The difference between plastic-lined steel pipe and plastic-coated steel pipe

Plastic-lined and plastic-coated steel pipes are both steel-plastic composite materials used in various industrial applications. While they share similarities, they differ in their structure, manufacturing processes, and specific applications. Below is a comparison highlighting key aspects such as definitions, classifications, manufacturing processes, and performance.

1. Definitions, Classifications, and Terminology

Plastic-Lined Steel Pipe:

Definition: Steel pipes with a plastic lining (such as polyethylene) on the inside, and often an external treatment of galvanization or painting.

Classification: Includes cold-water, hot-water, and rotomolded plastic-lined steel pipes.

Lining Materials: Polyethylene (PE), cross-linked polyethylene (PE-X), polypropylene (PP-R), and others.

Plastic-Coated Steel Pipe:

Definition: Steel pipes coated with a layer of plastic powder (e.g., polyethylene or epoxy resin) on both the inner and outer surfaces.

Classification: Includes polyethylene-coated and epoxy resin-coated steel pipes.

Coating Materials: Polyethylene powder, epoxy resin powder.

2. Product Labeling

Plastic-Lined Steel Pipe:

Cold water: SP-C

Hot water: SP-CR

External cold water: PSP-C

External hot water: PSP-CR

Plastic-Coated Steel Pipe:

PE-coated: SP-T-PE

Epoxy resin-coated: SP-T-EP

3. Manufacturing Process

Plastic-Lined Steel Pipe:

Lining Process: Adhesive is applied to the inner surface of the steel pipe, and the plastic is expanded to form a bond.

Rotomolding: Polyethylene powder is applied to the rotating steel pipe, followed by curing.

Plastic-Coated Steel Pipe:

Coating Process: Steel pipe is heated, coated with plastic powder, and then cured to form a composite product.

4. Implementation of Standards

Plastic-Lined Steel Pipe: Must meet standards such as CJ/T136, GB/T13663, and others for materials and adhesives.

Plastic-Coated Steel Pipe: Must comply with CJ/T120 standards, covering the coating material and the base pipe requirements.

5. Model Specifications

Plastic-Lined Steel Pipe: Suitable for pipes with a nominal diameter up to 500mm.

Plastic-Coated Steel Pipe: Suitable for pipes with a nominal diameter up to 1200mm.

6. Connection Methods

Plastic-Lined Steel Pipe and Plastic-Coated Steel Pipe:

Flange and groove connections must meet GB/T9119 and GB5135.11 standards.

For plastic-coated pipes, screw connections must meet GB/T7306.1.

7. External Anti-Corrosion

Plastic-Lined Steel Pipe: External anti-corrosion can be achieved through hot-dip galvanizing or plastic coating, meeting relevant standards.

Plastic-Coated Steel Pipe: The external anti-corrosion is either plastic-coated or galvanized, depending on the product.

8. Plastic Layer and Coating Thickness

Plastic-Lined Steel Pipe: The plastic layer thickness must comply with CJ/T136 standards.

Plastic-Coated Steel Pipe: Coating thickness should meet the CJ/T120 standards.

9. Performance Requirements

Plastic-Lined Steel Pipe:

Bonding strength: Minimum 0.3 MPa for cold water, 1.0 MPa for hot water.

Peel strength of the outer covering: ≥ 0.35 MPa.

External anti-corrosion: No corrosion or peeling after 24 hours in 3% sodium chloride solution.

Plastic-Coated Steel Pipe:

Pinholes: No electric sparks during testing.

Adhesion: Minimum 30 N/10mm for PE, grade 1-3 for epoxy resin.

Flattening: No cracks or peeling when flattened to specific ratios of pipe diameter.

Conclusion

While both plastic-lined and plastic-coated steel pipes serve similar functions in protecting steel pipes from corrosion, they differ in their production processes, materials, and performance characteristics. Plastic-lined pipes have a plastic layer on the interior, while plastic-coated pipes have a plastic coating on both the interior and exterior. Both types offer unique advantages, depending on the specific application and requirements.