Hydrotest pressure value has always been confused between equipment & piping. However the pressure vessle code as per ASME Section VIII, Div. 1 & the process piping code as per ASME B31.3 give different values of hydrotest.
ASME Sec. VIII, Div.1 (pressure vessel code) specifies hydrotest pressure as follows:
P = Design Pressure X 1.3 X (Stress Value of the metal at test temperature / Stress Value of the metal at design temperature)
ASME B31.3 (process piping code) specifies hydrotest pressure as follows:
P = Design Pressure X 1.5 X (Stress Value of the metal at test temperature / Stress Value of the metal at design temperature)
I have attached the relevant portions of both the codes for clarity.
This should help in clearing any doubts.
Regards,
Ankur.
.