Maximum patch size for tank shell replacement

[CCMech]

Is there a maximum patch size for tank shell replacement? If yes, how to determine the maximum size? I don't see it is required in API 653, but our client asked about the maximum size of the patches.

Thanks,

 

[JStephen]

I think there is a limitation on lap-welded patches, but not on replacement shell plate. You can replace an entire ring or more if needed.

 

[CCMech]

Thanks JStephen.

If to replace part of the ring, do I need to consider that when cut out the old shell, the roof will collapse?

 

[DSB123]

CCMech,
If you consider this to be a possibility then yes you need to check it. Any modifications/rapairs you intend to do need a full assessment to ensure the tank is "stable" during all operations you intend to do to is and under all possible loading scenario's otherwise you are not "engineering" the proposed repair !!!

 

[MJCronin]

CC....

Tell your "client" that the maximum patch size for a flat bottomed tank whould be one that is the exact size of the tank shell.