I have a quick question, how many repairs can we make to a bottom of a storage tank before it is required for us to replace it all ? If it is mentioned in API 653 which section will i found it ?
I'm a junior engineer in this filed that don't have much experience so i thought that it would be mentioned in the code. Thank you for your answer so it depends on its state.
You have a very valuable piece of capital equiment. Try not to treat it like an afterthought. How long would you patch the tires on your Mercedes? What risk are you and your company willing to take? Your first responsibility as a professional enginer should for the public safety. Failure can be an environmental disaster that might affect your grandchildren and beyond. Failure can be subtle (a small leak) and become very expensive to fix and remediate. Imagine yourself and your boss in front of a judge trying to explain why your ocmpany chose not to replace the bottom after multiple repairs. "The API standard did not say we had to" may not going get you very far, or explain it to the neighbors who were affected...
Above every thing else, it depends on the operation down time.
If you have spare tanks and can afford leaks hence wastage of product, no issues regarding pollution of the environment, you may use the tank forever.
What is normally done then?
Carry out MFL of the bottom plates, make an assessment, check the next shutdown opportunity and take the decision for repair or partial/ total replacement.
When contemplating replacing a tank bottom, inspect the shell also. Failing to understand the condition of the entire tank may result in real trouble. Allied Terminals Fertilizer Tank Collapse
November 12, 2008 a two-million-gallon liquid fertilizer storage tank collapsed at the Allied Terminal distribution facility in Chesapeake, VA.
Tank was originally designed and constructed in 1929 for petroleum product storage.
Report attached (it is useful to know what has happened so we can avoid repeating prior failures).
May be obsolete but Amoco covered many old bottoms with fiberglas / polyesther. Some FRP bottoms had to be 30 years old when I retired but I did not hear of problems ( I should have because I wrote up some of the procedures). Often these tanks were in locations where ground water was monitored for contamination.