Modification of tank bottom design API 650

[andimilan]

Is it allowed to modify by making a small pond on the floor of the API 650 tank design? Small pond that we need in order to suction pump to suck all the liquid in the tank and leaving little fluid on the part of the pond? If allowed, how safe way to modify it so as not to damage the structure of the tank? thank you

 

[JStephen]

Usually, that would be accomplished by installing a sump in the bottom, with the bottom sloped uniformly to the sump if drainage was critical. With an existing tank, you can add the sump, but may not get 100% drainage of the contents unless you want to do a lot of extra work. API-650 has typical sump details, and API-653 addresses repairs and modifications to existing tanks.