G / 1F Flat / Downhand

PB 2F Horizontal-Vertical

PC 2G Horizontal

PD 4F Horizontal-Vertical (Overhead)

PE 4G Overhead

PF 3G / 5G Vertical-Up

PG 3G / 5G Vertical-Down

H-L045 6G Inclined Pipe (Upwards)

J-L045 6G Inclined Pipe (Downwards)

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Welding Positions 2.17

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ISO

Welding position designation 2.17

Butt welds in plate (see ISO 6947)

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Flat - PA Overhead - PE

Vertical

up - PF

Vertical

down - PG

Horizontal - PC


Butt welds in pipe (see ISO 6947)

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Flat - PA

axis: horizontal

pipe: rotated

H-L045

axis: inclined at 45°

pipe: fixed

Horizontal - PC

axis: vertical

pipe: fixed

Vertical up - PF

axis: horizontal

pipe: fixed

Vertical down - PG

axis: horizontal

pipe: fixed

J-L045

axis: inclined at 45°

pipe: fixed


Fillet welds on plate (see ISO 6947)

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Flat - PA Overhead - PD

Vertical up - PF Vertical down - PG

Horizontal - PB


Fillet welds on pipe (see ISO 6947)

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Flat - PA axis: inclined at 45°

pipe: rotated

Overhead - PD axis: vertical

pipe: fixed

Vertical up - PF axis: horizontal

pipe: fixed

Vertical down - PG axis: horizontal

pipe: fixed

Horizontal - PB axis: vertical

pipe: fixed

Horizontal - PB axis: horizontal

pipe: rotated

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Plate/Fillet Weld Positions 2.17

PA / 1GPA / 1F

PC / 2GPB / 2F

PD / 4FPE / 4G PG / 3G

PF / 3G

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Pipe Welding Positions 2.17

Weld: Flat

Pipe: rotated

Axis: Horizontal

PA / 1G

Weld: Vertical Downwards

Pipe: Fixed

Axis: Horizontal

PG / 5G

Weld: Vertical upwards

Pipe: Fixed

Axis: Horizontal

PF / 5G

Weld: Upwards

Pipe: Fixed

Axis: Inclined

Weld: Horizontal

Pipe: Fixed

Axis: Vertical

PC / 2G

45o

Weld: Downwards

Pipe: Fixed

Axis: Inclined

J-LO 45 / 6G

45o

H-LO 45 / 6G

Travel Speed Measurement 2.18

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Definition: the rate of weld progression

measured in case of mechanised and automatic

welding processes

in case of MMA can be determined using ROL and arc

time

Welding Inspector

Welding Imperfections

Section 3

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Welding Imperfections 3.1

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All welds have imperfections

• Imperfections are classed as defects when they are of a

type, or size, not allowed by the Acceptance Standard

A defect is an unacceptable imperfection

• A weld imperfection may be allowed by one Acceptance

Standard but be classed as a defect by another Standard

and require removal/rectification


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Standards for Welding Imperfections

BS EN ISO 6520-1(1998) Welding and allied processes –

Classification of geometric

imperfections in metallic materials -

Part 1: Fusion welding

Imperfections are classified into 6 groups, namely:

1 Cracks

2 Cavities

3 Solid inclusions

4 Lack of fusion and penetration

5 Imperfect shape and dimensions

6 Miscellaneous imperfections


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Standards for Welding Imperfections

EN ISO 5817 (2003) Welding - Fusion-welded joints in steel,

nickel, titanium and their alloys (beam

welding excluded) - Quality levels for

imperfections

This main imperfections given in EN ISO 6520-1 are listed in

EN ISO 5817 with acceptance criteria at 3 levels, namely

Level B (highest)

Level C (intermediate)

Level D (general)

This Standard is „directly applicable to visual testing of welds‟

...(weld surfaces & macro examination)

Welding imperfections 3.1

classification

Cracks

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Cracks 3.1

Cracks that may occur in welded materials are caused generally by many factors and may be classified by shape and position.

Note: Cracks are classed as Planar Defects.

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Classified by Shape

•Longitudinal

•Transverse

•Chevron

•Lamellar Tear

Classified by Position

•HAZ

•Centerline

•Crater

•Fusion zone

•Parent metal

Cracks 3.1

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Longitudinal parent metal

Longitudinal weld metal

Lamellar tearing

Transverse weld metal

Cracks 3.1

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Transverse crack Longitudinal crack

Cracks 3.2

Main Crack Types

• Solidification Cracks

• Hydrogen Induced Cracks

• Lamellar Tearing

• Reheat cracks

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Cracks 3.2

Solidification Cracking

• Occurs during weld solidification process

• Steels with high sulphur impurities content (low ductility at elevated temperature)

• Requires high tensile stress

• Occur longitudinally down centre of weld

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Cracks 3.3

Hydrogen Induced Cold Cracking

• Requires susceptible hard grain structure, stress, low temperature and hydrogen

• Hydrogen enters weld via welding arc mainly as result of contaminated electrode or preparation

• Hydrogen diffuses out into parent metal on cooling

• Cracking developing most likely in HAZ

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Lamellar Tearing 3.5

• Location: Parent metal

• Steel Type: Any steel type possible

• Susceptible Microstructure: Poor through thickness ductility

• Lamellar tearing has a step like appearance due to the solid inclusions in the parent material (e.g. sulphides and silicates) linking up under the influence of welding stresses

• Low ductile materials in the short transverse direction containing high levels of impurities are very susceptible to lamellar tearing

• It forms when the welding stresses act in the short transverse direction of the material (through thickness direction)

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Gas Cavities 3.6

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Root piping

Cluster porosityGas pore

Blow hole

Herringbone porosity

Gas pore <1.5mm

Blow hole.>1.6mm

Causes:

•Loss of gas shield

•Damp electrodes

•Contamination

•Arc length too large

•Damaged electrode flux

•Moisture on parent material

•Welding current too low

Gas Cavities 3.7

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Root piping

Porosity

Gas Cavities 3.8

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Cluster porosity Herringbone porosity

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Crater pipe

Weld crater

Crater Pipe 3.9

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Crater pipe is a shrinkage defect and not a gas defect, it has

the appearance of a gas pore in the weld crater

Causes:

• Too fast a cooling

rate

• Deoxidization

reactions and

liquid to solid

volume change

• Contamination

Crater cracks

(Star cracks)

Crater pipe

Crater Pipe 3.9

Solid Inclusions 3.10

Slag inclusions are defined as a non-metallic inclusion caused by some welding process

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Causes:

•Slag originates from

welding flux

•MAG and TIG welding

process produce silica

inclusions

•Slag is caused by

inadequate cleaning

•Other inclusions include

tungsten and copper

inclusions from the TIG

and MAG welding process

Slag inclusions

Parallel slag lines

Lack of sidewall fusion with

associated slag

Lack of interun

fusion + slag

Solid Inclusions 3.11

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Elongated slag linesInterpass slag inclusions


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Typical Causes of Lack of Fusion:

• welding current too low

• bevel angle too steep

• root face too large (single-sided weld)

• root gap too small (single-sided weld)

• incorrect electrode angle

• linear misalignment

• welding speed too high

• welding process related – particularly dip-transfer GMAW

• flooding the joint with too much weld metal (blocking Out)

Lack of Fusion 3.13

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Incomplete filled groove +

Lack of sidewall fusion

1

2

1. Lack of sidewall fusion

2. Lack of inter-run fusion

Causes:

•Poor welder skill

• Incorrect electrode

manipulation

• Arc blow

• Incorrect welding

current/voltage

• Incorrect travel speed

• Incorrect inter-run cleaning

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Lack of sidewall fusion + incomplete filled groove

Lack of Fusion 3.13

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Weld Root Imperfections 3.15

Lack of Root FusionLack of Root Penetration

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Cap Undercut 3.18

Intermittent Cap Undercut

Undercut 3.18

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Cap undercutRoot undercut

Surface and Profile 3.19

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Incomplete filled groove Poor cap profile

Excessive cap height

Poor cap profiles and

excessive cap reinforcements

may lead to stress

concentration points at the

weld toes and will also

contribute to overall poor toe

blend

Surface and Profile 3.19

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Incomplete filled grooveExcess cap reinforcement

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Excessive root

penetration


Overlap 3.21

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An imperfection at the toe or root of a weld caused by metal

flowing on to the surface of the parent metal without fusing to it

Causes:

•Contamination

•Slow travel speed

•Incorrect welding

technique

•Current too low

Overlap 3.21

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Toe Overlap

Toe Overlap

Set-Up Irregularities 3.22

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Plate/pipe Linear Misalignment

(Hi-Lo)

Angular Misalignment

Linear misalignment is

measured from the lowest

plate to the highest point.

Angular misalignment is

measured in degrees


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Linear Misalignment


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Linear Misalignment

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Lack of sidewall fusion + incomplete filled groove

Incomplete Groove 3.23

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Concave Root

Causes:

• Excessive back purge

pressure during TIG welding

Excessive root bead grinding

before the application of the

second pass

welding current too high for

2nd pass overhead welding

root gap too large - excessive

„weaving‟

A shallow groove, which may occur in the root of a butt weld


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Concave Root



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Concave root Excess root penetration

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Causes:

• High Amps/volts

• Small Root face

• Large Root Gap

• Slow Travel

SpeedBurn through

A localized collapse of the weld pool due to excessive

penetration resulting in a hole in the root run



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Burn Through

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Causes:

• Loss or insufficient

back purging gas (TIG)

• Most commonly occurs

when welding stainless

steels

• Purging gases include

argon, helium and

occasionally nitrogen

Oxidized Root (Root Coking)

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Miscellaneous Imperfections 3.26

Arc strike

Causes:

• Accidental striking of the

arc onto the parent

material

• Faulty electrode holder

• Poor cable insulation

• Poor return lead

clamping

Miscellaneous Imperfections 3.27

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Causes:

• Excessive current

• Damp electrodes

• Contamination

• Incorrect wire feed

speed when welding

with the MAG welding

process

• Arc blowSpatter

Mechanical Damage 3.28

Mechanical damage can be defined as any surface material

damage cause during the manufacturing process.

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• Grinding

• Hammering

• Chiselling

• Chipping

• Breaking off welded attachments

(torn surfaces)

• Using needle guns to compress

weld capping runs

Mechanical Damage 3.28

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Mechanical Damage/Grinding Mark

Chipping Marks

Welding Inspector

Destructive Testing

Section 4

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Qualitative and Quantitative Tests 4.1

The following mechanical tests have units and are termedquantitative tests to measure Mechanical Properties

• Tensile tests (Transverse Welded Joint, All Weld Metal)

• Toughness testing (Charpy, Izod, CTOD)

• Hardness tests (Brinell, Rockwell, Vickers)

The following mechanical tests have no units and are termed

qualitative tests for assessing joint quality

• Macro testing

• Bend testing

• Fillet weld fracture testing

• Butt weld nick-break testing

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Mechanical Test Samples 4.1

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Tensile Specimens

Fracture Fillet

Specimen

CTOD Specimen

Charpy Specimen

Bend Test

Specimen

Destructive Testing 4.1

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Typical Positions for Test

Pieces

Specimen Type Position

•Macro + Hardness 5

•Transverse Tensile 2, 4

•Bend Tests 2, 4

•Charpy Impact Tests 3

•Additional Tests 3

WELDING PROCEDURE QUALIFICATION TESTING

2

3

4

5

top of fixed pipe

Definitions

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• Malleability

• Ductility

• Toughness

• Hardness

• Tensile Strength

Ability of a material to

withstand deformation

under static compressive

loading without rupture

Mechanical Properties of metals are related to the amount of deformation which metals can withstand under different circumstances of force application.

Definitions

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• Malleability

• Ductility

• Toughness

• Hardness


Ability of a material

undergo plastic

deformation under static

tensile loading without

rupture. Measurable

elongation and reduction

in cross section area

Mechanical Properties of metals are related to the amount of

deformation which metals can withstand under different

circumstances of force application.

Definitions

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• Malleability

• Ductility

• Toughness

• Hardness


Ability of a material to

withstand bending or the

application of shear

stresses by impact loading

without fracture.


Definitions

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• Malleability

• Ductility

• Toughness

• Hardness


Measurement of a

materials surface

resistance to indentation

from another material by

static load


Definitions

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• Malleability

• Ductility

• Toughness

• Hardness


Measurement of the

maximum force required to

fracture a materials bar of

unit cross-sectional area in

tension


Transverse Joint Tensile Test 4.2

Weld on plate

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Multiple cross joint

specimensWeld on pipe

Tensile Test 4.3

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All-Weld Metal Tensile

Specimen

Transverse Tensile

Specimen

STRA (Short Transverse Reduction Area)For materials that may be subject to Lamellar Tearing

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UTS Tensile test 4.4

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Charpy V-Notch Impact Test 4.5

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Objectives:

• measuring impact strength in different weld joint areas

• assessing resistance toward brittle fracture

Information to be supplied on the test report:

• Material type

• Notch type

• Specimen size

• Test temperature

• Notch location

• Impact Strength Value

Ductile / Brittle Transition Curve 4.6

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- 50 0- 20 - 10- 40 - 30

Ductile fracture

Ductile/Brittletransition point

47 Joules

28 Joules

Testing temperature - Degrees Centigrade

Temperature range

Transition range

Brittle fracture

Three specimens are normally tested at each temperature

Energy absorbed

Comparison Charpy Impact Test Results 4.6

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Impact Energy Joules

Room Temperature -20oC Temperature

1. 197 Joules

2. 191 Joules

3. 186 Joules

1. 49 Joules

2. 53 Joules

3. 51 Joules

Average = 191 Joules Average = 51 Joules

The test results show the specimens carried out at room

temperature absorb more energy than the specimens carried

out at -20oC

Charpy V-notch impact test specimen 4.7

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Specimen dimensions according ASTM E23

ASTM: American Society of Testing Materials

Charpy V-Notch Impact Test 4.8

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Specime

n

Pendulu

m

(striker)

Anvil (support)

Charpy Impact Test 4.9

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10 mm8 m

m2

mm

22.5o

Machined

notch

100% DuctileMachined

notch

Large reduction

in area, shear

lips

Fracture surface

100% bright

crystalline brittle

fracture

Randomly torn,

dull gray fracture

surface

100% Brittle

Hardness Testing 4.10

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Definition

Measurement of resistance of a material against

penetration of an indenter under a constant load

There is a direct correlation between UTS and

hardness

Hardness tests:

Brinell

Vickers

Rockwell


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Objectives:

• measuring hardness in different areas of a welded joint

• assessing resistance toward brittle fracture, cold cracking

and corrosion sensitivity within a H2S (Hydrogen Sulphide)

environment.

Information to be supplied on the test report:

• material type

• location of indentation

• type of hardness test and load applied on the indenter

• hardness value

Vickers Hardness Test 4.11

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Vickers hardness tests:

indentation body is a square based diamond pyramid

(136º included angle)

the average diagonal (d) of the impression is

converted to a hardness number from a table

it is measured in HV5, HV10 or HV025Adjustable shuttersIndentationDiamond

indentor

Vickers Hardness Test Machine 4.11

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Brinell Hardness Test 4.11

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• Hardened steel ball of given diameter is subjected for

a given time to a given load

• Load divided by area of indentation gives Brinell

hardness in kg/mm2

• More suitable for on site hardness testing

30KN

Ø=10mm

steel ball

Rockwell Hardness Test

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1KN

Ø=1.6mm

steel ball

Rockwell B Rockwell C

1.5KN

120 Diamond

Cone


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Hardness Test Methods Typical Designations

Vickers 240 HV10

Rockwell Rc 22

Brinell 200 BHN-W

usually the hardest region

1.5 to 3mm

HAZ

fusion line

or

fusion

boundary

Hardness specimens can also be used for CTOD samples

Crack Tip Opening Displacement testing 4.12

• Test is for fracture toughness

• Square bar machined with a notch placed in the centre.

• Tested below ambient temperature at a specified temperature.

• Load is applied at either end of the test specimen in an attempt to open a crack at the bottom of the notch

• Normally 3 samples

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Fatigue Fracture 4.13

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Location: Any stress concentration area

Steel Type: All steel types

Susceptible Microstructure: All grain structures

Test for Fracture Toughness is CTOD

(Crack Tip Opening Displacement)

Fatigue Fracture 4.13

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• Fatigue cracks occur under cyclic stress conditions

• Fracture normally occurs at a change in section, notch

and weld defects i.e stress concentration area

• All materials are susceptible to fatigue cracking

• Fatigue cracking starts at a specific point referred to as

a initiation point

• The fracture surface is smooth in appearance

sometimes displaying beach markings

• The final mode of failure may be brittle or ductile or a

combination of both

Fatigue Fracture

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• Toe grinding, profile grinding.

• The elimination of poor profiles

• The elimination of partial penetration welds and weld

defects

• Operating conditions under the materials endurance limits

• The elimination of notch effects e.g. mechanical damage

cap/root undercut

• The selection of the correct material for the service

conditions of the component

Precautions against Fatigue Cracks

Fatigue Fracture

Fatigue fracture occurs in structures subject to repeated application of tensile stress.

Crack growth is slow (in same cases, crack may grow into an area of low stress and stop without failure).

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Fatigue Fracture

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Initiation points / weld defects

Fatigue fracture surface

smooth in appearance

Secondary mode of failure

ductile fracture rough fibrous

appearance

Fatigue Fracture

• Crack growth is slow

• It initiate from stress concentration points

• load is considerably below the design or yield stress level

• The surface is smooth

• The surface is bounded by a curve

• Bands may sometimes be seen on the smooth surface –”beachmarks”. They show the progress of the crack front from the point of origin

• The surface is 90° to the load

• Final fracture will usually take the form of gross yielding (as the maximum stress in the remaining ligament increase!)

• Fatigue crack need initiation + propagation periods

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Fatigue fracture distinguish features:

Bend Tests 4.15

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Object of test:

• To determine the soundness of the weld zone. Bend

testing can also be used to give an assessment of

weld zone ductility.

