Steel-stainless steel composite steel pipes, copper-steel bimetal composite steel pipes, steel-plastic composite pipes, water supply ductile iron pipes... These various pipes are a series of metal pipes active in the outdoor water supply market. In order to facilitate relevant personnel to understand the characteristics of these products, this article introduces the above-mentioned pipes from the perspective of application.
The outdoor metal water supply pipes that are widely used in the market now mainly include steel pipes and water supply ductile iron pipes. Steel pipe
Steel pipes are divided into welded steel pipes and seamless steel pipes. In terms of anti-corrosion performance, it can be divided into protective layer type, unprotected layer type and texture type; according to wall thickness, there are ordinary steel pipes and thickened steel pipes.
Welded steel pipes are divided into spiral seam welded steel pipes and direct welded steel pipes. Spiral seam welded steel pipes are divided into automatic submerged arc welded steel pipes and high frequency welded steel pipes. Direct welded steel pipes are further divided into ordinary direct welded steel pipes and stainless steel welded steel pipes. steel pipe. Seamless steel pipes are divided into hot-rolled pipes and cold-rolled (drawn) pipes according to the manufacturing method, and their accuracy is divided into ordinary and advanced. The maximum nominal diameter of cold-rolled (drawn) pipes is 200 mm, and the maximum nominal diameter of hot-rolled pipes is 600 mm. Seamless steel pipes also include stainless steel seamless steel pipes. Stainless steel seamless steel pipes are divided into two types: hot-rolled, hot-extruded stainless steel seamless steel pipes and cold-rolled (drawn) stainless steel seamless steel pipes.
Unprotected steel pipes were usually called ungalvanized steel pipes (black iron pipes) in the past. Textured steel pipes mainly refer to stainless steel seamless steel pipes and stainless steel welded steel pipes. They have not been widely used in large and medium-sized outdoor water supply pipes due to cost, connection and other reasons.
The protective layer type (mainly refers to the inner wall of the pipe) now includes metal protective layer type and non-metallic protective layer type. The commonly used metal protective layer types include surface coating protective layer type and surface lamination protective layer type. . The most common type of surface coating protective layer is galvanized pipes. Galvanized pipes also include cold-dip galvanized pipes and hot-dip galvanized pipes. Hot-dip galvanized pipes are still widely used because of their dense and uniform protective layer, strong adhesion, and relatively good stability. . However, due to the insufficient density and uniformity of the protective layer and poor stability of the cold galvanized pipe, the service life of cold galvanized pipes is generally less than 5 years before rusting, resulting in "red water" and "black water", a serious iron smell, and various harmful bacteria exceeding the national drinking water level. According to water quality standards, use in domestic water supply pipelines has been banned in various places. According to different production processes, the surface lamination protective layer type can also be divided into physical covering composite steel pipes and chemical blasting covered composite steel pipes. Among them, the physical covering composite steel pipes currently produced include steel-stainless steel composite steel pipes and copper-steel bimetallic composite steel pipes. , both use physical methods to press the heated and softened thin-walled stainless steel pipes or cold thin-walled copper pipes onto the inner wall of the steel-based pipe through a certain process. The specifications of these two pipes are DNl5-DN300 and DNl5-DNl50 respectively. Physically covered composite steel pipe pipe connections are often connected with special accessories. Chemical blasting covered composite steel pipes include bimetal composite pipes.
Non-metallic protective layer types include non-metallic coating types and non-metallic lining types, "Technical Regulations for Steel-Plastic Composite Pipe Engineering for Building Water Supply" (CECSl25: 2001) (referred to as "Steel-Plastic Technology" Regulations") collectively refer to these two types of steel pipes as steel-plastic composite pipes, and depending on the basic materials to which the steel-plastic composite pipes are attached, they are divided into plastic-coated (lined) plastic welded steel pipes and plastic-coated (lined) plastic seamless steel pipes. According to the different non-metallic materials coated (lining), the current industry standard "Plastic-coated Composite Steel Pipe for Water Supply" (CJ/T120-2000) divides plastic-coated composite pipe for water supply into polyethylene (PE) steel-plastic composite pipe and epoxy resin (EP) steel-plastic composite pipes. Some manufacturers also produce ethylene-acrylic acid polymer (EAA) steel-plastic composite pipes. "Plastic-lined Composite Steel Pipes for Water Supply" (CJ/T136-2001) divides plastic-lined composite pipes for water supply into It is polyethylene (PE), rigid polyvinyl chloride (PVC-U), cross-linked polyethylene (PEX), chlorinated polyvinyl chloride (CPVC) and polypropylene (PP) steel-plastic composite pipes. Manufacturers classify steel-plastic composite pipes into flange type, grooved type and threaded type depending on the pipe connection methods and accessories. According to the heat resistance of the coating (lining) layer, they are divided into steel-plastic composite pipes for hot water and ordinary ones. Use steel-plastic composite pipes for sexual or cold water.
