China's pipeline market demand is growing and growing rapidly. The emergence of this situation is mainly caused by the following reasons: 1. China promotes the needs of energy conservation and environmental protection policies such as “central heating”, “cogeneration” and “triple supply”; 2. Accelerating and modernizing civilized urban construction High requirements for energy conservation and environmental protection; 3. In order to improve the quality of life of the people, the country's heating range extends from the severe “three north” areas (ie North China, Northeast China, Northwest China) to the “transition area” of the vast winter, cold and hot summer. demand. We have made great progress in research, development, application, etc.: In order to meet the rapid development of the direct buried steam pipeline, China's vast number of scientific and technical personnel, manufacturers in the direct buried steam pipeline technology research, development, application, etc., paid A lot of hard work has made great progress. The variety of insulation structure and selection of materials, the scale of engineering practice, no country in the world can compare with us.
Germany, Brugge, Soksam, Italy and the United States and other companies, their general diameter Φ500mm, the amount is not large, and currently China's Shandong Jinan, Hebei Shijiazhuang, Shaanxi Xi'an, Liaoning Dalian, Henan, Jiangsu and Zhejiang and other regions The direct buried steam pipeline has exceeded Φ500mm, and some have reached Φ900mm. The thermal insulation structure has internal sliding and external sliding. The selected high-resistance materials include microporous calcium silicate, glass wool shell, hot pressed perlite, silicon bead insulation material, and composite silicate. Insulation structure type, there are many types of insulation materials. Therefore, in the field of direct buried steam pipeline development and application, China is no less developed than the developed direct buried thermal insulation pipe from the transport medium steel pipe, polyurethane rigid foam plastic insulation layer and glass fiber reinforced plastic outer sheath (glass fiber reinforced plastic) tightly combined. It has good mechanical strength and excellent corrosion resistance. The first layer: working steel pipe layer, according to the design and customer requirements, generally use seamless pipe (GB8163) spiral welded pipe (GB9711; SY/T5038) and straight seam welded pipe (GB3092) . After the surface of the steel pipe is treated by advanced shot blasting and descaling process, the rust removal grade of the steel pipe can reach Sa2 grade in GB8923-standard, and the surface roughness can reach R=12.5 micron in GB6060.5 standard. After the surface of the steel pipe is decontaminated and rusted, a layer of anticorrosive material is applied. The first function is waterproofing, and the other is to improve the bonding surface between the heat insulating layer and the steel pipe to form a whole.
The second layer: a polyurethane insulation layer, which is formed by injecting a rigid polyurethane foam raw liquid into a cavity formed between the steel pipe and the special steel mold by a high-pressure foaming machine. That is commonly known as the "mold foaming process." Whether the polyurethane foam is full or not, there are any quality problems for direct inspection. Its role is to waterproof, but to keep warm, and the third is to support the weight of the heating network. When the temperature of the conveying medium is: -50 °C - 120 °C, the rigid polyurethane foam is used as the insulating layer; when the temperature of the conveying medium is -50 °C - 150 °C, the rigid polyurethane is used. The foam is made of insulation.
Polyurethane direct-buried insulation pipe, also known as "tube-in-pipe", consists of a "two-step process" consisting of a high-density polyethylene outer protective layer, a polyurethane rigid foam plastic pipe and a steel pipe. The insulation 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 bonding strength, so that the steel pipe, the outer casing and the heat insulation layer are between the three. Form a solid whole. Polyurethane direct-buried insulation tube foam has good mechanical properties and thermal insulation properties. Generally, it can withstand temperature of 120 ° C by modification or combination with other insulation materials to withstand temperature of 180 ° C. Outlined to adapt to urban district heating and work.
Polyurethane insulation direct buried pipes have become a relatively mature advanced technology in some developed countries. In the past ten years, China's heating engineering technicians have promoted the development of domestic pipe network technology to a higher level by digesting and absorbing this advanced technology. The practice results in more than ten years have fully proved that the laying method of polyamine cheese insulation direct buried pipe has many advantages compared with the traditional trench and overhead laying. The direct buried heat preservation pipe is made up of a steel pipe conveying medium, a high-density polyethylene outer casing, and a rigid polyurethane foam insulation layer between the steel pipe and the outer casing. This is also the polyamine cheese insulation directly buried pipe in China's heating project.