Impressed Current Cathodic Protection-An Overview

Soluble sacrificial anodes have been widely used since the 17th century as an important part of cathodic protection technology. By placing a sacrificial anode in the anodic position of a metal structure, oxidative corrosion occurs at the anode, thereby protecting the metal to be protected from corrosion. This method has a wide range of applications in environments such as soil, freshwater and seawater.

However, with the growing concern for special application requirements and cost control, insoluble applied current anodes were introduced in the 20th century as an alternative to soluble sacrificial anodes, especially in cathodic protection techniques for deep well anode beds and shallow buried anodes.

In this article, we will focus on applied current cathodic protection (ICCP ) and provide you with an in-depth understanding of this technology. We will discuss its working principle, advantages and applications in different fields to help you fully grasp this highly effective corrosion protection technology.

What Is Impressed Current Cathodic Protection?

Impressed Current Cathodic Protection is also called as  forced current cathodic protection, is a corrosion prevention technology that utilizes a DC power supply to provide a steady current. The technique provides effective cathodic protection to the metal structure to be protected by evenly dispersing the current into the surrounding electrolyte solution through an auxiliary anode, such as graphite, titanium-based mixed metal oxide (MMO), and so on. Unlike traditional sacrificial anode protection, forced current cathodic protection has a more permanent and stable protection effect by supplementing the corrosion current with an applied current.

During this process, a reference electrode is used to monitor and feedback the potential change of the protected metal structure relative to the electrolyte solution in real time, thus ensuring that the protection current is always in an optimal state. By precisely controlling the potential, over- or under-protection can be avoided.

Finally, cables and connecting parts effectively connect the DC power supply, anode, reference electrode and the protected metal structure to ensure accurate transmission of current and signals, thus realizing comprehensive and stable cathodic protection.

What Is ICCP System Working Principle?

ICCP is actually an electrochemical reaction process. In the absence of ICCP system, steel structures corrode in an oxygen or humid environment, producing rust. The specific electrochemical reaction process is as follows:
Negative pole: Fe-2e-=Fe2+
Positive pole: 2H2O+O2+4e-=4OH-
Fe2++2OH-=Fe(OH)2
4Fe(OH)2+2H2O+O2=4Fe(OH)3
2Fe(OH)3 + water loss in air = [Fe2O3-nH2O] (rust) + (3-n)H2O
During this natural corrosion process, steel continues to lose electrons and eventually rust forms, reducing the strength and durability of the steel structure.
When using Impressed Current Cathodic Protection, electrons are supplied to the steel structure or other metal structure to be protected by providing a direct current between the anode and cathode that is opposite to the natural corrosion current. In this way, instead of losing electrons, the metal structure becomes a cathode, thus preventing a corrosion reaction from occurring.

Specifically, Impressed Current Cathodic Protection prevents the steel structure from undergoing an oxidative corrosion reaction by releasing electrons (providing electrons to the cathode) and neutralizing the electron loss from the surface of the metal structure. As a result, the steel structure or metal component no longer loses electrons under the protective system, the corrosion reaction is inhibited, and the structure is effectively protected. This approach prevents corrosion of the metal structure by making it a cathode, greatly extending the service life of the metal material.

Impressed Current Cathodic Protection vs Sacrificial Anode

Working Principle

Sacrificial anode protection protects the target metal primarily by utilizing a metal that is more active than the target metal to undergo corrosion. Specifically, the sacrificial anode sacrifices itself during the corrosion process, releasing electrons to protect the desired metal from corrosion. For example, in metal structures such as ships and pipelines, active metals such as zinc, aluminum, or magnesium are usually used as sacrificial anodes to avoid corrosion of structures such as steel through their corrosion.

ICCP inhibits the corrosion reaction by applying an electric current to change the potential of the target metal. By applying a DC current between the metal structure and the applied anode, the metal surface becomes a cathode, which in turn prevents the metal from losing electrons and corroding. This method does not rely on the difference in activity of the metal, but rather controls the surface environment of the metal by applying current to fundamentally inhibit corrosion.

Application Scenario

Impressed Current Cathodic Protection is widely used for the protection of long, extensive, large and complex metallic structures such as petroleum pipelines, storage tanks, concrete structures, offshore engineering and ship hulls. The technology is particularly suitable for facilities that require long-term, continuous protection, as it provides a stable, adjustable current that ensures effective corrosion inhibition under harsh environmental conditions. In addition, municipal infrastructure (e.g., water supply pipelines, power facilities, etc.) often use applied current cathodic protection systems to ensure the long-term stable operation of facilities.

In contrast, sacrificial anode cathodic protection is more suitable for the application of small current demand, simple structure of the metal structures, especially in the low soil resistivity environment. For example, smaller pipelines, storage tanks, and other metallic structures can be cost-effectively protected against corrosion by sacrificial anode protection.

Maintenance

Sacrificial anode consumption rate is fast, need to be replaced periodically, maintenance workload is more compared with the applied current protection, ICCP system cycle is longer, and adjust the current output, maintenance operation is relatively simple.

Type

The main anode materials used in the ICCP system are titanium-based mixed metal oxide coatings. Common types of titanium-based MMO anodes include: MMO Anode Wire, MMO Ribbon Anode, MMO Linear Anode, MMO Tubular Anode, Titanium Anode Rod, Titanium Anode Disc, Titanium Anode Plate and so on.
The anode materials used for sacrificial anode protection mainly include active metals such as magnesium, aluminum and zinc. These sacrificial anode materials are capable of self-sacrificing during the corrosion process, releasing electrons to protect the metal structure from corrosion. Sacrificial anodes come in a variety of shapes, the common ones being:
Trapezoidal anodes, disk anodes, bangle anodes, etc.

Conclusion

ICCP and sacrificial anode protection are both effective cathodic protection techniques used to prevent corrosion of metal surfaces. Although both techniques are similar in their basic principle of inhibiting corrosion by altering the electrochemical environment of the metal, they differ in application complexity, cost and effectiveness.

The ICCP system, although higher in initial investment and more complex in structure, has a longer service life and higher safety, and is suitable for large, complex or long-term metal structures requiring corrosion protection. In contrast, sacrificial anode protection systems are simpler and less costly, and are suitable for environments with lower current demands, but they are not as effective and durable as ICCP systems.

To ensure the quality and longevity of ICCP systems, the performance of MMO titanium anodes is critical. Titanium-based Mixed Metal Oxide (MMO) anodes are an indispensable key component in ICCP systems due to their excellent corrosion resistance, stability and long life.

As a specialized manufacturer of titanium anodes, THT has been committed to producing high quality titanium anodes and providing MMO anodes and related technical support for ICCP systems in many countries. We have rich experience in providing customized solutions according to customers’ needs.

If you have any questions or concerns about cathodic protection, please feel free to contact us and we will be happy to provide you with professional technical advice and support.