Ultrasonic Level I Practice Questions, Worked From the Physics Up
Level I ultrasonic testing is set-up, calibration and recording to a written instruction — not interpretation. These fifteen original questions test what that scope actually requires: wavelength and velocity arithmetic, near field and dead zone, IIW block use, DAC construction, couplant control under ASME Section V Article 4, and the point where a Level I hands the indication to a Level II.
Every number on this page was checked before it was written. Velocities come from published acoustic property tables; the calibration, couplant and temperature requirements come from ASME BPVC Section V, Article 4; the qualification structure comes from ASNT SNT-TC-1A. Where a value could not be confirmed, the requirement is stated without it. That matters more at Level I than anywhere else, because a Level I is trained to execute a written instruction exactly and has no authority to correct it. A technician who memorises a wrong near-field constant will build a wrong set-up and record wrong data with complete confidence. The questions below are original, written on the published body of knowledge rather than copied from any examination, and each one carries the reasoning that makes the answer transferable to the next part you put a probe on.
Source: Checked August 2026 against published ASME BPVC Section V, Article 4 text (T-432 temperature, T-433 couplant contaminant limits, Figure T-434.2.1 basic calibration block, T-463 calibration checks, T-471 scanning) and ASNT SNT-TC-1A (Level I scope wording, Table 6.3.1A training and experience hours, recommended grading), plus ISO 2400 for the IIW Type 1 (V1) block and published acoustic property tables for carbon steel and aluminium. These values have carried unchanged through recent Section V editions. Confirm every number against the edition your construction code invokes before applying it on a job.
| Component | Basis | What it assesses | Where Level I authority ends |
|---|---|---|---|
| General examination | SNT-TC-1A topical outline for ultrasonic testing | Velocity, wavelength, near field, beam spread, attenuation, mode conversion | No acceptance-criteria judgement is tested or permitted |
| Specific examination | Employer written practice and procedures | The employer's own equipment, blocks, procedures and written instructions | Bounded entirely by the written instruction |
| Practical examination | Hands-on, on the actual equipment | Set-up, calibration, scanning and recording on a specimen | Records results; a Level II evaluates them |
| Training | SNT-TC-1A recommends 40 hours for UT Level I | Classroom instruction in ultrasonic principles and technique | Training alone confers nothing without experience and examination |
| Experience | SNT-TC-1A recommends 210 hours in UT and 400 total NDT hours | Supervised work in the method | Counted and documented under the employer's written practice |
| Grading | Composite 80% minimum, no written examination below 70%, practical 80% minimum | All three examinations taken together | Certification is issued by the employer, not by ASNT |
Questions 1-2: Where Level I authority starts and stops
Question 1. Scanning to a written instruction that sets the recording level at 20% DAC, you find a sharp, repeatable indication at 18% DAC that looks like a crack. What does a Level I do? Answer: record the data the instruction calls for, report the observation to the Level II, and change nothing. The reasoning is in ASNT SNT-TC-1A itself. A Level I is qualified to perform specific calibrations, specific NDT and specific evaluations for acceptance or rejection according to written instructions, and to record results. Raising or lowering a recording threshold is a procedure change, and procedure changes belong to the Level III who wrote it.
Question 2. The written instruction specifies a 5 MHz, 6 mm dual-element probe. Your kit has a 2.25 MHz single-element probe of the same diameter. Can you proceed? Answer: no, and the reasoning is physical rather than bureaucratic. Dropping from 5 MHz to 2.25 MHz more than doubles the wavelength, shrinks the near field in direct proportion to the frequency, and lengthens the dead zone. Swapping dual for single element also removes the crossed-beam geometry that made near-surface detection possible. The instruction's detection capability was demonstrated with the specified probe, and substituting silently invalidates it. Our plain-English walkthrough of ASME Section V Article 4 UT requirements covers the code layer underneath.
