ASNT NDT Level II common mistakes
ASNT NDT Level II · Understand the traps and how to avoid them.
On an aluminium tube or plate, records a conductivity change when the phase shift actually came from variation in probe lift-off/coupling.
Most lab scans are run with a fixed, well-coupled setup, so candidates learn the shortcut 'phase angle = conductivity' and never see the lift-off vector on the impedance plane.
What to do instead
Determine the lift-off vector with a plastic shim on the same alloy before scanning, then compare each anomalous signal against that vector: a true conductivity change follows the conductivity curve, a lift-off artifact follows the shim vector. Re-balance at the same lift-off and repeat the reading before recording a value.
Uses a conductivity reference standard of a different alloy, temper, or thickness (e.g., annealed vs. aged stock, or a 2024 block on a 7075 part) and reports the meter reading directly as the part's conductivity.
Usually only one reference block is on the bench, and the effect of alloy/temper/temperature on conductivity is not visually obvious during practice.
What to do instead
Match the standard to the part alloy, temper, and thickness, and measure both at the same temperature; where an exact match is impossible, apply the documented correction and record the alloy/temper of block and part in the report.
Yoke-inspects a longitudinal seam weld with the yoke straddling the seam so that the magnetic field runs along the weld axis, finds nothing, and clears the weld.
The yoke is applied the same way as for general plate inspection out of habit, and the field-parallel-to-defect geometry is invisible on the part.
What to do instead
Place the yoke so the field crosses the expected defect axis (legs on opposite sides of a longitudinal seam), and magnetize in two directions approximately 90 degrees apart; sketch the field direction on the technique sheet before inspecting.
Reads fluorescent indications under ordinary room light immediately after the white light is switched off, without dark adaptation or a black-light intensity check, and clears the part.
In the training booth the light is already dim and the meter/adaptation step is usually performed by the instructor, so it is never practised as a candidate task.
What to do instead
Verify black-light intensity at the inspection surface with a calibrated meter against the governing standard (commonly on the order of 1000 microwatts per square centimetre), allow the specified dark-adaptation time, and re-scan after a few minutes before signing a clear result.
Water-washes or sprays remover until the background is completely clean, then judges the part acceptable.
Candidates are taught to eliminate background to avoid false calls, and the same rinse that clears the background also flushes penetrant out of shallow, tight discontinuities.
What to do instead
Rinse at low pressure with the nozzle kept off the surface and stop as soon as the bulk surface penetrant is gone, accepting a light residual background; prove the wash technique on a known cracked or stepped test panel before production work.
Runs the penetrant process on a cold-shop part or a hot part outside the qualified temperature range and accepts the resulting weak or diffuse indications.
Temperature limits are buried in the written procedure and are rarely varied in training, while viscosity, dwell, and diffusion all change markedly outside the range.
What to do instead
Measure the part surface temperature with a contact thermometer before applying penetrant and bring part and materials into the qualified range (commonly 10 to 52 degrees C / 50 to 125 degrees F); if the part cannot be brought into range, use a technique qualified at that temperature.
Raises kV to shorten an over-long exposure on a thick section, then accepts the radiograph because the measured film density is within limits.
kV and mA both 'make the film darker' in the candidate's mental model, so the two controls are treated as interchangeable knobs.
What to do instead
Separate the roles explicitly: mA, time, and distance (inverse square) change intensity; kV changes penetrating power and therefore contrast and scatter. Set kV from the required penetration and the code's allowed range first, then adjust mA-minutes for density, and check sensitivity with the IQI rather than density alone.
Substitutes into the geometric unsharpness relation with the source size in millimetres and the distance in inches, or uses source-to-film distance where source-to-object distance is required.
The formula is memorized symbolically with no unit or dimension convention, and source-to-film distance is the value most often quoted on the technique sheet.
What to do instead
Write the relation out with its definitions (source size and source-to-object distance in the same units, object-to-film distance for the specimen thickness term) before substituting, and confirm the resulting value against the unsharpness limit in the governing code rather than against the previous shot.
Sets up a DAC or distance-amplitude curve on a flat, smooth reference block and applies it to a curved, rough forging or casting without transfer or curvature correction.
Reference blocks are the only calibration path drilled in training, and amplitude loss from surface finish, curvature, and couplant is not visible in the lab.
What to do instead
Measure the transfer correction between block and part (or use a reference with matched radius and finish), apply it to the gain, and re-scan; also confirm velocity and probe delay on the actual material before recording depths.
Performs the visual examination under general shop lighting, records no indications, and signs off the inspection.
The illumination requirement and the use of a light meter are procedural details that are seldom exercised in practice sessions.
What to do instead
Measure illumination at the inspection surface with a calibrated light meter, add task lighting until the level specified by the governing procedure is reached (commonly a minimum of 100 foot-candles, about 1076 lux, with more for fine detail), and record the measured value with the results.