Explore the most common defects in welding such as porosity, undercutting, incomplete penetration, and distortion. Learn how to identify, prevent, and troubleshoot these defects during the welding process.
Understanding Common Welding Defects
Study guide – concise, organized, and easy to read
| Category | Typical Appearance | Primary Cause | Typical Inspection Method |
|---|---|---|---|
| Porosity | Small, round gas‑filled cavities (often spherical) | Trapped gases, moisture, inadequate shielding gas, dirty base metal | Visual, radiographic (X‑ray), ultrasonic |
| Cracks | Linear openings, can be surface or internal | High stress, rapid cooling, hydrogen embrittlement, insufficient pre‑heat | Visual, dye‑penetrant, ultrasonic, magnetic particle |
| Lack of Fusion / Lack of Penetration | Unbonded areas at joint root or face; visible gaps | Incorrect torch angle, insufficient heat, poor fit‑up | Visual, radiographic, ultrasonic |
| Undercut | Groove cut into base metal along the toe of the weld | Excessive travel speed, high current, improper angle | Visual, profile measurement |
| Overlap | Weld metal runs over base metal without bonding | Too high travel speed, low current, incorrect angle | Visual |
| Spatter | Droplets of molten metal adhering to surrounding surface | Excessive current, poor shielding, incorrect polarity | Visual |
| Burn‑through / Blow‑through | Hole through the base metal | Excessive heat input, too high voltage/current | Visual, radiographic |
| Incomplete Joint Penetration (IJP) | Weld does not extend through the full thickness of the joint | Improper joint design, insufficient heat, poor positioning | Radiographic, ultrasonic |
| Distortion / Warping | Dimensional change of the workpiece | Uneven heating/cooling, restraint, high heat input | Dimensional inspection, laser scan |
| Metal Flow Defects (e.g., sagging, excessive reinforcement) | Excess metal buildup or sagging in the weld pool | Improper travel speed, high heat input, poor torch manipulation | Visual, profile measurement |
| Root Cause | Related Defects | Preventive Actions |
|---|---|---|
| Contamination (oil, rust, paint, moisture) | Porosity, lack of fusion, spatter | Clean workpiece, use dry consumables, store electrodes properly |
| Improper Shielding (gas flow, coverage) | Porosity, spatter, undercut | Verify gas flow rate, check nozzle condition, maintain proper distance |
| Incorrect Parameters (current, voltage, speed) | Burn‑through, undercut, lack of penetration, spatter | Follow welding procedure specification (WPS); perform trial welds |
| Poor Joint Fit‑up / Preparation | Lack of fusion, lack of penetration, cracks | Ensure proper bevel angles, root gaps, and edge preparation |
| Hydrogen Embrittlement (moisture, certain electrodes) | Cracks (hydrogen‑induced) | Use low‑hydrogen consumables, pre‑dry electrodes, keep humidity low |
| Excessive Heat Input | Distortion, grain growth, burn‑through | Control travel speed, use appropriate amperage, apply pre‑heat/cool‑down as required |
| Improper Technique ( |