The structure and selection of steel pipe fittings

l Foreword Pipe fittings are often used when changing the direction, elevation, or diameter of the pipe system, as well as the branch pipe from the main pipe. Pipe fittings refer to the parts used for pipeline connection composed of one or several parts, which is a kind of pipeline components. Its main functions are:

(1) connection of straight pipes

(2) changing the direction of the pipeline (fluid direction);

(3) diversion or collection of fluids;

(4) connection of pipes with different diameters;

(5) pipe ends Closed;

(6) Mounting support for instruments, valves, etc.;

(7) Relieve pipeline expansion and contraction, etc.;

(8 Hinge or rotation of pipes. From the material, pipe fittings can be roughly divided into metal pipe fittings and non-golden shoulder pipe fittings .Non-metal pipe fittings are generally used in specific corrosive environments. Most of the piping engineering uses metal pipe fittings. Metal pipe fittings include steel, cast iron and non-ferrous metal pipe fittings, of which steel metal pipe fittings are the most used. The following is an introduction to the types of steel metal pipe fittings in industrial pipelines and the points of attention when selecting them. 2 Types With the development of the petrochemical industry, engineering construction tends to be large and complex, and the pipe fittings used in piping engineering are based on There are many different working conditions. Among them, the pipe fittings used for changing the direction of the pipe, the branch of the pipe or the pipe connection of different sizes, the use environment is far more severe than the straight pipe. The materials used for the pipe fittings can be pipes, plates, Forgings, castings, bars and profiles, etc., can be processed by welding, stamping, casting or forging. Generally, the material and thickness of pipe fittings depend on the pipe fitting material, shape, size, and the fluid medium being transported. Pressure and other factors. The pipe fittings are classified according to their purpose and purpose, as shown in Table 1. Four-way, oblique, half-pipe joints, supporting seals, reducers, reducers, reducers, reducer joints, pipe end closed caps, blind plates (commercial law!), pipe plugs, and other short heads Pipes, flanges, threaded nipples, reinforced pipe joints (BOSS), etc.

(1) Elbows and miter elbows are often used in the bend of the pipeline to change the direction of the pipeline. Commonly used are 45 “elbows and 90″ Elbows. The bending radius is about 1.0 times the outer diameter of the pipe is called a short radius elbow. The bending radius is about 1.5 times the outer diameter of the pipe is called a long radius elbow. In the piping system layout, generally choose the long radius Elbow connection. Short-radius elbows are usually used in places where the installation position of the pipe system is relatively compact or in order to reduce costs. When short-radius elbows are used, the maximum working pressure should generally not exceed 0.8 times that of long-radius elbows of the same specification. Miter elbows are usually used for low pressure (design pressure s 2.0MPa), water and similar fluid medium conditions are relatively gentle on large-size pipes. When the single-section variable direction angle of the miter elbow is greater than 45”, it is not suitable Toxic and combustible media pipelines, or pipelines that are subject to vibration, pressure pulsation, and alternating loads due to temperature changes.

(2) Reducer joints and reducer short reducer joints are straight lines for two pipes of different sizes It is a pipe fitting that realizes pipe diameter reduction. There are concentric reducing joints and eccentric reducing joints. The center lines of the two pipes connected by concentric reducing joints are in a straight line, which is mainly used for vertical pipelines. There are more eccentric reducing joints Ground is used in horizontal pipelines. With straight side section reducer, GB12459 (DN20 x 15～500～300), made of seamless steel pipes; without straight-side reducing joints, GB/TI. MOI (DN350×300～1200×1000). Manufactured from steel plate or steel belt. usually. Reducing joints for large-diameter pipe connections are made of steel plates or steel belts, which are inexpensive and economical, but they do not have straight-side reducing joints. The alignment of the welding groove is more difficult than that of the reducer with straight side section, in small diameter pipes (below DN50). It is also often used to replace reducing joints for reducing pipe diameters. Reducing pup joints also have concentricity and eccentricity.

