A pattern-based methodology for reliability assessment of safety instrumented systems

Safety Instrumented Systems (SIS) act as important safety barriers in industrial systems for preventing hazardous accidents. It is therefore significant to study the reliability issues of SIS. As a matter of fact, SIS have common behaviors such as periodic test policies to discover dangerous undetected failures. Modeling patterns capitalize the experience from modeling SIS. By reusing modeling patterns, modeling mission can be simplified when assessing reliability and availability of systems. Few studies related to SIS have been conducted on patterns for reliability assessment. This paper proposes a pattern-based methodology for reliability assessment of SIS. To demonstrate the applicability, the proposed methodology is applied on an emergency depressurization system provided in an ISO technical report (ISO/TR 12489). The comparison is performed between results obtained using given modeling patterns and the ones from ISO/TR 12489. It is shown that the pattern-based methodology can serve as an effective tool for modeling SIS in a modular way.