CSWIP 3.2-Senior Welding Inspector-Level 3-WIS10-Rev 1 January 2011.pdf

7/25/2019 CSWIP 3.2-Senior Welding Inspector-Level 3-WIS10-Rev 1 January 2011.pdf

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CSWIP 3.2 - Senior Welding Inspector -Level 3

WIS10

Training & Examination Services

Granta Park, Great AbingtonCambridge CB21 6AL, UK

Copyright TWI Ltd


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Rev 1 January 2011Contents

Copyright TWI Ltd 2011

www.twitraining.com

CSWIP 3.2 - Senior Welding Inspector -Level 3

Contents

Section Subject

1 Duties of the Senior Welding Inspector

2 Terms and Defin itions

3 Planning

4 Codes and Standards

5 Calibration of Welding Equipment

6 Destructive Testing

7 Heat Treatment

8 WPS and Welder Qualif ications

9 Materials Inspection

10 Residual Stress and Distor tion

11 Weldabil ity of Steels12 Weld Fractures

13 Welding Symbols

14 NDT

15 Welding Consumables

16 MAG Welding

17 MMA Welding

18 Submerged Arc Welding

19 TIG Welding

20 Weld Imperfections

21 Weld Repairs

22 Arc Welding Safety

23 Appendices

24 Further Reading


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Section 1

Duties of theSenior Welding Inspector


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Rev 1 January 2011Duties of the Senior Welding Inspector


www.twitraining.com1-1

1 Duties of the Senior Welding Inspector

1.1 General

The Senior Welding Inspector has primarily a supervisory/managerial role,which could encompass the management and control of an inspectioncontract. The role would certainly include leading a team of WeldingInspectors, who will look to the Senior Welding Inspector for guidance,especially on technical subjects. The Senior Welding Inspector will beexpected to give advice, resolve problems, take decisions and generallylead from the front, sometimes in difficult situations.

The attributes required by the Senior Welding Inspector are varied and theemphasis on certain attributes and skills may differ from project to project.Essentially though the Senior Welding Inspector will require leadershipskills, technical skills and experience.

1.2 Leadership skil ls

Some aspects on the theory of leadership may be taught in the classroom,but leadership is an inherent part of the character and temperament of anindividual. Practical application and experience play a major part in thedevelopment of leadership skills and the Senior Welding Inspector shouldstrive to improve and fine tune these skills at every opportunity.

The skills required for the development of leadership include a:

Willingness and ability to accept instructions or orders from senior staffand to act in the manner prescribed.

Willingness and ability to give orders in a clear and concise manner,whether verbal or written, which will leave the recipient in no doubt as towhat action or actions are required.

Willingness to take responsibility, particularly when things go wrong,perhaps due to the Senior Welding Inspectors direction, or lack of it.

Capacity to listen (the basis for good communication skills) if and whenexplanations are necessary and to provide constructive reasoning andadvice.

Willingness to delegate responsibility to allow staff to get on with the job

and to trust them to act in a professional manner. The Senior WeldingInspector should, wherever possible, stay in the background, managing.

Willingness and ability to support members of the team on technical andadministrative issues.


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1.3 Technical skil ls

A number of factors make up the technical skills required by the SeniorWelding Inspector and these are a knowledge of:

Technology. Normative documents.

Planning.

Organisation.

Auditing.

1.4 Knowledge of technology

Welding technology knowledge required by the Senior Welding Inspector isvery similar to that required by the Welding Inspector, but with someadditional scope and depth.

Certain areas where additional knowledge is required are a:

Knowledge of quality assurance and quality control.

Sound appreciation of the four commonly used non-destructive testingmethods.

Basic understanding of steel metallurgy for commonly welded materialsand the application of this understanding to the assessment of fracturesurfaces.

Assessment of non-destructive test reports, particularly the interpretationof radiographs.

1.5 Knowledge of normative documents

It is not a requirement for Inspectors at any level to memorise the content ofrelevant normative documents, except possibly with the exception of takingexaminations.

Specified normative documents (specifications, standards, codes ofpractice, etc) should be available at the workplace and the Senior WeldingInspector would be expected to read, understand and apply therequirements with the necessary level of precision and direction required.

The Senior Welding Inspector should be aware of the more widely usedstandards as applied in welding and fabrication. For example:

BS EN ISO 15614 / ASME IX Standards for welding procedureapproval

BS 4872, BS EN 287 / ASME IX Standards for welder approval.

PED BS 5500 / ASME VIII Standards for quality of fabrication.

BS EN ISO 9000 2000 Standards for quality management.


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1.6 Knowledge of planning

Any project or contract will require some planning if inspection is to becarried out effectively and within budget.

See Section: Planning for more detailed information.

1.7 Knowledge of organisation

The Senior Welding Inspector must have good organisational skills in orderto ensure that the inspection requirements of any quality/inspection plan canbe met, within the allocated time, budget and using the most suitablepersonnel for the activity. Assessment of suitable personnel may requireconsideration of their technical, physical and mental abilities in order toensure that they are able to perform the tasks required of them. Otherconsiderations would include availability of inspection personnel at the timerequired, levels of supervision and the monitoring of the inspectors activitiesform start to contract completion.

1.8 Knowledge of quality/audit ing

There are many situations in manufacturing or on a project where the SeniorWelding Inspector may be required to carry out audits.

See section on: Quality Assurance/Quality Control and Inspection formore detailed information.

1.9 Man management

As mentioned above, the Senior Welding Inspector will have to direct andwork with a team of Inspection personnel which he may well have to pick.He will have to liaise with customer representatives, sub-contractors andthird party Inspectors. He may have to investigate non-compliances, dealwith matters of discipline as well as personal matters of his staff.

To do this effectively he needs skills in man management.

1.10 Recruitment

When recruiting an individual or a team the SWI will first have to establishthe requirements of the work. Among them would be:

What skills are definitely required for the work and what additional oneswould be desirable?

Are particular qualifications needed?

Is experience of similar work desirable?

What physical attributes are needed?

Is the work local, in-shop, on-site, in a third world country?

Does the job require working unsociable hours being away from homefor long periods?


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Is the job for permanent staff or for a fixed term?

If overseas what are the leave and travel arrangements?

What is the likely salary?

During subsequent interviews the SWI will need to assess other aspects of

the candidates suitability:

Has he the ability to work on his own initiative?

Can he work as part of a team?

If overseas has the person been to a similar location?

What is his marital/home situation?

Are there any Passport/Visa problems likely?

1.11 Morale and mot ivation

The morale of a workforce has a significant effect on its performance so the

SWI must strive to keep the personnel happy and motivated and be able todetect signs of low morale.

Low morale can lead to among other things, poor productivity, less goodworkmanship, lack of diligence, taking short cuts, ignoring safety proceduresand higher levels of absenteeism.

The SWI needs to be able to recognise these signs and others such aspersonnel not starting work promptly, taking longer breaks, talking in groupsand grumbling about minor matters.

A good supervisor should not allow his workforce to get into such a state.

He must keep them motivated by:

His own demeanour does he have drive and enthusiasm or is heseen to have no energy and generally depressed. The workforce willreact accordingly.

Is he seen to be leading from the front in a fair and consistent manner?

Favouritism in the treatment of staff, on disciplinary matters, theallocation of work, allotment of overtime, weekend working and

holidays are common causes of problems. Keep them informed in all aspects of the job and their situation.

Rumours of impending redundancies or cuts in allowances etc will notmake for good morale.

