Corrosion Mechanism Of Pipeline Steel Under Mechano-Electrochemical Effect

The study on the corrosion mechanism of pipeline steels under mechano-electrochemical(M-E)effect can not only provide a theoretical basis for the development,research,and application of pipeline steels but also provide suggestions for the risk assessment and integrity management of pipelines.Therefore,this article focuses on the corrosion problem of X80 pipeline steel under M-E effect in the acidic red soil simulation solution.Using multi-physical field coupling simulation technology,the two-dimensional(2D)and three-dimensional(3D)models considering the M-E effect are used to evaluate the integrity of pipelines.This work focus on the difference between 2D and 3D models considering M-E effect in assessing pipeline integrity and the influence of outer wall defect growth on the mechanical and electrochemical state of the inner wall surface.The main work of this dissertation is as follows:(1)Design and build a tensile test device for M-E effect.The relationship between open circuit potential and stress of X80 pipeline steel specimen in acidic red soil solution during the tensile process was determined by measuring the open circuit potential of the specimen.(2)In the case of the same geometrical size and the same stress condition,the 2D model has larger local stress,larger local plastic strain,more negative corrosion potential,and larger anode current density compared with the 3D model.When the geometrical size of the corrosion defect is the same,the stress in the defect center is the largest.When the geometrical size of the corrosion defect is the same,the stress in the defect center is the largest.For the safety assessment of corroded pipelines,the 2D model is often more conservative than the 3D model.(3)When the length and width of the outer wall corrosion defects remain unchanged,the deeper the defect depth is,the greater the stress on the inner wall surface,the more negative the corrosion potential is,and the more positive the anode current density is.When the defect depth is small,the maximum point of stress,anode current density,and the negative point of corrosion potential are not located in the center of the inner surface.With the change of internal pressure,the variation range of stress,corrosion potential and anode current density in the center area of the inner wall are larger than that in the non-center area.(4)In the process of the growth of the outer wall corrosion defects,the M-E effect significantly increases the corrosion velocity in the depth and length directions,but it is inhibited in the width direction.This is because,at this time,the defect can be regarded as a galvanic cell,the defect center is the anode,and the defect edge is the cathode corrosion speed decreases.(5)With the growth of defects in the outer wall,the stress on the inner wall surface increases,the corrosion potential becomes negative and the anode current density becomes positive.Under the influence of the different lengths of corrosion time,the greater the depth of the outer wall defect,the greater the variation range of the stress,corrosion potential,and anode current density at the center of the inner wall surface.