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Thread/Flange/Welding method

A. Threaded Valves: This type of connection is usually made by machining the leading and exit ends of the valve into tapered or straight pipe threads that allow it to be connected to a tapered pipe nipple or pipe. Because of the large leakage channels that can occur with this connection, these channels can be plugged with sealants, sealing tape, or fillers. If the material of the valve body can be welded, but the expansion coefficient is very different, or the working temperature varies in a wide range, the threaded connection must be sealed with honey. Threaded valves are mainly valves that pass nominally under 50mm. If the size of the passage is too large, it is very difficult to install and seal the joint. In order to facilitate the installation and removal of threaded connections, fittings can be used in place in the piping system. Valves with a nominal diameter of less than 50 mm can use pipe sockets as pipe joints, and the threads of the pipe sockets connect the two connected parts together.
B Flange-connected valves: Flanged valves are easy to install and remove. But the valves that are larger than the threaded ones are bulky and the corresponding price is high. So it applies to a variety of diameter and pressure pipeline connections. However, when the temperature exceeds 350 degrees Celsius, the bolts, gaskets, and flanges become slack, which also significantly reduces the load on the bolts, which may cause leakage for flanges that are subjected to strong forces.
C Welded Connection Valves: This type of connection is suitable for all pressures and temperatures and is more reliable than flanged connections when used under heavier loads. However, it is difficult to dismantle and re-install the welded connection valve, so its use is limited to the long-term reliable operation, or the use of conditions, high temperature occasions. Such as thermal power stations, nuclear power projects, ethylene engineering pipeline. Welded valves with nominal diameters below 50mm usually have a welding socket to receive the tube at the load plane end. As the socket welding forms a gap between the socket and the pipe, it may cause the crack to be corroded by certain media, and at the same time, the vibration of the pipe will make the connection part fatigued. Therefore, the use of the socket welding is limited. When the nominal diameter is larger, the conditions of use are higher, and the temperature is higher, the valve body often uses bevels for welding. At the same time, there are original requirements for the welding seam, and a skilled welder must be selected to complete this work.

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