The analysis of damage degree of oil and gas pipeline with type II plain dent

•We study on the ductile damage of the pipeline with type II plain dent.•Oyane ductile fracture criterion is used to dispose the results of finite element.•A specific expression of dent depth and the damage degree of pipeline is obtained.•The influence law of parameters change on the damage degree of pipeline is acquired.

Dent is a common type of defect in oil and gas pipelines and the assessment on dented pipelines is carried out with major international standards and specifications based on dent depth as the evaluation criteria. However, such evaluation criteria based on depth does not account for the impact of various parameters (e.g. parameters of dent, parameters of pipeline and the internal pressure of pipeline) on the evaluation result, as a result, many dented pipelines lose their efficacy, even though they meet the depth-based standards. The influence of parameters changes on the damage degree of II-type dented pipelines is investigated on the basis of Oyane's ductile fracture criterion and by the method adopting finite element numerical calculations. Finally, the non-linear regression analysis is conducted and based on the outputs, a specific expression of dent depth and pipeline damage degree is also acquired within a certain scope of application.