Cathodic Protection System Introduction
Corrosion protection is a never-ending process. In the battle against corrosion of critical metallic structures, such as ship hulls, submerged pipelines, and storage tanks, organizations rely on cathodic protection systems. Doing so helps you extend the useful working life of your metal assets and avoid failures caused by corrosion. This article provides information on cathodic protection basics.
A cathodic protection system connects one piece of metal to another piece of metal to move free electrons away from the metal needing protection. For example, when you need to protect a steel pipeline from corrosion, you connect it to a piece of metal such as zinc or magnesium and apply an electrical current.
The steel pipeline becomes a cathode, and the other piece of metal serves as an anode. In a battery, the positive electrode is called the cathode, and the negative electrode is known as the anode. Free electrons move from the cathodic pipeline to corrode the anode. In this way, the anode sacrifices itself to prevent the pipeline from becoming corroded. Oxidation, which is caused by the loss of electrons, occurs at the sacrificial anode.
A cathodic protection system (CP system) is essential for long-term infrastructure maintenance because it actively works to prevent critical infrastructure from corroding, thereby minimizing the number of repairs or replacements. In this way, cathodic protection systems reduce the total cost of ownership of your metallic assets, by avoiding the need for early replacement and reducing the need for maintenance and repairs.
Types of Cathodic Protection Systems
There are two main types of cathodic protection systems for corrosion control: galvanic (sacrificial) anodes and impressed current cathodic protection systems.
Galvanic anode protection: In a corrosion prevention system based on galvanic anode protection, you create a circuit between the sacrificial anode and the piece of metal you want to protect. Corrosion occurs at the anode instead of on the metallic structure when you use a current cathodic protection system.
Impressed current cathodic protection: When standard galvanic anode protection is insufficient, you can install an impressed current system to safeguard your structure. It uses a power source (a rectifier) to impress electrical current from the anode. The system rectifies alternating current (AC) from the power supply to direct current (DC), underscoring the need for AC mitigation.
Galvanic anode systems are passive systems as compared to impressed current systems, which are active. A benefit of impressed current systems is that you can adjust the amount of power so you can protect a larger metallic surface area.
Generally, impressed current systems are more efficient than galvanic cathodic protection systems because you can protect much larger structures due to the amount of electricity you apply. You can control the amount of power to address fluctuating changes in the environment. On the other hand, it’s easier to install galvanic anode systems, which are more suited for cases where you do not need to apply a strong electrical current.
Materials Used in Cathodic Protection
Materials commonly used in cathodic protection systems include magnesium, zinc, and aluminum.
Companies tend to use magnesium when protecting metal in soil or under fresh water, where you do not require a high level of current. You will see magnesium anodes used to protect water heaters and storage tanks as well as underground pipelines.
Zinc is applied for undersea protection, such as to protect submerged pipelines and ships’ hulls.
Because aluminum is well suited to work as a sacrificial anode, it is often used for protecting structures under fresh water, such as structures in rivers or lakes.
Design and Installation of Cathodic Protection Systems
What are the key considerations in the design of a cathodic protection system? First, know that the design is tailored to specific environmental conditions and infrastructure types. Factors include the type of soil and the amount of soil resistivity. Ideally, you will have a list of leak records from buried pipes to indicate how urgently cathodic protection is needed.
Designers and installers must also consider the location of a pipe or other metallic structure, in terms of future access. Whether you need a power supply will also affect the design and installation of your system.
During installation, you must conduct a site assessment and determine how the system should be configured. Accordingly, you will select the metal for the anode based on whether the structure (such as a pipeline) is buried in the soil or is underwater, such as a ship’s hull.
Because an impressed current system (ICCP system) requires a power source, you need to design the system with access in mind for regular maintenance and repairs.
Another issue to address is the environmental impact. Zinc is easy to recycle and has a minimal impact on the environment. You can also recycle aluminum anodes, which have a moderate impact. However, magnesium anodes will involve more management for the environment, as they can generate hydrogen gas during the process of mitigating corrosion.