1.12 Discipline

Any workforce must be working in a disciplined manner, normally to rulesand standards laid down in the Companys conditions of employment orrelevant company handbook. The SWI must have a good understanding ofthese requirements and be able to apply them in a fair and equitable

manner.


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He must have a clear understanding as to the limits of his authority knowing how far he can go in disciplinary proceedings.

The usual stages of disciplinary procedure are:

The quiet word. Formal verbal warning.

Written warning.

Possible demotion, transfer, suspension.

Dismissal with notice.

Instant dismissal.

Usually after the written warning stage the matter will be handled by theCompanys Personnel or Human Resources Department.

It is of vital importance that the company rules are rigorously followed asany deviation could result in claims for unfair or constructive dismissal.

In dealing with disciplinary matters the SWI must:

Act promptly.

Mean what he says.

Treat everyone fairly and as an adult.

Avoid constant complaining on petty issues.

Where there are serious breaches of company rules by one or two people

the rest of the workforce should be informed of the matter so that rumourand counter-rumours can be quashed.

Some matters of discipline may well arise because of incorrect workingpractices, passing off below quality work, signing for work which has notbeen done, etc.

In all such cases the SWI will need to carry out an investigation and applydisciplinary sanctions to the personnel involved. To do this:

First establish the facts by interviewing staff, from the relevant

records, by having rechecks on part of the job.

If any suspicions are confirmed, transfer/remove suspect personnelfrom the job pending disciplinary proceedings. If the personnel areemployed by a sub-contractor then a meeting with the sub-contractorwill be needed to achieve the same end.

Find out the extent of the problem, is it localised or widespread?

Is there need to inform the customer and third party inspector?

Formulate a plan of action, with other company departments wherenecessary, to retrieve the situation.

Carry out the necessary disciplinary measures on the personnel

involved.


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Convene a meeting with the rest of the workforce to inform them of thesituation and ensure that any similar lapses will be dealt with severely.

Follow up the meeting with a written memo.

1.13 Summary

The Senior Welding Inspectors role can be varied and complex, a numberof skills need to be developed in order for the individual to be effective in therole. Every Senior Welding Inspector will have personal skills and attributeswhich can be brought to the job, some of the skills identified above mayalready have been mastered or understood. The important thing for theindividual to recognise is not only do they have unique abilities which theycan bring to the role, but they also need to strive to be the best they can bystrengthening identifiable weak areas in their knowledge and understanding.Some ways in which these goals may be achieved is through:

Embracing facts and realities. Being creative.

Being interested in solving problems.

Being pro-active not reactive.

Having empathy with other people.

Having personal values.

Being objective.


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Section 2

Terms and Definit ions


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Rev 1 January 2011Terms and Definitions



2 Terms and Defin itions

NoteThe following definitions are taken from BS 499-1:1991 Welding terms andsymbols Glossary for welding, brazing and thermal cutting

WeldingAn operation in which two or more parts are united by means of heat,pressure or both, in such a way that there is continuity in the nature of themetal between these parts.

BrazingA process of joining generally applied to metals in which, during or afterheating, molten filler metal is drawn into or retained in the space betweenclosely adjacent surfaces of the parts to be joined by capillary attraction. In

general, the melting point of the filler metal is above 450C but always below

the melting temperature of the parent material.

Braze weldingThe joining of metals using a technique similar to fusion welding and a fillermetal with a lower melting point than the parent metal, but neither usingcapillary action as in brazing nor intentionally melting the parent metal.

WeldA union of pieces of metal made by welding.

Joint

Connection where the individual components, suitably prepared andassembled, are joined by welding or brazing.


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Type of joint Sketch Definition

Butt joint A connection between the endsor edges of two parts making an

angle to one another of 135-180inclusive in the region of the joint

T joint A connection between the end oredge of one part and the face ofthe other part, the parts makingan angle to one another of more

than 5up to and including 90inthe region of the joint

Corner joint A connection between the endsor edges of two parts making anangle to one another of more

than 30but less than 135in theregion of the joint

Edge joint A connection between the edgesof two parts making an angle to

one another of 0-30inclusive in

the region of the joint

Cruciform joint A connection in which two flatplates or two bars are welded toanother flat plate at right anglesand on the same axis

Lap joint A connection between two over-lapping parts making an angle to

one another of 0-5inclusive inthe region of the weld or welds


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2.1 Types of Welds

2.1.1 From configuration point of view

Butt weld Fillet weld

Autogenous weldA fusion weld made without filler metal. Can be achieved by TIG, plasmaelectron beam, laser or oxyfuel gas welding.

Slot weldA joint between two overlapping components made by depositing a filletweld round the periphery of a hole in one component so as to join it to thesurface of the other component exposed through the hole.

Butt weld

In a butt oint

In a T oint

In a corner oint


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Plug weldA weld made by filling a hole in one component of a workpiece with fillermetal so as to join it to the surface of an overlapping component exposedthrough the hole (the hole can be circular or oval).

2.1.2 From the penetration point of view

Full penetration weldA welded joint where the weld metal fully penetrates the joint with completeroot fusion. In US the preferred term is complete joint penetration weld or

CJP for short (see AWS D1.1.)

Partial penetration weldA welded joint without full penetration. In US the preferred term is partialjoint penetration weld or PJP for short.

2.2 Types of joint (see BS EN ISO 15607)

Homogeneous join tWelded joint in which the weld metal and parent material have no significantdifferences in mechanical properties and/or chemical composition. Example:two carbon steel plates welded with a matching carbon steel electrode.

Heterogeneous jointWelded joint in which the weld metal and parent material have significantdifferences in mechanical properties and/or chemical composition. Example:a repair weld of a cast iron item performed with a nickel base electrode.

Dissimilar jointWelded joint in which the parent materials have significant differences inmechanical properties and/or chemical composition. Example: a carbonsteel lifting lug welded onto an austenitic stainless steel pressure vessel.


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2.3 Features of the completed weld

Parent metalMetal to be joined or surfaced by welding, braze welding or brazing.

Filler metalMetal added during welding, braze welding, brazing or surfacing.

Weld metalAll metal melted during the making of a weld and retained in the weld.

Heat-affected zone (HAZ)The part of the parent metal that is metallurgically affected by the heat ofwelding or thermal cutting, but not melted.

Fusion line

Boundary between the weld metal and the HAZ in a fusion weld. This is anon-standard term for weld junction.

Weld zoneZone containing the weld metal and the HAZ.

Weld faceSurface of a fusion weld exposed on the side from which the weld has beenmade.

Root

Zone on the side of the first run farthest from the welder.

ToeBoundary between a weld face and the parent metal or between runs. Thisis a very important feature of a weld since toes are points of high stressconcentration and often they are initiation points for different types of cracks(eg fatigue cracks, cold cracks). In order to reduce the stress concentration,toes must blend smoothly into the parent metal surface.

Excess weld metalWeld metal lying outside the plane joining the toes. Other non-standard

terms for this feature: reinforcement, overfill.


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Root

Parentmetal

Weldmetal

HAZ

Weldzone

Fusionline

Weldface Toe

Parent

metal

Excessweld metal

Excessweld metal

Butt weld

Fusionline

Weldmetal

Root

Parentmetal

HAZ

W eldzone

Weldface

Toe

Parentmetal

Excessweld metal

Fillet weld


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2.4 Weld preparation

A preparation for making a connection where the individual components,suitably prepared and assembled, are joined by welding or brazing.

