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Title: | Catastrophic failure of urea prill-tower fan |
Authors: | Hegde S.R. Rakshan Kumar J.K. Sondar P. Dsilva P.C. |
Issue Date: | 2021 |
Citation: | Engineering Failure Analysis , Vol. 121 , , p. - |
Abstract: | 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 |
URI: | https://doi.org/10.1016/j.engfailanal.2020.105207 http://idr.nitk.ac.in/jspui/handle/123456789/15227 |
Appears in Collections: | 1. Journal Articles |
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