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Learn When Logic Solvers Are Appropriate for Overpressure Protection Systems

Learn When Logic Solvers Are Appropriate for Overpressure Protection Systems

An overpressure situation in pipes is dangerous and can lead to significant damages to property, pipe ruptures and even injuries and death. Having a system in place to prevent an overpressure situation is critical and one way to accomplish this is with a High Integrity Pressure Protection System (HIPPS). 

An HIPPS provides a barrier between high pressure and low pressure parts of an installation to prevent the release of fluid or gas into or otherwise contaminate the environment. An example of an HIPPS is in an offshore well platform where the subsea oil or gas lines can occasionally present a harmful pressure surge in the pipeline. The HIPPS is designed to shut off the source before the design pressure of the downstream process is exceeded, avoiding a rupture of a line or vessel.

An HIPPS consists of three main components:

  • Pressure transmitters
  • Logic solvers
  • Fast-acting shutoff valves

Many people assume that the logic solver has to be a safety PLC. But in many cases a discrete logic device for each loop, which avoids the complications and expense of a programmable solution, is a sensible option. The “Logic Solvers for Overpressure Protection” white paper shows how discrete logic devices such as the STA Safety Trip Alarm are suitable for use while providing a flexible, low-cost and user-friendly solution.

While the safety PLC approach offers advantages for installations where there are a high number of field I/O safety loops, many plants have few such loops. For these plants, discrete logic solutions offer several advantages including creating a simple architecture, reducing cabling costs and avoiding the development cost of application programming.

The STA is easy to install with its wide range of power supply options and its small package that helps to keep it separate from non-safety instrumentation. In the event of maintenance due to transients or failure, it can be readily swapped out at low unit and operational cost without interfering with the other processes in the plant. Local indication gives reassurance that the status of safety loops is reported directly.

The “Logic Solvers for Overpressure Protection” white paper shows safety engineers the steps needed to determine the right logic solver for their SIS. It shows the methodology and calculations for determining the applicability of logic solvers in SIL 1 and SIL 2 environments. It includes examples of system topologies and their associated Safety Integrity Level (SIL) calculations.

The STA Safety Trip Alarm is part of Moore Industries’ FS Functional Safety Series of instruments. Each of these instruments are designed and built in compliance with IEC 61508, the leading worldwide functional safety standard, and certified by exida for use in a Safety Instrumented System. In addition to our FS Series of products FMEDA (Failure Modes Effects and Diagnostic Analysis) reports available on many of our products that are used in safety applications.

Find out more information about these products at the FS Functional Safety Series section of our website. You can also download the related “Logic Solvers for Tank Overfill Protection” white paper

Published: July 13, 2015
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