HIPPS Valves: High Integrity Pressure Protection System Design and Selection

A High Integrity Pressure Protection System (HIPPS) is an instrumented safety function that protects downstream equipment from overpressure by closing dedicated valves to isolate the pressure source, rather than relieving the excess through a relief valve to flare. HIPPS is used where relieving is impractical or unsafe - very high flow rates, toxic or sour fluids, or where flare capacity is limited. Because a HIPPS is often the last line of defence against a loss-of-containment event, its valves are among the most rigorously specified in the plant.

How a HIPPS Works

A HIPPS consists of three parts: initiators (usually three pressure transmitters in a two-out-of-three voting arrangement), a logic solver (a certified safety PLC), and final elements (the HIPPS valves and their actuators). When two of three transmitters detect pressure approaching the design limit, the logic solver de-energises the actuators and the valves close within a defined time, isolating the overpressure source. The entire loop is designed to a Safety Integrity Level (SIL) - typically SIL 2 or SIL 3 - under IEC 61508 and IEC 61511.

What SIL Means for the Valve

SIL quantifies the probability that the safety function fails on demand (PFD). A higher SIL demands lower failure probability and higher diagnostic coverage. For the final-element valve, this translates into hard requirements on reliability, tight shutoff, fast and proven stroking, and the ability to test the valve without a full shutdown. The valve, actuator, solenoid, and any partial-stroke device are analysed together as the final element, and their combined failure rate must fit within the SIL budget allocated to the final element (often the largest contributor to loop PFD).

HIPPS Final-Element Valve Requirements

Why Two Valves in Series

Most HIPPS installations use two final-element valves in series, each with its own actuator and solenoid, in a one-out-of-two (1oo2) arrangement so that either valve closing achieves isolation. This redundancy raises the safety availability needed for SIL 3 and allows one valve to be partial-stroke tested or bypassed for maintenance while the other still provides protection. The valves are typically trunnion-mounted ball valves for fast, tight, fire-safe isolation, though through-conduit slab gate valves are used for pipeline and sandy or waxy service.

Partial Stroke Testing

A large HIPPS valve cannot be fully closed to test it without shutting the process down, yet SIL verification requires periodic proof testing to detect dangerous undetected failures. Partial stroke testing (PST) moves the valve a small amount (typically 10-20 percent) and confirms it responds, detecting a large fraction of stuck-valve failures while keeping the process running. PST capability - via a smart positioner or dedicated PST controller - is therefore a common HIPPS valve requirement and directly improves the achievable SIL by raising diagnostic coverage.

Specification Checklist

1. 1Define the SIL target (from the SIL determination / LOPA study) and the PFD budget allocated to the final element.
2. 2Select valve type for tight, fast, fire-safe isolation - trunnion ball (default) or through-conduit gate.
3. 3Specify spring-return fail-close actuation sized for the worst-case differential pressure and required stroke time.
4. 4Require an IEC 61508 device certificate with FMEDA failure-rate data for the valve-actuator-solenoid assembly.
5. 5Specify ISO 5208 Rate A / API 6D shutoff and API 607 or API 6FA fire testing.
6. 6Include partial stroke testing capability and define the proof-test interval.
7. 7Require NACE MR0175 materials for sour service and full EN 10204 3.1 traceability.

Vajra Industrial Solutions supplies HIPPS final-element valves - trunnion-mounted ball and through-conduit gate valves - with SIL 2/3 certified spring-return actuation, ISO 5208 Rate A tight shutoff, API 6FA fire-safe testing, partial-stroke-ready smart positioners, NACE MR0175 materials, and full FMEDA and traceability documentation for overpressure protection on oil, gas, and pipeline systems.