Rerate for lower MDMT

[TangoCleveland]

I posted this question in the Code Issues Forum, and thought maybe I could get more opinions here.

I have an SA516-70 (non-normalized) Div 1 Code Stamped vessel. It is stamped for 250 psig at -20F to 650F. Owner wants to reduce MAWP to get to MDMT of -50F. I believe I can use USC 66.1 chart to do this without impact testing. Preliminary results give me 185 psig at -50 to 650F. However, UCS 67 seems to tell me that weld procedures need to be impact tested - "MDMT used below shall be the MDMT . . . before applying the termprature reduction permitted by UCS-66(b)."

My question is, can the WPQ be impact tested after being used for vessel fabrication? Design was to 1999 edition of Div. 1.

Larry

 

[metengr]

Did you use Fig UCS-66.2 to determine the temperature reduction below the original MDMT of -20 deg F without having to perform impact testing? Since you are working with pressure vessel plate that is not normalized and tempered, thickness of the vessel will be critical for impact test exemptions.

Reading thru UCS-67, I would say that a reasonable approach would be to develop a new WPQR, based on the original used in vessel fabrication, and qualify with impact testing. Since the reduction in MDMT is considered an alteration of the vessel in accordance with NBIC guidelines, I would review this entire approach with your Inspector and Jurisdiction, if necessary. They may dictate otherwise.

 

[lostsailor]

Larry,
In my opinion, yes. Make sure that you meet all the requirements of UG-84 addressing impact testing of WPQ's as well as the requirements of UCS-66/67 and be sure to discuss it with the AIA that is going to be signing off on the alteration.
Regards,
RLS

 

[arto]

FYI- Several years ago, the French CODAP Code had a Charpy conversion factor of 0.66J/degC to adjust to different test temperatures.