Technical specifications of polyethylene-coated steel pipe

Polyethylene-coated steel pipes are widely used for protecting steel pipelines from corrosion and physical damage. These pipes are coated with one or more layers of polyethylene (PE) to enhance their durability, particularly in harsh environmental conditions. The coating process and the technical specifications ensure the pipes are resistant to corrosion, abrasion, and other damaging factors. Below are the key technical specifications for polyethylene-coated steel pipes.

1. Coating Material

Polyethylene (PE): The primary material used for the coating, providing excellent resistance to corrosion, moisture, and chemicals.

Adhesive Layer: In some coating systems (like 2PE or 3PE), an adhesive layer is used between the steel pipe and the polyethylene to ensure proper bonding and prevent delamination.

Epoxy Powder Layer (in 3PE coatings): For 3PE-coated pipes, an epoxy powder layer is applied beneath the polyethylene to enhance corrosion resistance.

2. Coating Thickness

The thickness of the polyethylene coating depends on the type of coating system and the application requirements:

2PE Coating:

Adhesive layer: Typically 170 to 250 microns.

Polyethylene layers: 2 to 3 mm each.

3PE Coating:

Epoxy powder layer (FBE): >100 microns.

Adhesive layer: 170 to 250 microns.

Polyethylene layer: 2.5 to 3.7 mm.

The coating thickness plays a crucial role in the pipe's ability to resist mechanical damage and provide effective corrosion protection.

3. Pipe Dimensions

Diameter: Polyethylene-coated steel pipes come in a wide range of diameters, typically from 1/2 inch to several inches (or larger for special applications).

Wall Thickness: The wall thickness of the steel pipe is determined by the required strength and pressure rating of the pipe. It can vary from schedule 10 to schedule 160, or more, depending on the application.

4. Adhesion Strength

The adhesion strength of the polyethylene coating is critical for ensuring long-term performance. It is typically measured by a peel test to determine the bond strength between the steel pipe and the polyethylene coating.

Peel Adhesion: Must meet a minimum adhesion strength to prevent the polyethylene from peeling off during transportation, installation, or operational stresses. The required adhesion strength is typically 15 N/mm or higher, depending on the pipe diameter and coating type.

5. Corrosion Resistance

The polyethylene coating provides excellent corrosion resistance, particularly in environments where the pipe is exposed to moisture, chemicals, or aggressive soil conditions. Polyethylene is chemically inert, which makes it an ideal choice for protecting steel pipes.

Cathodic Protection Compatibility: In the case of the 3PE coating, the epoxy layer provides a superior bond, enhancing the ability to apply cathodic protection (CP) and preventing corrosion under the coating.

6. Impact Resistance

Polyethylene-coated steel pipes offer significant protection against physical damage. The polyethylene layer provides an impact-resistant surface, minimizing damage during transportation and installation.

Impact Resistance Test: This can be tested using a standard impact test, where the pipe is subjected to specific impacts to assess its durability.

7. Abrasion Resistance

Polyethylene-coated pipes are highly resistant to abrasion, which is critical when the pipes are installed in environments with abrasive materials or subject to wear and tear.

Abrasion Resistance Test: Standard tests such as the Taber Abrasion Test can be used to evaluate the coating’s ability to withstand abrasion.

8. Temperature Range

Operating Temperature: Polyethylene coatings are effective in a wide range of temperatures, typically from -40°C to +80°C. However, the coating may have specific limitations depending on the grade of polyethylene used.

Installation Temperature: The pipe and coating system must be installed in conditions where the temperature does not fall below the minimum temperature for coating adhesion and curing.

9. Flexibility and Bending Radius

Polyethylene-coated steel pipes are flexible and can be bent within certain limits without damaging the coating. However, excessive bending may cause cracking or deformation of the coating.

Bending Radius: The minimum bending radius is usually specified by the manufacturer to ensure the integrity of the polyethylene layer during installation.

10. Testing and Quality Control

To ensure that polyethylene-coated steel pipes meet industry standards and perform effectively, a series of tests are conducted during production, including:

Visual Inspection: To check for any defects in the coating such as bubbles, cracks, or inconsistencies.

Coating Thickness Measurement: To ensure that the coating meets the specified thickness.

Adhesion Test: To verify the bond between the coating and the steel pipe.

Impact and Abrasion Tests: To check the physical durability of the coating.

Cathodic Disbondment Test: To assess the ability of the coating to resist disbondment in the presence of cathodic protection.

11. Applications

Polyethylene-coated steel pipes are used in a variety of applications, including:

Oil and Gas: For transporting oil, gas, and other hydrocarbons, particularly in harsh and corrosive environments.

Water and Sewerage: For municipal water supply and drainage systems.

Construction: In structural applications where corrosion resistance is critical.

Marine Environments: For underwater pipelines where resistance to saltwater corrosion is important.