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Welding Procedure

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For a given application, the main way of ensuring adequate weldquality is to specify the procedure and the skill level of the weldingoperator. Here, the alternative routes for welding procedure approvalare described together with the requirements for welder or weldingoperator approval.

Routes to welding procedure approval

The key document is the Welding Procedure Specification (WPS) whichdetails the welding variables to be used to ensure a welded joint willachieve the specified levels of weld quality and mechanical properties.

The WPS is supported by a number of documents (eg, a record of howthe weld was made, NDE, mechanical test results) which togethercomprise a welding approval record termed the WPAR (BS EN ISO15614) or PQR (ASME).

In both the European and ASME standards, there are a number of 'essential variables' specified which, ifchanged, may affect either weld quality or mechanical properties. Therefore, a change in any of the essentialswill invalidate the welding procedure and will require a new approval test to be carried out. The essentialvariables are detailed in the relevant specification but include material type, welding process, thickness rangeand sometimes welding position.

Fig. 1. Stages in welding and welder approval

The route followed to produce a WPS in BS EN ISO 15614 and the responsibilities of the manufacturer and theExaminer/Examining Body are shown in Fig.1.

The most common method of gaining approval is to carry out an approval test as described in BS EN ISO 15614-1 (steels) and 15614-2 (aluminium and its alloys). The manufacturer initially drafts a preliminary weldingprocedure (pWPS) which is used by one of the manufacturer's competent welders to prove that it is capable ofproducing a welded joint to the specified levels of weld quality and mechanical properties. The weldingprocedure approval record (WPAR) is a record of this weld. If the WPAR is approved by the Examiner, it is usedto finalise one or more WPSs which is the basis for the Work Instructions given to the welder.

It is noteworthy that the welder carrying out a satisfactory welding procedure approval test is approved for theappropriate range of approval given in the relevant standard (BS EN 287/BS EN ISO 9606, ASME IX or AWSD1.1).

The following options for procedure approval are also possible:

Welding procedure test (BS EN ISO 15614)

Approved welding consumable (BS EN ISO 15610)

Previous welding experience (BS EN ISO 15611)

Standard welding procedure (BS EN ISO 15612)

Pre-production welding test (BS EN ISO 15613)

The conventional procedure test (as specified in BS EN ISO 15614) does not always need to be carried out togain approval. But alternative methods have certain limits of application regarding, for example, weldingprocesses, materials and consumables as specified in the appropriate application standard or contractagreement.

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The welding procedure test method of approval is often a mandatory requirement of the Application Standard. Ifnot, the contracting parties can agree to use one of the alternative methods. For example, a welding procedurespecification can be approved in accordance with the requirements of BS EN ISO 15611 (previous experience) oncondition that the manufacturer can prove, with appropriate documentation, that the type of joint haspreviously been welded satisfactorily.

The American standard, ASME IX requires a welding procedure test (PQR) but AWS D1.1 will allow the use ofpre-qualified procedures within the limits detailed in the specification.

Welder approval

The welder approval test is carried out to demonstrate that the welder has the necessary skill to produce asatisfactory weld under the conditions used in production as detailed in the approved WPS or Work Instruction.As a general rule, the test piece approves the welder not only for the conditions used in the test but also for alljoints which are considered easier to weld.

As the welder's approval test is carried out on a test piece which is representative of the joint to be welded, it isindependent of the type of construction. The precise conditions, called 'essential variables', must be specified inthe approval test, eg material type, welding process, joint type, dimensions and welding position. The extent ofapproval is not necessarily restricted to the conditions used for the test but covers a group of similar materialsor a range of situations which are considered easier to weld.

It is important to note that a number of Amendments and Corrigenda have now been issued which affect therange of approval (see list of Relevant Standards).

