烟机入口管膨胀节失效分析

Failure analysis of expansion joint for inlet of flue gas expander

中国石油天然气股份有限公司大连石化分公司1.4 Mt/a重油催化裂化装置烟机入口管线共有四波铰链板膨胀节6台。编号为波2和波4的膨胀节分别在2011年和2012年出现波峰开裂失效,严重影响装置的正常运行。详细介绍了膨胀节运行情况及失效形式,并从应力因素、温度影响和金相组织变化等方面对膨胀节的失效原因进行分析,由此得出由于波峰处所承受过大的拉应力造成波峰开裂,铰链板垫板焊缝组织脆化导致焊缝开焊则是导致膨胀节开裂失效的根本原因。此外,波纹管材质内部的晶间腐蚀是其开裂失效的内在原因,而膨胀节波纹管因长期在高温环境下工作发生高温腐蚀疲劳、材料韧性降低也是最终导致开裂的重要原因。

6 expansion joints of bellow plates were installed on the inlet pipeline of flue gas expander of the 1. 4 MM RFCC unit in Petro China Dalian Petrochemical Company. The No. 2 and No. 4 expansion joints failed in 2011 and 2012 respectively,which seriously affected the normal operation of the unit. The operation and failure of the expansion joints were introduced in detail. The causes of failure of expansion joints were analyzed in respect of stress factor,impact of temperature and changes of metallurgy. It is concluded that the cracking of bellow peak resulting from excessive tension stress at the bellow peak and welds cracking caused by embritlement of welds of plates are the culprits for the cracking failure of expansion joints. In addition,the intergranular corrosion inside the bellow pipes is the internal cause of cracking failure. As the bellow expansion joints are operating under the high temperature for a long period,the high-temperature corrosion fatigue and reduction of material toughness are also the important causes of cracking.