Insulated steel pipes are steel pipes that, after undergoing a thermal insulation process, maintain the internal temperature of the working pipe within the required temperature range, in line with surface temperature demands, under various operating environments and the influence of external media. These pipes are extensively used in pipeline networks for the transportation of liquids and gases, as well as in thermal insulation projects for chemical pipelines, oil and chemical industries, centralized heating networks, central air conditioning ventilation systems, and municipal engineering projects. Steel-clad steel composite insulated pipes...
Steel-clad steel composite thermal insulation pipes can be divided into two major categories based on different sliding methods:
1. Internal sliding type: Insulation structure is composed of working steel pipe, aluminum silicate, drag-reduction layer, microporous calcium silicate, insulation layer, stainless steel fastening steel strip, aluminum foil reflective layer, polyurethane insulation layer, outer steel pipe, and outer anti-corrosion layer. Internal sliding type insulated steel pipes are structured from steel pipes for conveying medium + composite silicate or microporous calcium silicate + rigid polyurethane foam plastic + outer steel pipe + glass fiber reinforced plastic shell anti-corrosion protective layer. Various pipe fitting joints have mature insulation treatment technology and reliable quality.
2. External Sliding Type: The thermal insulation structure is composed of working steel pipe, glass wool thermal insulation and heat preservation layer, aluminum foil reflective layer, stainless steel fastening steel belt, sliding guide bracket, air thermal insulation layer, outer protective steel pipe, and outer anti-corrosion layer.
External sliding thermal insulation steel pipe structure: 1. Inner steel pipe 2. Zinc-rich primer 3. Sliding guide bracket 4. High-temperature resistant glass wool 5. Aluminum foil reflective layer 6. Air insulation layer 7. Outer steel pipe 8. Corrosion protection layer of outer steel pipe
Steel-clad steel composite thermal insulation pipes are a type of underground buried pipeline, which can be installed underground without concrete structure. The thermal expansion of the working steel pipe occurs within the outer pipe, thus reducing material costs, shortening construction time, and ensuring the safety of heating pipelines. They can be widely applied in different temperature environments safely, especially suitable for high-temperature steam pipeline projects. The operating temperature range is up to 150℃-450℃. The pipeline ends are generally sealed with polyethylene film or three-layer PE cold-skin tape to prevent moisture or water from entering before installation or during construction. The multi-layer wrapping of thermal insulation material effectively reduces heat loss, while control measures on the outer sheath surface prevent the formation of cold bridges, ensuring the temperature control of the anti-corrosion layer of the outer sheath. The multi-layer wrapping of aluminum foil reflects the heat loss effectively, making the steam pipeline more economical and reasonable. The drain system adopts a fully enclosed design, which is flexible in arrangement, reasonable in structure, and safe and reliable.
The moisture evacuation tube on the steel casing pipe can timely expel moist gases and also serve as an alarm signal tube for daily operation. The thermal compensation of the pipeline uses a corrugated tube compensator, which is installed inside the casing in a direct-burial form, eliminating the need for observation wells, making construction operations convenient and shortening the construction period. It is suitable for conveying steam or other mediums at pressures below 2.5MPa and temperatures below 350°C. The product, with a steel pipe as the outer protective layer, boasts high strength, resistance to damage, easy construction and maintenance, and a long service life. Polyurethane insulated steel pipes are used on medium and small-diameter hot oil transport pipelines or heating pipelines to reduce heat loss to the soil by adding an insulating composite layer to the exterior of the pipe. The commonly used insulating material is rigid polyurethane foam plastic, suitable for temperatures ranging from -185°C to 120°C. This material is soft in texture, and to enhance its strength, a layer of high-density polyethylene is applied externally to the insulating layer, forming a composite material structure to prevent groundwater from seeping into the insulation layer. The outer surface of the steel pipe is treated with shot blasting for rust removal and the inner surface of the protective tube is treated with corona discharge using high-pressure polyurethane foaming equipment to improve the adhesion performance of the insulating pipe. The insulating layer material is a rigid polyurethane foam with a density of 60kg/m3 to 80kg/m3, which fully fills the gap between the steel pipe and the casing, and has a certain degree of adhesion strength, forming a firm integrated structure among the steel pipe, outer casing, and insulating layer. Polyurethane foam has good mechanical and insulating properties, and can typically withstand temperatures of 120°C. Through modification or combination with other insulating materials, it can withstand temperatures up to 180°C.
