In most cases, when pumps will operate at relative low temperature, determining its required hydrostatic test pressure is simple and straight-forward. All that is needed is add a service factor, usually 50%, to its maximum allowable working pressure (MAWP) to determine the hydrotest pressure.
Example: A pump that will operate at 150 degrees Fahrenheit with an MAWP of 400 PSIG will have to be hydrotested at 600 PSIG, (or 400 x 1.5 = 600 PSIG.)
But if the pump were to operate at elevated temperature, a material temperature correction factor has to be applied to compensate for the lower allowable tensile stress of the material at the elevated temperature. This is important specially when using materials whose tensile strength degrade quickly with temperature, such as stainless steel.
Thus, the hydrostatic test pressure (P) should be calculated as follows:
MAWP P = -------- x 1.5 F
where F is the material temperature correction factor, and is equal to the ratio of the allowable material stresses at operating and ambient temperatures (taken from stress table.)
What should be the hydrostatic test pressure of the above cited pump if it were made of cast SA-351, CF8M316 stainless steel, and if it were to operate at 650 degrees Fahrenheit?
From ASME stress table, its allowable tensile stress is 17,500 PSI at ambient temperature (up to 100 degrees) and 11,500 PSI at 650 degrees Fahrenheit.
400 P = -- ---------------------- x 1.5 = 913 PSIG (11,500 / 17,500)