Does vessel skirt need PWHT? 1

[matay]

Hi,
We have a vertical pressure vessel with skirt.Vessel material is SS304 but skirt is SA51670 with 20 and 30mm thk. subsequently.Shell&heads do not need heat treatment but should I heat treat the skirt material? I'm looking at UCS-56 yes it needs but this part is nonpressure part? Can anyone help me about it?

 

[metengr]

matay;
How is the stainless vessel welded to the skirt? You can possibly butter the carbon steel side of the skirt that attaches to the shell with 309 stainless filler and PWHT separately. Once this is completed, you can weld the buttered skirt directly to the stainless steel vessel with no PWHT, using 308L or compatible filler metal.

 

[matay]

Metengr,
Skirt has 3 parts and bottom head is welded with top skirt part which is already the same material with Shell=SS304(20mmthk).Then second and the third parts of skirt are SA51670 with 20 and 30mm subsequently.
Other than filler material I need to know for this CS bottom part of skirt not directly welded to pressure part needs PWHT.Thanks.

 

[doct9960]

matay,

Your skirt do not need PWHT. The PWHT requirements on ASME VIII-1 are for welds on the pressure envelope.

 

[jte]

matay-

As doc pointed out, the welds you are talking about - circumferential on the skirt and not connecting to a pressure part - are out of the scope of Section VIII. So the code does not mandate anything besides good engineering judgement. However, applying code rules even though it is out of scope could be considered good engineering judgement. But what has me confused is why, specifically, you feel that the code requires a butt welded 30 mm thick SA516-70 plate to be PWHT? That's not the way I interpret Table UCS-56 Note (2)...

jt

 

[jte]

…and the governing thickness of a butt welded 20 mm to 30 mm plate would be… 20 mm, not 30 mm per Fig UCS-66.3(a)(1).

jt

 

[metengr]

If you use a minimum preheat of 200 deg F and low hydrogen electrodes, I would not PWHT.

 

[rhg]

The pressure vessel is for low temperature service?. See UCS 68 and nonmand. Appendix G.
Which is the operating temperature of the skirt?

regards
rhg

 

[juancito]

Matay,

Because of the s. steel thicknesses you mentioned, the vessel is expensive enough to justify that the skirt has say its first upper foot made from ssteel too.
And forget PWHT.

 

[jte]

juancito-

See Matay's post of 30 Mar 07 at 8:16. The top part of the skirt is stainless.

jt

 

[AravindSujay]

Hi,
Your vessel DOES NOT NEED PWHT. I disagree with metengr.

Regards,
Aravind Sujay

 

[matay]

Thank you all.I think skirt does not need PWHT under these conditions.

 

[matay]

But,
The skirt has 42mm baseplate and compression ring welded to skirt with 14mm throat fillet weld.Do you think this sirt part need PWHT?

 

[stanweld]

matay,
Strictly speaking the skirt does not require PWHT; however, if your design parameters involve fatigue service with sufficient stress or you are in a low temperature area and the skirt material has not been impact tested (assumed to be operating in the brittle regime at lowest ambient temperature), you may well wish to do so. Welding residual stress is additive to the applied loads in these cases.