Failure analysis on abnormal corrosion of economizer tubes in a waste heat boiler

Repeated shell side corrosion occurred on economizer tubes of a waste heat boiler. In order to find out the root cause of the corrosion, a series of characterization methods were conducted. First of all, the tubes were proved to be qualified A106 Gr.A steel in chemical compositions and metallographic structures. Then, both macroscopic and microscopic characteristics of the failed tube were observed thoroughly. After that, phase compositions of the deposits collected from failed tubes were analyzed. Content of sulfur and nitrogen of deposits was determined precisely as well. The results revealed that repeated failures were primarily owing to sulfuric acid dew point corrosion and the sulfur mainly came from waste liquid of methyl methacrylate (MMA). Finally, mechanisms of the failure were discussed in detail and practical countermeasures were put forward.