Localized corrosion and component failures: Causes, mechanism and remedial measures

Amongst the various types of failures of the components caused due to corrosion, a majority of them are attributed to localized type of attack of the environments on the surfaces of metals/alloys. The present talk incorporates the discussions on causes, mechanism and remedial measures adopted to control the localized type of corrosion attack. Initially, a brief background about the theoretical aspects of corrosion of metals is given. This includes the various types of cells that cause corrosion of metals and also about the thermodynamical approach to understand the phenomenon of corrosion. The subjects related to five types of localized corrosion, namely pitting, crevice, stress corrosion cracking, corrosion fatigue and intergranular corrosion, who are considered to be the most dangerous type and cause catastrophic failures, are discussed a bit in detail. Their mechanism, causes and remedial measures adopted to control the problems are described. The lecture also touches in brief, the principles involved in failure investigations. This describes the importance of site visit, collection of sample of corrosion products, visual observations, mechanical and chemical tests and fractographic studies. Finally, some examples of case studies of failed components are incorporated to illustrate the application of knowledge in pinpointing the causes of failures and suggest the remedial measures to avoid the recur¬rences of such failures.