1, overview
Grooved pipe fitting connection technology, also known as clamp connection technology, is the first technology to connect liquid and gas pipelines at present. Although this technology developed later in China than abroad, it was quickly accepted by the domestic market because of its advanced technology. From 1998 to now, after just a few years of development and application, it has gradually replaced the two traditional pipe connection methods of flange and welding. Not only is the technology more mature and widely recognized by the market, but it has also been actively guided by national laws and policies.
The application of grooved pipe connection technology makes the complicated pipeline connection process simple, fast and convenient. Pipeline connection technology has taken a big step forward.
2. Introduction of grooved pipe fittings
Grooved pipe fittings include two kinds of products: ① Pipe fittings that play the role of connection and sealing include rigid joints, flexible joints, mechanical tees and grooved flanges; (2) The pipe fittings that play the role of connecting transition include elbows, tees, crosses, reducing pipes and blind plates.
The groove connection pipe fittings, which play the role of connection and sealing, are mainly composed of sealing aprons, clamps and locking bolts. Put the rubber sealing ring located in the inner layer on the outer side of the connected pipeline and match with the pre-rolling groove, then fasten the rubber sealing ring with a fixture and then fasten it with two bolts. Because its rubber sealing ring and clamp are designed with unique sealable structure, the grooved connector has good sealing performance, and its sealing performance is enhanced with the increase of fluid pressure in the pipeline.
3. Advantages of grooved pipe connection
3. 1 Very easy to operate.
The connection operation of grooved pipe fittings is very simple, without special professional skills, and ordinary workers can operate after simple training. This is because the product dissolves a lot of fine technical parts into the finished product in a factory way. It only takes a few minutes to connect a pipe fitting, which greatly simplifies the technical difficulty of field operation and saves working hours, thus stabilizing the engineering quality and improving the working efficiency. This is also the general direction of installation technology development.
However, the traditional pipeline connection method of welding and flange connection not only requires welding workers to have corresponding skills, but also takes time, is difficult for workers to operate and is polluted by welding smoke. Due to the differences in operating space and welding skills, it is difficult to achieve satisfactory results in welding quality and appearance, thus affecting the overall quality of the project.
In addition, because the grooved pipe fittings are finished products, the operation space required on site is small, and the installation against the wall and corner can be truly realized, so that the operation difficulty is greatly reduced, the floor space is saved, and the effect of pipeline installation is beautified.
3.2 The original characteristics of the pipeline are not affected.
In the connection of grooved pipe fittings, it is only necessary to extrude a groove on the outer surface of the connected pipe with a grooving machine without destroying the inner wall structure of the pipe, which is the unique technical advantage of grooved pipe fittings connection. If the traditional welding operation is adopted, many pipes with anti-corrosion coating on the inner wall will be destroyed. Therefore, the specification stipulates galvanized pipe, plastic-lined steel pipe, steel-plastic composite pipe and so on. Welding and flange connection are not allowed, otherwise secondary treatment is needed.
3.3 Conducive to construction safety
With the connection technology of grooved pipe fittings, only cutting machine, grooving machine and hand for tightening bolts are needed on site, which is convenient for construction organization. However, welding and flange connection require complicated power cables, cutting tools, electric welding machines and oxygen and acetylene bottles, which brings complexity to the construction organization, as well as potential leakage and fire hazards. At the same time, the welding slag produced by welding and gas cutting inevitably falls into the pipeline, which is easy to block the pipeline valves and even equipment and pollute the water quality in the pipeline.
In addition, welding and flange connection inevitably require long-term high-intensity aerial work, which is also prone to production safety accidents.
3.4 The system has good stability and convenient maintenance.
The connection mode of grooved pipe fittings has unique flexible characteristics, which makes the pipeline have the ability to resist vibration, contraction and expansion. Compared with welding and flange connection, it increases the stability of pipeline system and adapts to temperature changes, thus protecting pipeline valves and reducing the damage of pipeline stress to structural parts.
Because the connection operation of grooved pipe fittings is simple, the required operating space becomes smaller, which brings many convenient conditions for future maintenance. When the pipeline needs to be repaired or replaced, just loosen the two clamps, and a section of pipeline can be replaced, rotated and modified at will. There is no need to destroy the surrounding walls, which reduces the maintenance time and cost.
3.5 Economic analysis
Because the connection operation of grooved pipe fittings is simple, it saves labor and time, so it has good economic benefits. Many articles have done economic analysis, and think that "the comprehensive benefit of the whole pipe network installation is higher than that of the flange connection, although the price of the single accessory of the clamp connection is higher". In comparison, the flange connection is treated as secondary galvanizing (which is also necessary according to the requirements of the specification).
Below, the author excerpts the comparative results of the article "On the Pipe System of Clamp Joints" in the fifth issue of Water Supply and Drainage magazine 200/KLOC-0 for readers' reference. See table 1 for details.
