17.2 VT Equipment: Direct, Remote, and Measuring Tools
Key Takeaways
- Direct VT is the qualified eye, with mirrors and gauges, inside the procedure's access and lighting limits; remote VT is a scope or camera when that geometry cannot be met.
- Use the named gauge: hi-lo for mismatch, an undercut gauge for toe grooves, a pit gauge for local depth, a feeler for gaps — the gauge does not replace the acceptance table.
- Remote VT requires a demonstrated resolution check, typically a procedure or code demonstration card at the same working distance, zoom, lighting, and angle as the examination.
- Drones and cameras are awareness and access tools until the written procedure qualifies them as remote visual equipment.
- Clean the optic, confirm focus, lighting, and battery, and re-check resolution before you write "no indications."
The ASNT NDT Level II visual-testing general exam lists VT Equipment as official VT topic 6. The items are not a catalog of brand names. They are asking which tool is direct and which is remote, which gauge reads the condition you named, when a remote system must demonstrate resolution, and why a Level II does not write no indications on a dirty, dim, or unfocused image.
The eye is still the primary sensor. Chapter 16 covered acuity, adaptation, and lighting as human factors. This section is the kit that gets a qualified view — or a qualified substitute image — onto the surface with the required access, angle, illumination, and measuring capability.
Direct visual: the eye, mirrors, and gauges
Direct visual examination means the inspector's eye meets the procedure's access geometry. ASME Section V, Article 9 (an industry/code fact, not an ASNT constant) is the document most stems have in mind: the eye typically within 24 in (600 mm) of the surface, at an angle not less than 30°, with stated illumination — often taught as about 100 fc (1000 lux) for general visual work. Use the edition and procedure in front of you. Those numbers are not an ASNT-published secret, and a different construction code can tighten them.
A mirror that preserves that geometry still counts as direct. You have not gone remote just because you used a weld mirror on the back of a fillet. You have gone remote when the image is formed by a borescope, fiberscope, videoscope, camera, or other system that replaces the eye at the surface.
Mirrors
Weld-inspection mirrors are telescoping, fixed, magnifying, or not. They exist for the back side of a fillet, the root of an open pipe, behind stiffeners, and inside sockets. Rules:
- A dirty or scratched mirror is a resolution loss. Clean it as you would a lens.
- A magnifying mirror changes field of view and working distance. Treat it as an optic (topic 5), not as "just a mirror."
- The mirror does not relax the lighting requirement. Light the surface, not the inspector's face.
Measuring tools — pick the gauge that matches the condition
Visual testing measures profile and surface geometry. The acceptance number lives in the construction code, specification, or procedure — AWS D1.1, ASME Section VIII, ASME B31.3, API 1104, a customer table — not in the gauge itself. The Level II's job is to use the right tool and write the right quantity.
| Tool | What it actually reads | Typical condition |
|---|---|---|
| Fillet-weld gauge (blade or variable) | Leg length and, on some blades, throat | Undersize fillet, insufficient throat |
| Cambridge / multi-purpose weld gauge | Leg, throat, reinforcement, some undercut, bevel angle | Multipurpose profile on accessible welds |
| Hi-lo / mismatch gauge | Offset of the two members at the joint | Misalignment, high-low |
| Undercut gauge (bridge or analog) | Depth of the toe groove below adjacent parent metal | Undercut |
| Pit gauge (bridge with dial or digital) | Depth of a cavity below the surrounding surface | Pitting, isolated corrosion, grind pits |
| Feeler gauges | Gap width | Root opening, overlap lift, a surface-breaking incomplete-fusion crevice, fit-up gap |
| Ruler / tape / scale | Length, spacing, remaining ligament | Indication length, pore spacing |
| Calipers / micrometers | Accessible thickness, OD, remaining stock | Local thinning when a pit-gauge bridge will not seat |
| Profile / contour gauge | A transferred shape | Reinforcement contour, underfill |
| V-WAC or undercut comparator | Visual comparison of undercut depth | Estimate when a mechanical gauge will not seat |
Rules the exam likes to trip:
- Hi-lo is not undercut. Mismatch is a step between members. Undercut is a melted groove in the parent at the toe. Using an undercut gauge on a hi-lo step, or a hi-lo gauge on a toe groove, is the wrong measurement.
- Feelers measure gaps, not depths. A feeler stack under an overlap lip is a legitimate gap check. It is not a pit-depth reading.
- Zero a dial pit gauge on adjacent sound surface, not on a paint ridge, a weld ripple, or the high side of a mismatch.
- A fillet gauge reads leg (and sometimes throat). It does not read "quality" and it does not reject a crack.
- The gauge reading is data. Accept or reject is the named table, not the brand of gauge.
Remote visual: scopes, cameras, and drones as awareness
When the eye cannot meet the direct-access geometry, the image is brought out. That is remote visual examination.
