Application of Prognostics and Health Management to Low Demand Systems: Use of Condition Data to Help Determine Function Test Interval

Many safety instrumented systems (SIS) such as emergency shut down (ESD) are designed as low demand systems, whose functionalities are only triggered under certain conditions once or fewer times a year. Reliability levels of several critical low demand systems were observed to be high on the Norwegian continental shelf (NCS) over the last 15 years [1]. In general terms, there is a lack of confidence in whether the functionality of a low demand system can be initiated and how well the system can perform upon a real demand. This paper studies such challenges and suggests the application of prognostics and health management (PHM) to evaluate the function test interval instead of remaining useful lifetime. The value of condition data is justified and reflected in the estimation of failure rate and function test interval. The application of PHM to low demand systems can help enhance a company’s confidence in system availability and operational reliability and its adherence to a predictive maintenance practice.