Pipe Fittings Applications and Categories

In the piping system pipe fitting plays a role of changing direction, diameter or elevation and closing the tube. In petrochemical plant, pipe has various kinds with many shapes and complex system; therefore, the category, material and amount of pipe fittings used are large. The standardization of nonmetallic and lining pipe fittings is lower than steel pipe fittings, so you should pay attention to the difference of manufacturing process, size, and performances. This article mainly introduces the steel pipe fittings.

 

Application and Category

It can be classified into Butt Welded Pipe Fitting, Socket Welding Pipe Fitting, Threaded Pipe Fitting, Flanged Pipe Fitting and other fittings. The first three ones are usually applied to pressure pipeline, while flanged one is always used in some special environment and has small application range.

 

1. Butt Welded Pipe Fitting

It is usually used in pipeline whose DN is larger than 50mm, which is widely applied to inflammable, combustible and high temperature medium pipeline. Butt welded has reliable connection, convenient construction, cheap price, no leakage and other advantages.

 

Common butt welded pipe fittings are elbow, tee, reducer and cap. The first three kinds are used in seamless steel pipeline or welded one according to push, press and other process. The last one 

adopts stamping by steel plate. All of them achieve the same strength with pipes, while its local stress concentration needs to be done by manufacturers. They design its strength and test it.

 

1) Pipe Elbow

Long Radius Elbow (R＝1.5DN): Usually preferentially adopting;

Short Radius Elbow (R＝1.0DN): It is usually used in size-limited situation. 

Bend (R＝nDN): It is applied to alleviate the washing and kinetic energy of medium at the turning. 

 

According to processing methods, it has pushing elbow, pressing elbow and welded miter elbow:

Pushing and pressing elbow: applying to small-to-medium-size pipeline which is strict about medium.

Welded miter elbow: it requires that bending radius should be 1.5 times less than its diameter. When its angle is more than 450 degrees, it is not suitable for toxic or combustible medium pipeline, or the pipeline produces alternating load due to mechanical vibration, pressure fluctuation and temperature variation.

 

2) Pipe Tee

It has straight tee, reducing tee and Y-shape tee, which is used to pipelines transmitting solid particle or being seriously erosion.

 

3) Pipe Reducer: Concentric Reducer and Eccentric Reducer

 

4) Pipe Cap: flat cap and elliptical cap.

Flat cap can be easily produced and its price is low. But its loading capacity is inferior to elliptical one, therefore, it is usually applied to the conditions when the DN is under 100 and medium pressure is less than 1.0MPa. The ratio of the diameter axle of elliptical cap is 2:1 and it is the most widely used head. As for pipes and its elements whose DN is less than 40, they seldom choose butt welding due to its thin wall, which will influence welding effect.

 

2. Socket Welding Pipe Fitting

In general, it is used to connect pipelines with thin wall, including elbow, tee, reinforcement tube, reinforcement joint, cap, pipe clamp, and so on. Reducing and thread nipple are socket fittings; elbow, tee, cap, reinforcement tube and others are mouthing fittings. Socket Weld is the connection between the two kinds; therefore, you should consider the combination and structure in applications.

 

3. Threaded Pipe Fitting

1) Common materials are forged steel, cast steel, cast iron and malleable iron, and process pipe of petrochemical plant often uses forged steel type.

 

2) It is mostly used in the connection between pipeline whose DN is less than 40 and its elements. It has Male Screw and Female Screw type. The former one has Threaded Nipple, while the later one has elbow, tee, cap and joint, etc. Due to its low strength joint and poor sealing property, its application is limited to the following conditions:

A. Threaded Pipe Fitting should adopt taper pipe thread;

B. It is not recommended to be used under 45℃ or over 200℃;

C. It is not allowed to use in toxic medium pipeline;

D. When applying to combustible gas pipeline, it should select seal weld to seal.

 

4. Flanged pipe fitting is usually used in special situation, whose practical using amount is small.