API 510 Temporary Fillet Weld Patch Repair

[jcneel]

According to API 510, Section 7.2.7, Fillet weld lap patches are acceptable for temporary repairs after being approved by experienced pressure vessel engineer. What calculations need to be done to evaluate and approve such a repair?

API 510 lists:

1. Allowable membrane stress not exceeded in vessel parts and patches
2. strain in patches does not exceed allowable stresses of the fillet welds.

How does one calculate these values. Is there someplace I can look as a sample to follow for such a review?

thanks

jcneel

 

[jte]

jcneel-

First, make sure that your jurisdiction is ok with fillet welded lap patches on vessels. We use them for piping, but California doesn't allow them to be used on vessels.

1. pr/t
2. Draw a free body diagram of a section cut. In addition to the membrane stress you'll have bending due to the offset between the mid-thickness of the shell and the mid-thickness of the patch. Since your weld has a thinner throat than the thickness of the patch plate, the weld will (in my experience) always govern the thickness of the plate.

Alternatively, if you can beg, borrow, or steal an advance version of ASME PCC-2 that could be a good resource. It deals with post construction issues such as this. Due to be released as a 2006 edition with sections which were approved as of the Code Committee meetings last week. Anyone know which sections were approved?

jt