Generation of welding defects and common weld nondestructive testing methods

Date：2022-03-07 14:05:19Views：1030

Overview of welding defects

Definition of welding defects:Imperfections in welded joints are called weld imperfections.

Common welding defects can be divided into four categories:

(1) The weld size does not meet the requirements: for example, the weld is too high, too wide, too narrow, the height difference is too large, and the weld transition to the base metal is not smooth.

(2) Welding surface defects: such as undercut, weld beading, concave, overflow, incomplete penetration, surface pores, surface cracks, etc.

(3) Internal defects of weld: such as pores, slag inclusion, cracks, incomplete fusion, tungsten inclusion, incomplete penetration of double-sided welding, etc.

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

1、 Welding defect

（1） Welding deformation

（2） External defects of welds

1. The weld reinforcement is too high

2. The weld is too concave

3. Weld undercut

4. Weld bead

5. Burn through

（3） Internal defects of welds

1. Incomplete penetration

2. Slag inclusion

3. Air hole

4. Cracks

(1) Thermal crack

(2) Cold crack

Hazards of welding defects:These defects reduce the cross-sectional area of the weld, reduce the bearing capacity, produce stress concentration and reduce the fatigue strength, which is easy to cause the damage or fracture of the weldment. Among them, the most harmful are welding cracks and incomplete fusion.

2、 Common weld nondestructive testing methods

1. Radiographic testing method (RT)

At present, the widely used radiographic inspection method is to use (x γ) After the penetrating radiation emitted by the ray source penetrates the weld, the film is sensitized, and the defect image in the weld is displayed on the processed radiographic film. Defects such as pores, slag inclusion, cracks and incomplete penetration in the weld can be found.

2. Ultrasonic flaw detection (UT)

Ultrasonic flaw detection has the advantages of high sensitivity, flexibility and convenience, short cycle, low cost, high efficiency and no harm to human body, but the display of defects is not intuitive and the judgment of defects is not accurate, which is greatly affected by the experience and technical proficiency of flaw detection personnel.

3. Penetrant testing (PT)

Liquid penetrant flaw detection is mainly used to inspect the groove surface, the groove surface after carbon arc air gouging or weld defect removal, the surface eradicated by tools and fixtures, and the surface opening defects of parts inconvenient for magnetic particle flaw detection.

4. Magnetic flaw detection (MT)

Magnetic flaw detection is mainly used to check surface and near surface defects. Compared with penetrant flaw detection, this method not only has high sensitivity and speed, but also can detect defects at a certain depth on the surface.

Other testing methods include: metallographic analysis of large workpieces; Ferrite content test; Spectral analysis; Portable hardness test; Acoustic emission test, etc.

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