Duplex thickness allowances and PWHT

[bruv]

A bit of background first: At our foundry we qualify our welders on 40mm plate with a 20mm weld. For the majority of materials this will qualify us to put up to 200mm of weld metal in 200mm walll thickness.

One of our metallurgically-knowledgable customers has contacted us with the following question. He will shortly be embarking on a large number of duplex qualifications, and would like to know the answer to this question:

"I paused for a few days to contemplate on some of the Section IX rules (or should I say, the lack of specific rules or guidance) regarding post-weld solution annealed duplex stainless steel with impact testing.  We believe that some of the rules (QW-403.6, for example), should be waived for duplex stainless steels which are solution heat treated after welding, even though the rules do not explicitly exempt duplex materials.  If the rules regarding were applied to a solution heat treated duplex stainless steel with impact qualification, your minimum base metal thickness would be 16 mm instead of 5 mm, and your maximum qualified thickness would be 44 mm instead of 200 mm."

I would like to know people's thoughts on whether they consider duplex stainless to exhibit an "upper transformation temperature", and if they consider that these rules apply to duplex stainless?

Many thanks

 

[Ballbearing1]

Bruv,
A little bit confused with your statement as you seem to be discussing both WPS's and WPQ's.
Will answer based on welder qualification.
1 20 mm plate with 20 mm weld metal is all that is required for unlimited thickness for welder quals. 40 mm thick coupon is for WPS.
2 QW403.6 is applicable to WPS only, not to welder quals.
3 There is no minimum thickness for welder quals, only maximum.

The rules regarding thicknesses for impact tested specimens and PWHTed Duplex will be found in your code of construction and not in ASME IX.
Hope that helps,
Regards,
BB

 

[DVWE]

Is there a specific alloy for this customer, or are there several alloys? Reason I ask is that they may have different P-Nos.

 

[metengr]

What exactly is the use of duplex stainless that requires impact testing? Are these for ASME Section VIII, Div 1 pressure vessel construction? Section IX as mentioned above is more of an independent section of the ASME B&PV Code that serves all applicable Code book sections by providing requirements for weld (brazing) and welder (bazer) qualification and does not spell out anything regarding PWHT or impact requirements. You need to discuss with your client what the intended application is for the duplex stainless steels.

 

[GRoberts]

Strictly from a technical standpoint, applying the 1.1T requirement to duplex is not inappropriate. The reasoning is that the cooling rate for duplex (similar to Q&T steels) is very important to avoid itermetallic precipitation. So the thickness of the test plate can have a significant effect on the cooling rate.