ASNT NDT Level II — Study Guide

ASNT NDT Level II — Study Guide

Credential: ASNT NDT Level II Issuing body: ASNT (American Society for Nondestructive Testing) Jurisdiction: USA — certification is employer-administered under SNT-TC-1A (the employer's written practice; certification is revoked on job change) or third-party under the ASNT 9712 scheme (ISO-9712 aligned) Level: Level II — the interpreter/operator: can set up and calibrate equipment, conduct tests, interpret and evaluate results, prepare written reports, and supervise Level I personnel Prerequisites: Documented training hours + work experience per method (example per the ASNT 9712 scheme: UT — 80 hours training, 1,600 hours experience with 840 in UT) Renewal: Every 5 years — by application or by examination Exam: General + Specific + Practical per method; minimum 70% on each, 80% composite

Level II is where NDT becomes a profession rather than a task. Level I follows a procedure; Level II understands the procedure well enough to know when it's lying.

1. Pathway — How the Certification Is Earned

1. Meet training and experience. Each method (UT, RT, MT, PT, ET, VT, LT, AE, IRT) has required formal training hours and supervised work-experience hours. The hours scale with the method's complexity — UT and RT demand the most.
2. Vision examination. Near-vision acuity and color-contrast discrimination (for PT/MT color indications) — documented annually in most written practices.
3. Pass three exams per method. General (theory of the method — closed-book), Specific (the employer's procedures, codes, and acceptance criteria — often open-procedure), Practical (hands-on: calibrate, inspect specimens with known discontinuities, interpret, and write the report). 70% minimum each, 80% composite.
4. Employer certification. Under SNT-TC-1A the employer certifies you via its written practice — change employers and you re-certify. Under ASNT 9712, certification is portable and ISO-9712 aligned.
5. Renew every 5 years by application (documented continuing activity) or re-examination.

Critical context: SNT-TC-1A is a recommended practice, not a law — but it is contractually invoked by most US construction and fabrication codes, which gives it the force of law on a project. Know the difference when a contract cites it.

2. Knowledge Domains

Domain A — Method physics (General exam, all methods)

Ultrasonics (UT). Sound above human hearing (>20 kHz; weld inspection typically 2–5 MHz). Longitudinal waves (particle motion parallel to propagation — travel in solids and liquids) vs shear waves (perpendicular — solids only; the workhorse for weld inspection via angle-beam probes). Key relations: wavelength λ = v/f (v in m/s or in/µs, f in Hz); near field N = D²/4λ (D = transducer diameter) — inspections must be beyond the near field where the beam is chaotic; beam spread half-angle sin θ = 1.22λ/D — higher frequency and larger diameter give tighter beams. Snell's law governs mode conversion at the wedge: sin θ1/v1 = sin θ2/v2 — this is how a plastic wedge generates a 45°/60°/70° shear wave in steel. Acoustic impedance Z = ρv — reflection at an interface scales with impedance mismatch; couplant exists to exclude air (Z mismatch steel-to-air reflects ~100%).

Radiography (RT). X-ray (tube — bremsstrahlung + characteristic) vs gamma (isotope — Ir-192, Co-60, Se-75; fixed energies, no power needed). Attenuation: I = I0 e^(−μx) — thicker/denser material attenuates more, casting the shadow image. Geometric unsharpness Ug = (source size × OFD)/SOD — smaller source and closer film sharpen the image. IQI (penetrameter) — the image-quality indicator whose visible wire/hole proves the required sensitivity (typically 2-2T: see the 2T hole in the wire/hole whose thickness is 2% of the specimen). Film density (1.5–4.0 typical range) and the characteristic curve; scatter control (lead screens, collimation, backscatter "B" marker).

Magnetic particle (MT). Ferromagnetic materials only. A magnetic field is induced (yoke, prods, coil, head-shot); surface/near-surface discontinuities distort the field, creating flux leakage that attracts particles. Field direction must be perpendicular to the expected discontinuity — hence two perpendicular magnetizations for full coverage. AC (surface, mobile particles) vs HWDC (deeper penetration); prod spacing and current rules (typically 90–110 A per inch of prod spacing for HWDC, 4–6 in. spacing); particle types (dry visible, wet fluorescent — fluorescent is more sensitive).