2.4.1 Features of the weld preparationAngle of bevelThe angle at which the edge of a component is prepared for making a weldin case of a V preparation for a MMA weld on carbon steel plates, this angle

is between 25-30. In the case of a U preparation for an MMA weld on

carbon steel plates, this angle is between 8-12. In case of a single bevelpreparation for an MMA weld on carbon steel plates, this angle is between

40-50. In case of a single J preparation for a MMA weld on carbon steel

plates, this angle is between 10-20.

Included angleThe angle between the planes of the fusion faces of parts to be welded. Inthe case of single V, single U, double V and double U this angle is twice thebevel angle. In case of single bevel, single J, double bevel and double J, theincluded angle is equal to the bevel angle.

Root faceThe portion of a fusion face at the root that is not bevelled or grooved. Itsvalue depends on the welding process used, parent material to be weldedand application; for a full penetration weld on carbon steel plates, it has avalue between 1-2mm (for the common welding processes).

GapThe minimum distance at any cross section between edges, ends orsurfaces to be joined. Its value depends on the welding process used andapplication; for a full penetration weld on carbon steel plates, it has a valuebetween 1-4mm.

Root radiusThe radius of the curved portion of the fusion face in a component preparedfor a single J, single U, double J or double U weld. In case of MMA,MIG/MAG and oxyfuel gas welding on carbon steel plates, the root radius

has a value of 6mm in case of single and double U preparations and 8mm incase of single and double J preparations.

LandThe straight portion of a fusion face between the root face and the curvedpart of a J or U preparation can be 0. Usually present in case of weldpreparations for MIG welding of aluminium alloys.


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2.4.2 Types of preparation

Open square butt preparation

This preparation is used for welding thin components, either from one orboth sides. If the root gap is zero (ie if components are in contact), thispreparation becomes a closed square butt preparation (not recommendeddue to the lack of penetration problems!).

Single V preparation

The V preparation is one of the most common preparations used in welding;it can be produced using flame or plasma cutting (cheap and fast). Forthicker plates a double V preparation is preferred since it requires less fillermaterial to complete the joint and the residual stresses can be balanced onboth sides of the joint resulting in lower angular distortion.

Double V preparation

The depth of preparation can be the same on both sides (symmetric doubleV preparation) or deeper on one side (asymmetric double V preparation).Usually, in this situation the depth of preparation is distributed as 2/3 of the

thickness of the plate on the first side with the remaining 1/3 on the

Angle ofbevel

Included angle

Gap Root face


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backside. This asymmetric preparation allows for a balanced weldingsequence with root back gouging, giving lower angular distortions. Whilstsingle V preparation allows welding from one side, double V preparationrequires both sides access (the same applies for all double sidepreparations).

Single U preparation

U preparation can be produced only by machining (slow and expensive).However, tighter tolerances obtained in this case provide for a better fit-upthan in the case of V preparations. Usually it is applied for thicker platescompared with single V preparation (requires less filler material to completethe joint and this lead to lower residual stresses and distortions). Similar withthe V preparation, in case of very thick sections a double U preparation canbe used.

Double U preparation

Usually this type does not require a land (exception: aluminium alloys).

GapLand

Included angle

Angle ofbevel

Root

radius

Rootface


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Single V preparation with backing strip

Backing strips allow the production of full penetration welds with increasedcurrent and hence increased deposition rates/productivity without thedanger of burn-through. Backing strips can be permanent or temporary.Permanent types are of the same material being joined and are tack weldedin place. The main problems related with this type of weld are poor fatigueresistance and the probability of crevice corrosion between the parent metaland the backing strip. It is also difficult to examine by NDT due to the built-in

crevice at the root of the joint. Temporary types include copper strips,ceramic tiles and fluxes.

Single bevel preparation

Double bevel preparation


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Single J preparation

Double J preparation

All these preparations (single/double bevel and single/double J) can be usedon T joints as well. Double preparations are recommended in case of thicksections. The main advantage of these preparations is that only onecomponent is prepared (cheap, can allow for small misalignments).

For further details regarding weld preparations, please refer to BS EN ISO9692 standard.

2.5 Size of butt welds

Full penetration but t weld

Actual throatthickness

Design throatthickness


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Partial penetration butt weld

As a general rule:

Actual throat thickness = design throat thickness + excess weld metal.

Full penetration butt weld ground flush

Butt weld between two plates of d ifferent thickness

Run (pass)The metal melted or deposited during one passage of an electrode, torch orblowpipe.

Single run weld Multi run weld

Design throat thickness= thickness ofthethinner plate

Actual throat thickness =maximumthicknessthrough the joint



Actual throat thickness=design throatthickness


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LayerA stratum of weld metal consisting of one or more runs.Types of butt weld (from accessibility point of view):

Single side weld Double side weld

2.6 Fillet weld

A fusion weld, other than a butt, edge or fusion spot weld, which isapproximately triangular in transverse cross section.

2.6.1 Size of fil let welds

Unlike butt welds, fillet welds can be defined using several dimensions.

Actual throat th icknessThe perpendicular distance between two lines, each parallel to a line joiningthe outer toes, one being a tangent at the weld face and the other beingthrough the furthermost point of fusion penetration.

Design throat thicknessThe minimum dimension of throat thickness used for purposes of design.Also known as effective throat thickness, symbolised on the drawing with a.

Leg lengthThe distance from the actual or projected intersection of the fusion facesand the toe of a fillet weld, measured across the fusion face, symbolised onthe drawing with z.

Leg length



Leg length


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2.6.2 Shape of fil let welds

Mitre fillet weldFlat face fillet weld in which the leg lengths are equal within the agreedtolerance. The cross section area of this type of weld is considered to be aright angle isosceles triangle with a design throat thickness a and a leglength z. The relation between design throat thickness and leg length is:

a = 0,707 z. or z = 1,41 a.

Convex fi llet weldFillet weld in which the weld face is convex. The above relation between theleg length and the design throat thickness written in case of mitre fillet weldsis also valid for this type of weld. Since there is an excess weld metalpresent in this case, the actual throat thickness is bigger than the designthroat thickness.

Concave fillet weldFillet weld in which the weld face is concave. The above relation between

the leg length and the design throat thickness written in case of mitre filletwelds is not valid for this type of weld. Also, the design throat thickness isequal to the actual throat thickness. Due to the smooth blending betweenthe weld face and surrounding parent material, the stress concentrationeffect at the toes of the weld is reduced compared with the previous type.This is why this weld is highly desired in case of applications subjected tocyclic loads where fatigue phenomena might be a major cause for failure.


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Asymmetrical fi llet weldFillet weld in which the vertical leg length is not equal with the horizontal leglength. The relation between the leg length and the design throat thicknesswritten in case of mitre fillet welds is not valid for this type of weld becausethe cross section is not an isosceles triangle.

Throatsize

Verticalleg size

Horizontal

leg size

Deep penetration fillet weldFillet weld with a deeper than normal penetration. It is produced using highheat input welding processes (ie SAW or MAG with spray transfer). Thistype of weld uses the benefits of greater arc penetration to obtain therequired throat thickness whilst reducing the amount of deposited metalneeded, thus leading to a reduction in residual stress level. In order toproduce a consistent and constant penetration, the travel speed must be

kept constant, at a high value. As a consequence, this type of weld isusually produced using mechanised or automatic welding processes. Also,the high depth-to-width ratio increases the probability of solidificationcentreline cracking. In order to differentiate this type of welds from theprevious types, the throat thickness is symbolised with s instead of a.


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2.6.3 Compound of butt and fil let welds

A combination of butt and fillet welds used in case of T joints with full orpartial penetration or butt joints between two plates with different thickness.Fillet welds added on top of the groove welds improve the blending of weldface towards parent metal surface and reduce the stress concentration atthe toes of the weld.

