Waterside fissures that form in the vicinity of weld attachments in boiler tubing are a problem in the paper industry, particularly in kraft recovery boilers where water leaks pose a serious safety hazard. This type of damage is generally called stress-assisted corrosion (SAC) in the paper industry. Although the mechanism is not fully understood, SAC is believed to involve preferential aqueous corrosion along narrow zones of cyclic strain where the protective magnetite oxide suffers mechanical damage. Metallurgical analyses suggest SAC largely involves oxygen corrosion during outage periods and boiler start-up. Other important factors would include high residual stresses in the steel at attachment weld locations and bends, and pH of the hydro water used when the boiler is fired. Examples and case histories are presented to illustrate SAC in recovery boilers.

Subject
Corrosion fatigue, Water, Recovery boilers, Tubes, Corrosion cracking, Fissures, Stress cracking, Stress, Internal surfaces, Boilers, Pitting, Oxygen, Residual stress
Keywords:
stress-assisted corrosion, corrosion fatigue, residual stress, oxygen corrosion, recovery boiler, attachment weld
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2004
Association for Materials Protection and Performance (AMPP)
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