How to Prevent Rust in GI Pipes?

How to Maintain GI Pipes to Prevent Corrosion?

Preventing rust in GI pipes (galvanized iron pipes) requires systematic protective measures that address their inherent weaknesses. Rust in GI pipes typically begins where the zinc coating is damaged or depleted. The following are comprehensive strategies and methods for preventing GI pipe rust.

Core Protection Strategies:

1. Active Protection (Cathodic Protection): Zinc, being more chemically active than iron, sacrifices itself to protect the iron substrate. This is an inherent property of galvanized pipes, but it consumes the zinc coating.

2. Passive Isolation (Barrier Protection): A dense protective layer is added to the outer surface of the pipe to isolate corrosive media such as water and oxygen from contact with the pipe surface.

GI Pipe Selection and Protection Measures:

Preventing rust in galvanized iron pipes requires a three-pronged approach: material quality, protective measures, and routine maintenance. This includes a systematic approach involving selecting the appropriate galvanizing thickness, proper installation, the use of anti-corrosion coatings, additional external protection, and standardized construction and maintenance procedures. ‌

1. Correct Selection and Installation
Failure to select the appropriate zinc coating thickness can result in the zinc coating being too thin, uneven, or damaged by scratches, cracks, or other defects on the galvanized pipe. This exposes the steel substrate to a corrosive environment. Impacts during transportation and installation, or untreated cut surfaces, can damage the zinc coating, reducing its service life.

Select zinc coating thickness based on the environment:
For normal indoor environments: Choose standard galvanized pipe with a zinc coating thickness of ≥ 45μm.
For high humidity, outdoor, or mild industrial environments: Choose thickened galvanized pipe with a zinc coating thickness of ≥ 65μm or 85μm.
For highly corrosive environments, such as coastal areas and heavy industrial zones: Reconsider material selection. For example, stainless steel pipe, plastic-coated composite pipe, etc. may not be the best choice.

Proper installation to protect the zinc coating:
When cutting and threading, use specialized tools to minimize damage to the zinc coating.
After installation, be sure to perform anti-corrosion treatment on any damaged areas, such as cuts and threads.

2. Treating Cuts and Damage
Surface Cleaning: Thoroughly remove burrs, iron filings, and rust from cuts with a wire brush or sandpaper.
Apply Zinc-Rich Paint: Zinc-rich paint contains a large amount of zinc powder, which continues to provide cathodic protection and seamlessly blends in with the existing galvanized layer.
Use Anti-Rust Paint: If zinc-rich paint is unavailable, apply a specialized anti-rust primer such as red lead anti-rust paint or epoxy zinc yellow primer, then apply a topcoat.

3. Adding External Protection (Enhanced Isolation)
a. Paint Protection: For outdoor applications, apply a weather-resistant anti-corrosion topcoat to the entire surface.
b. Wrapping with Anti-Corrosion Tape: Suitable for buried GI pipes or difficult-to-paint areas.

4. Use Protective Accessories

Use plastic or rubber gaskets where pipe supports, clamps, and other areas come into contact with the pipe to prevent friction and damage to the zinc coating and avoid galvanic corrosion.

5. Environmental Control and Routine Maintenance
Maintain a dry environment: Increase ventilation, reduce humidity, and avoid long-term condensation on the pipe surface.
Control temperature: Rapid temperature fluctuations can cause the zinc coating to crack.
Regular Inspection: Inspect the piping system (joints, cuts, threads, and other weak points) at least annually.
Prompt Treatment: If signs of white rust (a corrosion product of zinc) or red rust (a corrosion product of iron) are found, immediately sand them clean and reapply zinc-rich paint and topcoat.

Common Misconceptions:

Myth 1: "Galvanized pipes will not rust and require no maintenance."
Correct: The zinc coating is a consumable component and will degrade over time. Damaged areas must be treated.

Myth 2: "Applying ordinary paint directly to galvanized pipes."
Correct: The zinc coating has a smooth surface, and ordinary paint has poor adhesion and is prone to peeling. A dedicated primer (such as epoxy zinc yellow primer) must be used first.

Myth 3: "It's okay to use ordinary galvanized pipe for underground installations."

Correct: Soil is extremely corrosive, and the lifespan of ordinary galvanized pipes is very short. Additional anti-corrosion treatment is necessary.

Read more: Hot-dip Galvanized Seamless Pipe Production Process or Black Steel Pipe vs. Galvanized Steel Pipe