Damages due to corrosion in aqueous media
According to DIN EN ISO 8044, corrosion is "the reaction between metallic materials and their environment which leads to changes in the properties of the materials and the components and as a result of which the proper functioning of technical systems can be significantly impaired".
The different "pure" types of corrosion can be roughly subdivided as follows:
- Uniform surface corrosion
- Localised corrosion, e.g. pitting corrosion
- Selective corrosion, e.g. intercrystalline corrosion
If, in addition to chemical attack, there is also mechanical stress, a distinction is made between further types:
- Strain-induced corrosion
- Stress corrosion cracking
- Vibration corrosion cracking
- Erosion corrosion
- Cavitation corrosion
Based on the damage hypothesis at the beginning of the damage analysis, an investigation plan is determined: The analyses are used to determine the type and cause of corrosion and thus the cause of the damage.
Typical methods such as a SEM-EDX analysis are used to characterise corrosion products and to microscopically examine the damage pattern. A metallographic examination helps to characterise the material in terms of condition, microstructure and defects as well as to further define the type of corrosion. A chemical analysis of the material is also usually necessary to determine or exclude any deviations from the target composition.
In the case of stress corrosion cracking and intercrystalline corrosion, the susceptibility of the material can be checked in standardised test solutions and conditions.