Effect of small gap between tube and suction box on crevice corrosion formation of the dewatering tube

Abstract

Dewatering tube is a crucial equipment used to separate water and solids during papermaking process. The tube made of SS 316L stainless steel, responsible for supplying fresh water, failed during operation. The purpose of this research was to determine the cause of failure to prevent similar issues in the future. Methods used in this research mainly implements root cause analysis while considering all possible aspects contributing to the failure. Pitting Resistance Equivalent Number of 23.499 was obtained, indicating acceptable value of SS 316L localized corrosion resistance. However, the results of the examination indicated that the failure of the dewatering tube was caused by crevice corrosion. The crevice corrosion was formed due to trapped chlorine-containing water in the gap between the tube and suction box.  The chlorine content of 3.36 wt% was confirmed by EDS. The presence of chlorine deposits in the gap between suction box, in combination with operating temperature (70 – 80°C) and environment (pH 3.5 to 4.5) caused the localized corrosion reaction to occur, ultimately leading to tube leakage. The study’s results provide valuable insights for industries to mitigate the risk of similar issues of equipment that operates in corrosive environment in conjuction with elevated temperature.