[b]Cone bottom tank installation and exterior corrosion[/b]

[PW2006]

We used to have cone bottom carbon steel tanks (approx. 25ft dia. x 10ft high) sitting on approx. 2ft high gravel-band foundation. The typical installation procedures are: A 2ft high steel band, that has larger diameter than the tank is formed on a concrete slab at first, then gravels are added into the band until it reaches to certain height. Then we would form the slope of the gravels to match the shape of the cone bottom of the tank. After the slop of the gravel foundation is made (close enough), the tank is put on its top. Some minor adjustment can be made after that. We put non-corrosive water based liquid in the tanks.

Recently, I found that the exterior bottoms of these tanks have pretty bad corrosions at many areas (mainly along the outer, closer to the wall, areas). They are much worse than the flat bottom carbon tanks sitting directly on the concrete slab in the similar environment. I wonder how this would happen. All cone bottom tanks have the same exterior coating as the flat bottom steel tanks.

It is difficult to make the gravel slope to match the cone shape of the tank bottom. The original coating might have been damaged by the gravels during the installation. This is what I am guessing.

I wonder if you have similar bad experience with cone bottom steel tanks sitting on the gravel-band foundation or can explain how this happened. Do you have good suggestion about making the slope of the gravel to match the cone shape of the tank bottom?

Thanks.

 

[Perdido]

I wonder if the manufacturers are the same? Sure it is the same coating? Corrosion is specific to its local environment, if tanks are in the same environment then I would think the problem is a material issue not a design issue...

 

[MikeHalloran]

Plus, rainwater is pretty much guaranteed to run down the bottom surface of the conical tank, whereas it has no particular incentive to do so under a flat bottom tank.

Next time, you might consider extending the outside cylindrical wall of the tank down a few inches into the gravel, so the water will drip off before reaching the cone.





Mike Halloran
Pembroke Pines, FL, USA