Here are the 7 most common welding defects, their causes, effects, and how to prevent them:
✅ 1. Porosity
Definition: Gas pockets or voids trapped in the weld metal.
Cause:
- Contaminants like oil, rust, or moisture
- Improper shielding gas or technique
- Too fast travel speed
Effect: Weakens the weld and reduces corrosion resistance.
Prevention:
- Clean the base metal
- Use proper shielding gas flow
- Maintain correct welding parameters
✅ 2. Incomplete Penetration
Definition: Weld metal does not fully penetrate the joint thickness.
Cause:
- Low heat input
- Poor joint preparation or fit-up
- Incorrect electrode angle or size
Effect: Structural weakness and risk of failure under load.
Prevention:
- Increase current or voltage
- Improve joint design and alignment
- Use correct electrode or filler
✅ 3. Lack of Fusion
Definition: Weld fails to fuse completely with base metal or previous weld passes.
Cause:
- Inadequate heat
- Poor cleaning or surface oxide
- Incorrect torch angle
Effect: Reduces weld strength and can lead to cracking.
Prevention:
- Increase travel speed or heat
- Clean joint surfaces
- Adjust technique and torch angle
✅ 4. Undercut
Definition: A groove melted into the base metal next to the weld, not filled by weld metal.
Cause:
- Excessive current
- Fast travel speed
- Poor electrode angle
Effect: Creates stress concentration, reducing fatigue resistance.
Prevention:
- Reduce current
- Slow down the travel speed
- Maintain proper angle and arc length
✅ 5. Cracks
Definition: Fractures in or near the weld metal, either during or after welding.
Cause:
- High stress or restraint
- Wrong filler material
- Rapid cooling
Effect: Most dangerous defect; can lead to sudden failure.
Prevention:
- Use correct welding procedure
- Preheat thick sections
- Use post-weld heat treatment if required
✅ 6. Slag Inclusion
Definition: Non-metallic solid materials trapped in the weld.
Cause:
- Improper cleaning between passes
- Poor welding technique
- Wrong electrode angle
Effect: Reduces strength and may cause cracks.
Prevention:
- Clean slag between layers
- Use proper technique and electrode manipulation
✅ 7. Spatter
Definition: Small molten metal droplets scattered around the weld bead.
Cause:
- Excessive current
- Poor polarity settings
- Too long arc length
Effect: Affects appearance and may damage surfaces.
Prevention:
- Use anti-spatter spray
- Adjust current and arc length
- Maintain proper polarity
🧠 Bonus Welding Tips:
- Always clean metal surfaces before welding.
- Choose the right filler and shielding gas.
- Maintain proper machine settings and technique.
Would you like a printable chart of welding defects with images or a PDF inspection checklist?