Premature failure of seamless tubes made of 316Ti stainless steel in a boiler feed-water (BFW) heat exchanger occurred at a local steel complex, which led to about 65–70% service-life reduction. The heat exchanger is a fixed-tube-sheet type with hydrogen gas flowing inside the tubes and water circulating through the shell side. The cooled hydrogen gas is purged to box annealing furnaces to create a reducing atmosphere. Failure analysis was conducted on the tubes to determine the contributing factors to premature failure of the heat exchanger. Four issues including corrosion fatigue, pitting corrosion attack, under-deposit corrosion, and fouling contributed to the failure of the tubes in the heat exchanger. The pitting corrosion attack was caused by chloride in circulating water. Chloride was also detected in accumulated deposits on the tubes causing the under-deposit corrosion issue. Contamination of boiler feed-water with Ca, Si, Mg, and Cl occurred during the water treatment process, a congruent phosphate–pH treatment in an in-house water treatment unit. The quality of the supplied water to the heat exchanger does not meet the recommended specifications. As a major recommendation, the tubes of the heat exchanger must be manufactured of super duplex stainless steel UNS S32750, based on specifications of the ASTM A789 standard.

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