Short Answer:

Welding defects are the irregularities or imperfections that occur in a welded joint, which reduce its strength, appearance, and performance. These defects may develop due to poor welding technique, incorrect current setting, improper cleaning, or unsuitable materials.

Common welding defects include cracks, porosity, slag inclusion, undercut, lack of fusion, and incomplete penetration. These defects weaken the weld joint and can lead to failure during operation if not properly inspected and repaired. Therefore, careful welding procedures and inspection methods are essential to ensure defect-free welds.

Detailed Explanation :

Common Welding Defects

Welding defects are unwanted imperfections or irregularities that occur in a welded joint, making it weaker or unsafe for use. These defects can occur either on the surface of the weld or inside the weld metal. They reduce the strength, durability, and appearance of the welded structure. In mechanical and structural applications, such defects can cause leakage, fracture, or even total failure under load.

Defects in welding are generally caused by poor welding technique, incorrect selection of welding parameters, contamination of base metal, or improper preparation before welding. To ensure the quality and reliability of welds, it is important to understand the types, causes, and prevention of these common welding defects.

Cracks

Cracks are one of the most dangerous welding defects because they can easily propagate and lead to failure. They may appear on the surface, within the weld, or in the heat-affected zone (HAZ).

Types of cracks:
- Hot cracks: Occur at high temperature during solidification.
- Cold cracks: Form after the weld has cooled, often due to residual stress.
- Crater cracks: Form at the end of a weld bead when the arc is stopped suddenly.
Causes: Improper cooling rate, high residual stress, wrong filler material, or contamination.
Prevention: Proper preheating, controlled cooling, and use of correct welding parameters.

Porosity

Porosity refers to small gas pockets or voids trapped inside the weld metal. These appear like tiny holes or bubbles and weaken the weld joint.

Causes: Contaminated surface, moisture, rust, or improper shielding gas.
Prevention: Clean metal surface, proper gas flow, and correct electrode handling.

Porosity not only reduces strength but can also make the joint porous, leading to leakage in pressure vessels or pipelines.

Slag Inclusion

Slag inclusion occurs when non-metallic materials such as flux or oxides are trapped inside the weld metal. It creates weak spots and reduces bonding between layers.

Causes: Improper cleaning between passes, low welding current, or wrong electrode angle.
Prevention: Clean each weld layer before the next pass and use proper welding current and technique.

Slag inclusions are mostly seen in arc welding processes where flux is used.

Lack of Fusion

Lack of fusion occurs when the weld metal fails to fuse completely with the base metal or previous weld bead. It results in a weak joint that can separate under stress.

Causes: Low welding current, wrong torch angle, or improper joint preparation.
Prevention: Maintain sufficient heat, correct electrode angle, and proper edge preparation.

This defect is often found in thick metal plates where heat penetration is inadequate.

Incomplete Penetration

Incomplete penetration happens when the weld metal does not reach the root of the joint, leaving a gap or unfused area.

Causes: Low heat input, improper groove design, or fast travel speed.
Prevention: Use correct groove design, proper current, and slower welding speed.

Incomplete penetration greatly reduces the strength of the welded joint, especially under tensile loads.

Undercut

Undercut is a groove formed along the edges of the weld bead, where excessive melting occurs. It makes the joint weak and can lead to cracks under stress.

Causes: High welding current, incorrect torch angle, or fast travel speed.
Prevention: Maintain proper current, correct electrode angle, and moderate speed.

Undercut not only weakens the joint but also spoils the appearance of the weld.

Overlap

Overlap occurs when molten metal flows over the base metal surface without proper fusion. It forms a lump on the edge of the weld bead.

Causes: Low welding speed or high heat input.
Prevention: Proper welding speed and control of current.

Overlap can lead to poor appearance and potential stress concentration at the joint edge.

Spatter

Spatter refers to small droplets of molten metal that are thrown out of the weld pool during welding. They stick to the surrounding surface and spoil the appearance.

Causes: High current, long arc length, or improper polarity.
Prevention: Use correct current, maintain short arc length, and proper polarity.

Though spatter doesn’t affect joint strength much, it increases cleaning and finishing work.

Distortion

Distortion occurs due to uneven heating and cooling during welding, causing warping or bending of the welded parts.

Causes: Unequal expansion and contraction due to excessive heat.
Prevention: Use proper clamping, balanced welding on both sides, and controlled heat input.

Distortion affects dimensional accuracy and alignment of components.

Burn Through

Burn through occurs when excessive heat melts a hole through the base metal.

Causes: Too high current or slow welding speed.
Prevention: Use proper heat control and faster travel speed.

Burn through is especially common when welding thin metal sheets.

Conclusion

Welding defects are major issues that affect the strength, appearance, and safety of welded joints. Common defects such as cracks, porosity, slag inclusion, undercut, and lack of fusion result mainly from poor technique or incorrect parameters. By selecting proper welding conditions, maintaining cleanliness, and performing inspection after welding, most of these defects can be prevented. Ensuring defect-free welds is essential for achieving durable and reliable mechanical structures.