cup tank (tank in tank) design code

[cornemo]

I have to design a cup tank (a tank within a tank, the inner is the storage container, the outer is to capture the medium in case of leakage of the inner tank). In design codes for cylindrical storage tanks like API650 and EN 14015 a double-bottom is adressed briefly. However a cup tank is nowhere mentioned.

Before I start making up all kinds of design rules myself I want to check if there are design codes for such kind of tanks. Remember that the outer tank is just a leakage container and the inner is the actual non-pressurized (-5/+10 mbar) storage tank. If any of you can help me it would be highly appreciated. Also design considerations are welcome.

With regards, Corné

 

[IFRs]

I would design both to the same code since both serve the same purpose (storing liquid). The fact that the outer tank may never be used does not change it's intended service or design basis IMHO. It would be terrible if the inner tank leaked and the outer tank failed!

 

[kacarrol]

I think if you do a search for "double wall tanks" you may be able to find the code class that you are looking for. I've included an example below.

Good luck,
K

 

[JohnGP]

If cylindrical then use API 650 (or EN14015) as IFRs suggests. If the inner tank contents leaked out, then the outer tank needs to act like a normal tank and be designed accordingly.

I had a tank within a tank on one project - there was a separate liquid stream to the outer section, but even though there were small penetrations between the two areas the tank supplier designed the inner wall for external loading (to ASME VIII) to cover the scenario of outer section full, inner tank empty. Made for quite a thick inner wall, but thankfully not the situation you have.

Cheers,
John

 

[JStephen]

API-620 has some requirements that address double-wall tanks, though I think the assumption is that the outer tank need not contain the contents.

 

[wfjer]

UL-142 / UL-58

Both codes deal with primary and secondary containment tanks, UL-58 is for underground tanks, and UL-142 is for aboveground tanks.

 

[cornemo]

UL-142 only deals with pre-fabricated tanks. I need a code for field welded double wall steel storage tanks.

 

[JohnGP]

Use API 650 for both walls, as suggested above. There's not really any significant interaction effect between the two. You have to consider that the outer tank can retain the contents if the inner tank fails, but that's still just a normal tank design case.