Abstract:

Local corrosion defects on the inner surface of natural gas pipelines will induce sudden changes in the local flow field and affect the local corrosion process. The high-shear stress corrosion test device is used to conduct on-line electrochemical corrosion testing under the flow, and the influence of local corrosion pits on the local corrosion process is studied. The interfacial corrosion electrochemical signal of the specimens during the corrosion process is analyzed by electrochemical impedance spectroscopy (EIS). The composition and characteristics of the corrosion scale are characterized by scanning electron microscope (SEM),energy diffraction spectrum (EDS) and X-ray diffraction(XRD). The influence of flow field parameters on the corrosion mass transfer process is calculated and analyzed. The results show that surface defects will induce changes in the flow field and enhance the mass transfer at local locations. Therefore, the corrosion scale on the surface will show different microscopic forms with the change of flow velocity. In a high-intensity flow field, the locally enhanced wall shear stress will peel off part of the dense corrosion product film, resulting in the formation of electrochemical distribution of large cathodes and small anodes on the test surface, which promotes the corrosion process at local locations and accelerates the occurrence of local corrosion.

Key words: flow field, local corrosion pit, corrosion scale, process of mass transfer

摘要：

天然气管道内表面局部腐蚀缺陷会诱发局部流场突变影响局部腐蚀进程，利用高剪切力的冲刷腐蚀实验装置进行流动状态下的电化学腐蚀在线测试，研究了局部腐蚀深坑对局部腐蚀进程的影响。试样在冲刷腐蚀过程中的界面腐蚀电化学信号通过电化学阻抗谱进行分析，腐蚀产物膜的成分及特征通过扫描电子显微镜（SEM）、能量衍射谱图（EDS）以及X射线衍射（XRD）表征，并结合计算流体力学（CFD）分析了流场参数对腐蚀传质过程的影响。结果表明，表面缺陷会诱导局部位置流场发生变化，增强局部位置的传质作用，缺陷表面腐蚀产物也因此随着流速的变化而呈现不同的微观形态。在较高强度流场下，局部增强的壁面剪切力会剥离部分致密腐蚀产物膜，导致测试表面形成大阴极小阳极的电化学分布，促进局部位置的腐蚀进程，从而加速局部腐蚀发生。

关键词: 流场, 局部腐蚀坑, 腐蚀产物膜, 传质过程