Failure Investigation of Cooling Plates of a Blast Furnace
Premature failure of cooling plates of a blast furnace in service has been investigated. The cooling plates are water-cooled copper channels shielded by refractory lining. Industrial cooling water (ICW) flows at 5 bar pressure through the cooling plates. The investigation consisted of visual inspection, chemical analysis, microstructural examination by optical microscopy, energy-dispersive spectroscopy (EDS), and hardness measurement. Visual inspection revealed that the refractory lining on the component was damaged, thereby exposing the cooling plates to elevated temperatures of the furnace atmosphere. This led to overheating of the cooling plates. Chemical analysis revealed that the component was essentially pure copper (~99.24% purity). Microstructural analysis showed grain size variation across the section of the component. Also, annealing twins were revealed on optical examination. A through-thickness pit was identified on the failed component during the optical examination. The examination also revealed branched cracks associated with scale in the component. Energy-dispersive spectroscopy (EDS) confirmed the scale to be oxides indicating high-temperature oxidation of the component resulting in pitting. Analysis suggested overheating due to damage of the refractory lining as the prime cause of failure of the component.