Liquid penetrant (PT). Capillary action draws penetrant into surface-breaking discontinuities; developer draws it back out to form the indication. Steps: clean → apply penetrant → dwell (temperature- and material-dependent) → remove excess (water-washable, post-emulsifiable, or solvent-removable — removal method must not wash the defect) → apply developer → inspect under appropriate light. Visible dye (red on white developer) vs fluorescent (UV-A, darkened booth). PT finds surface-breaking defects only — and only on nonporous materials.

Eddy current (ET). AC coil induces eddy currents in conductive material; discontinuities perturb impedance, displayed as impedance-plane traces. Skin depth δ = √(ρ/πfμ) — higher frequency = shallower penetration (surface cracks); lower frequency = deeper (subsurface, tubing). Fill factor (tube inspection), lift-off (probe-to-surface distance — the dominant noise source), edge effects. Phase analysis separates defect signals from lift-off and permeability noise.

Visual (VT). Direct and remote (borescopes, cameras). Lighting, magnification, and — the Level II skill — knowing what to look for (the CWI-adjacent discontinuity vocabulary: cracks, undercut, overlap, porosity, misalignment).

Domain B — Calibration and technique (Practical exam core)

UT calibration. Distance calibration (IIW/V1 or V2 block — set the timebase so screen divisions equal known distances), sensitivity/TCG (time-corrected gain) or DAC (distance-amplitude correction) curves (equalize response across the inspection range — a reflector at 6 in. must read the same as at 2 in.), wedge delay and refracted-angle verification, resolution checks. The exam tests whether you calibrate before inspecting and whether you verify after (calibration checks bracket the work — drift invalidates results).

RT technique. Technique selection: source, film/detector, IQI placement (source side vs film side — and the "F" marker when film-side), exposure calculation from exposure charts, density verification. Film interpretation: distinguish porosity (round), slag (irregular), lack of fusion (linear, straight-edged), cracks (jagged linear), tungsten (bright white spots), undercut and burn-through signatures.

MT/PT technique. Bath concentration checks (settling test for wet fluorescent MT), UV-A intensity verification (≥1,000 µW/cm² at the surface), ambient light limits in the booth (<2 foot-candles for fluorescent), system performance checks (cracked chrome panel or known-defect specimens).

Domain C — Interpretation, evaluation, and codes (Specific + Practical)

Indication vs discontinuity vs defect. An indication is a response; a discontinuity is a real physical interruption; a defect is a discontinuity that exceeds the acceptance standard. Level II judgment lives in the second and third steps — and in knowing that relevant, nonrelevant, and false indications must be sorted before any evaluation (a magnetic particle buildup at a geometry change is nonrelevant; a scratch holding penetrant is false).

Acceptance criteria. From the construction code: ASME Section V (NDE methods) + Section VIII or B31.x (acceptance), AWS D1.1 Tables 6.1/8.1 (welds), API 1104 (pipelines). The Specific exam is open-procedure precisely because nobody memorizes all criteria — you must apply them: measure the indication, compare to the clause, disposition accept/reject/repair.

Reporting. The Level II report: equipment and calibration data, technique parameters, results sketch-mapped to the part, disposition, and traceability (procedure revision, personnel certification). The report is the legal record — in litigation, the inspection happened only if the report says so.

Domain D — Safety and the written practice

Radiation safety (RT). Time, distance, shielding; dosimetry (TLD/OSL badges, pocket dosimeters); boundary surveys (2 mR/hr controlled-area boundary per NRC/Agreement State rules); source handling and emergency procedures (crank-out source disconnect = the nightmare scenario — know the emergency response: evacuate, secure the boundary, notify the RSO). The General exam tests ALARA as a principle, not just a slogan.

The employer's written practice. Required by SNT-TC-1A: defines the levels, training/experience/exam requirements per method, vision requirements, and recertification rules for that employer. Level II personnel must know their own written practice — Specific exams are built from it.

