How to ensure that the elbow does not deform after welding?

　　Elbow is a kind of pipe fitting commonly used in plumbing installation. It is used to connect pipe bends and change the direction of pipe. Other names: 90 ° elbow, right angle bend, Aier bend, stamping elbow, pressed elbow, machine-made elbow, welded elbow, etc.

　　Elbow welding deformation, elbow welding will generally produce deformation, if the deformation exceeds the allowable value, it will affect the use. The main reason of welding deformation is uneven local heating and cooling of weldments.

　　Because the weldment is only heated to high temperature in local area during welding, the closer to the weld, the higher the temperature, the greater the expansion. However, the metal in the heating area can not expand freely because of the lower temperature of the surrounding metal, and the metal can not shrink freely when it is cooled. As a result, there is tensile stress in this part of the heated metal, while there is a balanced compressive stress in other parts of the metal. When these stresses exceed the yield limit of the metal, welding deformation will occur; when the stress exceeds the strength limit of the metal, cracks will appear.