4.1 Visual Testing (VT)
Key Takeaways
- VT is the most important NDE method and the CWI's primary responsibility — performed before, during, and after welding
- Minimum viewing conditions: 1,000 lux (~100 fc) illumination, 24 in. maximum distance, 30° minimum line of sight
- CWI near-vision requirement per AWS QC1 is Jaeger J2 at 12 in.
- VT detects only surface / surface-connected discontinuities — it is a surface method, not volumetric
- Key gauges: fillet weld gauge, bridge cam (Cambridge) gauge, Hi-Lo gauge, undercut gauge, taper gauge, protractor
- The bridge cam gauge is the most versatile tool — undercut, reinforcement, fillet size, bevel angle, and misalignment
Visual Testing: The Foundation of Weld Inspection
0 terminology, is the most widely applied and most important nondestructive examination method, and it is the primary, day-to-day responsibility of the Certified Welding Inspector (CWI). It is performed before, during, and after welding, which makes VT unique among all NDE methods: it is the only one that can prevent discontinuities rather than merely detect them after the fact.
The widely cited estimate that VT, properly executed, can catch the majority of the defects later found by volumetric methods reflects this preventive role — most rejectable conditions originate in poor fit-up, contaminated base metal, or incorrect technique that an attentive inspector flags before they are buried under weld metal.
VT detects only surface and surface-connected discontinuities. It is a surface method, not a volumetric one, so it cannot reveal subsurface porosity, internal cracks, or buried lack of fusion. Its value lies in low cost, immediate results with no processing time, and the breadth of conditions it covers across the entire weld lifecycle.
Standard Conditions for Visual Examination
The governing reference is AWS B1.11, Guide for the Visual Examination of Welds, supplemented by ASME BPVC Section V, Article 9 for code work; both specify the same minimum viewing conditions:
| Requirement | Specification |
|---|---|
| Illumination | Minimum 1,000 lux (~100 foot-candles) of white light at the examination surface |
| Maximum distance | Eye within 24 in. (600 mm) of the surface |
| Minimum angle | Line of sight not less than 30° to the examination surface |
| Vision (per AWS QC1) | Near-vision acuity of Jaeger J2 at 12 in. (or equivalent), retested at intervals |
| Aids | Mirrors, borescopes, fiberscopes, and magnifiers permitted; remote/aided VT recognized |
Exam trap: candidates often memorize an outdated "50 foot-candle" figure. The current B1.11 / ASME V minimum is 1,000 lux (~100 fc), with 24 in. maximum distance and a 30° minimum line of sight. The CWI's own near-vision requirement is Jaeger J2, verified per AWS QC1.
What the Inspector Looks For at Each Stage
The CWI's checklist changes across the weld lifecycle. Organizing VT by stage is a common exam framing:
| Before Welding | During Welding | After Welding |
|---|---|---|
| Joint fit-up, root opening, bevel angle | Interpass cleaning and temperature | Cracks (surface) |
| Base-metal condition (rust, oil, mill scale) | Arc behavior, technique, travel speed | Surface porosity |
| Preheat verification | Preheat/interpass maintenance | Undercut and overlap |
| WPS/PQR available; welder qualified | Bead sequence and placement | Weld size (fillet leg, throat) |
| Backing, runoff tabs, tack quality | Shielding gas flow / wind | Reinforcement height, crater, spatter |
The Inspector's Gauges (Critical for Part B)
Part B of the CWI exam uses replica specimens measured with hand gauges. Know each tool and what it measures:
| Tool | What it measures |
|---|---|
| Fillet weld gauge | Fillet leg size, throat; convexity/concavity (skew or standard) |
| Bridge cam gauge (Cambridge gauge) | The most versatile gauge — undercut depth, reinforcement height, fillet leg, bevel/prep angle, and misalignment |
| Hi-Lo gauge | Internal pipe misalignment (high-low) and internal root reinforcement |
| Undercut gauge | Depth of undercut to a fine resolution (e.g., 1/100 in.) |
| Taper (feeler) gauge | Root opening / gap width |
| Protractor | Bevel and groove angles |
Advantages and Limitations
| Advantages | Limitations |
|---|---|
| Lowest cost of any NDE method | Detects only surface / surface-connected discontinuities |
| Performed before, during, after — prevents defects | Highly inspector-dependent (skill, vision, fatigue) |
| Immediate results; no processing | Requires adequate lighting and physical access |
| Minimal equipment beyond hand gauges | Cannot size internal geometry or buried flaws |
The bridge cam gauge is the single most useful tool to master because it covers undercut, reinforcement, fillet size, prep angle, and misalignment with one instrument — making it the workhorse for Part B practical measurements and field inspection alike.
Worked Scenario: A Fillet Weld Acceptance Check
Suppose a WPS calls for a 1/4 in. 1 statically loaded connection. , and keeps the line of sight above 30°. Using the fillet weld gauge, the inspector confirms both legs meet the 1/4 in. minimum and checks for convexity that would reduce the effective throat. 1 permits undercut up to 1/32 in. for most cases, so a reading of 1/64 in. passes while 1/16 in. is rejectable. Overlap (cold lap rolling over the toe with no fusion) and surface cracks are automatic rejects regardless of size. The inspector also verifies there is no unacceptable surface porosity and that the weld profile is acceptable per the code's profile figures.
Every observation is documented; nothing is accepted from memory.
This scenario shows why VT is more than "looking": it is measurement against an acceptance standard using calibrated gauges, performed under controlled viewing conditions, with results recorded. A discontinuity is only a defect when it exceeds the acceptance criteria of the governing code — a distinction the CWI applies constantly during visual examination.
What is the minimum illumination required at the examination surface for visual weld examination per AWS B1.11 / ASME Section V?
A CWI must measure undercut depth, weld reinforcement height, fillet leg size, AND joint misalignment on a single replica specimen. Which gauge handles all of these?
Why is VT considered unique among NDE methods?