A reliability analysis method for Christmas tree in operating conditions based on FEMCA, FTA and numerical simulation

The installation and recovery process of Christmas tree is complex and technically difficult, and it bears high internal and external loads during production and has extremely high requirements for operation reliability. To ensure the safe operation of China's first domestically produced deepwater subsea Christmas tree installation and production conditions, a reliability analysis method for Christmas tree in operating conditions based on FEMCA, FTA and numerical simulation is established. Firstly, the FEMCA method is used to analyze the detailed operation steps of drill pipe installation method. The severity and hazard degree of the failure modes of each component during the installation and recovery process of Christmas tree are determined. The main failure modes are evaluated as deformation of the tree body, leakage of valve groups, leakage or blockage of connecting pipe fittings. Secondly, using the FTA method and based on the OREDA database, statistical analysis is conducted on the failure data and related failure modes. A fault tree model is established for 11 main component structures during the production operation, and the basic event probability, importance, and ranking of each component structure are calculated. The results shows that the average failure probability during production is 25.82 times per 106 hours, and its reliability parameters has an average failure interval of 4.42 years. The overall reliability level meets the production safety requirements. Thirdly, the stability numerical simulation analysis shows that the maximum stress ratio of the Christmas tree system under different ocean current conditions is 0.529, and the maximum bending moment is 7292 kN·m, and the safety operation window is established with the overall reliability level of the system meeting production safety requirements.