16.1 Purpose and Scope of VT

The ASNT NDT Level II visual testing (VT) general exam lists Purpose and Scope of VT as official VT topic 1. A candidate sits one method's 50-question general paper. If that method is VT, this topic is not "look at the weld and write a comment." It asks when visual testing is a standalone accept/reject method, when it is only a prerequisite to magnetic particle (MT), liquid penetrant (PT), radiographic (RT), or ultrasonic (UT) testing, and what VT cannot see even when the inspector's vision is perfect.

Visual testing is the NDT method that detects surface discontinuities and verifies surface condition, configuration, and dimensions by observing the part with the unaided eye, with simple optical aids, or with remote visual equipment. It is the oldest NDT method and the only one in which the inspector is the primary instrument. Every other method still ends in a visual act — reading a particle buildup, a bleed-out, a film, or an A-scan — but VT is the method whose official target is the surface itself.

First look and last look

Treat VT as both the first NDT method and the last NDT method on almost every job.

First. It is the cheapest, fastest screen. A Level II who starts a 2-inch carbon-steel groove weld by setting up an angle-beam calibration while the cap has 3/16 in (5 mm) of undercut, incomplete fusion at a visible start-stop, and a crater crack has wasted the shift. VT finds those conditions immediately, documents the as-found state, and tells you whether MT, PT, RT, or UT is even the right next method. AWS D1.1-type structural work and most fabrication travelers require a visual pass before volumetric sampling. In-service work starts the same way: walk down the line, look for leakage stains, distortion, missing fasteners, coating failure, and obvious cracks before you hang a crawler or shoot a film.

Last. After MT, PT, RT, or UT, VT is the as-left method. Confirm that prod burns were blended, that penetrant and developer were cleaned off, that film-cassette clips or UT couplant did not leave a condition the customer will reject, and that repair welding was visually acceptable before the next volumetric shot. Shipping a "UT-accepted" nozzle with slag still sitting in the cap is a VT failure, not a UT failure.

Do not confuse "first and last" with "optional." On many contracts VT is the required NDT method. On others it is required plus a sample of MT, PT, RT, or UT. The exam stem will tell you which role you are in. Read it.

Direct, remote, and translucent VT

ASME Boiler and Pressure Vessel Code Section V, Article 9 is the usual method article for visual examination when a construction or in-service code invokes it. Article 9 organizes technique into three families. Learn the access rule, not article-number trivia.

Direct visual — 24 in and 30°

Direct visual (ASME V Article 9 language used throughout industry) may usually be made when access is sufficient to place the eye within 24 in (610 mm) of the surface and at an angle not less than 30° to that surface. Mirrors may improve the angle. Magnifiers may be used. If you cannot meet that geometry, you are no longer doing direct VT — you are doing remote VT, or you do not have a valid visual examination.

Remote and translucent

Remote visual uses visual aids such as mirrors, telescopes, borescopes, fiber optics, cameras, or other suitable instruments. The remote system must have resolution capability at least equivalent to direct visual observation. A cheap USB camera that cannot resolve the same scratch the eye would see at 24 in is not an equivalent remote examination. Demonstrate resolution on a chart or a known feature the procedure names, then inspect.

Translucent VT is backlight inspection of materials that transmit light. It is in the article so you do not invent a "only metals" scope. It is not the default on a steel pressure vessel.

A pocket flashlight does not convert remote work into direct work. A mirror that lets you put the eye on the image at 24 in / 30° can still be direct. A video probe that puts the image on a monitor is remote, even if you are standing next to the nozzle.

When VT is the required method

VT is the required method when the referencing code, specification, or procedure makes visual examination the accept/reject NDT — not merely a courtesy walk-around.

AWS D1.1, Structural Welding Code — Steel, is the classic example. It requires that all welds be visually inspected. Visual acceptance criteria (profile, undercut, porosity, overlap, cracks, size) live in the D1.1 visual tables — statically loaded connections and the stricter cyclic tables. Magnetic particle or ultrasonic testing, when specified, is in addition to visual, not a substitute for it. A fabricator who "skips visual because we UT 10 percent" is not following D1.1.

