Study on Failure Possibility of Full Containment LNG Storage Tanks with API 581 Risk-based Inspection

Abstract

The total storage of full containment LNG storage tanks is very huge. Once the tank rupture or leakage, the consequence will be unimaginable. Therefore it is necessary to perform the risk-based inspection (RBI) and evaluation on LNG storage tanks, and the analysis on LNG storage tanks failure possibility is especially important in the RBI. Recently, Risk-based inspection (RBI) technology based on API 581 is gradually adopted and has become a new technology to determine economic feasibility and safety of equipment in petrochemical plants. However, there are limitations of applying API 581 to LNG equipment because of the unique structure of LNG storage tank (the metal inner tank and concrete outer tank). Therefore, a failure probability calculation model suitable for full containment LNG storage tanks is proposed. The domestic inner tank is usually made of 9%Ni, and its failure possibility can be calculate based on API581; the outer tank is usually made of pre-stressed concrete, and the failure possibility of structure durability can be calculated by the method of fuzzy mathematics; Then the failure possibility of the inner tank and the outer tank will be comprehensive considered by using cellulose model. Finally, by citing a real example, it also detailedly introduces the application of this proposed calculation model in the failure possibility analysis of full containment LNG storage tanks. This study provides a new approach for the evaluation of failure possibility on full containment LNG storage tanks.