• There are three ways to perform a bend test:

Root bend

Face bend

Side bend

Side bend tests are normally carried out on welds over 12mm in thickness

Bending test 4.16

Types of bend test for welds (acc. BS EN 910):

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Thickness of material - “t”

“t” up to 12 mm

“t” over 12 mm

Root / face

bend

Side bend

Fillet Weld Fracture Tests 4.17

Object of test:

• To break open the joint through the weld to permit examination of the fracture surfaces

• Specimens are cut to the required length

• A saw cut approximately 2mm in depth is applied along the fillet welds length

• Fracture is usually made by striking the specimen with a single hammer blow

• Visual inspection for defects

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Fracture should break weld saw cut to root

2mm

Notch

Hammer


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This fracture indicates

lack of fusion

This fracture has

occurred saw cut to root

Lack of Penetration

Nick-Break Test 4.18

Object of test:

• To permit evaluation of any weld defects across the fracture surface of a butt weld.

•Specimens are cut transverse to the weld

•A saw cut approximately 2mm in depth is applied along the welds root and cap

•Fracture is usually made by striking the specimen with a single hammer blow

•Visual inspection for defects

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Nick-Break Test 4.18

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Approximately 230 mm

19 mm

2 mm

2 mm

Notch cut by hacksaw

Weld reinforcement

may or may not be

removed

Nick Break Test 4.18

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Inclusions on fracture

lineLack of root penetration

or fusion

Alternative nick-break test

specimen, notch applied all

way around the specimen

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We test welds to establish minimum levels of mechanical

properties, and soundness of the welded joint

We divide tests into Qualitative & Quantitative methods:

Qualitative: (Have no units/numbers)

For assessing joint quality

Macro tests

Bend tests

Fillet weld fracture tests

Butt Nick break tests

Quantitative: (Have units/numbers)

To measure mechanical properties

Hardness (VPN & BHN)

Toughness (Joules & ft.lbs)

Strength (N/mm2 & PSI, MPa)

Ductility / Elongation (E%)

Summary of Mechanical Testing 4.19

Welding Inspector

WPS – Welder Qualifications

Section 5

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Welding Procedure Qualification 5.1

Question:

What is the main reason for carrying out a Welding Procedure

Qualification Test ?

(What is the test trying to show ?)

Answer:

To show that the welded joint has the properties* that satisfy

the design requirements (fit for purpose)

* properties

•mechanical properties are the main interest - always strength but

toughness & hardness may be important for some applications

•test also demonstrates that the weld can be made without defects

Welding Procedures 5.1

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Producing a welding procedure involves:

• Planning the tasks

• Collecting the data

• Writing a procedure for use of for trial

• Making a test welds

• Evaluating the results

• Approving the procedure

• Preparing the documentation


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In most codes reference is made to how the procedure are to

be devised and whether approval of these procedures is

required.

The approach used for procedure approval depends on the

code:

Example codes:

• AWS D.1.1: Structural Steel Welding Code

• BS 2633: Class 1 welding of Steel Pipe Work

• API 1104: Welding of Pipelines

• BS 4515: Welding of Pipelines over 7 Bar

Other codes may not specifically deal with the requirement of

a procedure but may contain information that may be used in

writing a weld procedure

• EN 1011Process of Arc Welding Steels

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The welding engineer writes qualified Welding Procedure

Specifications (WPS) for production welding


Production welding conditions must remain within the range of

qualification allowed by the WPQR

(according to EN ISO 15614)

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(according to EN Standards)

welding conditions are called welding variables

welding variables are classified by the EN ISO Standard as:

•Essential variables

•Non-essential variables

•Additional variables

Note: additional variables = ASME supplementary essential

The range of qualification for production welding is based on

the limits that the EN ISO Standard specifies for essential

variables*

(* and when applicable - the additional variables)

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WELDING ESSENTIAL VARIABLES

Question:

Why are some welding variables classified as essential ?

Answer:

A variable, that if changed beyond certain limits (specified by

the Welding Standard) may have a significant effect on the

properties* of the joint

* particularly joint strength and ductility

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SOME TYPICAL ESSENTIAL VARIABLES

• Welding Process

• Post Weld Heat Treatment (PWHT)

• Material Type

• Electrode Type, Filler Wire Type (Classification)

• Material Thickness

• Polarity (AC, DC+ve / DC-ve)

• Pre-Heat Temperature

• Heat Input

• Welding Position


Components of a welding procedure

Parent material• Type (Grouping)

• Thickness

• Diameter (Pipes)

• Surface condition)

Welding process• Type of process (MMA, MAG, TIG, SAW etc)

• Equipment parameters

• Amps, Volts, Travel speed

Welding Consumables• Type of consumable/diameter of consumable

• Brand/classification

• Heat treatments/ storage

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Components of a welding procedure

Joint design•Edge preparation

•Root gap, root face

•Jigging and tacking

•Type of baking

Welding Position•Location, shop or site

•Welding position e.g. 1G, 2G, 3G etc

•Any weather precaution

Thermal heat treatments•Preheat, temps

•Post weld heat treatments e.g. stress relieving

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Object of a welding procedure test

To give maximum confidence that the welds mechanical

and metallurgical properties meet the requirements of the

applicable code/specification.

Each welding procedure will show a range to which the

procedure is approved (extent of approval)

If a customer queries the approval evidence can be

supplied to prove its validity

Welding Procedures

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Summary of designations:

pWPS: Preliminary Welding Procedure Specification

(Before procedure approval)

WPAR (WPQR): Welding Procedure Approval Record

(Welding procedure Qualification record)

WPS: Welding Procedure Specification

(After procedure approval)

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Example:

Welding

Procedure

Specification

(WPS)

Welder Qualification 5.4

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Numerous codes and standards deal with welder qualification,

e.g. BS EN 287.

• Once the content of the procedure is approved the next

stage is to approve the welders to the approved procedure.

• A welders test know as a Welders Qualification Test (WQT).

Object of a welding qualification test:

• To give maximum confidence that the welder meets the

quality requirements of the approved procedure (WPS).

• The test weld should be carried out on the same material and

same conditions as for the production welds.

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Welder Qualification 5.4 & 5.5


Question:

What is the main reason for qualifying a welder ?

Answer:

To show that he has the skill to be able to make production

welds that are free from defects

Note: when welding in accordance with a Qualified WPS

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The welder is allowed to make production welds within the

range of qualification shown on the Certificate

The range of qualification allowed for production welding is

based on the limits that the EN Standard specifies for the

welder qualification essential variables


(according to EN 287 )

A Certificate may be withdrawn by the Employer if there is

reason to doubt the ability of the welder, for example

• a high repair rate

• not working in accordance with a qualified WPS

The qualification shall remain valid for 2 years provided there is certified

confirmation of welding to the WPS in that time.

A Welder‟s Qualification Certificate automatically expires if the welder has not

used the welding process for 6 months or longer.

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Welding Engineer writes a preliminary Welding Procedure

Specification (pWPS) for each test weld to be made

• A welder makes a test weld in accordance with the pWPS

• A welding inspector records all the welding conditions used

for the test weld (referred to as the „as-run‟ conditions)

An Independent Examiner/ Examining Body/ Third Party

inspector may be requested to monitor the qualification

process



The finished test weld is subjected to NDT in accordance with

the methods specified by the EN ISO Standard - Visual, MT or

PT & RT or UT

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Test weld is subjected to destructive testing (tensile, bend,

macro)

The Application Standard, or Client, may require additional

tests such as impact tests, hardness tests (and for some

materials - corrosion tests)


A Welding Procedure Qualification Record (WPQR) is prepared

giving details of: -

• The welding conditions used for the test weld

• Results of the NDT

• Results of the destructive tests

• The welding conditions that the test weld allows for

production welding

The Third Party may be requested to sign the WPQR as a true

record


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An approved WPS should be available covering the range of

qualification required for the welder approval.

• The welder qualifies in accordance with an approved WPS

• A welding inspector monitors the welding to make sure that the

welder uses the conditions specified by the WPS

EN Welding Standard states that an Independent Examiner,

Examining Body or Third Party Inspector may be required to

monitor the qualification process

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The finished test weld is subjected to NDT by the methods

specified by the EN Standard - Visual, MT or PT & RT or UT

The test weld may need to be destructively tested - for certain

materials and/or welding processes specified by the EN

Standard or the Client Specification



• A Welder‟s Qualification Certificate is prepared showing the

conditions used for the test weld and the range of qualification

allowed by the EN Standard for production welding

• The Qualification Certificate is usually endorsed by a Third

Party Inspector as a true record of the test


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Information that should be included on a welders test certificate are,

which the welder should have or have access to a copy of !

• Welders name and identification number

• Date of test and expiry date of certificate

• Standard/code e.g. BS EN 287

• Test piece details

• Welding process.

• Welding parameters, amps, volts

• Consumables, flux type and filler classification details

• Sketch of run sequence

• Welding positions

• Joint configuration details

• Material type qualified, pipe diameter etc

• Test results, remarks

• Test location and witnessed by

• Extent (range) of approval

Welding Inspector

Materials Inspection

Section 6

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Material InspectionOne of the most important items to consider is Traceability.

The materials are of little use if we can not, by use of an effective QA system trace them from specification and purchase order to final documentation package handed over to the Client.

All materials arriving on site should be inspected for:

• Size / dimensions

• Condition

• Type / specification

In addition other elements may need to be considered depending on the materials form or shape

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Pipe Inspection

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We inspect the condition(Corrosion, Damage, Wall thickness Ovality, Laminations & Seam)

Specification

Welded seam

Size

LP5

Other checks may need to be made such as: distortion tolerance, number of plates and storage.

Plate Inspection

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Size

We inspect the condition

(Corrosion, Mechanical damage, Laps, Bands & Laminations)

5L

Specification

Other checks may need to be made such as: distortion tolerance, number of plates and storage.

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Parent Material Imperfections

Lamination

Mechanical damage Lap

Segregation line

Laminations are caused in the parent plate by the steel making

process, originating from ingot casting defects.

Segregation bands occur in the centre of the plate and are low

melting point impurities such as sulphur and phosphorous.

Laps are caused during rolling when overlapping metal does not

fuse to the base material.

Lapping

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Lamination

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Laminations

Plate Lamination

Welding Inspector

Codes & Standards

Section 7

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Codes & Standards

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The 3 agencies generally identified in a code or standard:

The customer, or client

The manufacturer, or contractor

The 3rd party inspection, or clients representative

Codes often do not contain all relevant data, but may

refer to other standards

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Standard/Codes/Specifications

STANDARDS

SPECIFICATIONS CODES

Examples

plate, pipe

forgings, castings

valves

electrodes

Examples

pressure vessels

bridges

pipelines

tanks

Welding Inspector

Welding Symbols

Section 8

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Weld symbols on drawings

Advantages of symbolic representation:

• simple and quick plotting on the drawing

• does not over-burden the drawing

• no need for additional view

• gives all necessary indications regarding the specific joint to be obtained

Disadvantages of symbolic representation:

• used only for usual joints

• requires training for properly understanding of symbols

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The symbolic representation includes:

• an arrow line

• a reference line

• an elementary symbol

The elementary symbol may be completed by:

• a supplementary symbol

• a means of showing dimensions

• some complementary indications

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Dimensions

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In most standards the cross sectional dimensions are given to

the left side of the symbol, and all linear dimensions are give on

the right side

Convention of dimensions

a = Design throat thickness

s = Depth of Penetration, Throat thickness

z = Leg length (min material thickness)

BS EN ISO 22553

AWS A2.4

•In a fillet weld, the size of the weld is the leg length

•In a butt weld, the size of the weld is based on the depth of the

joint preparation

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A method of transferring information from the

design office to the workshop is:

The above information does not tell us much about the wishes

of the designer. We obviously need some sort of code which

would be understood by everyone.

Most countries have their own standards for symbols.

Some of them are AWS A2.4 & BS EN 22553 (ISO 2553)

Please weld

here


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Joints in drawings may be indicated:

•by detailed sketches, showing every dimension

•by symbolic representation


Elementary Welding Symbols(BS EN ISO 22553 & AWS A2.4)

Convention of the elementary symbols:

Various categories of joints are characterised by an elementary symbol.

The vertical line in the symbols for a fillet weld, single/double bevel butts and a J-butt welds must always be on the left side.

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Square edge

butt weld

Weld type Sketch Symbol

Single-v

butt weld

Elementary Welding Symbols

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Single-V butt

weld with broad

root face


Single

bevel butt

weldSingle bevel

butt weld with

broad root

face

Backing run

Elementary Welding Symbols

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Single-U

butt weld


Single-J

butt weld

Fillet weld

Surfacing

ISO 2553 / BS EN 22553

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Plug weld

Resistance spot weld

Resistance seam weld

Square Butt weld

Steep flanked

Single-V Butt

Surfacing

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Arrow Line

(BS EN ISO 22553 & AWS A2.4):

Convention of the arrow line:

• Shall touch the joint intersection

• Shall not be parallel to the drawing

• Shall point towards a single plate preparation (when only

one plate has preparation)

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(AWS A2.4)

Convention of the reference line:

Shall touch the arrow line

Shall be parallel to the bottom of the drawing

Reference Line

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or

Reference Line

(BS EN ISO 22553)

Convention of the reference line:

• Shall touch the arrow line

• Shall be parallel to the bottom of the drawing

• There shall be a further broken identification line above or

beneath the reference line (Not necessary where the weld

is symmetrical!)

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(BS EN ISO 22553 & AWS A2.4)

Convention of the double side weld symbols:

Representation of welds done from both sides of the joint

intersection, touched by the arrow head

Fillet weld

Double V

Double bevel

Double U

Double J

Double side weld symbols

ISO 2553 / BS EN 22553

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Arrow line

Reference lines

Arrow side

Other side Arrow side

Other side

ISO 2553 / BS EN 22553

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Single-V Butt flush cap Single-U Butt with sealing run

Single-V Butt with

permanent backing strip

M

Single-U Butt with

removable backing strip

M R

ISO 2553 / BS EN 22553

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Single-bevel butt Double-bevel butt

Single-bevel butt Single-J butt

ISO 2553 / BS EN 22553

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Partial penetration single-V butt

„S‟ indicates the depth of penetration

s10

1015

ISO 2553 / BS EN 22553

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s = Depth of Penetration, Throat

thickness

z = Leg length(min material thickness)

a = (0.7 x z)

a 4

4mm Design throat

z 6

6mm leg

az s

s 6

6mm Actual throat

ISO 2553 / BS EN 22553

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Arrow side

Arrow side

ISO 2553 / BS EN 22553

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Other side

Other side

s6

s6

6mm fillet weld

ISO 2553 / BS EN 22553

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n = number of weld elements

l = length of each weld element

(e) = distance between each weld element

n x l (e)

Welds to be staggered

Process

2 x 40 (50)

3 x 40 (50)111

ISO 2553 / BS EN 22553

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80 80 80

909090

6

6

5

5

z5

z6

3 x 80 (90)

3 x 80 (90)

All dimensions in mm

ISO 2553 / BS EN 22553

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All dimensions in mm

8

8

6

680 80 80

909090

z8

z6

3 x 80 (90)

3 x 80 (90)

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Supplementary symbols

Concave or Convex

Toes to be ground smoothly

(BS EN only)Site Weld

Weld all round

(BS EN ISO 22553 & AWS A2.4)

Convention of supplementary symbols

Supplementary information such as welding process, weld

profile, NDT and any special instructions

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Supplementary symbols

Further supplementary information, such as WPS number, or

NDT may be placed in the fish tail

Ground flush

111

Welding process

numerical BS EN

MR

Removable

backing strip

Permanent

backing strip

M

(BS EN ISO 22553 & AWS A2.4)

Convention of supplementary symbols

Supplementary information such as welding process, weld profile,

NDT and any special instructions

ISO 2553 / BS EN 22553

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ba

dc

ISO 2553 / BS EN 22553

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ConvexMitre

Toes

shall be

blended

Concave

ISO 2553 / BS EN 22553

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s = Depth of Penetration, Throat

thickness

z = Leg length(min material thickness)

a = (0.7 x z)

a 4

4mm Design throat

z 6

6mm leg

az s

s 6

6mm Actual throat

ISO 2553 / BS EN 22553Complimentary Symbols

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Field weld (site weld)

The component requires

NDT inspection

WPS

Additional information,

the reference document

is included in the box

Welding to be carried out

all round component

(peripheral weld)

NDT

ISO 2553 / BS EN 22553

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Numerical Values for Welding Processes:

111: MMA welding with covered electrode

121: Sub-arc welding with wire electrode

131: MIG welding with inert gas shield

135: MAG welding with non-inert gas shield

136: Flux core arc welding

141: TIG welding

311: Oxy-acetylene welding

72: Electro-slag welding

15: Plasma arc welding

AWS A2.4 Welding Symbols

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AWS Welding Symbols

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1(1-1/8)

60o

1/8

Depth of

Bevel

Effective

Throat

Root Opening

Groove Angle

AWS Welding Symbols

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1(1-1/8)

60o

1/8

GSFCAW

Welding Process

GMAW

GTAW

SAW

AWS Welding Symbols

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3 – 10

3 – 10

Welds to be staggered

SMAW

Process

10

3 3

AWS Welding Symbols

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1(1-1/8)

60o

1/8

FCAW

Sequence of

Operations

1st Operation

2nd Operation

3rd Operation

AWS Welding Symbols

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1(1-1/8)

60o

1/8

FCAW

Sequence of

Operations

RT

MT

MT

AWS Welding Symbols

4/23/2007 215 of 691

Dimensions- Leg Length

6/8

6 leg on member A

8

6Member A

Member B

Welding Inspector

Intro To Welding Processes

Section 9

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Welding Processes

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Welding is regarded as a joining process in which the work

pieces are in atomic contact

Pressure welding

• Forge welding

• Friction welding

• Resistance Welding

Fusion welding

• Oxy-acetylene

• MMA (SMAW)

• MIG/MAG (GMAW)

• TIG (GTAW)

• Sub-arc (SAW)

• Electro-slag (ESW)

• Laser Beam (LBW)

• Electron-Beam (EBW)

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20 8040 60 130 140120100 180160 200

10

60

50

40

30

20

80

70

90

100

Normal Operating

Voltage Range

Large voltage variation, e.g. +

10v (due to changes in arc

length)

Small amperage change

resulting in virtually constant

current e.g. + 5A.

