A practical guide to reading your own welds — before a CWI does it for you
Most new welders can't tell if their welds are good or bad until someone fails them on an inspection. That feedback loop is too slow. Learning to read your own welds — visually, in real time — is one of the most valuable skills you can develop.
Here are the 7 visual defects to look for every time you finish a bead. These are the same defects that DimeVision detects automatically — and the same ones CWIs look for on certification tests.
Porosity is trapped gas that didn't escape the weld pool before it solidified. It appears as small round holes on the surface of the bead, or as larger pits. Sometimes it's only visible when you grind the bead down — which is why it's so dangerous.
Subsurface porosity won't show on visual inspection. A bead can look clean and still be full of internal porosity. This is one area where AI photo analysis (looking at surface texture anomalies) can catch early indicators.
Undercut is base metal that melted away and wasn't replaced with filler. It appears as a depression or groove running parallel to the weld toe — the line where the bead meets the base metal. AWS D1.1 limits undercut depth to 1/32" (0.8mm) for structural applications.
Undercut creates a stress riser. Under cyclic loading — vibration, repeated flexing — cracks initiate at undercut locations and propagate. It's particularly dangerous in structural and heavy equipment welds.
Some spatter is normal in MIG and flux-core welding. Excessive spatter — covering a wide area around the bead — signals that your arc is unstable. It also means you're losing filler metal that should be going into the joint.
Spatter by itself doesn't always cause a rejection, but it indicates a settings problem that usually co-exists with other defects like porosity or inconsistent fusion.
Cold lap (also called overlap) is when the weld metal covers the surface of the base metal without actually fusing to it. The bead looks connected, but there's essentially no bond — it's just weld metal resting on top of the base material. This is one of the most dangerous defects because it passes visual inspection while providing zero strength.
Under the bead, there's a sharp crack-like feature at the interface. Under load, it fails suddenly and without warning.
Any visible crack is an automatic failure. Cracks can occur in the weld metal itself (hot cracks, forming during solidification) or in the heat-affected zone (cold cracks, forming after cooling). Crater cracks appear at the end of the bead where you stopped.
Cracks are the most serious weld defect. They propagate under load — once a crack starts, it grows.
A good weld bead has consistent width, consistent ripple spacing, and consistent height. Width variation more than 1/8" on a single pass indicates inconsistent travel speed, arc length, or technique.
Inspectors use bead consistency as a proxy for heat input control. An inconsistent bead means inconsistent penetration — some sections may be underheated (cold lap risk) and some overheated (undercut risk).
On mild steel, the heat tint around a weld is normal. But black or heavily oxidized appearance on the bead itself indicates inadequate shielding gas coverage or contamination. On stainless steel, the acceptable color range is gold → light straw → blue — anything darker (black, green, grey) means the chrome oxide layer was destroyed by atmospheric contamination, compromising corrosion resistance.
| Defect | Visual Sign | Primary Cause | First Fix |
|---|---|---|---|
| Porosity | Pits/holes in bead | Gas contamination | Check gas flow (25–35 CFH) |
| Undercut | Groove at weld toe | Voltage too high | Reduce voltage, slow travel |
| Spatter | Droplets around bead | Voltage too low | Raise voltage, check tip |
| Cold lap | Bead not fused to base | Amperage too low | Increase amps, aim at root |
| Cracks | Visible lines in bead | Various (see above) | Preheat, low-hydrogen rod |
| Inconsistent width | Varying bead size | Travel speed variation | Practice consistent movement |
| Wrong color | Black/grey on stainless | Gas coverage failure | Increase flow, add post-flow |
Take a photo of your weld bead and DimeVision will detect porosity, undercut, spatter, cracks, overlap, and more in seconds. Get the feedback your eyes might miss.
Upload My Weld →Check for these 7 visual signs: porosity (small holes or pits), undercut (groove along the weld edge), excessive spatter (metal droplets around the bead), cold lap (weld bead sitting on top without fusing), cracks (visible lines in or near the bead), inconsistent width (bead varies more than 1/8"), and poor color (grey/black instead of golden-silver on stainless, or excessive scaling on mild steel).
A bad MIG weld typically looks uneven — the bead width varies significantly, there may be holes (porosity), a groove running alongside the weld (undercut), metal spatter around the bead, or the bead may appear to sit on top of the metal rather than fusing into it. A good weld has uniform width, smooth ripples, and blends smoothly into the base metal on both sides.
Porosity in MIG welding is caused by gas contamination of the weld pool. Common causes include: insufficient shielding gas flow (check for 25–35 CFH), contaminated base metal (rust, oil, or mill scale), drafts blowing away shielding gas, moisture on the wire or base metal, and wire stick-out that is too long (more than 3/4").
Yes, undercut is a serious weld defect. It creates a stress concentration point where cracks can initiate under load. AWS D1.1 limits undercut to 1/32" for most structural applications. Undercut is typically caused by voltage that is too high, travel speed that is too fast, or incorrect gun angle.
Yes. DimeVision uses AI to analyze weld photos and detect common defects including porosity, undercut, spatter, cracks, and overlap. Upload a photo of your weld and get instant feedback on what needs to be corrected.
Last updated: March 24, 2026 | DimeVision Editorial Team