API 650-Bottom shape selection

[carletes]

Dear all,

I have seen storage tanks (crude oil, diesel, kerosene,..) which have different bottom types: some of them have conical shape (slope approx. 1:120) with the tank center being the highest point and a drawoff sump near the shell but in other cases the bottom has inverted conical shape with the tank center being the lowest and a drawoff sump in that center.
Does anybody knows the advantages/disadvantages of each solution?

Best regards and thank you

 

[JStephen]

The theoretical advantage to having a tank crowned up at the center is that if the center settles more than the edge, it won't load the floor in tension. But I don't know if that makes any big difference in practice.

Edge sumps require less piping, and don't have to dodge the center column. Center sumps should help avoid corrosion around the shell, and drain to a single point better.

 

[chicopee]

With the edge of the shell being higher then the center, all the sediment and water will tend to gravitate to the center for easy removal by the sump pump.

 

[MJCronin]

Carletes,

This particular issue is discussed in detail in Phillip Myers fine book "Aboveground Storage Tanks" (McGraw-Hill)

You will find different opinions by different "tank experts" on this issue. The best choice depends a lot on the liquid stored, the tank coating system and the expected design life of the tank.

In my understanding, for storage of crude, cone-up or flat bottom is preferred because corrosion is not concentrated in the center of the bottom. Corrosion there is harder to detect and repair. A downside is multiple water draw-off points on the tank perimeter

For storage of less aggressive liquids,...your choice

-MJC