Keep in mind the potential challenges you may face when installing cathodic protection systems, including electrical interference, such as from railways or power lines, which can interfere with the corrosion protection system you’ve designed.
In complex systems, you may find irregular distribution of current to be a major challenge, because you want to apply electrical current evenly to the entire structure needing protection. If the structure is buried in highly resistant soil, the resistance can disrupt the flow of electrical current that you direct into the system.
Cathodic Protection for Underground Storage Tanks and Pipelines
Cathodic protection is crucial for underground storage tanks and pipelines. These types of structures are more difficult for people to routinely access for assessment, maintenance and repairs. You want a system that prevents underground corrosion consistently and reliably for subsoil pipelines or tanks.
What’s more, cathodic protection designers must recognize the surrounding infrastructure, such as at a power plant with plenty of buried pipes, copper-grounding grids and reinforced concrete systems. These are examples of conditions that call for customized underground applications.
In the presence of underground congestion, from sewers to storm drains and iron piping, there is a mandate to prevent underground corrosion because it’s more challenging for cathodic protection tester workers to enter the environment for assessments and repairs.
Maintenance requirements for cathodic protection systems include ongoing inspections and tests and periodic adjustments to maintain the required level of protection in the face of components wearing out and degrading, especially amid changing environmental conditions. When considering undersea structures, such as oil rigs or underwater pipelines or docks, the water’s salinity can be a major factor in corrosion.
Cost Analysis and Supplier Considerations for Cathodic Protection
The cost of cathodic protection systems varies depending on factors such as the type of system and its size. Structural complexity also adds to the costs of cathodic protection. If you are working with a deepwater structure like an oceanic pipeline, factor in the added costs of transporting and supporting installation and maintenance personnel in such a harsh and remote environment.
You also must calculate the environmental impact of your system before installing it.
When preparing to deploy an impressed current cathodic protection system, you have to figure in not only the costs of setting up a power supply, but also the maintenance and repair costs that come from dealing with an external source of electricity (compared to passive galvanic anode systems that do not require power). Then, you determine the service life of the system with all of the attendant maintenance and potential repair costs.
What factors should you consider when selecting a cathodic protection supplier?
It’s best to work with a supplier that has a proven track record of working with cathodic protection systems. This underscores the importance of doing your due diligence and reading reviews from trusted, objective sources. Does the supplier have a good reputation for its expertise and being reliable? Do organizations respect this supplier for its level of service and responsiveness?
Real-Time Corrosion Monitoring and Cathodic Protection
Real-time corrosion monitoring enhances cathodic protection systems by giving you real-time insight into how the equipment works in corrosive environments. You want to avoid the massive costs of repairs or replacement that can come from not having a clear view of the state of your metallic structure.
The technology used in real-time corrosion monitoring includes coupon exposures (fairly simple devices) and data loggers that maintenance and inspection teams can carry by hand. More sophisticated systems, often deployed in complex environments that are difficult to access, involve remote data access to built-in surveillance systems, whether it’s a pipeline, storage container or underwater rig.
It's beneficial to integrate your corrosion monitoring system with cathodic protection because it enables proactive corrosion management, rather than merely reacting to problems as they arise and have already caused significant damage.
Key Takeaways
Cathodic protection systems safeguard valuable infrastructure, such as undersea and underground pipelines, storage tanks, and ships against corrosion. To safeguard these valuable metallic structures, facility owners and operators rely on cathodic protection as a key component in their corrosion prevention strategies.
The experts at SMARTCORR® provide a state-of-the-art cathodic protection system to help companies protect their infrastructure from corrosion. Our products connect steel to another piece of metal that needs safeguarding, moving free electrons away from the steel to corrode the sacrificial anode instead. They integrate with cathodic protection junction boxes that connect the CP components and give your maintenance and testing personnel access to the system.
We also offer a reliable corrosion monitoring system that gives you the peace of mind that comes from knowing you have a proactive solution in place rather than merely reacting to problems with corrosion. The system gives actionable data to inform you when to conduct inspections, maintenance, and repairs to prolong the useful service life of your metallic structures.