页岩气输送用转角弯头内腐蚀减薄原因分析

目的针对某页岩气输送平台用转角弯头发生严重内腐蚀减薄的问题开展原因分析,明确腐蚀类型及机理,指导防腐处理,提高转角弯头的服役安全性。方法以页岩气输送用转角弯头为研究对象,针对转角弯头内腐蚀减薄行为开展基础研究,通过宏观观察及尺寸测量分析内腐蚀的腐蚀形貌及分布,并进行理化检测、微观观察、物相分析,探究腐蚀产物,综合分析转角弯头内腐蚀减薄的原因。结果宏观分析发现,转角弯头内壁外弧侧与中性区过渡区域有壁厚发生突变而产生的腐蚀台阶,最大壁厚减薄率达63.4%。电子显微形貌与金相分析表明,弯头内壁的腐蚀坑呈纵深发展,逐层剥离,腐蚀产物疏松、形貌多样,且可观察到细菌形貌。腐蚀产物的能谱及XRD分析发现,管体内壁的腐蚀产物主要是Fe S、Fe2O3、Fe CO3等,内腐蚀可能与CO2、H2S、SRB等有关。结论弯头腐蚀减薄是硫酸盐还原菌(SRB)-CO2腐蚀协同作用的结果,SRB的存在对CO2腐蚀起催化作用。此外,Cl-对腐蚀产物膜的破坏和弯头外弧侧的冲刷加速了腐蚀作用。建议确定SRB细菌来源,以便有效投放杀菌剂,同时对管线内壁定期进行清理,避免菌落长期附着于管体内壁。此外,建议添加多级气液分离装置,严格控制气相中的含水量。

Cause Analysis for Internal Corrosion Thinning of Corner Elbow for Shale Gas Transportation

The work aims to analyze the cause of internal corrosion thinning of corner elbow used in a shale gas transformation platform, so as to determine the corrosion type and corrosion mechanism, put forward the anti-corrosion methods and improve the service safety of corner elbow. The corner elbow for shale gas transportation was taken as the research object to carry out basic research on corrosion thinning behavior in corner elbow, analyze corrosion morphology and distribution through macro observation and size measurement, explore the corrosion products through physical and chemical detection, micro observation and phase analysis, and comprehensively analyze the cause of corrosion thinning in corner elbow. Macroscopic analysis showed that there was a corrosion steps due to the sudden change in inner wall thickness between the outer arc side and the neutral zone, and the maximum thinning rate of wall thickness was 63.4%. The results of electron microscopy and metallographic analysis showed that the corrosion pits on the inner wall of the elbow developed in depth and peeled off layer by layer, and the corrosion products were loose with various morphologies. The results of energy spectrum and XRD analysis of the corrosion products showed that the corrosion products of the inner wall of the tube were mainly FeS, Fe2O3, FeCO3, etc. The internal corrosion might be related to CO2, H2S, SRB and so on. The synergistic action of sulfate reducing bacteria (SRB)-CO2 corrosion is the main reason for corrosion thinning of inner wall, while the existence of SRB catalyzes the CO2 corrosion. Meanwhile, the damage to corrosion product film and the erosion of elbow outside arc by Cl- accelerates the corrosion. It is suggested that the source of SRB be determined so as to effectively put fungicides in the pipeline. At the same time, the inner wall of the pipeline should be cleaned regularly to avoid long-term bacterial colonies attaching to the inner wall. In addition, a multi-stage gas-liquid separation device should be added to strictly control the moisture content in the gas phase.