What is CUPS Corrosion?
Corrosion Under Pipe Supports (CUPS) is a common and often overlooked issue in industrial piping systems, leading to significant structural damage and potential system failures. This type of corrosion occurs at the points where pipes rest on their supports, and is exacerbated by factors such as friction, trapped moisture, contact between dissimilar metals, and microbial activity. These elements collectively weaken the pipe over time and cause system failure, making it crucial to understand and address CUPS to maintain the integrity and safety of piping infrastructure.
Causes of External Corrosion Under Pipe Supports
Various factors contribute to external pipe corrosion, some of which are outlined below:
- Erosion of Protective Coating The erosion of the pipe’s protective paint coating is primarily attributed to the friction generated between the pipe and its supporting structure. This friction arises from both noticeable and imperceptible movements of the pipe, which can be attributed to several factors, including:
- Rotating Equipment: The presence of attached rotating equipment induces vibrations and movements.
- Fluid Flow: The flow of fluids within the pipe causes internal turbulence and external vibrations.
- Temperature Fluctuations: Day-night and seasonal temperature variations cause the pipe to expand and contract.
Over time, these friction forces gradually wear away the protective paint coating, leaving the surface of the pipe exposed to environmental elements. Consequently, this exposure leads to the onset of corrosion.
- Crevice Corrosion Crevice corrosion is a localized form of corrosion that occurs within narrow gaps or crevices, such as the junction between a pipe and its supports. This type of corrosion is primarily triggered by the entrapment of corrosive agents, including moisture, salts, chemicals, and pollutants, within these crevices. The stagnant conditions within these confined spaces give rise to differential oxygen concentrations and concentration cells, which accelerate the corrosion process. The presence of the crevice restricts oxygen access and hampers the flow of protective substances like inhibitors, thereby fostering a corrosive environment.
Over time, crevice corrosion can lead to the deterioration of metal surfaces, manifesting as pitting, cracking, or even structural failure. In the case of corrosion occurring under pipe supports, the concentrated corrosion within crevices can also compromise the integrity and stability of the supporting structures themselves, further jeopardizing the overall integrity of the entire piping system.
- Galvanic Corrosion Galvanic corrosion arises when two dissimilar metals or alloys come into electrical contact within the presence of an electrolyte, such as moisture or a corrosive fluid. In the context of corrosion under pipe supports, galvanic corrosion assumes particular significance. When pipe supports are constructed using different metals or alloys, or when pipes make contact with diverse metallic supports, a galvanic couple is formed. This sets off an electrochemical reaction, wherein one metal acts as the anode and undergoes corrosion, while the other metal functions as the cathode and remains protected.
Over time, galvanic corrosion can result in metal loss, deterioration of the affected components, and potentially lead to structural issues within the piping system. It is crucial to carefully consider the compatibility of metals used in the construction of pipe supports to minimize the risk of galvanic corrosion and ensure the long-term integrity of the system.
- Microbiologically-Influenced Corrosion (MIC) MIC is another significant cause of corrosion under pipe supports. MIC occurs when microorganisms, such as bacteria, fungi, or algae, colonize the surface of the pipes and create an aggressive environment. These microorganisms can produce corrosive byproducts, such as organic acids or sulfides, which attack the metal surface and promote corrosion. Additionally, the formation of biofilms, a slimy layer created by microbial activity, can trap moisture and corrosive substances against the pipe surface, accelerating the corrosion process.
Other Types of Corrosion in Piping Systems
- Pitting Corrosion: Pitting corrosion is a localized form of corrosion that leads to the creation of small holes or pits in the metal. This type of corrosion is particularly dangerous because it can cause significant structural damage with very little overall metal loss. Pitting is often initiated by chloride ions and can occur in environments where protective coatings are damaged or not present.
- Intergranular Corrosion: Intergranular corrosion occurs along the grain boundaries of metal. It is often a result of improper heat treatment or welding practices that cause the precipitation of carbides at grain boundaries. This type of corrosion weakens the metal along these boundaries, leading to potential structural failure.
- Stress Corrosion Cracking (SCC): SCC is the growth of crack formation in a corrosive environment. It typically occurs when a material is subjected to tensile stress and a corrosive environment simultaneously. This type of corrosion can lead to sudden and unexpected failure of ductile metals.
- Uniform Corrosion: Uniform corrosion occurs uniformly across the entire surface of the metal. This type of corrosion is generally predictable and easier to manage compared to localized forms of corrosion. However, it can still lead to significant metal loss over time if not properly managed.
Potential Product Solutions for Corrosion Protection
- FRP Supports: Fiber-reinforced plastic or polymer (FRP) supports offer several advantages for combating corrosion under pipe supports:
- Corrosion Resistance: FRP supports are highly resistant to chemical attack, making them ideal for environments with high exposure to corrosive substances.
- Vibration Dampening: FRP supports can be customized with materials that dampen vibrations, reducing wear and tear on the pipes.
- Thermal Expansion Accommodation: FRP supports can be designed with features like slotted holes and PTFE liners to allow for controlled axial movement, accommodating thermal expansion and contraction.
- Non-Conductive: Being non-conductive, FRP supports eliminate the risk of galvanic corrosion, which is a significant advantage when different metals are present in the system.
- Protective Coatings & Linings:
- Epoxy Coatings: Epoxy coatings provide a durable barrier against moisture and chemicals, protecting the underlying metal from corrosion.
- PTFE Liners: PTFE liners can reduce friction and prevent the buildup of corrosive substances in crevices and other vulnerable areas.
- Galvanic or Anodic Protection: Using sacrificial anodes can protect critical components from galvanic corrosion by redirecting the electrochemical reaction to the anode.
- Regular Maintenance and Inspection:
- Routine Inspections: Regularly inspecting pipes and supports for signs of corrosion can help identify and mitigate problems before they become severe. Major methods of inspection for CUPS corrosion include visual inspection, ultrasonic testing, radiographic testing, magnetic particle testing, and eddy current testing, among others. These techniques help detect surface and subsurface corrosion, ensuring the integrity of the piping system.
- Cleaning: Keeping pipes and supports clean from debris and corrosive substances helps maintain their integrity and prolongs their lifespan.
- Repair and Replacement: Promptly repairing or replacing damaged components prevents further corrosion and potential system failure.
Corrosion under pipe supports (CUPS) is a significant issue in industrial piping systems, particularly in coastal and offshore environments. Various types of corrosion, including crevice, galvanic, and microbiologically-influenced corrosion, can compromise the integrity of these systems. Fiber-reinforced plastic (FRP) supports offer an effective solution, providing corrosion resistance, vibration dampening, and the ability to accommodate thermal expansion. By incorporating FRP supports and other protective measures, industries can significantly reduce the impact of corrosion, ensuring the long-term reliability and safety of their piping systems. Regular maintenance and inspection further enhance these protective strategies, safeguarding industrial infrastructure from the detrimental effects of corrosion.
