脱硫装置中换热管束腐蚀破坏机理研究

On the corrosion failure mechanism of the heat exchanger bundle in the desulfurization units

为了研究醇胺法脱硫溶剂再生装置换热器管束不同腐蚀区域的腐蚀破坏机理,在该装置中腐蚀泄漏换热管束的重度腐蚀区、近腐蚀区、远腐蚀区及轻微腐蚀区分别截取腐蚀试样共4个;采用扫描电子显微镜(SEM)分析腐蚀试样的微观形貌,采用扫描电镜中搭载的能谱分析仪(EDS)分析了重腐蚀区和轻微腐蚀区试样的元素及其含量的差别;利用X射线衍射仪(XRD),进一步分析了重度腐蚀区和轻微腐蚀区试件表面腐蚀产物的物相。结果表明:醇胺法脱硫溶剂再生装置换热管束腐蚀破坏的主要原因是氨液受到热冲击后,析出湿H2S与换热管钢材发生电化学腐蚀,硫化物应力腐蚀、氢渗透、氢鼓泡及高速冲击等因素造成管壁腐蚀穿孔破坏。

The paper is aimed at making a study of the corrosiondamage mechanism of the heat exchange tube bundles in the solvent regeneration container. The stress of the given paper is to trace and determinate the alkanolamine desulfurization of the 4 zones of corrosion specimens through the individual and separate interception,that is,the severe corrosion zone,the near corrosion zone,the far corrosion zone and the slight corrosion zone of the corrosion leakage heat exchange tube bundles. To achieve the purpose,we have,first of all,analyzed the micro-morphology of the corroded samples via the scanning electron microscopy(SEM),which helps us to show that there exist corrosion pits and residues in the severely corroded samples. The surface of the specimen near the corrosion zone presents a brittle corrosion protrusion,and the micro-cracks may initiate on the protrusion.And,then,the surface embrittlement and cracking would come out in the specimens of the far-distant corrosion zone. And,further,the flake crystal products have been found adhering to the surface of the slightly corroded specimens. And, later, the difference of the elements and their contents between the heavy corrosion zone and the slight corrosion zone has been analyzed by EDS attached to the scanning electron microscope. Finally,further analysis has to be done for the phase of corrosion when the products are severely and slightly corroded at the surface of the specimens in the corroded areas by the X-ray diffraction(XRD). The results of our tests show that the main cause of the corrosion damage taking place in the heat exchanger tube bundles belongs to the electrochemical corrosion between the wet H2 S precipitated from the ammonia solution due to the thermal shock and increase of the temperature of the heat exchanger steel tube,in addition to the sulfide stress corrosion,the hydrogen permeation and bubbling,as well as the high-speed impact of the interchanging corrosion and the pipe wall perforation. All this may reveal that the corrosion process that takes place on the outer surface of the heat exchanger tube due to the slight corrosion by the lean amine solution,and the flake grains,which are accumulated to result in bigger blocks,and the intergranular boundaries developed into the micro-cracks. What is more,the leakage of the heat exchanger tubes can also be caused by the hydrogen corrosion due to the H2 S removal from the ammonia-rich solution in the tubes at higher temperatures,and the accelerated high-speed fluid impinging on the surface of the hydrogen bubbles.