PCN NDT Ultrasonic Testing Level 2 Exam common mistakes
PCN NDT Ultrasonic Testing Level 2 Exam · Understand the traps and how to avoid them.
Calculating a discontinuity's depth or size from the surface distance or sound path without confirming whether the indication is on the beam's near side or far side of the skip point, so a second-leg signal is reported at first-leg depth.
Candidates memorize the basic depth formulas for straight and angle beams but never practice deciding which leg the echo belongs to. On the exam, the geometry is given in prose and the candidate plugs numbers into the first formula that comes to mind.
What to do instead
Before any calculation, sketch the beam path on scratch paper, mark the skip point, and decide which leg produces the echo. Then apply the matching depth and surface-distance relationship for that leg. Practice a set of mixed first-, second-, and third-leg problems until the leg decision is automatic.
Choosing a transducer frequency or crystal size that cannot meet the required sensitivity or resolution for the stated material and thickness, for example using a large low-frequency probe for thin-section or fine-grain resolution work.
Frequency, wavelength, near-field length, and beam spread are studied as separate formulas rather than as trade-offs. Candidates pick the probe that gives a strong echo rather than the one that satisfies resolution and penetration requirements together.
What to do instead
For each practice scenario, write down the required penetration, resolution, and coverage first, then select frequency and size and justify the choice with wavelength, near-field, and beam-spread numbers. Learn the qualitative trade-off table by heart and apply it before computing.
Setting the reference gain and scanning sensitivity once at the start of the exam question and then reporting amplitudes or acceptance decisions without re-referencing after a change of probe, cable, or instrument setting.
Candidates treat calibration as a preliminary step rather than a continuing requirement. They also forget that cable length and probe changes shift the baseline, so amplitude comparisons become invalid.
What to do instead
Adopt a fixed routine: any change in probe, cable, or instrument setting triggers a re-check of the reference reflector before further evaluation. In exam questions, explicitly state the reference level used for each reported amplitude and note when a re-calibration was required.
Reporting a rejectable indication based on amplitude alone while ignoring length, geometry, and the acceptance criteria that apply to the specific product form and weld configuration.
Amplitude is the most visible number on the screen, so candidates equate a high echo with a defect. They skip the step of matching the indication to the written acceptance criteria for length and type.
What to do instead
For every indication, record amplitude, length by the specified method, depth, and character, then compare all of these against the applicable acceptance criteria before deciding. Practice classifying indications against criteria tables rather than judging by height on the screen.
Misidentifying the nature of an indication, calling a geometric reflection, mode-converted signal, or weld-cap echo a defect, or dismissing a real lack-of-fusion signal as geometry.
Candidates learn defect types as definitions without learning the dynamic behaviour that distinguishes them: movement with probe angle, response to focusing, and behaviour when the probe is rotated or the part is tapped.
What to do instead
Learn a recognition checklist for each indication type: does it move with probe angle, does it persist across the weld, does it respond to a second probe, and does it appear at a predictable geometric depth. Apply the checklist to every practice indication before assigning a type.
Confusing the roles of the reference block and the calibration block, or using a block whose material, surface finish, or thickness does not match the part under test, and then transferring that sensitivity directly to the workpiece.
Both blocks look similar and both are used during setup. Candidates memorize that blocks are used for calibration without learning which block establishes which parameter and why material matching matters for attenuation and velocity.
What to do instead
Build a short table pairing each block with the parameter it establishes and the matching requirements for material, velocity, and surface. Before using any block, state what it calibrates and whether it matches the part; transfer sensitivity with a correction when it does not.
Applying a distance-amplitude correction curve or transfer correction incorrectly, such as using a curve built for one probe on another, or omitting the transfer correction when couplant and surface conditions differ between block and part.
The correction is treated as a one-time instrument function rather than a measurement whose validity depends on the probe, the material, and the surface. Candidates also skip the transfer step because it seems like an optional refinement.
What to do instead
Treat every correction curve as tied to a specific probe and setup, and rebuild it after any change. Always perform and record the transfer correction when surface or couplant conditions differ, and state the corrected reference level in the answer.
Writing a technique or procedure answer that omits essential parameters, such as scan overlap, scan speed, coverage of the required volume, or the qualification of the operator, leaving a technically correct but incomplete method.
Candidates answer the question they find easiest, usually the probe and frequency, and forget that a procedure is judged on completeness of coverage and documentation, not on the probe selection alone.
What to do instead
Use a fixed procedure skeleton: material and geometry, standards and acceptance criteria, equipment and probe, calibration and reference blocks, scanning technique and coverage, recording and reporting. Fill every heading before writing the final answer.
Misreading or misapplying the acceptance criteria, for example mixing up amplitude thresholds, using the wrong length measurement method, or applying criteria for one weld or product type to another.
Criteria tables are dense and similar between standards. Under time pressure, candidates recall the general shape of a table rather than the exact clause that applies to the stated product and discontinuity type.
What to do instead
Practice reading criteria tables against worked examples, and always identify the product form, discontinuity type, and measurement method before selecting a clause. Quote the specific criterion in the answer so the reasoning can be checked.
Making unit and significant-figure errors, mixing millimetres and inches, microseconds and milliseconds, or reporting more decimal places than the measurement supports, and failing to sanity-check whether the result is physically plausible.
Calculations are done quickly and the answer is written without a plausibility check. Candidates also convert units mid-calculation and lose track of the factor.
What to do instead
Standardize on one unit system at the start of each problem, carry units through every step, and finish with a plausibility check against known values such as sound velocity in steel and typical near-field lengths. Report answers to the precision the input data supports.