Think of failure modes. Any failure of common seal gas skid component may shutdown all compressor units.
No stds that i'm aware of.

Minimum normal seal gas supply pressure must be greater than the max normal shutdown - settleout pressure of all downstream connected casings. And max normal also includes settleout pressure that would be reached when blocked in casing warms up to ambient in the case of refrigerant compressors in LNG liquifaction cycles. Obviously, seal gas hydrocarbon dewpoint considerations also apply.

Thank you both for the reply.

Most probably individual feeds from the common header (after the seal gas is conditioned via filters, dehydration, heaters etc) may have separate pressure let downs (or flow controls) and conditioned seal gas will have to be sized for the highest pressure required by the seals.

I guess maintaining dew point (due to J-T effect through PCVs) may be the key factor particularly for multi-stage casings in LNG application for deciding common seal gas conditioning skid vs separate skid.

All I was trying to find out whether can there be some case where common skid could pose challenge for multi-stage in LNG application and my guess is yes unless some one disagrees with logic....

edm123 (Mechanical)(OP)

If there is redundancy designed into it, the unit can still run.
If not, the unit will always trigger Alarm , Trip or not allowed a re-start .

Seal gas supply to each casing should preferably be on flow control to minimise seal gas demand. Running on seal chamber pressure control can lead to excessive seal gas demand during normal operation.

Thank you all for responding