Study On Characteristics Of Corrosion Volume Parameters On Residual Strength Of X80 Steel Pipes

As the main transportation mode of China's oil and gas resources,pipeline transportation bears an indelible task.The mileage of long-distance pipelines is increasing year by year as the demand for oil and gas increases year by year.At the same time,the pipelines are subject to corrosion and more and more accidents occur.Therefore,it is of vital importance to study the residual strength of corrosion-defective pipelines.Conservative judgments may lead to unnecessary replacement of the pipeline and the result of the advancement may lead to leakage or explosion of the pipeline,which will cause unnecessary damage.A large number of studies on factors affecting pipeline failure can clarify the degree of influence of various factors on corrosion pipeline failure pressure.Better protect pipelines from delaying pipeline failures and reduce unnecessary replacement and maintenance of pipelines.The existing residual strength evaluation method is insufficient in the adaptability of the X80 pipeline,especially for the application of different corrosion parameters.In this paper,the characteristics of the influence of volumetric corrosion parameters on the residual strength of X80 pipelines are studied from the two-volume corrosion and group corrosion systems,and we strive to improve the residual strength evaluation method of X80 pipeline.This paper first summarizes several oil and gas pipeline corrosion methods,including natural environment,medium corrosion,stray current,and other defect factors.Then,based on the mathematical model of gray correlation degree,the causative factors of pipeline corrosion are analyzed.The simulation provides a theoretical basis.After that,the NG-18 equation,ASME B31G-1984 standard,RSTRENG method,DNV RP-F101 standard and PCORRC method are introduced in detail,and applied to the X80 pipeline with corrosion defects,and the calculated values and full-scale pressures of each calculation formula are applied.The applicability of each formula is obtained by comparing the blasting data.The corrosion defect model was established by Solidworks software.The simulation analysis of the influence of corrosion volume defect parameters on the residual strength of the pipeline was carried out by the linear static analysis module in ANSYS WORKENCH.First,the corrosion volume defect model is divided into two types: single volume corrosion body and group corrosion.The main research contents are as follows:1.The single-volume corrosion model is simplified into two types: square and circular.The three-parameters of the axial length,axial angle and corrosion depth of the square volume defect corrosion are numerically simulated.It is found that when the axial length is less than 90 mm.As the length increases,the residual strength of the pipe decreases gradually,and the rate of decrease of the residual strength gradually decreases.When the corrosion length increases by 100 mm,the increase of the corrosion length of the pipe does not affect the residual strength.The increase will also cause a decrease in the residual strength of the pipe.The axial angle shows that the residual strength of the volume defect pipeline decreases with the increase of the corrosion angle in the range of 0~45°,and the gradual increase of the corrosion depth accelerates the pipeline caused by the increase of the corrosion axial angle.2.After exploring the influence of the single-parameter factor of axial length and angle on the residual strength of the pipeline,the interaction between the axial angle of corrosion and the axial length and corrosion depth is mainly developed.It is found that there is such a correlation between the angle and the length.With the increase of the angle in the range of 0~20°,the effect of the angle on the maximum equivalent stress of the pipeline exceeds the length,and the angle increases in the range of 20~45°.The effect of large,axial angles on the residual strength of the corroded pipe is also getting smaller and smaller.The gradual increase of the corrosion depth will accelerate the decrease of the residual strength of the pipeline due to the increase of the corrosion axial angle(0~45°).3.Circular corrosion defects mainly do a single volume model and a group model simulation study.It is found that the corrosion depth of the circular volume defect model has a similar effect to the square shape,while the diameter parameter has little effect on the residual strength of the pipe.In the aspect of group corrosion,two circular volume defect models are established,and the coefficient k is defined as the ratio of the sum of the radii of the two circles in the axial direction to the center-to-center distance.It is found that the value of k has a great influence on the residual strength of the pipeline in the axial direction.