External pipe corrosion can be controlled primarily through protective coatings and linings applied to the pipe's outer surface.
Methods for Controlling External Pipe Corrosion
Several methods are employed to mitigate external corrosion on pipes. These methods aim to create a barrier between the pipe material and the corrosive environment.
Protective Coatings
The application of protective coatings is a widely used method. These coatings act as a physical barrier, preventing corrosive substances from reaching the pipe surface.
- Galvanization: This process involves coating the pipe with a layer of zinc. The zinc acts as a sacrificial anode, corroding preferentially to the steel or iron of the pipe. This is particularly effective in preventing rust.
- Epoxy Coatings: These coatings offer excellent chemical resistance and adhesion properties, making them suitable for various environments.
- Polyurethane Coatings: Known for their durability and abrasion resistance, polyurethane coatings are often used in harsh conditions.
- Fusion Bonded Epoxy (FBE): FBE coatings provide superior corrosion protection and are commonly used in pipelines.
- Three-Layer Polyethylene (3LPE) and Polypropylene (3LPP) Coatings: These multi-layer systems offer enhanced protection against corrosion and mechanical damage.
Cathodic Protection (CP)
Cathodic protection is an electrochemical technique that reduces the corrosion rate of a metal surface by making it the cathode of an electrochemical cell.
- Sacrificial Anodes: More active metals (e.g., magnesium, zinc, aluminum) are electrically connected to the pipe. These anodes corrode preferentially, protecting the pipe.
- Impressed Current Cathodic Protection (ICCP): An external DC power source is used to supply current to the pipe, making it cathodic.
Regular Inspection and Maintenance
- Visual Inspections: Regularly inspect pipes for signs of corrosion, such as rust, pitting, or coating damage.
- Non-Destructive Testing (NDT): Techniques like ultrasonic testing, radiography, and electromagnetic testing can detect corrosion without damaging the pipe.
- Repair and Rehabilitation: Damaged coatings should be repaired promptly to prevent further corrosion. Severely corroded sections of pipe may need to be replaced.
Environmental Control
- Drainage: Ensure proper drainage around pipes to prevent water accumulation, which can accelerate corrosion.
- Soil Management: In buried pipelines, controlling the soil environment by reducing moisture content or adding corrosion inhibitors can be effective.
Example: Galvanized Steel Pipes
Galvanized steel pipes are commonly used in plumbing and construction due to their resistance to corrosion. The zinc coating provides a long-lasting protective layer, extending the lifespan of the pipe.
