Sheet Metal · 2022年8月6日

The application process of the clamp type joint of the fire pipe

Traditional fire-fighting pipeline connection methods (wire connection, welding) gradually exposed some shortcomings in engineering applications over time. A new type of fire-fighting piping interface, a clamp-type interface, has been applied in developed cities such as Beijing, Tianjin, and Shanghai. Its operation method is simple (using rolling or cutting method to slot in the factory or on-site), and easy to disassemble and repair. Because this process is not widely used in China, it has not been generally accepted by engineering and management personnel. The author compared the traditional fire management connection method and the clamp-type interface from the aspects of construction technology, engineering practice, installation cost, etc., and believes that the hoop-type connection is quick to install, easy to disassemble, and durable, and it can make the overall cost in the long run. Reducing it to a minimum is a fire-fighting pipe connection method that should be vigorously promoted and applied. 1. The evolution of the fire-fighting pipeline interface form. The fire-fighting pipe with a pipe diameter ≥ DN100 used a threaded interface in the past, which was very difficult to construct. This is due to the large pipe diameter and the shallow thread at the pipe interface, the connection is not firm, and it is easy to leak. But the thread is deep, the pipe wall at the interface thread is too thin, it is difficult to withstand the working pressure of the system, and it is easy to break. That is to say, the old fire protection design code requires that the pipe behind the alarm valve, regardless of the pipe diameter, requires the use of threaded connections. This is the main reason why this code needs to be revised. So, what solutions have always been used in later engineering practice? l. Pipes with diameters less than DN100 use threaded joints, pipes with diameters ≥ DN100 use welding or flange joints, and the inner wall of the pipe near the weld is not Then carry out anti-corrosion treatment. 2. The pipe diameter <DN100 adopts the wire tie interface, the pipe diameter ≥ DN100 adopts the welding interface, and the second galvanizing treatment is carried out after welding (first use welding installation, number and mark the pipe, then disassemble it and send it to the factory The galvanizing workshop is galvanized, and then installed in the correct seat), which is a mandatory local regulation in Beijing and Shanghai. 3. Pipe diameter< DN100 pipes use threaded connections, and fire-fighting pipes with a pipe diameter ≥ DN100 use clamp-type connectors. 2. Analysis of the pros and cons of several approaches 1. For the first approach mentioned above, as time goes by, more and more problems are exposed, and the problems become more and more serious. Because in the welding process, the high temperature destroys the galvanized layer near the pipe joints, iron and zinc form a potential difference to produce electrochemical corrosion, which shortens the life of the system, and the iron oxide on the inner wall of the pipe falls off during the operation of the system. Blocked the pipes and nozzles, affecting the normal use of the entire system. Project example: In a fire on the first floor of Shenzhen Science Museum this year, the sprinkler nozzle of the sprinkler system was opened by the high-temperature smoke of the fire, but no water flowed out. After the nozzle was removed, only a little yellow water flowed out. . Experts’ on-site investigation, discussion and analysis concluded that the fire tract was rusted near the welding joints, and iron oxide falling off the pipe blocked the pipes and sprinklers. This was the main reason for the failure of the fire extinguishing. The fire piping system of the Science Museum was no longer normal. Run, all should be replaced. The fire-fighting systems in buildings in many cities in China that use welding have the above-mentioned problems to varying degrees. Therefore, the first method is not acceptable, and it is also not allowed by the fire protection design code and the national standard. 2. Although the second method can guarantee the quality of the project, it has a high cost and a long construction period, and has fallen behind. Beijing, Shanghai and other places do not do it. 3. The third method is the clamp type interface, which should be said to be the best method at present. In the mid-1990s, some developed cities in China had more than one hundred buildings, especially large and important buildings, which introduced national clamp-type (groove) connectors. This kind of connector has a history of more than 70 years of production and application abroad, and is widely used in fire fighting systems, domestic water supply systems, and air conditioning systems. Its advantages are: simple installation, short construction period, safety and reliability, life exceeding the pipe itself can reach more than 30 years, management and maintenance are also convenient, the sealing rubber ring is corrosion-resistant, aging-resistant and has shock isolation performance. Third, the use of clamp-type connectors in some important domestic projects This kind of clamp connector has been introduced and used in Beijing, Tianjin, Shanghai, Shenzhen, Nanjing, Xiamen, Chengdu and other cities since the mid-1990s. It has been widely used in fire fighting systems, domestic water supply systems, hot water systems, Air Conditioning System. Some developers in our institute have conducted field investigations on the use of clamp connections in the fire protection systems of some important domestic projects, such as: Hong Kong New Airport, July 1st Return Memorial, Shanghai Pudong International Airport, Jin Mao Tower, Beijing Airport, Lufthansa Center, Guangzhou CITIC Plaza, International Electronics Building, IBM Shenzhen factory in Shenzhen, Window of the World, Baoan Stadium, Youth Palace, Happy Valley Phase II, Wenzhou Convention and Exhibition Center and other buildings all use this kind of interface in fire protection projects. 4. Economic comparison with other fire pipe connection methods
 Simple and fast 5. Clamp type connection urgently needs to be widely promoted and applied in the country. For many years, some engineers have been accustomed to fire pipe welding, which is simple in construction and low in initial cost. However, the fire protection project is a century-old project, and it is impossible to sit back and relax after completing the installation in one go. The previous article has given examples to illustrate the safety hazards of fire pipe welding. We need to strengthen management in terms of design, quality inspection, and fire protection acceptance, and resolutely put an end to the phenomenon of fire pipe welding. Compared with the flange connection, the initial cost of the clamp connection is 20-30% lower than that of the flange connection, the service life is longer than that of the flange connection, and the installation and maintenance are simple and quick. Its economic and technical advantages are obvious. Especially after several years of development, the domestic production technology of clamp-type connectors has been greatly improved. However, due to the influence of many years of traditional concepts, or due to insufficient understanding of domestic and foreign projects that have used clamp connections and achieved good results, some project managers in most areas of the country are not very accepting of this new type of connector. . As a designer, you should choose new products with high quality, safety and reasonable price to make them better popularized and applied. 6. Cautions for the selection of clamp-type connectors 1. The materials of clamp-type connectors are forged steel and ductile cast, and their pressure resistance is different. A reasonable selection should be made according to the actual needs of the project. 2. When inspecting clamp-type connectors, strictly inspect the ovality of the clamp, the fire resistance of the sealing ring and the anti-corrosion performance of the screw. 7. Concluding remarks The pipeline interface, seemingly a small problem, is actually a key problem of the entire system. If it is not done properly, it will affect the normal operation and use of the entire system and must be treated with caution. This issue has attracted great attention from relevant state departments. “Specifications for the Design of Automatic Sprinkler Systems” GBJ84.85 (Revised in 1999) Article 8.0.3, Article 8.0.4 emphasizes: “The alarm valve should be connected by threaded, flange or grooved connection. Part (clamp) connection”, “The pipes with a diameter equal to or greater than 100MM in the system shall be connected in sections by flange or grooved connection (clamp)”. It is imperative to implement the above-mentioned new regulations.

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