Corrosion Growth Characteristics Of X80 Pipeline Steel Prefabricated Defect In Simulated Ku'erle Soil Solution Under Applied Stress

In the producing,transporting and paving process of metal pipeline,different degree of damage and corrosion defects would inevitably appear.The corrosion defects caused by pipeline failure are in three forms of small hole leakage,big hole leakage and bursting,which are mainly related to the characteristics of the corrosion defects.Small hole leakage is usually caused by pitting corrosion,while big hole leakage by partial corrosion and bursting by uniform corrosion.The depth and length data of corrosion defects are often included in the residual strength model when evaluating dangers of bursting accident.It is not enough to provide the corrosion rate in the length direction when evaluating the ineffective time of a corrosion defect;meanwhile the rate of the length direction needs to be checked as well.So it is of great significance of researching the defecting growth of X80 pipeline steel in soil.X80 pipeline steel produced by Shagang Group is taken as the research object in this paper.The stress concentration area of specimen and its surrounding potential distribution are calculated by finite element analysis and COMSOL simulation.The results show that the stress concentration at defect ends is the most obvious and the stress concentration at defect ends in grooving shape is more serious.Different tensile stresses are pushed onto X80 pipeline steel with prefabricated defects,and the growth characteristics of the corrosion defects are studied by observations of three-dimensional morphology before and after corrosion defects,defect corrosion morphology observation and electrochemical tests.The results show that the stress concentration at defect ends is the most obvious and it is prone to corrosion the most,and the corrosion product film on the specimen surface will weaken its corrosion trend,and this trend is in growth with the increase of stress value.The corrosion electrochemical activities at the ends and the right edges of prefabricated defects on the surface of X80 pipeline steel,under different stresses,are under situ comparative study by electrochemical micro area test on alkaline medium in Ku'erle simulated soil solution.The results show that the stress concentration at defect ends is the most obvious and serious in corrosion while natural corrosion appears on the right edge without stress concentration phenomenon.