A dynamic failure analysis methodology for fault diagnosis of fatigue cracks of subsea wellhead connectors with material aging

Abstract

Subsea wellhead connector is the vital equipment that connects the subsea Christmas tree and the subsea wellhead, it can prevent the leakage in the high temperature and pressure oil and gas passage, support metal seals, and bear complex loads. But due to the fact that subsea wellhead connectors have complex working conditions and harsh working environment, it’s necessary to ensure the safety and reliability of its structure. This paper presents a methodology integrating FEA and DBN for fault diagnosis of fatigue cracks of subsea wellhead connectors with material aging. Considering the material strength aging over time and its structural reliability in the case of internal crack failure. Based on the crack size propagation theory, this paper analyzed the growth process from the initial crack to the critical crack size, and then established the Dynamic Bayesian network of the subsea wellhead connector considering the internal crack propagation. Through the above the method, the reliability of subsea wellhead connector is obtained, such as the structural influence of multi-factor variables on the failure probability. It is concluded that the structural failure probability of the subsea wellhead connector increases from 0.0228 to 0.2075 after 30 years of service in the case of cracks. In the absence of the relevant data, this paper presents a reference method for failure reliability assessment of mechanical structures considering material degradation and crack propagation, which can provide failure data to the fault diagnosis and digital twin of the subsea wellhead connector in the future.