Coating with Cathodic Protection

-A Digest from NACE International Publication 6A100 Coating Used in Conjunction with Cathodic Protection

Key Points for Protective Coatings

• Corrosion prevention by protective coatings is due to their dielectric properties;
• The dielectric properties will be deteriorated during the service due to moisture break-through;
• Coating has finite field life to prevent corrodants, e.g. water, oxygen, chloride,etc, reach to substrate
• Temperature, higher temperature usually means higher water permeation rate;
• Soil, acidic sulphate soil, soil stress may cause coatings’ crack, wrinkle, sag and disbondment.

Key Interactions between Coatings and Cathodic Protection

• Electrical Stress caused by Cathodic Protection- Cathodic disbondment;
• Severe electrical stress may be experience in urban environment;
• Water absorption: electroendosmosis assists moisture mitigating through coating
• Alkaline resistance: alkaline environment caused by cathodic reaction with very negative overpotential, which may lead to blister and other damage of coating;
• Pigmentation;
• Ionic resistance: migration of positive ions caused by impressed current, this may result in blister of coating;
• Shielding effects: dielectric properties of coating may prevent cathodic protection current reaching to the metal surface.