The designer must ensure that there is critical flow through the choke in order to eliminate the effects of downstream pressure variations on the formation. This is achieved when the FTHP is approximately 1.7 times the downstream flowline pressure.
By its very nature the choke is subjected to very high pressure drops, which can lead to mechanical problems. These are dealt with briefly below and are drawn from experience with chokes in several Opco's world wide.
Start up and shut down
With zero pressure in the flowline and maximum . . .