3. Key Equations (with units and assumptions)

• Wavelength: λ = v/f. Steel shear wave: v ≈ 3,230 m/s (0.127 in/µs). At 2.25 MHz: λ ≈ 1.44 mm. Assumption: isotropic homogeneous material.
• Near field: N = D²/4λ. A 0.5-in. diameter, 2.25 MHz shear probe in steel: N ≈ 1.1 in. — inspect beyond this distance.
• Snell's law: sin θ_incident/v1 = sin θ_refracted/v1 = sin θ_shear/v_shear. Wedge (v ≈ 2,730 m/s) to steel shear (3,230 m/s): incident ~36.6° gives 45° shear. Assumption: planar interface.
• Attenuation (RT): I = I0 e^(−μx). μ in cm⁻¹, x in cm. Explains exposure charts — doubling thickness needs exponentially more exposure.
• Geometric unsharpness: Ug = (S × OFD)/SOD. Keep Ug below code limits (often ≤ 0.020 in. for the required sensitivity).
• Skin depth (ET): δ = √(ρ/πfμ). Copper at 1 kHz: δ ≈ 2 mm. Assumption: nonmagnetic (μ = μ0); ferromagnetic materials need saturation.
• MT prod current: ~90–110 A per inch of prod spacing (HWDC). Assumption: 4–6 in. spacing on steel under ~3/4 in. thick — verify against the procedure.

4. Worked Examples

Example 1 — UT beam check. A 2.25 MHz, 0.5-in. diameter shear-wave probe inspects a 1-in.-thick weld. Is the inspection in the near field? Step-by-step: v_shear (steel) ≈ 0.127 in/µs; f = 2.25 MHz → λ = 0.127/2.25 = 0.0564 in. N = D²/4λ = 0.25/(4 × 0.0564) = 1.11 in. The sound path in the weld (skip distances) typically exceeds this after the first leg — but the first inch of path is near-field: be cautious interpreting near-surface indications on short paths, and note it in the technique. Lesson: the exam tests whether you check, not whether you memorize N.

Example 2 — RT exposure change. A technique gives density 2.5 at 100 Ci-min exposure on 0.75-in. steel. What exposure for 1.0-in. steel at the same density? Step-by-step: Attenuation is exponential — use the exposure chart or the rule that each additional half-value layer doubles exposure. Steel half-value layer for Ir-192 ≈ 0.5 in. Additional 0.25 in. ≈ half a half-value layer → exposure × ~1.4 ≈ 140 Ci-min. Lesson: RT exposure scales exponentially with thickness — linear guessing underexposes. (Exact value from the chart; the method is what's tested.)

Example 3 — MT field direction. A longitudinal weld seam must be inspected for transverse cracks. How do you magnetize? Step-by-step: Field must cross the expected discontinuity — transverse cracks run across the seam, so the field must run along the seam: use a coil around the part or prods placed across... careful: prods create field between the prods, so place prods on either side along the seam axis to drive current across it, field lines running lengthwise. Then rotate 90° for longitudinal cracks. Lesson: "two perpendicular directions" is the procedure requirement because one direction is blind to parallel discontinuities.

Example 4 — PT dwell on a cold part. A procedure specifies 10-minute dwell at 60–125°F. The part is at 45°F in an unheated shop. Step-by-step: Stop. Below the qualified temperature range, penetrant viscosity rises and capillary action slows — dwell time is invalid and indications may not develop. Warm the part into range or qualify a new dwell. Lesson: the Specific exam tests procedure limits, not just procedure steps.

Example 5 — Indication evaluation. UT finds a reflector at mid-wall in a groove weld, 6 dB above the DAC curve, 1.5 in. long. D1.1 statically loaded, weld is 1-in. thick. Step-by-step: Amplitude alone doesn't reject — D1.1 UT acceptance (Annex Q / Table 6.3 logic) uses indication rating = amplitude − attenuation − length factors vs. the D-level thresholds. A +6 dB over DAC with 1.5-in. length on 1-in. material computes to a rating well into reject territory (Class D limits for static are around +5 to +11 dB depending on thickness/length). Lesson: UT acceptance is a calculation, not a feeling — run the rating.

