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What Is High-Integrity Pressure Protection System (HIPPS)? | Process Engineering Glossary
What Is High-Integrity Pressure Protection System (HIPPS)?
In piping engineering and process engineering, a High-Integrity Pressure Protection System (HIPPS) is a safety instrumented system that prevents downstream equipment from exceeding its maximum allowable working pressure by detecting an overpressure condition upstream and rapidly closing one or more shutdown valves to isolate the high-pressure source. Unlike a pressure relief valve, which vents fluid to a flare or atmosphere after overpressure occurs, a HIPPS acts proactively to prevent the overpressure from ever reaching the protected equipment. It is the last instrumented line of defence between a high-pressure source and a lower-rated downstream system.
Applications of HIPPS
Wellhead and Subsea Protection
High-pressure wellheads produce fluids at pressures that may far exceed the design pressure of the downstream gathering and processing system. A HIPPS between the wellhead choke valve and the downstream low-pressure pipeline protects the pipeline from the wellhead shutin pressure in the event of a blocked outlet or choke valve failure. Subsea HIPPS systems are designed for operation at seabed conditions, where intervention for repair or maintenance is extremely difficult and expensive, demanding very high reliability and very long proof test intervals.
Pipeline Overpressure Protection
Long-distance high-pressure gas pipelines connect to lower-pressure distribution networks through pressure reduction stations. A HIPPS at the inlet to a pipeline section rated for a lower pressure protects that section from receiving the full upstream pipeline pressure if the pressure reduction station fails open. This protection eliminates the need for a large relief valve at the inlet, avoiding the associated gas venting and flare load that would otherwise result.
Offshore and Onshore Process Plants
Separator inlet and outlet systems in offshore and onshore oil and gas plants use HIPPS to protect downstream equipment from the high-pressure source connected to the separator inlet. Where the separator inlet pressure substantially exceeds the design pressure of the downstream liquid or gas handling equipment, a HIPPS between the separator and the downstream system provides the required overpressure protection without requiring undersized downstream equipment to handle the full source pressure.
Benefits of HIPPS
Proof Testing Complexity
Maintaining HIPPS SIL certification requires regular proof testing of all loop components at defined intervals. This testing is logistically demanding in an operating plant and may require partial or full shutdown of the protected section. Failure to complete proof testing on schedule invalidates the SIL certification and may require recalculation of the required relief capacity without HIPPS credit.
Common Cause Failure
A HIPPS that fails simultaneously in all its independent channels due to a common cause, such as a manufacturing defect in all three pressure transmitters from the same lot, provides no protection despite appearing functional. Common cause failure management requires using components from different manufacturers for each channel, careful installation separation, and diverse technologies where possible. This diversity adds complexity and cost to the HIPPS design and procurement.
Not a Substitute for Relief in All Scenarios
A HIPPS protects against specific, identified overpressure scenarios for which it is designed and SIL-certified. It does not protect against overpressure scenarios that were not considered in the design basis, nor against scenarios that develop faster than the process safety time allows for detection and valve closure. Residual relief protection, sized for the remaining overpressure scenarios not covered by the HIPPS, is typically required alongside the HIPPS rather than being eliminated entirely.
Limitations to Consider
Proof Testing Complexity
Maintaining HIPPS SIL certification requires regular proof testing of all loop components at defined intervals. This testing is logistically demanding in an operating plant and may require partial or full shutdown of the protected section. Failure to complete proof testing on schedule invalidates the SIL certification and may require recalculation of the required relief capacity without HIPPS credit.
Common Cause Failure
A HIPPS that fails simultaneously in all its independent channels due to a common cause, such as a manufacturing defect in all three pressure transmitters from the same lot, provides no protection despite appearing functional. Common cause failure management requires using components from different manufacturers for each channel, careful installation separation, and diverse technologies where possible. This diversity adds complexity and cost to the HIPPS design and procurement.
Not a Substitute for Relief in All Scenarios
A HIPPS protects against specific, identified overpressure scenarios for which it is designed and SIL-certified. It does not protect against overpressure scenarios that were not considered in the design basis, nor against scenarios that develop faster than the process safety time allows for detection and valve closure. Residual relief protection, sized for the remaining overpressure scenarios not covered by the HIPPS, is typically required alongside the HIPPS rather than being eliminated entirely.
HIPPS FAQ
What is a HIPPS in process engineering? A HIPPS is a safety instrumented system that protects downstream equipment from overpressure by detecting a high-pressure condition and rapidly closing shutdown valves to isolate the high-pressure source before the downstream equipment pressure exceeds its maximum allowable working pressure. Unlike a relief system that vents fluid after overpressure occurs, HIPPS prevents the event entirely. It is designed, verified, and maintained to a Safety Integrity Level under IEC 61511, with instrumentation comprising pressure transmitters in a voting arrangement, an independent logic solver, and fail-close final element valves. Process engineering and safety engineering jointly establish the required SIL through a layers of protection analysis, which determines how much risk reduction the HIPPS must provide.
How is a HIPPS documented on engineering drawings? The piping and instrumentation diagram shows the HIPPS pressure transmitters with their independent process taps, the logic solver connection, and the final element shutdown valves with their fail-close designation. The HIPPS loop is typically highlighted or designated with a specific tag convention to identify it as a safety instrumented function. The process hazard analysis documents the overpressure scenario, the required SIL level, and the basis for HIPPS credit in the protection layer assessment. The control valve or choke upstream of the HIPPS is shown upstream of the HIPPS boundary, with the protected downstream equipment clearly identified at its lower design pressure rating.
How does HIPPS interact with the pressure vessel design and piping specification? Taking HIPPS credit allows engineers to design downstream pressure vessels and associated piping for the HIPPS-protected pressure rather than the full upstream source pressure. The piping specification for the downstream section assigns a lower pressure class, reflecting the reduced design pressure that the HIPPS makes possible. The boundary between the upstream high-pressure piping class and the downstream lower-pressure class coincides with the HIPPS shutdown valve location. This boundary must be clearly shown on the piping and instrumentation diagram and confirmed in the piping class break documentation. Any failure of the HIPPS boundary integrity, through valve leakage or bypass, exposes the lower-rated downstream system to the full upstream pressure, which is why HIPPS valve selection and maintenance are treated with the same rigour as the pressure boundary itself.
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