4.1 Visual Testing (VT)
Key Takeaways
- VT is the most important NDE method and the primary responsibility of a CWI
- Minimum requirements: 50 foot-candles illumination, 24" max distance, 30° minimum angle
- CWI vision requirement: J1 near vision acuity at 12 inches on Jaeger chart
- VT is performed before, during, and after welding — it prevents defects, not just detects them
- Key VT tools: fillet weld gauge, bridge cam gauge, Hi-Lo gauge, taper gauge
- The bridge cam gauge is the most versatile tool — measures undercut, reinforcement, fillet size, bevel angle
4.1 Visual Testing (VT)
Visual Testing (VT) is the most widely used and most important NDE method. It is the primary responsibility of a CWI and is required before, during, and after welding. VT is the first line of defense in weld quality — most defects that can be detected by other NDE methods could have been prevented by effective visual inspection.
AWS B1.11 — Guide for Visual Inspection of Welds
AWS B1.11 is the standard guide for visual inspection practices. It defines minimum conditions for effective VT:
| Requirement | Specification |
|---|---|
| Lighting | Minimum 50 foot-candles (540 lux) on the inspection surface |
| Distance | Maximum 24 inches (600 mm) from the weld surface |
| Angle | No less than 30° to the inspection surface |
| Vision | Inspector must have near vision acuity of J1 at 12" (Jaeger chart) |
| Aids | Magnification, mirrors, borescopes may be used; magnifying devices ≤ 10× |
What VT Detects
| Before Welding | During Welding | After Welding |
|---|---|---|
| Joint fit-up and alignment | Arc characteristics | Cracks |
| Bevel angles and root opening | Interpass cleaning | Porosity (surface) |
| Base metal condition (rust, oil) | Electrode type and size | Undercut |
| Preheat verification | Preheat/interpass maintenance | Overlap |
| WPS/PQR availability | Pass sequence | Weld size (fillet leg, throat) |
| Welder qualification current | Travel speed/technique | Reinforcement height |
| Consumable condition/storage | Shielding gas flow | Crater condition |
| Backing/runoff tabs | Voltage and amperage | Spatter |
| Tack weld quality | Wind conditions | Incomplete joint penetration (root side) |
VT Tools for the Inspector
| Tool | Use |
|---|---|
| Fillet weld gauge | Measures fillet weld leg size, throat, and convexity/concavity |
| Bridge cam gauge (Cambridge gauge) | Multi-purpose: undercut depth, reinforcement height, fillet size, bevel angle, misalignment |
| Hi-Lo gauge | Measures pipe alignment (mismatch/high-low) and internal root reinforcement |
| Taper gauge | Measures root opening (gap width) |
| Protractor | Measures bevel angles |
| Steel rule / tape | General measurement |
| Magnifying lens | Closer inspection of surface indications |
| Flashlight | Supplemental lighting for confined spaces |
| Mirror / borescope | Inspect inaccessible areas |
Advantages and Limitations of VT
| Advantages | Limitations |
|---|---|
| Lowest cost of any NDE method | Detects only surface discontinuities |
| Can be performed before, during, and after welding | Inspector dependent (skill, vision, fatigue) |
| No special equipment needed beyond gauges | Cannot detect subsurface discontinuities |
| Immediate results — no processing time | Requires adequate lighting and access |
| Prevents defects (before/during inspection) | Not suitable for complex internal geometry |
For the Exam: VT minimum requirements (50 foot-candles, 24" distance, 30° angle) are frequently tested. Also know the inspector's vision requirement (J1 at 12" on Jaeger chart). The bridge cam gauge is the most versatile VT tool and should be familiar for Part B.
What is the minimum illumination required for visual testing per AWS B1.11?
What is the maximum viewing distance for visual inspection per AWS B1.11?
Which VT tool is the most versatile for measuring multiple weld attributes?