某天然气管道内腐蚀原因及防控措施

Corrosion Reasons and Control Measures of a Natural Gas Pipeline

目的分析某天然气管线典型管段的腐蚀特性,明确管线的腐蚀原因及机理。方法采用扫描电镜对管道内壁不同方位的腐蚀形貌进行表面和截面微观观察。采用X射线衍射和EDS方法进行成分定量分析。结合天然气管道输送天然气成分、清管记录等服役状况进行天然气管线的内腐蚀特性研究。结果 CO_2腐蚀是造成该天然气管道内腐蚀的主要原因,管段12点钟方向腐蚀坑深度约为0.18 mm,3点钟和6点钟方向腐蚀坑深度均约为0.1 mm,腐蚀产物以Fe_2O_3和FeCO_3为主,6点钟方位的腐蚀产物厚度最大,3点钟方位的腐蚀产物厚度最小,3点钟和6点钟方位的腐蚀产物主要以Fe、O、C为主,12点钟方位的腐蚀产物含有S元素,同时可能存在细菌腐蚀。SiO_2是管线内残余的污泥本身所含,该管道在投入工作前可能已经发生了腐蚀。针对性地提出了相关腐蚀防控措施,采取措施后换管频率降低了56%。结论天然气管线存在的内腐蚀多为局部腐蚀,运行过程中应尽可能地避免腐蚀的发生,及时采取相应的防控措施,以免造成不必要的损失。

The work aims to analyze corrosion characteristics of a typical pipe section of natural gas pipeline, and clarify the cause and mechanism of pipeline corrosion. Scanning electron microscope（SEM） was used for surface and section microscopic observation of corrosion morphology in different positions on inner wall of the pipeline. Quantitative analysis of the composition was carried out in X-ray diffraction and EDS method. Corrosion characteristics in the natural gas pipeline were studied by referring to such service conditions as natural gas composition delivered by the pipeline and pigging records. CO2 corrosion was the main cause of corrosion in this natural gas pipeline. The corrosion pit in 12 o＇clock direction was about 0.18 mm deep, and that in 3 o＇clock and 6 o＇clock direction was about 0.1 mm. The corrosion products were mainly Fe2O3 and FeCO3. The corrosion products in 6 o＇clock direction was the thickest, and those in 3 o＇clock direction were the thinnest. The corrosion products in 3 and 6 o＇clock direction were mainly Fe, O and C, and the corrosion products in 12 o＇clock direction contained S and may be subject to bacterial corrosion simultaneously, SiO2 was contained in the residual sludge in the pipeline itself, the pipeline may have been corroded before it was put into operation. Relevant corrosion prevention and control measures were put forward specifically, and frequency of pipeline replacement decreased by 56% after adoption of the measures. Internal corrosion of natural gas pipeline is mostly localized corrosion. During operation, corrosion shall be avoided as much as possible, and appropriate control measures shall be taken in time to avoid unnecessary losses.