Most unlined carbon steel smokestack failures are caused by corrosion inside the stack. Moisture in flue gases, when cooled to about 300 F or less, condenses against the stack internal surfaces. Because most fuels contain sulfur, sulfurous gases formed in combustion mix with the condensed moisture to form acids which severely attack steel, painted steel and other types of stack linings. The attack is more severe in the upper portions of the stack where low temperatures and condensation are most common.
An example of stack failure is shown in the photograph above. This steel stack section was used in ordinary boiler house bituminous coal service at the Oscar Mayer Company, Madison, Wis. The ⅜-inch steel stack was corroded beyond use after a service life of only seven years.
An economizer was installed to recirculate and extract heat from flue gases. Although this increased the boiler’s efficiency, it also intensified corrosion...
