Steel piles used underwater require protection from corrosion to ensure their longevity. This is especially important because the reaction of steel with seawater results in the formation of anodes and cathodes, which causes the flow of electricity and leads to the corrosion of the anodic areas of the piles. The chemically active surfaces of the underwater steel piles function as anodes, while less chemically active surfaces act as cathodes.
Maximizing Corrosion Protection for Underwater Piles: Strategies and Techniques
This article is Corrosion Protection for Underwater Piles. To prevent corrosion, it is essential to protect the underwater steel piles. Failure to do so can result in the deterioration of the anodic areas and eventual failure of the piles. The protection of underwater piles involves the use of various corrosion prevention techniques, including coatings, cathodic protection, and corrosion inhibitors. These techniques aim to slow down the corrosion process by reducing the rate of anode dissolution and thus extending the life of the piles.
Overall, the protection of underwater steel piles is crucial to ensure their durability and longevity. Corrosion prevention techniques must be implemented to minimize the formation of anodes and cathodes and reduce the rate of anodic dissolution. This can be achieved through the use of various techniques such as coatings, cathodic protection, and corrosion inhibitors.
What is Corrosion of Piles?
Corrosion is a term used to describe the degradation of metal as a result of its interaction with water and atmospheric air, or the oxidation of metals due to chemical reactions catalyzed by environmental factors. Essentially, when metal is exposed to certain elements in its environment, it can undergo chemical changes that cause it to break down over time. This process can be detrimental to the overall structural integrity of the metal, and can eventually lead to failure if left unchecked. It is important to understand the causes and mechanisms of corrosion in order to prevent it from occurring, and to develop effective methods for mitigating its effects.
What are Underwater Piles?
Piles play a crucial role in transferring the loads from the super structure to the ground, making them an essential substructure member of a building. However, when a structure is built in water, the piles need to be driven deep into the underwater strata. Unfortunately, being constantly submerged in water means that piles are prone to corrosion.
Controlling the corrosion of piles in water can be a challenging task. However, measures can be taken to protect them from corrosion. This is important because corrosion can weaken the piles and, in turn, compromise the entire structure’s stability. Therefore, implementing corrosion protection measures is crucial to ensure the longevity and durability of the building.
Zones of Corrosion of Underwater Steel Piles
Piles that are driven into water strata are subject to corrosion in different areas due to their contact with water. To simplify the analysis, these areas can be divided into four zones. Each zone has a distinct corrosion rate, which is illustrated in the figure.
Corrosion Protection Methods for Underwater Piles
Protective Coatings for Underwater Piles
Corrosion can be a significant problem for piles that are submerged in water. When the surface of a pile is exposed to water for an extended period, it can cause the metal to oxidize and rust, leading to the degradation of the pile. To prevent this from happening, it is necessary to coat the pile with a non-porous material that is anti-corrosive.
There are various types of coatings available for underwater piles that can provide effective protection against corrosion. These coatings are designed to create a barrier between the metal surface of the pile and the surrounding water, preventing any water from coming into contact with the metal.
One type of coating commonly used for underwater piles is epoxy coating. Epoxy is a polymer that is applied to the surface of the pile and cures into a hard, durable, and waterproof layer. Epoxy coatings are known for their excellent adhesion and chemical resistance, making them an ideal choice for underwater applications.
Another popular coating for underwater piles is polyurethane coating. Polyurethane is a synthetic resin that is resistant to corrosion, abrasion, and impact. When applied to a pile, it forms a protective layer that can withstand harsh underwater conditions.
Other coatings used for underwater piles include zinc-rich coatings, which provide an additional layer of protection against corrosion, and ceramic coatings, which offer excellent resistance to high temperatures and abrasion.
In summary, protecting underwater piles from corrosion is essential to ensure their longevity and structural integrity. Coating the piles with non-porous, anti-corrosive materials such as epoxy, polyurethane, zinc-rich coatings, or ceramic coatings can provide effective protection and extend the lifespan of the piles.
Inorganic Zinc Silicates Primers
Steel structures that are submerged in water, particularly those below the plash zone, are not typically coated with cathodic protective layers due to the fact that they are constantly immersed. However, there are a variety of anti-corrosive pigmented primers available, with inorganic zinc silicate being the most effective.
What makes inorganic zinc silicate the best option is that it can prevent rust creep or undercutting of the coating surrounding any damaged areas, and confines corrosion to the specific point of damage. This is a significant advantage as it prevents corrosion from spreading further beyond the initial area of damage.
High Build Epoxy Coatings
Epoxy coatings provide superior protection against abrasion and chemical damage compared to traditional primers and coats. The reason for this enhanced durability is that these coatings not only safeguard the metal surface, but they also offer added protection to zinc primers from harmful elements. Despite their many benefits, epoxy coatings do have a downside: they tend to be less resistant to sunlight and chalk. Exposure to these elements can cause the coating to fade quickly, leading to erosion and a reduction in the barrier protection provided by the system.
