Corrosive degradation and failure of vertical furnace wall tubes of a boiler

The failures of vertical furnace wall tubes of a co-generation boiler have been investigated. The thinned section failures, often accompanied by buckling prior to failure, were found to be due to acid attack as a consequence of “hideout”. The local corrosion and consequent thick and non-protective iron-oxide deposition at the sites of attack produced hot spots, which is evident from the microstructure of those regions. Decarburization by hydrogen generated during the corrosion process also contributed to the loss in strength of the material. The possibility of “alkali attack” as opposed to acid attack was ruled out by the various findings of this investigation.