Failure Analysis of Coke Dry Quenching Car Liners in Coke Plant

Coke dry quenching (CDQ) bucket is used to carry hot coke to CDQ chamber for cooling. The liners provided inside the bucket were getting buckled and cracked after 6–7 months of service. The thermography was carried out, and results showed that maximum temperature inside bucket is 600–650 °C. Chemical analysis revealed the failed liners were made of 600-QT spheroidized cast iron. Metallographic study showed decarburization, nodule decomposition, and thick scale in the hot(inner) side of liner plate. Pearlite graphite nodules decompose to cementite and ferrite, and hardness taken on the cementite globules (280 HV) confirms decomposition. Type IV and V graphites were observed in the heat affected zone, whereas in cold side of the liner plate VI graphite nodules were observed. Hardness variation was observed in the cracked sample along the thickness, and it showed lower hardness at hot surface due to ferritic structure, but at cold zone specified higher hardness was achieved. This nodules bursting, decarburization, and scale formation indicated microstructural degradation due to prolong use at high temperature (above 600 °C) in S.G iron. The microstructural deterioration resulted in lower hardness and decreased strength causing buckling and cracking. To enhance the service life of liner, austenitic heat-resistant casting steel with added Ni & Mo was recommended and it enhanced the service life by at least 150%.