This topic will cover common welding defects such as porosity, lack of fusion, spatter, cracking, and distortion. Students will learn how to identify these defects and understand their causes.
Introduction to Welding Defects
Quick reference guide for students, trainees, and professionals
1. Why Study Welding Defects?
| Reason |
Benefit |
| Safety |
Prevents catastrophic failures in pressure vessels, bridges, aircraft, etc. |
| Quality |
Ensures products meet specifications and standards (AWS, ISO, EN). |
| Cost Efficiency |
Early detection avoids costly re‑work, scrap, and downtime. |
| Certification |
Required knowledge for welders, inspectors, and engineers. |
2. Classification of Defects
| Category |
Definition |
Typical Causes |
Common Inspection Methods |
| Surface Defects |
Visible irregularities on the weld face or root. |
Improper technique, contamination, poor fit‑up. |
Visual inspection (VT), dye‑penetrant (PT). |
| Internal (Volumetric) Defects |
Flaws located inside the weld metal or HAZ. |
Gas entrapment, solidification issues, excessive heat. |
Radiographic (RT), ultrasonic (UT), phased‑array (PAUT). |
| Geometric Defects |
Deviations from the required shape or size. |
Incorrect welding parameters, misalignment, poor joint design. |
VT, dimensional measurement, 3‑D scanning. |
| Mechanical Property Defects |
Areas with reduced strength or toughness. |
Over‑tempering, rapid cooling, improper filler metal. |
Hardness testing, tensile testing, impact testing. |
3. Common Surface Defects
| Defect |
Appearance |
Primary Cause |
Remedy / Prevention |
| Cracks |
Linear, sharp‑edged openings. |
High residual stress, rapid cooling, hydrogen embrittlement. |
Pre‑heat, inter‑pass temperature control, low‑hydrogen electrodes. |
| Porosity |
Small round cavities, often clustered. |
Trapped gases, moisture, contaminated filler. |
Clean surfaces, proper storage of consumables, correct shielding gas flow. |
| Undercut |
Groove beside the weld toe, metal loss. |
Excessive travel speed, high voltage, incorrect angle. |
Adjust parameters, use proper torch angle, practice technique. |
| Lack of Fusion |
Unbonded area between weld and base metal. |
Insufficient heat input, poor joint preparation. |
Increase heat input, improve fit‑up, clean joint edges. |
| Spatter |
Droplets of molten metal adhering to surrounding area. |
High current, improper shielding, incorrect electrode angle. |
Optimize current, adjust shielding gas, maintain correct angle. |
| Overlap |
Weld metal flows over base metal without bonding. |
Excessive travel speed, low voltage, too much filler. |
Reduce travel speed, increase voltage, adjust filler rate. |
| Burn‑through |
Complete penetration of base metal, leaving a hole. |
Too high current or voltage, thin workpiece. |
Lower current/voltage, use appropriate filler size. |
4. Common Internal (Volumetric) Defects
| Defect |
Description |
Typical Location |
Root Cause |
Detection |
| Lack of Penetration (LOP) |
Weld does not fully fuse through joint thickness. |
Root of groove or fillet. |
Insufficient heat, poor joint design. |
RT, UT, visual check of root. |
| Lack of Fusion (LOF) |
Incomplete bonding between successive passes. |
Between passes or between weld and base. |
Low inter‑pass temperature, contamination. |
RT, UT. |
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