Attached Legs to 2:1 Elliptical Head

[chuckoehler]

Is there any design considerations to take into account when attaching legs directly the bottom head instead of attaching them to the shell. I want to use either channels or angle supports to attach the legs to the head. The vessel itself is an API 650 tank that is atmosperic.

 

[waskillywabbit]

I don't recall their being anything specifically mentioned in API 650 in regards to legs and I didn't see anything with quick glance, but I would think you would need to consider buckling, if there are any seismic or wind loadings, and certainly whether or not the thickness of the head will take the legs directly beneath it (punching through) as API 650 tanks are generally quite thin compared to ASME designed tanks.

Brian
Pressure Vessels and Autoclave Systems

http://www.mcabeeconstruction.com

The above comments/opinions are solely my own and not those of McAbee Construction.

 

[codeeng]

API 650 does not cover leg supports only flat bottom. If you want legs I would first consider putting them on the shell and design as a shear attachment. If they must go on the head then you should check using FEA such as NozzlePro.

 

[JStephen]

The main problem with legs is there is not a good analysis for them. FEA is one solution. You might consider if you can treat the leg attachment as an upside-down anchor chair per standard anchor chair methods. Or you can design a circular girder so that the girder itself carries all non-axisymmetric loads, leaving the tank itself axisymmetrically loaded. In many cases, on small tanks, it is more economical to beef up the connection details than to spend engineering time designing better ones.

Assuming you work out some way to adequately analyze the tank, there's no reason you couldn't put the legs on the elliptical head. I've noticed a bunch of little cone-bottom tanks on farms, and most of them have legs attaching to the cone with circular ring.

 

[PEHasan]

API 650 cpde does not cover for leg supports. All the tanks are flat bottom tanks and they are supposed to rest on concrete base or structural frame. Change your bottom from formed end to flat end and let the tank bottom rest on structural frame. Provide four leg supports for structural frame.

 

[jamesl]

In E. Megyesy's "Pressure Vessel Handbook", there are several pages dealing with stresses in the head caused by leg supports. You can find the formulas and a sample calculation.