ASME IX QW-453 query

[bruv]

Carrying out a procedure qualification for corrosion resistant overlay, QW-453 allows that a base metal thicknes of T < 25mm will qualify for an unlimited base metal thickness. If I do the same with a hard-facing overlay, I will only qualify for a maximum base metal thickness of 25mm. If I wish to weld onto a base metal greater than 25mm I will need to run another procedure qualification test on a plate of 25mm or more.

When it comes to performance qualification, requirements for corrosion resistant and hard facing overlay are identical - any base metal thicknes < 25mm will qualify to an unlimited thickness.

Can anyone explain why there is a difference in requirements from procedure to performance qualification on base metal allowances?

Thanks

 

[metengr]

bruv;
A procedure qualification is considered more restrictive because in this case the welding procedure specification, when followed, should result in a weld joint that meets minimum strength and minimum ductility requirements for service. For hardfacing the main criteria are minimum hardness and adequate fusion with the base metal. Base metal thickness is extremely important because of factors like cooling rate and preheat requirements which directly effect air hardening weld deposits for hardfacing. For corrosion resistant weld overlays, these weld metals are typically non-air hardening and are less effected by base metal thickness or cooling rate.

A welder performance qualification only signifies that a welder can deposit weld metal of acceptable quality, and not to demonstrate that the weld joint meets fitness for service requirements. Base metal thickness is not as important as weld deposited thickness.

 

[stanweld]

The base metal thickness qualified is the minimum thickness when T < 25 mm for corrosion resistant overlays There is potential for greater dilution of weld metal with the base metal when thin materials are overlayed for corrosion resistance. This could adversely effect the chemical analysis of the overlay deposit.

 

[bruv]

Thanks to you both. I now have another question.

I run two procedures, one on 10mm plate and one on 30mm plate. All variables are the same apart from the base plate thickness. Both procedures meet the minimum requirements. Can I use the procedure qualification on the 10mm plate also as a performance qualification to weld to plate of unlimited thickness?

 

[Metalmeister]

Bruv,

Without looking it up, I would say that a welder who successfully welds a PQR is automatically qualified in performance within the limits of essential variables given for performance qualification. OK - I just looked. See QW-301 and QW-453. It appears you can.

 

[DVWE]

Good info in this thread.

bruv,

I agree with Metalmeister. WPS qualification qualifies the welder or welding operator regardless if it is CRO, Hardfacing, or fabrication welding.

 

[Mr168]

DVWE: I'm assuming you mean procedure qualification? The limitations of a WPS can exceed those of what a weldor is qualified for from a WQT.

 

[DVWE]

Mr168,

Agreed. But not in this case. The welder will be qualified from 10mm to Unlimited.