Types of Welding Defects-a Closer Look

       

Lamellar tearing: Usually seen in low quality steels, lamellar tearing tends to take place in metals with low ductility, which is typically caused by the inclusion of non-metallic ingredients such as oxides and suphides used during the rolling process. The presence of inclusions showcase that the plate fails to tolerate contraction stresses during the short transverse direction.

Cracking: Caused due to thermal shrinkage, inappropriate procedure, poor design, or because of a combination of strain that accompanies thermal shrinkage and phase change, these defects result in cracking and high residual stresses.

Porosity: Gases trapped inside solidifying weld metals lead to defects attributed to porosity. These usually arise from damp consumables/metals, or dirt (oil or grease) settled on the area of the metal that has to be welded. Storage of all consumables in dry conditions and careful cleaning/degreasing of the metal prior to welding can alleviate the concerns of defects caused due to porosity.

Excess Penetration: These defects arise from too slow transverse/ too high heat inputs of the welding torch (electric or gas). Burning through or excess penetration proves to be a greater problem with thin sheets as higher level of skills are needed for balancing heat inputs and torch traverse while welding the same.

Lack of Fusion: To attain a good quality join it becomes essential to get a fusion zone that extends across the complete thickness of sheets being welded. While thicker materials normally need their edges cut at a V-like angle and require several passes to completely fill the V join with weld metal, thin sheet materials are capable of being joined with a pass, with a clean square edge proving as a satisfactory basis for joining. Lack of fusion resulting from very rapid traverse/ little heat of the welding torch (electric or gas) often leads to defects.

Inclusions: These defects caused due to unsuccessful welding occur when many runs are notched along a V join while joining a thick plate using flux coated or flux cored rods. Additionally, they take place when the slag covering a specific run is not completely removed after each run, and before the run that follows.

Undercutting: Here, the thickness of the welded sheets is decreased at the toe area of the weld because of incorrect procedure/ settings. The presence of stress concentration and any undercut further reduces the strength of the weld.