Failure of a Cooling Water Pump Shaft
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TECHNICAL ARTICLE—PEER-REVIEWED
Failure of a Cooling Water Pump Shaft . J. K. Rakshan Kumar . Sanjay Chawla . Pavankumar R. Sondar . Preetish C. Dsilva Subray R. Hegde
Submitted: 20 September 2020 / in revised form: 30 September 2020 / Accepted: 2 October 2020 Ó ASM International 2020
Abstract 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. Keywords Shaft Key Fractography Fatigue Heat treatment
P. R. Sondar (&) J. K. R. Kumar S. Chawla P. C. Dsilva S. R. Hegde Department of Metallurgical and Materials Engineering, National Institute of Technology Karnataka, Surathkal 575025, India e-mail: [email protected] P. C. Dsilva e-mail: [email protected]
Introduction Thermomechanical processing and heat treatment of steel components/structures are critical for ensuring optimal service lives. A minor lapse in the processing of engineering components specially that are used in dynamic loading conditions may cause major event/failure/accident during the service. In general, majority of the pump shafts fail either by corrosion or by fatigue and in many cases, corrosion initiates fatigue failure [1]. A study on failed recirculation pump shaft of nuclear power plant revealed that the shaft failed due to thermal fatigue. Cracks initiated along the shaft surface and propagated inwards by fatigue due to cyclic stresses arising from self-constraint [2]. In another study on failure of rotor shaft, cracks were observed on two fracture planes inclined at 45° to the shaft axis. Torsional vibrations caused fretting corrosion that led to the failure of the shaft [3]. In a separate study of water pump shaft failure, microstructural analysis revealed that the material was used in hot finished/annealed condition without hardening and tempering. The hardness measurements of the shaft confirmed the microstructural observations [4]. Yet another investigation on rotor shaft failure in
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