I'm currently carrying out a validation exercise for the manual venting of a 500 psi, 10km 24" NB natural gas pipeline via a manual blowdown station. The valve station comprises a 6in manual valve and associated downstream R.O. The take-off line and manual tail-pipe are vertically oriented directly off the top of the pipeline.
Initially it seems that the RO is somewhat oversized and flow is supersonic in the tailpipe downstream of the RO. The tailpipe is only a couple of metres long.
My concern is the sound pressure level in the vicinity of the tailpipe. My initial feeling is that the high flow rate and high mach No. will lead to potentially damaging sound levels in the region of the blowdown station. Has anyone got any experience on this? Are there any "rules of thumb" for this sort of thing to determine the sound level? Or should a silencer be specified as a rule in these conditions?
Most of the literature considers either tailpipes which are connected to a flare header, where fluid momentum is limited to prevent piping damage. In this case there aren't any bends so vibration should (??) not be an issue.
My question really is whether sonic flow can be tolerated in the (short) tailpipe, or is this something which will have to be validated by some accoustic simulation work to determine sound pressure levels and determine whether silencing is required.