Browsing by Author "Hegde, S.R."

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Annealing Behavior of Cold-Rolled Inconel 601
(Springer, 2024) Dsilva, P.C.; Padasale, B.; Vasavada, J.; Mishra, S.; Hegde, S.R.
Present study investigates isothermal annealing behavior of prior cold-worked Inconel 601 (aka, IN 601) sheets. The study comprehensively covers the annealing response of the material over wide cold-reduction and temperature ranges. Using structural characterization and mechanical testing, the study tracks strain-hardening, strain-aging, recovery, and recrystallization stages of IN 601 sheets as a function of degree of cold-reduction and annealing temperature. Using X-Ray diffraction analysis, hardness measurements, and tensile tests, the study reveals that prior cold-worked IN 601, irrespective of the degree of cold-reduction, consistently exhibits strain-aging during low-temperature (~ 0.4Tm) annealing. The investigation establishes that the ‘recovery stage’ is preceded by ‘strain-aging-stage’ during which the alloy exhibits superior strength and hardness than the strain-hardened and recovered states. Based on the thermomechanical experimental results, the current work proposes a recrystallization map that integrates the ‘strain-hardening’ and ‘strain-aging’ stages with the recovery and recrystallization stages. Additionally, microstructural analysis and SEM-EBSD analysis presented in this work indicate that, by suitably controlling strain-hardening and the recrystallization annealing, a refined microstructure comprising high aspect-ratio grains having high-angle grain-boundaries can be obtained that may improve both fatigue and creep properties of IN 601 sheets. © ASM International 2023.
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
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. © 2022
Deep cryogenic treatment of plain-carbon and low-alloy steels
(ASTM International service@astm.org, 2020) Sondar, P.R.; Hegde, S.R.
To improve the mechanical properties of steels, cryogenic treatment is often carried out as an intermediate step between quenching and tempering. The transformation of retained austenite into martensite is the main objective and principle behind the cryogenic treatment. Generally, high-alloy and high-carbon steels are subjected to cryogenic treatment, as they produce a high fraction of retained austenite during quenching as compared with low- and medium-alloy steels. This work analyses the effect of cryogenic treatment on EN8, a plain-carbon steel, and EN47, a low-alloy steel, through microstructural characterization, hardness measurements, and tensile tests. The work shows that influence of cryogenic treatment carried out after tempering is only marginal, whereas cryogenic treatment carried out before tempering yields much better mechanical properties. Experimental results obtained in this work confirm that EN47 responds slightly better than EN8 suggesting that low-alloying additions influence the cryogenic treatment of steels. This work established that by properly applying cryogenic treatment, the strength and hardness of both EN8 and EN47 steels can be increased by about 50 MPa and 3 HRC, respectively, as compared with conventional hardening and tempering treatment. © 2021 ASTM International. All rights reserved.
Effect of spheroidization of cementite in ductile cast iron
(University of Science and Technology Beijing, 2021) Basavaraj; Sondar, P.R.; Hegde, S.R.
The research aims to provide an alternative to austempering treatment of ductile cast iron with a simple and cost-effective heat-treatment process. This goal was accomplished by applying a simple one-step spheroidization heat treatment to the as-cast ductile iron, which would normally possess a coarse pearlitic microstructure to a significant extent. Spheroidization experiments involving isothermal holding below the lower critical temperature (A1) were conducted followed by standard mechanical testing and microstructural characterization for an experimental ductile iron. After improving the spheroidization holding time at a given temperature, the work shows that the ductility and toughness of an as-cast ductile iron can be improved by 90% and 40%, respectively, at the cost of reducing the tensile strength by 8%. Controlled discretization of the continuous cementite network in pearlitic matrix of the ductile iron is deemed responsible for the improved properties. The work also shows that prolonged holding time during spheroidization heat treatment leads to degradation of mechanical properties due to the inhomogenous microstructure formation caused by heterogeneous decomposition and cementite clustering in the material. The main outcome of this work is the demonstration of ductile cast iron’s necking behavior due to spheroidization heat treatment. © 2020, University of Science and Technology Beijing and Springer-Verlag GmbH Germany, part of Springer Nature.
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.
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
Failure Analysis of Cooling Tower Fan-Arm
(Springer, 2020) Padasale, B.; Kumar, J.K.R.; Sondar, P.R.; Cadambi, S.; Hegde, S.R.
This work presents failure investigation of cooling tower fan-arms commissioned in a chemical processing plant. The analysis aims at understanding the mechanism and root-cause of the failure. The investigation involves site visits, microstructural analysis, fracture surface analysis, hardness measurements, numerical stress analysis and experimental simulation. Work concludes that the fan-arms failed due to the lack of post-weld heat treatment, which caused localized stress-corrosion and pitting at critical locations that served as crack initiation sites. Fatigue loading condition and presence of residual stresses at the weld enabled easy propagation of cracks that led to recurring premature failure. Based on the root-cause and the mechanism identified in this analysis, proper pre-heating and post-weld heat treatment is recommended to relieve the residual stresses at the critical locations and thus to avoid/minimize such recurring failures in future. © 2020, ASM International.
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.
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.
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
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.
Hot corrosion behaviour of HVAF coatings deposited on Fe[sbnd]25Cr[sbnd]20Ni support hanger material
(Elsevier B.V., 2024) Ramanathan, P.; Gandimani, L.; K, S.; Cadambi, S.; Hegde, S.R.
