Hydro test pressure should be calculated as follow:
1) Hydro test pressure = 1.5 Times of Design Pressure.
2) For a design temperature above the test temperature, minimum test pressure can be calculated as:
Pt = (1.5 X P X St) / S
Where:-
P: Internal design pressure.
Pt: Minimum Test Pressure.
S: Allowable stress as design temperature.
4.) If the test pressure of piping exceeds the vessel pressure and it is not considered practicable to isolate piping from vessel, the piping and vessel may be tested together at test pressure of the vessel when approved by owner and provided the test pressure for vessel is not less than 115% of piping design pressure adjusted for temperature as per point
3) If a test pressure as per above would produce a stress in excess of the yield strength at test temp. The test pressure may be reduced to maximum pressure that will not exceed the yield strength at test temp.
Notes:
NBIC: National Board Inspection Code
MAWP: maximum allowable working pressure