A weld defect can be defined as an unacceptable defect during welding process. Unacceptable deviations in set technology and design called a weld defect.
Weld defects can occur at any stage of the welding process,
They are easily recognisable in the form of geometric errors. Such weld defects affects both inside and outside metal structures.
Various codes and standards such as BS EN ISO 6520-1, BS EN ISO 5817, BS EN ISO 10042 contains the weld defect tolerance limit.
In case of suspension exceeding these tolerance limits is considered a weld defect. It is important to correctly identify weld defects so that the cause can be determined. Measures are being taken to prevent further occurrences.
Table of Contents
Types of Welding Defects
- Cracks
- Undercut
- Porosity
- Overlap
- Lack of Fusion
- Lack of Penetration
- Spatter
- Distortion
- Arc Strike
- Burn Through
- Convex and Concave Weld
- Excessive Penetration
- Blow Holes
- Shrinkage Cavity
These are the common welding defects. Now wel will discuss about these welding defects in detail:
1. Cracks
Cracks in the welding is one of the most common defect. Cracks can occur due to bad quality weld or change in the temperature. Cracks can occur on the surface of weld or throughout the weld. Cracks reduces the strength of the welding. Cracks should be repaired properly to avoid any hazard.
Three types of cracks are hot cracks, cold cracks and lamellar tearing. Lamellar normally occurs in rolled steel plates.
2. Undercut
Undercuts are very serious welding defects. This types of defects occur in the parent material. As it occurs on parent metal, the object on which welding is performed can be useless.
Welding speed should be low to avoid these types of defects. Material quality should be good.
3. Porosity
Porosity in the welding can occur due to entrapment of gas or air bubbles in the weld metal. Trapped air and gases collapse over the period of time. Trapped gases break the surface of the welding section. To avoid these defects, there should not be trapped gases or air bubble in the welding section.
4. Overlap
Overlap is a welding defect in which welding material overflows on the welding surface of
the parent metal. Overlap should be removed with the correct tool.
5. Lack of Fusion
As the name suggest, lack of fusion is occur due to incomplete fusion between the weld metal with the parent metal. This defects also called as Cold lapping or cold shuts. Normally it occurs on the internal surface.
6. Lack of Penetration
Types type of welding defects occurs due to incomplete penetration. In this defect, welding is done only on the surface of joint. Joint does not penetrate completely.
7. Spatter
In this type of welding defects small globular weld metal droplets scattered during welding process and stuck to the base metal surface.
8. Distortion
Excessive heat in the welding process creates distortion. Thin metal plates are affected by excessive heat in the welding process. Shape of the object is deformed due to heat.
9. Arc Strike
Arc strike is normally occurs due to low concentration of workers. In this defect unwanted arcs are generated near the welding surface. Lots of visible spot occurs due to arc strike. Welding should be done carefully to avoid such mistakes.
10. Burn Through
In this welding defect holes are created in the parent material. High intensity arc penetrate the metal. To avoid such defects, arch intensity should be controlled.
11. Convex and Concave Weld
The primary reason for these types of defects are incorrect speed and high electrode current. These types of defects can be prevented by following the correct welding process with cautious. These defects can be minimised by using optimal welding current and proper electrode size.
12. Excessive Penetration
This type of welding defect occur due to excessive penetration through the joints. Due to high intensity penetration, It creates notches on the weld surface where high stress concentration
takes place.
13. Blow Holes
Blow holes are visible on the surface of weld. In this defect, generated gas during welding can not escape before molten metal solidification. Blow holes are spherical cavities
inside the bead.
14. Shrinkage Cavity
Shrinkage cavity is formed in the solidification process of the weld.