管线钢近中性pH值环境应力腐蚀开裂(SCC)是管线失效的一种重要形式,但其发生机理仍不清楚,现场实际发现其易发生在焊缝附近.采用动电位极化和电化学阻抗技术研究了外加拉应力对X80钢焊接接头在近中性pH值溶液中电化学行为的影响.结果表明:应力使X80钢母材和焊缝的腐蚀电位负移,腐蚀电流密度增大,应力促进了母材和焊缝的阳极溶解和阴极反应;在弹性变形区间,外加应力没有破坏腐蚀产物膜的完整性,腐蚀产物膜电阻几乎不变,应力使腐蚀产物膜乳隙结构变大,促进侵蚀性离子向电极表面扩散,母材和焊缝的电荷转移电阻明显减小;由于组织结构的原因,焊缝的应力影响系数比母材的大,X80钢焊缝比母材有更强的应力敏感性.
The electrochemical behavior of X80 steel weld joint in solution with near-neutral pH value under the tensile stress was studied by potentiodynamic polarization and electrochemical impendence spectrum.Results showed that the tensile stress led to decreased corrosion potential of X80 base steel and increased corrosion current.Meanwhile,both of anode dissolution and cathode reactions of the substrate steel and weld joint were accelerated by tensile stress.When the stress in the range of elastic deformation,the tensile stress did not broke the corrosion production film,and the film resistance was almost unchanged.The stress enhanced the porous structure of corrosion production film,which promoted the corrosive ions spreading to the surface of electrode and reduced largely the charge transfer resistance of substrate steel and weld joint.Owing to the distribution of organization structure,the stress-influence coefficient of weld joint was higher than that of substrate steel,and the X80 steel weld joint possessed stronger stress sensitivity than the substrate.
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