Recent Corrosion and Material-Related Problems in Recovery Boilers, 1992 Engineering Conference Proceedings

Corrosion and material factors are ongoing concerns for operation/maintenance personnel of recovery boilers in the pulp and paper industry. The problems can be as benign as uniform loss of wall thickness, e.g., wastage of outside surfaces of waterwall tubes. Or they may be more serious problems, such as localized corrosion/cracking, e.g., pitting corrosion, stress corrosion cracking, thermal fatigue cracking, and waterside stress-assisted corrosion/cracking. While the former are conducive to periodic inspection and replacement schedule planning, the latter are not readily assessable during periodic inspections and many times lead to unscheduled, sometimes catastrophic downtime.

Some recent corrosion and material problems are presented through case histories of field inspection/failure analyses. The case histories include stress corrosion cracking in superheater tubes, stress-assisted waterside corrosion/cracking in tertiary air box tube and buckstay weld attachments, and thermal fatigue cracks in screen tube space bar welds, smelt spouts, and smelt spout openings. While some of the cases may be isolated and unique to certain boiler operations, others can represent industrywide problems. The case histories identify vulnerable areas in recovery boilers and highlight the need for critical, focused fitness-for-purpose evaluations by a knowledgeable team using appropriate inspection methods.