Evaluation Of Corrosion Defects Of High-grade Oil And Gas Pipelines

As one of the five transportation systems in our country, pipeline is the most important way of transporting oil and gas resources. Due to the complexity of the service environment and the increase of service life, pipeline corrosion becomes one of the main forms of pipeline failure, which is a great threat to the safe operation of the pipeline. Corrosion defect evaluation of oil and gas pipelines can predict the residual strength of pipelines, which is an important means to ensure the safety of oil and gas pipelines. With the continuous development of the oil and gas pipeline construction, the high-grade pipelines are gradually increasing, which with the X80 as the representative, the study for corrosion defect evaluation of high-grade oil and gas pipeline is imminent.This thesis systematically studied the failure reasons of oil and gas pipeline by ISM theory, analysed the applicability of existing evaluation methods of pipeline corrosion defect for high-grade pipeline, and studied the effect of volumetrical corrosion defects on the residual strength of high-grade pipeline by finite element method. The main contributions of this thesis are as follow:(1) The ISM of pipeline corrosion failure with a 7-layer hierarchical structure was established. It clearly revealed the surface reasons, middle-layer causes and root causes for corrosion failure, as well as the intrinsic link between the various causes. This model provided guidance and reference for the control and prevention of pipeline corrosion failure.(2) This thesis showed that the ASME B31G method was not suitable for high-grade pipeline by studying the applicability of existing methods. Considering the conservation, accuracy and concentration of the evaluation results, DNV RP-F101?LPC-1 and PCORRC were more suitable for assessing the residual strength of X80 high-grade pipeline.(3) The finite element model of X80 high-grade pipeline was established based on ANSYS Workbench. The effect of volumetrical defect depth, length, width, axial angle, irregular-shape defects, pitting and combined defects on residual strength was analysed.(4) A formula for calculating residual strength of X80 high-grade pipeline was fitted based on finite element calculation, which had less error and higher applicability. The results provided an important reference for evaluating the corrosion defects of high-grade pipeline, and had guiding effect on improving the existing evaluation methods.