Near-Drum Tube Thinning of Generating Bank Tubes in Kraft Recovery Boilers

	Localized corrosion was occuring on generating bank tubes adjacent to the interface with the mud drum For many mills, tube replacement (up to 2000 tubes) was required every 3-6 years Erosion was initially thought to be the damage mechanism.

A custom-designed conductivity probe was built for insertion in the boilers. It was used to demonstrate that water vapour from the sootblowers was reacting with SO2 in the flue gas to form sodium bisulphate – a corrosive liquid salt – on the surface of the tubes. The solution was to adjust process operation to avoid formation of this salt in the boiler.