ASME Hydrostatic Test Pressure

[gjb1]

ASME NB-3531 now calls for a hydrotest pressure of 1.5 x Class Rating of valve. I believe the previous ASME code was previously 1.5 x design pressure which is much lower. For example if I have a valve taking say 160 bar the previous hydrostatic test pressure was 240 bar. Under the new ASME(ANSIB16.34) rules the hydrotest pressure is around 400 bar.

Can anyone give me advice on why this was hydrotest pressure was changed. Also I am seeking advice on what needs to done to existing plant (if anything) that now fails to satisfy the new ASME criteria and what is the position with new plant builds that plan to use old design of plant.

Thanks in advance

gjb