In summary, epoxy coatings are highly effective in protecting surfaces from abrasion and chemical damage. They offer an additional layer of defense for zinc primers, providing comprehensive protection to metal surfaces. However, it is important to be aware that epoxy coatings are vulnerable to sunlight and chalk, which can cause fading and erosion. By taking these factors into consideration, users can make informed decisions about the best type of coating for their specific needs.
Aliphatic Polyurethane Topcoats
Polyurethane is a type of material that does not serve as an anti-corrosion or corrosion barrier. However, it does offer several advantages such as excellent resistance to ultraviolet (UV) rays, as well as a high degree of flexibility and chemical resistance. In addition to these benefits, polyurethane also helps to maintain the cosmetic appearance of the material, including its color and shine.
One of the most significant advantages of polyurethane is that it provides a high level of protection to coating systems. This protection can help to ensure the longevity of the material and reduce the likelihood of damage or wear and tear. Additionally, polyurethane can help to enhance the overall durability of the material, which is especially important in applications where it may be exposed to harsh or challenging environments.
Despite not providing anti-corrosion properties, the benefits of polyurethane make it an attractive option for a wide range of applications. Whether it is used to protect the exterior of a building, the surface of a vehicle, or any other material that requires protection from the elements, polyurethane is a reliable and effective choice. Its high level of resistance to UV rays and flexibility, combined with its ability to maintain the cosmetic appearance of the material, make it an ideal solution for many industries and applications.
Zinc Rich Epoxy Primers
The given context describes a type of coating known as Inorganic Zinc Silicates Primer and High Build Epoxy Coating, which is a combination of two different coatings. This coating is designed to provide superior performance in harsh environmental conditions, making it more resilient and durable compared to other types of coatings.
One of the key benefits of this coating is its ability to maintain damaged areas and prevent the breakdown of the coating system. This is particularly important in industries such as marine, oil and gas, and mining where coatings are exposed to harsh and corrosive environments. In addition, the coating is effective in a wide range of ambient weather conditions, making it suitable for use in various geographical locations.
Overall, the Inorganic Zinc Silicates Primer and High Build Epoxy Coating is a highly effective solution for industries that require a robust and long-lasting coating system. Its ability to withstand harsh conditions and maintain damaged areas make it an ideal choice for applications where the coating is exposed to severe and corrosive environments.
Non-Skid Deck Coatings
Anti-slip coatings are formulated to have a high film build and typically do not require a zinc rich primer. In order to create a very pronounced profile, these coatings often incorporate coarse aggregates. If a primer is needed, epoxy varieties are typically used.
Cathodic Protection of Underwater Piles
Cathodic protection is a widely used technique to prevent corrosion on piles, particularly in underwater environments. The process involves utilizing electrochemical reactions to protect steel from corrosion. It is a well-established method that is preferred because of its effectiveness in preventing corrosion on steel in water.
In practice, the implementation of a cathodic protection system is relatively straightforward. Assuming there is corroding steel in seawater, all that is required is an anode, a power supply, and the expertise of an engineer. A protective circuit is established between the anode, steel (cathode), power supply, and electrolyte (seawater). This simple process is employed to install cathodic protection for underwater piles.
When steel is corroded, an anode with a power supply is placed near the steel in the water. The method of delivering the anode can vary depending on various factors. There are different types of anode delivery, which are employed based on the specific circumstances.
Pile Mounted Anode
The delivery method for anodes that can be attached directly to cathodes or piles is known as pile mounted anodes. These types of anodes are designed to ensure efficient current distribution in and around the piling. The challenge with placing anodes in remote areas is addressed by using pile mounted anodes. The Flat Back Pile Mounted Anode is a specific type of anode designed for H-Piles. It can also be modified for installation on sheet piling, making it a versatile option for different types of projects.
Pile Mounted Anode
Retractable Mount
An anode delivery system is employed in situations where the anode needs to be periodically replaced with a new one. This system is particularly useful when cathodic protection is only required intermittently, rather than on a continuous basis. By using this type of system, the anode can be easily and conveniently replaced when needed.
The purpose of employing an anode delivery system is to ensure that the cathodic protection process remains effective over time. Anodes are a critical component of cathodic protection systems, as they serve to attract corrosion-causing electrons away from the metal surface that is being protected. However, anodes can become depleted over time as they continue to attract these electrons. This is why it is necessary to periodically replace them with fresh anodes.
The advantage of using an anode delivery system is that it makes it easier to replace the anodes when necessary. This can be particularly beneficial in situations where the need for cathodic protection is not constant or predictable. By using this type of system, the anodes can be replaced quickly and easily, ensuring that the cathodic protection process remains effective and reliable.
Retractable mount
Sled Anode
Anodes for sleds can be created for use in either seawater or for burial in mud. When mounted on the seabed, the anodes provide optimal protection coverage for marine structures. By adjusting the concrete sled’s height, the mesh anode sled can also be designed to operate outside of the mud. The Post Tension Sled was created specifically to ensure that anodes remain functional even when resting in soft, silty sea beds. One of the benefits of this type of sled is that it has a low profile, which reduces the likelihood of damage from fishing nets or anchors.
