Faculty Publications
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Item Failure of a Cooling Water Pump Shaft(Springer, 2021) Sondar, P.R.; Kumar, J.K.R.; Chawla, S.; Dsilva, P.C.; Hegde, S.R.This study investigates the failure of an industrial cooling water pump which experienced a drive shaft failure. As per the fail-safe design, during adverse loading of the shaft, key should fail by shear. The key, if fails, can be easily replaced to resume the operation of the pump. However, this investigation reveals that both the key and the shaft failed due to materials processing issues. A detailed failure analysis was carried out including design calculations, visual inspection, dye penetrant inspection, magnetic particle inspection, hardness test, microstructural analysis, and fractography. The study found that the hardness of the shaft varied radially from the core to the surface. The subsurface of the shaft near the keyway, happened to be significantly softer than the key. During operation, the keyway widened by plastic deformation and caused rattling of the key. Due to rattling and vibration, the key developed numerous fatigue cracks and eventually failed by crack linkages. The shaft eventually failed by torsional shear near the midpoint of the keyway. The analysis adjudged hardness variation in the shaft due to materials processing issues as the root cause of the failure. © ASM International 2020.Item 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 LtdItem 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 LtdItem Creep cavitation damage of K-type thermocouples(Elsevier Ltd, 2023) Rakshan Kumar, J.K.; Bhattacharjee, D.; Dsilva, P.; Praveen, R.; Hegde, S.R.This work investigates premature failure of K-Type thermocouples that were used in a chemical processing plant. The work presents a detailed metallurgical failure analysis involving, site visit, visual inspection, metallography, optical microscopy, scanning electron microscopy, and fractography. The analysis reveals that the thermocouple wires endured creep cavitation damage during service and eventually failed by creep-rupture. Interestingly, the influence of creep on the degradation of industrial thermocouples is not detected and reported thus far. By presenting analytical stress calculations using temperature dependent materials properties, the current work reveals that the thermal expansion mismatch between various materials of thermocouple causes high tensile stresses in the thermocouple wires during elevated temperature services. The work concludes that high tensile stresses at elevated temperature operation caused premature creep failure of the K-type thermocouples. © 2022Item Failure of Soap Extruder Bolt Assembly(Springer, 2023) Kumar, J.K.R.; Mogra, N.; Padasale, B.; Dsilva, P.C.; Sondar, P.; Hegde, S.R.Present work investigates failure of EN8 steel bolt in a bolt–pin assembly that was used as a fastener in an industrial soap extruder. Unexpectedly, EN19 steel pin that is supposedly the sacrificial element in the assembly remained intact. The investigation follows standard failure-analysis procedure comprising, site-visit, visual inspection, metallography, mechanical-testing, design-analysis, numerical stress-analysis, and fractography. The design-analysis finds that the materials of construction were mistakenly swapped between the pin and the bolt that caused plastic-deformation, necking, and eventual failure of the bolt during operational peak-loading condition. The numerical stress analysis illustrates that the bolts failed at the thread-root region that acted as the stress-raiser. Additionally, the investigation finds that poor-quality machining left-behind jagged thread-root profile that increased the stress-concentration furthermore. The metallography and the fractography indicate that a transverse crack that was initiated at poorly machined thread-root led to the brittle fracture of the bolt. The investigation illustrates how human errors can cause recurring failure of critical components leading to production losses and makes suitable recommendations to prevent such failures in the future. © 2023, ASM International.