一氧化碳转化炉热壁集气管失效模式分析及改进措施研究

Failure analysis and improvement measures study on the hot wall gas collecting tube of carbon monoxide reforming furnace

针对一氧化碳转化炉热壁集气管发生的开裂事故,对开裂原因进行了分析。对开裂的集气管进行了宏观形貌检查,对材质进行了化学成分和力学性能检测,结果表明:各部位截取试样的化学组成差别很小,各元素组成均符合ASTM-B407的规定,可排除化学组成不合格对集气管开裂的影响;集气管材料力学性能发生了一定程度的弱化,部分试样的抗拉强度和延伸率低于最低值。对断口附近组织和裂纹进行了扫描电镜和能谱分析,结果表明:集气管长期在高温腐蚀条件下工作,其组织发生了粗化现象;晶界析出的高含铌碳化物和富铬碳化物在晶界处不断长大和溶解,弱化了晶界;蠕变孔洞和蠕变裂纹在晶界处产生。采用CAESAR II软件、ABAQUS有限元素分析法对热壁集气管的子单元进行了应力计算和蠕变计算,表明热壁集气管增设U型卡可有效改善整个管系的应力分布。提出了增加材料壁厚、改变短尾管与热壁集气管的连接形式、降低炉管恒力吊架载荷等措施,以解决热壁集气管的失效问题。

Aiming at the cracking accidents occurred in the hot wall gas collecting tube of carbon monoxide reforming furnace,the cracking causes are analyzed. The macroscopic morphology of the cracking tube is detected,and the chemical composition and mechanical property of the tube material are examined. The results show that the chemical compositions of samples cut from different sections have slight difference,and the elementary compositions accord with the stipulation of ASTM-B407,therefore,the cause of disqualification of chemical composition leading to tube cracking can be excluded. The mechanical properties of the tube material appear certain degree weakened,and the tensile strength and elongation of some samples are lower than the minimum value. The scanning electron microscope and energy spectrum analysis are carried out on the texture and crack near the fracture,and the results show that since the tube is operated under the conditions of high temperature and corrosion,the texture is coarsening,the carbides containing high niobium and chromium separated out from crystal boundary grow up and dissolve,and the crystal boundary is weakened,and the creep cavity and creep cracking are appeared in the crystal boundary. The stress and creep are calculated by CAESAR II software and ABAQUS finite element analysis on the hot wall gas collecting tube. The result indicates that the stress distribution of whole tube system can be improved by adding U-type clip. Some measures are pointed out to resolve the failure problem,including adding the wall thickness of tube,changing the connecting form of stub liner and hot wall gas collecting tube,and reducing the loading of constant hanger of furnace tube.