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Submission:
**Application of High-Density Polyethylene Shell Prefabricated Direct-Buried Insulation Pipe**
Dacheng Xiangdong Insulation Refractory Material Factory
Phone: 13473696600 | 15731614448
High-density polyethylene (HDPE) shell prefabricated direct-buried insulation pipes are widely used in various industrial and urban infrastructure projects. These pipes are designed for efficient thermal insulation and protection, making them ideal for both heating and cooling applications. The structure consists of three main layers, each playing a crucial role in the performance and durability of the system.
The **innermost layer** is the **working steel pipe**, which is typically made from seamless, spiral welded, or straight seam welded steel pipes, depending on the design requirements. Before installation, the steel pipe undergoes advanced surface treatment, including shot blasting and descaling, to achieve a surface cleanliness grade of Sa2 as per GB8923-1988 and a roughness level of R=12.5 microns according to GB6060.5-88. This ensures strong adhesion between the steel pipe and the subsequent insulation layers.
The **middle layer** is the **polyurethane foam insulation**, created through a high-pressure foaming process where liquid polyurethane is injected into the space between the steel pipe and the outer HDPE casing. This method, known as "tubular foaming," provides excellent thermal insulation, waterproofing, and structural support. It is suitable for conveying media with temperatures ranging from -50°C to 120°C.
The **outermost layer** is the **high-density polyethylene protective sheath**, pre-fabricated into a black or yellow plastic pipe with a specific wall thickness. After undergoing corona treatment, this layer acts as a shield against mechanical damage, corrosion, and water ingress, ensuring long-term protection for the inner insulation layer.
These pipes are commonly used in central heating systems, cold storage facilities, coal mines, oil ports, and chemical plants. However, it's important to note that HDPE has lower heat resistance compared to fiber-reinforced plastic (FRP), with a maximum operating temperature of around 60–70°C, while FRP can withstand up to 100–120°C. Therefore, careful consideration should be given when selecting the material based on environmental conditions.
**Key Advantages of HDPE Prefabricated Direct-Buried Insulation Pipes:**
1. **Cost-Efficient Construction**
Using HDPE as the protective layer can reduce construction costs by approximately 10%, while FRP offers even greater savings at 25%. This makes it an economical choice for large-scale projects.
2. **Low Heat Loss and Energy Efficiency**
With a thermal conductivity of λ=0.013–0.03 kcal/m·h·°C, these pipes significantly reduce heat loss. Their low water absorption rate (about 0.2 kg/m²) and high closed-cell density (around 92%) ensure superior insulation performance. Compared to traditional methods, they cut heat loss by more than 50%, achieving a network loss of only 2%, far below the international standard of 10%.
3. **Excellent Corrosion Resistance and Long Lifespan**
The tightly bonded polyurethane foam and HDPE/FRP outer shells prevent moisture and air penetration, offering exceptional anti-corrosion properties. When properly maintained, the service life can exceed 50 years—three to four times longer than conventional trench or overhead installations.
4. **Space-Saving and Environmentally Friendly**
Unlike traditional trench laying, these pipes do not require extensive excavation. They can be directly buried underground, reducing land use by over 50% and minimizing earthwork and concrete usage by 90%. Additionally, on-site jointing allows for faster installation, cutting construction time by about 50%.
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