Definition of Corrosion Corrosion is the deterioration of materials by chemical interaction with their environment.  The term corrosion is sometimes also applied to the degradation of plastics, concrete and wood, but generally refers to metals.

Anodic & Cathodic Reactions

Effects of corrosion Losses are economic and safety Reduced mechanical properties Downtime of equipment Leak of fluids Reduced value of goods

Uniform Corrosion: Rust! FORMS OF CORROSION Uniform Corrosion: Rust! Prevention: Paint Cathodic Protection

FORMS OF CORROSION Galvanic Corrosion Causes: Dissimilar metals Prevention: Choose metals close in galvanic series Have large anode/cathode ratios Insulate dissimilar metals Cathodic protection Described by Galvanic Series

Pitting and Creviced Corrosion FORMS OF CORROSION Pitting and Creviced Corrosion Causes: concentration gradients in electrolyte cause some areas high in ion concentrations that accelerate oxidation Prevention: Weld – don’t rivet Use non-absorbing gaskets Polish surfaces Avoid stagnant water

FORMS OF CORROSION Intergranular corrosion Stress corrosion Erosion

Corrosion prevention Applied Voltage Sacrificial Anode

Corrosion prevention Surface coatings & Passivation Some materials, such as Aluminum or Stainless Steel, form oxide barrier coatings that prevent oxidation at active surface – this is called “passivation” Surface can be coated with protective layers: painted, anodized, plated.

Corrosion prevention Design of structures Material selection Control the environment Inhibitors Protective Coatings