Numerical Simulation Of Stress Corrosion Micro-cracks Of High Strength Steel Pipeline

Pipeline is a safe,effective,uninterrupted and long-distance energy transportation way.With the increasing energy demand and the improvement of industrial technology,pipeline steel is developing towards high pressure,large diameter,high strength,high toughness and higher grade steel.At present,X100 pipeline steel has been gradually put into use.Because pipelines are mostly laid underground,corrosion problems are easy to occur due to soil corrosion environment,and stress corrosion cracking(SCC)is one of the main causes of accidents,which seriously threatens the safe operation of pipelines.SCC of high strength pipeline steel has become a research hotspot of pipeline steel corrosion.Based on this,this paper took X100 pipeline steel as the research object.Its SCC behavior and law under near neutral pH value environment was investigated.This paper adopted multi-physical field coupling simulation technology to simulate Von Mises stress and local current density of stress corrosion micro-crack front,and discussed the influence of boundary load,crack size,applied potential,pipeline material and distance between double cracks on stress corrosion of crack front.The research in this paper mainly consists of three parts:(1)A stress corrosion micro-crack model of high strength steel in near neutral pH environment was established by coupling the constitutive equation,electrochemical kinetic equation and Gutman model of the material with multi-physical field coupling simulation technology.Comsol Multiphysics was applied to implement the numerical simulation process of this model.The simulation values were compared with those in other literatures to show the reliability of this model.(2)The Von Mises stress and local current density at the crack front were analyzed when the boundary load,crack size,applied potential and material change.The research results show that when Von Mises stress at the crack defect exceeds the yield strength of the material,the anode current density near the crack tip will obviously increase and reach the maximum value at the crack tip.When the applied cathode potential is less than-1000 mV,the anode current density at the crack front decreases with a larger downward trend.Under the same conditions,the anode current density of X65 pipeline steel is one order of magnitude higher than that of X80 and X100 pipeline steel.(3)The influence of crack spacing on Von Mises stress and local current density at crack front when X100 pipeline steel contains double cracks was studied and analyzed,and the simulation results at fixed spacing were compared with those at single crack under the same conditions.Research results show that the greater the distance between the two cracks,the greater the Von Mises stress and anode current density at the crack front,while the smaller the cathode current density.When the distance between the two cracks is far greater than 374?m,the result can be approximately equal to that of a single crack.