High-Integrity Protection Systems (HIPS): Methods and Tools for Efficient Safety Integrity Levels Analysis and Calculations

Abstract

Summary High Integrity Protection Systems (HIPS) are more and more extensively used in the oil industry to replace conventional safety systems, and this paper aims to show how to efficiently evaluate their Safety Integrity Levels (SIL) as required by the IEC 61508 (1998) and 61511 (2003) standards. These standards provide rigorous formal processes to build the safety of Safety Instrumented Systems (SIS) and are very efficient from an organizational point of view. However, difficulties still arise with definitions and probabilistic calculations, and for this reason our company has developed a set of probabilistic methods and tools to overcome such difficulties. They are based on traditional holistic approaches and the powerful algorithms developed in the reliability field over the past 30 or 40 years: Fault Trees, Markov processes, and Monte Carlo simulation performed on behavioral models (e.g., Petri nets or formal languages). They are briefly analyzed in this paper using simple examples to highlight the principles. This paper is mainly focused on HIPS working in low-demand-mode (i.e., with less than one demand per year according to the standards) and HIPS such as High Integrity Pressure Protection Systems (HIPPS), but indications are given for HIPS functioning in continuous modes of operation. The main conclusions are that, when properly handled, Fault trees are very efficient for low-demand topside HIPS; that the Markovian approach is interesting but practicable only for very small systems; and that Monte Carlo simulation on behavioral models is efficient in all cases. From our point of view, these approaches are simpler to handle than the informative formulae proposed in the present issue of the standards. Therefore, we have begun to disseminate these approaches and we strongly recommend our contractors to use them.