Pressure Vessel Problem

If they are equal they will cancel out.

the widows in your house have 1 atmosphere acting on both inside and outside and are quite happy!

well yes but in a sphyrical pressure vessel the area on the internal surface is less than the area of the external surface.

Unless the vessel has thick walls, the area on the interior should exactly equal the area on the exterior.

Likewise a commercial diver's helmet stays dry inside with a "simple" neoprene seal around his neck, because when he's under 530 feet of seawater (16 atmosphere's pressure) the air being fed to him is regulated to that same pressure. As another has mentioned, more info is required in order to give a thoroughly appropriate response. What (construction) Code or Codes apply, for one thing.

IT doesnt matter what shape the vessel is 100 psi internal pressure is 100 psi. If you had 100 psi outside pressure you would have a net zero. I wouldnt assume that this means you could put another 100 psi into a tank that wasnt rated for it because of the outside pressure cancelling out some of it.

What you have to consider is that at some time one of the pressures is going to be different - or the purpose of the two spheres is of no importance surely.

Not necessarilly, the vessel could just be separating two different gasses at the same or similar pressures.

Whatever, it appears to me the thread doesn't give enough info' for a useful answer.

By definition if the pressure you are refering to is in psi and they are equal inside and out, the differences in surface area are normalized in "PSI" and the pressure would cancel each other to delta of zero.

A good reference is PRESSURE VESSEL HANDBOOK, by Eugene F. Megyesy, published by Pressure Vessel Publishing, Inc. P.O. Box 35365 Tulsa, Oklahoma 74153 USA.

There is also computer software that will guide you through the design process. It is called Compress provided by Codeware Inc., 3100 S. Gessner Rd., Suite 610 Houston, TX 77063. The codeware web site is:

http://www.codeware.com/

Thank you very much that link was very helpful

Hold gentlemen, it is a rule of thumb, and according to ASME & TEMA codes, that when you have a pressure vessel or part of a pressure vessel subjected to internal pressure, say P_int, and external pressure, P_ext, at this case you have to proceed your design pressure, P at 3 cases of loadings:

Case a: P = P_int

Case b: P = P_ext

Case c: P = P_int -P_ext

So the worst case shall be governed.

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