Non-Cylindrical Hydrostatic Test Presure 1

[AaronJ]

Hello,
I have a piece of equipment that is essentially U-shaped, with an inner and outer steel shell. The equipment is designed to carry hot material in the open U-shape, and is filled with water to keep the steel at an acecptable temperature. There are internal ribs that are welded to the inner shell along their length, and welded with plug welds to the outer shell at points. The inner shell is 12.7mm (1/2") plate, the outer shell is 6.35mm (1/4") plate. The outer shell inside diameter is 516mm (20.3"). Due to the location of the piece of equipment, it must be leak proof. The operating presure is 5 bar (73psi) and we have proposed a test presure of 7.5 bar ( 108psi) which is 150%, at the top end of the ASTM E1003-5 reccomendations for hydrostatic leak test.

However, during a review it was questioned weather the equipment would see 5 bar presure in operation, and wether it could handle the 7.5 bar test pressure. The cooling water is circulated such that it should never see full presure unless there is a blockage, however the problem of the hydrostatic test presure remains.

Does anyone have any tips on how to calculate the maximum presure the equipment could handle. I've reviewed as much of the Pressure Vessel code I could handle, but I don't deal with pressure vessels often.

Any Suggestions would be appreciated. We've proposed to take a quick look at this in Ansys, treating it as a 2-d problem and applying the pressure on the inside, but we'd like to have a hand calc to compare it to.

Cheers,

Aaron

 

[prex]

If, as I suppose, the temperature of the material (?) in contact with the wall is higher than 100 degC, and unless your vessel is open to the atmosphere, the only internal pressure being due to pump head, then you are building a pressure vessel and you should comply with pressure vessel codes.
Calculating the maximunm allowable pressure is not the matter of a formula. You can have buckling of the inner shell and many other issues: nozzles, heads etc.
You should consult a pressure vessel specialist. If you will ask for more advice here (but of course we won't design your vessel here...), please join a sketch of the beast as detailed as possible (the U shape you are describing is not clear to me).
Also, as a starting point, you must be able to calculate the maximum operating temperature (at mid wall) that the vessel walls will see: this will depend on water flow rate, flow arrangement (internal baffles?) and on the heat exchange with the material on outside.

prex

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[BillBirch]

AaronJ,
If you find that deflections will be excessive, can you allow external ribs to stiffen the outer bulkhead?
Failing that do you have a way to reliably limit the cw pressure, e.g trlief valve?
Regards,
Bill