Feed Water Chemistry-Related Corrosion Failures in Subcritical 250 MW Coal-Fired Boiler

This paper emphasis on the study of typical
premature failure of water wall tubes of two thermal power plant boiler of same capacity (250 MW) and same operational parameter but with different boiler water chemistry. The investigation concludes on the water-side corrosion in both of the cases. One boiler is running with coordinated phosphate treatment (CPT) and another with all volatile treatment (AVT). The causes of corrosion were discovered and proposed measures for their elimination were given. Visual examination, chemical analysis of deposits, oxide scale thickness measurement, and microstructural examination were carried to ascertain the probable cause/causes of failure. From the investigation, it was finally concluded that the combination of localized high tube metal temperature
and wall thinning due to under deposit corrosion led
to the premature tube failure in boiler running with CPT
and localized pitting corrosion in boiler running with AVT. Based on the results and discussions, a possible way to combat the corrosion was proposed.