Vo

lta

ge

Amperage

Required for: MMA, TIG, Plasma

arc and SAW > 1000 AMPS

O.C.V. Striking voltage (typical) for

arc initiation

Constant Current Power Source

(Drooping Characteristic)

Monitoring Heat Input

• Heat Input:

The amount of heat generated in the

welding arc per unit length of weld.

Expressed in kilo Joules per millimetre

length of weld (kJ/mm).

Heat Input (kJ/mm)= Volts x Amps

Travel speed(mm/s) x 1000

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4/23/2007 228 of 691

Weld and weld pool temperatures


4/23/2007 229 of 691


• Monitoring Heat Input As Required by

• BS EN ISO 15614-1:2004

• In accordance with EN 1011-1:1998

4/23/2007 230 of 691

When impact requirements and/or hardness requirements are

specified, impact test shall be taken from the weld in the highest

heat input position and hardness tests shall be taken from the

weld in the lowest heat input position in order to qualify for all

positions

Welding Inspector

MMA Welding

Section 10

4/23/2007 231 of 691

MMA - Principle of operation

4/23/2007 233 of 691

MMA welding

Main features:

• Shielding provided by decomposition of flux covering

• Electrode consumable

• Manual process

Welder controls:

• Arc length

• Angle of electrode

• Speed of travel

• Amperage settings

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Manual Metal Arc Basic Equipment

4/23/2007 235 of 691

Power source

Holding oven

Inverter power

source

Electrode holder

Power cablesWelding visor

filter glass

Return lead

Electrodes

Electrode

oven

Control panel

(amps, volts)

MMA Welding Plant

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Transformer:

• Changes mains supply voltage to a voltage suitable for welding.

Has no moving parts and is often termed static plant.

Rectifier:

• Changes a.c. to d.c., can be mechanically or statically achieved.

Generator:

• Produces welding current. The generator consists of an armature

rotating in a magnetic field, the armature must be rotated at a

constant speed either by a motor unit or, in the absence of

electrical power, by an internal combustion engine.

Inverter:

• An inverter changes d.c. to a.c. at a higher frequency.

MMA Welding Variables

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Voltage

• The arc voltage in the MMA process is measured as close to

the arc as possible. It is variable with a change in arc length

O.C.V.

• The open circuit voltage is the voltage required to initiate, or

re-ignite the electrical arc and will change with the type of

electrode being used e.g 70-90 volts

Current

• The current used will be determined by the choice of

electrode, electrode diameter and material type and

thickness. Current has the most effect on penetration.

Polarity

• Polarity is generally determined by operation and electrode

type e.g DC +ve, DC –ve or AC

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20 8040 60 130 140120100 180160 200

10

60

50

40

30

20

80

70

90

100

Normal Operating

Voltage Range

Large voltage variation, e.g. +

10v (due to changes in arc

length)

Small amperage change

resulting in virtually constant

current e.g. + 5A.

Vo

lta

ge

Amperage

O.C.V. Striking voltage (typical) for arc

initiation

Constant Current Power Source

(Drooping Characteristic)

MMA welding parameters

Travel speed

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Travel

speedToo highToo low

•wide weld bead contour

•lack of penetration

•burn-through

•lack of root fusion

•incomplete root

penetration

•undercut

•poor bead profile,

difficult slag removal


Type of current:• voltage drop in welding cables is lower with AC

• inductive looses can appear with AC if cables are coiled

• cheaper power source for AC

• no problems with arc blow with AC

• DC provides a more stable and easy to strike arc, especially with low current, better positional weld, thin sheet applications

• welding with a short arc length (low arc voltage) is easier with DC, better mechanical properties

• DC provides a smoother metal transfer, less spatter

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Welding current

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– approx. 35 A/mm of diameter

– governed by thickness, type of joint and welding

position

Welding

currentToo highToo low

•poor starting

•slag inclusions

•weld bead contour too

high

•lack of

fusion/penetration

•spatter

•excess

penetration

•undercut

•burn-through


Arc length = arc voltage

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Arc

voltageToo highToo low

•arc can be extinguished

•“stubbing”

•spatter

•porosity

•excess

penetration

•undercut

•burn-through

Polarity: DCEP generally gives deeper penetration

MMA - Troubleshooting

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MMA quality (left to right)current, arc length and travel speed normal;

current too low;

current too high;

arc length too short;

arc length too long;

travel speed too slow;

travel speed too high

MMA electrode holder

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Collet or twist type“Tongs” type with

spring-loaded jaws

MMA Welding Consumables

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The three main electrode covering types used in MMA welding

• Cellulosic - deep penetration/fusion

• Rutile - general purpose

• Basic - low hydrogen

(Covered in more detail in Section 14)

MMA Covered Electrodes

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Most welding defects in MMA are caused by a lack of welder

skill (not an easily controlled process), the incorrect settings

of the equipment, or the incorrect use, and treatment of

electrodes

Typical Welding Defects:

•Slag inclusions

•Arc strikes

•Porosity

•Undercut

•Shape defects (overlap, excessive root penetration, etc.)

MMA welding typical defects

Manual Metal Arc Welding (MMA)

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Advantages:

• Field or shop use

• Range of consumables

• All positions

• Portable

• Simple equipment

Disadvantages:

• High welder skill required

• High levels of fume

• Hydrogen control (flux)

• Stop/start problems

• Comparatively uneconomic when compared with some

other processes i.e MAG, SAW and FCAW

Welding Inspector

TIG Welding

Section 11

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Tungsten Inert Gas Welding

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The TIG welding process was first developed in the USA

during the 2nd world war for the welding of aluminum alloys

• The process uses a non-consumable tungsten electrode

• The process requires a high level of welder skill

• The process produces very high quality welds.

• The TIG process is considered as a slow process compared

to other arc welding processes

• The arc may be initiated by a high frequency to avoid scratch

starting, which could cause contamination of the tungsten

and weld

TIG - Principle of operation

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TIG Welding Variables

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Voltage

The voltage of the TIG welding process is variable only by the

type of gas being used, and changes in the arc length

Current

The current is adjusted proportionally to the tungsten

electrodes diameter being used. The higher the current the

deeper the penetration and fusion

Polarity

The polarity used for steels is always DC –ve as most of the

heat is concentrated at the +ve pole, this is required to keep

the tungsten electrode at the cool end of the arc. When

welding aluminium and its alloys AC current is used

Types of current

• can be DCEN or DCEP

• DCEN gives deep penetration

• requires special power source

• low frequency - up to 20 pulses/sec (thermal pulsing)

• better weld pool control

• weld pool partially solidifies between pulses4/23/2007 256 of 691

Type of

welding

current

can be sine or square wave

requires a HF current (continuos

or periodical)

provide cleaning action

DC

AC

Pulsed

current

Choosing the proper electrode

Current type influence

4/23/2007 257 of 691

++

+

++

+

++

+

--

-

--

-

--

-

Electrode capacity

Current type & polarity

Heat balance

Oxide cleaning action

Penetration

DCEN DCEPAC (balanced)

70% at work

30% at electrode

50% at work

50% at electrode

35% at work

65% at electrode

Deep, narrow Medium Shallow, wide

No Yes - every half cycle Yes

Excellent

(e.g. 3,2 mm/400A)

Good

(e.g. 3,2 mm/225A)

Poor

(e.g. 6,4 mm/120A)

ARC CHARACTERISTICS

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Volts

Amps

OCV

Constant Current/Amperage Characteristic

Large change in voltage =

Smaller change in amperage

Welding Voltage

Large arc gap

Small arc

gap

TIG - arc initiation methods

• simple method• tungsten electrode is in contact

with the workpiece!• high initial arc current due to the

short circuit• impractical to set arc length in

advance• electrode should tap the

workpiece - no scratch!• ineffective in case of AC• used when a high quality is not

essential

4/23/2007 259 of 691

Arc initiation

method

Lift arc HF start

need a HF generator (spark-

gap oscillator) that generates a

high voltage AC output (radio

frequency) costly

reliable method required on

both DC (for start) and AC (to

re-ignite the arc)

can be used remotely

HF produce interference

requires superior insulation

Pulsed current

• usually peak current is 2-10 times background current

• useful on metals sensitive to high heat input

• reduced distortions

• in case of dissimilar thicknesses equal penetration can be achieved

4/23/2007 260 of 691

Time

Curr

ent

(A) Pulse

time

Cycle

time

Peak

current

Background

current

Average current

one set of variables can be used in all positions

used for bridging gaps in open root joints

require special power source


Polarity Influence – cathodic cleaning effect

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Tungsten Electrodes

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Old types: (Slightly Radioactive)

• Thoriated: DC electrode -ve - steels and most metals

• 1% thoriated + tungsten for higher current values

• 2% thoriated for lower current values

• Zirconiated: AC - aluminum alloys and magnesium

New types: (Not Radioactive)

• Cerium: DC electrode -ve - steels and most metals

• Lanthanum: AC - Aluminum alloys and magnesium

TIG torch set-up

• Electrode extension

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Electrode

extension

Stickout 2-3 times

electrode

diameter

Electrode

extension

Low electron

emission

Unstable arc

Too

small

Overheating

Tungsten

inclusions

Too

large

Choosing the correct electrode

Polarity Influence – cathodic cleaning effect

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Tungsten Electrodes

4/23/2007 265 of 691

Old types: (Slightly Radioactive)

• Thoriated: DC electrode -ve - steels and most metals

• 1% thoriated + tungsten for higher current values

• 2% thoriated for lower current values

• Zirconiated: AC - aluminum alloys and magnesium

New types: (Not Radioactive)

• Cerium: DC electrode -ve - steels and most metals

• Lanthanum: AC - Aluminum alloys and magnesium

Tungsten electrode types

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Pure tungsten electrodes:

colour code - green

no alloy additions

low current carrying capacity

maintains a clean balled end

can be used for AC welding of Al and Mg alloys

poor arc initiation and arc stability with AC compared

with other electrode types

used on less critical applications

low cost


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Thoriated tungsten electrodes:

colour code - yellow/red/violet

20% higher current carrying capacity compared to

pure tungsten electrodes

longer life - greater resistance to contamination

thermionic - easy arc initiation, more stable arc

maintain a sharpened tip

recommended for DCEN, seldom used on AC

(difficult to maintain a balled tip)

This slightly radioactive


4/23/2007 268 of 691

Ceriated tungsten electrodes:

colour code - grey (orange acc. AWS A-5.12)

operate successfully with AC or DC

Ce not radioactive - replacement for thoriated types

Lanthaniated tungsten electrodes:

colour code - black/gold/blue

operating characteristics similar with ceriated

electrode


4/23/2007 269 of 691

Zirconiated tungsten electrodes:

colour code - brown/white

operating characteristics fall between those of pure

and thoriated electrodes

retains a balled end during welding - good for AC

welding

high resistance to contamination

preferred for radiographic quality welds

Electrode tip for DCEN

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Electrode tip prepared for low

current welding

Electrode tip prepared for high

current welding

Vertex

angle

Penetration

increase

Increase

Bead width

increase

Decrease

2-2

,5 t

imes

ele

ctr

od

e d

iam

ete

r

Electrode tip for AC

4/23/2007 271 of 691

Electrode tip groundElectrode tip ground and

then conditioned

DC -ve AC

TIG Welding Variables

4/23/2007 272 of 691

Tungsten electrodes

The electrode diameter, type and vertex angle are all critical

factors considered as essential variables. The vertex angle is

as shown

Vetex angle

Note: when welding

aluminium with AC

current, the tungsten end

is chamfered and forms a

ball end when welding

DC -ve

Note: too fine an angle will

promote melting of the

electrodes tip

AC


4/23/2007 273 of 691

Unstable

arc

Tungsten

inclusions

Welding

current

Electrode tip

not properly

heated

Excessive

melting or

volatilisation

Too

low

Too

high

Factors to be considered:

Penetration

Shielding gas requirements

• Preflow and postflow

4/23/2007 275 of 691

Preflow Postflow

Shielding gas flow

Welding current

Flow rate

too low

Flow rate

too high

Special shielding methods

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Pipe root run shielding – Back Purging to prevent

excessive oxidation during welding, normally argon.

TIG torch set-upElectrode extension

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Electrode

extension

Stickout 2-3 times

electrode

diameter

Electrode

extension

Low electron

emission

Unstable arc

Too

small

Overheating

Tungsten

inclusions

Too

large

TIG Welding ConsumablesWelding consumables for TIG:

•Filler wires, Shielding gases, tungsten electrodes (non-consumable).

•Filler wires of different materials composition and variable diameters available in standard lengths, with applicable code stamped for identification

•Steel Filler wires of very high quality, with copper coating to resist corrosion.

•shielding gases mainly Argon and Helium, usually of highest purity (99.9%).

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Tungsten Inclusion

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A Tungsten Inclusion always shows up as

bright white on a radiograph

May be caused by Thermal Shock of

heating to fast and small fragments

break off and enter the weld pool, so a

“slope up” device is normally fitted to

prevent this could be caused by touch

down also.

Most TIG sets these days have slope-

up devices that brings the current to

the set level over a short period of

time so the tungsten is heated more

slowly and gently

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Most welding defects with TIG are caused by a lack of welder

skill, or incorrect setting of the equipment. i.e. current, torch

manipulation, welding speed, gas flow rate, etc.

• Tungsten inclusions (low skill or wrong vertex angle)

• Surface porosity (loss of gas shield mainly on site)

• Crater pipes (bad weld finish technique i.e. slope out)

• Oxidation of S/S weld bead, or root by poor gas cover

• Root concavity (excess purge pressure in pipe)

• Lack of penetration/fusion (widely on root runs)

TIG typical defects

Tungsten Inert Gas Welding

Advantages

• High quality

• Good control

• All positions

• Lowest H2 process

• Minimal cleaning

• Autogenous welding

(No filler material)

• Can be automated

Disadvantages

• High skill factor required

• Low deposition rate

• Small consumable range

• High protection required

• Complex equipment

• Low productivity

• High ozone levels +HF

4/23/2007 281 of 691

Welding Inspector

MIG/MAG Welding

Section 12

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Gas Metal Arc Welding

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The MIG/MAG welding process was initially developed in the

USA in the late 1940s for the welding of aluminum alloys.

The latest EN Welding Standards now refer the process by the

American term GMAW (Gas Metal Arc Welding)

• The process uses a continuously fed wire electrode

• The weld pool is protected by a separately supplied

shielding gas

• The process is classified as a semi-automatic welding

process but may be fully automated

• The wire electrode can be either bare/solid wire or flux

cored hollow wire

MIG/MAG - Principle of operation

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MIG/MAG process variables

• Welding current

• Polarity

4/23/2007 286 of 691

•Increasing welding current

•Increase in depth and width

•Increase in deposition rate

MIG/MAG process variables

• Arc voltage

• Travel speed

4/23/2007 287 of 691

•Increasing travel speed

•Reduced penetration and width, undercut

•Increasing arc voltage

•Reduced penetration, increased width

•Excessive voltage can cause porosity,

spatter and undercut


4/23/2007 289 of 691

Types of Shielding Gas

MIG (Metal Inert Gas)

• Inert Gas is required for all non-ferrous alloys (Al, Cu, Ni)

• Most common inert gas is Argon

• Argon + Helium used to give a „hotter‟ arc - better for thicker

joints and alloys with higher thermal conductivity

MIG/MAG – shielding gases

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Type of material Shielding gas

Carbon steel

Stainless steel

Aluminium

CO2 , Ar+(5-20)%CO2

Ar+2%O2

Ar

MIG/MAG shielding gases

Argon (Ar):

higher density than air; low thermal conductivity the arc has a high energy inner cone; good wetting at the toes; low ionisation potential

Helium (He):

lower density than air; high thermal conductivity uniformly distributed arc energy; parabolic profile; high ionisation potential

Carbon Dioxide (CO2):

cheap; deep penetration profile; cannot support spray transfer; poor wetting; high spatter

4/23/2007 291 of 691

Ar Ar-He He CO2

MIG/MAG shielding gases

Gases for dip transfer:

• CO2: carbon steels only: deep penetration; fast welding speed; high spatter levels

• Ar + up to 25% CO2: carbon and low alloy steels: minimum spatter; good wetting and bead contour

• 90% He + 7.5% Ar + 2.5% CO2:stainless steels: minimises undercut; small HAZ

• Ar: Al, Mg, Cu, Ni and their alloys on thin sections

• Ar + He mixtures: Al, Mg, Cu, Ni and their alloys on thicker sections (over 3 mm)

4/23/2007 292 of 691

MIG/MAG shielding gasesGases for spray transfer

• Ar + (5-18)% CO2: carbon steels: minimum spatter; good wetting and bead contour

• Ar + 2% O2: low alloy steels: minimise undercut; provides good toughness

• Ar + 2% O2 or CO2: stainless steels: improved arc stability; provides good fusion

• Ar: Al, Mg, Cu, Ni, Ti and their alloys

• Ar + He mixtures: Al, Cu, Ni and their alloys: hotter arc than pure Ar to offset heat dissipation

• Ar + (25-30)% N2: Cu alloys: greater heat input

4/23/2007 293 of 691

Gas Metal Arc WeldingTypes of Shielding Gas

MAG (Metal Active Gas)

• Active gases used are Oxygen and Carbon Dioxide

• Argon with a small % of active gas is required for all steels (including stainless steels) to ensure a stable arc & good droplet wetting into the weld pool

• Typical active gases are

Ar + 20% CO2 for C-Mn & low alloy steels

Ar + 2% O2 for stainless steels

100% CO2 can be used for C - steels4/23/2007 294 of 691

MIG/MAG Gas Metal Arc Welding

Electrode orientation

4/23/2007 295 of 691

Penetration Deep Moderate Shallow

Excess weld metal Maximum Moderate Minimum

Undercut Severe Moderate Minimum

Electrode extension

•Increased extension

MIG / MAG - self-regulating arc

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Stable condition Sudden change in gun position

L19 mm

25 mmL‟

Arc length L = 6,4 mm

Arc voltage = 24V

Welding current = 250A

WFS = 6,4 m/min

Melt off rate = 6,4 m/min

Arc length L‟ = 12,7 mm

Arc voltage = 29V


WFS = 6,4 m/min

Melt off rate = 5,6

m/min

Current (A)

Vo

ltag

e (

V)

MIG/MAG - self-regulating arc

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Sudden change in gun position

25 mmL‟

Arc length L‟ = 12,7 mm

Arc voltage = 29V


WFS = 6,4 m/min


Current (A)

Vo

ltag

e (

V)

Re-established stable condition

25 mmL

Arc length L = 6,4 mm

Arc voltage = 24V


WFS = 6,4 m/min


Terminating the arc

• Burnback time

4/23/2007 298 of 691

– delayed current cut-off to prevent wire freeze

in the weld end crater

– depends on WFS (set as short as possible!)

