Failure analysis of SMS-1 EOT crane hoist C-hook

Abstract

A 40-ton capacity electric overhead traveling (EOT) crane hook failure was investigated for the root cause analysis. The analysis involves examination of drawing, visual inspection, chemical composition, microstructure, hardness, inclusion analysis, and fractography. From the drawing it was found that the hook failed at a thread groove where the stress concentration is maximum. The hook is a plain carbon steel grade. Visual inspection revealed fatigue striations on both sides on the diameter of the hook shaft, with the final fracture at the center. The chemical composition of the hook revealed lower carbon than the specification with lower hardness. The microstructure of the hook revealed a ferrite pearlite microstructure with no heat treatment, as there is no variation of microstructure from the surface to the core. A lot of large-sized manganese sulfide and silicate inclusions are found on the hook, revealing the steel is not a clean one. The fractography of the hook revealed fatigue striations with the final fracture in a rapid brittle mode with the cleavages seen through the scanning electron microscopy. Hence, it is suggested to use an alloy steel cleaned shaft with proper normalizing or Q&T heat treatment for a better life. Additionally, use of ultrasonic non-destructive testing (NDT) for the detection of cracks by periodic monitoring will help in preventing the accidental failures.