Industrial corrosion failure: Case studies

Abstract

The significance of corrosive processes on industrial failures is possibly less appreciated in our country than other industrialized nations. Whereas, there has been a proliferation of corrosion consultants in developed countries, it is only of late that we see the Indian industries realising the need for specialized treatment of their corrosion problems. Indeed, corrosion failures are insidious, and universal in occurrence. The forms and manifestations of the corrosive processes are too numerous. Moreover since corrosion is a function of alloy composition, environment, com¬ponent design, metallurgy, temperature and a host of other factors, generalization of corrosive processes and subsequent modelling proves to be futile. Thus corrosive failure analysis often turns out to be an exercise where component and industry specific diagnostic tools have to be employed, so that the failure analysis is often unique for the particular component tested. The solution of corrosive failures thus requires an understanding of the process environment, and sometimes an examination of the related processes, in addition to whatever information that can be gleaned from the affected component itself. The latter often requires thorough microscopic examination of the damaged part. Quite significant information about the corrosive process can often be found in the footprints left by the process, that is, the corrosion product or debris left near the site of corrosive attack. The analysis of the fluid environment that was in contact with the affected component is also often necessary. The microstructural examinations reveal irregularities in the component metallurgy as well as throw light on the physical manifestations of the corrosive pro¬cess. Environmental analysis yields clues on the corrosive species responsible for the process. Corrosion product analysis helps in determining the chemistry as well as mechanism of the process. So, these exercises carried out simultaneously often reveal enough information about the damage mechanism. The present paper illustrateds how the diagnostic methods can be employed to failure analysis through two case studies.