页岩气田集气站污水罐的腐蚀行为与冲刷特性研究

Corrosion Behavior and Erosion Characteristics of Sewage Storage Tank in Gas Gathering Station of a Shale Gas Field

某页岩气田集气站污水罐频繁发生穿孔,通过水样调查、统计分析等方法解析了穿孔原因及特征.采用失重计算、扫描电镜(SEM)观察、能谱分析及数值模拟等方法,研究了20#碳钢污水罐在常温常压下的腐蚀规律及流动冲刷特性,并提出了防护措施.研究结果表明:污水罐的穿孔主要受腐蚀与冲蚀的共同作用;随时间的增加,污水罐的均匀腐蚀速率逐渐降低,但小孔腐蚀风险增加;与污水罐内污水管口正对的罐底区域存在明显的冲蚀.通过将污水罐入口管道的长度从1.35 m降为0.85 m,污水冲击到罐底时的速度从18 m/s降为10 m/s,且自由射流截面扩大,可有效降低污水对罐底的冲蚀.通过采取材质优化、缓蚀剂加注及增加防冲板等措施,可有效降低污水罐腐蚀穿孔风险.

Perforation occurred frequently in sewage storage tank in gas gathering station of a shale gas field.Corrosion behavior and flow erosion characteristic of 20#carbon steel sewage storage tank under room temperature and pressure were investigated by using weight loss measurement,scanning electron microscopy observation,energy spectrum analysis and numerical simulation.The root-cause and characteristics of the perforation were analyzed,and anti-corrosion measures were proposed.The results showed that perforation of the sewage storage tank was mainly caused by the combined effect of corrosion and erosion.The general corrosion rate of the sewage tank gradually decreased with exposure time,but the risk of pitting corrosion increased.Erosion was obviously observed at the bottom of the storage tank facing the sewage pipe orifice.The velocity of the sewage hitting the bottom of the tank was reduced from 18 m/s to 10 m/s when the length of the sewage pipe located in the sewage storage tank was reduced from 1.35 m to 0.85 m.The expansion of the free jet cross-section was associated with the reduce of the erosion at the bottom of the tank by the sewage.The risk of corrosion and perforation of the storage tank can be reduced through measures such as material optimization,corrosion inhibitor and introduction of antiscouring plates.