SPWHT requirement

[Paulettaa]

Dear All

Please help me understand something regarding SPWHT of SA-516 70.
In the engineering spec. of the project it is mentioned that where PWHT is required the mill certificate is required for three cycles of PWHT. Does this mean that I have to sent test coupons to a laboratory and ask them to verify if mechanical requirements after three cycles of PWHT is acceptable as per the corresponding material spec.? Or is it necessary that this test be done by the manufacturer of the plate?

Other question is that when they mention minimum three cycles of PWHT, does it imply three heating, holding, and cooling procedures the same as those expected in real PWHT or just on heating, holding, and cooling with a time three times that of real situation?

The thickness of material is 75mm and 45mm if it helps.

Warm Regards

 

[SnTMan]

Paulettaa, you should maybe confirm with the client but:

Generally it is acceptable for a lab to perform the simulated heat treat and mechanical testing, reporting the results. Often the material supplier handles this, rather than the fabricator.

Also generally it is acceptable to perform the simulated heat treat in a single cycle of suitable duration, see UCS-85(c).

Regards,

Mike

The problem with sloppy work is that the supply FAR EXCEEDS the demand

 

[Trestala]

In one of our Clients that required 3x cycles simulation PWHT, plates that are to be procured should be sPWHT by material supplier (before any production), then additional production test plates are to be heat treated together with the vessel itself in which those plates are to be given to the Client.

Our supplier performed heating, holding, and cooling three times, e.g. heating -> 1 hr holding @ 625°C -> cooling -> then repeat again 2 times.

Regards,

 

[SJones]

Since the mechanical properties after PWHT are required to be shown on the inspection documents of the material, the normal expectation would be that the entity actually validating the inspection documents would be the one to undertake the heat treatment and testing. Thus, you may have to clarify with the specification owner whether use of a third party laboratory to provide a further inspection document for the additional testing in the PWHT condition would be acceptable.

For PWHT, refer to standards for the definition of a cycle. Normally, it is defined by the heating, holding and cooling parameters whereby simply extending the durations by three times would still only result in a single cycle.

Steve Jones
Corrosion Management Consultant

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

All answers are personal opinions only and are in no way connected with any employer.

 

[metengr]

Other question is that when they mention minimum three cycles of PWHT, does it imply three heating, holding, and cooling procedures the same as those expected in real PWHT or just on heating, holding, and cooling with a time three times that of real situation?

The purpose for this specific requirement is to ensure that the total accumulated time at PWHT temperature does not result in lowered mechanical properties and impact, if required, for the weld metal or base metal. The total time related to 3 simulation cycles is what is important, and not the cycle itself.

 

metengr is correct, total accumulated time at the holding temperature is the critical measure as far as the Code is concerned, not the number of cycles. The maximum lifetime number of anticipated cycles is what the calculation of total accumulated hold time for the simulation coupon is based on.
.
(I always balk at the use of the term 'simulated' in these exercises. The PWHT of the test coupons is quite real...)


"Everyone is entitled to their own opinions, but they are not entitled to their own facts."

 

[Paulettaa]

Thank you all for your responses.

I am just curious with many manufacturers of plates and many years of experience that all these companies have, is there any documented data that shows for carbon steels ( at least the most frequently used grades)that for what duration of exposure to PWHT temperatures there will be negligible drop in mechanical properties. For example, for SA-516 70 exposure to PWHT temperature less than X hours will not cause any harm to mechanical properties. Something like that will be very helpful in avoiding extra tests for future uses.

 

[metengr]

Paulettaa;
Carbon steel plates can vary in mechanical properties from original production because of the variability in the heat of steel and sourcing location. The simulated PWHT cycles is for the Purchaser's benefit/protection in the event a heat of steel has original or as-received properties that are at the minimum. In general, this is not a problem with carbon steel today but you don't want to categorize into a one size fits all.

 

[SnTMan]

In general, this is not a problem with carbon steel today...

This is demonstrated by Sec VIII, Div 1 exempting certain steels from simulated PWHT. See UCS-85(f).

Regards,

Mike

The problem with sloppy work is that the supply FAR EXCEEDS the demand

 

[Paulettaa]

metengr, I was thinking about something like exemption curves for impact test. We know that for many plates that cannot be exempted by UCS-66 curves impact testing is mandatory for which in most cases that I have faced, the impact energy is well above minimum required. However, there definitely are some combinations of thickness and MDMT for which impact testing is not required and all of these curves and results are based on experiments.

A similar scenario can be true for PWHT and exposure of material to the PWHT temperature. I was thinking that it might be possible that for a combination of duration of exposure and thickness there could be exemption curves for simulated PWHT and for some of them simulated PWHT be mandatory.

Warm Regards

 

[metengr]

Paulettaa
I believe SnTMan addressed this briefly in the post above. If you want to have your idea evaluated by the Code committee, start attending meetings. This would be a good importunity for professional development, networking and improving the Code itself with new ideas and industry experience.

 

[SnTMan]

Paulettaa, that is an interesting idea. I'd guess the steelmakers and test labs would have a pretty good feel for such a curve or other equivalent. Whether they would commit in writing is another question

The problem with sloppy work is that the supply FAR EXCEEDS the demand