Both questions test the same instinct, and it is the instinct the practical examination is really grading. SNT-TC-1A recommends 40 hours of classroom training plus 210 hours of ultrasonic experience and 400 total NDT hours before a UT Level I qualification, and it recommends a composite examination grade of at least 80% with no individual written examination below 70% and a practical grade of at least 80%. The full picture across every method is in our NDT training hours requirements guide.
Questions 3-5: Velocity, frequency and wavelength
Question 3. A 5 MHz straight-beam probe is used on carbon steel. What is the longitudinal wavelength? Answer: 1.18 mm, or 0.046 in. The working relationship is wavelength equals velocity divided by frequency. Longitudinal velocity in carbon steel is approximately 5,900 m/s, so 5,900 divided by 5,000,000 gives 0.00118 m. Why a Level I is asked this: wavelength sets the practical detection floor. A reflector much smaller than half a wavelength scatters too little energy back to the probe to produce a usable echo, which is the physical reason the written instruction specifies a frequency rather than leaving the choice to the technician.
Question 4. The same 5 MHz element is mounted on a 45 degree shear wedge. Does the wavelength change? Answer: yes, and it drops to 0.65 mm. Shear velocity in carbon steel is approximately 3,230 m/s, so 3,230 divided by 5,000,000 gives 0.000646 m. Shear wavelength in steel is roughly 55% of longitudinal wavelength at the same frequency. That is the physics behind angle-beam weld inspection: at identical frequency the shear beam resolves finer detail and avoids the mode conversion losses that afflict longitudinal waves at oblique incidence. The trade is higher attenuation and a shorter usable range.
Question 5. A digital thickness gauge calibrated on steel reads 12.7 mm on an aluminium plate. What is the true thickness? Answer: 13.6 mm. The gauge measures transit time and multiplies by an assumed velocity, so thickness equals velocity times transit time divided by two. Steel longitudinal velocity is about 5,900 m/s and aluminium about 6,320 m/s, so the true thickness is 12.7 multiplied by 6,320 divided by 5,900, giving 13.6 mm. The gauge under-read by 6.6%. This is the most common false reading in field thickness work, and the reason velocity calibration on the actual material precedes every survey.
Questions 6-8: Near field, beam spread and dead zone
Question 6. Calculate the near-field length for a 10 mm diameter, 5 MHz probe on carbon steel. Answer: 21.2 mm. The formula is N equals D squared times f, divided by 4V. Working it through: 0.010 squared is 0.0001, multiplied by 5,000,000 gives 500; four times 5,900 gives 23,600; 500 divided by 23,600 is 0.0212 m. Why it matters at Level I: inside the near field, contributions from different parts of the crystal face interfere and on-axis pressure swings through a series of maxima and minima. Two identical reflectors at different depths inside N return wildly different amplitudes.
Question 7. What is the minus 6 dB beam divergence half-angle for that same probe? Answer: approximately 3.5 degrees. For a disc element the relationship is sine of the half-angle equals 0.514 times V, divided by f times D. That gives 0.514 multiplied by 5,900, divided by 5,000,000 multiplied by 0.010, which is 0.0606, and the arcsine of that is 3.5 degrees. The 0.514 constant defines the half-amplitude edge of the main lobe. Divergence is what the written instruction compensates for when it specifies a scan index or an overlap. Lower frequency and smaller diameter both widen the beam.
Question 8. A 2.25 MHz contact probe cannot resolve a lamination 2 mm below the entry surface. Name two changes that attack the cause, and one that makes it worse. Answer: raise the frequency, and add a delay line or switch to a dual-element probe. Increasing gain makes it worse. The dead zone is the interval masked by the ring-down of the initial pulse and the receiver's recovery time, not a near-field effect. A shorter, more heavily damped pulse decays faster, and a delay line pushes the interface echo along the time axis so the near-surface metal falls in clear screen space. More gain simply extends the saturated region.