2.7 Welding posi tion, weld slope and weld rotation

Weld posi tionThe orientation of a weld expressed in terms of working position, weld slopeand weld rotation (for further details, please see ISO 6947).

Weld slopeThe angle between root line and the positive X axis of the horizontalreference plane, measured in mathematically positive direction (ie counter-clockwise).

Weld rotationThe angle between the centreline of the weld and the positive Z axis or a

line parallel to the Y axis, measured in the mathematically positive direction(ie counter-clockwise) in the plane of the transverse cross section of theweld in question.

Double bevel compound weld

Filletweld

Bevelweld


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Welding position Sketch Definition

Flat A welding position in whichthe welding is horizontal,with the centreline ofthe weld vertical. Symbol

according ISO 6947 PA.Horizontal-vertical A welding position in which

the welding is horizontal(applicable in case of filletwelds). Symbol accordingISO 6947 PB

Horizontal A welding position in whichthe welding is horizontal,with the centreline of theweld horizontal. Symbolaccording ISO 6947 PC

Vertical up A welding position in whichthe welding is upwards.

Symbol according ISO 6947 PF.

Vertical down A welding position in whichthe welding is downwards.Symbol according ISO 6947 PG

Overhead A welding position in whichthe welding is horizontal andoverhead, with the centre-line of the weld vertical.Symbol according ISO 6947 PE.

Horizontal-overhead

A welding position in whichthe welding is horizontal andoverhead (applicable incase of fillet welds). Symbolaccording ISO 6947 PD.

PF

PG


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Tolerances for the welding positions.

2.8 Weaving

Transverse oscillation of an electrode or blowpipe nozzle during thedeposition of weld metal. This technique is generally used for vertical upwelds.

Stringer beadA run of weld metal made with little or no weaving motion.


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Section 3

Planning


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Rev 1 January 2011Planning



3 Planning

3.1 General

The Senior Welding Inspector is usually involved in planning for inspectionat one or more of the following stages of a project:

Pre-contractIdentification of the job requirements, recruiting and allocating suitablytrained and qualified staff, gathering together relevant normativedocuments, technical data and drawings, producing work/inspectionschedules and quality plans as well as general administration.

In-contract Application of inspection methodologies to the requirements of thecontract specification, production and collection of inspection and testreports/documentation.

Post-contractCompilation of inspection reports, certification and test data.

There are a number of methods of planning for inspection activities, themethod selected being dependant on a number of factors, primarily therequirements of the client and the specific project.

The various methods are:

In-situ inspection; an inspector(s) placed permanently at the work place. Theinspector would be expected to work independently, responsible for using

the allocated inspection time in a useful and expedient manner. Periodicvisits to the work place would be made by the Senior Inspector.

3.2 Gantt charts

Gantt charts define stages of production and estimated work time for eachstage.

A Gantt chart is a popular type of bar chart/graph that illustrates a projectschedule ie list of a project's terminal elements. Terminal elements comprisethe work breakdown structure (WBS) of the project and are the lowestactivity or deliverable, with intended start and finish dates. Terminalelements are not further subdivided.

Terminal elements are the items that are estimated in terms of resourcerequirements, budget and duration linked by dependencies and schedules.

An example of a typical Gantt chart that could be used to plan inspectionactivities for either manufacturing or construction is shown below.

The WBS/task elements are listed on the left hand side and the start andcompletion of each activity is represented by a bar to the right of the activity.


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The time period in this example is represented in months, both planned andactual. Some Gantt charts may show time in weeks, which can also bebroken down into days.

Example of a Gantt chart

Any Project Phase 1 Inspection Schedule

Workbreakdownstructure

(WBS)

2011

January February March April May June

Recruit andallocateinspection staff

Reviewfabricationdrawings

Review WPSs,WPQRsandWATCs

Witness and testWPSs, WPQRs

Witness welderqualificationtests

Prepare qualityplans

Visualinspection offirstproduction

welds

Legend

Planned duration

Actual durat ion

Planned milestone

Actual milestone


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3.3 Crit ical path analysis (CPA)

Critical path analysis (CPA) is a powerful project management tool thathelps to schedule and manage complex projects. Developed in the 1950s tocontrol large defence projects, CPA has been used routinely since then. As

with Gantt charts, CPA helps plan all tasks that must be completed as partof a project. They act as the basis both for preparation of a schedule and ofresource planning. During management of a project, they allow monitoringof achievement of project goals.

CPA can also show where remedial action needs to be taken in order to geta project back on course.

The benefit of using CPA over Gantt charts is that CPA formally identifiestasks which must be completed on time in order for the whole project to becompleted on time and also identifies which tasks can be delayed for a while

if resources need to be reallocated to catch up on missed tasks.

A further benefit of CPA is that it helps to identify the minimum length of timeneeded to complete a project. Where there is a need to run an acceleratedproject, fast track, it helps to identify which project steps should beaccelerated in order to complete the project within the available time. Thishelps to minimise cost while still achieving objectives.

The disadvantage of CPA is that the relation of tasks to time is not asimmediately obvious as with Gantt charts. This can make them more difficultto understand for someone who is not familiar with the technique.

CPA is presented using circle and arrow diagrams. The circles show eventswithin the project, such as the start and finish of tasks. Circles are normallynumbered to allow identification of them. An arrow running between twoevent circles shows the activity needed to complete that task. A descriptionof the task is written underneath the arrow. The length of the task is shownabove it. By convention, all arrows run left to right.

An example of a very simple diagram is shown below:

Simple circle and arrow

1 24 Wks

Recruit & allocate

inspection

staffSimple Circle and Arrow

0 4A

START


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This shows the start event (circle 1) and the completion of the recruit andallocate inspection staff task (circle 2). The arrow between the two circlesshows the activity of carrying out recruit and allocates inspection staff. Thetime allocated for this activity is 4 weeks.

In the example above, the numbers above the circles show the earliestpossible time that this stage of the project will be reached.

Where one activity cannot start until another has been completed and whenother activities need to be scheduled it is useful to tabulate the terminalelements and allocate time against each activity. For example the inspectionactivities for a project could be shown as:

IdentificationTerminalelement/activity

Scheduledcompletion

Timeallocated

A

Recruit and allocate

inspection staff

To be completed first

4 weeks

B

Review fabricationdrawings, materialand consumablecertificates

Start when A iscompleted

2 weeks

CReview WPSs,WPQRs andWATCs

Start when A iscompleted 2 weeks

D

Prepare quality plansand identify

inspectionrequirements

Start when B iscompleted

3 weeks

EWitness and testWPSs andWPQRSs

Start when C iscompleted 2 weeks

FWitness welderqualification tests

Start when C, D andE are completed

2 weeks

GVisual inspection andtesting of productionwelds

Start when F iscompleted 9 weeks

Total time allocated 24 weeks

The above tabulated terminal elements can now be shown as an algorithm,see the following example


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3-5

Critical path analysis for example inspection project.

Start 1 2 3 5 6

4

A B D

CE

F

4 wks 2 wks 3 wks 2 wks

2wks

2wks0 4 6

6

11 13


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In the example, the activities of B and C cannot be started until A has beencompleted.

This diagram also brings out a number of other important points:

Within CPA, reference to activities is made by the numbers in the circlesat each end. For example, task A would be called activity 1-2.

Task B would be activity 2-3.

Activities are not drawn to scale. In the diagram above, activities are 8,4, 3 and 2 weeks long.

