Research On LNG Carrier Safety Instrumented Systems Design And Assessment

LNG carriers are widely used in the entire LNG industrial chain; it’s involved in almost every aspects like production, storage, transportation, and regasification and so on. LNG powered ships have advantages such as saving energy and clean, so it also has good prospects. LNG has potential risks of fire and explosion, in addition volume of LNG carriers became larger and some carriers equipped complex functions in recent years. Considering these potential dangerous factors the safety issues should be attention. To reduce risks that may occurred to an acceptable level, LNG ship must be protected by safety instrumented systems.There is no specific standard on safety instrumented system for LNG carriers. The purpose of this research is study on the way of the design and analysis for LNG carrier safety instrumented systems. The main work is as follows:This article introduces the concept about SIS. Expounds three different analysis methods HAZOP and Event tree analysis and Layer of protection analysis, Discusses several different methods to determine the safety integrity levels in detail. Using a combination of HAZOP and Risk Graph methods, considering three different risks, personal injury, environmental damage and loss of property determine the LNG tank high level safety instrumented system should achieve SIL2.Summarize the major LNG ship accidents, design safety functions for each type of incident, combined with the specification requirements, and design the logical of the emergency shutdown system. Trigger signal and the actions of each section were discussed in detail. Fire and gas systems and emergency shutdown systems in which different layers of protection, the detectors for FGS system layout has been designed, and discusses the output response.This article describes the basis theoretical of reliability assessment, it discusses the three different safety instrumented system evaluation methods, calculates lool structure by three methods as an example, the calculation results of the three methods were compared. Checking high level safety instrumented system’s SIL verification by using Markov model method. Proposed improved method based sensors and actuators redundancy and improved method based on non-redundant configuration, both methods can eventually make the SIL achieve the requirements.