Three-Layer Structure of Pre-insulated Direct-buried Pipe
Designed for municipal district heating and cooling pipeline networks, suitable for conveying media with operating temperatures ranging from 3°C to 140°C.
Applicable Standard: GB/T 29047-2021
Service Pipe Layer
Manufactured from seamless steel pipe, spiral welded steel pipe, or straight seam welded steel pipe according to project requirements.
PUR Insulation Layer
High-density rigid polyurethane foam is injected between the service pipe and HDPE jacket through a high-pressure foaming system.
HDPE Outer Jacket
High-density polyethylene outer jacket provides reliable underground protection.
Key Features
Three-layer Bonded Structure
The service steel pipe, rigid polyurethane foam, and HDPE casing form an integrated pre-insulated system for direct burial.
Low Heat Loss
Rigid polyurethane insulation helps reduce distribution losses in district heating and cooling networks.
Moisture and Corrosion Protection
The high-density polyethylene casing protects the insulation layer from groundwater, soil moisture, and external corrosion exposure.
Wide Diameter Range
Reference configurations cover DN20 to DN1400, supporting branch lines, municipal networks, and large-diameter transmission projects.
Factory-controlled Production
Pipe-in-pipe foaming, casing extrusion, pipe preparation, and dimensional inspection are completed before delivery to reduce site work.
Optional Alarm Wire System
Pre-warning wires can be incorporated when required by the project leakage monitoring specification.
Complete Fitting Package
Matching elbows, tees, insulated valves, reducers, and joint insulation materials can be supplied as a coordinated system.
Performance Specifications
| Main Performance Indicator | Reference Standard | Standard Requirement |
| Density (kg/m³) | EN 253, Clause 5.2.1 CJ/T 114, Clause 5.2.1 | ≥944 (EN 253) ≥940 (CJ/T 114) |
| Elongation at Break (%) | EN 253, Clause 5.2.7 CJ/T 114, Clause 5.2.6 | ≥350 |
| Yield Strength (MPa) | CJ/T 114, Clause 5.2.6 | ≥19 |
| Thermal Stability | EN 253, Clause 4.3.1.3 | ≥20 min at 210°C |
| Environmental Stress Cracking Resistance | EN 253, Clause 4.3.2.8 | ≥300 h |
| Longitudinal Reversion (%) | EN 253, Clause 5.2.4 CJ/T 114, Clause 5.2.7 | ≤3 |
| Long-Term Mechanical Performance | EN 253, Clause 5.2.6 CJ/T 114, Clause 5.2.8 | No failure after 2,000 h at 80°C and 4.0 MPa |
| Difference in Melt Flow Rate (g/10 min) | EN 253, Clause 4.3.1.2 CJ/T 114, Clause 5.2.4 | ≤0.5 |
| Inner-Surface Corona Treatment | ABB Technical Requirements | ≥50 dyn/cm / ≥75% |
Polyurethane Foam
| Main Performance Indicator | Reference Standard | Standard Requirement |
| Average Cell Size (mm) | EN 253, Clause 5.3.2.1 CJ/T 114, Clause 5.3.1 | <0.5 (EN 253) ≤0.5 (CJ/T 114) |
| Closed-Cell Content (%) | EN 253, Clause 5.3.2.2 CJ/T 114, Clause 5.3.2 | ≥88 |
| Density (kg/m³) | EN 253, Clause 5.3.3 CJ/T 114, Clause 5.3.4 | ≥60 |
| Compressive Strength (MPa) | EN 253, Clause 5.4.5 CJ/T 114, Clause 5.3.7 | ≥0.3 |
