Pipe Joint

the connection at the ends of pipes that ensures tight sealing and strength. In some cases, pipe joints must also provide for rapid assembly and disassembly or a change in the direction of the line of pipe. The most common types used for general-purpose metal pipes are welded, flanged, threaded, and bell-and-spigot joints.

Welded joints are made between straight sections of pipe of the same diameter by butt-welding the pipe ends. Fittings are welded on where there are bends, branches, or changes in diameter in the line. Flanged joints are used where a line must be disassembled and assembled frequently. They consist of two flanges on the ends of the pipes being connected, a gasket, and fastening studs or bolts with nuts. Welded and flanged joints are used for pipe diameters up to 2,000 mm and internal pressures up to 1,000 meganewtons per m² (MN/m²).

Threaded joints are made with pipes whose ends are threaded on the outside and fittings that have internal threads. With cylindrical threading, a seal is made by winding packing (usually hemp smeared with red lead) around the joint to fill the gaps between the threads on the pipe and the threads on the fitting. With conical threads, a seal is achieved without the packing. Threaded joints are used mainly for pipes having diameters up to 50 mm; with cylindrical threading, such joints are used for pressures up to 2.5 MN/m², and with conical threading, for pressures up to 25 MN/m².

Bell-and-spigot joints are used for pig-iron, ceramic, and concrete pipes that have short flares on one end. The gap between the spigot and bell ends of the connected pipes is sealed with packing material, such as lead, rubber, or cement. The advantages of bell-and-spigot joints include low manufacturing costs and the possibility of shifting the pipes axially. Such joints are used with pipes 50–500 mm in diameter for pressures up to 1 MN/m².

Tubing with diameters less than 10 mm. used in the oil and gasoline lines of motor vehicles, tractors, and other machines at pressures up to 2 MN/m², uses special fittings for connections. The tubing ends may be flared, or spherical or conical unions may be used.

Conical flanged glass pipe is joined by means of flange fittings and clamping bolts. The flange fittings, together with rubber inserts that mate with the surfaces of the pipe flanges, are put on the ends of the pipes, and a rubber or fluorocarbon-plastic gasket is laid in the butt joint between the pipes. Springs are often placed between the nuts of the clamping bolts and the flange fitting in order to reduce the possibility of breaking the pipe.

Quick-release pipe connections feature a collar with special clamps that allow the joint to be separated by the unscrewing of only one bolt. Hinged joints permit one pipe to be turned at angles up to 30° relative to the axis of the other pipe. These joints are usually used for pipe diameters of 25–500 mm and pressures up to 1 MN/m².