graphitic corrosion
Corrosion processes such as graphitic corrosion were caused in cast iron, which refers to the selective leaching of iron from the material, producing a weakened graphite skeleton. This form of corrosion happens mostly in the marine environment, and buried pipelines, or water systems, where it can deteriorate or reduce the strength of the material but retain its original shape.
Key Features:
- Selective Process of Corrosion: Dissolution of the iron matrix by some electrochemical reactions while at the same time graphite remains intact. Good structural shape, then brittle and soft.
- Common Causes: Moisture, acids, and oxygen form the environments of most open-air corrosive regions. Occurs in gray cast iron since graphite-rich microstructure. Presence of differential aeration cells in buried or submerged components.
- Effects and Detection: The honeycomb-like surface becomes porous and gets reduced mechanical strength. Ultrasonic testing, hardness testing, and visual inspection can detect this.
- Prevention Methods: Use of protective coats like epoxy, galvanizing, or bituminous coatings. Use of cathodic protection in underground pipelines. Regular maintenance and inspection of iron structures constructed in corrosive environments.
- Industry Impact: It is common in water mains, pump casings, ship hulls, and engine blocks. Such undetected failure can cause failures of critical components, leading to very expensive repairs or replacements.
Graphitic corrosion is a silent but severe degradation process in cast iron that compromises its structural integrity. Mechanisms and prevention strategies concerning it should, therefore, be well understood since they are necessary for the long-term reliability of iron-based components.