Stress corrosion cracking in tinplate destined for legume and pet food packaging

Problems associated with stress corrosion of tinplate cans for foodstuffs are occurring at an increasing rate. The appearance of stress corrosion usually entails heavy financial penalties and high risk to the food. Unfortunately, at present, no practical measures exist to counteract this phenomenon. Stress corrosion is a type of localised corrosion which develops by way of the simultaneous action of particular media, which, in the absence of stress, may be only mildly aggressive or even non-aggressive, and a stress which is lower than that required for purely mechanical cracking. The aim of the present work was to study the susceptibility of tinplate to stress corrosion in different test media simulating foodstuffs. To this end, two approaches were used: an electrochemical technique, fast and slow polarisation, and a dynamic-mechanical technique, the slow strain rate test. The results of both tests enabled identification of the environment-material combination most susceptible to this type of corrosion. In particular, it emerged that the most critical environment for the development of stress corrosion is a solution simulating meat products at pH 6, whereas the most sensitive material was found to be tinplate produced from single reduction continuous annealing steel.