Rerate for lower MDMT 1

[TangoCleveland]

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

 

[codeeng]

Its quite common to append additional test results, like impact tests, to an existing PQR.

 

[stanweld]

While it is common to append impact test qualification results to an existing ASME IX qualified welding procedure, it is not common practice to to rerate a vessel after so long a time in operation to a lower MDMT when impact testing is so obviously required. Assuming one had in one's possesion the original welding procedures, how can one assure that the new impact tested procedures comply with the actual welding procedures used in fabricating the vessel with regard to the supplementary essential variables, especially regarding heat input parameters?

 

[TangoCleveland]

stanweld,
I had the same concerns, that's why I posted the question. It's probably up to the jurisdiction or the AI. What we're planning, if the customer OKs it, is to install a nozzle on the longitucinal weld seam, and use the nozzle cutout to provide Charpy specimens. If the weld impacts are OK, we can rerate down. If they're not, client has an extra nozzle on the vessel. It's 54" ID and about 8 feet long.

Larry

 

[stanweld]

TangoCleveland,
Have yopu discussed this with your AI? More than likely the nozzle weld was made with E7018 electrodes or E71T1-M. The E7018 will more than likely pass but the E71T1-M will not. Main seams will more than likely have been made with SAW and most likely will not meet impacts at -50F. Most shops weld with F72-XXXX flux filler combinations.

If I were the AI, I would not permit the rerate unless the main seams were similarly checked. Weld repairs by you would have to made with -50F impact test qualified procedures. A further problem, unless the SA-516 steel was impact tested at -50F do not assume that it or the HAZ will meet the -50F absorbed energy requirements. More than likely, it will not.

 

[metengr]

This is an alteration in accordance with guidelines referenced in the NBIC because you are rerating to a lower MDMT. See Part RC-3022 in the 2004 Edition of the NBIC. The Jurisdiction AND the AI will need to review and approve.

 

[codeeng]

As I see it you could go back to your original manufacturer and have him re-qualify the welding procedure to include impact testing. This would be better than cutting a hole in the vessel.

 

[stanweld]

TangoCleveland,
Working for a Company that routinely performs maintenance and NBIC repairs and alterations in Power, Pulp and Paper and Petrochemical industries, I have, on a number of occasions, had to inform the Owner that its proposed rerate or other alteration plan could not be done and alternate plans were made or the original plan discarded. I would recommend the same to you in this instance.

After discussing with your AI and his/her supervision and the jurisdiction if required fully discuss the ramifications and requirem,ents with the Owner.