Moore Industries-International has published a technical white paper exploring the possibilities available to designers of Safety Instrumented Systems (SIS) using logic solvers as part of an overpressure protection system. Available for download, the “Logic Solvers for Overpressure Protection” white paper provides examples of straightforward pressure protection system topologies and associated PFDavg (Average Probability of Failure upon Demand) calculations and Safety Integrity Level (SIL) classifications.
A high integrity pressure protection system (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 a 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.
The “Logic Solvers for Overpressure Protection” white paper shows safety engineers the steps needed to determine the right logic solver for their SIS. In many cases, a discrete logic device in the safety loop can serve as the logic solver in a HIPPS application instead of a complex and expensive safety PLC. The white paper shows the methodology and calculations for determining the applicability of logic solvers in SIL 1 and SIL 2 environments. In many cases, discrete logic devices such as the STA Safety Trip Alarm are suitable for use while providing a flexible, low-cost and user-friendly solution.