Hazards of Welding Defects to Welded Components

1.Cause stress concentration

The stress distribution in the welded joint is complex and uneven. The stress value at some points is much larger than the average stress value, which is called stress concentration. There are many reasons for stress concentration. The existence of process defects in the weld is one of the more important factors.

Cracks, incomplete penetration and other defects in the weld make the section discontinuous and produce large stress concentration under the action of external force. When the stress exceeds the fracture strength of the metal material at the front of the defect, the material will crack and damage.

2.Shorten service life

If the defect size exceeds a certain limit, after multiple cycles, the defect will expand until the component breaks.

3.Cause embrittlement

It is the rapid and sudden fracture of structural parts without plastic deformation. The welding quality has a great impact on the brittle fracture of products.

Welding defect

1.Welding deformation

The workpiece usually deforms after welding. If the deformation exceeds the allowable value, it will affect the use. The main reason is that the local heating and cooling of the weldment are uneven. Because the weldment is only heated to high temperature in the local area, the closer it is to the weld, the higher the temperature. Because the metal in the heating area is blocked by the metal with low surrounding temperature, it cannot expand. During cooling, the restraint of the surrounding metal cannot shrink freely, Therefore, this part of the heated metal has tensile stress, while other parts of the metal have balanced compressive stress. When the stress exceeds the metal yield pole, it will deform, and when it exceeds the metal strength limit, it will lead to cracks.

2.External defects of welds

(1) Excessive weld reinforcement

This phenomenon occurs when the welding groove is too small or the current is too small. In order to improve the fatigue life of pressure vessels, it is necessary to strengthen the high leveling of welds.

(2) The weld is too concave

The strength of the joint is reduced due to the reduction of the working section of the weld.

(3) Weld undercut

The depression formed along the weld edge on the workpiece is called undercut, which not only reduces the working section of the joint, but also causes serious stress concentration at the undercut.

(4) Weld bead

The molten metal flows to the unmelted workpiece and accumulates to form a weld bead. The weld bead has no effect on the static load strength, but it will cause stress concentration and reduce the dynamic load strength.

(5) Burn through

It means that part of the molten metal leaks out from the reverse side of the weld, reducing the strength of the joint.