Large ring-in-ring tank from steel?

[MartinLe]

In the wastewater field, you sometimes use ring in ring tanks, like here:

http://www.monostore.com/uk/index.php/website_uk/category/aeration_tanks

Is there any company that build such tanks from glass lined steel?
What would be the major challenges? What if the outter ring is roofed?

I'm asking a very open ended question here, I know. Usually we build with concrete, now a tender may force us to use steel, and I need to udnerstand the problems and possibilities.

 

[JStephen]

A steel tank shell is very efficient when loaded in hoop tension due to internal pressure. When pressure is on the outside, this is no longer the case, and the shell can be subject to buckling, and would typically require additional thickness and/or additional stiffeners.

From a cost perspective, you will always be ahead if you can build two round steel tanks side by side, adjusting diameters as needed, rather than one inside the other.

 

[fegenbush]

First, I agree with everything JStephen said if the assumption is that it is possible for fluid to be in the outer ring/tank while the inner ring/tank is dry is correct.

Second, while it is possible to use a *welded* steel tank for the inner tank with the necessary stiffeners, it may not be economical to do so. However, you mentioned glass lined steel. Glass lined tanks that I have seen are all bolted. These are not suitable for the external pressure required for the inner tank.

If there exists no possibility of external pressure on the inner tank by design, it may be possible to construct such a tank system from glass lined steel.

 

[JohnGP]

I've seen it in steel on a previous metals project, a 13.6m diameter shop fabricated tank with another tank inside, I think about 6m diameter. Roof over the top. There was communication between the spaces, but the inner tank was designed for blocked openings and full external pressure load. It was therefore quite thick, but the arrangement necessary because of a lack of space in the area it had to go. As I recall it made for interesting confined space entry requirement to access the inner tank.

I can't imagine glass lined - maybe epoxy or rubber?

 

[JStephen]

Something else I'll point out is that how practical it is, is highly dependent on the size and depth of the tanks.

 

[MartinLe]

Thanks for the input.

In normal operation, both tanks will be filled to about the same level, but we want to be able to empty one - so we might have the case that the inner tank is emnpty and bears the static pressure from the liquid in the outter ring.

Also, our suppliers for steel tanks (if we build with steel) bolt their tanks.

Last not least, operating procedure seems to be to start with the top of the tank, build a section, lift it up on jacks, build the next section, etc. I've never done such a thig, but I assume additionaö headaches with a ring-in-ring situation.