Rationale for not specifying maximum soaking time for PWHT

[srijey]

When there is enough evidence to prove that the notch toughness decreases with extended soaking time, why ASME code does not specify maximum limit on the soaking time for PWHT?

 

[TGS4]

Accordingly, it is not intended that this Section be used as a design handbook; rather, engineering judgement must be employed in the selection of those sets of Code Rules suitable to any specific service or need

If you have a different take on it, please bring said information forward to the Code Committees so that they may (if there is deemed a need) incorporate such into the rules.

 

[metengr]

Because the committee cannot write all encompassing code rules and there are enough cautionary statements to allow one to work around this issue. If you need to qualify material and there is a known notch toughness issue with PWHT you don't use the material if PWHT is required and notch toughness is mandated.


My problem is placing time constraints and what if notch toughness is not important as in Section I?

 

[rhg]

Excess of minimum soaking time is waste money.

Regards

rhg

 

[srijey]

I agree that UCS 56 cannot address post construction PWHT cycles; however it should indicate as a note to complement with Section IX QW407.2. Before taking to code committee, I like to confirm that 80% aggregate time is just an 'uncertainty number' to accommodate the future (or erroneous prolonged soak) PWHT cycles. I understand EN/BS standards have a specified range - is that correct? The actual effect on material properties due to extended hours or number of cycles of soaking varies with the materials of construction. We in the corporate sector put an 'arbitrary' limit of max three PWHT cycles for shop new construction PQR. I'm weary of this 'opinion'.

 

[srijey]

I guess I need to revise my question here as the QW 407 requirements (80% of the anticipated PWHT cycle time) are focused only for production welds, certainly post construction requirements are not taken into account. 80% or 120%, it is still an arbitrary # which may not truly represent all future repairs even in production shop. Hence my revised question shall be: Can we not expect UCS 56 in Sec VIII to caution the adverse effects of extended soaking time and to remind to meet the Sec IX welding qualification requirements?

 

[metengr]

The Code book is not an engineering handbook, and will never be a handbook. Again, expertise is required and the code book provides only minimum requirements. Ultimately, the engineer decides on material selection and joining.