管线钢应力腐蚀过程中固/液界面的动态变化研究

During the stress corrosion cracking of pipeline steel in soil environment, due to the lack of general corrosion and obvious corrosion products, it is difficult to predict which and when the pipeline steel in service will be failure. This project aims to combine digital holography, scanning electrochemical microscopy, potentiodynamic polarization technique, potentiostatic polarization technique and electrochemical impedance spectroscopy to study the processes of stress corrosion cracking. The spatial resolution of digital holography is high and the temporal resolution of scanning electrochemical microscopy is high, so we combine the two techniques to study the occurrence and the development of stress corrosion cracking from three-dimensional visualization. The main objective of the present work is to study the effects of the influencing factors in the corrosion environment on the stress corrosion cracking of pipeline steel by using the real-time and in situ techniques, and the relationship between the factors and the degree of the stress corrosion cracking will be established. The focus is on the early stage of the stress corrosion cracking, in which the small micro-cracks have been just formed on the surface of the electrode. Thus, new methods for preventing pipeline steel from stress corrosion cracking will be developed by interfering the formation of the small cracks or repairing the micro-cracks.

管线钢在服役过程中可能会发生应力腐蚀开裂，特别是在最为薄弱的焊头部位，应力腐蚀开裂事故发生较多。本项目拟把数字全息术，扫描电化学显微镜技术等现场观测方法与电化学阻抗谱、动电位极化曲线、电化学噪声和电位电流分析等腐蚀电化学测试方法相结合，利用数字全息术较高的时间分辨率和扫描电化学显微镜较高的空间分辨率，从不同的角度三维可视化实时原位观测管线钢应力腐蚀发生发展的全过程。研究重点将放在发生应力腐蚀开裂的第一阶段，分析各种环境影响因素对应力腐蚀的发生发展产生的影响，构建各影响因子与应力腐蚀发展程度之间的关系，并建立相关的数学模型，找到干扰微小裂纹形成或修复微小裂纹的方法，从而探讨应力腐蚀的发生发展过程、机理和本质，并尝试发展预测和防止应力腐蚀的新方法。

应力腐蚀开裂是影响油气输送管线长期安全运行的重要因素之一，因此国内外专家学者对管线钢的应力腐蚀开裂极为重视。本项目充分利用数字全息术较高的时间分辨率和扫描电化学显微镜技术较高的空间分辨率，结合电化学阻抗技术，动电位极化技术和恒电位极化技术等传统的电化学测试方法，对埋地管线钢的应力腐蚀开裂的动态过程进行了三维可视化实时原位研究，获得了一系列研究成果：用数字全息术研究应力腐蚀发生发展过程中电极/溶液界面扩散层的动态变化，探求应力腐蚀发生发展过程、机理和影响因素；用扫描电化学显微镜研究应力腐蚀发生初期电极表面的电化学活性分布的动态变化，探讨点蚀和应力腐蚀的关系；用扫描电化学显微镜监测应力腐蚀发生发展过程中电极表面各种离子浓度的变化，讨论应力腐蚀发生发展时电极表面膜的成分变化；利用扫描电镜等非原位技术，推测应力腐蚀发生时电极表面膜的变化情况；综合分析一系列实验结果，探讨应力腐蚀的影响因素和机理，探求延缓和避免应力腐蚀的方法和手段。