quality and inspection

7/28/2019 Quality and Inspection

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Quality and Inspection

D.DHANASEKAR M.E.,Mem.A.S.M.E.,Design Engineer - mechanical


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Important definitions

Quality The totality of features and characteristics of a productor service that bear on its ability to satisfy a given need.

QualityAssurance The system, including all activities, documentation andfunctions concerning the achievement of the required

quality.Quality

ControlThe operational techniques and activities that ensure

the product or service quality complies with specified

requirements. It is also the use of such techniques and

activities.Specification The document that prescribes in detail, the requirements

with which the product or service has to comply.Inspection The process of measuring, examining, testing, gauging,

or otherwise comparing the item with the applicable

requirements.Certification The authoritative act of documenting compliance with

requirements.


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Main Types of Inspection

Design

Checking he dimensions so that these are consistent with

satisfactory operationsChecking the materials for their strength, toughness, stiffness

etc.

Check is often done by a third party.

These checks involve examination of drawings, specifications,

calculations and computer program listings.

Manufacture

The manufacture of basic components such as steel sections

and plates, bolts and welding consumables requires the

following checks :

Identification of batch.

Chemical analysis.

Mechanical testing.

Dimensional checks - external, internal.


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Stages of Inspection

Completion of calculations.

Completion of working drawings.Completion of shop drawings.

Manufacture of basic products.

Delivery to and removal from store.

Procedure trials.Operator qualification tests (particularly welding).

Completion of preparation of materials (cutting, drilling, etc.).

Completion of jigging, and fitting up of components.

Completion of shop assembly (welding, etc.).

Completion of preparation for protective coating.Completion of protection coating.

Completion of assembly on site.

Completion of erection on site.


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Methods of Inspection

Identification

Steel plates and sections are identified by the cast number. Individual

pieces are marked permanently by hard stamping or indelible painting.

Welding rods usually have the standard or grade to which they are madeembossed or marked on each item. The batch number is marked on the

bag or container in which they are supplied.

Structural components are given identification numbers by the fabricator.

All materials and components should be traceable back to source at anystage of the project.

Drawings and revisions to them should be clearly identified & superseded

issues withdrawn from the shop.

Test certificates should have an unique identification number.


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Chemical analysis

Analysis of steel is normally carried out for each cast. Levels of carbon andmanganese have a direct bearing on strength.

Levels of Cr, Mo, V, Ni, Mn, Cu etc are into account in measuring

weldability by the use of the Carbon Equivalent Formula.

Levels of S & P should also be controlled to ensure weldability.

Most structural steel specifications have defined limits of carbon,manganese, sulphur and phosphorus.

Mechanical tests

Tensile test is carried out by the steel supplier on each batch of a particular

cast, product form and grade. A typical batch may be 40 to 50 tonnes.

Charpy V-notch test is to assess the notch-ductility of the steel at therelevant temperature. This test must be carried out at the prescribed

temperature which may vary from Room Temperature (+20C) to -50C or

60C depending on the specified toughness grade. The requirement is that

the energy absorption is not less than the specified minimum energy at the

test temperature (usually 27 Joules)

Material Test Certificate


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Other Mechanical tests

These include the through-thickness ductility test, for

determining the resistance to lamellar tearing, the bend

test for butt welds, the nick break test for fillet welds and

a bend test for shear connectors.

The quality of trial welds is usually assessed by taking a

macro-section through the weld. This section is then

polished and etched to reveal the fusion boundary andheat affected zone (HAZ). A hardness survey is then

done to find the peak hardness.

Material Test Certificate


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A range of simple tools is used to check

dimensional accuracy

Thicknesses of plates may be checked with a

micrometre gauge. Lengths and cross-

sections are checked with steel tapes.

Straightness of beams and columns are

checked with a line pulled taut between the

ends. The departure from the straight ismeasured between the side of the member

and the line at different positions along the

member.

Flatness of plate elements is checked with a

steel or aluminium straight edge and a feeleror dial gauge.

