Pressure Variations During Warm Hydrotesting

Abstract In the pressure vessels and heat exchanger manufacturing, some codes and specifications require the final acceptance test (hydrotest) to be performed at temperature higher than the ambient temperature. This may also be a code requirement depending on the conditions. This is done to reduce the risks of embrittlement under stress which may happen on certain high-strength materials (especially Cr–Mo steels). The execution of a hydrotest in warm conditions poses some challenges including the pressure variations induced by the temperature drop during the hydrotest duration. This essay provides a simple practical methodology for calculating such pressure variations with the aim of properly preparing the system to perform the hydrotest.