Generally, common welding defects can be divided into four categories:

Weld size does not meet the requirements: such as welding seam super high, super wide, too narrow, high and low difference is too large, weld transition to the base material is not smooth.

Welding surface defects: such as edge biting, welding bulge, concave, overflow, incomplete welding, surface pores, surface cracks, etc.

Internal defects of weld: such as porosity, slag inclusion, cracks, failure to fuse, tungsten inclusion, failure to penetrate double-sided welding, etc.

The performance of welded joints does not meet the requirements: the mechanical properties and corrosion resistance of welded joints are reduced due to overheating, burning and other reasons.

The harm of welding defects to welded components mainly includes the following aspects:

(1) cause stress concentration

The stress distribution in welded joints is very complex. Where there is a sudden change in the cross-section of the structure, the stress distribution is particularly uneven, and the stress value at some points may be many times larger than the average stress value, which is called stress concentration.

There are many reasons for stress concentration, among which the defects in welding seams are one of the most important factors.

There are cracks, incomplete welding and other defects with sharp notches in the weld, so that the weld section is discontinuous, mutation parts, under the action of external forces will produce a great stress concentration.

When the stress exceeds the fracture strength of the metal material at the front of the defect, the material will crack and destroy.

(2) Shorten the service life

For the member under low cycle fatigue load, if the size of the defect in the weld exceeds a certain limit, the defect will continue to expand and grow up after a certain cycle, until the member fracture occurs.

(3) cause brittle crack, endangering safety

Brittle fracture is a kind of low stress fracture, which is a rapid and sudden fracture of structural parts without plastic deformation.

Welding quality has a great influence on the brittle fracture of the product.

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