Study On The Damage Law Of Two Types Of Depressions On Oil And Gas Pipelines

Due to the flammable, explosive and toxic characteristics of petroleum and natural gas, their storage and transportation process of security become the focus of attention. Accidents caused by pipeline failure also attracted enough attention.The survey found that the pipeline mechanical damage is the most important factor affecting the pipeline security of operational phase.Dent, as the most common type of mechanical damage, is a significant threat to pipeline safety.Therefore, it is necessary to conduct in-depth research on mechanical behavior of pipeline dent, to achieve reasonable evaluation of pipeline safety.The following aspects of the damage degree for pipeline dent are studied in this paper:First, a large number of domestic and foreign literature research, analysis of previous studies in dent types, evaluation methods and application range.So as to find the supplement and improvement of dent on basis of the existing research.Secondly, plastic deformation of the metal material is analyzed, and a criterion of critical hole expansion ratio, which can be used for the three axis degree of different stress, is found.The macroscopic critical expansion ratio is used to establish the damage model, which is applied to the safety evaluation process of the oil gas pipeline, to judge whether the pipeline is cracking.Then, analysis the on-line detection data of dents withconcave Angle,select the ellipsoid model as calculation model, change ellipsoid size to simulation different dent. For dents without concave angle, according to the results of on-line detection of pipeline and analysis such dent formation mechanism, then the calculation model- hoop stick model is presented, and simulation of different-sized dents without concave angle can be achieved by changing the curvature radius of hoop stick.According to the ductile damage model research the stress state and strain variation of pipeline dent area in loading process.The results shows that stress is mainly based on hoop stress and axial stress, which is close to the two direction stress state. Depth less effect on the stress state, and the change of damage is mainly affected by equivalent strain.Internal pressure has a larger affect on strain, so as to make the second damage of dents is larger. For same depth of thetwo dents,the maximum damage of dent with concave angle is 2?3times of dent without concave angle, which indicate that dent type has a large impact on pipeline damage.Finally, analysis the two types of dent depth and damage regularity in different application trace parameters, parameters pipeline and operation pressure in practical application.One dimension regression results shows that pipeline safety evaluation is not accurate only by dent depth, because the expression is effected by the parameters.The analysis of multiple regression provides a more accurate calculation formula for damage degree of the pipeline used in practical engineering, which provides a guarantee forsafety evaluation of the pipeline.