Treat every VT observation as a three-step chain: verify the technique conditions, name the discontinuity with measured size, then apply the procedure's acceptance criteria before any disposition. The vocabulary (indication, discontinuity, defect), the technique limits (illumination, distance, viewing angle), and report completeness are the content to drill. Study with mock-up scenarios and gauges, and treat readiness scores as learning milestones, not pass predictions.
Calling It Right: Indication vs. Discontinuity vs. Defect
An indication is what you observe; a discontinuity is a confirmed interruption or irregularity in the material; a defect is a discontinuity that the written acceptance criteria reject. Keeping the three terms separate is a working skill, not wordplay.
The three words sit on a decision ladder. At the bottom is the indication: a light pattern, shadow, or surface feature you notice. Confirm it against the surface and it becomes either a condition (such as weld ripples or spatter, usually nonrelevant unless the procedure says otherwise) or a discontinuity (such as undercut, a pore, or a crack). Only after the procedure's acceptance criteria are applied does a discontinuity become a defect. Writing 'defect' in your report before you have measured anything against a criteria table overstates what you actually know at that moment.
Train the ladder with a forced-labeling drill: take five weld photographs or mock-up views and, for each, write what you observed, the named discontinuity or condition, whether the indication is relevant or nonrelevant, and—if you are given a criteria table—the disposition. When no table is supplied, the only correct fourth entry is 'discontinuity, disposition pending criteria.' Repeat the drill until the order feels automatic, then swap photo sets with a colleague and challenge each other's labels. The drill sharpens exactly the step where loose vocabulary collapses a sound observation into an unsupported conclusion.
- Indication: the observed evidence, before interpretation
- Discontinuity: a confirmed interruption or irregularity in the material
- Condition / nonrelevant indication: surface features such as ripples or spatter, unless the procedure says otherwise
- Defect: a discontinuity that fails the applicable acceptance criteria
Direct or Indirect? Matching the Technique to Access and the Procedure
Direct VT means the unaided eye views the surface, with aids like mirrors or magnifiers if the procedure permits; indirect VT uses borescopes, video, or other remote means when access blocks direct viewing. The written procedure defines which technique applies.
Direct visual testing is the default: the eye is positioned at the object within the distance and angle limits the written procedure states. VT training materials commonly teach benchmark values such as a maximum viewing distance of 600 mm (about 24 inches) and a viewing angle of at least 30 degrees to the surface; treat these as example values your own procedure would specify, not universal constants. Magnifiers and mirrors do not convert direct viewing into indirect testing when the procedure allows them as aids. Indirect testing is justified when geometry, distance, or hazard prevents direct access—tube interiors, tank internals, or hot surfaces.
The application habit is to reason from access first, then from the procedure. Consider a circumferential weld inside a 100 mm pipe: direct viewing is physically impossible, so the authorized answer is an indirect technique—typically a borescope with its own illumination—provided the procedure permits it and the image quality is adequate for the assessment required. A tempting but weaker choice in a scenario is to reach for a camera or magnifier because it seems more thorough; a technique the procedure does not authorize produces results with no standing. Ask first: can I meet the distance and angle limits directly? If not, which indirect method does the procedure name, and what equipment checks does it require?
| Aspect | Direct VT | Indirect VT |
|---|---|---|
| Access requirement | Eye at or near the surface, within procedure limits | Used when direct access is impossible or impractical |
| Typical aids | Mirrors, magnifiers (if procedure allows) | Borescopes, fiberscopes, video/camera systems |
| Key procedure constraints | Viewing distance and viewing angle limits | Equipment type, resolution/verification checks, lighting capability |
| Example limitation | Cannot reach inside small-bore pipe | Image quality may limit detection of fine discontinuities |
Illumination First: Verifying Conditions Before You Judge an Indication
An observation taken under unverified lighting, distance, or angle is not a defensible result. Before interpreting anything, confirm the surface illumination against the procedure's stated minimum and confirm your eye position meets the stated distance and angle.
VT training materials commonly teach a benchmark minimum of about 100 foot-candles (roughly 1,000 lux) on the surface for direct visual testing; your procedure supplies the value that governs your work. Verification means a light meter reading at the actual surface, not an impression of brightness, plus a check that shadows and glare are not hiding the weld toe or the heat-affected zone. Also confirm the surface condition the procedure requires—cleaned, deslagged, dry—because spatter and scale can mask exactly the indications you are hunting. These checks take a minute and they convert 'I think I saw' into 'I observed under stated conditions.'
Worked scenario: you are examining a butt weld on structural plate. The bay is dim, but you call an undercut 'rejectable' from visual impression alone. The mistake is twofold—judging size without verified illumination, and dispositioning without a measurement. The better sequence: pause, take a light meter reading at the weld surface, reposition the lamp until it meets the procedure's minimum, then measure the undercut's depth and length with a weld gauge and compare the numbers to the procedure's criteria table. Why it matters: an observation made outside the stated conditions can be discarded in any review, and an unmeasured call cannot be rechecked by anyone reading your report.
Naming Weld Discontinuities: Undercut, Porosity, Cracks, and Look-Alikes
Level II VT work requires naming surface discontinuities by their visible signature: undercut as a groove at the weld toe, porosity as rounded voids, cracks as sharp, tight linear breaks. Correct naming drives which criteria clause applies.