Contact tip

Workpiec

e

Burnback time 0.05 sec 0.10 sec 0.15 sec

14 mm

8 mm 3 mm

Current - 250A

Voltage - 27V

WFS - 7,8 m/min

Wire diam. - 1,2 mm

Shielding gas -

Ar+18%CO2

Insulatin

g slag

Crater fill

MIG/MAG - metal transfer modes

Set-up for dip transfer Set-up for spray transfer

4/23/2007 299 of 691

Electrode

extension

19-25 mm

Contact tip

recessed

(3-5 mm)

Contact tip

extension

(0-3,2 mm)

Electrode

extension

6-13 mm

MIG/MAG - metal transfer modes

Current/voltage conditions4/23/2007 301 of 691

Current

Voltage

Dip transfer

Spray

transfer

Globular

transfer

Electrode diameter = 1,2 mm

WFS = 3,2 m/min

Current = 145 A

Voltage = 18-20V

Electrode diameter = 1,2 mm

WFS = 8,3 m/min

Current = 295 A

Voltage = 28V

MIG/MAG-methods of metal transfer

4/23/2007 303 of 691

Dip transfer

Transfer occur due to short circuits

between wire and weld pool, high

level of spatter, need inductance

control to limit current raise

Can use pure CO2 or Ar- CO2

mixtures as shielding gas

Metal transfer occur when arc is

extinguished

Requires low welding current/arc

voltage, a low heat input process.

Resulting in low residual stress

and distortion

Used for thin materials and all

position welds


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Spray transfer

Transfer occur due to pinch effect NO contact between wire and weld pool!

Requires argon-rich shielding gas

Metal transfer occur in small droplets, a large volume weld pool

Requires high welding current/arc voltage, a high heat input process. Resulting in high residual stress and distortion

Used for thick materials and flat/horizontal position welds


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Pulsed transfer

Controlled metal transfer, one droplet per pulse,

No transfer between droplet and weld pool!

Requires special power sources

Metal transfer occur in small droplets (diameter equal

to that of electrode)

Requires moderate welding current/arc voltage, a

reduced heat input . Resulting in smaller residual

stress and distortion compared to spray transfer

Pulse frequency controls the volume of weld pool,

used for root runs and out of position welds

MIG/MAG - metal transfer modesPulsed transfer

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Controlled metal transfer. one droplet

per pulse. NO transfer during

background current!

Requires special power sources

Metal transfer occur in small droplets

(diameter equal to that of electrode)

Requires moderate welding current/arc voltage, reduced

heat input‟ smaller residual stress and distortions

compared to spray transfer

Pulse frequency controls the volume of weld pool, used

for root runs and out of position welds


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Globular transfer

Transfer occur due to gravity or

short circuits between drops and

weld pool

Requires CO2 shielding gas

Metal transfer occur in large drops

(diameter larger than that of

electrode) hence severe spatter

Requires high welding current/arc

voltage, a high heat input process.

Resulting in high residual stress

and distortion

Non desired mode of transfer!

4/23/2007 315 of 691

O.C.V. Arc Voltage

Virtually no Change.

Voltage

Flat or Constant Voltage Characteristic Used With

MIG/MAG, ESW & SAW < 1000 amps

100 200 300

33

32

31

Large Current Change

Small Voltage

Change.

Amperage

Flat or Constant Voltage Characteristic

MIG/MAG welding gun assembly

4/23/2007 316 of 691

Contact

tip

Gas

diffuser

Handle

Gas

nozzle

Trigger WFS remote

control

potentiometer

Union nut

The Push-Pull gun


4/23/2007 318 of 691

PROCESS CHARACTERISTICS

• Requires a constant voltage power source, gas supply, wire

feeder, welding torch/gun and „hose package‟

• Wire is fed continuously through the conduit and is burnt-off

at a rate that maintains a constant arc length/arc voltage

• Wire feed speed is directly related to burn-off rate

• Wire burn-off rate is directly related to current

• When the welder holds the welding gun the process is said

to be a semi-automatic process

• The process can be mechanised and also automated

• In Europe the process is usually called MIG or MAG

4/23/2007 322 of 691

Most welding imperfections in MIG/MAG are caused by lack of

welder skill, or incorrect settings of the equipment

•Worn contact tips will cause poor power pick up, or transfer

•Bad power connections will cause a loss of voltage in the arc

•Silica inclusions (in Fe steels) due to poor inter-run cleaning

•Lack of fusion (primarily with dip transfer)

•Porosity (from loss of gas shield on site etc)

•Solidification problems (cracking, centerline pipes, crater

pipes) especially on deep narrow welds

MIG/MAG typical defects

WELDING PROCESS

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Flux Core Arc Welding

(Not In The Training Manual)

Flux cored arc welding

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FCAW

methods

With gas

shielding -

“Outershield”

Without gas

shielding -

“Innershield”

With metal

powder -

“Metal core”

“Outershield” - principle of operation

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“Innershield” - principle of operation

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ARC CHARACTERISTICS

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Volts

Amps

OCV

Constant Voltage Characteristic

Small change in voltage =

large change in amperage

The self

adjusting arc.

Large arc gap

Small arc gap

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Insulated extension nozzle

Current carrying guild tube

Flux cored hollow wire

Flux powder

Arc shield composed of vaporized and slag forming compounds

Metal droplets covered

with thin slag coating

Molten weld pool

Solidified weld metal and slag

Flux core

Wire joint

Flux core wires

Flux Core Arc Welding (FCAW)

Flux cored arc welding

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FCAW

methods

With gas

shielding -

“Outershield”

Without gas

shielding -

“Innershield”

(114)

With metal

powder -

“Metal core”

With active

gas shielding

(136)

With inert gas

shielding (137)

FCAW - differences from MIG/MAG

• usually operates in DCEP but some “Innershield” wires operates in DCEN

• power sources need to be more powerful due to the higher currents

• doesn't work in deep transfer mode

• require knurled feed rolls

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“Innershield” wires use

a different type of

welding gun

Backhand (“drag”) technique

Advantages

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preferred method for flat or horizontal position

slower progression of the weld

deeper penetration

weld stays hot longer, easy to remove dissolved

gasses

Disadvantages

produce a higher weld profile

difficult to follow the weld joint

can lead to burn-through on thin sheet plates

Forehand (“push”) technique

Advantages

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preferred method for vertical up or overhead

position

arc is directed towards the unwelded joint , preheat

effect

easy to follow the weld joint and control the

penetration

Disadvantages

produce a low weld profile, with coarser ripples

fast weld progression, shallower depth of penetration

the amount of spatter can increase

FCAW advantages

• less sensitive to lack of fusion

• requires smaller included angle compared to MMA

• high productivity

• all positional

• smooth bead surface, less danger of undercut

• basic types produce excellent toughness properties

• good control of the weld pool in positional welding especially with rutile wires

• seamless wires have no torsional strain, twist free

• ease of varying the alloying constituents

• no need for shielding gas

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FCAW disadvantages• limited to steels and Ni-base alloys

• slag covering must be removed

• FCAW wire is more expensive on a weight basis than solid wires (exception: some high alloy steels)

• for gas shielded process, the gaseous shield may be affected by winds and drafts

• more smoke and fumes are generated compared with MIG/MAG

• in case of Innershield wires, it might be necessary to break the wire for restart (due to the high amount of insulating slag formed at the tip of the wire)

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Advantages:

1) Field or shop use

2) High productivity

3) All positional

4) Slag supports and

shapes the weld Bead

5) No need for shielding

gas

Disadvantages:

1) High skill factor

2) Slag inclusions

3) Cored wire is

Expensive

4) High level of fume

(Inner-shield)

5) Limited to steels and

nickel alloys

FCAW advantages/disadvantages

Welding Inspector

Submerged Arc Welding

Section 13

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• Submerged arc welding was developed in the Soviet Union

during the 2nd world war for the welding of thick section steel.

• The process is normally mechanized.

• The process uses amps in the range of 100 to over 2000, which

gives a very high current density in the wire producing deep

penetration and high dilution welds.

• A flux is supplied separately via a flux hopper in the form of either

fused or agglomerated.

• The arc is not visible as it is submerged beneath the flux layer

and no eye protection is required.

Submerged Arc Welding Introduction

SAW Principle of operation

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Principles of operation

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Factors that determine whether to use SAW chemical

composition and mechanical properties required for the weld

deposit

• thickness of base metal to be welded

• joint accessibility

• position in which the weld is to be made

• frequency or volume of welding to be performed

SAW methods

Semiautomatic Mechanised Automatic


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- +

Power

supply

Filler wire spool

Flux hopper

Wire electrode

Flux

Slide rail

SAW process variables

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• welding current

• current type and polarity

• welding voltage

• travel speed

• electrode size

• electrode extension

• width and depth of the layer of flux

SAW process variables

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Welding current

•controls depth of penetration and the amount of

base metal melted & dilution

SAW operating variables

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Current type and polarity

•Usually DCEP, deep

penetration, better

resistance to

porosity

•DCEN increase

deposition rate but

reduce penetration

(surfacing)

•AC used to avoid

arc blow; can give

unstable arc

SAW Consumables(Covered in detail in Section 14)

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Fused fluxes advantages:

•good chemical homogeneity

•easy removal of fines without affecting flux

composition

•normally not hygroscopic & easy storage and handling

•readily recycled without significant change in particle

size or composition

Fused fluxes disadvantages:•difficult to add deoxidizers and ferro-alloys (due to

segregation or extremely high loss)

•high temperatures needed to melt ingredients limit the

range of flux compositions

SAW Consumables

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Agglomerated fluxes advantages:

• easy addition of deoxidizers and alloying elements

• usable with thicker layer of flux when welding

• colour identification

Agglomerated fluxes disadvantages:

• tendency to absorb moisture

• possible gas evolution from the molten slag leading to

porosity

• possible change in flux composition due to segregation or

removal of fine mesh particles

SAW equipment

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Power sources can be:

• transformers for AC

• transformer-rectifiers for DC

Static characteristic can be:

• Constant Voltage (flat) - most of the power sources

• Constant Current (drooping)

SAW equipment

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Constant Voltage (Flat Characteristic) power sources:

• most commonly used supplies for SAW

• can be used for both semiautomatic and automatic welding

• self-regulating arc

• simple wire feed speed control

• wire feed speed controls the current and power supply

controls the voltage

• applications for DC are limited to 1000A due to severe arc

blow (also thin wires!)

ARC CHARACTERISTICS

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Volts

Amps

OCV

Constant Voltage Characteristic

Small change in voltage =

large change in amperage

The self

adjusting arc.

Large arc gap

Small arc gap

SAW equipment

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Constant Current (Drooping Characteristic) power sources:

• Over 1000A - very fast speed required - control of burn off

rate and stick out length

• can be used for both semiautomatic and automatic welding

• not self-regulating arc

• must be used with a voltage-sensing variable wire feed

speed control

• more expensive due to more complex wire feed speed

control

• arc voltage depends upon wire feed speed whilst the power

source controls the current

• cannot be used for high-speed welding of thin steel

SAW equipment

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Welding heads can be mounted on a:

Tractor type carriage

• provides travel along straight or

gently curved joints

• can ride on tracks set up along the

joint (with grooved wheels) or on

the workpiece itself

• can use guide wheels as tracking

device

• due to their portability, are used in

field welding or where the piece

cannot be moved

Courtesy of ESAB AB

Courtesy of ESAB AB


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Welding current

•too high current: excessive excess weld metal

(waste of electrode), increase weld shrinkage and

causes greater distortions

•excessively high current: digging arc, undercut,

burn through; also a high and narrow bead &

solidification cracking

•too low current: incomplete

fusion or inadequate penetration

•excessively low current:

unstable arc


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Welding voltage•welding voltage controls arc

length

•an increased voltage can increase pick-up of alloying elements

from an alloy flux

•increase in voltage produce a

flatter and wider bead

•increase in voltage increase

flux consumption

•increase in voltage tend to

reduce porosity

•an increased voltage may

help bridging an excessive

root gap


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Welding voltage

•low voltage produce a

“stiffer” arc & improves

penetration in a deep

weld groove and resists

arc blow

•excessive low voltage

produce a high narrow

bead & difficult slag

removal


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Welding voltage

•excessively high voltage

produce a “hat-shaped” bead

& tendency to crack


increase undercut & make slag

removal difficult in groove

welds


produce a concave fillet weld

that is subject to cracking


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Travel speed

•increase in travel speed: decrease heat input & less

filler metal applied per unit of length, less excess

weld metal & weld bead becomes smaller


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Travel speed

•excessively high speed

lead to undercut, arc

blow and porosity

•excessively low speed

produce “hat-shaped” beads

danger of cracking

•excessively low speed produce rough beads and

lead to slag inclusions


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Electrode size

•at the same current, small electrodes have higher

current density & higher deposition rates


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Electrode extension•increased electrode extension adds resistance in the

welding circuit I increase in deposition rate, decrease in

penetration and bead width

•to keep a proper weld shape, when electrode extension is

increased, voltage must also be increased

•when burn-through is a problem (e.g. thin gauge), increase

electrode extension

•excessive electrode extension: it is more difficult to

maintain the electrode tip in the correct position


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Depth of flux

•depth of flux layer influence the appearance of weld

•usually, depth of flux is 25-30 mm

•if flux layer is to deep the arc is too confined, result is

a rough ropelike appearing weld

•if flux layer is to deep the gases cannot escape & the

surface of molten weld metal becomes irregularly

distorted

•if flux layer is too shallow, flashing and spattering will

occur, give a poor appearance and porous weld

SAW technological variables

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Travel angle effect - Butt weld on plates

Penetration Deep Moderate Shallow

Excess weld metal Maximum Moderate Minimum

Tendency to undercut Severe Moderate Minimum


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Earth position +

-

Direction of

travel

•welding towards earth produces backward arc blow

•deep penetration

•convex weld profile


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Earth position+

-

Direction of

travel

•welding away earth produces forward arc blow

•normal penetration depth

•smooth, even weld profile

Weld backing

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Backing strip

Backing weld

Copper backing

Starting/finishing the weld

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SAW variants

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Twin wire SAW welding •two electrodes are feed

into the same weld pool

•wire diameter usually 1,6 to

3,2 mm

•electrodes are connected

to a single power source & a

single arc is established

•normally operate with

DCEP

•offers increased deposition

rate by up to 80% compared

to single wire SAW

SAW variants

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Wires can be oriented

for maximum or

minimum penetration

SAW variants

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Tandem arc SAW process •usually DCEP on lead

and AC on trail to reduce

arc blow

•requires two separate

power sources

•the electrodes are active

in the same puddle BUT

there are 2 separate arcs

•increased deposition

rate by up to 100%

compared with single

wire SAW

SAW variants

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SAW tandem arc

with two wires

Courtesy of ESAB AB

SAW variants

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Single pool - highest deposition rate

Twin pool - travel speed limited by undercut;

very resistant to porosity and cracks

SAW variants

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Tandem arc SAW process - multiple wires

•only for welding thick

sections (>30 mm)

•not suitable for use in

narrow weld

preparations (root

passes)

•one 4 mm wire at 600 A,

6.8 kg/hr

•tandem two 4 mm wires

at 600 A, 13.6 kg/hrCourtesy of ESAB AB

SAW variants

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Strip cladding needs a

special welding head

SAW variants

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Narrow gap welding

•for welding thick

materials

•less filler metal required

•requires special groove

preparation and special

welding head

•requires special fluxes,

otherwise problems with

slag removal

•defect removal is very

difficult

SAW variants

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Hot wire welding

•the hot wire is connected to power source & much

more efficient than cold wire (current is used entirely

to heat the wire!)

•increase deposition rates

up to 100%

•requires additional

welding equipment,

additional control of

variables, considerable

set-up time and closer

operator attention

SAW variants

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SAW with metal powder addition

•increased deposition rates up to 70%; increased welding speed

•gives smooth fusion, improved bead appearance, reduced penetration and dilution from parent metal & higher impact strength

•metal powders can modify chemical composition of final weld deposit

•does not increase risk of cracking

•do not require additional arc energy

•metal powder can be added ahead or directly into the weld pool

SAW variants

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SAW with metal powder addition

•magnetic attachment of powder

•SAW with metal cored wires

SAW variants

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Storage tank

SAW of circular

welds

Courtesy of ESAB AB

Advantages of SAW

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• high current density, high deposition rates (up to 10 times

those for MMA), high productivity

• deep penetration allowing the use of small welding grooves

• fast travel speed, less distortion

• deslagging is easier

• uniform bead appearance with good surface finish and good

fatigue properties

• can be easily performed mechanised, giving a higher duty

cycle and low skill level required

• provide consistent quality when performed automatic or

mechanised

• Virtually assured radiographically sound welds

• arc is not visible

• little smoke/fumes are developed

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Advantages

• Low weld-metal cost

• Easily automated

• Low levels of ozone

• High productivity

• No visible arc light

• Minimum cleaning

Disadvantages

• Restricted welding

positions

• Arc blow on DC

current

• Shrinkage defects

• Difficult penetration

control

• Limited joints


Welding Inspector

Welding Consumables

Section 14

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BS EN 499 MMA Covered Electrodes

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Covered Electrode

Toughness

Yield Strength N/mm2

Chemical composition

Flux Covering

Weld Metal Recovery

and Current Type

Welding Position

Hydrogen Content

E 50 3 2Ni B 7 2 H10

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Welding consumables are any products that are used up in

the production of a weld

Welding consumables may be:

• Covered electrodes, filler wires and electrode wires.

