Shutdown Systems and Their Effect on Commissioning

As all process industries strive for safer plant designs, shutdown systems are becoming more complex. For projects in the oil and gas industries, the process licensor often provides the initial design for the shutdown system (sometimes called Safety Instrumented System). During the detailed design phase, additional layers of complexity can be added as the various parties involved in a project (owner, licensor, EPC contractor, programmer, etc.) add devices and/or logic based on their past experiences. These additions are made with the best of intentions, however as the level of complexity increases, so does the potential for difficulties during plant commissioning. These difficulties can result in a significant number of plant shutdowns and subsequent restarts. Since a large percentage of safety incidents occur during plant startups and shutdowns, the argument can be made that more complex shutdown systems can lead to a decrease in overall plant safety rather than the intended increase. This paper will discuss the author's experiences with shutdown systems during the commissioning of sulfur recovery units in overseas oil refineries and gas plants and provide general suggestions for future design considerations which are applicable to all shutdown systems.