Multipurpose Segmented Sacrificial Anodes
One of two major Cathodic Protection (CP) methods utilized in industry is the application of sacrificial anodes. The most common active metal alloys utilized for sacrificial anodes are magnesium, zinc, and aluminum.
- Magnesium Alloys
- Pure magnesium alloys: 1.75 V driving voltage.
- Standard magnesium alloys: 1.55 V driving voltage.
- Zinc Alloys
- Zinc is the oldest active metal utilized for sacrificial anodes.
- Aluminum Alloys
- Aluminum is an active metal that immediately forms an aluminum oxide (alumina) layer on its surface when exposed to corrosive environments. The oxide layer behaves like a protective coating, creating a physical barrier between the alloy surface and the environment. Therefore, pure aluminum cannot be utilized as a sacrificial anode.
Sacrificial Anode Material Selection Process
Magnesium sacrificial anodes should be selected under the following conditions:
- Electrolyte pH greater than 5.
- Concentration of chloride ions is not considerable.
- Liquid resistivity is greater than 2,000 Ω-cm.
- For resistivities greater than 5,000 Ω-cm, high-potential magnesium alloys should be selected.
Zinc sacrificial anodes should be selected under the following conditions:
- Concentration of carbonates and bicarbonates is not considerable.
- Temperature is less than 120°F (50°C).