2 - Fundamentals and Concepts of Corrosion and Electrochemical Corrosion Protection

Abstract

The term “corrosion” is used to describe the reaction of a material with its surroundings that produces measurable changes on the material and can lead to damage. With metallic materials and aqueous solutions, the reactions in general are of an electrochemical nature. However, in addition, pure chemical reactions or entirely physical processes can also occur. This depends on the extent of the reaction and the demands on the function of a material or medium, which should always be considered together. Damage is said to occur when this function is impaired. Corrosion protection is designed to prevent such detrimental action. Types of damage can be classified as uniform or localized metal removal and corrosion cracking or detrimental effects to the environment from the corrosion products. Local attack can take the form of shallow pits, pitting, selective dissolution of small microstructure regions of the material, or cracking. Detrimental effects are certainly not the case with buried pipelines, but must be considered for environments in vessels and containers. It is common to classify corrosion into particular types when different results of reactions lead to definite forms of corrosion effects. The most important are uniform corrosion, shallow pitting corrosion, pitting corrosion, crevice corrosion, intergranular corrosion, and those with accompanying mechanical action—stress corrosion and corrosion fatigue.