X70钢及其焊缝在含Cl;高pH值溶液中电化学噪声行为研究

Electrochemical Noise Behavior of X70 Steel and Its Weld in Cl--containing High pH Solution

研究了不同外加电位下X70钢母材及其焊缝在含Cl;的高pH溶液中电化学噪声行为,并针对电化学噪声数据进行统计分析,得到表征点蚀萌生和发展的特征图谱。结果表明,电化学噪声技术可以有效监测X70钢的腐蚀过程,电流噪声幅值大小一定程度上反映了局部腐蚀萌生和发展过程。当X70钢处于阳极极化时,电化学噪声的能量密度谱(EDP)由低阶区向高阶区迁移,点蚀由亚稳态发展为稳态。当电位位于活化-钝化转变区时,EDP处于亚稳态点蚀区。外加电位为稳定钝化区时,母材的EDP处于点蚀诱导期,耐点蚀性能较好;而焊缝能量较高,EDP表明已经形成少量稳态点蚀。相同条件下,X70钢母材相对于焊缝的EN波动幅度较小,能量密度较小,表明焊缝的钝化膜自我修复能力较差,容易发生腐蚀。焊缝具有更高的能量密度,点蚀发展较快。

The electrochemical corrosion behavior of X70 steel and its weld in a Cl--containing Na2 CO3+NaHCO3 solution by various applied potentials was studied by means of electrochemical noise(EN) technique. Statistical analysis was conducted on the EN data to obtain the specific spectrum to characterize the initiation and development of the pitting. The results showed that the EN technique could effectively monitor the pitting process of X70 steel, while the amplitude of current noise reflected the initiation and development process of localized corrosion. When X70 steel was anodic polarized, the energy density spectrum(EDP) of EN moved from low-order zone to high-order zone, correspondingly, the pitting developed from metastable state to steady state. When the applied potential was in the activation-passivation zone, the EDP located in the metastable pitting zone. When the applied potential rose to stable passivation zone, the EDP of the substrate corresponds a pitting initiation period and the pitting resistance of the substrate was better. While the EDP for the weld with higher energy indicated that a small amount of steady-state pitting has been formed. By the same applied potential, the fluctuation range of EN and energy density of the substrate was small in comparison with the weld, indicating that the passivation film of the weld had a poor re-healing ability and was prone to be attacked. Due to that the weld had higher energy density, therefore, on which pitting developed faster than on the substrate.