In the example the numbers above the circles indicate the earliestpossible time that this stage in the project will be reached.

CPA is an effective and powerful method of assessing:

What tasks must be carried out.

Where parallel activity can be performed.

The shortest time in which you can complete a project.

Resources needed to execute a project.

The sequence of activities, scheduling and timings involved.

Task priorities.

The most efficient way of shortening time on urgent projects..

An effective CPA can make the difference between success and failure oncomplex projects. It can be very useful for assessing the importance ofproblems faced during the implementation of the plan.

3.4 Programme evaluation and review technique (PERT)

PERT is a variation on CPA but takes a more sceptical view of timeestimates made for each project stage. To use it, estimate the shortestpossible time each activity will take, the most likely length of time and thelongest time that might be taken if the activity takes longer than expected.

The formula below is used to calculate the time for each project stage:

Shortest time + 4 x likely time + longest time

6

This helps to bias time estimates away from the unrealistically short time-scales normally assumed.

A variation of both CPA and PERT is a technique known as reversescheduling, which the completion date for the last terminal element for theproject is determined and then all other operations are worked back fromthis date, each operation having its own target date.


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3.5 Summary

The Senior Welding Inspector doe not need to have an in-depth knowledgeof planning and would not be responsible for the planning of inspectionactivities on a large project or contract; this would be the responsibility of the

planning team or planning department.

However the SWI does need to have a basic understanding of projectplanning as inspection tasks must link in with other terminal activities toensure that inspection tasks are carried out on a timely and cost effectivebasis, in accordance with the planning system being used on a particularproject or contract.


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Section 4

Codes and Standards


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4.3 Auditing

Auditing is a term originating from accountancy practice which involves anindependent accountant checking the accounts of a company to see if theaccounts are fair and accurate. A similar checking process is now widely

practised in manufacturing and construction industries and inspectionpersonnel will be involved in the carrying out of this operation.

Different types of audits may be performed:

Full audit of a company, usually carried out by a third party such as aCertifying Authority, checking the company for the award of a QAaccreditation system such as ISO 9000 or ASME stamp.

Major audit by a potential customer prior to placement of a largecontract. This is usually carried out to demonstrate the company has allthe necessary facilities, plant, machinery, personnel and quality systems

in place to enable them to successfully complete the contract. Part audits carried out as ongoing demonstration that the quality system

is working properly.

An example of the latter case would be where a Senior Inspector isresponsible for signing-off the data book or release certificate for a product.After checking that all the necessary documents are in the package and thatthey have been correctly completed and approved where necessary, theSWI would look at a part of the job a beam, a piece of pipework etc andcrosscheck against the drawings, mill certificates, inspection reports etc thatall comply with the job requirements.

4.4 Codes and standards

It is not necessary for the Inspector to carry a wide range of codes andstandards in the performance of his/her duties. Normally the specification ormore precisely the contract specification is the only document required.However the contract specification may reference supporting codes andstandards and the inspector should know where to access these normativedocuments.

The following is a list of definitions relating to codes and standards which

the Inspector may come across whilst carrying inspection duties

4.4.1 Definitions

Normative document:Provides rules, guidelines or characteristics for activities or their results.

The term normative document is generic and covers documents such asstandards, technical specifications, codes of practice and regulations.*


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StandardDocument established by consensus and approved by a recognised body.

A standard provides, for common and repeated use, guidelines, rules, andcharacteristics for activities or their results, aimed at the achievement of the

optimum degree of order in a given context. *

Harmonised standardsStandards on the same subject approved by different standardising bodies,that establish interchangeability of products, processes and services, ormutual understanding of test results or information provided according tothese standards*

Code of practiceDocument that recommends practices or procedures for the design,manufacture, installation, maintenance, utilisation of equipment, structures

or products.

A code of practice may be a standard, part of a standard or independent ofa standard.*

RegulationDocument providing binding legislative rules that is adopted by anauthority.*

Author ityBody (responsible for standards and regulations legal or administrativeentity that has specific tasks and composition) that has legal powers andrights.*

Regulatory authorityAuthority responsible for preparing or adopting regulations.*

Enforcement authori tyAuthority responsible for enforcing regulations.*

Specification

Document stating requirements. Meaning full data and its supportingmedium stating needs or expectations that is stated, generally implied orobligatory.**

ProcedureSpecified way to carry out an activity or a process.* Usually it is a writtendescription of all essential parameters and precautions to be observed whenapplying a technique to a specific application following an establishedstandard, code or specification


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Instruction Written description of the precise steps to be followed based on anestablished procedure, standard, code or specification.

Quality plan

A document specifying which procedures and associated resources shall beapplied by whom and when to a specific project, product, process orcontract.*

* ISO IEC Guide 2 Standardisation and related activities General vocabulary.** EN ISO 9000 2000 Quality management systems Fundamentals andvocabulary.

4.5 Summary

Application of the requirements of the quality manuals, the standards andcodes of practice ensure that a structure or component will have anacceptable level of quality and be fit for the intended purpose.

Applying the requirements of a standard, code of practice or specificationcan be a problem for the inexperienced Inspector. Confidence in applyingthe requirements of one or all of these documents to a specific applicationonly comes with use over a period of time.

If in doubt the Inspector must always refer to a higher authority in order toavoid confusion and potential problems.


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BS No. Title

BS499: Part 1 Glossary of welding terms.

BS 709 Methods of destructive testing fusion welded joints and weld

metal in steel.BS 1113 Specification for design and manufacture of water-tube steam

generating plant.

BS 1453 Specification for filler materials for gas welding.

BS 1821 Specification for class I oxy -acetylene welding of ferritic steelpipe work for carrying fluids.

BS 2493 Low alloy steel electrodes for MMA welding

BS 2633 Specification for class I arc welding of Ferritic steel pipe work forcarrying fluids.

BS 2640 Specification for class II oxy - acetylene welding of carbon steelpipe work

for carrying fluids.BS 2654 Specification for manufacture of vertical steel welded non-

refrigerated storage tanks with butt-welded shells for thepetroleum industry.

BS 2901 Part 3: Filler rods and wires for copper and copper alloys.

BS 2926 Specification for chromium & chromium-nickel steel electrodesfor MMA

BS 2926 Specification for chromium & chromium-nickel steel electrodesfor MMA

BS 3019 TIG welding.

BS 3604 Steel pipes and tubes for pressure purposes; Ferritic alloy steel

with specified elevated temperature properties for pressurepurposes.

BS 3605 Specification for seamless tubes.

BS 4515 Specification for welding of steel pipelines on land andoffshore.

BS 4570 Specification for fusion welding of steel castings.

BS 4677 Specification for arc welding of austenitic stainless steel pipework for carrying fluids.

BS 4872 Part 1: Approval testing of welders when procedure approval is notrequired. Fusion welding of steel.

BS 4872 Part 2: TIG or MIG welding of aluminium and its alloys.

BS 6323 Specification for seamless and welded steel tubes forautomobile, mechanical and general engineering purposes.

BS 6693 Method for determination of diffusible hydrogen in weld metal.

BS 6990 Code of practice for welding on steel pipes containing processfluids or their residues.

BS 7191 Specification for weldable structural steels for fixed offshorestructures.

BS 7570 Code of practice for validation of arc welding equipment.


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BS EN No Title

BS EN 287 Part 1: Qualification test of welders - Fusion welding - Steels.

BS EN 440 Wire electrodes and deposits for gas shielded metal arcof non-alloy and f ine grain steels.

BS EN 499 Covered electrodes for manual metal arc welding of nonalloy and fine grain steels.

