What are common categories of welding defects?

• A. Dents, rust, scratches.
• B. Only porosity.
• C. Porosity, lack of fusion, lack of penetration, cracks, undercut, burn-through, and misalignment.
• D. Spatter and noise.

Answer: (C)

Welding defects are flaws that can weaken or compromise a joint, and they fall into several common defect modes. The main categories you’ll see are porosity, lack of fusion, lack of penetration, cracks, undercut, burn-through, and misalignment. Porosity means gas pockets form in the weld metal, often from contamination, moisture, or insufficient shielding; it reduces the weld’s strength and makes it more susceptible to leakage or fatigue. Lack of fusion happens when the weld metal doesn’t properly fuse to the base metal, typically due to insufficient heat, poor technique, or dirty surfaces, leading to a weak bond. Lack of penetration is when the weld fails to extend through the joint thickness, leaving an under-welded root that can fail under load. Cracks are fractures that can occur during cooling (hot cracks) or over time (hydrogen-induced or cold cracks), and they are critical because they can propagate under stress. Undercut is a groove at the weld toe where base metal is melted away, reducing cross-sectional strength. Burn-through is a weld that has consumed too much base metal, creating a hole and compromising the joint. Misalignment happens when the pieces aren’t properly aligned, resulting in gaps, uneven welds, and poor load transfer.

Other options describe issues that aren’t the fundamental defect categories you focus on when assessing weld integrity. Surface dents, rust, and scratches are surface conditions rather than core weld defect modes, and spatter or “noise” are more about surface quality or process artifacts than the primary defect families. The listed categories together capture the most common, recognized defect modes inspectors look for in practice.