Angles are measured with a protractor or, in

the case of shallow angles, they are

measured as the slope (cotangent) of the

angle, e.g. 1 in 20, 1 in 10, etc.

Dimensional Measurements

On site, levels are checked

with a surveryor's automatic

level and, for short lengths,

by a spirit level. Columns are

plumbed with a theodolite or

a vertical plumb line.

Fit up of machined parts is

checked with a set of feeler

gauges or a taper feeler

gauge.


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Non Destructive Testing


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Visual Inspection

Visual inspection will detect external

corrosion, most likely associated with

damage to the riser's protective

coatings.

Rope access

Marine growth

Visual inspection will detect gross weld

discontinuities like crater cracks,

reinforcement, weld profile, arc strikes,spatter etc.


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Penetrant Testing

Scientific Principles

Penetrant solution is applied to the

surface of a precleaned component. The

liquid is pulled into surface-breakingdefects by capillary action. Excess

penetrant material is carefully cleaned

from the surface. A developer is applied

to pull the trapped penetrant back to the

surface where it is spread out and

forms an indication. The indication ismuch easier to see than the actual

defect.

Main Uses

Used to locate cracks, porosity, and

other defects that break the surface of

a material and have enough volume to

trap and hold the penetrant material.

Liquid penetrant testing is used to

inspect large areas very efficiently and

will work on most nonporous

materials.

Main advantages

Large surface areas or large

volumes of parts/materials can beinspected rapidly.

Indications are produced directly

on surface of the part providing a

visual image of the discontinuity.

Equipment investment is minimal.


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Penetrant Testing

Main disadvantages

Detects only surface breaking

defects.

Surface preparation is critical as

contaminants can mask defects.

Requires a relatively smooth andnonporous surface.

Post cleaning is necessary to

remove chemicals.

Requires multiple operations under

controlled conditions.

Chemical handling precautions are

necessary (toxicity, fire, waste).


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Magnetic Particle Testing


Alternating electrical current is passed

through a coil producing a magnetic

field. When the coil is placed near aconductive material, the changing

magnetic field induces current flow in

the material. These currents travel in

closed loops and are called eddy

currents. Eddy currents produce their

own magnetic field that can bemeasured and used to find flaws and

characterize conductivity, permeability,

and dimensional features.

Main Uses

Used to detect surface and near-surface

flaws in conductive materials, such as

the metals. Eddy current inspection is

also used to sort materials based on

electrical conductivity and magnetic

permeability, and measures the

thickness of thin sheets of metal and

nonconductive coatings such as paint.

Main advantagesDetects surface and near surface

defects.

Test probe does not need to

contact the part.

Method can be used for more than

flaw detection.

Minimum part preparation is

required..


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Main disadvantages

Only ferromagnetic materials can beinspected.

Proper alignment of magnetic field and

defect is critical.

Large currents are needed for very largeparts.

Requires relatively smooth surface.

Paint or other nonmagnetic coverings

adversely affect sensitivity.

Demagnetization and post cleaning is

usually necessary.


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Eddy current Testing


A magnetic field is established in a

component made from ferromagnetic

material. The magnetic lines of forcetravel through the material, and exit and

reenter the material at the poles.

Defects such as crack or voids cannot

support as much flux, and force some

of the flux outside of the part. Magnetic

particles distributed over thecomponent will be attracted to areas of

flux leakage and produce a visible

indication.

Main Uses

Used to inspect ferromagnetic

materials (those that can be

magnetized) for defects that result in a

transition in the magnetic permeability

of a material. Magnetic particle

inspection can detect surface and near

surface defects.

Main advantagesLarge surface areas of complex

parts can be inspected rapidly.

Can detect surface and subsurface

flaws.

Surface preparation is less critical

Magnetic particle indications are

produced directly on the surface of

the part and form an image of thediscontinuity.


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Main disadvantages

Only conductive materials can beinspected.

Ferromagnetic materials require special

treatment to address magnetic

permeability.

Depth of penetration is limited.

Flaws that lie parallel to the inspection

probe coil winding direction can go

undetected.

Skill and training required is moreextensive than other techniques.

