A High Integrity Pressure Protection System (HIPPS) is a Safety Instrumented System (SIS) designed to prevent an unsafe condition caused by pressure arising (e.g. due to separator outlet blocked in the choke valve downstream, blocked pipeline, etc).
The decision to utilize a HIPPS in addition of utilize a PSV shall be based on the study of risk. The aim of this study is to determine a certain SIL requirement.
This study will conclude whether some process condition need to have a HIPPS or its ok to protect it by a PSV valve only.
A High Integrity Pressure Protection System typically is a complete functional loop consisting of:
– The initiators which detect the high pressure.
– A Logic Solver, which processes the input from the initiators and transmits an output to the final elements.
– The Final Elements, which consists of a valve actuated by solenoids.
In general, the HIPPS required a minimum SIL 3 certification for a complete loop above (sensor, logic solver, and final element). Therefore the HIPPS architecture of the initiators, logic solver, and final elements shall be determined by using a SIL calculation. But in typical the architecture of the HIPPS will consist of 3 pressure transmitter, redundant logic solver, and 2 shutdown valve to achieve SIL 3 requirement. See VOTING LOGIC for more detail information about loop architecture selection to achieve certain SIL requirement.
Another unique design of the HIPPS valve is the closing time of the valve that must be as fast as possible. In general application the HIPPS valve closure time requirement is calculated and simulated by using a dynamic simulation. The aim of the fast closure time in the HIPPS valve is to protect the downstream of the valve from a very high pressure condition that can happen in a very fast time.
As an example and illustration, let’s say we have a separator downstream of the production manifold that needs to be protected from a high pressure due to separator outlet blocked. The separator design pressure is 800 psig, and the pressure downstream of the choke valve through the production manifold can be as higher as 1500 psig. With this condition and known flow rate to separator, the pressure arising time can be calculated.
If the normal operating pressure of the separator is 600 psig, then time pressure arising from 600 psig to 800 psig must be calculated. Lets say, after some calculation the time needed by the separator to arise it pressure from 600 psig to 800 psig is 4 second, then this 4 second will be the minimum closing time of the HIPPS valve. If the closing time of the HIPPS valve is more than 4 second, the pressure inside the separator will arise more than its design pressure when the outlet is blocked and will endanger the platform (event though there will always be a PSV installed in the separator).