Failure of porcelain coated heating elements used in regenerative air preheaters

Sulfuric acid dew point corrosion is still a matter of concern with respect to early failure of heating elements used for air preheating in thermal power plants. Therefore, corrosion protection by means of porcelain enamel coatings is widely used. However, insufficient protective properties of the coating can result in a drastic decrease in service life. In the present study, failure analysis was comparatively performed on damaged heating elements showing different degrees of damage after approximately 1.5 years in service in a thermal power plant. The analytical results indicated that a lower degree of damage was observed for the heating element having higher content of silica. The protective properties of coatings decreased with the increasing pore density formed in the coating layer. The heating element coated with a harder porcelain layer was less severely attacked.