MDMT allowable range.

[Genetix]

Dear respected experts.

I would like to inquire about the following problem.

I have a vessel with MDMT -46 deg C CS Carbon steel
PQR only specifies impact test at -45 deg C. (only 1 deg C difference)
I wonder if PQR is acceptable to be used on the vessel.
Is there some provisions in the ASME code that allows it?
Thanks in advance for your reply.

Best regards,
Genetix
ME/Petroluem

 

[r6155]

Data in documents shall be equals.
Modify documents to the same data

Regards
r6155

 

[Geoff13]

As a general rule for ASME, either you meet the rule, or you don't. There's no "close enough".

I'm a vessel designer rather than a welding expert, however it appears you may have a Division 1 option, depending on your material.

Clause UG-84(b)(2) states "Unless permitted by Table UG-84.4, impact test temperature shall not be warmer than the minimum design metal temperature". This table permits impact test temps for some materials to be slightly higher than the MDMT. Since PQR's are covered in UH-84(h) I would expect this table applies to PQR's as will as the base metal. This would be consistent with UG-84(g)(4).

 

[david339933]

Standard Designation: BPV Section VIII Div 1
Edition/Addenda:
Para./Fig./Table No:
Subject Description: Section VIII, Division 1 (1989 Edition, 1990 Addenda); UG-84(b)(2) and Table UG-84.4
Date Issued: 09/13/1991
Record Number: BC91-413
Interpretation Number : VIII-1-92-11
Question(s) and Reply(ies):
Question (1): Is it permissible to use a Welding Procedure qualified in accordance with Section IX, including all supplementary requirements of Section VIII, Division 1, in the construction of a vessel using Part UCS material having a Specified Minimum Yield Strength equal to or less than 40 ksi when the specified MDMT is -60°F but the procedure qualification test plates were impact tested at -50°F?

Reply (1): Yes.

Question (2): For a vessel as described in Question (1), may material impact tested at -50°F (e.g., SA-516 70N, SA-350 LF2) be used?

Reply (2): Yes.

Question (3): For a vessel as described in Question (1), may the vessel (production) test plates be impact tested at -50°F?

Reply (3): Yes.

Question (4): For any of the conditions described above, is it required to include "Table UG-84.4" in the Remarks section of the Manufacturer's Data Report Form?

Reply (4): Yes.

 

Unless you can show that there was rounding off or some administrative error and the temperatures are in fact equal, then no.
See above comments.

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