MATEC Web Conf.
Volume 165, 201812th International Fatigue Congress (FATIGUE 2018)
|Number of page(s)||10|
|Section||Fatigue of Structures / Vibrations / in Service Fatigue Failures|
|Published online||25 May 2018|
Failure analysis of a 40 ton crane hook at a Hot Strip Mill
R&D and Scientific Services, Tata Steel Limited, Jamshedpur - 831 001, India
* Corresponding author: Address: Metallurgical Laboratories and QA Group, R&D and Scientific Services, Tata steel Ltd., Jamshedpur 831 001, India Tel.: +91 809284714; fax: +91 657 234395. E-mail address email@example.com
There have been accounts of repeated failure of crane hooks at the coil yard of a Hot Strip Mill which pose a serious threat to safety in the area. More than 4 hooks failed in less than 5 years. The crane hook (rated for 36000 kg) failed from the threaded shank while lifting a load of 18143 kg. The metal in the hook was revealed by chemical analysis to be killed IS: 4367 20C15 steel. The hook rod failed from a step where there was a cross sectional change and the locations were associated with machining and chatter marks. Such cross-sectional changes are the potential sites of stress concentrations leading to crack initiations. Fracture surfaces of broken pieces of hook reveal initiation of beach marks from both sides with granular rough surface at the middle of fracture zone. Beach marks initiated from both sides indicate origin of reverse bending fatigue. Distinct granular rough zone at the middle is due to final brittle fracture. Microstructure of the polished sample revealed numerous inclusions which indicate that the steel was not clean .Such a huge number of inclusions are not desirable as they can act as stress concentration sites and lead to fatigue crack initiation. Etched microstructure of failed hook reveals coarse cast structure having inhomogeneous microstructure with a mixture of ferrite and pearlite (which meant lower fatigue strength). This inhomogeneous coarser cast structure is outcome of lower reduction ratio during rolling followed by improper heat treatment process. The fracture was concluded to have occurred due to stress concentration from the step region due to inferior material (Inclusion and Improper Heat treatment process). Preventive maintenance and condition monitoring procedures should be applied to identify and minimize the risk(s) Establishment of an NDT procedure for regular basis inspection of the structural members (welded joints and hookshaped steel rods during incoming inspection and in-service).
Key words: Crane Hook / Hot Strip Mill / Beach marks / cast structure / Fatigue
© The Authors, published by EDP Sciences, 2018
This is an Open Access article distributed under the terms of the Creative Commons Attribution License 4.0, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. (http://creativecommons.org/licenses/by/4.0/).
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