API 653 - Max sizes for Patch Repair Plates on Tank Shell.
API 653 - Max sizes for Patch Repair Plates on Tank Shell.
(OP)
Hello All,
Looking at the method of using patch repair plates on the tank shell.........
In API 653 clause 9.3.1.7 it clearly states the maximum size of lapped patch plates is 48inches in height and 72 inches in length.
It also states in clause 9.3.1.10 that patch repair plates shall not be lapped onto other patch repair plates.
However it doesn't say in the code that you cant 'Butt weld' patch plates to one another? Therefore can you get a patch plate 48in x 72in and butt weld it to another patch repair plate of the same size?
My opinion is that you CANNOT butt weld patch plates to one another as by doing so you in effect make it one bigger patch plate, and therefore break the max allowable patch plate rule. Otherwise you would be allowed to use butt welded patch repairs right around the complete circumference of a tank or right up the tank shell height, which of course is a big NO NO!?
What is everyone elses thoughts on this as the code is not clear or is poorly worded?
Also are you allowed to carry out patch repairs to the inside of the tank shell? I have looked in API 653 and cannot see any details to say you can. All patch repairs are written in the context of being applied to the outside of the tank shell only?
Appreciate your comments/thoughts on the above.
Looking at the method of using patch repair plates on the tank shell.........
In API 653 clause 9.3.1.7 it clearly states the maximum size of lapped patch plates is 48inches in height and 72 inches in length.
It also states in clause 9.3.1.10 that patch repair plates shall not be lapped onto other patch repair plates.
However it doesn't say in the code that you cant 'Butt weld' patch plates to one another? Therefore can you get a patch plate 48in x 72in and butt weld it to another patch repair plate of the same size?
My opinion is that you CANNOT butt weld patch plates to one another as by doing so you in effect make it one bigger patch plate, and therefore break the max allowable patch plate rule. Otherwise you would be allowed to use butt welded patch repairs right around the complete circumference of a tank or right up the tank shell height, which of course is a big NO NO!?
What is everyone elses thoughts on this as the code is not clear or is poorly worded?
Also are you allowed to carry out patch repairs to the inside of the tank shell? I have looked in API 653 and cannot see any details to say you can. All patch repairs are written in the context of being applied to the outside of the tank shell only?
Appreciate your comments/thoughts on the above.





RE: API 653 - Max sizes for Patch Repair Plates on Tank Shell.
API 653 allows the use of lapped patch repair, but is not well stated the code to use. I mean, if we a had a look to
the cluase 9.3.4.2, it states:
"The repair plate is designed to withstand the hydrostatic pressure load between the repair plate and the
shell assuming a hole exists in the shell using a joint efficiency of 0.35"
My question is: How to perform a calculation? I don't think you have to use the formulas in 4.3.2 / 4.3.3, because
the stability of the tank is already assured by 9.3.4.1.
Any of you have already had this issue??
Thanks in advance
RE: API 653 - Max sizes for Patch Repair Plates on Tank Shell.
RE: API 653 - Max sizes for Patch Repair Plates on Tank Shell.
Do any of you have any comments or feedback with regards to the original post?
RE: API 653 - Max sizes for Patch Repair Plates on Tank Shell.
RE: API 653 - Max sizes for Patch Repair Plates on Tank Shell.
Just to clarify in your last response.....
"If the repairs are so extensive that you are considering butt welding lap patches together, I'd recommend a butt welded patch for the entire area."
Do you actually mean if the repairs are so extensive you would recommend a butt welded a shell insert plate replacement for the entire area?
As i mentioned the code only allows a max patch size of 48in x 72in and you cannot butt weld 2 patches of this size together?
RE: API 653 - Max sizes for Patch Repair Plates on Tank Shell.
RE: API 653 - Max sizes for Patch Repair Plates on Tank Shell.
This was my thoughts also but is nice to get a second opinion as the code is not clear on this subject.
Thanks for your feedback.
RE: API 653 - Max sizes for Patch Repair Plates on Tank Shell.
RE: API 653 - Max sizes for Patch Repair Plates on Tank Shell.