石脑油裂解炉对流段炉管泄漏原因分析

Analysis on leakage of convection section furnace tube of naphtha cracking furnace

采用宏观检查、超声波测厚、光谱分析、金相组织观察、扫描电子显微镜和X射线衍射等方法对泄漏炉管进行了分析,结果表明炉管底部焊缝附近腐蚀最为严重,腐蚀速率高达0.574 mm/a。炉管底部腐蚀产物的主要成分为Fe_(3)O_(4)和FeSO_(4)·H_(2)O,表明在炉管投料运行、烧焦、再投料运行的循环生产过程中,H_(2)O,O_(2),H_(2)S等腐蚀介质先后与炉管发生了腐蚀反应。从裂解炉结构、生产工艺、焊缝及热影响区、原料腐蚀性等方面对炉管的腐蚀原因进行了分析,炉管腐蚀穿孔部位的液相水为其发生溶解氧腐蚀、湿硫化氢腐蚀、硫酸腐蚀提供了腐蚀环境。受焊缝及热影响区的影响,炉管腐蚀穿孔部位形成了“小阳极、大阴极”的电化学腐蚀反应体系,焊缝及热影响区的金属成为电化学反应的阳极,不断溶解,并发生腐蚀穿孔。

The leaking furnace tube was analyzed by means of macro examination,ultrasonic thickness,spectral analysis,metallurgical structure observation,SEM and XRD methods.The analysis results show that the corrosion near the weld at the bottom of the furnace tube is the most serious,and the corrosion rate is as high as 0.574 mm/a.The main components of corrosion products at the bottom of furnace tube are Fe_(3)O_(4) and FeSO_(4)·H_(2)O indicates that in the cyclic production process of furnace tube in the circulation process of feeling,operation,burning and feeding again,corrosive media such as H_(2)O,O_(2) and H 2S have successively reacted with furnace tube.The causes of furnace tube corrosion are analyzed from the aspects of cracking furnace structure,production process,weld and heat affected zone,and feedstock corrosivity.It can be seen that the liquid phase water at the corrosion perforation of furnace tube provides a corrosion environment for dissolved oxygen corrosion,wet hydrogen sulfide corrosion and sulfuric acid corrosion.Affected by the weld seam and heat affected zone,an electrochemical corrosion reaction system of“small anode and large cathode”is formed at the corrosion perforation area of the furnace tube.The metal in the weld and heat affected zone becomes the anode of the electrochemical reaction,dissolves continuously,and corrosion perforation occurs.