- Rigid borescopes — straight tubes, drilled holes, heat-exchanger tubes with a straight run. Best glass, no winding path.
- Fiberscopes — winding paths, engines, valve bodies. Coherent bundle; broken-fiber discipline from topic 5 still applies.
- Videoscopes — the same paths, plus recording and measurement software. Distal camera; digital zoom is still empty magnification.
- Cameras — tank interiors, confined spaces, weld-root cameras on orbital heads. The display and the recording are now part of the "eye."
- Drones / UAVs — awareness and access scouting on tank roofs, stacks, flare structures, and large vessels. A drone video is not automatically a qualified remote VT. The written procedure must qualify the platform the same way it qualifies any remote system: lighting, resolution demonstration, color, stability, and inspector qualification. Do not tell the exam that a pretty fly-over replaces Article 9 remote visual.
Lighting attachments
Remote and direct work both fail in the dark. Typical attachments:
- Distal LEDs on the scope tip
- Coaxial illumination through the optic (good inside a hole; can wash texture)
- A separate flashlight or drop-light for direct work
- Reflectors and snoots that throw grazing light along a surface
White light of the stated intensity at the surface is a VT requirement. Color temperature matters: a cold blue LED cast can hide rust and heat tint; a warm cast can hide some oxides. UV-A belongs to fluorescent PT or MT, not to a white-light VT exam — do not mix the methods.
On remote gear, a lamp that is too close glares and burns out a pit. A lamp that is too dim, or a battery that has sagged, makes a crack disappear. Intensity is measured at the work, not at the bulb.
When remote VT requires demonstrated resolution
This is the high-value sentence on topic 6.
Remote visual examination requires a demonstrated resolution capability. Typical demonstration is a procedure or code resolution card — a character of specified height, a graded pattern, or the demonstration piece the procedure names — placed at the same working distance, angle, lighting, zoom, tip, and display that will be used on the part. ASME Section V, Article 9 requires the remote system to show that it can resolve the required detail. Training commonly cites a character on the order of 1/32 in (0.8 mm), or whatever character the procedure names. Use the procedure. Do not invent a single ASNT-published character size.
Why remote needs the card and direct visual does not use it the same way: in direct work the qualified eye and the stated lighting are the sensor. In remote work the objective, sensor or bundle, illumination, cable, compression, and display are now in the chain. Factory literature is not a job-site demonstration.
If the card cannot be read, do not start. If you change tip, cable, display, or zoom after the demo, re-demonstrate. A "no indications" report from a system that could not read its own card is not an examination.
Care, cleanliness, battery, and the "no indications" trap
A Level II who writes NI / no indications on a dirty optic has examined the dirt.
Work this checklist before you call the surface clean:
- Optics clean. Fingerprints, spatter film, condensation, grease, and scratched windows destroy resolution. Clean with the approved wipe and solvent, not a shirt tail.
- Focus. Rack through focus on a known feature — a letter stamp, the resolution card, a weld ripple — at the working distance. An out-of-focus crack is invisible.
- Lighting. Intensity at the surface, not at the lamp. Battery lamps sag. Replace or recharge before the exam, not after you "didn't see anything."
- Battery and recording. A dying videoscope dims the LEDs and then dies mid-scan. Start with known charge. If the procedure requires a record, confirm that the recorder is actually writing.
- Color and white balance. A blue cast hides rust; a warm cast hides some oxides. Neutralize before you interpret color.
- Broken fibers and dead pixels. Map them so you do not call them pits, and so they do not hide a real pit.
- Coverage. If the tip cannot reach the far tube end, you did not examine the far tube end. Write the uninspected length. Do not imply a complete exam.
The exam loves the stem: the inspector reported no indications; a customer later found a crack; the scope window was filmed with grease and the LEDs were dim. Correct action is clean, restore lighting and charge, confirm focus and resolution, and re-examine — not "the crack grew overnight," and not "stand by the original NI."
Realistic exam scenarios
An inspector uses a hi-lo gauge to "measure undercut" at a toe. Wrong tool. Hi-lo reads member offset; undercut is a melted groove measured with an undercut gauge or a seated bridge.
A remote header exam starts without a resolution card because the inspector's Jaeger card was current that morning. The Jaeger check qualifies the eye, not the camera chain. Demonstrate the remote system on the card at the job setup.
Drone footage of a tank roof is filed as the official VT without a procedure that qualifies the platform. That is awareness video, not a completed remote visual examination.
Topic 6 language is short: direct versus remote, the named gauge, the resolution card, and no "NI" on a dirty, dim, or unfocused image.
When does remote visual testing require a demonstrated resolution check?
Which tool is the correct first choice to measure the offset of two members at a weld joint (high-low / mismatch)?
An inspector writes "no indications" after a remote tube exam. Review shows the distal window was filmed with grease and the LEDs were dim from a low battery. What is the correct Level II action?