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Study on Steel-Plastic Interface Bond Strength of Steel Wire Skeleton Plastic Composite Pipes ——High-Pressure Water Transmission Applications Based on GB/T 32439 Standard

0 Comments / / Post by by 孙飞虎

1. Research Background


Steel Wire Skeleton Plastic Composite Pipes (SRTP), with a "high-strength steel skeleton + HDPE" structure (Figure 1), are increasingly used in urban water and gas networks. While their ring stiffness reaches SN12.5, interface bond failures account for 53% of leaks (2024 CPPIA data), especially under high pressure (>1.6MPa).

2. Core Issue: Interface Failure Mechanism

2.1 Bond Failure Modes


Through universal testing machines (GB/T 18369-2008) and SEM, three failure modes were identified:
![Failure Mode Schematic](Figure 2)


  • Interface debonding (68%): Bond strength <3.5MPa
  • Plastic tearing (22%): Insufficient HDPE strength
  • Steel corrosion (10%): Electrochemical corrosion at interface gaps

2.2 Key Influencing Parameters


Parameter GB Requirement Field Measurement Influence
Steel plating thickness (μm) ≥85 (galvanized) 70-80 ★★★★☆
Plastic MI (g/10min) 0.2-0.5 0.6-0.8 ★★★☆☆
Winding angle (°) 54.7±2° 50-58° ★★★☆☆

3. Interface Bond Optimization

3.1 Steel Surface Treatment


Comparison of pretreatment methods:


Treatment Surface Roughness Ra(μm) Bond Strength (MPa) Salt Spray Life (h)
Galvanized 3.2-4.5 4.1 1500
Galvanized + sandblasting 5.8-7.2 5.6 2500
Galvanized + chemical texturing 4.5-6.0 5.2 2000


Breakthrough:


  • Sandblasting creates 3D anchor structures (Figure 3)
  • Bonding area increased by 40%

3.2 Plastic Modification


Using PE-g-MAH as compatibilizer:


PE-g-MAH Content (%) Steel-Plastic Bond (MPa) Plastic Tensile Strength (MPa) MI
0 4.2 24 0.7
3 6.8 26 0.5
5 6.5 25 0.4

4. Structural Design Optimization

4.1 Winding Angle Optimization


Finite element analysis showed:


  • 54.7° winding angle carries 72% of hoop stress
  • ±2° deviation increases stress concentration by 18%

4.2 Double-Layer Structure


Innovative "inner plastic-steel-outer plastic" co-extrusion (Figure 4):


  • Inner HDPE: 3.0mm (corrosion resistance)
  • Outer HDPE: 4.5mm (steel protection)
  • PE-g-MAH interlayer: 0.3mm

5. Engineering Solutions

5.1 High-Pressure Standard


Based on GB/T 32439-2015, internal indicators:


Parameter GB Requirement Optimized Standard Test Method
Steel-plastic bond (MPa) ≥3.5 ≥6.0 GB/T 18369-2008
Hydrostatic strength (MPa) ≥4PN 4.5PN GB/T 6111-2018
RCP resistance Pass Crack length <100mm Full-scale test

5.2 Electrofusion Welding Process


"Four-Stage" welding control:


  1. Preheat: 120℃ for 60s
  2. Melting: 210℃ for 180s
  3. Pressure: 0.1MPa for 120s
  4. Cooling: Natural cooling <60℃

6. Field Test Case: Cross-River Water Project


Index Traditional SRTP Optimized SRTP Standard Requirement
Operating pressure (MPa) 1.6 2.0 -
5-year leakage rate (%) 2.1 0.3 ≤1.0
Joint tensile strength (kN) 85 120 ≥80

7. Future Technologies

7.1 Nano-Interface Enhancement


50nm TiO₂ coating on steel wires (Figure 5) increases bond strength by 30%.

7.2 Smart Welding Monitoring


Integrated infrared thermography + pressure sensors for real-time monitoring of:


  • Welding temperature distribution (±2℃ accuracy)
  • Interface bond quality grading (I/II/III)


Conclusion
This paper establishes a high-pressure reliability system through interface modification + structural design + process control. As a professional supplier, we provide:
✅ Custom high-pressure SRTP pipes (PN1.0-PN2.5)
✅ Steel-plastic bond strength testing
✅ Electrofusion welding process certification


Keywords: Steel wire skeleton plastic composite pipe, steel-plastic interface, bond strength, high-pressure water transmission, GB/T 32439
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