BS EN 3834-Parts 1 to 5

Quality requirements for fusion welding of metallicmaterials

BS EN 756 Wire electrodes and flux wire combinations for submergedarc welding of non-alloy and fine grain steels.

BS EN 760 Fluxes for submerged arc welding.

BS EN 970 Non-destructive examination of fusion welds - visualexamination.

BS EN 910 Destructive tests on welds in metallic materials - Bend tests.

BS EN 12072 Filler rods and wires for stainless steels.

BS EN ISO 18274 Aluminium and aluminium alloys & magnesium alloys. Nickel& nickel alloys.

Note:The Inspector should have an awareness of standards pr inted in bold.

BS EN NUMBER TITLE

BS EN 1011Part 1:Part 2:Part 3Part 4.

Welding recommendations for welding of metallic materialGeneral guidance for arc welding.Arc welding of ferr it ic steels.Arc welding of stainless steelsArc welding of aluminium and aluminium alloys.

EN 1320 Destructive tests on welds in metallic materials.EN 1435 Non-destructive examination of welds - Radiographic

examination of welded joints.

BS EN 10002 Tensile testing of metallic materials.

BS EN 10020 Definition and classification of grades of steel.

BS EN 10027 Designation systems for steels.

BS EN 10045 Charpy impact tests on metallic materials.

BS EN 10204 Metallic products - types of inspection documents.

BS EN 22553 Welded, brazed and soldered joints - symbol icrepresentation on drawings.

BS EN 24063 Welding, brazing, soldering and braze welding of metal.Nomenclature of processes and reference numbers forsymbolic representation on drawings.

BS EN 25817 Arc welded joints in steel. Guidance on quality levels forimperfections.

BS EN 26520 Classif ication of imperfections in metallic fusion welds,with explanations.

BS EN 26848 Specification for tungsten electrodes for inert gas shielded arcwelding and for plasma cutting and welding.


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ISO No Title

ISO 857 - 1 Welding and allied processes - Vocabulary - Part 1 -Metal welding processes.

ISO 6947 Welds - Working posit ions - definitions of angles of slopeand rotation.

ISO 9606 2 Qualification test of welders fusion welding.Part 2 Aluminium & aluminium alloys.

ISO 15607 Specification and qualification of welding procedures formetallic materials - General rules.

ISO 15608 Welding - Guidelines for a metallic material grouping system.

ISO 15609 - 1 Specification and qualification of welding procedures formetallic materials - Welding procedure specification - Part 1:Arc welding.

ISO 15610 Specification and qualification of welding procedures for metallicmaterials- Qualification based on tested welding consumables.

ISO 15611 Specification and qualification of welding procedures for metallic

materials- Qualification based on previous welding experience.ISO 15613 Specification and qualification of welding procedures for metallic

materials - Qualification based on pre-production-welding test.

ISO 15614 Specification and qualification of welding procedures formetallic materials - Welding procedure test.

Part 1

Part 2Part 3Part 4Part 5

Part 6Part 7Part 8Part 9:Part 10Part 11Part 12Part 13

Arc and gas welding of steels and arc welding of nickel and nickelalloys.Arc welding of aluminium and its alloys*Welding procedure tests for the arc welding of cast irons*Finishing welding of aluminium castings*Arc welding of titanium, zirconium and their alloys.

Copper and copper alloys*Not usedWelding of tubes to tube-plate joints.Underwater hyperbaric wet welding*Hyperbaric dry welding*Electron and laser beam weldingSpot, seam and projection welding*Resistance butt and flash welding*

Note:The Inspector should have an awareness of standards pr inted in bo ld.*Proposed


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Section 5

Calibration ofWelding Equipment


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5 Calibration of Welding Equipment

5.1 Introduction

BS 7570 - Code of practice for validation of arc welding equipment astandard that gives guidance to:

Manufacturers about the accuracy required from output meters fitted towelding equipment to show welding current and voltage, etc.

End users who need to ensure that the output meters provide accuratereadings.

The Standard refers to two grades of equipment - standard and precisiongrade.

Standard grade equipment is suitable for manual and semi-automatic

welding processes.

Precision grade equipment is intended for mechanised or automatic weldingbecause there is usually a need for greater precision for all weldingvariables as well as the prospect of the equipment being used for higherduty cycle welding.

5.2 Terminology

BS 7570 defines the terms it uses such as:

CalibrationOperations for determining the magnitude of errors of a measuring instrument,etc.

ValidationOperations for demonstrating an item of welding equipment or weldingsystem conforms to the operating specification for that equipment or system.

AccuracyCloseness of an observed quantity to the defined, or true, value.

Thus, when considering welding equipment, those that have output metersfor welding parameters (current, voltage and travel speed, etc.) can becalibrated by checking the meter reading with a more accurate measuringdevice and adjusting the readings appropriately.

Equipment that does not have output meters (some power sources forMMA, MIG/MAG) cannot be calibrated but they can be validated, that is tomake checks to see that the controls are functioning properly.


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5.3 Calibration frequency

BS 7570 recommends re-calibration/validation at:

Yearly intervals (following an initial consistency test at 3 monthly

intervals) for standard grade equipment. Six monthly intervals for precision grade equipment.

However, the Standard also recommends that re-calibration/validation maybe necessary more frequently. Factors to consider are:

Equipment manufacturers recommendations.

Users requirements.

If the equipment has been repaired it should always be re-calibrated.

If there is reason to believe the performance of the equipment hasdeteriorated.

5.4 Instruments for calibration

Instruments used for calibration should:

Be calibrated by a recognised calibrator using standards traceable to anational standard.

Be at least twice and preferably five times, more accurate than theaccuracy required for the grade of equipment.

For precision grade equipment it will be necessary to use instrumentswith much greater precision for checking output meters.

5.5 Calibration methods

The Standard gives details about the characteristics of power source types,how many readings should be taken for each parameter and guidance onprecautions that may be necessary.

For the main welding parameters the Standard recommends:

CurrentDetails are given about the instrumentation requirements and how to

measure pulsed current but there are requirements specified, orrecommendations made, about where in the circuit current measurementsshould be made. The implication is that current can be measured at anyposition in the circuit the value should be the same.

VoltageThe standard emphasises that for processes where voltage is pre-set (onconstant voltage the power sources) the connection points used for thevoltmeter incorporated into the power source may differ from the arcvoltage, which is the important parameter. To obtain an accurate measure ofarc voltage, the voltmeter should be positioned as near as practical to the

arc.


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Power

Source

Wire Feeder

17

{arc voltage4

5

32

6

This is illustrated by the figure belowwhich shows the power source voltagemeter connected across points 1 and 7.

An example of a welding circuit (for MIG/MAG).

However, because there will be some voltage drops in sections 1-2, 3-4 and6-7 due to connection points introducing extra resistance into the circuit, thevoltage meter reading on the power source will tend to give a higher readingthan the true arc voltage.

Even if the power source voltmeter is connected across points 3 and 7(which it may be) the meter reading would not take account of anysignificant voltage drops in the return cable - section 6-7.

The magnitude of any voltage drops in the welding circuit will depend oncable diameter, length and temperature and the Standard emphasises the

following:


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It is desirable to measure the true arc voltage between points 4-5 but forsome welding processes it is not practical to measure arc voltage soclose to the arc.

For MMA, it is possible to take a voltage reading relatively close to the arcby connecting one terminal of the voltmeter through the cable sheath as

close as ~2m from the arc and connect the other terminal to theworkpiece (or to earth).

