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A Case Study-Caustic Gouging Of Boiler Tubes

Caustic corrosion is sometimes referred to as “caustic attack or “caustic gouging.” Corrosion of this type may result from internally fouled heat transfer surfaces and the presence of sodium hydroxide in the boiler water; and concentrated solutions of alkali where the normal washing of the tube metal ID is restricted after Departure from Nucleate Boiling (DNB), i.e., when the steam bubble release exceeds the rinsing rate.

Product Number: 51322-17780-SG
Author: Suresh Divi, Sri Krishna Chimbli
Publication Date: 2022
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Caustic corrosion also referred to as “Caustic attack” or “Caustic gouging” generally results from the fouled heat transfer surfaces on boiler tubes and due to the presence of sodium hydroxide in the boiler water. Once the caustic concentrations reached a certain level the caustic attack occurs and results in irregular wall thinning or gouging of the tube water side surface. The damage progresses through the tube wall until it ruptures. Such caustic corrosion failure was observed in one tube from a utility’s boiler. This paper presents the laboratory metallurgical analysis of the failed tube including welds and the process fluids and its effects on the caustic corrosion. The laboratory analysis includes chemical analysis, scale deposit analysis, metallography, and hardness tests.

Caustic corrosion also referred to as “Caustic attack” or “Caustic gouging” generally results from the fouled heat transfer surfaces on boiler tubes and due to the presence of sodium hydroxide in the boiler water. Once the caustic concentrations reached a certain level the caustic attack occurs and results in irregular wall thinning or gouging of the tube water side surface. The damage progresses through the tube wall until it ruptures. Such caustic corrosion failure was observed in one tube from a utility’s boiler. This paper presents the laboratory metallurgical analysis of the failed tube including welds and the process fluids and its effects on the caustic corrosion. The laboratory analysis includes chemical analysis, scale deposit analysis, metallography, and hardness tests.

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