Influence Of Interaction Between Corrosion Defects On Pipeline Failure Pressure

As an important part of offshore oil and gas resources exploration,submarine pipelines are known as the lifeline of offshore oil and gas production systems.Corrosion of metal pipelines is inevitable,and corrosion is one of the main factors resulting in pipeline failure.Accurate assessment of residual strength of corroded pipelines is the premise for ensuring safe operation of pipelines as well as the basis for deciding replacement of existing pipelines.It is of great significance for extending the service life of the pipeline and ensuring the safe production of oil and gas fields.After several decades of development,the assessment methods of failure pressure for corroded pipelines with single defect are presented in various codes.However,the actual distribution of corrosion defects is random.And corroded pipelines are composed of colonies of defect with different sizes.The interaction between adjacent corrosion defects has a significant influence on the failure mode and failure pressure of corroded pipeline.Thereby,combined with full size burst tests and numerical analysis,failure mechanism and failure pressure of corroded pipelines with colonies of corrosion defects under internal pressure are studied.The effects of interaction between corrosion defects on the failure mode and the failure pressure of pipelines are revealed.Based on the sensitivity study on failure pressure of corroded pipeline with two defects,the minimum interaction distance between corrosion defects is determined.The interaction criterion of corrosion defects under internal pressure is proposed and validated.The contents of research are as follows:(1)Sizes of pipelines such as pipe diameter,wall thickness and residual wall thickness of corrosion defects are measured by using the pipeline geometry measuring machine invented by Dalian University of Technology.Then,using complex loads testing machine developed by DUT,the burst tests of corroded pipeline with single defect under internal pressure are performed.The influence of corrosion depth and length on failure mode and failure pressure of corroded pipeline is studied.(2)A three-dimensional nonlinear finite element model of pipeline with single corrosion defect under internal pressure is established and validated.According to the results of burst tests,the failure criteria for steel pipeline with different strength are proposed.Based on the sensitivity analysis of the factors affecting the failure pressure of steel pipeline with single defect,and the experimental and analytical results,a simplified expression predicted the failure pressure of pipeline with a single corrosion defect is suggested.(3)Based on the basic combination form of two corrosion defects,and considering the cases of pipelines with different sizes of two longitudinal or circumferential defects,the burst tests under internal pressure was carried out by using the complex loads testing machine.Through the analysis of measured results of burst tests,the influence of interaction between corrosion defects on the failure mode and failure pressure of pipeline is revealed.(4)A three-dimensional nonlinear finite element analysis model for pipeline with two corrosion defects under internal pressure is established.The influence of corrosion depth,corrosion length,corrosion width and corrosion spacing between two defects is studied.According to the results of burst tests and numerical results,the interaction criterion of corrosion defects under internal pressure is proposed and validated.