Double Wall Vertical Tank - Anchor Chair

[TLHS]

Hey all,

I was just having a think about vertical double wall storage tanks with anchor chairs for overturning based on seismic loading. I don't know if I've seen this detailed before. Has anyone hit this situation? Presumably the chairs have to get welded to both the primary and secondary, which means the plates need to penetrate through the secondary? For wind it would seem like just the external secondary would hold it in place, but with earthquakes the inertial load is all transferred in the primary internal shell.

 

[JStephen]

I would say the inner and outer walls have to be connected to transfer vertical loads, but that connection doesn't necessarily imply an anchor chair attached to the inner shell. IE, it would seem you could anchor the outer shell with conventional chairs, and connect the two shells at the top or any other convenient point so that the inner shell is also held down by the outer shell.

 

[TLHS]

I was thinking about that. But if the inner shell is attached at the top, does that mean you'll get pendulum situation going if there's an interstitial space? It doesn't feel reliable.

 

[HTURKAK]

I am not sure that i got the full picture...Is this a tank for storage of refrigerated liquefied gas ? what is the size of space between two shells ? If so, pls provide some info. regarding the insulation ..

Assuming the tank is atmospheric and ambient temperature, if i would need double wall ( for some reasons say ,area restrictions 9,i would provide anchorage to the outer shell and use minimum space between two shells ( say 1200 mm) and extend the bottom plates to the outer shell.. and i would design the annular plt ( assuming membrane element ) to transfer the seismic effects to exterior shell anchorage ..

 

[Geoff13]

Double wall tanks usually store refrigerated or cryogenic products (API 620 Annex Q or R). In this case the inner tank will thermally contract too much for a rigid connection like an anchor chair, and thus an anchor strap is required. However a standard anchor chair is OK for the outer tank.

The inner tank anchor strap will have to go through the outer tank bottom, but the outer tank is just an insulation jacket so good seal welding will do the trick.

 

[TLHS]

Double wall tanks that I typically see are intended as secondary containment in leiu of containment berms or similar for petrochemical or other environmentally harmful items. If insulated, the insulation is external to the secondary shell. (missed the post two up. will come back and provide more detail when I've got some time)