Cathodic Protection (CP) is a widely used technique to prevent corrosion in buried or submerged steel structures such as pipelines, storage tanks, offshore platforms, and marine vessels. By making the metal surface act as a cathode of an electrochemical cell, CP significantly extends the life of infrastructure and reduces repair costs.
Two main types of CP systems exist: Sacrificial Anode Cathodic Protection (SACP) and Impressed Current Cathodic Protection (ICCP).
🔧 How Cathodic Protection Works
When steel is exposed to soil or water, it naturally corrodes due to electrochemical reactions. Cathodic protection interrupts this process by supplying electrons, which stop the steel from losing its own electrons (corroding).
- In SACP, a more reactive metal (anode) corrodes instead of the steel.
- In ICCP, an external power source applies current to protect the structure.
Simplified Design Requirements for Gas and Liquid Dehydration and Hydrate Inhibition Systems
🛡️ Types of Cathodic Protection Systems
1. Sacrificial Anode Cathodic Protection (SACP)
- Uses aluminum, zinc, or magnesium anodes.
- Simple to install and maintain.
- Best for small structures such as ship hulls, small tanks, and pipelines.
- Anodes must be replaced when consumed.
2. Impressed Current Cathodic Protection (ICCP)
- Uses an external DC power source with inert anodes (graphite, titanium, or mixed metal oxide).
- Suitable for large structures like long pipelines, offshore platforms, and storage tanks.
- Provides better control and longer service life compared to sacrificial systems.
- Requires careful monitoring to prevent overprotection and coating damage.
✅ Advantages of Cathodic Protection
- Extends service life of steel structures.
- Reduces maintenance and repair costs.
- Can be applied to both old and new structures.
- Effective in harsh environments (soil, seawater).
- Works with coating systems for enhanced protection.
⚠️ Disadvantages & Challenges
- ICCP requires continuous power supply.
- Overprotection can cause coating blistering or hydrogen embrittlement.
- Installation and monitoring can be costly for large projects.
- Sacrificial anodes need periodic replacement.
🌍 Applications of Cathodic Protection
Cathodic protection is used across industries, especially in oil & gas, marine, and construction sectors. Some common applications include:
- Pipelines: Buried and subsea pipelines transporting oil, gas, and water.
- Storage Tanks: Underground and above-ground steel tanks.
- Marine Structures: Ships, offshore rigs, and harbor facilities.
- Reinforced Concrete: Bridges, piers, and parking garages.
- Industrial Plants: Cooling water systems, heat exchangers, and refineries.
🧪 Coating and Cathodic Protection
For best results, CP systems should be used alongside coatings that have:
- Strong alkali resistance
- High dielectric strength (to resist current passage)
- Excellent adhesion strength to steel
Testing for cathodic disbondment resistance is crucial before applying coatings in CP systems.
🔍 Frequently Asked Questions (FAQs)
1. What is the difference between sacrificial anode and impressed current cathodic protection?
Sacrificial systems use reactive metals that corrode instead of steel, while ICCP uses an external power source to supply protective current.
2. Where is cathodic protection most commonly used?
It is widely used in oil & gas pipelines, storage tanks, ships, offshore rigs, and reinforced concrete structures.
3. What are the disadvantages of ICCP?
ICCP systems require a reliable power supply, regular monitoring, and higher initial cost compared to sacrificial anode systems.
4. How long does a cathodic protection system last?
A well-maintained ICCP system can last 20–30 years, while sacrificial systems depend on anode consumption rates.
5. Can cathodic protection be used on concrete?
Yes. CP is used to protect steel reinforcement inside concrete structures like bridges, piers, and parking garages.