New MDMT Requirement - Derating of Pressure Vessel

[Iyer S]

We have a pressure Vessel ID 5,029mm X 12,920mm OAL x 24/20mm Thk – SA 516 Gr.60N + HIC, Originally Designed as per Div 1 with MDMT of -2 Deg C, U stamped.
There is a Process Requirement to Revise the MDMT to -29 Deg C.

For the new MDMT, the vessel need to be "R" Stamped.

We have the following documents.
1. MTCs of all Shell / Dished End Plates, having Different Heat Nos, all Impact Tested at -46 Deg C (at colder temp than required MDMT of -29 Deg C)
2. PQRs for all pressure parts welding have been Impact Tested at - 29 Deg C.

With the above documents (1 and 2), can we approach ASME Inspector for "R" Stamp?
Is it Mandatory that all the Welding Consumables (Pressure parts welding)impact Tested at -29 Deg C or Colder? (The QC Dossier with us, does not included MTCs for the Welding Consumables)..

Need an expert advise

Regards

 

[metengr]

My expert advise is to review the National Board Inspection Code (NBIC), Part 3 for the rules to follow for an alteration. This will require an organization in possession of a valid National Board R-Certificate to perform Repairs and Alterations. The organization will have an Inspector who has an R endorsement. It is not an ASME Inspector.

The reduction in MDMT is an alteration. Your other option is to review API 510 for alterations to pressure vessels.