For MIG/MAG the nearest practical connection points have to be 3-5 buta change from an air-cooled to a water-cooled torch or vice-versa mayhave a significant effect on the measured voltage.

Voltage drops between points 5-6 will be insignificant if there is a goodconnection of the return cable at point 6.

The Standard gives guidance about minimising any drop in line voltage byensuring that:

The current return cable is as short as practical and is heavy, lowresistance, cable.

The current-return connector is suitably rated and firmly attached and sodoes not overheat due to high resistance.

The standard gives data for line voltage drops (DC voltage) according tocurrent, cable cross section and cable length (for both copper andaluminium cables).

Wire feed speed

For constant voltage (self-adjusting arc) processes such as MIG/MAG thestandard recognises that calibration of the wire feeder is generally notneeded because it is linked to current.

If calibration is required, it is recommended that the time be measured (inseconds) for ~1m of wire to be delivered (using a stopwatch or electronictimer).

The length of wire should then be measured (with a steel rule) to anaccuracy of 1mm and the feed speed calculated.

Travel speedWelding manipulators, such as rotators and robotic manipulators, as well asthe more conventional linear travel carriages, influence heat input and otherproperties of a weld and should be checked at intervals.

Most of the standard devices can be checked using a stopwatch andmeasuring rule, but more sophisticated equipment, such as a tacho-generator, may be appropriate.


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Section 6

Destructive Testing


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6 Destruct ive Testing

6.1 Introduction

European Welding Standards require test coupons that are made forwelding procedure qualification testing to be subjected to non-destructivetesting and then destructive testing.

The tests are called destructive tests because the welded joint is destroyedwhen various types of test piece are taken from it.

Destructive tests can be divided into 2 groups, those used to:

Measure a mechanical property quantitative tests

Assess the joint quality qualitative tests

Mechanical tests are quantitative because a quantity is measured amechanical property such as tensile strength, hardness and impacttoughness.

Qualitative tests are used to verify that the joint is free from defects theyare of sound quality - and examples of these are bend tests, macroscopicexamination and fracture tests (fillet fracture and nick-break).

6.2 Test types, test pieces and test object ives

Various types of mechanical tests are used by material manufacturers andsuppliers to verify that plates, pipes, forgings, etc. have the minimumproperty values specified for particular grades.

Design engineers use the minimum property values listed for particulargrades of material as the basis for design and the most cost-effectivedesigns are based on an assumption that welded joints have properties thatare no worse than those of the base metal.

The quantitative (mechanical) tests that are carried out for weldingprocedure qualification are intended to demonstrate that the joint propertiessatisfy design requirements.

The emphasis in the following sub-sections is on the destructive tests andtest methods that are widely used for welded joints.

6.2.1 Transverse tensile tests

Test objectiveWelding procedure qualification tests always require transverse tensile teststo show that the strength of the joint satisfies the design criterion.

Test specimensA transverse tensile test piece typical of the type specified by EuropeanWelding Standards is shown below.


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Standards, such as EN 895, that specify dimensions for transverse tensiletest pieces require all excess weld metal to be removed and the surface tobe free from scratches.

Test pieces may be machined to represent the full thickness of the joint but

for very thick joints it may be necessary to take several transverse tensiletest specimens to be able to test the full thickness.

Test methodTest specimens are accurately measured before testing. Specimens arethen fitted into the jaws of a tensile testing machine and subjected to acontinually increasing tensile force until the specimen fractures.

The tensile strength (Rm) is calculated by dividing the maximum load by thecross-sectional area of the test specimen - measured before testing.

The test is intended to measure the tensile strength of the joint andthereby show that the basis for design, the base metal properties, remainsthe valid criterion.

Acceptance cri ter iaIf the test piece breaks in the weld metal, it is acceptable provided thecalculated strength is not less than the minimum tensile strength specified,which is usually the minimum specified for the base metal material grade.

In the ASME IX code, if the test specimen breaks outside the weld or fusion

zone at a stress above 95% of the minimum base metal strength the testresult is acceptable.

6.2.2 All -weld tensile tests

Test objectiveThere may be occasions when it is necessary to measure the weld metalstrength as part of welding procedure qualification particularly for elevatedtemperature designs.

The test is carried out in order to measure not only tensile strength but alsoyield (or proof strength) and tensile ductility.

Parallellength


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All weld tensile tests are also regularly carried out by welding consumablemanufacturers to verify that electrodes and filler wires satisfy the tensileproperties specified by the standard to which the consumables are certified.

Test specimens

As the name indicates, test specimens are machined from welds parallelwith their longitudinal axis and the specimen gauge length must be 100%weld metal.

Test methodSpecimens are subjected to a continually increasing force in the same waythat transverse tensile specimens are tested.

Yield (Re) or proof stress (Rp) are measured by means of an extensometerthat is attached to the parallel length of the specimen and is able toaccurately measure the extension of the gauge length as the load isincreased.

Round tensile specimen from a weldingprocedure qualification test piece.

Round tensile specimen from anelectrode classification test piece.


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Typical load extension curves and their principal characteristics are shownbelow.

Tensile ductility is measured in two ways:

% elongation of the gauge length (A%).

% reduction of area at the point of fracture (Z%).

Load-extension curve for a steel thatshows a distinct yield point at theelastic limit.

Load-extension curve for a steel (or othermetal) that does not show a distinct yieldpoint; proof stress is a measure of theelastic limit.


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The figures below illustrate these two ductility measurements.

6.2.3 Impact toughness tests

Test objectiveCharpy V notch test pieces have become the internationally acceptedmethod for assessing resistance to brittle fracture by measuring the energyto initiate, and propagate, a crack from a sharp notch in a standard sizedspecimen subjected to an impact load.

Design engineers need to ensure that the toughness of the steel that is usedfor a particular item will be high enough to avoid brittle fracture in serviceand so impact specimens are tested at a temperature that is related to the

design temperature for the fabricated component.

C-Mn and low alloy steels undergo a sharp change in their resistance tobrittle fracture as their temperature is lowered so that a steel that may havevery good toughness at ambient temperature may show extreme brittlenessat sub-zero temperatures, as illustrated in following figure.


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Test temperature, C

The transition temperature is defined as the temperature mid-way betweenthe upper shelf (maximum toughness) and lower shelf (completely brittle). Inthe above the transition temperature is 20C.

Test specimensThe dimensions for test specimens have been standardised internationallyand are shown below for full sized specimens. There are also standarddimensions for smaller sized specimens, for example 10mm x 7.5mm and10mm x 5mm.

Charpy V notch test piece dimensions for full sized specimens.

Impactenergy(Joules)

Upper shelf energy

Lower shelf energy

Transition range

Ductile fracture(0% crystallin ity)

Brittle fracture(100% crystallinity)


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Specimens are machined from welded test plates with the notch positionlocated in different locations according to the testing requirements buttypically in the centre of the weld metal and at positions across the HAZ asshown below.

Typical notch positions for Charpy V notch test specimens from double V buttwelds.

Test methodTest specimens are cooled to the specified test temperature by immersion inan insulated bath containing a liquid that is held at the test temperature.

After allowing the specimen temperature to stabilise for a few minutes it isquickly transferred to the anvil of the test machine and a pendulum hammerquickly released so that the specimen experiences an impact load behindthe notch.


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The main features of an impact test machine are shown below.

The energy absorbed by the hammer when it strikes each test specimen isshown by the position of the hammer pointer on the scale of the machine.Energy values are given in Joules (or ft-lbs in US specifications).

Impact test specimens are taken in triplicate (3 specimens for each notchposition) as there is always some degree of scatter in the results,particularly for weldments.

