Seeking approval - welder testing and welding procedures

TWI Bulletin, March - April 1996

Bill Lucas is Welding Technology Manager for the arc and laser department at TSI, which he joined in 1970. He is an active member on several welding engineering standards committees, including WEE 36, 'Approval Testing of Welding Procedures and Welders'.

Bob Spiller is a Principal Welding Engineer at TWI with many years' experience giving advice and guidance to fabrication companies on engineering standards and industrial codes of practice. He joined TWI in 1965.

Fabrication standards and codes of practice ensure that a structure or component will have an acceptable level of quality and be fit for the intended purpose. Bill Lucas and Bob Spiller explain these approval procedures.

• Application and design
• Specification and approval of welding procedures
• Approval of welders

There are also specific standards covering material specifications, consumables, welding equipment, testing and health and safety. British Standards are used to specify the requirements, for example, in approving a welding procedure, they are not a legal requirement but may be cited by the Regulatory Authority as a means of satisfying the law. Health and Safety guidance documents and codes of practice may also recommend British Standards.

Codes of practice differ from standards in that they are intended to give recommendations and guidance, for example, on the validation of power sources for welding. It is not intended that they should be used as a mandatory or contractual document. Most fabricators will be working to one of the following:

• company or industry specific standards
• national BS (British Standard)
• European BS EN (British Standard European Standard)
• US AWS (American Welding Society) and ASME (American Society or Mechanical Engineers)
• International ISO (International Standards Organisation)

In European countries, the trend is to replace national standards with EN standards in support of the 'Single European Market'. When a European standard becomes available, the national standard must be withdrawn. When there is no equivalent or competing European standard, the national standard can be retained. For example, BS EN 287 replaces BS 4871 but BS 4872 remains as a valid standard.

Standards also include new designations, for example, for welding processes and welding position, Fig.1.

With welded joints, the type of application will determine the level of quality and the fitness-for-purpose demanded of the weld. For example, the demands placed on welds in pressure vessels operating at high temperatures and pressures will be quite different from those welds in bridges which have to withstand fatigue through traffic and wind loads.

An application standard will include guidelines covering materials, design of joints, welding and joining processes, welding procedure, welder qualification and inspection and whether approved welding procedures are required for the type of application and the skill level required of the welder or operator, Table 1. Standards are periodically revised to ensure that the fabrications will meet the performance and service requirements.

Table 1: Examples of application codes and standards and related welding procedure and welder qualification standards

Table 2: Welding procedure, welder qualification approval and quality acceptance standards

Specification and approval of welding procedures and welders

The distinction between a weld procedure approval and a welder qualification approval test can be described as follows:

• The welding procedure approval test is carried out by a fabricator's competent welder to show that the proposed welding procedure will produce a welded joint to satisfy the specified levels of weld quality and mechanical properties.
• The welder qualification approval test is to examine a welder's individual skill in producing a satisfactory test weld. The test may or may not be performed using a qualified welding procedure.

Standard specifications and codes

Fabricators who undertake work to produce structures and components usually require some form of welding procedure and/or welder approval. The requirement for approvals are determined by the relevant application standard - the relevant British and European standards are listed in Table 2.

BS EN 288 Part 3 and ASME IX would be appropriate for welders on high quality work such as pressure vessels, pressure vessel piping and offshore structures and other products where the consequences of failure, stress levels and complexity mean that a high level of welded joint integrity is necessary. In situations where the level of acceptance is less demanding, an approved welding procedure may not be necessary but the welder would be qualified in accordance with the requirements of BS 4872 and AWS D1.1. This fabrication work could be for small to medium building frames and general light structural and non-structural work.

Quality acceptance

Guidance on levels of imperfections in arc welded joints in steel are given in BS EN 25817, defining three levels of acceptance for imperfections. These are: moderate (level D); intermediate (level C) and stringent (level B). Guidance levels for aluminium joints are given in ISO/DIS 10042.2.

Minimising the cost of using fabrication standards

Costs can be minimised for qualifying welding procedures and welders, and in maintaining welder qualifications. Welding engineers at TWI often advise Member Companies on cost-effective methods of meeting the requirements of the new European standards, and over the years have developed the following recommendations:

Welding procedures

• Previous BS welding procedure approvals can remain valid providing the intent of the technical requirements of the new European standard are satisfied. For example, BS 4870 required one transverse tensile or three transverse bend tests which is considered to be equivalent to two transverse tensile and four transverse bend tests in BS EN 288 Part 3.
• For a material thickness of greater than 12mm, impact tests are required in the new standard. However, only the additional tests need be carried out to make a BS 4870 approval equivalent to a BS EN 288 approval.
• The intention of BS EN 288 (the new European standard) is that approval can be obtained by one of the following methods (Fig.2):

  - welding procedure tests part 3 or 4
  - approved welding consumables part 5
  - previous welding experience part 6
  - standard welding procedure part 7
  - pre-production welding test part 8

  Conventional procedure test does not always need to be carried out to gain approval, but each method has certain limits of application regarding, for example, welding process, material and consumable.

• The method of approval of a welding procedure is often a mandatory requirement of an Application Standard, if not, the method can be agreed between the contracting parties: for example, a welding procedure specification may be approved on condition that the manufacturer can prove, with appropriate documentation, that he has previously satisfactorily welded the type of joint and materials in question.

Welder qualification

• The European standard (BS EN 287) for welder qualification recognises only one skill level, but testing may or may not be carried out in accordance with an approved welding procedure; without an approved welding procedure, the welding parameters must be recorded.
• When a welding procedure is not required to be approved (for technical or contractual reasons), the welder can be approved to BS 4872 which is a valid British standard.
• In BS EN 287, the welder's approval can be extended at six-monthly intervals by the employer/welding co-ordinator, for up to two years.
• After two years, prolongation of the welder's qualification will need approval of the examiner or test body, who will require proof that the welder's performance has been of the required quality during the period of validity. Therefore, it is essential that records of work, inspection records, tests and supervisor's comments on the welder's performance are maintained by the company.
• BS EN 287 requires records of volumetric testing (otherwise a retest will be required), but volumetric testing of a production weld within the range of approval will satisfy this requirement.

Conclusion

Fabricators should be aware of the range of national, European and US standards which are commonly used in welding structures and components (examples are given in Table 1 ). Awareness is difficult as new European fabrication standards are not only replacing the national British Standards but also extending their scope. For example, there are currently five parts (3 to 8) of BS EN 288 which cover the various methods of approving welding procedures. Further parts are in preparation which will extend BS EN 288, for example, to cover approval for welding processes such as laser and electron beam welding (EN 288 Part 15).

In the interest of eliminating barriers to trade in the European countries, BS standards will progressively be replaced with BS EN standards. Once work has started on a new European standard, all work on an equivalent national standard must cease, and once the new European standard is made available a national standard must be withdrawn.

Fabricators are, therefore, advised to monitor the work of CEN Technical Committee TC 121 which is responsible for European activities on fabrication standards. This committee has already prepared draft amendments to BS EN 288 Parts 1 to 3 and BS EN 287 Parts 1 and 2. Welding engineers at TWI will help companies keep abreast of developments in standards and when seeking clarification of the new standards. TWI has also developed a range of computer software for storing welder procedure specifications and welder qualifications. Figure 3 and 4 show a typical PC and a screen display from TWI's Weldspec for Windows program.