Stress Corrosion Cracking Rates in High Yield Austenitic Alloy Tubing
Cold work in austenitic alloy tubing accelerates stage II stress corrosion crack growth up to 4.5E-7 m/s when stress intensity exceeds critical thresholds.
Slip Dissolution
Meaning
Mechanistic model for stress corrosion cracking describes the process where metal atoms dissolve at the tip of a crack when a protective oxide film is ruptured by plastic strain. Researchers use the slip dissolution theory to explain how crack growth occurs in environments where the metal would normally be passive. The model links the electrochemical reaction rate at the bare metal surface to the frequency of film rupture events.
Passive Film
Formation of a thin oxide layer protects the bulk material from the surrounding corrosive medium. When the metal underneath deforms, the brittle film breaks, and slip dissolution begins at the newly exposed site.
Crack Extension
Velocity of the crack depends on how quickly the metal can repassivate after a rupture. If the environment prevents the film from reforming, the slip dissolution process continues unchecked, leading to rapid failure. This relationship allows engineers to predict the life of a component based on the strain rate and the electrolyte chemistry.
Growth Prediction
Mathematical models based on this mechanism are used to set the inspection intervals for power plants and chemical reactors. Because the slip dissolution rate is sensitive to small changes in water chemistry, it is a primary factor in the design of corrosion mitigation strategies. A failure to account for this mechanism can lead to unexpected leaks in high-pressure piping.