Under normal circumstances, when we use the pipe bending workpiece, we often need to connect it with the corresponding pipe first.  This is mainly to change the direction of the pipe.  At present, we can choose different connection modes to ensure the use.  Therefore, in the actual use, we need to combine the actual situation to choose the appropriate connection mode.  
 

Here are four common ways of joining. The first is to weld directly.  In general, some pressure pipes, such as gas, steam, air and vacuum pipes, can be welded.  If the pipe diameter is large, electric welding should be used;  If the thickness of the bending workpiece is less than 3.5mm, gas welding can be used.  It should be noted that the compensator cannot be welded.  
 
The second common connection is socket welding.  Usually, this type of connection is used for pipe connections that require high tightness.  Therefore, when connecting the elbow workpiece to the pipe, socket welding can be used instead of thread connection, which can make the structure stable, but also has high pressure resistance, and the construction is more convenient.  
 

The third kind is called flange connection, compared with other ways, this kind of connection is mainly applied to some large pipe diameter, sealing requirements of bending workpiece and pipe connection, such as vacuum tube, etc.  Of course, this approach can also meet the requirements of other occasions.  
 
The last one belongs to the thread connection. In practical work, this kind of connection is generally applied to the pipe connection within 50mm in diameter.  In different situations, we need to choose a suitable way for the connection of the elbow workpiece and pipe to ensure the use.