Reliability Measures for Liquefied Natural Gas Receiving Terminal Based on the Failure Information of Emergency Shutdown System

Abstract

Natural Gas (NG), one of the cleanest, most efficient and useful of all energy sources, is a vital component of the world's energy supply. To make the NG more convenient for storage and transportation, it is refined and condensed into a liquid called liquefied natural gas (LNG). In an LNG site, safety is a long-team critical issue. The emergency shutdown system (ESS) in the LNG receiving terminal is used to automatically stop the pumps and isolate the leakage section. Fault tree analysis (FTA) has been widely used to characterize the logical functional relationships among components and subsystems of a system, and to identify the root causes of failures in a system. In the conventional FTA for the ESS, we assume that exact failure probabilities of events are available. However, in real applications the FTA for the ESS needs to be done at an early design or manufacturing stage at which certain new components may have to be used without failure data. Also, sometimes due to environmental changes in the ESS during the operation periods, it is difficult to gather past exact failures data for the FTA. Hence there may not be sufficient information for a conventional FTA. In this research, we propose an intuitionistic fuzzy (IF) sets theory based approach for the FTA which can be used when the conventional FTA cannot. We generate the IF fault-tree interval and the IF reliability interval for the ESS. Based on IF-FTA, we also present an algorithm for finding the critical components and determining weak paths in the ESS for which the key improvement event must be made.