Numerical Analysis of Structural Strength and Safety Characteristics for Subsea tree

Abstract

With the development of offshore oil and gas exploration, the number of Subsea trees has increased rapidly, which has become the mainstream model of oil and gas development. Subsea tree has been in the marine environment for a long time, which bearing complex environmental load and working load, and the failure probability is high. What’s more, the structure of subsea tree components is difficult to repair and replace, the damage of its structure will not only affect the normal transmission of oil and gas, but also cause serious marine environmental pollution and ecological disaster. Therefore, in this paper, a set of risk analysis and evaluation method suitable for Subsea tree is proposed, which helps to find the potential risks and weak links before operation. The main contents and innovations of this paper are as follows: The fault data of underwater subsea tree is difficult to statistics, the structural strength and safety characteristics of subsea tree is analyzed by using fuzzy fault tree analysis method, which results to the importance of fuzzy probability of subsea tree system is analyzed. Based on the OREDA database, a fault tree is established for the above fault events of the underwater Subsea tree. "Subsea tree fault" is selected as the top event, which is analyzed from throttling module fault, subsea tree body fault, tubing hanger fault and hydraulic connector fault. In order to further determine the failure mode and its weak links, the safety risk assessment of subsea tree is carried out on the basis of the failure mode of subsea tree and the failure frequency of its subsystem. Analytic hierarchy process (AHP) and technique for order preference by similarity to ideal solution (TOPSIS) are used to evaluate the multi-index risk of underwater subsea tree leakage scenario. The weight vector of each evaluation index is determined by AHP, and a comprehensive evaluation index system is constructed based on the principle of TOPSIS. Then it is proposed to calculate the comprehensive advantages of internal leakage and external leakage from three aspects: environmental safety, leakage probability and economic loss. The example analysis shows that the risk value of external leakage is higher than that of internal leakage, which indirectly verifies the feasibility and III effectiveness of the proposed comprehensive evaluation index system. Based on the risk assessment of Subsea tree, Bayesian network method is used to analyze the safety characteristics of fault polymorphism, fuzziness and dynamics for underwater subsea tree system and its components. Fuzzy set theory is introduced into Bayesian analysis, which considered the polymorphism of system and component faults and the variation law of failure probability, and this method is applied to the safety characteristic analysis of underwater subsea tree.