Dear Neil,

The program will actually perform the calculation either way, but it depends on the input. There is a check box under the "Miscellaneous" tab that asks if the Nozzle (or the diameter limit) is outside of the 80% (spherical) limit of the head. If this is the case, check the box and the program will indeed use the appropriate equation for required thickness due to internal pressure.

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Scott Mayeux
COADE Inc.