Fe[sbnd]25Cr[sbnd]20Ni cast alloy is used as the material of construction for support hangers in fired heaters of oil refineries. These hangers support heater tubes in the fired heaters and are susceptible to hot corrosion due to Na2SO4 and V2O5 containing corrosive ash, especially when low-grade fuels are burnt. API recommends 50Cr[sbnd]50Ni cast-alloy for constructing the support hangers in highly corrosive atmospheres which, is highly expensive as well as brittle. To overcome this problem, in this work, coatings of 50Cr[sbnd]50Ni and 20Cr[sbnd]80Ni were applied on Fe[sbnd]25Cr[sbnd]20Ni substrates by HVAF process. The coatings were characterized by: Optical Microscopy, SEM-EDS Analysis, XRD Analysis, and Raman Spectroscopy. To study the hot corrosion behaviour of these coated specimens, a cyclic hot-corrosion test was carried out at 700 °C using 20 % Na2SO4–80 % V2O5 salt slurry. Along with the coated specimens, cast specimens of Fe[sbnd]25Cr[sbnd]20Ni and 50Cr[sbnd]50Ni were also subjected to the hot-corrosion test. Thus, Type-II hot corrosion behaviour of all four specimens were analyzed comparatively by weight-change measurements, cross-sectional metallography, SEM-EDS, XRD, and Raman-Spectroscopy. The Fe[sbnd]25Cr[sbnd]20Ni cast specimen displayed the least corrosion resistance. The corrosion resistance of the 50Cr[sbnd]50Ni coated specimen and the 50Cr[sbnd]50Ni cast specimen was found to be intermediate and quite comparable. 20Cr[sbnd]80Ni coated specimen recorded the best corrosion resistance. The corrosion mechanism and beneficial effects of high nickel-containing HVAF coatings against hot corrosion are presented. © 2024 Elsevier B.V.
Influence of ?-Phase on the Grain Shape and Mechanical Properties of Inconel 718
(Springer, 2025) Padasale, B.; Hegde, S.R.
The present work comparatively studies the thermomechanical processing of mill-annealed, aged, and solution-treated IN718 strips to study the influence of ?-phase precipitates on the grain aspect ratio and the mechanical properties. Prior-treated strips were subjected to thermomechanical processing by cold rolling followed by recrystallization annealing. The processed strips were then mechanically tested and characterized by: hardness measurement, tensile testing, microstructural analysis, electron backscatter diffraction (EBSD) analysis, and x-ray diffraction (XRD) analysis. The results suggest that the recrystallized strips do not show any crystallographic texture, yet possess orthotropic properties along the rolling and transverse directions. The microstructural features correlate well with the mechanical properties, suggesting that the precipitates of ?-phase positively influence the recrystallization kinetics and grain refinement. However, the presence of large fraction of coarse ?-phase precipitates adversely influence the grain aspect ratio and the tensile properties. The study reveals that solution-treated IN718, when subjected to suitable thermomechanical processing, yields a highly refined microstructure with high aspect ratio and superior mechanical properties, especially in the rolling direction. © ASM International 2025.
Premature failure of superheater tubes in a fertilizer plant
(Elsevier Ltd, 2021) Dsilva, P.C.; Bhat, S.; Banappanavar, J.; Kodancha, K.G.; Hegde, S.R.
This work presents an unique premature failure of steam superheater tubes in a fertilizer plant. The heat exchanger tube bundle made of SA 213 grade T11 steel suffered from wall thinning in the vicinity of baffles causing reduction in wall thickness of the tubes leading to perforation and leakage of steam from the tube-side into the shell-side during service. The work presents details of metallurgical failure analysis involving: site inspection, visual inspection, chemical analysis, X-Ray diffraction, microstructural analysis, and computational fluid dynamics analysis. The qualitative and quantitative chemical analyses and X-Ray diffraction carried out on superheater residue followed by microstructural analysis of failed tubes confirmed that the tubes suffered from aggressive corrosion attack at certain locations due to hot flue gas carrying alkaline salts and refractory fines. To understand the mechanism of thinning and the reasons for the tube bundle failure only at certain locations, a detailed CFD analysis was carried out on model of the heat exchanger which simulated the flow pattern of the hot gas. The analysis comprehensively demonstrates that the hot gas carrying both corrosive and erosive species caused erosion-corrosion of the tubes in the vicinity of tube-baffle junction that lead to wall thinning and subsequent failure of the tube bundle. Suitable remedial measures are suggested to minimize such failures in future. © 2020 Elsevier Ltd
Role of δ-phase on recrystallisation behaviour of Inconel 718
(SAGE Publications Inc., 2024) Padasale, B.; Potphode, L.; Dsilva, P.C.; Hegde, S.R.
The present work investigates the annealing behaviour of prior-coldworked Inconel 718 (IN718) sheets over wide reduction and temperature ranges by performing cold-rolling and isothermal annealing, followed by mechanical testing and structural characterisation. The study reveals that, with increasing annealing temperature, the prior-coldworked alloy shows non-monotonic M-Type variation with double peak-hardening at 0.3Tm and 0.6Tm. The study discovers that the first peak is due to the ‘static–strain–aging phenomenon’ that precedes recovery-softening. The second peak-hardening is due to precipitation-hardening, following which, the alloy softens due to recrystallisation. Supported by SEM, electron back-scattered diffraction and X-Ray diffraction results, the investigation suggests that the precipitation of fine rod-shaped δ-phase creates numerous nucleation sites at the shear bands that cause recrystallisation-burst at 0.75Tm. However, above 0.75Tm absence of the δ-phase activates grain-boundary migration resulting in rapid grain-coarsening. © The Author(s) 2024.