PSV sizing, vapor liquid flow

[mpor]

I have to size several PSV for two phase flow case,
procedure is based on HEM (the isentropic nozzle model included in PRODE PROPERTIES),
my question is about discharging piping,
I have calculated (with PRODE PROPERTIES) the critical speed for gas+liquid in discharging line,
my problem is that in discharging line I have values about 50% of calculated speed of sound, could that be a problem ?
Should that mean that we have to redesign the piping ?

[carlo.stenali]

Hi mpor,
to calculate mach number for gas, liquid or two phase flow in Excel use the method
=StrSS(stream)
available in PRODE PROPERTIES,
which returns speed of sound, from that value you can calculate mach number,
the values you mentioned (mach number up to 0.7) are quite usual for flare networks, discharging piping etc.
for a safe design you must evaluate stress on piping (at discharging conditions)

[cstaff]

thanks Carlo