The Analysis Of Failure And Reliability Of Submarine Pipeline

Submarine pipeline is the key part of transportation system of marine oil and gas, and thus its security problems become more and more concerned. In the process of actual working, submarine pipeline will be affected by different load, such as sea water, corrosion, environment etc. So it is worth of certain engineering application value studying these problems. With the aid of finite element software and Matlab programming tools, the method of numerical simulation analysis is adopted for the failure problem of submarine pipeline in this paper, and the failure probability of pipeline corrosion is evaluated according to the measured data. The detailed research content is presented as follows:The finite element model of submarine pipeline is built in the ocean environment, which is spanning on the rough seabed. Considering the environment for submarine pipeline under gravity and water impacting, the maximal displacement, maximum stress and maximum strain of submarine pipeline is calculated by the method of finite element numerical simulation. And the influence of steady-state vibration and transient vibration to the instability or failure of the submarine pipeline are analyzed. The numerical results show that the maximal displacement, maximum stress and maximum strain of submarine pipeline is bigger in transient conditions than steady-state condition, and they are similar to a quadratic curve with pipe length.The finite element model of pipeline is built with semi elliptical surface crack, including crack and fatigue failure, and a kind of local surface nanocrystallization method is presented to improve the fatigue life of submarine pipeline. Through the numerical simulation, the J-integral around the crack tip and the fatigue life of pipeline are calculated in different size of load. On this basis, a special method of surface nanocrystallization is adopted to the crack tip of pipeline. The calculation results show that, under the same circumstances, the J-integral of pipeline is reduced in some degree after nanometer surface treatment, which can prevent the crack propagation of the pipeline, and the fatigue life of pipeline is promoted greatly, which can extend the service time of the pipeline.For specific engineering problems, the reliability of submarine pipeline under corrosion is analyzed by improved method of unitary HL-RF, which can be used to obtain the relevant failure probability. According to the probability distribution (mean and coefficient of variation) of length and thickness of pipe, length and depth of corrosive crack, the internal pressure of pipeline, corresponding function are obtained. The curve of failure probability of pipeline along to the change of running is discussed under different coefficient of variation, and the curve of failure probability of pipeline along to the change of mean under different running time at the same time. Then the failure probability and reliability of pipeline can be analyzed.