PWHT 2

[ikarga]

In what conditions there is a need (must) for heat treatment of complete pressure vessel?

 

[metengr]

Pressure vessel geometry, lethal service conditions, etc.

 

[r6155]

If ASME VIII Div 1: Material, thickness, welding, temperature, vessel contents.

Regards
r6155

 

[SnTMan]

When client requires it.

Regards,

Mike

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

 

[jte]

I'm wondering whether the emphasis on "complete" in the original post is meant to imply that perhaps only the weld seams, but not the unwelded areas, be PWHT. If that is the intent, then I suspect that after a thorough discussion with the client / end user, then you may find that some areas of the vessel may be exempt from PWHT. Actually, something like studs and manway covers are likely not considered a part of the "complete" vessel in many cases.

Now, if one is to envision a PHWT of the welds only, then the state of stress in the vessel would be quite interesting. Certainly worthy of an FEA to evaluate the stresses during PWHT. And said FEA would likely indicate that the PHWT will leave yield level residual stresses when completed. In other words, such a proposal is likely to be completely impractical for the vast majority of cases.

 

[ikarga]

Thank you guys. Actually, I didn't find any requirements in ASME VIII for heat treatment of complete vessel, but in technical requirements Client just put "PWHT" without to specify is this for complete vessel. Just want to know what ASME require and what is a good engineering practice.

Regards

 

[XL83NL]

@jte:

I'm wondering whether the emphasis on "complete" in the original post is meant to imply that perhaps only the weld seams, but not the unwelded areas, be PWHT

It can only be w.r.t. the welds, otherwise it wouldnt be called Post Weld Heat Treatment. HT (Heat Treatment), with a different purpose, may also be specified as per VIII-1. Think for example of certain alloys which are formed beyond a certain strain limit (see UNF-79). However I dont think this HT is done in the same step as PWHT.

 

[r6155]

@ ikarga
See UW-40 (a)(1) heating the vessel as a whole in an enclosed furnace.
This procedure is preferable and should be used
whenever practicable.

Regards
r6155

 

[jte]

XL83NL-

Yeah, I get that, but my point is try to imagine heat treating only the welds without heat treating the rest of the vessel. For example by using electric resistance heaters placed only on the welds and HAZ. Not something I'd like to try!

I think with ikarga's clarification, the answer becomes "If the client said "PWHT" then thou shall assume it means the entire vessel. If the client wanted a vessel with only certain parts PWHT, then they would have taken the time to call that out specifically."

 

[r6155]

Always PWHT ,as UW-40(a)(1), is a good engineering practice, required or not. It is like to say that spot RT is a good engineering practice (required or not).

Regards
r6155

 

[ikarga]

OK, guys, this morning got an additional explanation from Client - we will do just welds PWHT (price of contract should be changed if we have to do COMPLETE HT of vessel.
Thank you for your efforts, especialy to r6155 - UW-40(a)(1) was crucial for Client.

Thank you all
Regards

 

[pdiculous963]

Be very careful heat treating only welds. There is a good chance you will distort the vessel and produce excessive plastic strains if the PWHT is not done properly.