WELDING PROCEDURES
1. What is a Welding Procedure Specification (WPS)?
A welding procedure is a form of works instruction to the welder, detailing how a particular weld or type of weld is to be made. As a minimum it will list the process to be used, materials to be welded, joint type, thickness, consumable, position and welding conditions (amps, volts, travel speed). Depending on the end use of the component being welded there may also be requirements on heat input, preheat and interpass temperatures and post weld heat treatment.
Welding procedures are usually qualified by means of a test piece welded in accordance with a national or international Standard, the most common being ISO 15614, ASME IX and AWS D1.1. Although different in the detail, all three of these have a similar approach in that they require welding of a test piece which is then subjected to NDT followed by destructive (mechanical) testing.
Provided everything passes, the test results are compiled into a document called a Procedure Qualification Record (PQR), which is an exact record of how the test piece was welded, the results of the testing and the resultant qualified range of approval. The PQR provides proof that what you are proposing to do in production is effective in meeting the standard requirements. It is a QA document and would not normally be issued to production.
The WPS is derived from the PQR and this is issued to production, and is an instruction to the fabricator and welder. It can also be used by inspection to ensure that welding is being carried out correctly. It is usually possible to derive more than one WPS from a single PQR, and care should be taken in selecting the test piece type and dimensions to get the maximum range of approval from the test.
2. How do I go about qualifying a welding procedure?
Focussing on the ISO 165XX series of standards the basic process is:
3. How do I turn this into a WPS?
Each of the conditions recorded during test has a range of approval. Using ISO 15614-1 for reference, if you welded a 20mm thick plate using a single vee preparation with a fully penetrating root pass and no backwelding, welded in more than one pass, this would give you a qualified thickness range of ≥10mm≤40mm for single or double sided multipass butt joints, and would also cover multipass fillet welds of unlimited throat thickness on plates of ≥10mm≤40mm. If you qualify it on S355 material this will also approve welding of S235 and S275, but note that lower strength material never approves higher strength material.
Each separate joint covered by the PQR would need its own WPS to be written, detailing the joint configuration, thickness range etc and each WPS must reference the supporting PQR. The WPS does not need to be signed by the certifying body, although some clients may expect it to be so.
4. Further advice
GWE Ltd can offer assistance in the process of qualifying a WPS by:
A welding procedure is a form of works instruction to the welder, detailing how a particular weld or type of weld is to be made. As a minimum it will list the process to be used, materials to be welded, joint type, thickness, consumable, position and welding conditions (amps, volts, travel speed). Depending on the end use of the component being welded there may also be requirements on heat input, preheat and interpass temperatures and post weld heat treatment.
Welding procedures are usually qualified by means of a test piece welded in accordance with a national or international Standard, the most common being ISO 15614, ASME IX and AWS D1.1. Although different in the detail, all three of these have a similar approach in that they require welding of a test piece which is then subjected to NDT followed by destructive (mechanical) testing.
Provided everything passes, the test results are compiled into a document called a Procedure Qualification Record (PQR), which is an exact record of how the test piece was welded, the results of the testing and the resultant qualified range of approval. The PQR provides proof that what you are proposing to do in production is effective in meeting the standard requirements. It is a QA document and would not normally be issued to production.
The WPS is derived from the PQR and this is issued to production, and is an instruction to the fabricator and welder. It can also be used by inspection to ensure that welding is being carried out correctly. It is usually possible to derive more than one WPS from a single PQR, and care should be taken in selecting the test piece type and dimensions to get the maximum range of approval from the test.
2. How do I go about qualifying a welding procedure?
Focussing on the ISO 165XX series of standards the basic process is:
- Select the appropriate test piece for the joints that you will be welding n production. If you are careful in your selection you can get several WPS s from one PQR.
- Draw up a provisional WPS (pWPS). This is a preliminary instruction to the welder who will be carrying out the test. It will contain the information listed above concerning process, amps, volts etc. If the procedure is to be impact or corrosion tested then additional instruction concerning heat input etc may be needed. ISO 16509 lists the variables that need to be included in a pWPS.
- Weld the test piece following as closely as possible the instructions in the pWPS, remembering though that it is provisional, so the conditions needed to make the weld may vary slightly from those instructed. A full record of welding should be made, recording the amps, volts, travel speed, number of runs and weld pass sequence. The test should ideally be witnessed by an independent third party and GWE recommend that you use a Notified Body, examples of which are Lloyds Register, DNV, TWI CL, Zurich Certification. If the procedure is being qualified for work that will fall under the Pressure Equipment Directive then it is a requirement that the procedure test (and welder qualification tests) are witnessed by a Notified Body.
- Carry out NDT and mechanical testing, again this should ideally be witnessed by the same body that witnessed welding.
- Compile the record of welding, test results and resulting range of approval into the PQR document. Some clients will also want to see material certificates, NDT operators qualifications and various other supporting documentation. This should all then be signed and stamped by the witnessing body.
- Your procedure is now qualified.
3. How do I turn this into a WPS?
Each of the conditions recorded during test has a range of approval. Using ISO 15614-1 for reference, if you welded a 20mm thick plate using a single vee preparation with a fully penetrating root pass and no backwelding, welded in more than one pass, this would give you a qualified thickness range of ≥10mm≤40mm for single or double sided multipass butt joints, and would also cover multipass fillet welds of unlimited throat thickness on plates of ≥10mm≤40mm. If you qualify it on S355 material this will also approve welding of S235 and S275, but note that lower strength material never approves higher strength material.
Each separate joint covered by the PQR would need its own WPS to be written, detailing the joint configuration, thickness range etc and each WPS must reference the supporting PQR. The WPS does not need to be signed by the certifying body, although some clients may expect it to be so.
4. Further advice
GWE Ltd can offer assistance in the process of qualifying a WPS by:
- Review of drawings to identify required WPS
- Advise on process, consumable etc to achieve requirements while achieving maximum productivity
- Writing the pWPS and specifying the test piece type and dimensions
- Instruct the welder on correct technique, supervise welding of the test piece
- Writing the production WPS once the PQR has been signed off by the certifying body.
