What Does Environmental Cracking (EAC) Mean?
Environmental cracking refers to a brittle fracture of a typical ductile material where the environment’s corrosive effect is the actual causing agent.
Cracking corrosion is caused by various conditions that can result in different forms of corrosion damage like:
- Corrosion fatigue
- Stress corrosion cracking
- Hydrogen attack
- Season cracking
- Sulfide stress cracking
- Stepwise cracking
- Liquid embrittlement
Environmental cracking is also known as caustic embrittlement, which refers to the cracking in riveted boiler plates made from steel, or as environmentally-assisted cracking (EAC). In the past, it was known as season cracking.
Corrosionpedia Explains Environmental Cracking (EAC)
Environmental cracking occurs from the combined function of these components:
- Tensile stress
- Susceptible material
- A particular environment or chemical species
For instance, if copper with its alloys are vulnerable to the compounds of ammonia, mild steels are vulnerable to alkalis, while stainless steels are vulnerable to chlorides. There is no single mechanism that can describe environmental cracking. There are several different models to explain environmental cracking, such as:
- Film-rupture - Stress ruptures local passive films and create an active-passive cell. New passive films undergo rupture again, and this cycle goes on until failure.
- Adsorption - Various chemical species go through adsorption onto the cracked surface and reduce stress fractures.
- Embrittlement - Atoms of hydrogen diffuse onto the crack tip and cause embrittlement to the metal. Embrittlement of hydrogen is the main mechanism related to environmental cracking, especially in alloys like titanium and steels.
- Active path - Compounds and intermetallics are formed along pre-existing paths such as grain boundaries.
Ways of preventing the occurrence of environmental cracking include:
- Controlling hardness
- Controlling stress levels
- Controlling potential
- Controlling temperature
- Avoiding chemical species that are associated with environmental cracking
- Using materials that are not prone to cracking under a specified environment