Note: In 2005, the market price of grooved pipe fittings dropped significantly compared with 200 1.
4. Scope of application of grooved pipe connection
As an advanced pipeline connection method, grooved pipe fittings can be laid or buried, that is, there are rigid joints and flexible joints. Therefore, it has a wide range of applications.
① According to the system, it can be used for fire water system, air conditioning hot and cold water system, water supply system, petrochemical pipeline system, thermoelectric and military pipeline system, sewage treatment pipeline system, etc.
② According to the pipe material, it can be used to connect steel pipes, copper pipes, stainless steel pipes, plastic-lined steel pipes, ductile iron pipes, thick-walled plastic pipes, hoses, valves with steel pipe joints and flange joints.
5. Policies and regulations support
Due to the advanced technology and obvious advantages of grooved pipe fittings, the domestic installation market first recognized it, and then many national policies and regulations also affirmed and supported it. It has gradually become the mainstream technology of pipeline connection.
Article 4. 1.3 of Code for Acceptance of Construction Quality of Building Water Supply, Drainage and Heating Engineering (GB50242-2002) stipulates: "Galvanized pipes with a pipe diameter greater than 100mm shall be connected by flanges with clamping sleeves or special fittings, and the welded joints between galvanized steel pipes and flanges shall be galvanized twice". According to Article 4. 1. 1 and Article 4. 1.3 of this specification, "it is applicable to the quality and acceptance of indoor water supply and fire hydrant system pipeline installation works with working pressure not greater than 1.0MPa".
Article 4. 1.3 has three meanings: ① Welded pipes are not allowed for indoor fire fighting pipes and water supply pipes. (2) When the pipe diameter specification is greater than DN 100, flange or ferrule connection should be adopted, and welding mode should be eliminated. (3) When welding and flange connection are adopted, the second galvanizing shall be carried out. The author thinks that it is generally impossible to galvanize twice, which actually cancels the possibility of welding and flange connection.
Article 9. 1.2 of Code for Acceptance of Construction Quality of Ventilation and Air Conditioning Engineering (GB50243-2002) stipulates: "Galvanized steel pipes shall be connected by screws. When the pipe diameter is greater than DN 100, clamps, flanges or welded connections can be used, but the welds and heat-affected surfaces should be treated with anticorrosion. " In fact, the possibility of welding and flange connection is also ruled out.
Article 9. 1.2 lists clamp connection as the first choice for large-diameter pipeline connection. The secondary treatment of flange and welded connection is also stipulated. The specification has been tilted towards the fixture connection technology.
It has become the practice of most designers to use galvanized steel pipes for cold and hot water pipes of air conditioners. The water quality of air conditioning water system plays an important role in the safe and economic operation of the system. Since galvanized steel pipes must be used in fire fighting pipes, there is no reason why galvanized steel pipes should not be used in air conditioning water systems.
Article 5. 1.3 of Code for Construction and Acceptance of Automatic Sprinkler Fire Extinguishing System (GB 50261-96) in 2003 stipulates: "The pipe network shall be installed with thread, grooved pipe joint or flange connection"; Article 5. 1.4A7 stipulates that, when trench pipe joint is used for connection, "the pipeline connection between the buried pipe and the water pump room shall be flexible, and the bolts and nuts of the buried trench pipe joint shall be treated with anti-corrosion." Article 5. 1.5 stipulates: "When flanges are connected, the welded parts of welded flanges shall be galvanized again before connection." The word "should" is used in all provisions here, and the connection mode of grooved pipe joint extends from exposed installation to buried installation.
Article 7.5.2 of National Technical Measures for Civil Building Engineering Design-Water Supply and Drainage Volume (2003 edition) stipulates that when the pipe diameter of fire water supply pipeline system is less than or equal to DN 80 mm, threaded connection is adopted, and when the pipe diameter is greater than DN 80 mm, clamp connection, flange connection or welding can be adopted. Because the clamp connection requires small construction space and easy maintenance, it is a better connection method at present. "
It is not difficult to see from the provisions on clamp connection in the above-mentioned normative documents that with the passage of time, specifications and technical measures are more inclined to clamp connection technology, and the wording has changed from "may" to "should" and from "only open" to "open" or "buried". Its development trend can be roughly seen.
6, market product quality evaluation
Because the connection of grooved pipe fittings involves water supply, fire fighting, petrochemical industry, military industry and other fields, the industry management system is strict. First of all, the product must conform to the industry standard of grooved pipe fittings issued by the Ministry of Construction (CJ/T 156-200 1), and its material should be ductile iron, and meet the requirements of the current national standard "Ductile Iron Castings" (CB/T 1348). Secondly, it must pass the inspection of national fixed fire extinguishing system and refractory quality supervision and inspection center. So as to control the high-quality and orderly development of the government industry.
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