Hi Ranka,

In the cited Code paragraph, there is mention of several "pure" loadings that are really very rarely encountered in the real world. These are offered for "completeness". The bearing stress is a pure compressive stress. There are also allowable stress magnitudes provided for pure tension (e.g. the stress in hanger rods under ideal conditions) and pure shear (be aware of this limit if you have a very heavy valve near a support). These are not intended to be combined stresses.

The Codes address thermal (displacement) stress ranges with equations for calculating combined stresses using Tresca failure theory. In the High Pressure section of B31.3, Von Mises failure theory is used in the equation for required wall thickness.

Of course, the above is just my opinion and it is not necessarily the opinion of ASME or any Code Committee.

Best regards, John.

[ November 15, 2001: Message edited by: John Breen ]