1. General Corrosion (Uniform Attack Corrosion)
Definition: Corrosion that occurs uniformly over a large surface area.
Example: Rusting of iron in the atmosphere.
Prevention:
Use of corrosion-resistant materials (e.g., stainless steel).
Application of protective coatings (e.g., paint, galvanization).
Regular maintenance and cleaning to remove corrosive agents.
Use of corrosion inhibitors in the environment.
2. Localized Corrosion
A. Pitting Corrosion:
Definition: Formation of small, localized holes or pits on the surface.
Example: Pitting of stainless steel in chloride-rich environments.
Prevention:
Use of materials resistant to pitting (e.g., high-alloy stainless steels).
Application of protective coatings.
Control of the environment (e.g., reducing chloride ion concentration).
B. Crevice Corrosion:
Definition: Occurs in confined spaces where the access of the working fluid is limited.
Example: Corrosion under gaskets, washers, or deposits.
Prevention:
Proper design to eliminate crevices.
Use of welds instead of rivets or bolts.
Regular cleaning to remove deposits.
C. Fretting Corrosion:
Definition: Caused by repeated cyclic rubbing between two surfaces.
Example: Corrosion at contact points in machinery due to vibration.
Prevention:
Lubrication to reduce friction.
Use of anti-fretting coatings.
Designing to minimize relative motion between surfaces.
D. Galvanic Corrosion:
Definition: Occurs when two different metals are in electrical contact in a corrosive environment.
Example: Corrosion of a steel pipe connected to a copper fitting.
Prevention:
Use of metals with similar electrochemical potentials.
Electrical insulation between dissimilar metals.
Application of protective coatings.
Use of sacrificial anodes.
E. Corrosion Fatigue:
Definition: Accelerated cracking due to the combined effect of cyclic stress and a corrosive environment.
Example: Cracking of metal components in aircraft due to repeated stress and exposure to the environment.
Prevention:
Reducing cyclic stresses through design modifications.
Use of corrosion-resistant materials.
Application of protective coatings.
Avoiding environments that promote corrosion.
3. Structural Corrosion
• Definition: Affects the structural integrity of materials, leading to weakening and potential failure.
• Example: Deterioration of steel beams in bridges, causing reduced load-bearing capacity.
Prevention:
Use of corrosion-resistant materials.
Application of protective coatings.
Regular inspections and maintenance.
Cathodic protection.
4. Biological Corrosion
Definition: Caused by the activity of microorganisms, such as bacteria, algae, or fungi, which induce or accelerate corrosion processes.
Example: Corrosion of metal surfaces in pipelines due to sulfate-reducing bacteria.
Prevention:
Use of biocides to control microbial growth.
Regular cleaning and maintenance to remove biofilms.
Use of materials resistant to biological attack.
Coatings that inhibit microbial attachment.