ASME Section V Article 9 does not, by itself, tell you a vessel is acceptable. A referencing book — ASME Section VIII, Section I, B31.1, B31.3, NBIC, and similar — tells you when visual examination is required and which acceptance standard applies. Article 9 tells you how to perform the examination: procedure, direct versus remote versus translucent, lighting, and documentation. On the general exam, "ASME V Article 9" means the method rules; "AWS D1.1 visual" means a common structural acceptance and 100-percent visual requirement.

VT is also the required method when the discontinuity of interest is inherently visual and surface access is available:

• Undercut, overlap, incomplete fusion at a visible face, crater cracks, arc strikes, and excessive or insufficient reinforcement
• Weld size and fit-up (leg, throat, mismatch, root opening) checked with gauges
• Corrosion, pitting, coating failure, leakage residue, and mechanical damage on accessible surfaces
• Dimensional and configuration checks that no volumetric method is designed to replace

When VT is a prerequisite to other methods

VT is a prerequisite when another method is the official accept/reject technique but you still must look first (and usually last).

• Before PT: confirm the surface is clean enough for capillary action, that you are not pouring penetrant on a grossly rejectable weld, and that openings are not plugged with slag or paint. PT will not fix a VT reject you refused to see.
• Before MT: confirm coating is within the procedure's allowed thickness, identify the zone, and note geometry that will give nonrelevant particle buildup.
• Before RT or UT: identify the weld, mark stations, and document geometry (high-low, excessive cap, backing, consumable inserts) that will confuse a film or an A-scan. Do not "discover" a 1/8 in mismatch for the first time on a radiograph.
• After any method: as-left cleanliness and repair visual.

Prerequisite VT does not mean "unofficial." If the procedure says perform visual examination before penetrant testing, a skipped visual is a procedure violation even if the PT is clean.

What VT cannot do

Write these limitations in the same sentence structure the exam uses.

1. Subsurface discontinuities. VT cannot detect slag trapped between passes, mid-wall porosity, incomplete fusion on a hidden bevel, laminations inside plate, or a hydrogen crack that does not break the examination surface. Those are RT, UT, or (if near-surface and ferromagnetic) MT problems.
2. Tight, closed, or filled surface cracks without lighting, access, contrast, and cleanliness. A fatigue crack shut by residual compression, a crack packed with oxide or paint, or a crack finer than the available resolution can be surface-breaking and still invisible. Poor lighting, a 10° viewing angle down a nozzle, and mill scale are enough to hide it. VT did not "fail as a method" — the examination conditions failed.
3. Remaining wall and hidden corrosion. An accessible pit is a VT call. Thinning on the opposite face of a pipe is an ultrasonic thickness (or profile RT) call.
4. Material properties. VT does not measure hardness, toughness, residual stress, or chemistry.

If the stem gives a buried slag line and asks which method is appropriate, the answer is not VT. If the stem gives a visible undercut and asks which method is primary, the answer is VT — not "start with UT."

Surface preparation sits inside scope, not in a later "nice to have" topic. Slag, spatter, oil, water, loose scale, and peelable coatings are contrast killers. Many weld codes require slag removal before visual acceptance of the weld. A painted toe is not a VT surface for crack detection until the procedure allows inspection through that coating or the coating is removed.

Realistic exam scenarios

A structural fabricator works to AWS D1.1. The traveler shows 10 percent ultrasonic testing on complete-joint-penetration welds. The Level II skips visual on the remaining 90 percent because "they are getting UT." That is a failed understanding of scope: D1.1 visual applies to all welds; UT is additional.

A vessel nozzle inside radius cannot be placed within 24 in at 30°. The inspector uses a video probe, demonstrates that the probe resolves the procedure's resolution target, and records remote VT. That is in scope.

A Level II reports "no cracks" on a painted toe in a dark tank with a dying flashlight, then MT finds a 40 mm toe crack after coating removal. VT did not miss a subsurface condition — it never had lighting, contrast, or a prepared surface.

A shop wants to accept remaining wall on a corroded elbow by "looking at it." Accessible pits can be described visually. Hidden thinning cannot. Send it to ultrasonic thickness.

Topic 1 language is short: first and last, direct versus remote, required versus prerequisite, and the two hard cannots — subsurface, and closed surface conditions you did not light or access.