Faculty Publications

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Author: search.filters.author.Rakshan Kumar, J.K.Subject: search.filters.subject.Visual inspection

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    Catastrophic failure of urea prill-tower fan
    (Elsevier Ltd, 2021) Hegde, S.R.; Rakshan Kumar, J.K.; Sondar, P.R.; Dsilva, P.C.
    This work presents failure investigation of a prill-tower fan that was in service for about 20 years in a urea plant. All the fan-blades and the plummer blocks fractured catastrophically during the plant-operation, shocked the plant personnel, and caused a huge shutdown loss. Standard failure analysis procedure involving: site visit, visual inspection, microstructural analysis, fracture analysis, analytical stress calculation and FEM analysis was followed. The investigation confirms that the fan-blades having numerous dents and nicks were operating in a mild corrosive atmosphere of ammonium hydroxide. The fracture analysis suggests that a pre-existing dent on the trailing edge of a blade corroded to form a pre-crack that aligned perpendicular to the long axis of the blade. When the pre-crack grew to a critical size, a small chunk of the blade fractured from the vicinity and ejected towards the blade-tip by centrifugal force. Because of confined space around the fan and limited blade-tip clearance, this triggered a chain reaction of blade fracture and rattled the entire array of fan-blades. The analysis establishes that the plummer blocks failed due to mechanical imbalance of the fan-shaft caused by the blade failure. The investigation concludes that presence of dents and nicks on the fan-blades is the root-cause for this catastrophic failure. Grinding-off of the surface defects to eliminate stress raisers is recommended for averting such a failure in future. © 2020 Elsevier Ltd
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    Failure Analysis of a Bucket Elevator Shaft
    (Springer, 2021) Gurudath, B.; Kumawat, K.K.; Tejaswi, V.; Sondar, P.R.; Rakshan Kumar, J.K.; Hegde, S.R.
    Present work investigates the in-service break down of a bucket elevator in a chemical processing plant. The elevator was used for lifting bulk Di-Ammonium Phosphate and broke down due to premature failure of a shaft made of EN19 steel. The investigation comprises a detailed metallurgical failure analysis involving site visit, visual inspection, fractography, and metallography. The investigation reveals that, about 2 years prior to the failure, the shaft was tack-welded to the sprocket hub and a gib-head key near the keyway to avoid the frequent loosening of the key. The inspection during the site visit confirms that the shaft-sprocket assembly was subjected to in-service jerky loading condition along with uneven stress distribution due to misaligned counterweight. The investigation concludes that a crack was initiated in the shaft at the heat affected zone of the tack-welded spot, propagated transversely by fatigue due to in-service cyclic loading, and terminated catastrophically by a brittle fracture during the service. Tack welding, coupled with uneven stress distribution in the shaft due to misaligned counterweight system, is adjudged the root cause of this failure. Suitable remedial measures are suggested to avoid such a failure in the future. © 2021, ASM International.
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    Failure analysis of a fire water jockey pump shaft
    (Elsevier Ltd, 2022) Padasale, B.; Kulkarni, G.S.; Rakshan Kumar, J.K.; Cadambi, S.; Hegde, S.R.
    This work presents failure investigation of a fire water jockey pump shaft that is installed in the fire-station of a petrochemical plant. The jockey pump is driven by a 130 kW motor at about 1480 RPM whose shaft and the coupling key are made of 40C8 steel and 55C8 steel respectively. The drive-shaft of one of the pumps fractured after running for approximately 110 h, while its twin remained functional. The failure analysis involves visual inspection, hardness measurements, metallography, fractography, analytical design calculations, and numerical stress analysis. The analysis concludes that usage of square-ended key in the round-ended keyway is the primary cause, and usage of dissimilar materials for the shaft and the key is the secondary cause for the premature failure. The present work recommends a modified key design and use of the same grade of steel for both the shaft and the key to avoid such failures in the future. © 2022 Elsevier Ltd