Dear All,

DEP 31.38.01.11-Gen (February 2012), Section 2.3.4, states that for slow valve closing speed surge pressure can be calculated as below:

P_surge = (0.02 * L * density * fluid_velocity * valve_closure_speed) / DN

where L is the piping lenght between pump and valve and DN the nominal diameter in pipe.

The same section states as below:

"The maximum surge pressure develops when the valve closes rapidly relative to the piping lenght. Using SI units, the maximum surge pressure is calculated by the Joukovski formula:

P_surge = system_sonic_velocity * density * fluid_velocity "

I tried to use both formulas, and Joukovski yields a higher value of surge pressure. With such value my system fails, whereas with the surge pressure I get from the first formula the system pass.

Since the slow valve closing speed is exactly my case, do you think I can use the first formula rather then Joukovski even if it's less conservative?

Thank you for your valuable opinion.

Hello Pune...You can coordinate with the process engineer if they have performed a detailed surge analysis..From this analysis they can give the differential pressure vs time profile for each leg in your piping system...Then you can perform a time history dynamic analysis to get the response of the piping system due to surge load...Usually if your closing time is slow enough then this surge forces can be taken by the piping system..Joukuwsky formula is a conservative approach but if your having problem in your system it would be best to consult the process engineers...Sometimes they can mitigate this problem by doing some tweaking in how the system shuts down usually slowing down valve closing time...Anyway you can download the 4th Dynamic webinar by Dave (Time History Analysis in Caesar II) to have a feel on how the dynamic analysis is done in Beam Element softwares....From this webinar you can see that the Force time data from a hydraulic software can be imported to a Mechanical software (Caesar II)...