PWHT Holding Time

[EuroWeld]

Hello All,

I have a question about the holding time for PWHT of unalloyed carbon steel like (S)A-516-70. In the past I once have seen a procedure in which the holding time was miscalculated. As per ASME VIII div 1 UCS-56 is stated that the holding time is one hour per inch of the used material thickness. In this procedure an holding time of 8 hours for 1 inch of material was stated, and was carried out according to it.

Wat could be the concequences of this longer holding time?
This situation was an PWHT according to the ASME code, but this is a general question.

Thanks in advance,

 

[metengr]

EuroWeld;
An extended PWHT time could result in reduced notch toughness for the weld and/or base material HAZ.

 

[EuroWeld]

Besides reduced notch toughness is a reduced hardness also a possibility? And is it possible to predict and/or calculate this values in advance? So yes, how?

Thanks,

 

[metengr]

EuroWeld;
For carbon steel supplied in the normalized condition, there should be little to no change after 8 hours for a subcritical PWHT. For Normalized and tempered condition, yes, there will be a softening.

Here is what you need to do for this so called nonconformance. Obtain a coupon of nearly the same material and heat treatment condition, cook it for 8 hours at the stated PWHT temperature and run hardness tests to evaluate the effects. This is my view if I were the client or the Inspector or the Jurisdiction. Trying to pencil whip this is a waste of time.

 

[EuroWeld]

Metengr,

Thanks for your response.
Making a test coupon is a good idea. Above situation happened months ago. Gonna make two test coupons and perform pwht, one according to the code and the other with eight hours holding time. I will post the results when known.

But in general can something like this can be predicted or calculated?

 

[metengr]

EuroWeld;
For quenched and tempered low alloy pressure vessel steels you can try to predict softening using parametric equations for hardness at time and temperature. This works because of changes in carbide structure, size and type over time at PWHT temperature. However, having real data to deal with a nonconformance speaks volumes and is defendable.

 

[metengr]

Euroweld;
Review here

http://www.arcelormittal.com/NA/pla...uctBrochure/ARCELORMITTAL_PRESSURE_VESSEL.pdf

 

[SJones]

What was the PWHT cycle of the test weld to qualify the WPS? The holding time has a supplementary essential variable restriction. It should have had at least 6.4 hours if toughness testing is required!

Steve Jones
Materials & Corrosion Engineer

http://www.linkedin.com/pub/8/83b/b04

 

[EuroWeld]

Metengr

Thanks for your reply, this is enough information for a few days.
This is usefull infomation.

Sjones,

Do you mean according to ASME IX QW-407.2?
You mean 80% of a total of eight hours?

I don't know exactly but as far that I can remember it was one hour holding time for the wps. I'm not sure that there were notch-toughness requirements in this particulair project. I will check.

Thanks for your response,