| Thermal Conductivity Before Aging [W/(m·K)] | EN 253, Clause 5.4.5 CJ/T 114, Clause 5.3.7 | ≤0.033 |
| Water Absorption | EN 253, Clause 5.3.5 CJ/T 114, Clause 5.3.6 | After immersion in boiling water for 90 minutes, water absorption shall not exceed 10% of the original volume. |
Complete Pre-Insulated Pipe Assembly
| Main Performance Indicator | Reference Standard | Standard Requirement |
| Exposed Steel Pipe Length at Pipe End (mm) | EN 253, Clause 4.5.1 CJ/T 114, Clause 4.4.1 | ≥150 |
| Increase in Outer Casing Diameter (%) | EN 253, Clause 5.4.1 CJ/T 114, Clause 5.4.1 | ≤2 |
| Axial Eccentricity | EN 253, Clause 4.5.3 CJ/T 114, Clause 4.4.3 | Refer to Clause 4.5.3 |
| Expected Service Life and Shear Strength After Aging at 170°C for 1,450 h (N/mm²) | EN 253, Clauses 5.4.2 and 5.4.4 CJ/T 114, Clauses 5.4.2 and 5.4.3 | ≥0.12 at 23°C ≥0.08 at 140°C |
| Impact Resistance | EN 253, Clause 5.4.6 CJ/T 114, Clause 5.4.6 | Refer to Clause 5.4.6 |
| Alarm Wire Insulation Resistance | CJ/T 114, Clause 4.4.6 | 20 MΩ–∞ |
| Creep Performance | EN 253, Clause 4.5.7 | Over 30 years, creep deformation ≤20 mm |
Standard Size Range
| Nominal Diameter | Steel Pipe OD x WT mm | HDPE Casing OD x WT mm | Insulation Thickness mm |
| DN20 | 25×3 | 90×3 | 29.5 |
| DN25 | 32×3 | 100×3 | 31 |
| DN32 | 42×3 | 110×3 | 31 |
| DN40 | 45×3 | 120×3 | 34.5 |
| DN50 | 60×3.5 | 125×3 | 29.5 |
| DN65 | 76×4 | 140×3 | 29 |
| DN80 | 89×4 | 160×3 | 32.5 |
| DN100 | 114×4 | 200×3.2 | 39.8 |
| DN125 | 140×4.5 | 225×3.4 | 39 |
| DN150 | 159×4.5 | 250×3.6 | 41.6 |
| DN200 | 219×6 | 315×4.1 | 43.1 |
| DN250 | 273×6 | 365×4.8 | 40 |
| Nominal Diameter | Steel Pipe OD x WT mm | HDPE Casing OD x WT mm | Insulation Thickness mm |
| DN300 | 325×7 | 420×5.2 | 40.5 |
| DN350 | 377×7 | 500×5.6 | 53.7 |
| DN400 | 426×7 | 550×6 | 54.2 |
| DN450 | 478×7 | 600×6.3 | 51.2 |
| DN500 | 529×7 | 655×6.6 | 53.2 |
| DN600 | 630×8 | 760×7.6 | 53.5 |
| DN700 | 720×8 | 850×8.3 | 53 |
| DN800 | 820×9 | 960×9.1 | 56 |
| DN900 | 920×10 | 1054×9.8 | 53 |
| DN1000 | 1020×10 | 1155×10.6 | 53.5 |
| DN1200 | 1220×12 | 1380×12.5 | 65 |
| DN1400 | 1420×14 | 1580×15 | 64 |
Pre-insulated Pipe Elbow
Designed for pipeline direction changes in district heating and cooling networks, the pre-insulated elbow provides continuous thermal insulation and reliable protection for underground pipeline systems.
Pre-insulated Pipe Tee
Used for pipeline branching and connection applications, the pre-insulated tee ensures efficient heat preservation, structural stability, and long-term operational reliability.
Pre-insulated Ball Valve
A fully insulated valve solution designed for flow control in pre-insulated pipeline systems, offering excellent sealing performance and thermal insulation properties.
Field Joint Insulation System
Applied at pipeline connection points during installation, the field joint insulation system restores the insulation layer and ensures continuous thermal protection, waterproofing, and long-term durability.
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