HIPPS is part of the Safety Instrumented System (SIS) to avoid overpressure by shutting off the source and collecting the pressure on the system’s upstream side. Instruments provide the security function in HIPPS. The Safety Loop is made up of one or more initiators, final elements, and a logic solution.
HIPPS provides protection against overpressure by rapidly isolating the source that causes overpressure, reducing the risk profile of the plant. The industry is increasingly moving towards the use of HIPPS to reduce flare loading and to avoid the effect of pressure venting on the environment. The accredited SIL3 quality required for this application can be given by Independent HI.
Design & Construction:
A standard HIPPS will include 2 or 3 final elements in series and is often expected to shut down for gas within 2-3 seconds and for liquids within 6-8 seconds depending on the pipeline temperature, flow rate and pipeline diameter and grade.
A pressure sensing system can detect the initiator of the shut-down series (peak pressure surge). Three sensors are attached to the logic solver in this case, which is designed to vote with a 2oo3 logic (2 out of 3).
If the predefined pressure parameters are exceeded, the final elements and the process are shut down by the Logic Solver.
HIPPS safety loop:
A safety loop is a functional unit with input (Initiator), Logic Solver and output (Final Element). The role is structured in such a way that signals are transmitted from one to the other to protect a system. It de-energizes the suggested theory to fly.
Mechanical switches or electronic pressure transmitters are the required pressure sensing initiators. A safety loop can consist of one or more sensors to meet the safety function requirements.
Mechanical systems are most widely used in complex self-contained systems. These can be stand-alone with no external power source requirement and thus ideal for remote locations.
Usually, remote sensing uses electronic voting devices using force transmitters. We allow full contact with the security system and enable automated monitoring. The role of communication reduces the chance of spurious trips.
The transmitters are connected through trip amplifiers to a dedicated logic solver. The logic solver, especially the programmable ones, is probably the most complex device in the loop.
Between the pressure sensing part and the final element, the actuator is a vital component. It should be specifically designed over an extended service life for quick, reliable stroking.
Upon failure, the final component is to be closed. This action should be generated by energy, which is frequently springs independent of external sources. These actuators are designed to deliver five times the closing thrust required by the final element (including any ‘ break-out ‘ forces).
The shut-off valve in critical applications must meet the requirements of high safety standards. The final element is designed to be a highly reliable valve and to retain strong shut-off capabilities under all conditions to maintain the integrity of the operation of the elements.