Prequalified CVN tested D1.1 WPS's ?

Date 09-18-2002 19:43

It has been my experience that when CVNs are required, the client usually insists on reviewing the PQR, to determine if the WPS parameters are consistent. In some cases the charpy values are considerable higher than the minimum acceptable values. In those cases, strict compliance with the PQR parameters is less of an issue. However, if the charpy values are near the minimum, the WPS should be written with more attention to detail regarding heat input. If I was reviewing a subcontractors WPS (that required low temp toughness) I would not accept prequalified procedures. Charles Hall

By steveho (*)

Date 09-18-2002 20:35

Thank you, I think. Any other opinions appreciated.

By R. Johnson (**)

Date 09-19-2002 13:37

While most filler metals have a minimum specified charpy impact value, most codes have a different test temperature and impact value for welding procedures. The particular code I work with does not allow prequalified welding procedures and anyhow it asks for chary values in the weld metal and heat affected zone. I find it difficult to believe that your application is not concerned with the HAZ. Therefore a test plate would be necessary to qualify your WPS.
I do not have the latest edition of D1.1 but section 4.1.1.3 refers to Annex III and I believe that if you are welding under D1.1 you could not use a prequalified procedure for CVN.

By steveho (*)

Date 09-19-2002 19:12

Thanks, I feel much the same as the general consensus indicates. But as any devil's advocate might say, and after already having checked 2002's 4.1.1.2, 4.1.1.3 and III3.5, such basically and simply requires only 'that when required, CVN testing needs be done'. D1.1's rqmt's for CVN WPS's, especially in single pass applications, don't seem to give rise to precluding a Fabricator from utilizing the filler Mfgr's prequalified essential variables only due to slightly varying HAZ's for different base metals. But if it is really of issue (in all cases), then the Engr' would certainly and simply disapprove all such WPS's (prequalified or qualified), but until one identifies why it would be disapproved, I can't see why it would or should.

In other words, as Engr's do approve new and/or revised WPS's documenting CVN essential variables (actually tested by a Fabricator), as long as a CVN WPS's variables also abide by Table 4.5 and/or 4.6 as appropriate, as both table's only restrict base metal changes 'outside' one's specifically tested group, then again, why wouldn't he/she also approve a prequalified CVN WPS ?

By R. Johnson (**)

Date 09-20-2002 13:11

The filler metal manufacturer impact values and test temperature are derived from the filler metal specifications. Most application requirements for impacts are based upon different criteria. For example, E7018 has a 20/15 ft-lb requirement at -20F. I have a job application for 15/10 ft-lb at -30F. They do not equate and a PQR must be performed to prove out not only the weld metal in the as welded condition but also the welding procedure parameters by checking the HAZ. Once a procedure is qualified then limitations on heat input come into play. Having a manufacturer weld metal test data is next to unless if you are not controlling amperage, voltage, travel speed, preheat, postheat and base metal thickness in your WPS. And your WPS is derived from the original test configuration of your test plate for the PQR. Prequalified welding procedures do not address all of these variables when charpy impact values are required for the weld procedure. That is why the D1.1 welding code leaves it open with the "when required" statement.
What does your job specifications demand? What CVN value and test temperature is mandated? What is the approving engineering asking for? What application will the completed weldment be used in?
It sounds like the specifications are too loose and subject to wide intrepretation. Go back to the engineer and ask what the requirements are and then you can make a determination if prequalified procedures are appropriate. If any CVN requirements are specified then prequalified welding procedures cannot be used. The filler manufacturer makes no claims on HAZ values for their product, they cannot because they do not know if you even purchased a base metal that will support good HAZ values.
As for Tables 4.5 and 4.6, if you look closely at the heat input requirements you will see that you are restricted to less than a 10% increase (except for GTAW) and would therefore require re-qualification. If you have no baseline PQR test results and only a prequalified procedure what are you comparing your increase to? Table 4.5 and 4.6 are there for procedure qualification and therefore you should have started with a tested WPS.