Each common weld discontinuity has a recognizable surface signature. Undercut is a linear groove melted into the base metal at the toe or root of the weld, often with a sharp edge you can catch with a gauge tip. Porosity appears as rounded, individual or clustered surface pores. Incomplete fusion or penetration may show as an unfilled groove or a tight seam at a joint edge. Arc strikes are small melt spots outside the intended weld area, and spatter is fused metal balls sitting on the surface—frequently a condition rather than a discontinuity unless the procedure restricts it. Cracks deserve special respect: they are typically tight, sharp-ended, and may show oxidation or branching.
Practice the distinctions with a naming worksheet: set out mock-up coupons or high-quality photos showing undercut, surface porosity, an arc strike, spatter, and a suspected crack, and for each write the name, the visible features that support it (location, shape, edge character), and what additional check you would make—depth gauge for undercut, orientation and end sharpness for a crack. Where a look-alike is genuinely ambiguous, the disciplined entry is 'linear indication, cause not confirmed' rather than a confident wrong name. Misnaming a crack as a shallow gouge, for instance, points you to the wrong criteria clause and understates the finding's significance.
From Observation to Disposition: Applying the Written Criteria, Not Memory
A disposition is legitimate only when it cites the procedure's acceptance criteria applied to a measured indication. Grouping rules, size limits, and length limits are read from the document in force, not recalled from experience.
Acceptance criteria are written as limits on measurable quantities: maximum pore size, cumulative length of undercut, permitted number of indications per length of weld, and rules for aligned or clustered indications. Two habits make application reliable. First, record the measured numbers before forming any opinion—depth, length, and spacing for each relevant indication. Second, read the grouping clauses explicitly: criteria often treat several small indications differently when they align or cluster, so the pattern matters as much as any single size. Note which procedure revision you are working to, since criteria can change between revisions.
Worked scenario: a procedure permits individual surface pores up to 2 mm but rejects aligned porosity. You find three 1.5 mm pores in a line along the weld. The tempting call is to accept, because every pore is under 2 mm. The better decision: recognize the alignment, apply the procedure's clause covering aligned indications, and record the pattern, the spacing between pores, and each pore's size in the report. Why it matters: the disposition flows from how the criteria group indications, not from individual sizes alone—accepting on size while ignoring pattern would misreport the weld's condition.
Reports That Stand Up: Recording Technique, Conditions, and Findings
A VT report must let a reader reconstruct what was done and what was found: technique used, conditions verified, equipment identified, the procedure revision applied, and each relevant indication mapped with location and measured size.
At Level II, the expected working responsibilities include reading and understanding the inspection procedure, performing the inspection, and ensuring complete and accurate documentation of results. Complete means a reader could repeat your examination and reach your evidence: the direct or indirect technique used and why, the illumination verification, the viewing distance and angle achieved, equipment identifiers (borescope model, gauge used), the procedure and revision number, and the item identity and weld locations. Findings belong on a sketch or map with coordinates, not in prose alone, so anyone can locate the indication you recorded.
Check your own reports with a completeness pass: cover the report and, from memory, list what another inspector would need to retrace the examination. If anything on that list is missing—say, the illumination reading or the criteria revision—your report is incomplete. Also practice writing findings neutrally: 'Undercut, 0.8 mm deep × 12 mm long, at 3 o'clock, depth gauge, exceeds 0.5 mm limit per Table 2' states facts and a cited comparison. Reserve 'defect' and 'reject' for entries where the cited limit is actually exceeded, and record 'disposition pending' where criteria interpretation is being escalated rather than guessing a disposition yourself.
A Four-Week Sequence with a Self-Check Rubric and Readiness Checks
Structure preparation in four weeks: vocabulary, technique and conditions, criteria application, then full reports under time. Measure progress with a ten-item labeling rubric; treat the score as a learning milestone, not a prediction of exam results.
A practical exercise to repeat weekly: build or obtain five stations—mock-up coupons or detailed photographs—containing undercut, surface porosity, an arc strike or spatter, a suspected crack, and one clean weld. At each station, complete the full chain: verify stated lighting and viewing conditions, name the indication, mark relevant or nonrelevant, measure where a gauge applies, and write a one-line disposition citing a criteria table. Expected observations: you should consistently catch the dim-lighting condition if one is planted, correctly label spatter as a condition unless criteria say otherwise, and refuse to disposition the ambiguous linear indication without more evidence.
Adaptable sequence: Week 1, drill the indication–discontinuity–defect ladder and build a naming worksheet from the discontinuity list. Week 2, work with a light meter, weld gauges, and mirror or borescope on mock-ups, recording distance and angle for each setup. Week 3, apply sample criteria tables to measured indications, including grouping and alignment clauses. Week 4, write complete reports under time and run the free practice questions linked below, then review every error against the chain. If your employer sponsors practical training, ask to join a supervised mock inspection; for application routes, eligibility documentation, and exam logistics, check the issuer directly at asnt.org/certification.
- Rubric item 1 — Naming: for each station, gives indication type, discontinuity or condition, and relevance, with the visible features that support it (2 points per station set)
- Rubric item 2 — Conditions: states the illumination minimum, the measured reading, and the distance/angle achieved (2 points)
- Rubric item 3 — Measurement: uses the correct gauge and records depth, length, and spacing numbers before any opinion (2 points)
- Rubric item 4 — Disposition: cites the specific criteria clause applied, including grouping or alignment rules (2 points)
- Rubric item 5 — Report: technique, equipment, procedure revision, and mapped indication locations all present (2 points)
- Readiness check A: two consecutive drill sessions at 8/10 or better with no unverified-condition observations
- Readiness check B: a timed report that another person can follow to retrace the examination without asking questions
- Readiness check C: you can explain, in one sentence each, why direct vs. indirect was chosen for three different access situations
References and further reading
Use these references to explore the concepts and check the latest information from the relevant organizations.