I. Research Background
PE gas pipes occupy 65% of the urban gas piping market due to the advantages of corrosion resistance, ease of construction, and long service life (China Urban Gas Association, 2024). However, environmental stress cracking (ESC) causes 38% of pipeline leakage accidents, especially in the heat fusion joints and branch pipe tees are more concentrated (Figure 1).
Second, the core issue: stress cracking mechanism analysis
1. Classification of failure modes
Type Causes Typical scenarios
Slow crack growth (SCG) Long-term hydrostatic stress + small molecule infiltration After 5-8 years of use in buried pipeline
Rapid Crack Progression (RCP) Impact loading + insufficient material toughness Mechanical impact during construction backfill
Weld cracking Improper heat fusion process + crystal zone defects dn≥110mm Pipe joints
2. Key influencing factors
Through full-scale pressure test (GB/T 15558.1-2015) and crack tip opening displacement (CTOD) test, it is found that:
Material Melt Flow Rate (MFR): ESC life is reduced by 40% when MFR>0.5g/10min
Welding Temperature Window: The optimum temperature is 210±5℃, out of the range of unfused defects are easy to produce.
Backfill soil pH: when pH＜5.5, the risk of stress cracking increases by 2.3 times.
Experimental research on material modification
1. Optimization of bimodal PE resin formulation
Comparison of the effect of different copolymerization monomer content on ESC performance (ASTM D1693 standard):
Material type Copolymer monomer (α-olefin) content (wt%) ESC life (h) Elongation at break (%)    
PE80 2.1 320 680    
PE100 RC 3.2 1200 750 (special material for anti-cracking)
PE100 2.8 580 720    
Modification breakthrough:
Introduced octene copolymer monomer to increase crystallinity to 65%.
Adopting bimodal molecular weight distribution, SCG resistance is increased by 2.5 times.
2. Nanocomposite Reinforcement Technology
Addition of 5wt% graphene-montmorillonite hybrids (Figure 2), realized:
Tensile strength increased from 25MPa to 31MPa.
60% reduction in crack propagation rate
Extension of weathering resistance from 20 to 30 years.
Construction process optimization
1. Three-stage control method for hot-melt connection
According to ISO 21307 standard, formulate welding parameter matrix:
Pipe size (dn) Heating time (s) Switching time (s) Cooling time (min) Weld shear strength (MPa)    
63mm 40 ≤5 6 ≥22    
110mm 70 ≤6 8 ≥24 (after optimization)
160mm 110 ≤8 12 ≥20    
2. Stress relief design
The “flexible transition” structure solves the stress concentration in the tee part:
Adopting R=1.5D large curvature elbow to replace the right angle tee.
Add axial stress relaxation layer within 100mm on both sides of the weld.
Lay 50mm thick elastic sand bedding layer (compression modulus <100MPa) when burying.
V. Engineering Verification Cases
Comparative test results of a town gas project:
Indicator Traditional PE100 pipe Optimized PE100 RC pipe Enhancement effect
Probability of 40 years life prediction 68% 92% +35
Weld leakage rate (times/year/km) 0.72 0.15 -79
Repair Response Time 45 minutes 12 minutes -73%.
Frontier Technology Outlook
1. Self-repairing Intelligent Pipeline
Embedded with microcapsule repair agent (Fig. 3), epoxy resin is released when cracks are detected, and cracks under 0.2mm are repaired automatically.
2. Digital Twin Monitoring
Real-time monitoring through distributed fiber optic sensors:
Pipeline stress distribution cloud map
Early warning of crack expansion rate (accuracy ±0.01mm/h)
Conclusion
This paper cracks the problem of PE gas pipe stress cracking through the three-dimensional system of material upgrading + process optimization + intelligent monitoring. As a professional supplier, we offer:
✅ PE100 RC pipe customization service
✅ Full life cycle stress analysis report
✅ Emergency plan for gas pipe leakage
Keywords: PE gas pipe, stress cracking resistance, hot melt connection, gas safety, GB 15558