The reasons for perforation of heat exchange tube in stripper air cooler of continuous reforming unit were analyzed by means of chemical composition analysis,metallographic structure analysis,scanning electron microscopy observation and energy spectrum analysis.The survey found that the chemical composition of heat exchange tube material meets the chemical composition requirements of No.10 steel material except for the low content of Si element.Metallographic structure of each part of heat ex-change tube is ferrite+pearlite with no significant difference.There are two layers of corrosion products on the outer wall of heat exchange tube,The outer corrosion products are mainly iron oxides,while the inner corrosion products are mainly zinc and iron oxides and scale.The surface of galvanized heat exchange tube had undergone severe scaling before corrosion occurred.Perfora-tion of heat exchange tube was caused by external corrosion,mechanism of corrosion perforation is oxygen concentration cell cor-rosion.Due to poor medium flow in the gap between scale layer on outer surface of heat exchange tube and metal outer wall,con-centration cell corrosion was developed inside and outside the gap,ultimately causing under-deposit corrosion at scaling area and leading to local corrosion thinning until perforation.
关键词
10号钢/汽提塔顶空冷器/换热管/外壁腐蚀
Key words
No.10 steel/stripper air cooler/heat exchange tube/external wall corrosion
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