Double-Wall Corrugated Polyethylene Pipe (HDPE Structured-Wall Sewer Pipe)
Table of Contents
What Is a Double-Wall Corrugated PE Pipe?
Double-wall HDPE corrugated pipes (also called structured-wall sewer pipes) are engineered composite pipes used for gravity sewerage and drainage systems.
They consist of two layers:
Outer Layer – Corrugated Structural Wall
- High stiffness & resistance to soil pressure
- Withstands deep burial and road load
Inner Layer – Smooth HDPE Wall
- Excellent hydraulic flow
- Less sedimentation
- Anti-fouling surface
These pipes are manufactured using PE80, PE100, or PP-B depending on national standards.
Key Functions in Wastewater Systems
- Gravity transportation of domestic sewage
- Stormwater drainage
- Municipal wastewater pipelines
Underground drainage for roads & industrial zones
Comparison with Concrete, PVC & GRP
Pipe Type | Weight | Corrosion | Jointing | Lifetime | Stiffness |
HDPE Corrugated | Very Light | Excellent | Rubber-seal coupler | 50+ years | SN2–SN16 |
Concrete Pipe | Very Heavy | Poor | Mortar bell joint | 20–40 years | High |
PVC Sewer Pipe | Light | Medium | Rubber seal | 25–40 years | SN2–SN8 |
GRP Pipe | Medium | Excellent | Lamination | 40–50 years | High |
HDPE corrugated provides the best combination of:
✔ lifespan
✔ corrosion resistance
✔ installation speed
✔ cost-efficiency
✔ hydraulic performance
Structural Design & Molecular Composition
Corrugated pipes use High-Density Polyethylene (HDPE) with:
- High molecular weight
- High ESCR (Environmental Stress Crack Resistance)
- Excellent resistance to corrosive sewer gases (H₂S, methane, ammonia)
Material Requirements (Per EN 13476 / ISO 21138)
- Density: 0.94–0.97 g/cm³
- Melt Flow Rate (MFR): 0.3–1.5 g/10 min
- Carbon black: 2–2.5% (UV stability)
- OIT ≥ 20 minutes
- Tensile properties conforming to ISO 527
Applications in Wastewater Systems
International Standards & Certifications
ISO 21138 – Structured-Wall Sewer Pipes
Defines:
- Pipe types (Type A, B, C)
- Material requirements (HDPE, PP-B)
- Ring stiffness, flexibility & buckling resistance
- Joint tightness under pressure & vacuum
- Impact resistance
Creep ratio
EN 13476 (Europe)
Covers:
- Pipe dimensions (DN/OD 110–1200+)
- Profile geometries (C, D, K)
- Stiffness classes SN2–SN16
- Ring flexibility test
- Drop test impact requirements
- Long-term deflection behavior
- Leak tightness under 0.5 bar internal/external pressure
ASTM F2306 (USA)
Standard for HDPE dual-wall corrugated drainage pipes.
Covers:- Corrugated outer layer geometry
- Smooth inner wall
- Stiffness & deflection
- UV resistance
Joint integrity
- Corrugated outer layer geometry
ISIRI 9118 (Iran National Standard)
Specifies:
- SN classification
- Dimensions & tolerances
- Mechanical testing
- Chemical & biological resistance
- Long-term creep ratio
Joint tightness under infiltration/exfiltration tests
SN Stiffness Classes & Structural Performance
Corrugated pipes are classified by Ring Stiffness (SN):
SN Class | Stiffness (kN/m²) | Application |
SN2 | 2 | Light agricultural drains |
SN4 | 4 | Residential sewage |
SN8 | 8 | Standard municipal networks |
SN10 | 10 | Industrial zones |
SN12.5 | 12.5 | Deep burial or heavy soil |
SN16 | 16 | Heavy traffic areas (roads, highways, airports) |
Dimensions, Profiles & Joint Systems
Common Diameters
- DN 160
- DN 200
- DN 250
- DN 315
- DN 400
- DN 500
- DN 600
- DN 800–1200 (special industrial supply)
Joint Types
- Rubber gasket + coupler
- Bell & spigot joint
- Heat shrink sleeve (special use)
- Manhole connectors (EPDM)
All joints must provide watertightness per EN 681-1.
- Rubber gasket + coupler
Installation Requirements
Bedding
- Fine sand or soft granular material
- No sharp stones under pipe
Haunching & Backfilling
- Proper compaction around lower third of pipe
- Compaction must meet proctor values
- Avoid excessive loads before bedding is stable
Burial Depth
- Minimum: 0.8 m
- Heavy traffic: up to 6–8 m depending on SN class
Slope
- For sewage: typically 0.5–1% gradient
Technical Properties
Mechanical Properties
- Long-term creep resistance
- High impact strength
- High flexibility → absorbs soil movement
- Resistant to repeated traffic load cycles
Hydraulic Properties
- Smooth internal wall
- Manning’s coefficient n = 0.010–0.012
Low friction, high flow capacity
Environmental Properties
- UV stabilized
- 100% corrosion proof
- Biological & chemical resistance
- Suitable for H₂S-rich sewer gas environments
Design Considerations
Engineers must consider:
- Traffic load (AASHTO)
- Soil type
- Water table level
- Pipe deformation limits
- SN selection
- Thermal expansion
QC & Testing Requirements
Hydrostatic Tests
20°C at 100 h
80°C at 165 h
80°C at 1000 h
Material Tests
OIT
MFR
Tensile strength
FNCT / PENT
Dimensional Control
Ovality
Wall thickness
SDR compliance
Advantages
- Lightweight → quick installation
- Corrosion-free
- Long life (50+ years)
- Easy cutting & field modification
- Excellent hydraulic efficiency
- Flexible under soil movement
Maintenance & Lifecycle
- Minimal maintenance needed
- Cleaning with jetting systems allowed
- Minimal maintenance needed
FAQs
SN8 is standard.
Yes—SN12.5 & SN16 are designed for roads & highways.
Yes, the inner wall is suitable for jet cleaning.
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