• Shielding or oxy-fuel gases.

• Separately supplied fluxes.

• Fusible inserts.

Welding consumables

Welding Consumable Standards

MMA (SMAW)

• BS EN 499: Steel electrodes

• AWS A5.1 Non-alloyed steel

electrodes

• AWS A5.4 Chromium

electrodes

• AWS A5.5 Alloyed steel

electrodes

MIG/MAG (GMAW) TIG (GTAW)

• BS 2901: Filler wires

• BS EN 440: Wire electrodes

• AWS A5.9: Filler wires

• BS EN 439: Shielding gases

SAW

• BS 4165: Wire and fluxes

• BS EN 756: Wire electrodes

• BS EN 760: Fluxes

• AWS A5.17: Wires and fluxes

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Welding Consumable Gases

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welding gases

• GMAW, FCAW, TIG, Oxy- Fuel

• Supplied in cylinders or storage tanks for large quantities

• Colour coded cylinders to minimise wrong use

• Subject to regulations concerned handling, quantities and positioning of storage areas

• Moisture content is limited to avoid cold cracking

• Dew point (the temperature at which the vapour begins to condense) must be checked

Welding Consumables

Each consumable is critical in respect to:

• Size, (diameter and length)

• Classification / Supplier

• Condition

• Treatments e.g. baking / drying

• Handling and storage is critical for consumable control

• Handling and storage of gases is critical for safety

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The three main electrode covering types used in MMA welding

• Cellulosic - deep penetration/fusion

• Rutile - general purpose

• Basic - low hydrogen

MMA Covered Electrodes


Welding consumables for MMA:

• Consist of a core wire typically between 350-450mm in length and from 2.5mm - 6mm in diameter

• The wire is covered with an extruded flux coating

• The core wire is generally of a low quality rimming steel

• The weld quality is refined by the addition of alloying and refining agents in the flux coating

• The flux coating contains many elements and compounds that all have a variety of functions during welding

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Function of the Electrode Covering:

• To facilitate arc ignition and give arc stability

• To generate gas for shielding the arc & molten metal from air contamination

• To de-oxidise the weld metal and flux impurities into the slag

• To form a protective slag blanket over the solidifying and cooling weld metal

• To provide alloying elements to give the required weld metal properties

• To aid positional welding (slag design to have suitable freezing temperature to support the molten weld metal)

• To control hydrogen contents in the weld (basic type)

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1: Electrode size (diameter and length)

2: Covering condition: adherence, cracks, chips and concentricity

3: Electrode designation

EN 499-E 51 3 B

Arc ignition enhancing materials (optional!)

See BS EN ISO 544 for further information

Covered electrode inspection


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Plastic foil sealed cardboard box•rutile electrodes

•general purpose basic electrodes

Tin can•cellulosic electrodes

Vacuum sealed pack

•extra low hydrogen electrodes

Courtesy of Lincoln Electric

Co

urt

es

y o

f L

inc

oln

Ele

ctr

ic


Cellulosic electrodes:

• covering contains cellulose (organic material).

• produce a gas shield high in hydrogen raising the arc voltage.

• Deep penetration / fusion characteristics enables welding at high speed without risk of lack of fusion.

• generates high level of fumes and H2 cold cracking.

• Forms a thin slag layer with coarse weld profile.

• not require baking or drying (excessive heat will damage electrode covering!).

• Mainly used for stove pipe welding

• hydrogen content is 80-90 ml/100 g of weld metal.4/23/2007 397 of 691


4/23/2007 398 of 691

Cellulosic Electrodes

Disadvantages:

• weld beads have high hydrogen

• risk of cracking (need to keep joint hot during welding to allow

H to escape)

• not suitable for higher strength steels - cracking risk too

high (may not be allowed for Grades stronger than X70)

• not suitable for very thick sections (may not be used on

thicknesses > ~ 35mm)

• not suitable when low temperature toughness is required

(impact toughness satisfactory down to ~ -20°C)


Advantages:

• Deep penetration/fusion

• Suitable for welding in all positions

• Fast travel speeds

• Large volumes of shielding gas

• Low control

Disadvantages:

• High in hydrogen

• High crack tendency

• Rough weld appearance

• High spatter contents

• Low deposition rates

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Cellulosic Electrodes


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Rutile electrodes:

• covering contains TiO2 slag former and arc stabiliser.

• easy to strike arc, less spatter, excellent for positional

welding.

• stable, easy-to-use arc can operate in both DC and AC.

• slag easy to detach, smooth profile.

• Reasonably good strength weld metal.

• Used mainly on general purpose work.

• Low pressure pipework, support brackets.

• electrodes can be dried to lower H2 content but cannot be

baked as it will destroy the coating.

• hydrogen content is 25-30 ml/100 g of weld metal.


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Rutile electrodes

Disadvantages:

• they cannot be made with a low hydrogen content

• cannot be used on high strength steels or thick joints -

cracking risk too high

• they do not give good toughness at low temperatures

• these limitations mean that they are only suitable for general

engineering - low strength, thin steel


Advantages:

• Easy to use

• Low cost / control

• Smooth weld profiles

• Slag easily detachable

• High deposition possible with the addition of iron powder

Disadvantages:

• High in hydrogen

• High crack tendency

• Low strength

• Low toughness values

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Rutile Electrodes

MMA Welding ConsumablesRutile Variants

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High Recovery Rutile Electrodes

Characteristics:

• coating is „bulked out‟ with iron powder

• iron powder gives the electrode „high recovery‟

• extra weld metal from the iron powder can mean that weld

deposit from a single electrode can be as high as 180% of

the core wire weight

• give good productivity

• large weld beads with smooth profile can look very similar to

SAW welds


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High Recovery Rutile Electrodes

Disadvantages:

• Same as standard rutile electrodes with respect to hydrogen

control

• large weld beads produced cannot be used for all-positional

welding

• the very high recovery types usually limited to PA & PB

positions

• more moderate recovery may allow PC use


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Basic covering:

• Produce convex weld profile and difficult to detach slag.

• Very suitable for for high pressure work, thick section steel and for high strength steels.

• Prior to use electrodes should be baked, typically 350°C for 2 hour plus to reduce moisture to very low levels and achieve low hydrogen potential status.

• Contain calcium fluoride and calcium carbonate compounds.

• cannot be re-baked indefinitely!

• low hydrogen potential gives weld metal very good toughness and YS.

• have the lowest level of hydrogen (less than 5 ml/100 g of weld metal).


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Basic Electrodes

Disadvantages:

• Careful control of baking and/or issuing of electrodes is essential to maintain low hydrogen status and avoid risk of cracking

• Typical baking temperature 350°C for 1 to 2hours.

• Holding temperature 120 to 150°C.

• Issue in heated quivers typically 70°C.

• Welders need to take more care / require greater skill.

• Weld profile usually more convex.

• Deslagging requires more effort than for other types.

Basic Electrodes

Advantages

• High toughness values

• Low hydrogen contents

• Low crack tendency

Disadvantages

• High cost

• High control

• High welder skill required

• Convex weld profiles

• Poor stop / start properties

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Covered Electrode

Toughness

Yield Strength N/mm2

Chemical composition

Flux Covering

Weld Metal Recovery

and Current Type

Welding Position

Hydrogen Content

E 50 3 2Ni B 7 2 H10


Electrodes classified as follows:

• E 35 - Minimum yield strength 350 N/mm2

Tensile strength 440 - 570 N/mm2









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AWS A5.1 Alloyed Electrodes

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Covered Electrode

Tensile Strength (p.s.i)

Welding Position

Flux Covering

E 60 1 3

AWS A5.5 Alloyed Electrodes

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Covered Electrode

Tensile Strength (p.s.i)

Welding Position

Flux Covering

Moisture Control

Alloy Content

E 70 1 8 M G


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TYPES OF ELECTRODES

(for C, C-Mn Steels)

BS EN 499 AWS A5.1

• Cellulosic E XX X C EXX10

EXX11

• Rutile E XX X R EXX12

EXX13

• Rutile Heavy Coated E XX X RR EXX24

• Basic E XX X B EXX15

EXX16

EXX18

Electrode efficiency

75-90% for usual electrodes

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up to 180% for iron powder electrodes

Mass of weld metal deposited

Electrode Eficiency =

Mass of core wire melted

Covered electrode treatment

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Cellulosic

electrodes

Rutile

electrodes

Use straight from the

box - No baking/drying!

If necessary, dry up to

120°C- No baking!

Vacuum

packed basic

electrodes

Use straight from the pack

within 4 hours - No

rebaking!

Covered electrode treatment

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After baking, maintain in

oven at 150°C

Basic electrodesBaking in oven 2 hours

at 350°C!

Use from quivers at

75°C

If not used within 4

hours, return to oven

and rebake!Weld

Limited number of

rebakes!

TIG Consumables

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Welding Consumables

TIG Welding ConsumablesWelding consumables for TIG:

•Filler wires, Shielding gases, tungsten electrodes (non-consumable).

•Filler wires of different materials composition and variable diameters available in standard lengths, with applicable code stamped for identification

•Steel Filler wires of very high quality, with copper coating to resist corrosion.

•shielding gases mainly Argon and Helium, usually of highest purity (99.9%).

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TIG Welding Consumables

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Welding rods:

•supplied in cardboard/plastic tubes

•must be kept clean and free from oil and dust

•might require degreasing

Courtesy of Lincoln Electric

Fusible Inserts

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Before Welding

Pre-placed filler material

After Welding

Other terms used include:

EB inserts (Electric Boat Company)

Consumable socket rings (CSR)

Fusible Inserts

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Consumable inserts:

• used for root runs on pipes

• used in conjunction with TIG welding

• available for carbon steel, Cr-Mo steel, austenitic stainless

steel, nickel and copper-nickel alloys

• different shapes to suit application

Radius

Fusible Inserts

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Application of consumable inserts

Shielding gases for TIG welding

Argon

• low cost and greater availability

• heavier than air - lower flow rates than Helium

• low thermal conductivity - wide top bead profile

• low ionisation potential - easier arc starting, better arc stability with AC, cleaning effect

• for the same arc current produce less heat than helium -reduced penetration, wider HAZ

• to obtain the same arc arc power, argon requires a higher current - increased undercut

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Helium

• costly and lower availability than Argon

• lighter than air - requires a higher flow rate compared with argon (2-3 times)

• higher ionisation potential - poor arc stability with AC, less forgiving for manual welding

• for the same arc current produce more heat than argon -increased penetration, welding of metals with high melting point or thermal conductivity

• to obtain the same arc arc power, helium requires a lower current - no undercut

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Hydrogen

• not an inert gas - not used as a primary shielding gas

• increase the heat input - faster travel speed and increased penetration

• better wetting action - improved bead profile

• produce a cleaner weld bead surface

• added to argon (up to 5%) - only for austenitic stainless steels and nickel alloys

• flammable and explosive

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Nitrogen

• not an inert gas

• high availability - cheap

• added to argon (up to 5%) - only for back purge for duplex stainless, austenitic stainless steels and copper alloys

• not used for mild steels (age embritlement)

• strictly prohibited in case of Ni and Ni alloys (porosity)

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MIG / MAG Consumables(Gases Covered previously)

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Welding Consumables

MIG/MAG Welding Consumables

Welding consumables for MIG/MAG

• Spools of Continuous electrode wires and shielding gases

• variable spool size (1-15Kg) and Wire diameter (0.6-1.6mm) supplied in random or orderly layers

• Basic Selection of different materials and their alloys as electrode wires.

• Some Steel Electrode wires copper coating purpose is corrosion resistance and electrical pick-up

• Gases can be pure CO2, CO2+Argon mixes and Argon+2%O2

mixes (stainless steels).

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MIG/MAG Welding Consumables

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Welding wires:

•carbon and low alloy wires may be copper coated

• stainless steel wires are not coated

•wires must be kept clean and free from oil and dust

•flux cored wires does not require baking or drying

Courtesy of Lincoln Electric Courtesy of ESAB AB

Flux Core Wire Consumables(Not in training manual)

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Welding Consumables

Flux Core Wire Consumables

Functions of metallic sheath: Function of the filling powder:

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provide form stability to the wire

serves as current transfer during welding

stabilise the arc

add alloy elements

produce gaseous shield

produce slag

add iron powder

Types of cored wire

• not sensitive to moisture pick-up

• can be copper coated, better current transfer

• thick sheath, good form stability, 2 roll drive feeding possible

• difficult to manufacture

• good resistance to moisture pick-up

• can be copper coated

• thick sheath

• difficult to seal the sheath

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Seamless

cored wire

Butt joint

cored wire

Overlapping

cored wire

sensitive to

moisture pick-

up

cannot be

copper coated

thin sheath

easy to

manufacture

Core elements and their function

Aluminium - deoxidize & denitrify

Calcium - provide shielding & form slag

Carbon - increase hardness & strength

Manganese - deoxidize & increase strength and toughness

Molybdenum - increase hardness & strength

Nickel - improve hardness, strength, toughness & corrosion resistance

Potassium - stabilize the arc & form slag

Silicon - deoxidize & form slag

Sodium - stabilize arc & form slag

Titanium - deoxidize, denitrify & form slag4/23/2007 436 of 691

SAW Consumables

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Welding Consumables

SAW Consumables

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Welding fluxes:

• are granular mineral compounds mixed according to various

formulations

• shield the molten weld pool from the atmosphere

• clean the molten weld pool

• can modify the chemical composition of the weld metal

• prevents rapid escape of heat from welding zone

• influence the shape of the weld bead (wetting action)

• can be fused, agglomerated or mixed

• must be kept warm and dry to avoid porosity

SAW Consumables

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• Fused fluxes are normally not hygroscopic but particles can

hold surface moisture so only drying

• Agglomerated fluxes contain chemically bonded water. Similar

treatment as basic electrodes

• If flux is too fine it will pack and not feed properly. It cannot be

recycled indefinitely

Welding flux:

• might be fused or agglomerated

• supplied in bags

• must be kept warm and dry

• handling and stacking requires careCourtesy of Lincoln Electric

SAW Consumables

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Fused Flux:

Baked at high temperature, glossy, hard and black in colour,

cannot add ferro-manganese, non moisture absorbent and

tends to be of the acidic type

Fused Flux

• Flaky appearance

• Lower weld quality

• Low moisture intake

• Low dust tendency

• Good re-cycling

• Very smooth weld

profile

SAW Consumables

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TYPES OF FLUX

FUSED (ACID TYPE)

• name indicates method of manufacture

• minerals are fused (melted) and granules produced by

allowing to cool to a solid mass and then crushing or by

spraying the molten flux into water

• flux tends to be „glass-like‟ (high in Silica)

• granules are hard and may appear shiny

• granules do not absorb moisture

• granules do not tend break down into powder when being

re-circulated

• are effectively a low hydrogen flux

• welds do not tend to give good toughness at low

temperatures

SAW Consumables

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Fused fluxes advantages:

•good chemical homogeneity

•easy removal of fines without affecting flux

composition

•normally not hygroscopic easy storage and

handling

•readily recycled without significant change in

particle size or composition

Fused fluxes disadvantages:

•difficult to add deoxidizers and ferro-alloys (due to

segregation or extremely high loss)

•high temperatures needed to melt ingredients limit

the range of flux compositions

SAW Consumables

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Agglomerated Flux:

Baked at a lower temperature, dull, irregularly shaped, friable,

(easily crushed) can easily add alloying elements, moisture

absorbent and tend to be of the basic type

Agglomerated Flux

• Granulated appearance

• High weld quality

• Addition of alloys

• Lower consumption

• Easy slag removal

• Smooth weld profile

SAW Consumables

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Agglomerated fluxes advantages:

• easy addition of deoxidizers and alloying elements

• usable with thicker layer of flux when welding

• colour identification

Agglomerated fluxes disadvantages:

• tendency to absorb moisture

• possible gas evolution from the molten slag leading to

porosity

• possible change in flux composition due to segregation or

removal of fine mesh particles

SAW Consumables

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TYPES OF FLUX

AGGLOMERATED (BASIC TYPE)

• name indicates method of manufacture

• basic minerals are used in powder form and are mixed with a binder to form individual granules

• granules are soft and easily crushed to powder

• granules will absorb moisture and it is necessary to protect the flux from moisture pick-up - usually by holding in a heated silo

• granules tend to break down into powder when being re-circulated

• are a low hydrogen flux - if correctly controlled

• welds give good toughness at low temperatures

SAW Consumables

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Mixed fluxes advantages:

•several commercial fluxes may be mixed for highly

critical or proprietary welding operations

Mixed fluxes disadvantages:

•segregation of the combined fluxes during

shipment, storage and handling

•segregation occurring in the feeding and recovery

systems during welding

•inconsistency in the combined flux from mix to mix

Mixed fluxes - two or more fused or bonded fluxes are

mixed in any ratio necessary to yield the desired

results

SAW filler material

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Welding wires can be used to weld:

•carbon steels

•low alloy steels

•creep resisting steels

•stainless steels

•nickel-base alloys

•special alloys for surfacing applications

Welding wires can be:

•solid wires

•metal-cored wires

SAW filler material

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Welding wires:•carbon and low alloy wires are copper coated

•wires must be kept clean and free from oil and dust

•stainless steel wires are not coated

Courtesy of Lincoln ElectricCourtesy of Lincoln Electric

SAW filler material

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Copper coating functions:

•to assure a good electric contact between wire

and contact tip

•to assure a smooth feed of the wire through the

guide tube, feed rolls and contact tip (decrease

contact tube wear)

•to provide protection against corrosion

Welding Inspector

Non Destructive Testing

Section 15

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Non-Destructive Testing

A welding inspector should have a working knowledge of NDT methods and their applications, advantages and disadvantages.

