Pneumatic Test Pressure Basis - Why Less then Hydrostatic?

[Enginator]

Anyone know why the pneumatic test pressures of B31.1 and B31.3 are less than the hydrostatic (110% vs 150%)? Best I can come up with is safety. Pressure is pressure (given all other conditions identical), which means the hydrostatic test is more rigorous.

 

[metengr]

Enginator;
You are correct. Fluids that are compressible can store a tremendous amount of energy. Water is not compressible, as such, so if the vessel were to fail you would spew some water versus having a release of stored energy.