........so in summation:

For use with the B31 Code for Pressure Piping:

The full thermal range is the coldest temperature that the piping will experience to the hottest temperature that the piping will experience. It would be the summation of the installation temperature to coldest temperature and the installation temperature to the hottest temperature. Keep in mind there might only be a few full cycles and many, many partial cycles and that is why the B31 Codes provide an equation for calculating the equivalent total cycles (and this becomes the indicator for the "f" value in calculating the allowable stress range.

Also remember that the B31 Codes currently require the use of the materials modulus of elasticity at 70 degrees F when calculating the thermal STRESS range for these thermal (displacement) ranges.

When you calculate the loadings (forces and moments) on the equipment you would use the OPERATING temperature and the modulus of elasticity at the operating temperature. You may find that this makes a great difference in very hot systems and very cold systems.

You can see why it might be necessary to make quite a few loading cases in your analyses.

Regards, John