HIPPS system becomes a practical application under many circumstances.
The basic HIPPS system is composed of two Trunnion shutdown ball valves that are automated either pneumatically or hydraulically.
The redundancy is another risk mitigation tool that increases the assurance that the upstream pressure source is contained.
The actuator commands are driven by normally supplying three pressure transmitters on the process line to monitor pressure, should the pressure exceed the desired set point, this information is relayed to the logic solver, (PLC based or solid state), that determines the need to close the valves.
The three pressure transmitters work normally in a 2003 voting logic, should one device fail to properly operate.
The logic solver normally works in a 1oo2 voting logic and it’s determined to be less likely to fail.
The redundant PLC or solid state devices work as a team to make the most accurate determination of the information sent to it, ensuring that the HIPPS closure is warranted and mitigating spurious nuisance trips.
Each system is engineered to meet the demands of classification of SIL ll or SIL lll. It is important to note that SIL level is applied to the system and not just to a device, as a single device on its own cannot achieve SIL level as a SIS function.
The logic solver uses inputs from the initiators, pressure transmitters, and other devices as required by the safety analysis, to close the valve.
The logic solver can either be PLC or Solid State devices. PLC’s are redundant to mitigate spurious trips or erroneous closers by failed PLC logic.
In the event a single PLC or solid state device fails, an alarm is generated to the DCS to initiate maintenance on the system.
These same alarms can be generated for any of the components in the HIPPS package, valve, actuator, pressure transmitter, solenoids, position indicating device and others as required.
The logic solver can be configured in any type of cabinet suitable for the area classification or environmental condition at site. CAM Valves will provide the components as well as the programming and engineering, HMI, installation, commissioning, start up, and maintenance of the system.
Pressure transmitters are supplied in a 2oo3 configuration, installed on the process pipe, pipe stand or cabinet mounted.
They can be separate or on a manifold.
If any of the transmitters fails to operate within its design parameters, alarms are generated to DCS for maintenance and the systems evolves to a 1oo2 logic within the logic solver.
All our HIPPS systems are engineered and de-signed to IEC codes 61508/11 and are certified by third party analysis for SIL III or SIL IV. Once a HIPPS system is installed, it must be tested throughout its life in the system that will allow the system to maintain its SIL certification.
Our serviceteam can maintain the system through its life cycle to the required safety level should any changes occur or be required.
HIPPS (High Integrity Pressure Protection System), is a Safety Instrumented System (SIS).
The primary function of a HIPPS is to protect personnel and downstream equipment against an overpressure scenario or an upset condition coming from the upstream pressure source.
HIPPS also helps to protect the environment by limiting the need to flare bypass or pressure regulator relieved gas or other product.
To mitigate the risk of this overpressure scenario, the HIPPS system uses inputs from pressure sensors to detect and demand closed, a dedicated set of valves, thus preventing further downstream pressurization.
The final elements, or valves, may only contribute 50% of the PFD calculation, but if they do not close tight, then the rest of the system is near useless. It is for this reason that we would recommend the use of two valves in series and not use soft seated valves as the soft seats can easily be damaged when closing under high differential and at the speeds that are demanded by the HIPPS system. (For Cryogenic Service and HIPPS system together in one design, the seats insert recommended will be KEL-F ©).
Generally PEEK seats or Metal seats are preferred. Most any valve can pass the shop test, it is in the field, in service where the reliability needs to be calculated from. Calculations for PFD should be generated from valves in similar service, and not many valves are in HIPPS applications.
Many valves fail in the field as they will not close after remaining in the open position for extended periods of time, or the seats get damaged and fail to seal tight. (This is one of the most important facts).
Another consideration is the stem and the connection of the stem to the ball. Many times the actuators are designed for 1.5 to 2.0 times the valves normal operating torque and HIPPS valves are sized to close, not open.
Careful attention needs to be paid to the stems maximum allowable applied torque, “MAST”.
HIPPS valves close quickly and the starts and stops generate considerable strain on the valve stems, the larger the valve, the more mass and inertia that is implied on the valve stem and connection that can cause stems to exceed their stress levels.