Impact specimen on the anvil showing thehammer position at point of impact

Impact testing machine

Charpy V notch test pieces before and after testing


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Acceptance cri ter iaEach test result is recorded and an average value calculated for each set ofthree tests. These values are compared with the values specified by theapplication standard or client to establish whether specified requirementshave been met.

After impact testing, examination of the test specimens provides additionalinformation about their toughness characteristics and may be added to thetest report:

% crystallinity the % of the fracture face that has crystallineappearance which indicates brittle fracture; 100% indicates completelybrittle fracture.

Lateral expansion the increase in width of the back of the specimenbehind the notch as indicated below; the larger the value the tougherthe specimen.

A specimen that exhibits extreme brittleness will show a clean break. Bothhalves of the specimen having a completely flat fracture face with little or nolateral expansion.

A specimen that exhibits very good toughness will show only a small degreeof crack extension, without fracture and a high value of lateral expansion.

6.2.4 Hardness testing

Test objectivesThe hardness of a metal is its resistance to plastic deformation determinedby measuring the resistance to indentation by a particular type of indenter.

A steel weldment with hardness above a certain maximum may besusceptible to cracking, either during fabrication or in service, and weldingprocedure qualification testing for certain steels and applications that require


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the test weld to be hardness surveyed to ensure that are no regions of theweldment that exceed the maximum specified hardness.

Specimens prepared for macroscopic examination can also be used fortaking hardness measurements at various positions of the weldment

referred to as a hardness survey.

Test methodsThere are 3 widely used methods for hardness testing:

Vickers hardness test uses a square-base diamond pyramid indenter.

Rockwell hardness test uses a diamond cone indenter or steel ball.

Brinell hardness test uses a ball indenter.

The hardness value being given by the size of the indentation producedunder a standard load, the smaller the indentation, the harder the metal.

The Vickers method of testing is illustrated below.

2

ddd 21


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Both Vickers and Brinell methods are suitable for carrying out hardnesssurveys on specimens prepared for macroscopic examination of weldments.

A typical hardness survey requires the indenter to measure the hardness inthe base metal (on both sides of the weld), in the weld metal and across the

HAZ (on both sides of the weld).

The Brinell method gives an indentation that is too large to accuratelymeasure the hardness in specific regions of the HAZ and is mainly used tomeasure hardness of base metals.

A typical hardness survey (using Vickers hardness indenter) is shownbelow:

Hardness values are shown on test reports as a number followed by lettersindicating the test method, for example:

240HV10 = hardness 240, Vickers method, 10kg indenter load.

22HRC = hardness 22, Rockwell method, diamond cone indenter(scale C).

238HBW = 238 hardness, Brinell method, tungsten ball indenter.

6.2.5 Crack tip opening displacement (CTOD) testing

Test objectiveCharpy V notch testing enables engineers to make judgements about risksof brittle fracture occurring in steels, but a CTOD test measures a material

property - fracture toughness.

Fracture toughness data enables engineers to carry out fracture mechanicsanalyses such as:

Calculating the size of a crack that would initiate a brittle fracture undercertain stress conditions at a particular temperature.

The stress that would cause a certain sized crack to give a brittle fractureat a particular temperature.

This data is essential for making an appropriate decision when a crack isdiscovered during inspection of equipment that is in-service.


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Test specimensA CTOD specimen is prepared as a rectangular (or square) shaped bar cuttransverse to the axis of the butt weld. A V notch is machined at the centreof the bar, which will be coincident with the test position - weld metal orHAZ.

A shallow saw cut is then put into the bottom of the notch and the specimenis then put into a machine that induces a cyclic bending load until a shallowfatigue crack initiates from the saw cut.

The specimens are relatively large typically having a cross section B x 2Band length ~10B (B = full thickness of the weld). The test piece details areshown below.

Test methodCTOD specimens are usually tested at a temperature below ambient andthe temperature of the specimen is controlled by immersion in a bath ofliquid that has been cooled to the required test temperature.

A load is applied to the specimen to cause bending and induce aconcentrated stress at the tip of the crack and a clip gauge, attached to thespecimen across the mouth of the machined notch, gives a reading of theincrease in width of the mouth of the crack as the load is graduallyincreased.

For each test condition (position of notch and test temperature) it is usualpractice to carry out three tests.


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Below illustrates the main features of the CTOD test.

Fracture toughness is expressed as the distance that the crack tip openswithout initiation of a brittle crack.

The clip gauge enables a chart to be generated showing the increase inwidth of the crack mouth against applied load from which a CTOD value iscalculated.

Acceptance cri ter iaAn application standard or client may specify a minimum CTOD value thatindicates ductile tearing. Alternatively, the test may be for information so thata value can be used for an engineering critical assessment.

A very tough steel weldment will allow the mouth of the crack to open widelyby ductile tearing at the tip of the crack whereas a very brittle weldment willtend to fracture when the applied load is quite low and without any extensionat the tip of the crack.


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CTOD values are expressed in millimetres - typical values might be~12mm and bent so that the full joint thickness is tested (sidein tension).

Longitud inal bendTest specimen taken with axis parallel to the longitudinal axis of a butt weld;

specimen thickness is ~12mm and the face or root of weld may be tested intension.


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Test methodBend tests for welding procedure qualification (and welder qualification) areusually guided bend tests.

Guided means that the strain imposed on the specimen is uniformlycontrolled by being bent around a former with a certain diameter.

The diameter of the former used for a particular test is specified in the code,having been determined by the type of material that is being tested and theductility that can be expected from it after welding and any PWHT.

The diameter of the former is usually expressed as a multiple of thespecimen thickness and for C-Mn steel it is typically 4t (t is the specimenthickness) but for materials that have lower tensile ductility the radius of theformer may be greater than 10t.

The standard that specifies the test method will specify the minimum bendangle that the specimen must experience and this is typically 120-180.

Acceptance cri ter iaBend test pieces should exhibit satisfactory soundness by not showingcracks or any signs of significant fissures or cavities on the outside of the

bend.


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Small indications less than about 3mm in length may be allowed by somestandards.

6.3 Fracture tests

6.3.1 Fillet weld fracturesTest objectiveThe quality/soundness of a fillet weld can be assessed by fracturing testpieces and examining the fracture surfaces.

This method for assessing the quality of fillet welds may be specified byapplication standards as an alternative to macroscopic examination.

It is a test method that can be used for welder qualification testing accordingto European Standards but is not used for welding procedure qualification toEuropean Standards.

Test specimens

A test weld is cut into short lengths (typically 50mm) and a longitudinalnotch is machined into the specimen as shown below. The notch profile maybe square, V or U shaped.

Test methodSpecimens are made to fracture through their throat by dynamic strokes(hammering) or by pressing, as shown below. The welding standard orapplication standard will specify the number of tests (typically 4).

Moving pressHammer stroke


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Test reports should also give a description of the appearance of the fractureand location of any imperfection.

6.4 Macroscopic examination

Transverse sections from butt and fillet welds are required by the EUStandards for welding procedure qualification testing and may be requiredfor some welder qualification testing for assessing the quality of the welds.

This is considered in detail in a separate section of these course notes.

Macro examination Micro examination

Objectives

Detecting weld defects. (macro). Measuring grain size. (micro).

Detecting brittle structures, precipitates.

Assessing resistance toward brittle fracture, cold cracking and corrosionsensitivity.


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European Standards for De

Documents

CSWIP 3.2-Senior Welding Inspector-Level 3-WIS10-Rev 1 January 2011.pdf