sPWHT on normal CS steel in Pressure Vessels 1

[Martin_Arc]

Hi All,

we have a pending order with an US Oil Major which contains of:

Seamless Pipes in A106 (thickness<19mm)
Plates in A516 gr70 (t>19mm)
Flanges in A105 and A350 LF2
Forged Nozzles in A105 and A350 LF2

The materials are needed for a pressure vessel.

After some weeks they come back to us asking for a simulated post weld heat treatment on all materials.
This sound strange to me. As far as I know ASME does not require a PWHT for such materials. So why a sWPHT.

My experience/feeling with steel in oil and gas tells me this request is invalid, but since I am not an engineer I cannot find correct literature to support this.

Or am I mistaken and is the sPWHT a valid request?

thanks,
Martin

 

[SJones]

The purchaser is seeking to verify that the mechanical properties of the materials are maintained at design levels after being subjected to PWHT. It is an integrity assurance exercise that needs to be funded by the purchaser if it is not required by the standards in the purchase order. Since they appear to have fired in this request after placing the order, you may wish to negotiate a reasonable variation to contract.

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.

 

[DVWE]

A lot of refinery equipment is PWHT because of service, not because of code thickness requirements.

 

[Ehzin]

To elaborate on DVWE's point, there are a few failure mechanisms for carbon steel that can be mitigated by way of PWHT. The immediate one I think of is anhydrous ammonia although I currently don't have much experience with the fine details of it. I think a lot of issues related to cracking/weld cracking can be solved by PWHT/Stress relieving although don't quote me on that. If you're interested in learning more a useful resource to have a general understanding of common failure mechanisms is API 571: Damage Mechanisms Affecting Fixed Equipment in the Refining Industry. It'll have a wealth of information although don't expect it to make you an expert on any failure mechanism. I've used it as a general resource and then I'd defer to more detail texts for specifics.

Thanks,
Ehzin

 

[metengr]

ASME Boiler and Pressure Vessel Code provides minimum requirements and that includes PWHT. Buyer beware that one can always specify above and beyond code requirements depending on service conditions. I have seen one pressure vessel failure in litigation caused by stress corrosion cracking because the Design Engineer failed to take into account residual stress and the effects of environment. The Code did not require PWHT but we know that PWHT can indeed be specified by contract.

 

[r6155]

Be careful with your client. Another asking may be in short time with extra cost for you.

Regards
r6155

 

[racookpe1978]

Asking for "a simulated PWHT on all material"?

Their request, regardless of "client requests above Code minimum" itself makes little sense phrased that way.
Recommend strongly that t hey be asked to clarify exactly what a simulated PWHT analysis is, on material not yet welded.

 

[mk3223]

IMO, the sPWHT is one of the supplementary requirement for the steel plates per ASTM A20. It requires the coupon sample for extra heat treatment and mechanical test.

 

[david339933]

Why do sPWHT on material of a vessel when welding was done without PWHT, and WPSs used may not allow PWHT?

 

[DVWE]

The OP didn't state whether or not the vessel gets PWHT...chances are it probably does.

Either way, sometimes (not often) vessels within a refinery can get repurposed from a service that doesn't require PWHT to a service that does require PWHT.

 

[david339933]

If that is the case, then this thread was over after your first post.....service will often dictate PWHT requirements over code requirements.
Interesting second statement.....how is a vessel able to undergo PWHT when the welds are not qualified as such?

 

[SJones]

@david339933 read the OP carefully, it is not actually a pressure vessel that is the subject, it is the component materials. It would appear that another entity will complete the vessel fabrication for which it is assumed that PWHT will be applied with the necessary code compliance for welding.

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.

 

[david339933]

Ah yes....that makes much more sense....Thanks Steve!

 

[DVWE]

how is a vessel able to undergo PWHT when the welds are not qualified as such?

By ensuring it was welded with dual qualified WPSs - with & without PWHT.

 

[david339933]

Well, yes but my point was when welds are not qualified as such....dual WPSs has qualified welds.....it is hard to plan re-purposing of a vessel.

 

[DVWE]

I understand your point, david.

I'm just trying to provide the OP some reasoning why his client is requesting sPWHT.

1. The vessel will get PWHT.
2. The end user is planning for future PWHT.
3. Could be other reasons I'm not aware of.