API 653 Tank Bottom Replacement

[JGard1985]

Happy Friday

Looking at replacing the entire bottom of a 60' diameter tank. Given the foundation configuration and some other challenges, the recommended solution is to install a second bottom over the existing bottom as specified in API 653 9.10.2. Looking for a couple bench marks from members

- Confirmation there isn't an API-653 standard detail for this repair (I didn't see one). Multiple references that the floor must cut through shell with double sided fillet welds
- Non-corrosive material cushion (Sand gravel or concrete). Would love to hear experiences with each. I was leaning toward sand but a contractor prefers concrete)
Typical plate spacing?
- Any horror stories or experiences you'd incorporate beyond the code
-Need for a leak detection system if there wasn't one installed previously
-Galvanic Corrosion 9.10.2.4: What is standard practice? Leaving tank floor in place and adding a cathodic protection system. Is there enough cushion that can prevent the need for a protection system with say concrete?


Thank you so much

 

[HTURKAK]

Dear JGard1985 (Structural) ,

This subject has been discussed in past with several threads.
I would like to answer some of your queries ;

-The code explains the requirements pls look 9.10.2.1.1 through 9.10.2.1.6. The common practice is shell slotting (complete severing of the tank wall ) 100-150mm above the bottom .

- The use of 100mm concrete spacer should be preferred. Radial grooves could be added for leak detection.

-If you choose sand for spacer material , you will need C.P. for external corrosion.


P.S. In case of ambient temperature tank and If the tank bottom plates completely supported by the foundation in the critical zone, you may consider fiberglass internal lining of the existing bottom as an option.