In addition, according to the coating method, it is divided into a combination of external galvanizing and internal coating (grooved water supply steel-plastic composite pipe, threaded water supply steel-plastic composite pipe, etc.) and an internal and external fully coated steel-plastic composite pipe (French water supply steel-plastic composite pipe). Blue type water supply steel-plastic composite pipe). According to the different metal materials of the outer coating, plastic-lined composite steel pipes are divided into external galvanized type, external plastic-coated type and external galvanized aluminum alloy type plastic-lined composite steel pipes (manufacturers also call them alloy steel-plastic composite pipes). In addition, there is also a large category of injection-molded steel pipes. Currently, polypropylene (PP) and polyvinyl chloride (PVC) water supply steel pipes are known, but they are not confirmed in the "Steel-Plastic Technical Regulations". Steel-plastic composite pipe is a relatively good anti-corrosion pipe. Currently, the larger pipe diameters range from DN125 to DN300. Its use in water supply in large and medium-sized outdoor pipes is subject to certain limitations.
Welded steel pipes and galvanized welded steel pipes for low-pressure fluid transportation also have differences between ordinary steel pipes and thickened steel pipes. For welded steel pipes, the thickening of the pipe wall will increase its pressure-bearing capacity, but compared with seamless steel pipes, the cost is still among the low-cost steel pipes. The wall thickness of seamless steel pipes varies in pressure due to various grades and materials.
We know that steel pipes have the best mechanical strength and can withstand high internal and external pressures. The weldability of the pipe body is conducive to the manufacture of various pipe fittings, especially for pipelines with complex terrain and high requirements. . Ease of corrosion is its biggest disadvantage. However, if the internal and external protection of steel pipes is properly handled, the service life is also very long. According to reports, a 1-meter-diameter pipe in Shanghai Yangshupu Water Plant has been used for 60 years and is still in good condition.
At present, steel pipes with socket welding interfaces have been widely used abroad. It is the second generation product of traditional steel pipes. It changes the butt weld interface of traditional steel pipes to lap weld interfaces, which improves the quality of the interface welds, reduces stress concentration in the circumferential welds, and avoids pipe explosions and leaks. In 1999, Guangzhou City's Liuwuzhou water transmission project with a daily water supply of 1.2 million cubic meters was the first in China to install nearly 10 kilometers of DN2000-DN2400 socket-type welded interface steel pipes, of which nearly 3 kilometers were river-crossing pipe sections. So far in good condition.
The "expanded socket-type flexible interface steel pipe" obtained the Chinese patent in 2000 has been first used in Guangzhou Water Company. Its performance and advantages are better than the second generation steel pipe, filling the "low-end" market. Cost-effective production of steel flexible interface pipes is a blank at home and abroad. This pipe uses advanced expansion molding technology to expand both ends of the steel pipe into a new pipe shape with sockets. After expansion, the strength and rigidity of the steel pipe are improved. This process uses lower processing costs to obtain a socket-type flexible interface with high molding dimensional accuracy. Expanded flexible socket-type interface steel pipe is the third generation of new advanced steel pipe developed after the "socket-type rigid interface steel pipe". It has the advantages of easy installation, short construction time, safety, etc. Its promotion can effectively improve the quality level of pipelines. .
In pipe sections that require rigid connections such as crossing rivers and overhead, fillet welding can be performed on the overlapping surfaces where the sockets are inserted to obtain high-quality rigid interface connections. Water supply cast iron pipe
Water supply cast iron pipe can withstand large working pressure (0.45~1.00MPa), is corrosion-resistant, and is cheap. The inner wall of the pipe is smoother after being coated with asphalt, so it is widely used in external water supply pipes. But its disadvantages are hard and brittle, heavy, and difficult to construct. The nominal diameter ranges from DN75 to DN1500, and the working pressures include 0.45, 0.75, 1.00MPa, etc.
The joints of cast iron pipes usually include socket type, flange type and flexible interface. Water supply cast iron pipes are divided into two types according to different manufacturing materials: water supply gray cast iron pipes and water supply ductile iron pipes. Compared with water supply gray cast iron pipes, water supply ductile iron pipes have the advantages of high strength, great toughness, good sealing performance, strong corrosion resistance, and convenient installation and construction. They have become an alternative to water supply gray cast iron pipes.
Water supply gray-mouth cast iron pipes were often called water supply cast iron pipes in the past. Water supply gray-mouth cast iron pipes are divided into sand-type centrifugal cast iron straight pipes and continuous cast iron risers according to different casting methods. Sand-type centrifugal cast iron straight pipes are divided into sand-type centrifugal cast iron straight pipes according to wall thickness. Divided into two levels: P and G, continuous cast iron risers are divided into LA according to wall thickness. Level A and B. These have relatively detailed and complete technical information in various design manuals that have been published and used.
Water supply ductile iron pipes are divided into K-type mechanical flexible interface pipes and T-type socket-type flexible interface pipes according to different interface methods. The promotion and application of this kind of pipe was originally hindered by the small number of accessories. Now it has been basically alleviated. There are large manufacturers specializing in the production of accessories for domestic construction. According to the existing data, a comprehensive comparison of the pressure-bearing and corrosion-resistant functions of water supply ductile iron pipes, as well as various costs such as pipe construction, excavation, and maintenance, shows that the pipe diameter selected for actual construction is between DN200 and DN800, and its advantages are more prominent.
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