High-Integrity Pressure Protection System (HIPPS)
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The HIPPS is a specific application of a safety instrumented system (SIS) designed in accordance with IEC 61508. The function of a HIPPS is to protect the downstream equipment against overpressure by closing the source. Usually this is done by timely closing of one or more dedicated safety shutoff valves to prevent further pressure rise of the piping downstream from those valves. A HIPPS is also commonly referred to as a “high-integrity pipeline protection system,” because many HIPPS design/cost studies are associated with field layout pipeline/flowline designs. HIPPS is applied in a subsea field development. Application of HIPPS allows for the use of a lower pressure rated flowline compared to the wellhead and tree equipment. Because length, wall thickness, and pressure ratings are the major cost-driving factors for flowlines, the flowline can be an expensive item in subsea field development. Because a subsea HIPPS is installed upstream of the flowline, the design pressure of it can be lower than the well shutdown pressure. Thus the wall thickness can be reduced, which directly cuts its cost. The HIPPS is designed as a system that detects rising pressure in a flowline and quickly shuts one or more isolation barrier valves before the pressure can rise too high. This requires a very reliable and highly available system as well as a fastacting system. Therefore, the main components of a HIPPS are as follows:
- Pressure (and other) transmitters;
- Logic;
- Redundant barrier valves.
Topside equipment will be needed to supply the necessary electrical and hydraulic power, which will be transmitted to the subsea equipment via an umbilical. Subsea equipment located adjacent to the barrier valves will provide the actual detection and actuation mechanisms. A second HIPPS barrier valve is also monitored on either side by pressure transmitters, which provides redundancy in case of failure or leakage of the first valve. The topsides equipment comprises:
- Master control system;
- Electrical power unit;
- Uninterruptible power supply (UPS);
- Hydraulic power unit. The subsea equipment comprises:
- Umbilical and termination/distribution unit;
- HIPPS subsea control module and mounting base;
- SAM and mounting base;
- Hydraulic jumpers;
- Process barrier valves and position indicators;
- Maintenance, venting, and test valves.
To ensure availability and prevent erroneous shutdowns, usually more than one transmitter is employed in a “two out of three”(2003) voting (triplicate) configuration, and different makes of sensor can be used to avoid common fault modes. Either the transmitters themselves and/or the detection logic will act in such a way that a failed transmitter is seen as a “high” pressure and therefore trips the system. The control hardware monitors the transmitters and closes the barrier valves when high pressure is detected. The detection and activation system is inevitably an electronic system, and it should be independent of any other platform or subsea system. This usually results in use of a dedicated subsea controller that is located in an SCM adjacent to the barrier valves themselves. The HIPPS control module (HCM) monitors the transmitters and closes the valves in the event excessive pressure is detected. This operates via a certified fixed-logic electronic system and is not dependent on microprocessors or links to the surface. Thus, each trip is preset and cannot be changed without physical access to the controller. This requires careful attention to hydraulic design to ensure pulses do not inadvertently trip the system.
References
[1] Society for Underwater Technology, Subsea Production Control, SUT, Subsea Awareness Course, 2008.
[2] B. Laurent, P.S. Jean, L. Robert, First Application of the All-Electric Subsea Production System Implementation of a New Technology, OTC 18819, Offshore Technology Conference, Houston, 2006.
[3] C.P. William, Subsea Control Module, U.S. Patent 6,161,618, 2000.
[4] International Electro-technical Commission, Functional safety of electrical/electronic/ programmable electronic safety-related systems, IEC 61508, 2010.
[5] J. Davalath, H.B. Skeels, S. Corneliussen, Current State of the Art in the Design of Subsea HIPPS Systems, OTC 14183, Offshore Technology Conference, Houston, 2002.
[6] International Organization of Standards, Petroleum and natural gas industries - Design and operation of subsea production Systems - Part 6: Subsea production control systems, ISO 13628, 2000.
