CO₂腐蚀是海洋天然气管道发生泄漏失效的主要原因之一，实践表明：在已出现管道腐蚀的区域，若腐蚀垢层覆盖均匀，则垢层下发生的腐蚀明显少于腐蚀垢层覆盖不完整区域的。为明确该现象的产生原因，采用扫描电子显微镜（SEM）和X射线衍射（XRD）等技术，研究了管道腐蚀失效部位的腐蚀垢层表面微观形貌和化学成分。结果表明：腐蚀垢层为含有微量FeS的FeCO₃腐蚀产物。通过电化学方法研究了CO₂腐蚀过程中腐蚀垢层的存在对X65钢CO₂腐蚀行为的影响，结果表明：在FeS和FeCO₃腐蚀垢层存在的条件下，X65钢在CO₂中的均匀腐蚀速率降低；当FeCO₃腐蚀产物膜完全覆盖于金属基体表面时，金属基体发生点蚀的可能性会明显降低；反之，若覆盖在金属基体表面的FeCO₃腐蚀产物膜呈疏松多孔或覆盖不完整时，将会在金属基体表面形成微小的原电池结构，进而导致金属基体表面发生点蚀的倾向增强。

CO₂ corrosion is one of the main reasons for leakage failure of offshore natural gas pipelines, practice showed in the area where pipeline corrosion occurred, if the corrosion scale layer in the area was uniformly covered, the corrosion phenomenon under the scale layer was significantly less than that in the area where the corrosion scale layer was not complete.In order to determine the reason for this phenomenon, electron scanning microscopy (SEM) and X-ray diffraction (XRD) were used to analyze the surface microstructure and chemical composition of the corrosion scale layers at the corrosion failure sites of pipelines.Electrochemical technologies were used to study the effect of scale layers on CO₂ corrosion of X65 steel. The results show that the uniform corrosion rate of X65 steel in CO₂ declined in the existence of FeS and FeCO₃ corrosion scale layers; when FeCO₃ corrosion film completely covered on the surface of metal substrate, the possibility of pitting of metal substrate would be significantly lower;on the contrary, if FeCO₃ corrosion film covering on the metal substrate surface was loose and porous or incomplete, a tiny galvanic cell structure would be formed on the metal substrate surface, thus leading to an increased tendency of pitting on the metal substrate surface.