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2019

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Four connection methods of stainless steel valves

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Stainless steel valves are now used in chemical industry, papermaking, mining, petrochemical, petroleum, electric power, liquefied gas, food, pharmaceuticals, water supply and drainage, municipal administration, mechanical equipment supporting, electronic industry, urban construction and other fields. Valves are control components in pipeline fluid transportation systems. Stainless steel valves are used to change the passage section and the flow direction of the medium. They have the functions of diversion, regulation, check, throttling, cut-off, diverting or overflow pressure relief.

 

Stainless steel valves are now used in chemical industry, papermaking, mining, petrochemical, petroleum, electric power, liquefied gas, food, pharmaceuticals, water supply and drainage, municipal administration, mechanical equipment supporting, electronic industry, urban construction and other fields. Valves are control components in pipeline fluid transportation systems. Stainless steel valves are used to change the passage section and the flow direction of the medium. They have the functions of diversion, regulation, check, throttling, cut-off, diverting or overflow pressure relief.

   The connection work of the end face of stainless steel valves is the basic work that the staff must master. There are mainly four connection methods:

  1. Flange connection

    The connection is achieved with the help of flanges, gaskets and bolts. Flange-connected valves are very convenient to install and disassemble. It is suitable for a wide range of nominal diameters and pressures. The flange connected to the valve can be divided into flat welding flange, butt welding flange, socket welding flange, integrated flange, etc.; according to the sealing surface form, it can be divided into full plane flange, raised table flange, Concave and convex face flanges, grooved and grooved face flanges and ring and grooved face flanges. The selection of various flange structural forms and sealing surface forms depends on different operating conditions. Generally speaking, flat welding flanges are mostly used under relatively mild operating conditions due to their low structural strength and rigidity, such as low-pressure circulating water valves, general low-pressure compressed air valves, etc. Their advantages are low price and easy installation. convenient. The neck and tapered transition structure, strength and rigidity of the butt welding flange are relatively good, and it can be connected with the pipe for non-destructive testing, so it can be used in occasions with harsh working conditions, such as oil, gas and chemical media. Socket welding structure is commonly used in pipelines with PN≤10.0MPa and DN≤40. The sealing surface of the valve is also selected based on its operating conditions. The full-plane structure is often used with the flat welding structure. When the conditions are relatively mild, the boss surface is often used with the butt welding and socket welding structures, which are widely used. . The convex and concave surfaces are often used with butt welding and socket structures. The use of grooved and tenon surfaces is similar to that of convex and concave structures. The ring and groove surface structures are often used with butt welding structures.

     

  2. Threaded connection

    Threaded connections are detachable connections and are often used in situations where welding is not suitable or disassembly is required. Threaded connections are divided into internal threaded connections and external threaded connections. For internal thread connections, the end of the valve body is usually processed into a tapered or straight female thread, and the pipe connected to it is processed into a tapered or straight male thread. External thread connection is a valve whose end of the valve body is processed into a male thread to facilitate the installation and removal of the threaded end. Compared with the welding connection method, the threaded connection of the valve has low strength and strong sealing. When used in petrochemical equipment, it is often restricted by the following conditions:

    Mostly used in pipelines with DN≤40;

    Threaded pipe fittings should use tapered pipe threads;

    Stainless steel valves with threaded connections must not be used for the management of highly toxic media;

    Threaded connection valves are not recommended for use when the medium temperature is above 200°C and below -45°C;

    Threaded connection valves are not recommended for use in locations where stress corrosion, crevice corrosion, or variable loads may occur due to vibration, pressure pulsation, and temperature changes;

    When threaded connection valves are used on combustible gas pipelines, seal welding should be used for sealing.

     

  3. Solder connection

    Valves using this connection method are suitable for various pressures and temperatures, and are more reliable than flange connections when used under heavier conditions. However, it is difficult to disassemble and maintain welded valves, so its use is limited to situations where it can usually operate reliably for a long time, or where the operating conditions are severe and the temperature is high. Welded valves with nominal diameters below 50mm are usually connected by socket welding. Since socket welding forms a gap between the socket and the pipe, the gap may be corroded by certain media. At the same time, the vibration of the pipe will fatigue the connection part, so the use of socket welding is subject to certain restrictions.

  4. Internal self-tightening connection

    It is a self-tightening connection using medium pressure. Its sealing ring is installed on the inner cone at a certain angle with the side facing the medium. The medium pressure is transmitted to the inner cone and then to the sealing ring. On the cone surface at a certain angle On the valve body, two component forces are generated, one is parallel to the center line of the valve body and outward, and the other is pressed against the inner wall of the valve body. This latter component is the self-tightening force. The greater the medium pressure, the greater the self-tightening force. Therefore, this connection form is suitable for high-pressure valves.

    There are many other connection forms for stainless steel valves. Different types of valves use different connection methods, depending on the actual situation.