Failure Analysis of Coke Dry Quenching Car Liners in Coke Plant
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TECHNICAL ARTICLE—PEER-REVIEWED
Failure Analysis of Coke Dry Quenching Car Liners in Coke Plant Urbi Pal . Piyas Palit . Jitendra Mathur . Prabhash Gokarn . Avishek Maharana
Submitted: 27 January 2020 / in revised form: 27 July 2020 / Accepted: 7 September 2020 Ó ASM International 2020
Abstract 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%.
U. Pal (&) P. Palit J. Mathur P. Gokarn Central Laboratories, Scientific Services Division, Tata Steel Limited, Kalinganagar, India e-mail: [email protected] A. Maharana Mechanical Maintenance, Blast Furnace, Tata Steel Limited, Kalinganagar, India
Keywords Liners S.G iron Nodule bursting Microstructural degradation
Introduction Quenching is the process whereby hot coke is cooled as soon as feasible after being pushed from the oven. Coke can be cooled by the circulation of inert gas or by indirect use of water. The most common method of quenching coke is with water, known as ‘‘wet quenching.’’ Dry quenching cools hot coke without bringing the coke in direct contact with water. In the CDQ process, coke is cooled by an inert gas. The coke dry quenching (CDQ) system includes a twostage CDQ chamber, boiler and dust recovery network. Hot coke is pushed into bucket car which transports the coke to the CDQ unit. The coke is charged into the CDQ chamber. Inert gas is circulated in a closed circuit between the cooling chamber and the boiler, where heat from the coke is recovered and transferred into steam with heat exchangers. Cooled coke is discharged from the bottom of cooling chamber. Heat from the hot coke is recovered with minimum operating costs. The schematic of CDQ process flow is shown in Fig. 1. A
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