It sounds like an unreasonable expectation to me.  There are always changes from what is expected on a preliminary PQR. The actual parameters they use are what get mechanically and non-destructively tested.  Just because they may have varied slightly from what the originally predicted is no reason to reject anything.  If I saw that in a specification, I'd charge at least double for any planned PQRs, and what are you getting for your money? 

If "we" proposed this change, do you have access to the person who proposed it and to their reasoning?

What's the point of the preliminary PQR sheet to begin with?

I can see a restriction on a pass-by-pass basis so you don't have such a variation from pass to pass that the "official" PQR parameters are meaningless.  But I can't see rejecting an internally consistent PQR that would have been perfectly acceptable if not compared to a preliminary proposal.

Hg

Dave

Speaking for the PQR test only.  Please remember the PQR test can be run with a mechanized tractor.  It is the test of a particular electrode and shielding medium run at a given set of parameters.  It is the only way for the fabricator to maintain a constant travel speed.   An experienced fabricator would already know what the sweet spot for his welding operation is.  Some cheat because they have gotten away with it before.  Others submit a PQR for approval only after they have worked it out previously or have experience using it.  If a PQR is being run, and the fabricator varies from it. the CWI shouldn't reject it.  He should record it, and that will be the new WPS parameter based on the qualified procedure.

I think 1 volt is perferctly reasonable.  Most wire fed operations work best at an optimum voltage that is a whole number and a fraction.  (I.E. 34.7 volts)  A few tenths of a volt either way, and the optimum is lost.  The typical +/- 7% allowance is way out of the box for the optimum.  +/- 1 volt is very generous.

I think +/- 10 amps is too tight. simple variations in stick-out get a variation of up to 30 volts in one pass on the same joint.

Having said all this, it is also important to remember that voltage meters and especially clampmeters that update twice a second, will have variations in amperage greater than 25%.  These readings are not a realistic indicator of true average amps or volts.  Constant Wire Feed Speed and consistant electrical stick-out are better parameter builders.

To be realistic, if a PQR is also used to cover semi-automatic welding (Hand held and guided), a fabricator has to qualify several procedures to account for the variations inherrent in manually controlled welding procedures. (At least four PQRs.)  Charpy values must be proven for each PQR parameter set and travel speed.

Be aware; Most SAW passes  will not fully re-melt tack welds.  This is especially true if it is a parameter for a single pass 5/16 inch Fillet Weld. Thus unpreheated tack welding should be prohibited, unless the fabricator can prove that he can re-melt them in a production sized mock up!. 

 

Dave
the prelim PQR is really to seek approval from the client as to the process and method of welding, not so much amps
the PQR test is what matters, I have never heard of a % change or actual change tolerance betweeen a prelim and an actual PQR test
10amps or 1 volt, well it would depend on the process GTA or MMA is constant current so the volts could vary more than 1 volt along the length of the test plate
GMA is constant voltage so the amps would vary more than 10 amps along the length of the test plate anyway
as has been suggested the actual pqr is what matters as it is this test plate that is mechanically tested to verify the joint if welded the same as the test will survive in service
maybe there is some confusion, maybe they are talking abotu the WPS, these parameters are tight even for a WPS generally they are a % of the amps or volts that were used for the test plate to allow for operator variation not absolute values
and the % vary depending on the process for the reasons mentioned previously
Regards
Flash
www.technoweld.com.au

4.6 Preparation of WPS
The manufacturer or Contractor shall prepare a written
WPS that specifies all of the applicable essential variables
referenced in 4.7. The specific values for these
WPS variables shall be obtained from the procedure
qualification record (PQR), which shall serve as written
confirmation of a successful WPS qualification.

Maybe I am missing something here, please let me know if I am. Based on para. 4.6, I thought the whole point of a PQR was to test the welding parameters metallurgically/mechanically and which if it successfully meets the mechanical requirements, can then be used to define the parameters for your WPS within said essential variables?

This seems to be putting the cart before the horse to me. That preliminary pqr is just to get a starting point, if actual values are recorded during the process, and those values can be lived with by engineering, whats the problem?

Regards,
Gerald