Staining of Engineering Components

There are literally hundreds of publications which begin by referring to the expense incurred through the depredations of rust. Consequently the technical literature on the occurrence of rust and on its nature is voluminous and, the basic principles involved in its formation being known, it might seem nearly impossible to contribute anything fresh to the subject. However, even though the basic conditions necessary for rust formation are well known and explanations of the rusting mechanism are likely to be amended only in detail, there are considerable difficulties in applying the knowledge to individual problems where rust prevention is necessary. Some of these difficulties stem from the loose manner in which the term ‘rusted ’ is applied, others from lack of correlation between cause and effect, between the type of oxide or hydroxide found and the original factors responsible for the phenomenon, and still others through lack of a clear specification of the degree of rust prevention required, which could be permanent or temporary, continuous or intermittent, complete or partial, depending on economic rather than technical considerations. It is proposed to consider in this article the stain stage of rusting, because this is the period at which it might be possible to obtain the maximum amount of information on the rusting process.