High Integrity Pressure Protection Systems - HIPPS
HIPPS is an acronym for High Integrity Pressure Protection System, and a High Integrity Pressure Protection System is an independent Safety Instrumented System designed to detect unsafe high pressure conditions and close isolation valves thereby reliably isolating the source of overpressure from lower rated downstream piping and equipment.
HIPPS systems are not part of the plant's control system, nor part of its emergency shutdown system; they are standalone systems with a high Safety Integrity Level. The recommended safety integrity levels for HIPPS would be either SIL 3 or SIL 4.
Why use a HIPPS
Over pressure protection is commonly dealt with in process plants by using a relief system. The relief system provides an alternative route for fluids, such that when a set pressure is exceeded flow is directed away from piping and equipment that would be otherwise subjected to dangerous over pressurses. This alternative route usually leads to a flare or venting system, to prevent further inflow of fluids, whereas a HIPPS aims at stopping the inflow of excess fluids and containing them within the system. This means that when using a HIPPS system process fluids are not released to the atmosphere when high pressures are encountered; both an economic and environmental benefit.
In subsea oil and gas applications relief systems are not practicable and are not used. Subsea HIPPS systems are ideal in this situation. A subsea HIPPS module can be located in the production flow line between the source pressure, i.e a production well, and standard subsea equipment such as the production manifold. If the pressure at the HIPPS module exceeds the trip point, which is predetermined based on the pressure ratings of the downstream equipment, the HIPPS module valves will close, thereby preventing the over pressurization of the equipment downstream of the HIPPS module.
Components of a HIPPS System
The main components of a High Integrity Pressure Protection System are:
- Pressure Sensors; three sensors, usually transmitters, are used. Each sensor can have its own individual tapping into the pipeline, or a High Integrity Manifold Block can be used to tap into the line with each sensor connected to the manifold. High Integrity Manifold Blocks have mechanical, tamper proof interlocks, that permit only one pressure transmitter to be isolated or vented at any one time.
- Logic Solver; either a solid state or Programmable Electronic System, which receives and processes the input signal from the pressure sensors and transmits the output to the Solenoid Valves in the final control element.
- Final Control Elements; usually two shutdown valves (ball or butterfly) each fitted with redundant SOVs and fast acting valve actuators.
Redundancy within a HIPPS System
Components within a HIPPS system are generally provided with redundancy to meet the required Safety Integrity Level of the system. For example:
- Final control elements are arranged in series to give a one out of two (1oo2) arrangement. If either valve closes, a safe situation results. It is usual for partial stroke testing capability to be built into each HIPPS shutdown valve.
- Two solenoid valves are fitted to each shutdown valve in a one out of two (1oo2) arrangement. Tripping either SOV will allow the shutdown valve to close.
- Pressure sensors are configured in a two out of three (2oo3) arrangement. In this arrangement, if any two transmitters detect a high pressure this will prompt a shutdown to occur.
- The Logic Solver has redundancy built into it by the use of redundant components e.g. I/O Cards, relays, communication cards and power modules.
HIPPS Compliance Standards
High Integrity Pressure Protection Systems are designed and built according to three main international standards.
The International Electrotechnical Commission (IEC) standard 61511 (Functional Safety — Safety Instrumented Systems for the Process Industry Sector), part 1, part 2 and part 3,
IEC standard 61508 Functional Safety of Electrical/Electronic/Programmable Electronic Safety-related Systems, and
ANSI/ISA S84.01: Application of Safety Instrumented Systems of the Processed Industries.
Advantages of HIPPS Systems
High Integrity Pressure Protection Systems may offer operators significant CAPEX and OPEX savings.
For example, OPEX savings include no loss of valuable process fluids through venting or flaring due to a high pressure upset, though HIPPS systems have an inherent OPEX cost - see disadvantages below.
And CAPEX savings may be achieved when designing new installations by using HIPPS systems e.g.
- Reduce the requirements for expensive flare systems and pressure relief valve manifolds,
- Offer significant weight savings for offshore installations, due to reduced piping required in flare and venting systems,
- Allow pressure ratings for downstream piping and instrumentation to be reduced. This is especially applicable for wellhead installations.
Disadvantages of HIPPS Systems
HIPPS systems act by closing an inlet flow stream, therefore this closure may lead to partial, or total plant shutdown and resulting production losses.
HIPPS cannot be applied for overpressure scenarios such as fire and thermal expansion.
Higher OPEX costs associated with stricter requirements of maintenance, testing and inspection,
Technical Library
The following pages on Control and Instrumentation.com feature more aspects related to plant safety systems and HIPPS systems:
