ADVANCED RISK ASSESSMENT OF LNG STORAGE TANKS BASED ON RISK-BASED MAINTENANCE PLANNING

摘要

Risk Based Maintenance (RBM) is a new technique to provide optimum inspection or maintenance plans according to relative potential risk. In the present study, a new RBM technique for LNG storage tanks was developed. The technique is composed of a three stage-procedure in order to assess the risk in view of simplicity or strictness due to design information and operation histories of tanks. The first procedure could provide the tank risk itself briefly to compare the relative risk among plural tanks. The second is also a simplified method based on the severity of consequence particularly. After the higher risk tank on site is identified, each component or location consisted of the tank is assessed with a semi-quantitative method according to detail information by the third method. Therefore, the risk of each component could be compared. Based on the result, the maintenance procedure would be prioritized among assessed locations. In this study, these procedures were applied to RBM assessment on two LNG tanks made of 9%Ni steel and aluminum alloy respectively as the inner tank material. As results, it is found that weld joints in annular plate with shell plate or welded region on bottom plates hold the higher risk in the tanks. Furthermore, the risk after 10 or 20 years future could be assessed according to the prediction of aged conditions by this procedure.