Fares Innal

Safety and operational integrity evaluation and design optimization of safety instrumented systems

The control of risks generated by modern industrial facilities could not be guaranteed without the use of safety instrumented systems (SIS). The failure of SIS to achieve their assigned functions could result in huge consequences with respect to both (i) the safety of the monitored system (relating to the SIS safety integrity) as well as (ii) its production availability due to false trips (relating to the SIS operational integrity). Furthermore, these two aspects are usually antagonistic. Therefore, the assurance of this double performance comes first by a thoughtful design of SIS. In that case, the aim of this paper is twofold. First, it focuses on the establishment of generic analytical formulations allowing the assessment of the SIS performance regarding safety integrity and operational integrity. Second, it deals with SIS architecture design optimization. The optimization problem is firstly addressed by a preliminary search for a balance between the above two quantities relying on the analysis of the structure of KooN architectures. Then, a more general and suitable approach based on genetic algorithms is proposed, where several performance indicators and the costs of purchase and maintenance are expected to be considered simultaneously. This general approach is illustrated through an application example.

Two-terminal reliability analysis for multi-phase communication networks

Prediction methodology of durability of locomotives diesel engines / L. P. Lingaitis, S. V. Mjamlin, D. Baranovsky, V. Jastremskas // Eksploatacja i Niezawodnosc. — 2012. — Vol. 14, № 2. — P. 154—159.

Piecewise Deterministic Markov Processes based approach applied to an offshore oil production system

This paper is keeping with the topic of two papers which treated dynamic reliability problems and were presented in previous conferences. Its aim is to confirm the potentialities of a method which combines the high modeling ability of the piecewise deterministic processes and the great computing power inherent to the Monte Carlo simulation. This method is now applied to a simplified but realistic offshore oil production system which is a hybrid system combining continuous-time and discrete-time dynamics. The results thus obtained have been compared with those given by an ad hoc Petri net model for comparison and validation purposes.

PFDavg generalized formulas for SIS subject to partial and full periodic tests based on multi-phase Markov models

IEC 61508 is a standard on design and operation of safety-instrumented systems (SISs) which has been adapted by many national regulations as the recommended way to achieve high-reliability systems. Many decisions about the design of SIS rely on the results from reliability assessments. It is therefore important that the reliability assessments are able to capture key properties of the system, such as the consideration of regular partial and full proof tests. IEC 61508 has proposed analytical formulas for commonly used architectures. Unfortunately, these formulas do not explicitly include the contribution of partial tests and consequently their use is mainly restricted to full proof tests. In addition, the already existing formulas dealing with partial tests disregard the different repair times. The aim of this paper is to (i) extend the PFDavg formulas given in IEC 61508 by including partial tests impact and, (ii) investigate their consistency based on multi-phase Markov models related to 1oo1 and 1oo2 architectures and (iii) to establish new generalized formulations in light of the results related to the investigation process, which account for the different repair times. Different comparisons are performed throughout the paper in order to validate the set of the derived formulations.

Safety Integrity Evaluation of a Butane Tank Overpressure Evacuation System According to IEC 61508 Standard

IEC 61508 standard provides a structured approach relying on hazards identification in order to establish safety requirements for safety instrumented systems (SISs). It aims at designing and operating the SIS within a reliability confidence that meets these requirements. The object of this paper is to give a concise description of IEC 61508 approach and to demonstrate it for the evaluation of safety barriers intervening against overpressure implemented on a butane storage tank. Specifically, the risk graph and layer of protection analysis approaches suggested in IEC 61508 for the determination of safety requirements are illustrated. In addition, it is shown that the use of more elaborate reliability approaches, such as fault tree and Markov graph, could be required for an effective risk assessment process. Actually, these approaches allow to consider the real configuration and operating conditions of the studied system.