Crevice corrosion related problems

The three major forms of concentration cell corrosion are crevice corrosion, tuberculation, and underdeposit attack. Each form of corrosion is common in cooling systems. Many corrosion-related problems in the cooling water environment are caused by these three forms of wastage. The next three chapters—Chap. 2, Crevice Corrosion, Chap. 3, Tuberculation, and Chap. 4, Underdeposit Corrosion — will discuss cooling water system corrosion problems. 

In discussing environment, we can look at its effect on a macro scale, e.g. in the atmosphere, in the ocean, etc. and also examine effects on a micro scale, i.e. what is happening on the metal surface or over short distances. Due to the great variety of environments in which metals are put to use, the range of corrosion problems are equally numerous. Often, similar types of corrosion occur in many environments and may stem from similar mechanisms these have been given specific names which indicate how the corrosion has occurred. For example, under-deposit corrosion and crevice corrosion are related, both being due to oxygen concentration cells. 

In the case of the nickel alloys, the stability of the passive layer is a problem. The alloys depend on the oxide films or the passive layers for corrosion resistance and are susceptible to crevice corrosion. The conventional mechanism for crevice corrosion assumes that the sole cause for the localized attack is related to compositional aspects such as the acidification or the migration of the aggressive ions into the crevice solution [146]. These solution composition changes can cause the breakdown of the passive film and promote the acceleration and the autocatalysis of the crevice corrosion. In some cases, the classic theory does not explain the crevice corrosion where no acidification or chloride ion build up occurs [147]. 

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