Faculty Publications
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Publications by NITK Faculty
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Item 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 LtdItem 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.Item Failure Analysis of Reciprocating CO2 Compressor(Springer, 2021) Dsilva, P.C.; Shetty, P.; Sondar, P.R.; Ganesh Kumar, B.; Hegde, S.R.This work presents failure analysis of a heavy-duty, four-stage, double-action, reciprocating CO2 compressor, which resulted in the shutdown of an ammonia plant. The failure occurred in the fourth stage of the compressor, during which the piston rod, piston rings, a suction valve, and associated valve cage are found fractured. The failure analysis includes details of site visit, visual inspection, dye penetrant test, fractography, and microstructural analysis. Furthermore, Xanthoproteic test was conducted on the extracts of the failed piston rings that confirmed the presence of bacterial cellular protein. When the morphology of the failed piston ring was studied using a scanning electron microscope, unique degradation features and the presence of bacterial metabolic products were observed conforming to the growth of bacteria. In-service biodegradation of the piston ring material (polyether ether ketone composite) is adjudged as the root cause for the compressor failure. © 2021, ASM International.Item Failure of hydraulic lathe chuck assembly(Elsevier Ltd, 2022) Sondar, P.R.; Gurudath, B.; Ahirwar, V.; Hegde, S.R.Present work provides a detailed failure investigation of a hydraulic lathe chuck assembly that comprises a plunger, three jaws, and three jaw-carriers that are made of carburized, tempered and sub-zero treated EN36C steel. The chuck assembly suffered premature failure of the plunger and one of the jaw carriers during the service in a CNC lathe. The investigation comprises a detailed metallurgical failure analysis involving: visual inspection, fractography, metallography, and hardness measurements. The analysis concludes that plunger failed first by fatigue fracture that is originated at a sharp corner of a T-slot. The mating jaw-carrier failed in the next event due to instant misalignment and overstressing during the lathe operation. The investigation concludes that design flaw and improper heat treatment cycle as the reasons for the premature failure of the assembly. Through experimental simulation of the heat-treatment cycles using EN36C specimens, the work suggests that carburizing, cryogenic treatment and then tempering is the proper sequence for achieving the best combination of mechanical properties that should extend the service life of the chuck-assembly. © 2021 Elsevier Ltd