The Classification and Common Processing Methods of Elbows 

Bends are bended by complete sets a set of bending equipment for bending. Bends can be manufactured by the cool simmering and hot pushing two technologies. No matter which kind of machine equipment or pipe, most of them use bends for oil transportation, gas transportation, fluid transportation, bridge construction project, etc. The materials for bends include cast iron, stainless steel, alloy steel, malleable cast iron, carbon steel, non-ferrous metal and plastic.

Classification of bends
Carbon steel bends: ASTM/ASME A234 WPB, WPC
Alloy bends: ASTM/ASME A234 WP 1-WP 12
Stainless steel bends: ASTM/ASME A403
Low temperature steel bends: ASTM/ASME A402 WPL3-WPL 6
High performance steel bends: ASTM/ASME A860 WPHY 42-46-52-60-65-70

The bend can be divided into the long-radius bend and the short-radius bend according to their radius of curvature. The long-radius bend means that its radius of curvature equals 1.5 times the outer diameter of pipes, that is, R=1.5D. The short-radius bend means that its radius of curvature equals the outer diameter of pipes, that is, R=1.0D.(D is the diameter of the bend. R is the radius of curvature.) According to the pressure rating, bends can be divided into 17 kinds, including SCH5s, SCH10s, SCH10, SCH20, SCH30, SCH40s, STD, SCH40, SCH60, SCH80s, XS; SCH80, SCH100, SCH120, SCH140, SCH160, XXS. Among them, the most commonly used bends are the STD and XS bends.

The introduction of five frequent methods of processing bends 
1. The stamping/punching method: Use cores with taper to extend pipe end to the required size and shape on the punch.

2. The bending method: There are three methods which are commonly used. One is called the stretching method. Another is called the stamping method. The third is the rolling method. There are three to four rollers, among which two are fixed rollers and one is the adjustable roller. The finished products of pipe fitting are bent if the distance of fixed rollers is adjusted.

3. The bulging method: One method is to put rubber into pipes, and use the punch for making bends formed. Another method is hydraulic pressure bulging forming. Fill the middle part of pipes with liquid. The pressure of liquid makes bends formed in the needed shape. The production of bellows mostly uses this method.

4. The forging method: Use the swaging machine to extend the end and a part of the pipe to reduce the outer diameter of the pipe fitting. Swaging machines frequently used include the rotation type, the connecting rod type and the roller type.

5. The rolling method: In general, mandrel is not used. It is suitable for round edges inside the thick-wall pipe.