Questions 9-11: Calibration blocks and distance calibration
Question 9. Which feature of the IIW Type 1 block (V1, ISO 2400) locates the beam index point of an angle-beam probe? Answer: the 100 mm radius quadrant. Every ray leaving the exit point travels the same 100 mm to that arc regardless of its angle, so the echo peaks when the exit point sits directly over the engraved centre mark. Read the index point against the scale on the block edge. The metric V1 is a 300 by 100 by 25 mm steel block carrying that 100 mm radius, a 50 mm diameter plastic-filled hole, a 1.5 mm side-drilled hole and a machined slot.
Question 10. Which V1 feature verifies the refracted angle? Answer: the 50 mm diameter plastic-filled hole, read against the angle scale engraved on the block face. Direct the beam at the insert from the side, peak the echo, and read the angle opposite the index point. Verification matters because the wedge angle stamped on the probe is nominal for one assumed material velocity. Wedge wear, temperature and a different part velocity all move the true refracted angle, and a beam sitting 3 degrees off nominal puts your plotted reflector at the wrong depth through the weld.
Question 11. Calibrating a straight beam to a 0-100 mm range on the 25 mm dimension of the V1 block, what should the screen show and which two controls get you there? Answer: four evenly spaced back-wall echoes at 25, 50, 75 and 100 mm, set with the zero-offset or delay control and the range or velocity control. Two controls are needed because two independent errors exist. Probe and wedge delay shifts everything by a constant, an offset. Wrong velocity stretches or compresses the whole sweep, a slope. Peaking the first echo fixes the offset, peaking the last fixes the slope, and you iterate until both sit.
Questions 12-13: Building a DAC as a Level I task
Question 12. On an ASME basic calibration block you are told to construct a DAC from the side-drilled holes. Which reflector sets the primary reference level, and what must not change afterwards? Answer: the hole returning the highest amplitude response sets the reference. Peak it to 80% full screen height, record that gain, and do not touch the gain again while the remaining points are plotted. The block itself is defined in ASME BPVC Section V, Article 4, Figure T-434.2.1, with side-drilled holes at one quarter, one half and three quarters of the block thickness, and notches 2% of the thickness deep and at least 1 in long. The method requirements sit in our ASME BPVC Section V compliance reference.
Question 13. Why does a DAC curve fall away with sound path when every hole is the same diameter? Answer: two mechanisms, both physical. Beam spread means less of the emitted energy strikes a small reflector at long range and less of the scattered energy is recaptured by the crystal. Separately, the material attenuates the wave through absorption and scattering as it travels. The DAC is the empirical record of both effects for this material, this probe and this couplant together, which is exactly why the curve must be rebuilt when any one of the three changes.
Questions 14-15: Couplant and temperature control
Question 14. You are handed a couplant for an austenitic stainless steel weld. What must the certificate show, and what would the answer be for a nickel alloy? Answer: not more than 250 ppm of halides, chlorides plus fluorides, for austenitic stainless steel and titanium; not more than 250 ppm sulfur for nickel-base alloys. ASME BPVC Section V, Article 4, T-433.2 sets both. The reasoning is metallurgical rather than acoustic. Residual chlorides concentrate on the surface and drive chloride stress-corrosion cracking in austenitic grades, and sulfur embrittles nickel alloys at service temperature. The couplant you leave behind can create the flaw you were sent to find.
Question 15. The calibration block is at 15 degrees C and the vessel surface is at 43 degrees C. Do you proceed? Answer: no. Article 4 requires the calibration block and the examination surface to be within 25 degrees F, which is 14 degrees C, of each other, and this is a 28 degree C difference. Velocity in the part and in the wedge both shift with temperature, moving the refracted angle and the depth scale at the same time. One further rule sits alongside it: the same couplant used for calibration must be used for the examination, because a different couplant changes transmission at the interface and shifts every amplitude on the screen.
Scanning discipline the practical examination grades
Two numbers from ASME BPVC Section V, Article 4 turn up in almost every practical examination because they are the ones candidates skip. Each pass of the search unit must overlap at least 10% of the transducer dimension perpendicular to the direction of the scan, and search unit movement must not exceed 6 in./s, which is 150 mm/s, unless the procedure qualifies a faster rate. Both exist to stop a real reflector passing through the beam faster than the instrument can capture and display its peak amplitude.
