Plastic-coated steel pipes for municipal water supply and drainage

Plastic-coated steel pipes for municipal water supply and drainage are composite pipes widely used in urban water supply, drainage, fire protection, and other pipeline systems. They combine the strength of metal pipes with the corrosion resistance of polymer materials. Below is a detailed introduction to this material:

1. Structure and Characteristics
Base pipe material: Typically made of seamless steel pipes or welded steel pipes (e.g., Q235 carbon steel) as the base material.
Coating materials:
Inner coating: Epoxy resin (EP), polyethylene (PE), or polyvinyl chloride (PVC), with a thickness generally ranging from 0.3 to 1.0 mm.
Outer coating: Epoxy powder, polyethylene (2PE/3PE), or polyurethane, used for corrosion resistance and mechanical protection.
Advantages:
Strong corrosion resistance: The coating isolates water from metal contact, preventing rust and extending service life (up to 50 years).
Low fluid resistance: Smooth inner wall and low friction coefficient ensure high water transmission efficiency.
High mechanical strength: Strong pressure-bearing capacity (typically up to 1.0–2.5 MPa) and good impact resistance.
Hygienic and environmentally friendly: Epoxy coating complies with drinking water hygiene standards (e.g., GB/T 17219).
Easy installation: Can be welded, flange-connected, or grooved-connected (coating protection required).

2. Main Application Scenarios
Water supply systems: Municipal main pipelines, residential water supply, and direct drinking water pipelines.
Drainage systems: Sewage and rainwater discharge pipelines (chemical corrosion-resistant coating required).
Fire protection systems: Fire sprinkler pipelines and hydrant systems.
Special environments: Buried installation, humid or corrosive soil environments.

3. Implementation Standards
Domestic standards:
CJ/T 120-2016 "Plastic-Coated Composite Steel Pipes for Water Supply"
GB/T 5135.20-2010 (Plastic-Coated Steel Pipes for Fire Protection)
GB/T 5750-2022 (Hygienic Standards for Drinking Water)

4. Production Process
1. Surface treatment: Sandblasting and rust removal of steel pipes (Sa2.5 grade).
2. Preheating: Heating to 180–220°C (epoxy coating) or 200–250°C (PE coating).
3. Coating: Electrostatic spraying or dip coating process.
4. Curing: High-temperature curing to form a dense coating.

5. Selection Considerations
Coating selection:
Epoxy resin (EP): Suitable for drinking water and resistant to chemical corrosion.
Polyethylene (PE): Good wear resistance, ideal for buried pipelines.
Polyvinyl chloride (PVC): Low cost but poor temperature resistance.
Pipe diameter and pressure: Common sizes range from DN15 to DN2000; pressure ratings should be selected based on design requirements.
Connection methods:
Flange connection: Easy disassembly but requires coating repair at joints.
Grooved connection: Fast installation but requires specialized clamps.
Welding: Requires reserved welding sections and post-weld recoating.

6. Construction and Maintenance
Transportation and storage: Avoid collisions to prevent coating damage.
Buried installation: Requires anti-corrosion layers (e.g., 3PE) and cathodic protection (if necessary).
Inspection and testing: Includes coating thickness testing (magnetic thickness gauge), spark leak detection (≥1500V), and hydrostatic pressure testing.

7. Comparison with Other Pipes
| Feature | Plastic-Coated Steel Pipe | Ductile Iron Pipe | PVC/PE Pipe |
| Corrosion Resistance | Excellent (coating protection) | Moderate (requires anti-corrosion layer) | Excellent (but sensitive to UV) |
| Pressure-Bearing Capacity | High (≥1.6 MPa) | High | Low (0.6–1.0 MPa) |
| Service Life | Over 50 years | 30–50 years | 20–30 years |
| Cost | Medium to High | Medium | Low |

8. Common Issues
Coating damage: Requires specialized repair agents (e.g., epoxy repair patches).
Joint leakage: Ensure sealing integrity during welding or flange connection.
Frost heave impact: Burial depth must be below the frost line to avoid low-temperature brittleness.