Every welder has been there — you pull back your helmet, look at your bead, and something's not right. Whether you're a first-timer or a ticketed boilermaker, weld defects happen. The difference between a good welder and a great one is knowing exactly what went wrong and how to fix it.
Real Weld Photos: What Good vs. Defective Looks Like
Before diving into each defect, here's what the difference looks like in a real shop environment:
✅ Good weld — consistent ripple, clean toes, no spatter. ARCPEX MIG200, synergic mode.
❌ Defective weld — porosity, spatter, irregular bead. Contamination or wrong gas flow.
1. Porosity — The Bubble Problem
Porosity appears as small holes or pits on or below the weld surface. It's one of the most common defects and one of the most preventable. Notice the spatter and surface irregularities — classic signs of contamination or incorrect gas flow.
Why it happens:
- Contaminated base metal (oil, rust, moisture, mill scale)
- Wrong shielding gas flow rate (too high or too low — target 15–25 CFH for MIG)
- Arc length too long, allowing atmospheric contamination
- Wet or damaged flux coating on stick electrodes
How to fix it:
- Clean base metal thoroughly with a wire brush and acetone before welding
- Check gas flow — 15–25 CFH for MIG, 15–18 CFH for TIG
- Maintain a consistent, short arc length
- Store 7018 electrodes in a rod oven to prevent moisture absorption
2. Slag Entrapment — The Hidden Trap
Slag entrapment occurs when flux residue gets trapped inside or at the toes of the weld bead instead of floating to the surface. Notice the dark inclusions at the weld toes in the example above.
— 18-year-old ticketed welder & boilermaker, r/Welding
Why it happens:
- Amperage too low — slag doesn't have enough heat to float out
- Improper electrode angle — slag runs ahead of the puddle
- Not cleaning slag between passes on multi-pass welds
- Travel speed too fast, trapping slag before it can escape
How to fix it:
- Increase amperage slightly — for 7018 1/8", try 130–140A instead of 125A
- Maintain a 10–15° drag angle (electrode tilted back in direction of travel)
- Always chip and wire brush thoroughly between passes
- Slow down your travel speed to give slag time to rise
3. Burn-Through & Distortion on Thin Metal
Burn-through happens when too much heat melts completely through the base metal. The example above shows severe distortion and burn-through — a common result of using the wrong process or settings on thin gauge material.
Why it happens:
- Too much heat input for the material thickness
- Welding too slowly in one spot
- Wrong process selected for thin gauge metal
- No tack welds to hold alignment before full welding
How to fix it:
- Switch to TIG welding for thin material — superior heat control via foot pedal
- Use stitch welding (short welds with cooling time between) instead of continuous beads
- Reduce amperage and increase travel speed
- Tack weld every 2–3 inches before running full beads
4. First Weld Bead — What "Good Enough" Actually Looks Like
— r/Welding user bnt1716
Signs of a decent first weld:
- ✅ Consistent bead width throughout
- ✅ No major undercut at the toes
- ✅ Arc started and maintained without sticking
- ✅ Bead is fused to the base metal (not sitting on top)
Common beginner issues and fixes:
- Spatter on sides → Amperage slightly high, or arc too long. Reduce by 5A or shorten arc.
- Uneven ripple pattern → Travel speed inconsistent. Practice maintaining a steady pace.
- Bead too tall and narrow → Moving too fast or amperage too low.
- Bead too wide and flat → Moving too slow or amperage too high.
How to Read Your Weld Bead Like a Pro
Clean AC TIG aluminum bead — stack-of-dimes pattern, visible oxide cleaning halo, no porosity. ARCPEX TIG200P, 85A, 120Hz AC. This is the target.
Your weld bead is a diagnostic tool. Compare every bead you run against this reference table:
| Bead Appearance | Likely Cause | Fix |
|---|---|---|
| Too wide & flat | Too slow / too hot | Speed up or reduce amps |
| Too narrow & tall | Too fast / too cold | Slow down or increase amps |
| Spatter everywhere | Arc too long / wrong gas | Shorten arc, check gas flow |
| Undercut at toes | Too hot / wrong angle | Reduce amps, adjust angle |
| Porosity (holes/pits) | Contamination / gas issue | Clean metal, check gas flow rate |
| Slag inclusions | Too cold / wrong angle | Increase amps, adjust drag angle |
| Burn-through | Too hot / too slow | Reduce amps, speed up, switch to TIG |
| Lack of fusion | Too fast / too cold / wrong angle | Slow down, increase amps, adjust torch angle |
Choosing the Right Machine to Avoid Defects
The right machine eliminates half the variables before you even strike an arc. Here's what each process is best suited for:
ARCPEX MIG200 — Best for Beginners & Production
- ✅ Synergic auto-set eliminates parameter mismatch (main cause of porosity)
- ✅ MIG · Flux Core · Lift TIG · Stick · Aluminum MIG
- ✅ 110V/230V dual voltage · ~22 lbs
ARCPEX ACDC TIG200P — Best for Thin Metal & Aluminum
- ✅ Pulse TIG mode prevents burn-through on thin material
- ✅ AC TIG for aluminum · DC TIG for steel/stainless/titanium
- ✅ Foot pedal compatible — real-time heat control
FAQ: Welding Defects
What causes porosity in MIG welding?
How do I fix slag entrapment in stick welding?
How do I prevent burn-through on thin metal?
What does undercut look like and how do I fix it?
Is my first weld good enough?
The Right Machine Prevents Half Your Defects
ARCPEX machines with synergic auto-set and pulse TIG control eliminate the most common causes of weld defects before you strike an arc.
Shop MIG200 — $399.99 → Shop TIG200P — $539.99 →
