1 reply to this topic

[bacardii]

As per ASME B31.3, for normal fluid service:

 

The minimum hydrostatic test pressure for metallic piping is given by the following equation.

 

PT = 1.5 x PD x ST/SD

where: PT = minimum test gage pressure

PD = internal design gage pressure

ST = allowable stress value at test temperature

SD = allowable stress value at design temperature

 

Whereas,

 

The pneumatic test pressure is as per the following equation.

 

PT = 1.1 X PD

where: PT = test gage pressure

PD = internal design gage pressure

 

My concern is, Why there there is no consideration of the temperature correction factor during Pneumatic Test. i.e. Why ST/SD is not considered in pneumatic test pressure calculations?

 

Anyone please?

[fallah]

 

bacardii,

 

Actually the value equal to 1.1*DP for pneumatic test pressure is the minimum value for this test, and as per ASME B.31.3 the pneumatic test pressure can be increased to the lesser of the:

- 1.33 times the design pressure

- The pressure that would produce longitudinal stress in excess of 90% of the yield strength of any component at the test temperature

 

Then one can include the temperature correction factor in pneumatic test pressure determination provided that above limitations would be considered.

 

Bottom line, i think the reason behind the fact that ASME B31.3 hasn't insisted on considering such correction factor in pneumatic test pressure  is: Inreasing the gas (normally air) temperature during gas pressurization to reach the test pressure even with regard to the statement there that the pressure shall be gradually increased...