The calibration-check rules are the other half of that discipline. If a point on the DAC has dropped by 20% or 2 dB in amplitude, every data sheet since the last valid calibration check is marked void and the affected work is re-examined. If a point has moved along the sweep line by more than 10% of the sweep reading or 5% of full sweep, whichever is greater, the distance range is corrected, the correction is noted in the examination record, and all recorded indications since the last valid check are re-examined and their values changed on the data sheets.
A Level I who understands why those thresholds exist stops treating the end-of-shift check as paperwork. A 2 dB drop leaves an echo at about 79% of its original height, which is why the code pairs 2 dB with 20% — the two describe the same loss. That loss is enough to push a reflector sitting on the DAC down below a recording level and out of the report. The check is the only mechanism that catches a cracked wedge, a drying couplant film, a warming part or a failing pulser before a shift of data becomes unusable.
What changes when you move to Level II
Level II is where interpretation begins. SNT-TC-1A recommends a further 40 hours of training and 630 hours of ultrasonic experience against 1,200 total NDT hours for a UT Level II, and the examination shifts from whether you followed the instruction to whether the indication is acceptable under the construction code. The natural next step from this page is the UT Level II practice questions, which work through flaw sizing, transfer correction, weld geometry, plotting and acceptance criteria with the same worked-reasoning format.
The commercial gap is wide, and it comes down to one thing. A Level II can sign a report; a Level I cannot. That single difference is what the NDT Level II salary data reflects, and it is why US employers treat Level I as a route rather than a destination. The technicians who move fastest are the ones who learn the physics behind the set-up rather than the button sequence, because the physics transfers to the next instrument and the button sequence does not.
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What is a UT Level I actually allowed to do?
SNT-TC-1A qualifies a Level I to perform specific calibrations, specific ultrasonic testing and specific evaluations for acceptance or rejection according to written instructions, and to record results, under instruction or supervision from a Level II or III. Set up, calibrate, scan, record. Judging an indication against a construction code's acceptance criteria is the Level II function.
How do you calculate ultrasonic wavelength?
Wavelength equals velocity divided by frequency. A 5 MHz longitudinal wave in carbon steel at 5,900 m/s gives 5,900 divided by 5,000,000 = 1.18 mm. The same element on a shear wedge, at 3,230 m/s, gives 0.65 mm. Wavelength sets the detection floor: a reflector far below half a wavelength returns too little energy to produce a usable echo.
What is the difference between the near field and the dead zone?
The near field is the interference zone in front of the crystal where on-axis pressure swings through maxima and minima; its length is D squared times f, divided by 4V. The dead zone is the interval masked by the ring-down of the initial pulse and the receiver's recovery. Higher frequency shortens both; more gain lengthens the dead zone; a delay line moves it out of the part.
Which IIW block feature finds the beam index point?
The 100 mm radius quadrant on the IIW Type 1 (V1) block. Every ray leaving the exit point travels the same 100 mm to that arc whatever its angle, so the echo peaks when the exit point sits over the engraved centre mark. The 50 mm plastic-filled hole, read against the engraved angle scale, verifies the refracted angle.
What couplant limits does ASME Section V set for stainless steel?
Couplant used on austenitic stainless steel or titanium must not contain more than 250 ppm of halides — chlorides plus fluorides — and couplant used on nickel-base alloys must not contain more than 250 ppm sulfur, under ASME BPVC Section V, Article 4, T-433.2. Chlorides drive stress-corrosion cracking; sulfur embrittles nickel alloys. The same couplant must be used for calibration and examination.
What score do you need to pass a UT Level I examination?
SNT-TC-1A recommends a composite grade of at least 80% across the general, specific and practical examinations, with no individual written examination below 70% and a practical examination grade of at least 80%. Recommended prerequisites for UT Level I are 40 hours of training, 210 hours of ultrasonic experience and 400 total NDT hours.