(3) Branch pipe connection pipe The function of branch pipe connection pipe fitting is to lead the branch pipe from the main pipe, including two-way, four-way, branch pipe stand, half pipe joint, etc. ll Tee is used for the connection between the main pipe and the branch pipe, usually there are equal diameter tee, reducing tee and oblique tee. Diagonal three-way is usually used instead of three-way to transport solid particles or more serious erosion and corrosion pipelines (bJ socket welding connection (c1 threaded connection Figure 1 pipe stand 2) four-way is used at the intersection of the main pipe and the branch pipe to realize the pipeline is divided into Four-way. Because of the poor versatility in the installation and production process, it is rarely used in actual projects.

3) The branch pipe station is often used in occasions where the operating pressure is high and the diameter of the three-way is outside the scope of the reduction. Because the branch pipe station adopts an overall strengthened structure. Reliable strength and widely used It is connected with the main pipe by fillet welding. It can be butt welded, socket welded and threaded connection with the branch pipe. There is no corresponding pipe fitting standard in our country. The well-known enterprise standard is like BONNEY FORGE. See Figure 14 for its structure.) Half pipe joints are usually used to connect pipes with branch pipe sizes below DN50 and are welded to the main pipe. Connect with branch pipe by socket welding or threaded connection. .

5) The function of the reinforced pipe joint is the same as that of the branch pipe stand and the half pipe joint. Used for branch connection of small diameter pipes (below DN50). Except for the welding groove on the connecting side with the main pipe, the shape of the other parts is the same as that of the half pipe joint.

6) Plug-in pipe fittings (SWEE L), as shown in Figure 12, are also pipe fittings used for pipeline branching, which can be used as a substitute for the tee. Compared with Yuntong, the plug-in pipe fittings have fewer welds and adopt butt welded connections, which can be photographed and inspected, and the quality can be guaranteed. my country has also voted for the corresponding pipe fitting standards. At present, there are not many 7l pipe fittings with extrusion molding interface (EXTRUDED ourr[E~l”HEADER), as shown in Figure

3. On a section of main pipe, multiple branch pipe connections are processed by extrusion molding method at certain intervals , Compared with branch pipe welding connection and tee, branch pipe stand, etc., the welding seam is less. The workload is small and the pipe fittings are of good quality. At present, there is no corresponding pipe fitting standard in China. It can be selected according to the enterprise standard of the manufacturer. Tee connections are often used. If the branch exceeds the reduced diameter range of the tee, especially for small-caliber branch pipes, they are often replaced by branch pipe joints, half pipe joints, reinforced pipe joints and other branch connection pipe fittings.

(4) Pipe joints are used for instruments or /]’, straight line connection of lzl diameter pipes (below DN50). The connection forms are socket welding or threaded connection.

(5) It is mainly used for small diameter low-pressure pipelines, used for parts that need to be frequently assembled and disassembled, or as Use threaded pipe fittings for the final adjustment of the pipeline. The structure should be metal surface contact seal (schematic diagram 4(a)), and the structure of gasket seal (schematic diagram 4(b)) is usually used to transport water, oil, air, etc. Generally, the pipeline is made of malleable cast iron. In addition, the use requirements and price are also factors considered when selecting.

(6) Pipe caps are used for pipe fittings with closed ends of the pipe. Blind flanges are often used for the same purpose to facilitate Purge and cleaning of pipes. Generally, pipe caps or blind flanges are used in accordance with the requirements of the pipe connection size and considering the economic efficiency or the possibility of future expansion in the project. The connection forms of the pipe caps are threaded, bearing Insert and butt welding connection.

(7) (Internal and external) short thread is used to adjust the diameter of the large / l, o inner and surface processing threads, mostly used for upper and lower drainage pipes, sanitary pipes and other pipelines

3 The connection of the pipe fittings is based on the required performance of the pipe connection