The Analysis Of Reliability Of Submarine Pipeline With Corroded Defect

At present,the undersea oil and gas exploitation has become a strategic demand in energy area for China.Through the undersea exploitation process,submarine pipelines are one of the most important equipment.Because of the complicated seabed environments,the corrosion of submarine pipelines is a major cause for structural failure.When pipelines are corroded by sea water,the carrying capacity of pipelines will reduce dramatically.Therefore,the analysis of the limit carrying capacity,failure mode and reliability of corroded pipe is of great significance and application value of engineering.This paper employed numerical simulation method to conduct this problem,the main research work concentrated on:Study the limit carry capacity and failure mode of pipes with a corroded defect under the internal pressure.Based on the analytical formulas of the limit carrying capacity of the perfect pipe and four kinds of burst failure criterions,the destruction process of corroded pipelines under internal pressure is obtained.By studying the effect of corroded defects on limit carrying capacity,the advantages and disadvantages,application ranges,accuracy can be assessed.The analytical expression is also derived to calculate the limit carrying capacity of compressed pipelines.The results show that the analytical formula based on the Mises criterion is the upper bound of the burst pressure,and the analytical solution of the burst pressure under the Tresca criterion is the lower limit of the actual carrying capacity of the pipeline.Results also show that the size of corrosion defects has a direct influence on the bearing capacity of submarine pipelines.Analyze the ultimate load-bearing capacity and failure mechanism of corroded pipes under axial compression pressure.Results indicate that there is a critical value for the length of corrosion defects,and the carrying capacity tends to a certain critical value when the length exceeds this value.On this basis,the effect of combined axial compression and internal pressure on limit carrying capacity of pipelines with corroded defects is studied.Further analysis of failure modes and development regulations is discussed in this paper.Results reveal that with the increase of the internal pressure,the ultimate axial bearing capacity of the pipeline decreases first,then increases,and finally decreases.This phenomenon is due to the local strain and overall deformation.Results also show that the thickness ratio of corroded pipeline has less influence on the ultimate axial bearing capacity.Adopt the Monte Carlo random selection method,the failure probability and remaining life of corroded pipe is calculated.According to the probability distribution of the pipe outside diameters,including pipe thickness,corroded defect length,corroded defect depth,operating pressure and corroded velocity,this paper studies the effect of corroded defect,operating pressure,variation coefficient and elapsed time on the probability of failure combined with the limit state equation of corroded pipelines.The numerical results show that the corrosion depth,corrosion length and operation pressure will increase the failure probability of the pipeline.The increase of the coefficient of variation such as corrosion length,corrosion depth and operation pressure can increase the failure probability,when the running time is relatively long,the influence on the failure probability of the pipeline is reduced.