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Highlights: [•] Excessive vibration of the exhaust fan. [•] Repeated failures of bearings. [•] Cracks in the concrete foundations. [•] Experimental and numerical modal analysis of the fan’s rotating wheel. [•] Vibration analysis during the fan’s operation. [ABSTRACT FROM AUTHOR]

Abstract: This article describes the findings of an investigation on the failure of a cooling fan gearbox. The failure analysis was aimed at identifying the root cause of the gear damage in order to prevent their reoccurrence. Detailed investigation using several characterisation techniques such as visual and metallographic examinations, hardness testing, and different chemical analyses showed that the gears failed by contact fatigue accelerated by alternating high loads. The failure contributing factors are discussed and identified. Practical corrective actions were suggested in order to avoid similar failures. [Copyright &y& Elsevier]

Abstract: Fatigue failure of holding U-bolt of a cooling fan blade is analyzed. Fractography of the fracture surface reveals the characteristics of a fatigue fracture. Finite element modeling is used for stress analyzing. Analysis of the loading conditions indicates that the bolts are under multiaxial fatigue. Effective alternating and mean stresses are obtained based on the multiaxial fatigue criteria. By using the modified Goodman approach and considering the notch effect, effective stress amplitude, is obtained for all nodes. The highest stress amplitude is obtained at six critical nodes. Fatigue life for the most critical node is determined as 3.63 million cycles. [Copyright &y& Elsevier]

Abstract: The present work was carried out to investigate the failure mechanism of a power plant forced draft fan (FDF) blade made of 2014-T6 Al alloy, using visual examination, microstructural characterizations, study of the fracture surface and hardness testing. Based on the obtained results, surface defects including corrosion pits due to the existence of Cl ion and also erosion pits due to mechanical action of particles in the air entering from the filtration system and abrading on the fan blades surfaces, increased the probability of surface crack initiation. Cyclic loading and stress concentration on these surface defects influenced the fatigue life of the blade due to elevating the mean stress and resulted in fatigue failure of the investigated FDF component. [Copyright &y& Elsevier]

Abstract: The catastrophic failure of the main blower of a petroquimical plant boiler is discussed. The preliminary analysis of all the damage suffered by the machine indicated that the rotor was subject to strong unbalanced forces due to the breakage of one or more blades. Root Cause Analysis (RCA) was employed to determine the events responsible for failure. It could be established the bearing box nearest to the gearbox was damaged first, and the consequent displacement that was transmitted through the coupling, tore the gearbox out of its base. The reconstruction and analysis of the deformations of the analyzed parts allowed identifying the initiation of the fracture at the cone rotor. Manufacture defects contributed to the occurrence of the failure due to an excess rotating speed overload. [Copyright &y& Elsevier]

Abstract: During operation of the radial fan with a diameter of the rotating wheel of approximately 3m the machine crashed. The goal of the analysis by numerical and experimental methods of mechanics was to identify failure sequences of the individual parts of the fan and their reasons. Analysis of residual stresses in the rotating wheel of the fan as well as measurement of vibrodiagnostic parameters in the running fan of the same type were used to solve the task. [Copyright &y& Elsevier]

Abstract: The failure analysis of a generator rotor fan blade was investigated by mechanical analysis and metallurgical examination of fracture surface. Fracture took place at the airfoil root, surface examination showed that the blade had cracked by a high cycle fatigue mechanism. However, there was no evidence of material defect. A series of analytical, finite element and experimental analysis was utilized to determine the steady-state stresses and dynamic characteristic of the blade. Possibly the failure was due to aerodynamical disturbances that resulted in a state of resonant condition of vibration. The simulation of blade with final crack showed the stress intensity factor (SIF) under these condition exceed the critical SIF and final fracture could be occurred under analyzed stresses. [Copyright &y& Elsevier]

• SEM images from the fracture surface indicate fatigue failure of diaphragms. • The actual stress distribution in the diaphragm was computationally estimated. • The fatigue life of diaphragm under actual service life was predicted. • A Modification to design of sound generator body is proposed. Sonic soot blower, utilizing an oscillating diaphragm, generates acoustic waves for cleaning of equipment such as boiler and furnace to increase their efficiency. Based on earlier research by NRI (Niroo Research Institute), one of the main reasons disrupting the regular function of sonic soot blower is the failure of the diaphragm. The failure of circular Ti-6Al-4V sheets employed as the diaphragms is investigated by using SEM images. Based on these images, fatigue failure is found in the governing failure mechanism. A modification to the arrangement of the blower is proposed by introducing a gap between the diaphragm and its seat to improve the fatigue performance. A computational fluid dynamics (CFD) analyses are performed using the Ansys CFX software for estimation of pressure distribution on the diaphragm during service loading, and the results are introduced to the finite element (FE) model developed by the Abaqus software for calculation of stresses induced in the diaphragm. Variation of Mises stress at the center of the diaphragm, where the maximum stress developed, is extracted from the FE model for one period as a stress spectrum for one operation interval. A stress-life approach is employed to assess the fatigue life of the diaphragm subjected to estimated stress spectra. According to the prediction, increasing the gap size by 0.1 mm results in extension of life up to 2.75e10 spectrum passes, which are significantly higher than the desirable lifetime (5 years) of the diaphragm. Further increase of gap size leads to higher fatigue life, however, considering the decrease of efficiency as the gap size is increased, the gap size of 0.1 mm would be the optimum configuration. [ABSTRACT FROM AUTHOR]