COMMON GALVANIC CATHODIC PROTECTION APPLICATIONS
The following provides examples of various galvanic CP systems that are implemented on port infrastructure to provide corrosion mitigation.
Galvanic CP can take many forms and be implemented on a wide variety of structures.
This section is to give the reader an overview of the common types.
1. Submerged
Submerged systems are when the anodes are directly exposed to water and protect steel and reinforced concrete structures that are below the water line.
The most common form of this application is the attachment of anodes directly to piles or bulkhead walls.
Commonly the galvanic metal is cast around a steel core that is welded or bolted to the structure to be protected.
Often these kinds of anodes are extremely durable, require little to no monitoring or maintenance, and can be designed for a service life of up to 30 years.
Because they typically must be installed by divers, the cost for these systems can be high.
However, because of their durability, there is little worry that they will not provide CP over their design life.
Another common form of a submerged CP system is to build a frame that holds several anodes, known as a sled.
The sled is placed on the mudline a significant distance away from the structure to be protected and connected via a wire.
Because the sled has a wire run out through the mudline and is a distance from the structure, it is susceptible to damage from dredging and boat operations.
2. Buried
Soil galvanic CP takes the form of anodes that are buried in the soil to protect structures like pipelines and the soil side of bulkhead walls (Figure 7).
Commonly the anodes used in this application are magnesium or zinc.
These metals cannot be directly installed into the soil, they are placed in a bag with a mixture of bentonite and coke breeze.
This material keeps the anode actively corroding which allows it to provide a protective current to the structure.
3. Encasement
A method of galvanic CP that can help to strengthen an existing structural element as well as mitigate corrosion is to perform an overbuild that implements galvanic cathodic protection, also referred to as a galvanic CP encasement.
A galvanic CP encasement is where a structural element is surrounded by concrete, in which galvanic anodes are placed within the new concrete to protect the original element that is being encapsulated from corrosion.
The overbuilt section can include reinforcement for crack control or structural strengthening if the original element has badly deteriorated.
4. Concrete Embedded
Galvanic anodes can be embedded within concrete elements to protect the steel reinforcement from corrosion (Figure 15 & Figure 16).
Embedding the anodes in the concrete provides a more durable CP system that is protected from external damage or deterioration.
Embedded galvanic CP can be designed for up to a 30-year life span.
There are two primary types of embedded galvanic CP, Type 1 which is installed in concrete repairs and Type 2 which is installed within sound concrete to prevent concrete repairs.
Embedded galvanic anodes consist of zinc as a sacrificial metal encased in an activating mortar.
When connected to the reinforcing steel within the completed concrete repairs, a small level of protective current is generated to mitigate the formation of new corrosion sites in the surrounding concrete.
Embedded galvanic anodes are available in a range of sizes and shapes.
Embedded anodes lend themselves to providing targeted protection to areas that have a higher exposure to water and chlorides than the surrounding elements.
By installing this CP system in these higher-risk areas, the overall structure’s service life can be extended through the efficient targeted use of CP.
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