Failure analysis of a pair of failed chain links

The failure of a pair of metal chains during a towing operation in a particularly aggressive environment is examined. Evaluation of the cause of failure is carried out through visual observation, optical and scanning electron microscope analyses of various surfaces, including fracture surfaces, in combination with hardness and tensile tests. Visual examination revealed a high reduction in the resistant section near the contact zones between contiguous links, where the chains then failed. The chemical composition and percentage of elements present on the surface showed a high presence of corrosion products. The main cause of the chain link failure was due to corrosive wear, which markedly wore down the chain by reducing its resistant section resulting in overloading of the remaining net section area of the chain. Corrosive wear also removed the case-hardened layer induced by carbo-cementation. In order to assess the effect of corrosive wear power, an analytical evaluation was proposed. This method, although approximate, succeeds in assessing the reduction in chain strength induced by corrosive wear. Better inspection and maintenance would have allowed for early detection of the presence of the corrosive wear phenomenon, while a metal material with greater resistance to corrosion would certainly have postponed and/or prevented the manifestation of this problem, ensuring a longer service life. In this way, the initially planned safety coefficient of 2, in relation to the static breaking load, can also be reduced.