Failure Analysis of Liner Plates of Wet Coke Quenching Car
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TECHNICAL ARTICLE—PEER-REVIEWED
Failure Analysis of Liner Plates of Wet Coke Quenching Car Kaushal Kishore . Goutam Mukhopadhyay
Submitted: 6 December 2018 / in revised form: 9 May 2019 / Published online: 10 June 2019 ASM International 2019
Abstract 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 interdendritic 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%. Keywords Coke Liners Stress corrosion cracking Intergranular Crack branching Thermal stresses K. Kishore (&) G. Mukhopadhyay R&D and Scientific Services, Tata Steel Limited, Jamshedpur 831007, India e-mail: [email protected]
Introduction BF–BOF (blast furnace–basic oxygen furnace) route of steel making remains one of the most popular for large tonnage production [1]. Coke is the key raw material for iron making in a blast furnace serving manifold purposes [2]. It functions as the primary source of reducing agent, directly or indirectly by producing CO gas. In addition, it provides permeability to the bed and allowing the countercurrent reactions to occur and hence allowing the smooth operation of the blast furnace. Moreover, it is the main source of heat. However, coke is not readily available in nature and it requires destructive distillation of metallurgical coal [3]. Figure 1 shows the process flow chart of different stages of coke making and its use in the blast furnace. The coke-making process consists of mixing of coal received from different mines in pre-determined proportions followed by comminution in crushing mills with automated hammers. These are screened thereafter to prepare blended coal. This serves as the raw material for coke makin
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