Interpretation VIII-1-95-50 1

[Genetix]

My understanding of the interpretation is that you cannot conduct heat treatment of heads with extreme fiber elongation > 5% prior to welding it to shell section. Is it correct? If that's the case, for a long vessel with PWHT not required as per material and thickness, you would have to heat treat the whole vessel just because of the heads' heat treatment requirement? I really think it's impractical and costly. Need expert opinion.

Thanks.

Interpretation: VIII-1-95-50
Subject: Section VIII, Division 1 (1992 Edition, 1993 Addenda); UCS-79(d)
Date Issued: March 13, 1995

File: BC94-684

Question (1): A cold formed head has to be heat treated to fulfill the requirements of UCS-79(d) in Section VIII, Division 1. Does the term "heat treated subsequently" mean just after forming and prior to any other operation?

Reply (1): No.

Question (2): If Reply (1) is no, then will PWHT in accordance with UCS-56 satisfy the requirements of UCS-79(d) following welding of the head to the vessel?

Reply (2): Yes.

 

[metengr]

Incorrect. The interpretation is addressing sequencing of fabrication steps. Yes, you can heat treat the heads either prior to welding or after welding.

 

[Genetix]

Thanks metengr

 

[Mech2325]

Please someone clarify the reply (2) as "yes". If the vendor chooses to "post weld heat treat" the seam locally, how would the requirement of heat treatment be exempted?

 

[Genetix]

The reply on (2) specify that the heat treatment temperature and time as per UCS-56 can satisfy the requirement of UCS-79.

 

[Mech2325]

Yes, but i am asking what if the seam is locally heat treated, as here you are talking about PWHT and it can be localized also. In this case, how come the head is exempted from UG 79 requirement. This is a bug in compress software also. If you check in the option of PWHT, then the software does not give you the warning of EFE increase from 5%. In such a case, of the vendor chooses to do pwht locally of seams only and not the entire vessel, then the designer may miss the requirement of "stress relieving" as per UG-79.

 

[metengr]

The issue is using PWHT for weld seams AND the head due to exceeding EFE. The Code view is I can use PWHT to achieve both if staged properly during fabrication. Either way, the heads must be subjected to a thermal treatment at some point if the EFE is exceeded and what the Code is stating is that I can use PWHT to achieve this.