Failure Analysis of Liner Plates of Wet Coke Quenching Car
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Quenching of coke after carbonization is an important step that influences its strength and reducibility in a blast furnace. During the wet coke quenching process, hot coke from 1200 °C is brought down to a temperature of around 100–150 °C by impingement with jets of water. It was observed that the liners of quenching car buckets would fail during service in 15 days to 1 month. Chemical analysis revealed the failed liners were made of heat resistant HK 40 cast alloy. Multiple cracks were observed to have initiated from the surface and propagated through the material. Microscopic analysis showed crack branching with inter-dendritic propagation. Furthermore, WDS elemental mapping revealed that there was a significant concentration of S and Cl with marked decrease in concentration of Cr preferentially along the crack propagation paths. These suggest that stress corrosion cracking (SCC) is the primary mode of failure. Thermal stresses during sudden quenching of coke can be attributed to provide the stress needed for SCC. It appears that the mechanism of SCC is lowering in energy required for crack propagation in the presence of certain environment and alloy combination. Cyclic thermal stress reversals and difference in coefficient of thermal expansions of carbides and austenite leading to thermal stresses would have contributed to the failures. A ferritic-pearlitic steel liner which is not susceptible to SCC in the working environment was recommended, and it enhanced the service life by at least 400%.
KeywordsCoke Liners Stress corrosion cracking Intergranular Crack branching Thermal stresses
Authors would like to acknowledge the management of Tata Steel Limited for allowing to publish this work.
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