Hydrotest Pressure for Natural Gas Piping

The manual and control valves should probably have been selected to withstand the hydrotest pressure that would be imposed later. Relief valves, on the other hand, might be set for somewhat less. The usual technique is to plug the relief valve connections, conduct the hydrotest, and then reinstall the relief valves. (Perhaps with a further pneumatic test to check for small leaks.)

Mr Louis, Please take care with ASME B31.3 Parr. 345.4.2 (Chapter VI), 2008/2010 There are significant changes with respect to

ASME B31.3 2004

Pt=1.5PRr instead of Pt=(1.5PSt)/S

And yes, excluding pipe supports and Bolts, You have to check all the componets of the system: "....... ratio of component pressure rating........."

WP

For Natural Gas service, normally valves are selected with back seat arrangement to seal the gland in full open condition. In that case valves can be full opened and then hydrotest to the selected pressure.

Normally only valve body is subjected to hydraulic test of 1.5 times design pressure by their manufacturer. Please check with the valve manufacturer for other parts like gland or seal etc. If no, then carry out test in parts by removing the valves and blanking at flanges. Valves with welded ends can be blanked at bonnet after removing its internals.

I think you need to check the design pressure of the control valves,manual valves etc which must have been considered taking into account the pressure drop across the valves and most important the operating pressure of the piping circuit.This has to be compared with the hydro test pressure requirement of 156 kg/cm2,if they are less then better arrange blind (without valves ) and go ahead for hydro testing