Standards - Approval of welding procedures, welders and welding
operators
For a given application, the main way of ensuring adequate
weld quality is to specify the procedure and the skill level of the
welding operator. Here, the alternative routes for welding procedure
approval are described together with the requirements for welder or
welding operator approval.
AC TIG welding of aluminium cryogenic pressure vessel
Courtesy
of Air Products PLC
Routes to welding procedure approval
The key document is the
Welding Procedure Specification (WPS) which details the welding variables
to be used to ensure a welded joint will achieve the specified levels of
weld quality and mechanical properties.
The WPS is
supported by a number of documents (eg a record of how the weld was made,
NDE, mechanical test results) which together comprise a welding approval
record termed the WPAR (EN288) or PQR (ASME).
In both the European and ASME standards, there are a number of
'essential variables' specified which, if changed, may affect either weld
quality or mechanical properties. Therefore, a change in any of the
essentials will invalidate the welding procedure and will require a new
approval test to be carried out. The essential variables are detailed in
the relevant specification but include material type, welding process,
thickness range and sometimes welding position.
The route followed to produce a WPS in EN 288 and the responsibilities
of the manufacturer and the Examiner/Examining Body are shown in Fig.
1.
Fig. 1. Stages in welding and welder approval
The
most common method of gaining approval is to carry out an approval test as
described in EN 288 Pt3 (steels) and Pt4 (aluminium and its alloys). The
manufacturer initially drafts a preliminary welding procedure (pWPS) which
is used by one of the manufacturer's competent welders to prove that it is
capable of producing a welded joint to the specified levels of weld
quality and mechanical properties. The welding procedure approval record
(WPAR) is a record of this weld. If the WPAR is approved by the Examiner,
it is used to 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 the appropriate range of approval
given in the relevant standard (EN 287, ASME IX or AWS D1.1).
EN 288 also permits the following options for procedure approval:
- Welding procedure test
- Approved welding consumable
- Previous welding experience
- Standard welding procedure
- Pre-production welding test
The conventional procedure test (as specified in Parts 3 or 4) does not
always need to be carried out to gain approval. But alternative methods
have certain limits of application regarding, for example, welding
processes, materials and consumables as specified in the appropriate
application standard or contract agreement.
The welding procedure test method of approval is often a mandatory
requirement of the Application Standard. If not, the contracting parties
can agree to use one of the alternative methods. For example, a welding
procedure specification can be approved in accordance with the
requirements of Part 6 (previous experience) on condition that the
manufacturer can prove, with appropriate documentation, that the type of
joint has previously been welded satisfactorily.
The American standard, ASME IX requires a welding procedure test (PQR)
but AWS D1.1 will allow the use of pre-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 a
satisfactory 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 all joints 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 is independent of the type of
construction. The precise conditions, called 'essential variables', must
be specified in the approval test eg material type, welding process, joint
type, dimensions and welding position. The extent of approval is not
necessarily restricted to the conditions used for the test but covers a
group of similar materials or 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 the range of approval (see list of Relevant
Standards).
In EN 287, the certificate of approval testing is issued under the sole
responsibility of the Examiner / Examining Body. The welder approval
certificate remains valid subject to the requirements of the application
standard. In EN 287, it can be extended at six monthly intervals by the
employer for 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 or her performance has been of the required standard during the
period of validity. As the Examiner will normally examine the company's
records on the welder's work and tests as proof that he has maintained his
skill, it is essential that work records are maintained by the company.
It should also be noted that EN 287 requires records of tests ie half
yearly documentation about X-ray or ultrasonic inspections or test reports
on fracture tests must be maintained with the welder's approval
certificate (tests on production welds will satisfy this requirement).
Failure to comply will necessitate a retest.
American standards have similar requirements although the extent of
approval of the welding variables are different to those of EN 287.
Welding operator approval
When required by the contract or
application standard, the welding operators responsible for setting up
and/or adjustment of fully mechanised and automatic equipment must be
approved but the personnel operating the equipment do not need approval.
In clarifying the term 'welding operator', personnel who are using the
equipment (loading and unloading robotic equipment or operating a
resistance welding machine) do not require approval.
As specified in EN 1418, approval of operators of equipment for fusion
welding and resistance weld equipment 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 for welders' in EN 287 is recommended but not mandatory.
Prolongation of the welding operator approval is generally in
accordance with the requirements of EN 287. 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 longer than 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 body providing there is proof of
production welds of the required quality, and appropriate test records
maintained with 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
EN 287: Part 1. Steels
(Amendment 9665,
August 1997)
(Amendment 9804, January 1998)
(Corrigenda No 1, April
1998)
Part 2.Aluminium and alloys
(Amendment No 9733, November
1997)
(Corrigenda No 1 June, 1998)
EN 288: Part 3. Steels
(Amendment No 9736, November
1997)
(Corrigenda No 1, June 1998)
EN 1418 : 1998 Welding personnel - Approval testing of welding
operators for fusion welding and resistance weld setters for fully
mechanised and automatic welding of metallic materials
REPRODUCED - COURTESY TWI-UK
