Test Vs Working Pressure

[millsjj]

Hi,

This is a very entry level question but when doing the pressure calculation for a pressure vessel based on ASME, should I be using working pressure or Hydrotest pressure for my calcs? Not sure if the calculations factor in the allowance for the hydro or if that should be my value for the calcs.

Thanks

 

[metengr]

You should be using design pressure.

 

[marty007]

There are three pressures to consider:

Operating (working) pressure -> Normal operation.
Design pressure -> higher than operating pressure - takes into account relief valve set pressures.
Hydrotest pressure -> Additional 30% over design pressure (with some correction for design/hydrotest temperature).

For ASME you calculate for design pressure.

Many customers will also have requirements that you calculate the stresses during hydrotest and ensure they do not exceed typically 90% of yield (rough rule of thumb, many additional considerations).