In the construction of underground pipeline projects, pipe materials must not only withstand the high pressure of internal fluids, but also face the severe challenges of complex underground chemical corrosion, electrochemical erosion, and soil load.
3PE Coated SSAW Steel Pipe, with its superior structural strength and advanced anti-corrosion technology, has become the core choice for long-distance underground water, gas, and municipal pipeline projects.
I. What is 3PE Coated SSAW Steel Pipe?
This product combines two leading technologies: SSAW (Spiral Submerged Arc Welding) provides the structural foundation for large-diameter pipes, while 3PE (Three-Layer Polyethylene Coating) provides an indestructible protective layer.
The three-layer structure of the 3PE anti-corrosion coating:
- Bottom Layer: Fusion-bonded epoxy powder (FBE > 100μm) Bonds directly to the steel pipe surface, providing excellent adhesion and resistance to cathodic disbondment.
- Middle Layer: Adhesive (AD, 170~250μm) Acts as a bridge, tightly bonding the bottom epoxy powder to the top polyethylene layer.
- Top Layer: High-density polyethylene (HDPE, 1.5~3.7mm) Provides mechanical protection against moisture penetration, soil stress, and acid/alkali corrosion.
II. Core Technological Advantages: Why is it the Preferred Choice for Underground Engineering?
i. Superior Corrosion Resistance and Extended Service Life
According to the standard GB/T 23257-2017 “Polyethylene Anti-corrosion Coating for Buried Steel Pipelines,” the 3PE anti-corrosion coating combines the mechanical properties of epoxy powder with the chemical resistance of polyethylene. Research data shows that 3PE Coated SSAW Steel Pipe has a design service life of up to 50 years in underground environments, far exceeding traditional epoxy coal tar anti-corrosion coatings.
ii. High Strength and Economy of SSAW Structure
Spiral welded pipe (SSAW) allows for the production of large-diameter pipes using narrow steel strips. For underground water diversion projects, SSAW can easily achieve diameters of over 1000mm, and due to its uniform weld stress distribution, its pressure resistance and safety fully comply with API 5L standards.
iii. Low water absorption and high insulation
The extremely low water absorption rate (<0.01%) of the polyethylene surface ensures its electrical insulation in humid underground environments, greatly reducing the operating costs of cathodic protection systems.
III. Technical Parameter Reference Table
Understanding the specific specifications of the anti-corrosion coating and pipe material is crucial during the selection process. The following is a comparison based on standard specifications:
Table 1: Performance Indicators of 3PE Anti-corrosion Coating (Based on DIN 30670 / GB/T 23257)
| Property | Unit | Requirement (Typical Value) |
|---|---|---|
| Peel Strength (20 ± 5°C) | N/cm | ≥ 100 |
| Impact Resistance | J | ≥ 8 × Wall Thickness (mm) |
| Electrical Strength (Holiday Test) | kV | ≥ 25 (No breakdown) |
| Water Absorption | % | ≤ 0.05 |
| Environmental Stress Cracking Resistance (ESCR) | h | ≥ 1000 |
Table 2: Specification Range of SSAW Carbon Steel Pipe Substrate
| Parameter | Range |
|---|---|
| Outer Diameter (OD) | 219 mm – 3020 mm |
| Wall Thickness (WT) | 5 mm – 25.4 mm |
| Standard | API 5L, ASTM A252, GB/T 9711 |
| Common Grades | Q235B, Q355B, X42, X52, X65 |
IV. Selection Recommendations for Underground Pipeline Engineering
Given the complexity of underground engineering projects, the following points should be considered when purchasing 3PE Coated SSAW Steel Pipe:
- Grading Selection: Select the corrosion protection layer grade (ordinary or reinforced) based on the soil’s corrosivity level (strong, medium, weak). Reinforced 3PE has a thicker polyethylene layer, suitable for areas with complex geological structures.
- Weld Treatment: SSAW pipes have high spiral welds; during corrosion protection construction, ensure the coating thickness is uniform at the “slope peak” to avoid thinning zones.
- Joint Repair Technology: The joint repair after on-site pipe connection is a weak point in corrosion protection. It is recommended to use radiation cross-linked polyethylene heat shrinkable tape to ensure the corrosion protection level at the joint is consistent with the pipe body.