5. Standards/Regulations Cross-Reference

• SNT-TC-1A: the recommended practice defining Levels I/II/III, training/experience/exam minima, and the employer's written practice. The organizational document behind the credential.
• ASNT 9712 / ISO 9712: the third-party, ISO-aligned certification scheme — portable across employers; 5-year renewal by application, 10-year re-examination.
• ASME BPVC Section V: NDE methods and requirements; Section VIII Div. 1/2, B31.1/B31.3, B31.8: acceptance criteria by construction code.
• AWS D1.1 Clause 6 + Annex Q: weld inspection and UT acceptance tables.
• API 1104: pipeline weld inspection criteria.
• ASTM E-series: E164 (UT welds), E94/E1742 (RT film), E709 (MT), E165 (PT), E1004 (ET) — the test-method standards behind the procedures.
• 10 CFR 34 / state radiography rules: RT licensing, boundary, and dosimetry requirements — the law behind the safety domain.

6. Pitfalls & Trap Patterns

1. The 70/80 rule. 70% minimum each exam, 80% composite. A 100% Practical doesn't save a 68% General.
2. Indication ≠ defect. Questions describe an MT buildup at a keyway and ask for disposition — it's nonrelevant until proven otherwise. Evaluate, don't just report.
3. Field direction in MT. Every MT scenario question secretly asks "is the field perpendicular to the crack?" Get this reflex automatic.
4. Calibration bracketing. Calibrate before, verify after. A procedure violation question often hides here.
5. SNT-TC-1A is employer-based. "I was Level II at my last job, so I'm Level II here" — wrong. New employer, new certification (unless ASNT 9712).
6. RT safety numbers. Boundary dose rates, dosimetry, and emergency response are free points if memorized — and the exam always asks.
7. UT: amplitude is not size. A high-amplitude reflector can be a small favorably-oriented defect; a low-amplitude one can be a large rough crack. Sizing needs technique (6 dB drop, etc.), not just gain.

Exam strategy: General = physics — derive from λ=v/f, Snell, attenuation, skin depth rather than memorizing factoids. Specific = procedure application — read the actual procedure clause, including notes and exceptions. Practical = do the work in order (calibrate → inspect → interpret → report) and document everything; examiners fail sloppy documentation faster than missed calls.

7. Practice Problems

1. A 5 MHz longitudinal probe (v = 5,900 m/s in steel) inspects a 25-mm plate. Compute λ and the near-field length for a 12-mm diameter crystal. Answer: λ = 5,900/5,000,000 = 1.18 mm. N = 144/(4 × 1.18) = 30.5 mm — longer than the plate is thick; near-field effects dominate the first backwall. Use a smaller crystal or lower frequency, or account for it.

2. Why must MT inspection use two perpendicular field directions? Answer: Flux leakage requires the field to cross the discontinuity. A field parallel to a crack produces no leakage — that crack orientation is invisible. Two directions cover all orientations.

3. An RT film shows round dark spots scattered in a weld. MT of the same weld shows nothing. Interpret. Answer: Internal porosity (volumetric, round) — RT sees it, MT can't (subsurface, and porosity's weak leakage field). Consistent: volumetric defects are RT/UT territory.

4. A PT procedure's dwell is 10 min at 60–125°F. The inspector dwells 20 min at 55°F "to be safe." Identify the errors. Answer: Temperature below the qualified range invalidates the dwell (viscosity/capillary effects); extended dwell doesn't compensate for out-of-range temperature. Follow the procedure or requalify.

5. ET at 100 kHz vs 1 kHz on copper tubing: which finds surface cracks, which finds deeper wall loss? Answer: 100 kHz (shallow skin depth) for surface cracks; 1 kHz (deeper penetration) for wall loss — but with lower surface sensitivity. Frequency selection is depth selection.

6. Define the difference between a nonrelevant and a false indication, with one example each. Answer: Nonrelevant: a real magnetic/geometric response not from a defect (MT buildup at a keyway). False: no discontinuity at all — contamination holding penetrant (a scratch or lint).

7. Under SNT-TC-1A, a newly hired Level II from another company wants to inspect on day one. What must happen first? Answer: The new employer must certify them under its own written practice — review of records, possibly re-examination (General/Specific/Practical per the practice). Prior certification doesn't transfer.

Original ETS reference writing, verified against public sources on 2026-09-30. Thin sourcing is flagged inline. Not legal advice — confirm current editions with the issuing body.