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How to Check Weld Quality: A Complete Visual Guide

Good welds hold. Bad welds fail. Here's how to tell the difference — with checklists and expert tips.

Analyze Your Welds with AI

Why Weld Quality Matters

A bad weld isn't just ugly — it's dangerous. Failed welds cause:

The good news: Most weld defects are visible if you know what to look for. This guide teaches you visual inspection — the first line of quality control.

The 5-Second Quality Check

Before diving deep, scan for these immediate red flags:

If you see any of these: Grind it out and re-weld.

What a Good Weld Looks Like

Visual Characteristics of Quality Welds

MIG Weld (Ideal):

Common Weld Defects

1. Porosity (Gas Holes)

What it looks like: Small bubbles or holes in the weld face. Can be surface-level or internal. Looks like tiny craters or Swiss cheese.

Causes:

How to fix:

  1. Clean base metal thoroughly (grind to shiny metal)
  2. Store electrodes in dry place
  3. Check gas flow rate (20-25 CFH for MIG)
  4. Block wind if welding outdoors

2. Undercut

What it looks like: Groove or notch melted into base metal at weld edges. Creates a stress riser (weak point).

Causes:

How to fix:

  1. Lower voltage or amperage
  2. Slow down travel speed
  3. Maintain 10-15° travel angle
  4. Use smaller weaving motion

3. Lack of Fusion (Cold Lap)

What it looks like: Weld metal sitting on top of base metal. Visible gap between weld and base metal.

Causes:

How to fix:

  1. Increase amperage/voltage
  2. Slow down significantly
  3. Maintain proper work angle (10-15°)
  4. Clean metal to shiny surface

4. Cracks

What it looks like: Linear breaks in weld or heat-affected zone. Can be longitudinal (along weld) or transverse (across).

Cracks cannot be repaired. You must grind out entire cracked area plus 1" beyond and re-weld.

Causes:

5. Excessive Spatter

What it looks like: BB-sized metal balls around weld. Rough, irregular weld surface.

Causes:

How to fix:

  1. Adjust voltage and wire speed
  2. Maintain 1/4" to 3/8" stickout
  3. Clean or replace contact tip
  4. Improve joint fit-up

The Visual Inspection Checklist

Surface Inspection

Edge Inspection

Testing Your Welds (Beyond Visual)

1. Hammer Test (Destructive)

How: Weld two plates together, let cool, hit with ball-peen hammer, bend until breaks.

Pass: Plate bends, weld holds
Fail: Weld cracks or separates

2. File Test (Destructive)

How: Cut through weld cross-section, file smooth, inspect for fusion lines.

Look for: No gaps between weld and base metal

Using Technology to Check Welds

DimeVision AI Analysis

What it does:

Try it: dimevision.app

FAQ

Q: Can a weld look good but be bad?

Yes. Lack of fusion and internal porosity aren't always visible. That's why codes require additional testing for critical welds.

Q: How do I know if I have enough penetration?

Look for fusion lines at the root (inside corner). On thick material, you may need to cut and etch a test piece to verify.

Q: What's the most common defect for beginners?

Porosity. Usually from inadequate cleaning. Clean your metal!

Q: How accurate is AI weld inspection?

Good for surface defects and learning. Not a replacement for certified inspectors on critical welds. Use it as a learning tool and first-pass filter.

Quick Reference: Defect Severity

Defect Cosmetic Only Reject Immediately
Porosity Scattered small pores Large or clustered pores
Undercut < 1/32" deep > 1/16" deep
Cracks — ANY crack = reject

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