Surface finish and roughness may

interfere.

Reference standards are needed for

setup.


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Ultrasonic Testing


X-rays are used to produce images of

objects using film or other detector that

is sensitive to radiation. The test objectis placed between the radiation source

and detector. The thickness and the

density of the material that X-rays must

penetrate affects the amount of

radiation reaching the detector. This

variation in radiation produces animage on the detector that often shows

internal features of the test object.

Main Uses

Used to inspect almost any material

for surface and subsurface defects. X-

rays can also be used to locates and

measures internal features, confirm

the location of hidden parts in an

assembly, and to measure thickness

of materials.

Main advantages

Can be used to inspect virtually all

materials.

Detects surface and subsurface

defects.

Ability to inspect complex shapes

and multi-layered structures

without disassembly.


required.


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Ultrasonic Testing

Main disadvantages

Only conductive materials can beinspected.

Ferromagnetic materials require special

treatment to address magnetic

permeability.

Depth of penetration is limited.

Flaws that lie parallel to the inspection

probe coil winding direction can go

undetected.

Skill and training required is more

extensive than other techniques.

Surface finish and roughness may

interfere.

Reference standards are needed for setup.


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Radiographic Testing

Main disadvantages

Extensive operator training and skillrequired.

Access to both sides of the structure is

usually required.

Orientation of the radiation beam to non-volumetric defects is critical.

Field inspection of thick section can be

time consuming.

Relatively expensive equipment investmentis required.

Possible radiation hazard for personnel.


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Radiographic Testing


High frequency sound waves are sent

into a material by use of a transducer.

The sound waves travel through thematerial and are received by the same

transducer or a second transducer. The

amount of energy transmitted or

received and the time the energy is

received are analyzed to determine the

presence of flaws. Changes in materialthickness, and changes in material

properties can also be measured.

Main Uses

Used to locate surface and subsurface

defects in many materials includingmetals, plastics, and wood. Ultrasonic

inspection is also used to measure the

thickness of materials and otherwise

characterize properties of material

based on sound velocity and

attenuation measurements.

Main advantagesDepth of penetration for flaw

detection or measurement is

superior to other methods.

Only single sided access is

required.Provides distance information.


required.

Method can be used for much

more than just flaw detection.


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Destructive Testing


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HYDROSTATIC TEST

This is a nondestructive test used to check the quality of

welds on closed containers such as pressure vessels andtanks. The test usually consists of filling the vessel with

water and applying a pressure greater than the working

pressure of the vessel. Sometimes, large tanks are filled with

water which is not under pressure to detect possible leakage

through defective welds. Another method is to test with oil

and then steam out the vessel. Back seepage of oil from

behind the liner shows up visibly.


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Welding Procedure

Specification


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Welding Procedure Specification(WPS) is a Formatted Document

that is mandatory for any Firm desirous of Designing and

manufacturing Pressure vessels and structures as per StandardCodes. WPS is deemed to have been approved if certain tests are

satisfactorily conducted on Weld Coupons prescribed in

Procedure Qualification Tests

Topics covered

Procedure Qualification Record (PQR)is a Formatted Documentthat is accompanied with WPS. PQR becomes a valid document

only when the prescribed tests conducted on Weld Coupons pass

the acceptance criteria stipulated by the Code. Every WPS must

have at least one PQR.

Welder Performance Qualification (WPQ)is a Document that is

necessary to prove the ability of the welder to deliver sound and

good quality welds. The codes generally permit the evaluation of

the welder to be done by the use of non-destructive tests viz.

Radiography. Only with this document, a welder is certified.


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A WPS is a document that describes how welding is to be carried

out in production. They are recommended for all welding

operations and many application codes and standards make themmandatory.

What information should they include?

Sufficient details to enable any competent person to apply the

information and produce a weld of acceptable quality. The

amount of detail and level of controls specified on a WPS is

dependant on the application and criticality of the jointto bewelded.


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For most applications the information required is

generally similar to that recorded on a Procedure

Qualification Record (PQR) or Welding Procedure ApprovalRecord (WPAR), except that ranges are usually permitted

on thicknesses, diameters, welding current, materials,

joint types etc.

