Improvement Of Risk-based Inspection (RBI) For LNG Tank Risk Assessment

Liquefied natural gas(LNG)technology allows natural gas to exist in liquid form,facilitates the storage and transportation of natural gas,and promotes natural gas trade and promotes the development of natural gas applications.Liquefied natural gas has both the characteristics of natural gas flammable and explosive,but also has the characteristics of low temperature characteristics of low temperature liquid,in the event of leakage,will lead to serious consequences,equipment,business,environment and people's lives and create a serious threat The Therefore,in the LNG storage,LNG tank leakage failure has become a need to focus on the issue.Risk-based Inspection(RBI)is to analyze the results of the test to determine the causes of defects,and the use of appropriate measures to prevent,thereby reducing the risk of equipment.API 581 resource file gives the RBI method for refining and petrochemical enterprises.The failure data in API 581 originated from the historical failure data of 26 petrochemical enterprises in Europe and America and established according to the principle of statistics.Because of the low technological level,poor material performance and overtime service in China compared with developed countries,The general failure frequency can be proposed by API 581 is not effectively used for the risk assessment of LNG tanks in China.In order to solve this problem,the general failure frequency of LNG storage tank is modified by mapping transformation method so that it can be applied to the risk assessment of LNG storage tank in China.Through the establishment of LNG tank leakage accident tree and analysis,the minimum cut and structural importance of LNG tank leakage accident tree is obtained,and the weak link of LNG tank leakage failure system is determined,and the safety work level and the safety countermeasure are improved.The Bayesian network is used to modify the duality of the bottom event of LNG tank leakage accident tree.Finally,the failure results of a LNG storage tank are analyzed by DNV PAST&SAFETI software,and the effect area under the different leakage pore size and the effect area calculated by using the modified model are used for the risk calculation formula.The correctness of the modified model is verified and analyzed.