Application of FRP Composites for Corrosion Protection of Underwater Piles
FRP is a cost-effective solution for repairing substructure parts as it can be mixed with wet concrete. Typically, repairing these parts involves enlarging them to accommodate new ties. However, when FRP is used, the corroded part of the element is carefully removed and the FRP-induced concrete is applied instead. This not only provides the lost tensile capacity but also offers lateral support to the steel. Moreover, since FRP is applied with concrete, it protects against the spreading of corrosion to other piles while providing UV coating on the wrap of the right color.
FRP repairs also offer aesthetic benefits that are often overlooked. The use of FRP can enhance the appearance of the repaired structure, making it look as good as new. It is an efficient and practical solution that not only addresses structural damage but also improves the overall aesthetics of the repaired area. Therefore, using FRP to repair substructure parts is an excellent choice for those who want to save time, money, and effort while ensuring the durability and visual appeal of the repaired structure.
FRP Wrapping for Corroded Bridge Piles
Try Alternate Methods to protect sheet piling from corrosion:
- Anti-corrosive coatings are a highly effective solution for preventing corrosion.
- Some popular types of anti-corrosive coatings include coal tar epoxy coating, glass flake epoxy coating, duplex coating systems, and hot dip galvanization.
- Thicker sheet piles or thicker sections of sheet piles can also be used to prevent corrosion.
- Coal tar epoxy coating is a type of coating that uses coal tar as the main component to prevent corrosion.
- Glass flake epoxy coating is a type of coating that uses small flakes of glass within the epoxy to prevent corrosion.
- Duplex coating systems involve using both an anti-corrosive primer and a topcoat to provide maximum protection.
- Hot dip galvanization involves immersing steel in molten zinc to provide a protective layer against corrosion.
- Thicker sheet piles or thicker sections of sheet piles can help prevent corrosion by increasing the amount of material between the steel and the environment, making it more difficult for corrosion to occur.
Below some installation pictures of divers during depleted anode replacement and supplemental current.
FAQs About Underwater Piles Corrosion Protection
1. How do you protect sheet piling from corrosion?
There are a few other ways to protect sheet piling from corrosion:
- Cathodic Protection: This technique involves applying a direct electric current to the sheet piling to prevent corrosion. Cathodic protection can be achieved through two methods: sacrificial anode or impressed current systems.
- Polymer Coatings: Polymer coatings such as polyethylene, polypropylene, or PVC coatings are highly effective at protecting sheet piling from corrosion. These coatings can provide a barrier against corrosive elements and can be applied to both the interior and exterior surfaces of the sheet pile.
- Concrete Encasement: Sheet piling can be encased in concrete to prevent corrosion. This technique is often used for sheet piling that is exposed to harsh environmental conditions or where aesthetics are important.
- Regular Maintenance: Regular inspection and maintenance can help prevent corrosion and prolong the life of the sheet piling. Cleaning, painting, and repairing any damage can help maintain the protective coating and prevent corrosion.
It is important to choose the appropriate protection method for the specific application and environment in which the sheet piling will be used.
2. What are the protection methods against corrosion?
Here are some common methods of protection against corrosion:
- Protective Coating: Applying an anti-corrosive coating such as paint, powder coating, or galvanizing can help prevent the metal from coming into contact with the environment and therefore, avoid corrosion.
- Metal Plating: Applying a thin layer of a more corrosion-resistant metal onto the surface of the metal can act as a barrier and prevent corrosion.
- Corrosion Inhibitors: These are chemicals that can be added to the metal to form a protective layer and prevent corrosion from happening.
- Sacrificial Coatings: These coatings are made from a more reactive metal and are designed to corrode instead of the metal they are protecting. This way, the metal remains unharmed.
- Environmental Measures: Controlling the environment around the metal structure by removing moisture, reducing the amount of salt in the air, or reducing the acidity of the environment can prevent corrosion.
- Modifying the Design: Changing the design of the metal structure to reduce the contact area between the metal and the environment or using materials that are less susceptible to corrosion can prevent corrosion.
3. What is the corrosion allowance for piles?
The corrosion allowance for piles refers to the additional thickness of the steel that is added to the design to compensate for any expected corrosion during the service life of the structure. The corrosion allowance is typically added to the design thickness of the pile and varies depending on the expected rate of corrosion and the design life of the structure.
In natural soils, the British Standard BS 8004 recommends a maximum corrosion rate of 0.015mm/year/side for piles and suggests that no other protection is required. This corrosion rate is consistent with the rates derived from Eurocode 3 and is used as a basis for determining the corrosion allowance for piles in natural soils.
The corrosion allowance for piles can also vary depending on the environmental conditions and exposure to corrosive agents such as moisture, salt, and chemicals. Therefore, it is important to consider the expected service life and the environmental conditions when determining the appropriate corrosion allowance for piles.