Reasons for Perforation and Leakage of Stainless Steel Heat Exchange Tubes in a Reboiler

Some heat exchange tubes in a reboiler at the bottom of ammonia rectification tower in sewage stripping plant of a company were perforated and leaked when used less than 2 a. The reasons for perforation and leakage of S30403 heat exchange tubes were investigated through macroscopic analysis, chemical analysis, microstructure observation for the failed tube body, morphology and composition analysis for the scale layer on the tube surface. The results showed that the heat exchange tube leakage originated from outer wall. H₂S dissolved in ammonia water on the shell side was ionized to produce HS^- which destroyed the oxide film on the surface of the heat exchange tubes, causing the corrosion reaction between metal and dissolved oxygen. The corrosion products deposited gradually and formed scale layer, leading to under-deposit corrosion. At the same time, enrichment and concentration of Cl^- in subscale occlusion area caused autocatalytic acidification and accelerated the progress of under-deposit corrosion, resulting in perforation and leakage of the heat exchange tubes finnally.