Four basic NDT methods

• Radiographic inspection (RT)

• Ultrasonic inspection (UT)

• Magnetic particle inspection (MT)

• Dye penetrant inspection (PT)

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Non-Destructive TestingSurface Crack Detection

• Liquid Penetrant (PT or Dye-Penetrant)

• Magnetic Particle Inspection (MT or MPI)

Volumetric & Planar Inspection

• Ultrasonics (UT)

• Radiography (RT)

Each technique has advantages & disadvantages with respect

to:

• Technical Capability and Cost

Note: The choice of NDT techniques is based on consideration

of these advantages and disadvantages

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Radiographic Testing (RT)

Radiographic Testing

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The principles of radiography

• X or Gamma radiation is imposed upon a test object

• Radiation is transmitted to varying degrees

dependant upon the density of the material through

which it is travelling

• Thinner areas and materials of a less density show as

darker areas on the radiograph

• Thicker areas and materials of a greater density show

as lighter areas on a radiograph

• Applicable to metals,non-metals and composites


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X – Rays

Electrically generated

Gamma Rays

Generated by the decay

of unstable atoms


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Source

Radiation beam Image quality indicator

Radiographic film with latent image after exposure

Test specimen


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Density - relates to the degree of darkness

Contrast - relates to the degree of difference

Definition - relates to the degree of sharpness

Sensitivity - relates to the overall quality of the radiograph

Densitometer

Radiographic Sensitivity

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7FE12

Step / Hole type IQI Wire type IQI

Radiographic Sensitivity

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Wire Type IQI

Step/Hole Type IQI

Radiographic Techniques

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Single Wall Single Image (SWSI)

• film inside, source outside

Single Wall Single Image (SWSI) panoramic

• film outside, source inside (internal exposure)

Double Wall Single Image (DWSI)

• film outside, source outside (external exposure)

Double Wall Double Image (DWDI)

• film outside, source outside (elliptical exposure)

Single Wall Single Image (SWSI)

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IQI‟s should be placed source side

Film

Film

Single Wall Single Image Panoramic

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• IQI‟s are placed on the film side

• Source inside film outside (single exposure)

Film


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• IQI‟s are placed on the film side

• Source outside film outside (multiple exposure)

• This technique is intended for pipe diameters

over 100mm

Film


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Radiograph

• Identification

ID MR11

• Unique identificationEN W10

• IQI placing

A B• Pitch marks indicating readable film length


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Radiograph


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Film

• IQI‟s are placed on the source or film side

• Source outside film outside (multiple exposure)

• A minimum of two exposures

• This technique is intended for pipe diameters less than 100mm


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Shot A Radiograph

• Identification

ID MR12

• Unique identification EN W10

• IQI placing

1 2• Pitch marks indicating

readable film length

4 3


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Elliptical Radiograph

1 2

4 3

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Radiography

PENETRATING POWER

Question:

What determines the penetrating power of an X-ray ?

•the kilo-voltage applied (between anode & cathode)

Question:

What determines the penetrating power of a gamma ray ?

•the type of isotope (the wavelength of the gamma rays)

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Radiography

GAMMA SOURCES

Isotope Typical Thickness Range

• Iridium 192 10 to 50 mm (mostly used)

• Cobalt 60 > 50 mm

• Ytterbium < 10 mm

• Thulium < 10 mm

• Cesium < 10 mm


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Advantages

• Permanent record

• Little surface preparation

• Defect identification

• No material type limitation

• Not so reliant upon operator

skill

• Thin materials

Disadvantages

• Expensive consumables

• Bulky equipment

• Harmful radiation

• Defect require significant

depth in relation to the

radiation beam (not good

for planar defects)

• Slow results

• Very little indication of

depths

• Access to both sides

required

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Comparison with Ultrasonic Examination

ADVANTAGES

good for non-planar defects

good for thin sections

gives permanent record

easier for 2nd party interpretation

can use on all material types

high productivity

direct image of imperfections

Radiographic TestingComparison with Ultrasonic Examination

DISADVANTAGES

• health & safety hazard

• not good for thick sections

• high capital and relatively high running costs

• not good for planar defects

• X-ray sets not very portable

• requires access to both sides of weld

• frequent replacement of gamma source needed (half life)

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Ultrasonic Testing (UT)

Ultrasonic Testing

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Main Features:

• Surface and sub-surface detection

• This detection method uses high frequency sound waves,

typically above 2MHz to pass through a material

• A probe is used which contains a piezo electric crystal to

transmit and receive ultrasonic pulses and display the

signals on a cathode ray tube or digital display

• The actual display relates to the time taken for the

ultrasonic pulses to travel the distance to the interface and

back

• An interface could be the back of a plate material or a defect

• For ultrasound to enter a material a couplant must be

introduced between the probe and specimen

Ultrasonic Testing

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Digital

UT Set,

Pulse echo

signals

A scan

Display

Compression probe checking the material Thickness

Ultrasonic Testing

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defect

0 10 20 30 40 50

defect

echo

Back wall

echo

CRT DisplayCompression Probe

Material Thk

initial pulse

Ultrasonic Testing

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Angle Probe

UT SetA Scan

Display

Ultrasonic Testing

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initial pulse

defect echo

defectdefect

defect

0 10 20 30 40 50

CRT Display

0 10 20 30 40 50

initial pulse

defect echo

CRT Display

½ Skip

Full Skip

Ultrasonic Testing

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Advantages

Rapid results

Both surface and

sub-surface detection

Safe

Capable of measuring the

depth of defects

May be battery powered

Portable

Disadvantages

Trained and skilled operator

required

Requires high operator skill

Good surface finish required

Defect identification

Couplant may contaminate

No permanent record

Calibration Required

Ferritic Material (Mostly)

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Ultrasonic Testing

Comparison with Radiography

ADVANTAGES

•good for planar defects

•good for thick sections

•instant results

•can use on complex joints

•can automate

•very portable

•no safety problems (‘parallel’ working is possible)

•low capital & running costs

Ultrasonic TestingComparison with Radiography

DISADVANTAGES

• no permanent record (with standard equipment)

• not suitable for very thin joints <8mm

• reliant on operator interpretation

• not good for sizing Porosity

• good/smooth surface profile needed

• not suitable for coarse grain materials (e.g., castings)

• Ferritic Materials (with standard equipment)

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Magnetic Particle testing (MT)

Magnetic Particle Testing

Main features:• Surface and slight sub-surface detection

• Relies on magnetization of component being tested

• Only Ferro-magnetic materials can be tested

• A magnetic field is introduced into a specimen being tested

• Methods of applying a magnetic field, yoke, permanent magnet, prods and flexible cables.

• Fine particles of iron powder are applied to the test area

• Any defect which interrupts the magnetic field, will create a leakage field, which attracts the particles

• Any defect will show up as either a dark indication or in the case of fluorescent particles under UV-A light a green/yellow indication

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Electro-magnet (yoke) DC or AC

Prods DC or AC

Collection of ink

particles due to

leakage field


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A crack like

indication


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Alternatively to contrast inks, fluorescent inks may be used

for greater sensitivity. These inks require a UV-A light source

and a darkened viewing area to inspect the component


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Typical sequence of operations to inspect a weld

• Clean area to be tested

• Apply contrast paint

• Apply magnetisism to the component

• Apply ferro-magnetic ink to the component during

magnatising

• Iterpret the test area

• Post clean and de-magnatise if required


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Advantages

• Simple to use

• Inexpensive

• Rapid results

• Little surface preparation

required

• Possible to inspect through

thin coatings

Disadvantages

• Surface or slight sub-surface

detection only

• Magnetic materials only

• No indication of defects

depths

• Only suitable for linear

defects

• Detection is required in two

directions

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Comparison with Penetrant Testing

ADVANTAGES

• much quicker than PT

• instant results

• can detect near-surface imperfections (by current flow

technique)

• less surface preparation needed

DISADVANTAGES

• only suitable for ferromagnetic materials

• electrical power for most techniques

• may need to de-magnetise (machine components)

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Penetrant Testing (PT)

Penetrant TestingMain features:

• Detection of surface breaking defects only.

• This test method uses the forces of capillary action

• Applicable on any material type, as long they are non porous.

• Penetrants are available in many different types:

• Water washable contrast

• Solvent removable contrast

• Water washable fluorescent

• Solvent removable fluorescent

• Post-emulsifiable fluorescent

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Penetrant Testing

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Step 1. Pre-Cleaning

Ensure surface is very Clean normally with the use of a solvent

Penetrant Testing

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Step 2. Apply penetrant

After the application, the penetrant is normally left on the

components surface for approximately 15-20 minutes (dwell

time).

The penetrant enters any defects that may be present by

capillary action.

Penetrant Testing

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Step 3. Clean off penetrant

the penetrant is removed after sufficient penetration time (dwell

time).

Care must be taken not to wash any penetrant out off any

defects present

Penetrant Testing

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Step 3. Apply developer

After the penetrant has be cleaned sufficiently, a thin layer of

developer is applied.

The developer acts as a contrast against the penetrant and

allows for reverse capillary action to take place.

Penetrant Testing

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Step 4. Inspection / development time

Inspection should take place immediately after the developer

has been applied.

any defects present will show as a bleed out during

development time.

After full inspection has been carried out post cleaning is

generally required.

Penetrant Testing

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Colour contrast Penetrant

Fluorescent Penetrant Bleed out viewed under a UV-A light source

Bleed out viewed under white light

Penetrant Testing

Advantages

• Simple to use

• Inexpensive

• Quick results

• Can be used on any non-porous material

• Portability

• Low operator skill required

Disadvantages• Surface breaking defect only

• little indication of depths

• Penetrant may contaminate component

• Surface preparation critical

• Post cleaning required

• Potentially hazardous chemicals

• Can not test unlimited times

• Temperature dependant

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Penetrant Testing

Comparison with Magnetic Particle Inspection

ADVANTAGES

•easy to interpret results

•no power requirements

•relatively little training required

•can use on all materials

DISADVANTAGES

•good surface finish needed

•relatively slow

•chemicals - health & safety issue

Welding Inspector

Weld Repairs

Section 16

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Weld RepairsWeld repairs can be divided into 2 specific areas:

• Production repairs

• In service repairs

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Weld Repairs

A weld repair can be a relatively straight forward activity, but in many instances it is quite complex, and various engineering disciplines may need to be involved to ensure a successful outcome.

• Analysis of the defect types may be carried out by the Q/C department to discover the likely reason for their occurrence, (Material/Process or Skill related).

In general terms, a welding repair involves What!

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Weld Repairs

A weld repair may be used to improve weld profiles or extensive metal removal:

•Repairs to fabrication defects are generally easier than repairs to service failures because the repair procedure may be followed

•The main problem with repairing a weld is the maintenance of mechanical properties

•During the inspection of the removed area prior to welding the inspector must ensure that the defects have been totally removed and the original joint profile has been maintained as close as possible

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Weld RepairsIn the event of repair, it is required:

• Authorization and procedure for repair

• Removal of material and preparation for repair

• Monitoring of repair Weld

• Testing of repair - visual and NDT

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Weld RepairsThere are a number of key factors that need to be considered

before undertaking any repair:

• The most important - is it financially worthwhile?

• Can structural integrity be achieved if the item is repaired?

• Are there any alternatives to welding?

• What caused the defect and is it likely to happen again?

• How is the defect to be removed and what welding process is to be used?

• What NDE is required to ensure complete removal of the defect?

• Will the welding procedures require approval/re-approval?

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Weld Repairs• Cleaning the repair area, (removal of paint, grease, etc)

• A detailed assessment to find out the extremity of the defect. This may involve the use of a surface or sub surface NDE method.

• Once established the excavation site must be clearly identified and marked out.

• An excavation procedure may be required (method used i.e. grinding, arc-air gouging, preheat requirements etc).

• NDE should be used to locate the defect and confirm its removal.

• A welding repair procedure/method statement with the appropriate welding process, consumable, technique, controlled heat input and interpass temperatures etc will need to be approved.

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Weld Repairs• Use of approved welders.

• Dressing the weld and final visual.

• A NDT procedure/technique prepared and carried out to ensure that the defect has been successfully removed and repaired.

• Any post repair heat treatment requirements.

• Final NDT procedure/technique prepared and carried out after heat treatment requirements.

• Applying protective treatments (painting etc as required).

• (*Appropriate’ means suitable for the alloys being repaired and may not apply in specific situations)

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Weld Repairs• What will be the effect of welding distortion and residual

stress?

• Will heat treatment be required?

• What NDE is required and how can acceptability of the repair be demonstrated?

• Will approval of the repair be required – if yes, how and by whom?

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Production Weld Repairs

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Before the repair can commence, a number of elements need

to be fulfilled:

If the defect is surface breaking and has occurred at the fusion

face the problem could be cracking or lack of sidewall fusion.

If the defect is found to be cracking the cause may be

associated with the material or the welding procedure

If the defect is lack of sidewall fusion this can be apportioned

to the lack of skill of the welder.

In this particular case as the defect is open to the surface, MPI

or DYE-PEN may be used to gauge the length of the defect and

U/T inspection used to gauge the depth.

Weld RepairsThe specification or procedure will govern how the defective areas are to be removed. The method of removal may be:

•Grinding

•Chipping

•Machining

•Filing

•Oxy-Gas gouging

•Arc air gouging

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Defect Excavation

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Arc-air gouging

Arc-air gouging features

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• Operate ONLY on DCEP

• Special gouging copper

coated carbon electrode

• Can be used on carbon

and low alloy steels,

austenitic stainless steels

and non-ferrous materials

• Requires CLEAN/DRY

compressed air supply

• Provides fast rate of metal removal

• Can remove complex shape defects

• After gouging, grinding of carbured layer is mandatory

• Gouging doesn‟t require a qualified welder!


Production Repairs

• are usually identified during production inspection

• evaluation of the reports is usually carried out by the Welding Inspector, or NDT operator

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Plan View of defect


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Side View of defect excavation

D

W

Side View of repair welding

In Service Weld RepairsIn service repairs

• Can be of a very complex nature, as the component is very likely to be in a different welding position and condition than it was during production

• It may also have been in contact with toxic, or combustible fluids hence a permit to work will need to be sought prior to any work being carried out

• The repair welding procedure may look very different to the original production procedure due to changes in these elements.

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In Service Weld RepairsOther factors to be taken into consideration:

Effect of heat on any surrounding areas of the componenti.e. electrical components, or materials that may becomedamaged by the repair procedure.

This may also include difficulty in carrying out any requiredpre or post welding heat treatments and a possiblerestriction of access to the area to be repaired.

For large fabrications it is likely that the repair must alsotake place on site and without a shut down of operations,which may bring other elements that need to beconsidered.

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Weld Repairs

• Is welding the best method of repair?

• Is the repair really like earlier repairs?

• What is the composition and weldability of the base metal?

• What strength is required from the repair?

• Can preheat be tolerated?

• Can softening or hardening of the HAZ be tolerated?

• Is PWHT necessary and practicable?

• Will the fatigue resistance of the repair be adequate?

• Will the repair resist its environment?

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Weld repair related problems• heat from welding may affect dimensional stability and/or

mechanical properties of repaired assembly

• due to heat from welding, YS goes down, danger of collapse

• filler materials used on dissimilar welds may lead to galvanic corrosion

• local preheat may induce residual stresses

• cost of weld metal deposited during a weld joint repair can reach up to 10 times the original weld metal cost!

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Welding Inspector

Residual Stress & Distortion

Section 17

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Residual stress

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Residual stresses are undesirable because:

they lead to distortion

they affect dimensional stability of the

welded assembly

they enhance the risk of brittle fracture

they can facilitate certain types of

corrosion

Residual Stresses

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The heating and subsequent cooling from welding produces expansion and contractions which affect the weld metal and adjacent material.

If this contraction is prevented or inhibited residual stress will develop.

The tendency to develop residual stresses increases when the heating and cooling is localised.

Residual stresses are very difficult to measure with any real accuracy.

Residual stresses are self balancing internal forces and not stresses induced whilst applying external load

Stresses are more concentrated at the surface of the component.

The removal of residual stresses is termed stress relieving.

Stresses

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Normal Stress

Stress arising from a force perpendicular to the

cross sectional area

Compression

Tension

Stresses

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Shear Stress

Stress arising from forces which are parallel to, and

lie in the plane of the cross sectional area.

Shear Stress

Stresses

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Hoop Stress

Internal stress acting on the wall a pipe or cylinder

due to internal pressure.

Hoop Stress

Residual Stresses

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Longitudinal

Along the weld – longitudinal residual stresses

Transverse

Across the weld – transverse residual stresses

Short Transverse

Through the weld – short transverse residual stresses

Residual stresses occur in welds in the following directions

Residual stress

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Heating and

cooling causes

expansion and

contraction

Residual stress

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In case of a heated

bar, the resistance

of the surrounding

material to the

expansion and

contraction leads

to formation of

residual stress

Summary

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1. Residual stresses are locked in elastic strain, which is

caused by local expansion and contraction in the weld

area.

2. Residual stresses should be removed from structures

after welding.

3. The amount of contraction is controlled by, the volume of

weld metal in the joint, the thickness, heat input, joint

design and the materials properties

4. Offsetting may be used to finalise the position of the joint.

5. If plates or pipes are prevented from moving by tacking,

clamping or jigging etc (restraint), then the amount of

residual stresses that remain will be higher.

Summary

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6. The movement caused by welding related stresses is

called distortion.

