Failure analysis of arch section tube in fired boiler of a captive power plant

A damaged boiler tube removed from the inclined portion of the arch section of the fuel fired furnace of a captive power plant was sent to this laboratory for investigation. Examination revealed that there was thinning of the tube due to loss of material by corrosion in localized regions located at the bottom-half of the tube. Analysis showed that the corrosion was set in due to scaling on the tube surface preferentially in the inclined portion of the tube due to separation of dissolved and un-dissolved solids in water. Material removal was also promoted by galvanic corrosion due to deposition of copper on the tube surface. Study showed that corrosion resulted in significant hydrogen damage in the material in the form discrete cracks at the grain boundaries. The hydrogen damage was found to be confined to the affected regions only. The material of construction of the boiler tubes was found to conform to specification in terms of chemical composition, microstructure and hardness. A detailed analysis of the failure is presented in this report