Testing Materials for Resistance to Fireside Corrosion in Kraft Recovery Boilers, 1994 Engineering Conference Proceedings

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Specimens of SA-192 boiler tube, 304L plate and SA-192 boiler tube sprayed with 465P and 7001 coatings were exposed to hot, flowing gases (either H2S or CH3SH) for durations ranging from 1 to 50 days. Relative to SA-192 carbon steel, 304L was found to corrode at much lower rates, a result which would be expected from field experience. Some spalling of the corrosion product was observed on 304L during long duration tests. This suggests that more extreme environmental conditions (higher temperatures, or longer exposure times) might cause unacceptable corrosion of 304L.

Results which showed that methyl mercaptan was more than 4 times as corrosive to SA-192 carbon steel as hydrogen sulphide at equivalent gas concentrations were reconfirmed, but the effect on 304L was found to be the inverse. The stainless steel corroded more rapidly in hydrogen sulphide than in methyl mercaptan. Both 465P and 7001 metal spray coatings suffered from significant sulphur penetration into the coating. Based on these results, neither coating would be recommended as suitable for long-term protection in kraft recovery boilers. These laboratory results closely mirror field experience, and provide further validation of the test method.