7. The directions of contractional stresses and distortion is

very complex, as is the amount and type of final distortion,

however we can say that there are three directions:

a. Longitudinal b. Transverse c. Short transverse

8. A high percentage of residual stresses can be removed by

heat treatments.

9. The peening of weld faces will only redistribute the

residual stress, and place the weld face in compression.

Types of distortion

Angular distortion

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Distortion

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Angular Distortion

Bowing Distortion Longitudinal Distortion

Transverse Distortion

Distortion

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Factors which affect distortion

• Material properties and condition

• Heat input

• The amount of restrain

• The amount of weld metal deposited

Control of distortion my be achieved in the following way:

•The used of a different joint design

•Presetting the joints to be welded – so that the metal distorts

into the required position.

•The use of a balanced welding technique

•The use of clamps, jigs and fixtures.

Distortion

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• Distortion will occur in all welded joints if the material are

free to move i.e. not restrained

• Restrained materials result in low distortion but high

residual stress

• More than one type of distortion may occur at one time

• Highly restrained joints also have a higher crack tendency

than joints of a low restraint

• The action of residual stress in welded joints is to cause

distortion

Distortion

Factors affecting distortion:

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parent material properties

amount of restrain

joint design

fit-up

welding sequence

Factors affecting distortion

Parent material properties:

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thermal expansion coefficient - the greater the value, the greater the residual stress

yield strength - the greater the value, the greater the residual stress

Young‟s modulus - the greater the value (increase in stiffness), the greater the residual stress

thermal conductivity - the higher the value, the lower the residual stress

transformation temperature - during phase transformation, expansion/contraction takes place. The lower the transformation temperature, the lower the residual stress


Joint design:

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weld metal volume

type of joint - butt vs. fillet, single vs. double side

Amount of restrain:thickness - as thickness increase, so do the stresses

high level of restrain lead to high stresses

preheat may increase the level of stresses (pipe

welding!)

Fit-up:misalignment may reduce stresses in some cases

root gap - increase in root gap increases shrinkage


Welding sequence:

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number of passes - every pass adds to the total

contraction

heat input - the higher the heat input, the greater

the shrinkage

travel speed - the faster the welding speed, the

less the stress

build-up sequence

Distortion prevention

Distortion prevention by pre-setting

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a) pre-setting of fillet joint to

prevent angular distortion

b) pre-setting of butt joint to

prevent angular distortion

c) tapered gap to prevent

closure

Distortion

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Pre-set or Offsetting:

The amount of offsetting required is generally a function of

trial and error.


Distortion prevention by pre-bending using strongbacks and wedges

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Distortion

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Clamping and jigging:

The materials to be welded are prevented from moving by the clamp or jig the main advantage of using a jig is that the elements in a fabrication can be precisely located in the position to be welded. Main disadvantage of jigging is high restraint and high levels of residual stresses.

Distortion preventionDistortion prevention by restraint techniques

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a) use of welding jigs

b) use of flexible

clamps

Distortion preventionDistortion prevention by restraint techniques

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c) use of strongbacks

with wedges

d) use of fully welded

strongbacks


Distortion prevention by design

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Consider eliminating the welding!!

a) by forming the plate

b) by use of rolled or extruded sections


Distortion prevention by design

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consider weld placement

reduce weld metal volume

and/or number of runs


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The volume of weld metal in a joint will affect the amount of local expansion and contraction, hence the more weld deposited the higher amount of distortion

Preparation angle 60o



Distortion preventionDistortion prevention by design

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use of balanced welding


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- Transverse Shrinkage

Fillet Welds 0.8mm per weld where the leg length

does not exceed 3/4 plate thickness

Butt weld 1.5 to 3mm per weld for 60° V joint,

depending on number of runs

- Longitudinal Shrinkage

Fillet Welds 0.8mm per 3m of weld

Butt Welds 3mm per 3m of weld

Allowances to cover shrinkage

Distortions prevention by design


Distortion prevention by fabrication techniques

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tack weldinga) tack weld straight through

to end of joint

b) tack weld one end, then use

back-step technique for

tacking the rest of the joint

c) tack weld the centre, then

complete the tack welding

by the back-step technique



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back to back assembly

a) assemblies tacked together

before welding

b) use of wedges for

components that distort on

separation after welding



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use of stiffeners

control welding process by:

- deposit the weld metal as quickly as possible

- use the least number of runs to fill the joint


Distortion prevention by welding procedure

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reduce the number of

runs required to make a

weld (e.g. angular

distortion as a function

of number of runs for a

10 mm leg length weld)



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control welding techniques by use

balanced welding about the neutral axis

control welding techniques by keeping

the time between runs to a minimum



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control welding techniques by

a) Back-step welding

b) Skip welding


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Back-skip welding technique

Back-step welding technique

1. 2. 3. 4. 5. 6.

1. 2. 3. 6.4. 5.

Distortion preventionDistortion - Best practice for fabrication corrective techniques

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using tack welds to set up and maintain the joint gap

identical components welded back to back so welding can be

balanced about the neutral axis

attachment of longitudinal stiffeners to prevent longitudinal

bowing in butt welds of thin plate structures

where there is choice of welding procedure, process and

technique should aim to deposit the weld metal as quickly as

possible; MIG in preference to MMA or gas welding and

mechanised rather than manual welding

in long runs, the whole weld should not be completed in one

direction; back-step or skip welding techniques should be used

Distortion corrective techniques

Distortion - mechanical corrective techniques

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Use of press to correct bowing in T butt joint

Distortion corrective techniquesDistortion - Best practice for mechanical corrective techniques

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Use packing pieces which will over correct the distortion so

that spring-back will return the component to the correct shape

Check that the component is adequately supported during

pressing to prevent buckling

Use a former (or rolling) to achieve a straight component or

produce a curvature

As unsecured packing pieces may fly out from the press, the

following safe practice must be adopted:

- bolt the packing pieces to the platen

- place a metal plate of adequate thickness to intercept the

'missile'

- clear personnel from the hazard area


Distortion - thermal corrective techniques

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Localised heating to

correct distortion

Spot heating for

correcting buckling



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Line heating to correct angular

distortion in a fillet weld

Use of wedge shaped heating

to straighten plate



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Wedge shaped heating to correct distortion

a) standard rolled

steel sectionb) buckled edge of

plate

c) box fabrication

General guidelines:

•Length of wedge = two-thirds of the plate width

•Width of wedge (base) = one sixth of its length (base to apex)



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•use spot heating to remove buckling in thin sheet structures

•other than in spot heating of thin panels, use a wedge-shaped

heating technique

•use line heating to correct angular distortion in plate

•restrict the area of heating to avoid over-shrinking the component

•limit the temperature to 60° to 650°C (dull red heat) in steels to

prevent metallurgical damage

•in wedge heating, heat from the base to the apex of the wedge,

penetrate evenly through the plate thickness and maintain an even

temperature

Welding Inspector

Heat Treatment

Section 18

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Heat Treatment

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Why?

Improve mechanical properties

Change microstructure

Reduce residual stress level

Change chemical composition

How?

Flame oven

Electric oven/electric heating blankets

induction/HF heating elements

Where? LocalGlobal

Heat Treatments

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Many metals must be given heat treatment before and after welding.

The inspector’s function is to ensure that the treatment is given correctly in accordance with the specification or as per the details supplied.

Types of heat treatment available:

•Preheat

•Annealing

•Normalising

•Quench Hardening

•Temper

•Stress Relief

Heat TreatmentsPre-heat treatments

• are used to increase weldability, by reducing sudden reduction of temperature, and control expansion and contraction forces during welding

Post weld heat treatments

• are used to change the properties of the weld metal, controlling the formation of crystalline structures

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Post Weld -Heat Treatments

Post Hydrogen Release (according to BS EN1011-2)

Temperature: Approximately 250 C hold up to 3 hours

Cooling: Slow cool in air

Result: Relieves residual hydrogen

Procedure: Maintaining pre-heat / interpass temperature after completion of welding for 2 to 3 hours.

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Post Weld Heat Treatments

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(A) Normalised

(B) Fully Annealed

(C) Water-quenched

(D) Water-quenched & tempered

A B

C D

Post Weld Heat Treatments

The inspector, in general, should ensure that:

• Equipment is as specified

• Temperature control equipment is in good condition

• Procedures as specified, is being used e.g.

o Method of application

o Rate of heating and cooling

o Maximum temperature

o Soak time

o Temperature measurement (and calibration)

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Post Weld Heat Treatment Cycle

Time

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TemperatureSoakingTemperature

and time at the

attained temperature

Heating Soaking Cooling

heating rate Cooling rate

Variables for heat treatment process must be carefully controlled

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Post Weld Heat TreatmentRemoval of Residual Stress

Temperature (°C)

100 200 300 400 500 600 700

Yield

Strength

(N/mm2 )

100

200

300

400

500Cr-Mo steel - typical

C-Mn steel - typical

• At PWHT temp. the yield

strength of steel reduced

so that it it is not strong

enough to give restraint.

• Residual stress reduced

to very low level by

straining (typically < ~

0.5% strain)

Heat Treatment

Recommendations

• Provide adequate support (low YS at high temperature!)

• Control heating rate to avoid uneven thermal expansions

• Control soak time to equalise temperatures

• Control temperature gradients - NO direct flame impingement!

• Control furnace atmosphere to reduce scaling

• Control cooling rate to avoid brittle structure formation

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Post Weld Heat Treatment Methods

Gas furnace heat treatment

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Advantages:

Easy to set up

Good portability

repeatability and

temperature uniformity

Disadvantages:

Limited to size of parts


HF (Induction) local heat treatment

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Advantages:

High heating rates

Ability to heat a

narrow band

Disadvantages:

High equipment

cost

Large equipment,

less portable


Local heat treatment using electric heating blankets

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Advantages:

Ability to vary

heat

Ability to

continuously

maintain heat

Disadvantages:

Elements may

burn out or arcing

during heating

Welding Inspector

Cutting Processes

Section 19

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Use of gas flame

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Welding GougingBrazing

Heating Straightening

Cutting

Blasting Spraying

Regulators

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Oxygen regulator Fuel gas regulator

Regulator type

Single stage

Two stage

used when slight rise in delivery

pressure from full to empty cylinder

condition can be tolerated

used when a constant delivery

pressure from full to empty

cylinder condition is required

Flashback arrestors

Flashback - recession of the flame into or back of the mixing chamber

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Flashback

flame

quenched

at the

flashback

barrier

Flame

barrie

r

Built-

in

check

valve

Normal

flow

Reverse

flow

Flashback

Built-in

check

valve

stops

reverse

flow

SAFETY SAFETY SAFETY

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A jet of pure oxygen reacts with iron, that has been preheated to its ignition point, to produce the oxide Fe3O4 by exothermic reaction.This oxide is then blown through the material by the velocity of the oxygen stream

Different types of fuel gases may be used for the pre-heating flame in oxy fuel gas cutting: i.e. acetylene, hydrogen, propane. etc

By adding iron powder to the flame we are able to cut most metals - “Iron Powder Injection”

The high intensity of heat and rapid cooling will cause hardening in low alloy and medium/high C steels they are thus pre-heated to avoid the hardening effect

Oxyfuel gas cutting process

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Oxyfuel gas cutting equipment

The cutting torch

Neutral cutting flame

Neutral cutting flame with oxygen cutting stream

Oxyfuel gas cutting related terms

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Oxyfuel gas cutting quality

• Good cut - sharp top edge, fine and even drag lines, little oxide and a sharp bottom edge

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Cut too fast -pronounced break in the drag line, irregular cut edge

Cut too slow - top edge is melted, deep groves in the lower portion, heavy scaling, rough bottom edge



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Preheat flame too high -

top edge is melted,

irregular cut, excess of

adherent dross

Preheat flame too low -

deep groves in the lower

part of the cut face



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Irregular travel speed - uneven

space between drag lines,

irregular bottom with adherent

oxide

Nozzle is too high above the works - excessive melting of the top edge, much oxide

Mechanised oxyfuel cutting

• can use portable carriages or gantry type machines and obtain high productivity

• accurate cutting for complicate shapes

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OFW/C advantages/disadvantages

Disadvantages:

1) High skill factor

2) Wide HAZ

4) Slow process

5) Limited range of consumables

3) Safety issues

Advantages:

1) No need for power supply, portable

3) Low equipment cost

4) Can cut carbon and low alloy steels

5) Good on thin materials

2) Versatile: preheat, brazing, surfacing, repair, straightening

6) Not suitable for reactive & refractory metals

Special oxyfuel operations• Gouging

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Rivet cutting

Special oxyfuel operations

• Thin sheet cutting

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Rivet washing

Cutting Processes

Plasma arc cutting

• Uses high velocity jet of ionised gas through a constricted nozzle to remove the molten metal

• Uses a tungsten electrode and water cooled nozzle

• High quality cutting

• High intensity and UV radiation – EYES !

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Cutting ProcessesAir-arc for cutting or gouging

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Air-arc gouging features

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• Operate ONLY on DCEP

• Special gouging copper

coated carbon electrode

• Can be used on carbon

and low alloy steels,

austenitic stainless steels

and non-ferrous materials

• Requires CLEAN/DRY

compressed air supply

• Provides fast rate of metal removal

• Can remove complex shape defects

• After gouging, grinding of carbured layer is mandatory

• Gouging doesn‟t require a qualified welder!

Welding Inspector

Arc Welding Safety

Please discuss

Section 20

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Safety

• Electrical safety• Heat & Light

– Visible light– UV radiation - effects on skin

and eyes

• Fumes & Explosive Gasses• Noise levels• Fire Hazards• Scaffolding & Staging• Slips, trips and falls• Protection of others from

exposure

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Welding Inspector

Weldability Of Steels

Section 21

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Weldability of SteelsDefinition

It relates to the ability of the metal (or alloy) to be welded with mechanical soundness by most of the common welding processes, and the resulting welded joint retain the properties for which it has been designed.

is a function of many inter-related factors but these may be summarised as:

•Composition of parent material

•Joint design and size

•Process and technique

•Access

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Weldability of Steels

The weldability of steel is mainly dependant on carbon & other alloying elements content.

If a material has limited weldability, we need to take special measures to ensure the maintenance of the properties required

Poor weldability normally results in the occurrence of cracking

A steel is considered to have poor weldability when:

• an acceptable joint can only be made by using very narrow range of welding conditions

• great precautions to avoid cracking are essential (e.g., high pre-heat etc)

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The Effect of Alloying on SteelsElements may be added to steels to produce the properties required to make it useful for an application.

Most elements can have many effects on the properties of steels.

Other factors which affect material properties are:

•The temperature reached before and during welding

•Heat input

•The cooling rate after welding and or PWHT

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Steel Alloying Elements

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Iron (Fe): Main steel constituent. On its own, is relatively soft, ductile, with low

strength.

Carbon (C): Major alloying element in steels, a strengthening element with

major influence on HAZ hardness. Decreases weldability.

•typically < ~ 0.25%

Manganese (Mn): Secondary only to carbon for strength, toughness and

ductility, secondary de-oxidiser and also reacts with sulphur to form

manganese sulphide.

< ~0.8% is residual from steel de-oxidation

•up to ~1.6% (in C-Mn steels) improves strength & toughness

Silicon (Si): Residual element from steel de-oxidation.

•typically to ~0.35%


Phosphorus (P): Residual element from steel-making minerals. difficult to reduce below < ~ 0.015% brittleness

Sulphur (S): Residual element from steel-making minerals

< ~ 0.015% in modern steels

< ~ 0.003% in very clean steels

Aluminium (Al): De-oxidant and grain size control

•typically ~ 0.02 to ~ 0.05%

Chromium (Cr): For creep resistance & oxidation (scaling) resistance for elevated temperature service. Widely used in stainless steels for corrosion resistance, increases hardness and strength but reduces ductility.

•typically ~ 1 to 9% in low alloy steels

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Nickel (Ni): Used in stainless steels, high resistance to corrosion from acids, increases strength and toughness

Molybdenum (Mo): Affects hardenability. Steels containing molybdenum are less susceptible to temper brittleness than other alloy steels. Increases the high temperature tensile and creep strengths of steel. typically ~ 0.5 to 1.0%

Niobium (Nb): a grain refiner, typically~ 0.05%

Vanadium (V): a grain refiner, typically ~ 0.05%

Titanium (Ti): a grain refiner, typically ~ 0.05%

Copper (Cu): present as a residual, (typically < ~ 0.30%) added to ‘weathering steels’ (~ 0.6%) to give better resistance to atmospheric corrosion

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Classification of Steels

Mild steel (CE < 0.4)• Readily weldable, preheat generally not required if low hydrogen

processes or electrodes are used

• Preheat may be required when welding thick section material, high restraint and with higher levels of hydrogen being generated

C-Mn, medium carbon, low alloy steels (CE 0.4 to 0.5)

• Thin sections can be welded without preheat but thicker sections will require low preheat levels and low hydrogen processes or electrodes should be used

Higher carbon and alloyed steels (CE > 0.5)

• Preheat, low hydrogen processes or electrodes, post weld heating and slow cooling may be required

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Process Cracks

• Hydrogen Induced HAZ Cracking (C/Mn steels)

• Hydrogen Induced Weld Metal Cracking (HSLA steels).

• Solidification or Hot Cracking (All steels)

• Lamellar Tearing (All steels)

• Re-heat Cracking (All steels, very susceptible Cr/Mo/V steels)

• Inter-Crystalline Corrosion or Weld Decay (stainless steels)

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CrackingWhen considering any type of cracking mechanism, three elements must always be present:

• Stress

Residual stress is always present in a weldment, through unbalanced local expansion and contraction

• Restraint

Restraint may be a local restriction, or through plates being welded to each other

• Susceptible microstructure

The microstructure may be made susceptible to cracking by the process of welding

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Cracks


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May occur:

• up to 48 hrs after completion

• In weld metal, HAZ, parent metal.

• At weld toes

• Under weld beads

• At stress raisers.

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Also know as:

Cold Cracking, happens when

the welds cool down.

HAZ cracking, normally occurs

in the HAZ.

