Table of Contents
5.4.2 Stress Corrosion Cracking (SCC)
Stress corrosion cracking (SCC) is characterized by the following damage symptoms
- Unusually rapid crack growth (Fig. "Stress corrosion cracking").
- Embrittlement, i.e. decreased contraction at fracture
- Decrease in operating life under static loads
- Decrease in fracture energy/fracture toughness (KIC > KISCC)
Therefore, crack initiation and fracturing of engine parts, along with their associated consequences, are likely damage types.
A stress corrosion cracking system consists of a material sensitive to the specific acting media under sufficiently high tension. The most susceptible are hard, i.e. high-strength, material variants that are subjected to high loads due to their high strength. This can lead to spontaneous catastrophic failure of the affected parts. Stress corrosion cracking can be prevented, if one of these criteria for the development of this corrosion type can be eliminated through suitable measures.
The typical SCC systems in compressors are shown in the above table. It can be seen that almost all material families can suffer SCC damage under certain conditions, although the probability of it occurring varies. The most common and aggressive corrosive media are watery media containing chlorine ions. SCC can be caused without watery electrolytes by hot salt on titanium alloys (Fig. "Special experiments"), and by sulfur as a decomposition product on Ni-alloys.