If a WPS is used in conjunction with approved welding

procedures then the ranges stated should be in accordance

with the approval ranges permitted by the welding

procedure.


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However careful consideration should be given to the ranges

specified to ensure they are achievable, as the ranges given by

welding procedure standards do not always represent good

welding practice. For example welding positions permitted by

the welding procedure standard may not be achievable or

practical for certain welding processes or consumables.


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EN 288 Part 2 European Standard For Welding Procedure

Specifications

This part of EN 288 defines the contents of a Welding Procedure

Specification in the form of a list of information that should be

recorded. For some applications it may be necessary to supplement or

reduce the list. For example only in the case of a procedure requiring

heat input control would there be a necessity to quote travel speed or

run-out length for manual processes.

ASME IX American Boiler and Pressure Vessel Code

QW 250 Lists the variables for each welding process,all the variablesstated should be addressed. The range permitted by the WPS isdictated by the PQR or PQRs used to qualify it.


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Typical Items That Should Be Recorded in W.P.S:-

Common to all Processes .

Procedure number

Process type

Consumable Size, Type and full Codification.

Consumable Baking Requirement if applicable

Parent material grade and spec.

Thickness range.

Plate or Pipe, Diameter rangeWelding Position

Joint Fit Up, Preparation, Cleaning, Dimensions etc.

Backing Strip, Back Gouging information.

Pre-Heat (Min Temp and Method)

Interpass if Required (Maximum Temperature recorded )Post Weld Heat Treatment. If Required (Time and Temp)

Welding Technique (weaving, max run width etc.)

Arc Energy Limits should be stated if impact tests are

required


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Specific To

Welding

Processes

MMA TIG MIG / FCAW SAW

Welding current yes yes yes yes

Type of Welding

current Polarityyes yes yes yes

Arc voltage yes yes

Pulse parameters

(Pulse time

current)

If auto is Used If auto is Used

Welding Speed yes yes yes

Wire configuration yes

Shielding gas

(comp,flow rate)yes yes

Purge gas (comp &

flow rate)If auto is Used If auto is Used

Tungsten electode

Diameter and type.yes

Nozzle diameter yes yes

Type of Flux yes

Nozzle Stand OffDistance yes


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Sketches

A sketch of the joint configuration is required which should

include the basic dimensions of the weld

preparation. Some indication of the run sequence is also

beneficial, particularly if the correct sequence is essential

to ensure the properties of the weld are maintained.Production Sequence

Whilst this is good practice it is not a requirement of either

ASME 9 or EN288 Part 2; it could be issued as a separate

QA procedure if preferred.

Non Destructive Testing

A WPS is primarily concerned with welding not N D T, thisactivity should be covered by separate N D T procedures.


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Welding Procedure Specification

Weld Procedure No. : 30P1TIG1 Issue 1

Procedure Qualification Record No. : WP T17/AManufacturer : Raichur TPS

Location : Pent House

Welding Process : Manual TIG

Joint type : Single sided Butt weld

Method of preparation & cleaning : Machine & degrease

Parent metal specification : Grade 304L

Parent Metal thickness : 3 to 8 mm

Wall pipe O.D : 25 to 100 mm

Weld position : All position

Weld progression : Upwards


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Joint design Welding sequence

Run Process Size of Filler Voltage

1 TIG 1.2 mm N/A

2 & sub TIG 1.6 mm

Current

7080 A

80100 A N/A

Polarity

DCDC

Wire speed

N/AN/A

Travel speed

N/AN/A

Heat Input

N/AN/A


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Welding consumable

(type, designation & trade name)

BS 2901 Part 2

308S92

Shielding Gas

Flow rate

Argon 99.99 % Purity

812 LPM

Electrode (type & Dia) 2% thoriated W; 2.4 mm

Details of back gouging Gas backing

Pre-heat temperature

Inter-pass temperature

5 C

200 C

Post Weld Heat Treatment

(Time, temp, method,CR)

N/A

N/A


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Production sequence


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