12. Corrosion

Corrosion is defined as the interaction between a metal and its environment that results in changes in the properties of the metal, and which may lead to significant impairment of the function of the metal. In most cases the interaction between the metal and the environment is an electrochemical reaction where thermodynamic and kinetic considerations apply. Depending on the characteristics of the corrosion system various types of corrosion occur.

In this chapter all test methods available today are described. For scientific purposes as well as investigations in the laboratory so called conventional electrochemical test methods with direct current are primarily used (Sect. 12.1). In addition, newer techniques have been proposed (Sect. 12.1) that are based on dynamic system analysis (Sect. 12.2.1) or that allow study of corrosion processes in situ with spatial resolution down to 20 μm (Sects. 12.2.2 and 12.2.3). In the following sections a distinction has been made between testing for performance of corrosion protection measures such as inhibitors (Sect. 12.8) and testing that focuses on specific types of corrosion. In this context it is advisable to differentiate between corrosion without (Sect. 12.4) and with mechanical loading (Sect. 12.5) including hydrogen-assisted cracking (Sect. 12.8) which has some similarities to stress corrosion. High-temperature corrosion (Sect. 12.6) has a different mechanistic background than electrolytic corrosion because it is a corrosion process at a metal/gas or metal/salt interface. Exposure and on-site testing (monitoring) require specific considerations in the design of test facilities, probes and the interpretation of results (Sect. 12.4).

Another important source of information regarding corrosion testing is that edited by Baboian [12.1].