Repair / Alteration Joint Efficiency 1

[fabtank]

Can a repair or alteration to a pressure vessel result in a decreased joint efficiency, given the calculations are done to support the new joint efficiency?
We have a vessel repair that we will not be able to perform 100% RT of the repair as would be required for a 100% Joint Efficiency.
If we have the calculations to show the vessel will meet the design criteria with an 85% joint efficiency can this be done?

 

[metengr]

Yes. per the NBIC one can derate but one cannot increase joint efficiency for re-rating.

Rationale;
First see footnote 10 below in 2013 Edition, NBIC Part 3, Section 3.4.2 Re-Rating

Re-rating: Except as provided for Yankee Dryers in Supplement 5, this code does not provide rules for de-rating boilers or pressure vessels; however, when the MAWP and/or allowable temperature of a boiler or pressure vessel is reduced, the Jurisdiction where the object is installed should be contacted to determine if specific procedures should be followed.

Now see 3.4.1 (a) Revised calculations verifying the new service conditions shall be prepared in accordance with the “R”
Certificate Holder’s Quality Control System. Establishing a higher joint efficiency to re-rate a pressureretaining
item is not permitted;

 

[Haiker]

In Section VIII if you can't RT you are allowed to UT. Not sure about NBIC though?