In BS EN 287/BS EN ISO 9606, the certificate of approval testing is issued under the sole responsibility of theExaminer/Examining Body. The welder approval certificate remains valid subject to the requirements of theapplication standard. In BS EN 287/BS EN ISO 9606, it can be extended at six monthly intervals by the employerfor up to two years provided the welder has been successfully welding similar joints. After two years,prolongation of the welder's qualification will need approval of the Examiner who will require proof that his orher performance has been of the required standard during the period of validity. As the Examiner will normallyexamine the company's records on the welder's work and tests as proof that he has maintained his skill, it isessential that work records are maintained by the company.

It should also be noted that BS EN 287/BS EN ISO 9606 requires records of tests, ie half yearly documentationabout X-ray or ultrasonic inspections or test reports on fracture tests must be maintained with the welder'sapproval certificate (tests on production welds will satisfy this requirement). Failure to comply will necessitate aretest.

American standards have similar requirements although the extent of approval of the welding variables aredifferent to those of BS EN 287/BS EN ISO 9606.

Welding operator approval

When required by the contract or application standard, the welding operators responsible for setting up and/oradjustment of fully mechanised and automatic equipment must be approved but the personnel operating theequipment do not need approval. In clarifying the term 'welding operator', personnel who are using theequipment (loading and unloading robotic equipment or operating a resistance welding machine) do not requireapproval.

As specified in BS EN 1418, approval of operators of equipment for fusion welding and resistance weldequipment setters can be based on:

welding a procedure test

pre-production welding test or production test

production sample testing or a function test.

It should be noted that the methods must be supplemented by a functional test appropriate to the welding unit.However, a test of knowledge relating to welding technology which is the equivalent of 'Job knowledge forwelders' in BS EN 287/BS EN ISO 9606 is recommended but not mandatory.

Prolongation of the welding operator approval is generally in accordance with the requirements of BS EN 287/BSEN ISO 9606. The welding operator's approval remains valid for two years providing the employer/welding co-ordinator confirms that there has been a reasonable continuity of welding work (period of interruption no longerthan six months) and there is no reason to question the welding operator's knowledge.

The validity of approval may be prolonged for further periods of two years by the examiner / examining bodyproviding there is proof of production welds of the required quality, and appropriate test records maintainedwith the operator's certificate.

When working to ASME IX, operators for both mechanised and automatic welding equipment require approval.The essential variables are different to those in welder approval.

Relevant Standards

BS EN 287-1:2004 Qualification test of welders - fusion welding - Part 1: steels

BS EN ISO 15614Specification and qualification of welding procedures for metallic materials - Welding Procedure test. Part 1 Arcand gas welding of steels and arc welding of nickel and nickel alloys.

Part 2: Arc welding of aluminium and its alloys

Part 3: Fusion and pressure welding of non-alloyed and low-alloyed cast irons

Part 4: Finishing welding of aluminium castings

Part 5: Arc welding of titanium, zirconium and their alloys

Part 6: Arc and gas welding of copper and its alloys

Part 7: Overlay welding

Part 8: Welding of tubes to tube-plate joints

Part 9: Underwater hyperbaric wet welding

Part 10: Hyperbaric dry welding

Part 11: Electron and laser beam welding

Part 12: Spot, seam and projection welding

Part 13: Resistance butt and flash welding

BS EN ISO 9606-2: 2004

Qualification test of welders - fusion welding. Part 2: Aluminium and aluminium alloys

BS EN ISO 15612: 2004Specification and qualification of welding procedures for metallic materials - Qualification by adoption of astandard welding procedure.

BS EN ISO 15610: 2003Specification and qualification of welding procedures for metallic materials - Qualification based on testedwelding consumables.

BS EN ISO 15611: 2003Specification and qualification of welding procedures for metallic materials - Qualification based on previouswelding experience.

BS EN 1418 : 1998 Welding personnel - Approval testing of welding operators for fusion welding and resistanceweld setters for fully mechanised and automatic welding of metallic materials

Bill Lucas prepared the information in this article in collaboration with Oliver Smith, John Weston and GeneMathers.

For further information on WPSs see Welding Procedures

For more information and/or techncial enquiries please contact us.

TWI Ltd, Granta Park, Great Abington, Cambridge, CB21 6AL, United Kingdom Tel: +44 (0)1223 899000

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