Pressure Vessel Repair based on ASME VIII
Pressure Vessel Repair based on ASME VIII
(OP)
We have a thinned down pressure vessel and as an immediate repair, we have installed a patch plate on the thinned down portion. Does ASME allow this repair method for a long term? Or shall I recommend sectional replacement? Where in the ASME code is this topic discussed? By the way, the operating conditions of the vessel is about 4 psig and 350 deg C.





RE: Pressure Vessel Repair based on ASME VIII
Regards, John
RE: Pressure Vessel Repair based on ASME VIII
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Regards, John
RE: Pressure Vessel Repair based on ASME VIII
RE: Pressure Vessel Repair based on ASME VIII
A "scab patch" or surface patch plate is worse then having a hole in the vessel. If you hole thru under the scab you have made a new problem area. The pressure will extend to a large surface area that may be weaker then your vessel wall. Depending on what you have in this vessel it could let go when the fillet welds break and the contents under the patch flash.
People die from this kind of thing.
RE: Pressure Vessel Repair based on ASME VIII
I concur w/ deanc, you are playing w/ fire.
Brian
RE: Pressure Vessel Repair based on ASME VIII
Steve Braune
Tank Industry Consultants
www.tankindustry.com
RE: Pressure Vessel Repair based on ASME VIII
4psi yes-maybe not so much of a problem. 350 C-ouch!--whats in the tank?
Why take a chance? Still bad practice.
RE: Pressure Vessel Repair based on ASME VIII
Did you really mean four psig? Just to make sure.
RE: Pressure Vessel Repair based on ASME VIII
Must confess. The 350C didn't sink in. At that temp, i would expect insulation, so delta issue might not be too bad.
I agree that lap patches could be poor practice, especially if mis-applied to a high hoop stress application. But, recognized Codes and Standards permit them when designed properly. Yeah, the high temp issues would still concern me on this one.
Steve Braune
Tank Industry Consultants
www.tankindustry.com
RE: Pressure Vessel Repair based on ASME VIII
RE: Pressure Vessel Repair based on ASME VIII
Why not put scab on side of wall that is corroding? Would that soothe your concerns any?
Steve Braune
Tank Industry Consultants
www.tankindustry.com
RE: Pressure Vessel Repair based on ASME VIII
That could work and has often been used to protect against errosion/corrosion. One may also wish to weld build up the corroded area and or apply a corrosion resistant barrier? The scab patches that I referenced have been on the outside surface and have been done so for the sake of expediency and initial lower cost so as not to require draining/cleaning the tank. Tank may remain in service during repair.
RE: Pressure Vessel Repair based on ASME VIII
Yes,I agree with you that in limited applications a lap patch could be OK. Water tank,oil tank,something that could not be drained and properly fixed. Small hole---maybe a coupling per UW-16(f)????
Back in the days of rivets,what else could one do? They were however required to be applied from the inside.
It would be a good idea if used,calc. for thickness,use plug or slot welds to attach and the outside fillet only to seal.
The big problem is that scab patches are misused,just sloppy work and are dangerous in many cases. Had to cut too many of them out and do a proper fix in the past.