Pipeline insulation

Insulated pipelines are thermal‑insulation pipes used for the conveyance of liquids, gases, and other media. Their primary function is to minimize heat loss during transportation while preventing low‑temperature media from absorbing heat and high‑temperature media from losing heat to the environment. They are widely employed in district heating, petrochemical processing, central air conditioning, and other applications.

Mainstream Classification and Structural Characteristics

Polyurethane insulated pipeline ‌

Structure: Composed of three layers—inner working steel pipe, polyurethane foam insulation layer, and a high-density polyethylene outer protective casing.

Applicable temperature: -70 °C ~120 ℃, commonly used in urban district heating secondary networks and central air-conditioning ventilation ducts.

Core Advantage: Thermal conductivity as low as 0.016W/m.k , the heat loss is only that of conventional piping. 25% , the overall construction cost can be reduced 10%-25% , with a service life of up to 30-50 Year.

Steel‑jacketed composite insulated pipeline ‌

Structure: Both the inner and outer layers are steel pipes, with the space between filled with high‑temperature‑resistant insulation materials such as aluminum silicate and glass wool. It is available in two configurations: internal sliding and external sliding.

Applicable temperature: Can withstand up to 350 ℃ high-temperature steam, commonly used in the main high-temperature steam networks of power plants and chemical industrial parks.

Key Advantages: Strong pressure resistance; the external‑sliding design is well suited to areas with high water levels and abundant rainfall, allowing direct underground installation without the need for concrete structures.

Common insulation materials

Polyurethane foam: Closed-cell content ≥ 97% , with an extremely low water absorption rate, it is the mainstream insulation material for conventional heating pipelines.

Rock wool / Glass wool: maximum operating temperature 600 °C, non-combustible and sound-absorbing, suitable for high-temperature industrial piping applications.

Aerogel Insulation Blanket: A next‑generation, high‑efficiency thermal insulation material with a thermal conductivity far lower than that of conventional materials, ideally suited for advanced insulation applications in new energy, petrochemicals, and other high‑end industries.

Rubber‑plastic foam: features an elastic closed‑cell structure, is moisture‑proof and flame‑retardant, and is commonly used for air‑conditioning refrigerant lines and low‑temperature pipe insulation.

When selecting insulation for pipelines under different temperature conditions, the medium temperature should be the primary criterion, supplemented by a comprehensive assessment of factors such as pressure and installation environment. The following is a precise selection guideline organized by temperature range:

Cryogenic operating conditions ( -196 °C ~-40 °C) ‌

Compatible pipe types: polyurethane insulated pipes, LNG Specialized elastic felt insulation pipe.

Compatible insulation materials: polyurethane foam and low-temperature‑resistant specialized rubber‑plastic materials.

Applicable scenarios: Liquefied natural gas transportation, cryogenic fluid pipelines, and cold‑storage insulation piping.

Key selection criteria: Must have a closed-cell content of ≥ 98% The moisture‑proof structure prevents water vapor ingress that could compromise thermal insulation; the insulation layer thickness shall be determined in accordance with condensation‑prevention requirements.

Medium- and low-temperature operating conditions ( -40 °C ~120 °C) ‌

Compatible pipe types: pre‑insulated direct‑buried polyurethane insulated pipes, black jacket insulated pipes, PPR Composite insulated pipe

Compatible insulation materials: polyurethane foam, rubber‑plastic sponge, and glass wool.

Applicable scenarios: district heating networks, chilled and hot water piping for central air-conditioning systems, and conventional domestic hot water distribution.

Key selection criteria: Working pressure ≤ 2.5MPa When prioritizing, choose polyurethane insulated pipes; their heat loss is only a fraction of that of conventional pipelines. 25% , with a design life of up to 30~50 Year.

Medium and high temperature operating conditions ( 120 °C ~350 °C) ‌

Compatible pipe types: steel‑jacketed steam insulated pipes, overhead insulated steel pipes

Compatible insulation materials: rock wool, glass wool, aluminosilicate fiber

Applicable scenarios: steam transmission in power plants, high-temperature process pipelines in chemical industrial parks, and primary heating networks for district heating.

Key selection considerations: Prioritize steel‑jacketed, externally sliding pipe structures, which are well suited for high‑water‑level areas and can accommodate thermal expansion and contraction of the pipeline. The outer protective steel casing is designed to… 3PE Anti-corrosion treatment.

Ultra-high temperature operating conditions ( 350 °C ~600 above ℃) ‌

Compatible pipe types: aluminosilicate fiber high-temperature insulated steel pipes, detachable insulation jackets

Compatible insulation materials: aluminosilicate fiber, aerogel insulation blanket

Applicable scenarios: industrial furnace pipelines, boiler main steam pipelines, and high-temperature flue gas conveyance pipelines.

Key selection considerations: Employ a multi-layer composite insulation structure, with an outer stainless steel protective layer to prevent material pulverization and delamination at high temperatures.

Quality Standards

-  See the standard: Polyurethane direct‑buried pipes are primarily manufactured in accordance with GB/T 29047-2021 “High-Density Polyethylene Outer Jacket Rigid Polyurethane Foam Pre‑Insulated Direct‑Bury Insulation Pipes and Fittings,” with steel‑jacketed steam pipes in compliance with the relevant standards. CJ/T200 — 2004 Standards, etc.

-  Check the insulation layer specifications: polyurethane density ≥ 60kg/m ³. Closed-cell content ≥ 88%-97% , thermal conductivity ≤ 0.033 W/(m · K) , water absorption ≤ 0.2kg/m ².

-  Inspect the outer protective jacket: The density of the high-density polyethylene outer protective jacket shall be ≥ 950kg/m ³ (20 °C ) , the wall thickness must be sufficient, and the surface should be free of visible scratches, cracks, or bubbles.

-  Work pipe: The surface shall be treated by shot blasting to remove rust, with a rust removal grade reaching Sa2 Grade, surface roughness R=12.5 About one micrometer.

-  On-site preliminary assessment: Press the foam at the pipe end to check for compactness and any softness; observe whether the cell structure is uniform and fine. The reserved length at the pipe end is generally not less than… 150mm。

Application scenarios

-  Municipal district heating: Polyurethane direct‑buried insulated pipes account for the largest share, and demand is robust in northern heating‑retrofit projects.

-  Petrochemical industry: oil and gas pipelines, LNG Demand in the pipeline transportation sector has grown significantly.

-  High-temperature steam pipelines: Steel‑jacketed, steel‑insulated pipes are used for steam transmission and in steam pipeline networks within chemical plant areas.

-  Cold‑storage engineering: cold storage facilities, district cooling, and low‑temperature medium transport; some components are resistant to… -90 °C.

-  Other fields: It is also used in central air-conditioning ventilation ducts, coal mining, the power industry, shipbuilding, metallurgy, and other sectors.