Investigation On Uitimate Load Capacity And Failure Mechanism Of Corroded Submarine

Submarine pipelines are the lifeline in the exploitation of offshore oil and gas resources, and they play an important role in the development and production of offshore oil and gas fields as well as transportation of products. Due to the harsh marine environment that most of these pipelines are located in, deterioration caused by corrosion is inevitable. According to relevant statistical data, corrosion is known to be one of the major reasons causing submarine pipelines failure, which would result in not only economical loss but also severe environmental pollution. Consequently appropriate residual strength evaluation of corroded pipelines is vitally important and timely repair or replacement can avoid pipeline failure. All these above have important theoretical and practical significance for the design and evaluation of submarine pipelines.Based on previous research results, a series of studies on the ultimate load capacity and failure mechanism of corroded submarine pipelines under service load and complicated environmental loads have been carried out. The research work conducted and results obtained in this paper can be summarized into three aspects listed as follows.(1) The ultimate load capacity and failure mechanism of submarine pipelines with single corrosion defects under internal pressure. Comparative analysis were carried out between analytical solutions for burst pressure of end-capped defect-free pipes on the basis of Mises, Tresca, ASSY, TS and UYC criteria to draw their limitations. In order to determine the failure criterion of corroded pipelines under internal pressure, finite element simulations were conducted to verify the burst tests of corroded pipelines. The FEA results and the estimated burst pressure according to the specification formulas were compared to indicate the deficiencies of the specification, and then a new limit load solution was proposed based on a large number of FEA results.(2) The ultimate load capacity and failure mechanism of corroded submarine pipelines under combined internal pressure and axial compression. By using numerical simulation method, parameter sensitivity analyses were conducted to analyze the effects of varying internal pressure, corrosion defect size and piping geometry on the ultimate load capacity and failure mode of corroded submarine pipelines under combined internal pressure and axial compression. It indicated the effect of corrosion width and length on the buckling mode and ultimate load capacity of corroded submarine pipelines under axial compression.(3) The ultimate load capacity and failure mechanism of corroded submarine pipelines under combined internal pressure and bending. The analytic solutions of corroded submarine pipelines under combined internal pressure and bending on the basis of NSC criteria were summarized, and then the effects of corrosion defect size, stress state of corrosion area and different internal pressures on the ultimate load capacity and failure mode of corroded submarine pipelines were completely analyzed. At last the FEA results and the estimated maximum moments according to the proposed formulas on the basis of NSC criteria were compared to determine formulas’range of application.