Faculty Publications
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Item 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.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 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