Basic knowledge of pipe fittings


1.Definition of pipe fitting

Pipe fittings refer to the parts and components that together with the steel pipe constitute the pipe system. In the medium transport plays a medium transport, diversion, diversion, change the flow, closure of the role.

2.Classification of pipe fittings

Generally, we call all kinds of fittings except straight pipes in the pipe system as pipe fittings. But customarily, we call elbow, tee, reducer, cap and various pipe joints pipe fittings. At the same time, we called flange, valve, expansion joint, pipe support, etc respectively.

The pipe fitting is mainly subdivided as follows:

2.1 It can be divided into three types according to the connection mode between pipe fitting and straight pipe during construction:

1) Butt welding pipe fittings (BW)

2) Socket pipe fittings (SW)

3) Threaded pipe fittings (TH)

2.2 According to whether there is a weld on the surface of the pipe fitting, it can be divided into two categories:

1) Seamless pipe fittings

2) Welded pipe fittings

carbon steel pipe fittings

3.Nominal diameter and nominal pressure of pipe fitting

3.1 Nominal diameter

The nominal diameter is represented by DN followed by an integer. It is the diameter data stipulated in the national standard, and the calculation basis when selecting pipes, fittings and valves.

Nominal diameter is not the outside diameter of pipe fitting, but a nominal diameter related to the inside diameter and outside diameter. For exampleDN150. The unit "mm" after the number is omitted, and the corresponding pipe outer diameter is 159 in metric system and 168.3 in British system. Therefore, "DN" in the pipe fitting is only a conceptual value and cannot indicate the specific outside diameter of the pipe. Therefore, the number after the letter "DN" does not represent the measured value and cannot be used for the purpose of calculation.

At present, the nominal diameter classification at home and abroad is basically the same. Inch is used in the United States, and mm is used in China. 1inch = 25.4mm.

3.2 Nominal pressure

Nominal pressure refers to the steel pipes or pipe fittings maximum allowable design pressure (working pressure) at 0 ~ 200 ℃ room temperature. P is the pressure sign. There are two ways of representing nominal pressure. One is the European PN system, with the unit of Mpa (bar in the old version of the standard, which is commonly referred to as kilogram force, 1bar 0.1mpa), expressed as pn1.6mpa. The other is the CLASS American system, in psi (pounds per square inch), expressed as the CL600.

3.3 Outer diameter and wall thickness of pipe fitting

3.3.1 Outer diameter of pipe fittings

The outer diameter of pipe fitting is divided into two series, metric system and imperial system (In some standards, also known as A series, B series). The outer diameter is specified in the standard. Outside diameter dimensions not in standard are non - standard dimensions.

3.3.2 Wall thickness of pipe fitting

The method that the wall thickness series of pipe fitting expresses in different standard is different also.

1) A series of wall thickness indicated by the pipe gauge number (Sch).

The number of the Sch pipe is the ratio of the allowable stress of the material under the design pressure and the design temperature multiplied by 1000 and rounded.

The tube number is not the wall thickness, but the wall thickness series. The same pipe diameter, in different pipe gauge its wall thickness varies.

2) American ANSI and MSS method of expressing wall thickness by pipe weight. The wall thickness is divided into three types.

(1) Standard weight steel tube, expressed as STD.

(2) Thickened steel tube, expressed as XS.

(3) Extra thick steel pipe, expressed as XXS.

The pipes of Sch40 DN 250mm are equivalent to STD pipes.

The pipes of Sch80 DN 200mm are equivalent to XS pipes.

Chinese, ISO and some Japanese standards use the wall thickness dimension to indicate the wall thickness series. 3, 3.5, 4, 4.5, 5, 5.5, 6mm etc.