Pre-fabricated polyurethane insulated steel pipes are structured in three layers from the inside out:
One Layer: Working Pipe Layer - Generally, seamless steel pipes, spiral steel pipes, and straight seam steel pipes are selected according to design and customer requirements. The surface of the steel pipes has been treated with advanced shot blasting rust removal technology, achieving a rust removal grade of Sa2 as per GB/T8923-1988 standard and a surface roughness of R=12.5 micrometers as per GB6060.5-88 standard.
Second Layer: Polyurethane Insulation Layer: Made by injecting the raw liquid of rigid polyurethane foam plastic into the cavity between the steel pipe and the outer sheath with a high-pressure foam machine in one go, commonly known as "foamed-in-place pipe-in-pipe".
Three Layers: High-density polyethylene protective layer - Pre-fabricated black or yellow polyethylene plastic pipes with specified wall thickness. Polyethylene is odorless, non-toxic, feels like wax, and has excellent low-temperature resistance, with a low operating temperature of -70 to -100°C. It has good chemical stability, can withstand the erosion of most acids and bases (not resistant to oxidizing acids), is not soluble in general solvents at room temperature, has low water absorption, but can slowly dissolve in certain organic solvents due to its linear molecular structure without swelling, and has excellent electrical insulation properties. Its functions include protecting the polyurethane insulation layer from mechanical damage and providing corrosion and water resistance.
High-Density Polyethylene Polyurethane Foam Insulated Steel Pipe complies with standards SY/T114-2000 and SY/T115-2001.
Advantages and characteristics of polyurethane insulated steel pipes:
1. Cost Reduction: According to calculations by relevant departments, polyurethane-insulated steel pipes typically reduce construction costs by around 25% (when using glass fiber as the protective layer) and 10% (when using high-density polyethylene as the protective layer). 2. Low Heat Loss, Energy Savings: The thermal conductivity of polyurethane is: λ = 0.013–0.03 kcal/m·h·°C, which is significantly lower than that of other commonly used pipe insulation materials, improving insulation effectiveness by 4 to 9 times. Additionally, its water absorption rate is very low, about 0.2 kg/m². The low water absorption rate is due to the closed-cell structure of polyurethane foam, which is around 92%. The low thermal conductivity and low water absorption, combined with the protective layer and the excellent waterproof properties of high-density polyethylene or glass fiber, alter the traditional situation of供热 pipelines being "dressed in wet cotton," greatly reducing overall heat loss in the heating pipelines. The heat loss in the heat network is 2%, much less than the international standard of 10%. 3. Corrosion Resistance, Good Insulation, Long Service Life: The tightly adhered polyurethane rigid foam insulation layer on the outer surface of the steel pipe effectively prevents air and water intrusion, offering excellent corrosion resistance. Moreover, its foam cells are all closed, with very low water absorption. The high-density polyethylene and glass fiber shells also provide good corrosion resistance, insulation, and mechanical properties. As a result, the outer surface of the working steel pipe is less prone to erosion from external air and water. With proper internal water quality management, as indicated by foreign literature, the service life can reach over 50 years, which is 3 to 4 times longer than traditional trench or elevated pipeline installations. Performance Advantages: Pre-fabricated buried steel pipe insulation has several distinct advantages over traditional pipe insulation methods: 1. It does not require the construction of large, extensive trenches; the insulation pipes are simply buried underground, greatly reducing the land occupation for construction, which is beneficial for environmental protection. It also cuts the earthwork by over 50% and reduces the amount of masonry and concrete by 90%. Moreover, the insulation pipe construction and on-site trenching can be done simultaneously, requiring only on-site joints, which can shorten the construction period by over 50%.
2. Excellent thermal insulation performance, with heat loss just 25% of traditional piping materials. Long-term operation can save a substantial amount of energy and significantly reduce energy costs.
3. Highly waterproof and corrosion-resistant, it does not require an auxiliary trench and can be directly buried underground or in water. Construction is simple and quick, with a low overall cost.
4. Excellent corrosion and impact resistance even under low temperatures, allowing direct burial in frozen soil.
5. Life span up to 30-50 years; proper installation and use can significantly reduce pipeline maintenance costs.
6. Equipped with an alarm system that automatically detects pipeline leakage faults, accurately indicates fault locations, and triggers automatic alarms.
