Analysis Of The Cause Of Failure And Improvement For Second Regenerator Exhaust-heat Boiler

Exhaust-heat boiler is an important installation in petrochemical enterprise catalytic device that used for the recycling of flue gas heat and produces steam. Its normal operation has a very important influence on energy consumption and efficiency of the catalytic device. This paper analyzed the immanent and external factors of leakages and researched the improvement to prevent leakages. This research is of great significance for long period safe operation of devices.Sinopec Shanghai Gaoqiao Company’s1#catalytic device second regenerator exhaust-heat boiler was installed to use at the end of1997and was leaked in February2010. A large number of cracks were found on evaporation segment tube bank and boiler drum welds which gave rise to leakages. The cause of cracking was analyzed by means of chemical composition, mechanical properties, metallographic analysis, fractography and water quality of boiler. Based on the failure analysis, the improvement was proposed on design, construction and water quality administration. They measures had good effects in practical applications. The conclusions were arrived at as follows:Cracks on second regenerator exhaust-heat boiler evaporation segment tube bank and boiler drum welds originated from inside of drum and caused by caustic induced stress corrosion cracking. The mainly reason is bad weld quality which resulted in a lager welding stress. This is the main immanent factor of caustic induced stress corrosion cracking.1#catalytic second regenerator exhaust-heat boiler demineralized water and desalinated water’s mixing ratio was not fixed. Alkaline boiler water severely exceeded the standard caused by the improper process control which is the external factor of caustic induced stress corrosion cracking.The research of improvement measures on second regenerator exhaust-heat boiler was studied. The radial arrangement of tube banks were increased in the structure design. Welding and construction scheme modifications can further reduce the stress generated during welding. Through the operation administration, softened water and phosphate dosage can be controlled. The measure of process management should be taken to prevent boiler water and alkaline from concentrating or exceeding the standard.The effects of improvement measures in practical applications showed that the analysis of causes of cracks on evaporation segment tube bank and boiler drum welds were correct. The improvement measures were effective and had excellent effects.