The rusting of ordinary steel is the most common form of corrosion and overall adds up to a
high proportion of the total cost attributed to corrosion. General corrosion, in which the
whole of the exposed metal surface is attacked, may lead to failure in the engineering sense,
but this is usually avoided by the application of suitable control measures. All corrosion,
however, is not of the general type and localised effects may pose more complex problems,
especially in the engineering context. It is important to realise that corrosion characteristics
are not inherent properties of alloys, as are yield strength, electrical conductivity and the like,
since they relate to a combination of alloy and environment. Consequently, an alloy may be
very resistant to corrosion in a particular environment, yet perform poorly in another, and
even in a given environment factors like temperature, rate of flow and geometrical aspects
may be critical. In any event, the significance of corrosion to the engineer is that it leads to
loss of engineering function and the following examples have been chosen to illustrate this in
a variety of the branches of engineering. They also serve to define some of the commoner
forms of aqueous corrosion and their various consequences