Study On The Destruction And Safety Of Buried Pipelines In Permafrost Regions

With the rapid development of China's national economy and the increasing demand for energy,oil and natural gas have become indispensable and important energy sources in people's lives.As the main transportation method of oil and natural gas,pipelines play an important role in the extraction and transportation of oil and natural gas.Oil and gas pipelines inevitably suffer from freezing and thawing hazards when crossing high-cold frozen soil areas,and the pipelines will bend and deform.At the same time,the pipeline will inevitably cause different defects in the pipeline generation and operation.This article discusses and analyzes the behavior of the buried oil pipeline in the frozen soil area from the cause of the crack and the type of defect.Preliminary discussion and analysis of corrosion crack defects.Based on the elastoplastic fracture mechanics and linear elastic fracture mechanics in fracture mechanics,the stress and strain of the pipeline are analyzed by changing the internal pressure load of the pipeline,the thickness of the pipeline insulation layer and the temperature load inside and outside the pipeline.By controlling changes in the crack length and crack orientation of the pipeline,the effects of crack J integral and stress intensity factor K on the defect behavior were further analyzed.The finite element model with initial semi-elliptical crack defects was established in the finite element software,and the following conclusions were drawn based on the simulated cloud image:The ANSYS finite element software was used to simulate and analyze the pipe diameter,internal pressure,insulation layer thickness and temperature difference between pipes and soil in the permafrost zone.There is a linear positive correlation,and the thickness of the insulation layer has a linear negative correlation with the pipeline stress;The increase in the thickness of the insulation layer plays an effective role in reducing the stress and strain on the pipeline to a certain extent,but as the thickness of the insulation layer increases,the reduction effect also gradually decreases;In the simulation data of this paper,when the thickness of the insulation layer is 10mm,it is the best choice from the comprehensive consideration of economy and effect;The insulation layer can not only effectively reduce the stress on the pipeline,but also reduce the stress and strain on the pipeline when there is a temperature difference between the pipe and soil;From the point of view of simulation value,K_I is positive and K_II and KIII have positive and negative,and the positive and negative numbers represent the direction;K_Iis basically much larger than K_II and K_III;When the axial crack length increases,the change curve of J integral and the change curve of K_I are almost the same;Under the same conditions,in the value of the J integral generated by the axial crack and the circumferential crack,the axial crack is much larger than the circumferential crack.This article also analyzes the safety of cracked pipelines,compares several common pipeline residual life formulas,summarizes their advantages and disadvantages,and obtains a more suitable prediction method in actual engineering.