Delayed cracking, as it takes

time for the hydrogen to

migrate. 48 Hours normally but

up to 72,

Under-bead cracking, normally

happens in the HAZ under a

weld bead


There is a risk of hydrogen cracking when all of the 4 factors occur together:

•Hydrogen More than 15ml/100g of weld metal

•Stress More than ½ the yield stress

•Temperature Below 300oC

•Hardness Greater than 400HV Vickers

•Susceptible Microstructure (Martensite)

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Precautions for controlling hydrogen cracking

• Pre heat, removes moisture from the joint preparations, and slows down the cooling rate

• Ensure joint preparations are clean and free from contamination

• The use of a low hydrogen welding process and correct arc length

• Ensure all welding is carried out is carried out under controlled environmental conditions

• Ensure good fit-up as to reduced stress

• The use of a PWHT

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• Hydrogen is the smallest atom known

• Hydrogen enters the weld via the arc

• Source of hydrogen mainly from moisture pick-up on

the electrodes coating, welding fluxes or from the

consumable gas

H2

H2

H2

H2H2

Moisture on the electrode or grease on the wire

Water vapour in the air or in the shielding gas

Oxide or grease on the plate

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Hydrogen absorbed

in a long, or

unstable arc

Hydrogen introduced in

weld from consumable,

oils, or paint on plate

Cellulosic electrodes

produce hydrogen as a

shielding gas

Hydrogen

crack

Martensite forms from γ H2 diffuses to γ in HAZ

H2H2



Susceptible Microstructure:

Hard brittle structure – MARTENSITE Promoted by:

A) High Carbon Content, Carbon Equivalent (CE)

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Heat input (Kj/mm) = Amps x Volts x arc time

Run out length x 103 (1000)

CEV = %C + Mn + Cr+Mo+V + Ni+Cu

6 5 15B) high alloy content

C) fast cooling rate: Inadequate Pre-Heating

Cold Material

Thick Material

Low Heat Input.


Typical locations for Cold Cracking

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•HSLA or Micro-Alloyed Steels are high strength steels

(800MPa/N/mm2) that derive their high strength from small

percentage alloying (over-alloyed Weld metal to match the

strength of parent metal)

•Typically the level of alloying is in the elements such as

vanadium molybdenum and titanium, nickel and chromium

Strength. are used. It would be impossible to match this micro

alloying in the electrode due to the effect of losses across an

electric arc (Ti burn in the arc)

•It is however important to match the strength of the weld to

the strength of the plate, Mn 1.6 Cr Ni Mo

HICC in HSLA steels

Hydrogen Scales

List of hydrogen scales from BS EN 1011:part 2.

Hydrogen content related to 100 grams of weld metal deposited.

• Scale A High: >15 ml

• Scale B Medium: 10 ml - 15 ml

• Scale C Low: 5 ml - 10 ml

• Scale D Very low: 3 ml - 5 ml

• Scale E Ultra-low: < 3 ml

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Potential Hydrogen Level Processes

list of welding processes in order of potential lowest hydrogen content with regards to 100g of deposited weld metal.

•TIG < 3 ml

•MIG < 5 ml

•ESW < 5 ml

•MMA (Basic Electrodes) < 5 ml

•SAW < 10ml

•FCAW < 15 ml

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Weldability


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Usually Occurs in Weld Centerline

Solidification CrackingAlso referred as

Hot Cracking: Occurring at high temperatures while the weld is hot

Centerline cracking: cracks appear down the centre line of the bead.

Crater cracking: Small cracks in weld centers are solidification cracks

Crack type: Solidification cracking

Location: Weld centreline (longitudinal)

Steel types: High sulphur & phosphor concentration in steels.

Susceptible Microstructure: Columnar grains In direction of solidification

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Factors for solidification cracking

• Columnar grain growth with impurities in weld metal (sulphur,

phosphor and carbon)

• The amount of stress/restraint

• Joint design high depth to width ratios

Liquid iron sulphides are formed around solidifying grains.

High contractional strains are present

High dilution processes are being used.

There is a high carbon content in the weld metal

• Most commonly occurring in sub-arc welded joints


• Sulphur in the parent material may dilute in the weld metal to form iron sulphides (low strength, low melting point compounds)

• During weld metal solidification, columnar crystals push still liquid iron sulphides in front to the last place of solidification, weld centerline.

• The bonding between the grains which are themselves under great stress and may now be very poor to maintain cohesion and a crack will result, weld centerline.

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Solidification CrackingAvoidance

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Deep, narrower weld bead

On solidification the

bonding between the grains

may now be very poor to

maintain cohesion and a

crack may result

Shallow, wider weld bead

On solidification the

bonding between the

grains may be adequate to

maintain cohesion and a

crack is unlikely to occur

HAZ HAZ

Intergranular liquid filmColumnar grains Columnar

grains


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Precautions for controlling solidification cracking

•The first steps in eliminating this problem would be to choose a low

dilution process, and change the joint design

Grind and seal in any lamination and avoid further dilution????

Add Manganese to the electrode to form spherical Mn/S which form

between the grain and maintain grain cohesion

As carbon increases the Mn/S ratio required increases

exponentially and is a major factor. Carbon content % should be a

minimised by careful control in electrode and dilution

Limit the heat input, hence low contraction, & minimise restraint


Precautions for controlling solidification cracking

• The use of high manganese and low carbon content fillers

• Minimise the amount of stress / restraint acting on the joint during welding

• The use of high quality parent materials, low levels of impurities (Phosphor & sulphur)

• Clean joint preparations contaminants (oil, grease, paints and any other sulphur containing product)

• Joint design selection depth to width ratios

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Solidification cracking in Austenitic Stainless Steel

• particularly prone to solidification cracking

• large grain size gives rise to a reduction in grain boundary area with high concentration of impurities

• Austenitic structure very intolerant to contaminants (sulphur, phosphorous and other impurities).

• High coefficient of thermal expansion /Low coefficient of thermal conductivity, with high resultant residual stress

• same precautions against cracking as for plain carbon steels with extra emphasis on thorough cleaning and high dilution controls.

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Cracks

Lamellar Tearing

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Lamellar Tearing

Factors for lamellar tearing to occur

Cracks only occur in the rolled plate !

Close to or just outside the HAZ !

Cracks lay parallel to the plate surface and the fusion boundary of the weld and has a stepped aspect.

• Low quality parent materials, high levels of impurities

• Joint design, direction of stress

• The amount of stress acting across the joint during welding

• Note: very susceptible joints may form lamellar tearing under very low levels of stress

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Lamellar Tearing

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Tee fillet weld Tee butt weld

(double-bevel)

Corner butt weld

(single-bevel)

Susceptible joint types combined with susceptible rolled plate

used to make a joint.

High stresses act in the through thickness direction of the plate

(know as the short transverse direction).

T, K & Y joints normally end up with a tensile residual stress

component in the through thickness direction.

Lamellar Tearing

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Critical area

Critical

area

Critical area

Lamellar Tearing

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Modifying a corner joint to avoid lamellar tearing

Susceptible Non-Susceptible

Prior welding both plates may be grooved to avoid lamellar tearing

An open corner joint may be selected to avoid lamellar tearing

Lamellar Tearing

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Precautions for controlling lamellar tearing

• The use of high quality parent materials, low levels of

impurities

• The use of buttering runs

• A gap can be left between the horizontal and vertical

members enabling the contraction movement to take

place

• Joint design selection

• Minimise the amount of stress / restraint acting on the

joint during welding

• Hydrogen precautions

Lamellar TearingCrack type: Lamellar tearing

Location: Below weld HAZ

Steel types: High sulphur & phosphorous steels

Microstructure: Lamination & Segregation

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Occurs when:

High contractional strains are through the short

transverse direction. There is a high sulfur content in

the base metal.

There is low through thickness ductility in the base

metal.

There is high restraint on the work

Short Tensile (Through Thickness) Test

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The short tensile test or through thickness test is a

test to determine a materials susceptibility to

lamellar tearing

Friction Welded Caps

Short Tensile Specimen

Through

Thickness

Ductility

Sample of Parent Material

The results are given as a STRA value

Short Transverse Reduction in Area

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High contractional

strains

Lamellar tear

Restraint

Lamellar Tearing

Welding Inspector

Practical Visual Inspection

Section 22

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Leg Length Gauge

G.A.L.

S.T.D.

10mm

16mm

L

Throat Thickness Gauge

G.A.L.

S.T.D.

10mm

16mm

Fillet Weld Gauges

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HI-

LO

S

ing

le P

urp

os

e W

eld

ing

Ga

ug

e

1

2

3

4

5

6 Root gap

dimension

Internal

alignment

HI-LO Welding Gauge

Plate / Pipe Inspection

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Remember in the CSWIP 3.1 Welding Inspectors

examination your are required to conduct a practical

examination of a plate test weld, complete a thumb

print sketch and a final report on your findings

Time allowed 1 hour and 15 minutes

The code is provided

Plate Inspection Examination

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1) Use a pencil for the arrow lines, but make all

written comments and measurements in ink

only

3) Do not forget to compare and sentence your

report

2) Report everything that you can observe

4) Do not forget to date & sign your report

5) Make any observations, such as

recommendations for further investigation for

crack-like imperfections.

Plate Inspection Points

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After you have observed an imperfection and

determined its type, you must be able to take

measurements and complete the thumb print report

sketch

The first thumb print report sketch should be in the

form of a repair map of the weld. (i.e. All

observations are Identified Sized and Located)

The thumb print report sketch used in CSWIP exam

will look like the following example.

Plate Thumb Print Report

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After you have completed your thumb print report

sketch of your test plate the next step is to complete

your final report again the report must be completed in

ink (no pencil).

The report must be completed to your thumb print

sketch, do not leave any boxes empty, every box must

be completed or dashed out. You must also make any

comments you feel are necessary regarding any

defects observed.

The report form used in CSWIP will look like the

following example.

Plate Inspection Final Report

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Remember in the CSWIP 3.1 Welding Inspectors

examination your are required to conduct a

practical examination of a pipe test weld, complete

a thumb print sketch and a final report on your

findings

Time allowed 1 hour and 45 minutes

The code is nominated e.g API 1104

Pipe Inspection

Welding Inspector

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Application & Control of Pre heat

Section 23

Welding TemperaturesDefinitions

Preheat temperature

• is the temperature of the workpiece in the weld zone immediately before any welding operation (including tack welding!)

• normally expressed as a minimum Interpass temperature

– is the temperature in a multi-run weld and adjacent parent metal immediately prior to the application of the next run

– normally expressed as a maximum

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Minimum interpass temperature = Preheat temperature

Pre heat maintenance temperature = the minimum temperature in the

weld zone which shall be maintained if welding is interrupted and shall be

monitored during the interruption.

Pre-heat Application

Furnace - Heating entire component - best

Electrical elements -Controllable; Portable; Site use; Clean; Component cannot be moved.

Gas burners - direct flame impingement; Possible local overheating; Less controllable;Portable; Manual operation possible; Component can be moved.

Radiant gas heaters - capable of automatic control; No flame impingement; No contact with component; Portable.

Induction heating - controllable; Rapid heating (mins not hours); Large power supply; Expensive equipment

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Measuring pre heat in Welding

Parameters to be measured:

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welding current

arc voltage

travel speed

shielding gas flow rate

The purposes

of measuring

Demonstration of

conformance to

specified requirements

preheat/interpass

temperature

force/pressure

humidity

Welding

process

control

Pre-heat Application

Application Of Preheat

• Heat either side of joint

• Measure temp 2 mins after heat removal

• Always best to heat complete component rather than local if possible to avoid distortion

• Preheat always higher for fillet than butt welds due to different combined thicknesses and chill effect factors.

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Pre-Heat Application

Manual Gas Operation

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Electrical Heated Elements

Welding Temperatures

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Point of Measurement

BS EN ISO 13916

t < 50 mm

A = 4 x t but max. 50 mm

the temperature shall be

measured on the surface

of the workpiece facing the

welder

Welding Temperatures

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Point of Measurement

BS EN ISO 13916

t > 50mm

A = 75mm minimum

the temperature shall be

measured on the face

opposite to that being

heated

allow 2 min per every 25

mm of parent metal

thickness for temperature

equalisation

Combined Thickness

The Chilling Effect of the Joint

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Combined Thickness

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The Chilling Effect of the Joint

Combined Thickness

Combined chilling effect of joint type and thickness.

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The Chill Effect of the Material

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Heating Temperature Control

• TEMPILSTICKS - crayons, melt at set temps. Will not measure max temp.

• Pyrometers - contact or remote, measure actual temp.

• Thermocouples - contact or attached, very accurate, measure actual temp.

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Temperature Test Equipment

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Temperature sensitive

materials:

•crayons, paints and

pills

•cheap

•convenient, easy to

use

•doesn‟t measure the

actual temperature!


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Contact thermometer

•Accurate

•Easy to use

•Gives the actual temperature

•Requires calibration

•suitable for moderate

temperatures


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Thermocouple

• based on measuring the thermoelectric potential difference

between a hot junction (on weld) and a cold junction

• accurate method

• measures over a wide range of temperatures

• gives the actual temperature

• need calibration


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Thermistors

• temperature-sensitive resistors

whose resistance varies inversely

with temperature

• used when high sensitivity is

required

• gives the actual temperature

• need calibration

• can be used up to 999°C

Temperature test equipment

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Devices for contactless measurement

• IR radiation and optical

pyrometer

• measure the radiant energy

emitted by the hot body

• contactless method, can be

used for remote measurements

• very complex

• for measuring high

temperatures

Welding Inspector

Calibration

Section 24

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Calibration, validation and monitoringDefinitions:

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Measurement = set of operations for determining a value of a

quantity

Repeatability = closeness between successive measuring

results of the same instrument carried out under the same

conditions

Accuracy class = class of measuring instruments that are

intended to keep the errors within specified limits

Calibration = checking the errors in a meter or measuring

device

Validation = checking the control knobs and switches provide

the same level of accuracy when returned to a pre-determined

point

Monitoring = checking the welding parameters (and other

items) are in accordance with the procedure or specification

Calibration and validation

Frequency - When it is required?

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once a year unless otherwise specified

whenever there are indications that the

instrument does not register properly

whenever the equipment has been

damaged, misused or subject to severe

stress

whenever the equipment has been rebuild

or repaired

See BS EN ISO 17662 for details!

Welding parameter calibration/validation

Which parameters need calibration/validation?

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depends on the welding process

see BS EN ISO 17662 and BS 7570 for details

How accurate?

depends on the application

welding current - ±2,5%

arc voltage - ±5%

wire feed speed - ±2,5%

gas flow rate - ±20% (±25% for backing gas flow rate)

temperature (thermocouple) - ±5%

PAMS (Portable Arc Monitor System)

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What does a PAMS measure?

Welding

current (Hall

effect

device)

Arc voltage

(connection

leads)Temperature

(thermocouple)

Wire feed

speed

(tachometer)

Gas flow

rate

(heating

element

sensor)

PAMS (Portable Arc Monitor System)

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The purposes of

a PAMS

For calibrating

and validating

the welding

equipment

For measuring

and recording

the welding

parameters

Use of PAMS

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Wire feed speed

monitoring

Incorporated pair of

rolls connected to a

tachogenerator

Use of PAMS

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Shielding gas flow

rate monitoring

Heating element

sensor

Summary• a welding power source can only be calibrated if it has

meters fitted

• the inspector should check for calibration stickers, dates etc.

• a welding power source without meters can only be validated that the control knobs provide repeatability

• the main role is to carryout “in process monitoring” to ensure that the welding requirements are met during production

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Welding Inspector

Macro/Micro Examination

Section 25

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Macro Preparation

Purpose

To examine the weld cross-section to give assurance that: -

• The weld has been made in accordance with the WPS

• The weld is free from defects

Specimen Preparation

• Full thickness slice taken from the weld (typically ~10mm thick)

• Width of slice sufficient to show all the weld and HAZ on both sides

plus some unaffected base material

• One face ground to a progressively fine finish (grit sizes 120 to ~ 400)

• Prepared face heavily etched to show all weld runs & all HAZ

• Prepared face examined at up to x10 (& usually photographed for records)

• Prepared face may also be used for a hardness survey

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Micro PreparationPurpose

To examine a particular region of the weld or HAZ in order to:-

• To examine the microstructure

• Identify the nature of a crack or other imperfection

Specimen Preparation

• A small piece is cut from the region of interest

(typically up to ~ 20mm x 20mm)

• The piece is mounted in plastic mould and the surface of interest

prepared by progressive grinding (to grit size 600 or 800)

• Surface polished on diamond impregnated cloths to a mirror finish

• Prepared face may be examined in as-polished condition & then lightly

etched

• Prepared face examined under the microscope at up to ~ x 600

Macro / Micro ExaminationObject:

• Macro / microscopic examinations are used to give a visual evaluation of a cross-section of a welded joint

• Carried out on full thickness specimens

• The width of the specimen should include HAZ, weld and parent plate

• They maybe cut from a stop/start area on a welders approval test

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Macro / Micro ExaminationWill Reveal:

• Weld soundness

• Distribution of inclusions

• Number of weld passes

• Metallurgical structure of weld, fusion zone and HAZ

• Location and depth of penetration of weld

• Fillet weld leg and throat dimensions

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• Visual examination for

defects

• Cut transverse from the

weld

• Ground & polished P400

grit paper

• Acid etch using 5-10%

nitric acid solution

• Wash and dry

• Visual evaluation under 5x

magnification

• Report on results

• Visual examination for

defects & grain structure

• Cut transverse from a

weld

• Ground & polished P1200

grit paper, 1µm paste

• Acid etch using 1-5%

nitric acid solution

• Wash and dry

• Visual evaluation under

100-1000x magnification

• Report on results

Macro Micro

Metallographic Examination

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Macro examination Micro examination

61769477 welding-inspection-cswip-gud

Engineering

2nd world

thumb print

handling readily

high contractional

measure actual

molten slag

melt ingredients

austenitic