Storage tank with concrete floor

[mp662]

I have a firewater tank complying with NFPA code that requires an inspection every 3 years.  It also requires an internal inspection complying with API 653.  3 years ago, it was inspected and the floor was shot.  At that time, a concrete floor was poured in the tank and put back in service.  Our new inspector says that since it doesn't have a metal floor, it does not comply with API code and thus won't pass NFPA inspection.  I wanted to get your thoughts on the validity of this claim

If it needs a new floor, it will be difficult to install as it is a very old riveted tank. Second part of my question is: what is the best way to install a new floor on a riveted tank, where the tank wall plates overlap?

 

[gr2vessels]

First, you need an expert to assess the condition of the tank, if it can take the full load of water or less.
Then you only need to install an internal rubber or plastic lining, attached to the junction of the shell and roof. You need to prevent condensation penetrating behind the lining, between the shell and lining. You might also need to assess the concrete surface for smoothness or fill in a layer of fine compacted sand. You might need to install new nozzles cut in the shell, to replace the welded ones with bolted nozzles.
I assume you can drain the tank and provide a good internal paint for extended service life, if not already provided in form of powder coated or painted bolted sections.
Cheers,
gr2vessels

 

[IFRs]

I would agree with your inspector. You were given bad advice to pour a slab inside this tank. Installing a secondary bottom in a riveted tank with a sand or concrete spacer is fairly common and most qualified tank companies can do it for you. They deal with the laps without much difficulty. The tank is currently not really good - the concrete is probably not very well sealed to the tank shell and the water is probably between the shell and the concrete as well as under the concrete slab.

 

[JStephen]

Check the wording on the NFPA requirement. I was thinking it required a "structural" inspection, which would not necessarily be the same as an API-650 inspection. If you have a hole in the floor and it's leaking, that's a problem for a water tank, a major problem with an oil tank, but not necessarily a structural problem, either.

 

[chicopee]

Wording in these codes are important and you may also find an exception to the metal floor, so read these codes carefully. A rubber liner mentioned above is favored by many and as a matter of fact one of our clients does have a concrete floor and rubber liner in their sodium hydroxide riveted tank. This liner is replace every three years.