Fracture of a Leaf Chain for Lifting Clamps

Leaf chains are flexible lifting devices which are often used as a link between crane hook and the load to be lifted. Actually, they are not designed for diagonal pulls, but for clean tensile stress. In practice, however, slight diagonal pull situations are often inevitable. A certain degree of security against such unscheduled load cases, is therefore generally expected from these lifting devices, which means that the production engineer assumes that leaf chains behave “tenderly”. In the present failure analysis, this was also the case until the leaf chain manufacturer changed the chain link supplier. The chain links this supplier delivered were no longer quenched and tempered but case hardened instead, which actually makes them more wear-resistant but also less tolerable towards the kind of bending loads inevitably occurring with diagonal pulls. As a result the leaf chain fractured and the load dropped during the lifting of a 6.5 t casing component. Since all occupational safety rules of the engineering company were followed, there were no further consequential damages except for some damages to the casing component.