The production process and construction process of polyurethane insulation pipes follow strict industrial standards and on-site engineering specifications. Its core lies in the precision composite and systematic installation of the three-layer structure, ensuring long-term safety and energy efficiency.

Production process

The manufacturing of polyurethane insulation pipes mainly adopts two mature processes: "one-step method" and "two-step method". The two-step method is currently the mainstream, which first prefabricates the outer protective pipe through a high-density polyethylene (HDPE) extruder, and then penetrates the working steel pipe that has undergone Sa2.5 level shot blasting rust removal. The bracket is fixed with galvanized iron wire at intervals of 1.5 meters, and flanges or clamps are installed at both ends for sealing, with reserved injection holes. Then, mix the isocyanate (component A) and polyol (component B) at a ratio of 1:1.05, inject them into the annular cavity through the high-pressure foaming machine, complete the chemical foaming reaction at 20 – 30 ℃, and form a rigid polyurethane foam layer with a closed cell ratio of ≥ 90%. After foaming, it needs to stand and mature for 5 – 10 minutes. After the foam is fully solidified, remove the blocking pieces, put on the sleeve and block the pouring hole. Finally, the density, compressive strength, closed cell rate and air tightness are tested. After passing the test, spray the product logo and enter the finished product area. The one-step method is suitable for small-diameter pipes with DN ≤ 500, which integrates the steel pipe conveyor line with HDPE extrusion and polyurethane pouring synchronously to achieve continuous production. However, it requires extremely high equipment accuracy and correction system, and is prone to eccentricity problems.

Construction process

On site construction is centered around "prefabrication+direct burial". Firstly, the insulation pipes transported to the construction site are inspected for appearance and parameters, and the use of damaged or substandard products is strictly prohibited. The pipeline connection adopts welding method, and the weld seam needs to undergo 100% non-destructive testing. After the welding is completed, the joint insulation treatment is carried out immediately, using heat shrink tape or electric fusion welding process to ensure that the thickness of the insulation layer is not less than that of the main pipeline. Waterproof sealing is done at the joint. Before laying, it is necessary to excavate a trench with a burial depth lower than the frozen soil layer in Linyi area (0.8-1.2m), and lay a 100-200mm fine sand cushion layer at the bottom of the trench. After the pipeline is in place, it is strictly prohibited to use hard objects such as stones and bricks during backfilling. Fine sand or soil that has been sieved must be used and compacted layer by layer to avoid deformation of the outer protective pipe under pressure. After the backfilling is completed, a pressure test shall be conducted: first, water and exhaust shall be filled, and the pressure shall be stabilized for 10 minutes to confirm that there is no leakage. Then, the pressure shall be increased to 1.5 times the working pressure, and a 1kg small hammer shall be used to lightly tap the weld seam to check for water leakage; Reduce the working pressure again and maintain it for 30 minutes. If the pressure drop does not exceed 0.2atm, it is considered qualified. If a leakage alarm line is configured, it needs to be powered on to test whether the signal transmission is normal, and the positioning accuracy should be controlled within ± 1m. After all the processes are completed, construction records, pressure test reports, concealed engineering images and other materials shall be submitted, and can only be delivered after being signed and confirmed by the supervisor.

Regional adaptation and technological evolution

In the Linyi area of Shandong Province, due to the mixture of clay and sandy soil, the groundwater level fluctuates greatly. It is recommended to use high specification insulation pipes with a density of ≥ 70kg/m ³ and a closed cell rate of ≥ 93% to enhance the ability to resist frost heave and soil stress. In recent years, the industry has been promoting green process innovation, such as using water foaming technology to replace traditional fluorine foaming agents and reduce environmental impact; Some enterprises have piloted nano modified polyurethane to reduce the thermal conductivity to below 0.020 W/(m · K); Intelligent sensing integration technology is gradually being applied. By embedding fiber optic temperature and leakage monitoring systems in the insulation layer, real-time perception and fault warning of pipeline operation status can be achieved, significantly improving the level of intelligent operation and maintenance.