Determining hydrostatic test pressure


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.)


Example

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?

Solution

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)


Next: More on hydrostatic testing


R: 1109-DEHY
C: testing
F: test hydrostatic calculation


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