乙烯裂解炉石脑油进料线腐蚀泄漏分析

Corrosion Leakage Analysis of Naphtha Feeding Line in Ethylene Cracking Furnace

乙烯装置备用裂解炉对流段石脑油进料线发生腐蚀泄漏,对其宏观腐蚀形貌、剩余厚度、化学成分、金相组织和腐蚀产物进行了分析,分析结果表明:其直管与弯头连接的焊缝部位有一水滴状的腐蚀穿孔,穿孔部位及弯头背弯部位腐蚀减薄最为严重,最小剩余厚度分别为1.85 mm和2.19 mm。化学成分符合标准要求,金相组织无异常,腐蚀产物中主要含有S,O和Fe等元素。从腐蚀介质、管道结构和开停工等方面对进料线的腐蚀泄漏原因进行了分析,其腐蚀机理主要为湿硫化氢腐蚀,在"腐蚀-腐蚀产物被冲刷剥离-腐蚀"的循环重复作用下,管道焊缝及弯头背弯部位优先发生腐蚀减薄及穿孔泄漏。

Methods of macroscopic corrosion morphology, residual thickness, chemical composition, metallographic structure and corrosion products was used to analyze the leakage of naphtha feeding line in convection section of standby cracker in ethylene unit. The results showed that there was a corrosion perforation shaped like water drop at weld seam between straight pipe and elbow. Serious corrosion thinning was found at parts of perforation and elbow pipe with the smallest remaining thickness 1.85 mm and 2.19 mm, respectively. Chemical composition and metallographic structure met the standard requirements. Corrosion products mainly composed of S, O and Fe. Leakage of feeding line was studied in respects of corrosion medium, pipeline structure, start-up and shutdown. Wet hydrogen sulfide corrosion was judged to be the main corrosion mechanism. Under the repeated action of "corrosion-corrosion products wash-off-corrosion", corrosion thinning and perforation occurres preferentially on pipeline weld seam and elbow pipe.