Floor-to-shell weld stresses in an aboveground storage tank

[CanucKev]

I'm not sure whether this is the right forum for a question about an AST, but here goes anyway. I'm trying to determine the stresses that a tank's edge settlement will cause in its floor-to-shell weld for a presentation my boss is making on it later this week. Does anyone have any advice/suggestions as to where I could find more info on that? So far I've only found brief mentions of it in large articles (for example, API 653 just says "Edge settlement increases secondary stress at the bottom-to-shell weld. If weld repairs are made ... in an area where settlement exceeds 1/2 of B_e, these additional stresses should be evaluated by an engineer..." (B.3.4.7) What are the secondary stresses?)

Thanks in advance.

 

[vesselguy]

The secondary stresses they're talking about are the resultant bending stresses caused by the deformation of the tank floor/shell. I am not aware of any closed form equation you can use to evaluate that. If I was doing it, I would use finite element analysis to do this. I recall FE-Pipe has a module that will evaluate stresses in this area due to settlement. You can ask your boss to either pay for a full copy or rent time from them.

 

[fortmceng]

Only through a Finite Element Analysis you could determine stresses. Also, in edge settlement you would have to check plastic strain. I don't remember off hand but in API 653 it is mentioned that how much is allowed. If the strain exceeds the allowable limits you would have to replace plate section apart from correcting the edge settlement issue. There are consultants who could do this type of FEA fairly quickly and they are not too expensive (provided you have all the drawings including foundation detail).