Study PCN Level 2 Ultrasonic Testing by practising the full decision chain, not isolated facts: calibrate range and reference levels, compute beam path and skip distance, plot indications on a weld cross-section, choose the correct sizing method, and write reports that another qualified person could retrace. Two worked scenarios below show a plausible mistake, the better decision, and why the difference matters. A four-phase sequence and self-check rubric tell you when your reasoning is exam-ready as learning milestones.
Why decibel arithmetic breaks down mid-calculation
Decibel moves are always relative to a stated reference. Every calculation must chain reference gain, transfer correction and scanning gain in one annotated line, otherwise sign and order errors compound silently.
Recall the mechanics: a change of 6 dB doubles or halves the displayed amplitude, and successive changes multiply their linear factors while their decibel values add. Errors appear when you switch reference levels halfway through a calculation, or mix decibel values with distances and angles in the same step. The fix is procedural, not mathematical. Write one chain before you calculate: reference gain, then transfer correction, then scanning gain, then evaluation level, annotating each number with what it represents.
Drill this with three-step problems rather than single-step recall. For example: a side-drilled hole sets your reference level; an indication reads 8 dB above that reference level; a transfer correction of minus 2 dB applies. State the indication's amplitude relative to the reference after correction, and name the basis of every figure. Expected observation: your speed and accuracy improve noticeably once the chain is written out first, because the arithmetic itself is trivial once the references are unambiguous.
- Always state the reference before quoting any amplitude in dB.
- Apply transfer correction before comparing an indication to a curve.
- Label every number in your working as gain, correction, or reading.
Range calibration and beam path: getting geometry right first
A correct range calibration maps screen position to real beam path or surface distance. Every depth and surface-distance readout depends on it, so recalibrate whenever the probe angle, wedge or range changes.
Practise range calibration on standard reference blocks until the sequence is automatic: establish the zero, set known reflectors to their correct beam-path positions, and confirm the screen covers half skip and full skip for the thickness being examined. With angle beam probes, distinguish carefully between beam path length and surface distance, because report formats and plotting methods use one or the other. A readout that looks like a depth is only a depth if the range was calibrated in that mode.
Trace this example in your notes: the same reflector produces one beam-path reading on a 60-degree probe and a different one on a 70-degree probe, yet describes a single physical point. Sketching both probe positions on one cross-section makes the relationship visible. Then check your observations: screen marks match the block's known reflector spacings, and you can state, for any screen position, whether it falls in half-skip or full-skip territory for the test thickness. If you cannot, calibration, not interpretation, is your study priority.
Skip distance, dead zone, and mislabelled geometric echoes
Skip distance and dead zone define where the beam can and cannot resolve indications. Mislabelling weld geometry as a defect usually comes from evaluating an echo position without plotting it against the joint design.
For a full skip in a plate of thickness t with probe angle theta, the surface distance is two t times tan theta, and the beam path is two t divided by cos theta. Dead zones near the entry surface mean shallow reflectors may be missed or misread on some setups. Worked scenario one: on a 15 mm single-V butt weld with a permanent backing bar, scanned with a 60-degree probe, a strong indication appears at roughly full-skip surface distance. The plausible mistake is reporting lack of fusion because the amplitude is high. The better decision is to plot the beam path first: the echo position coincides with the backing bar and weld toe, known geometric reflectors. Confirm by scanning from the opposite side and with a second probe angle; a geometric reflector shifts predictably, a flaw does not. It matters because the first answer rejects an acceptable weld.
Turn this into a routine exercise. Draw the weld cross-section to a known scale, mark the half-skip and full-skip surface distances, and mark where root, fusion faces and heat-affected zones project on the screen for each probe angle you plan to use. Expected observations: you can name, in advance, the screen positions where geometric echoes from the root and toe are expected, and you can explain which regions the chosen angle cannot interrogate at all. That pre-plotted map is what turns echo reading from guesswork into evaluation.
Sizing decisions: dB drop and DAC answer different questions
The dB drop technique measures a reflector's length from how its echo falls as the probe moves, while DAC compares echo amplitude to a calibrated reference curve. Use the method the written procedure specifies, and never substitute one silently.
Worked scenario two: a planar indication in a butt weld gives a maximum echo, and the echo remains above half the maximum amplitude over a probe travel of, say, 12 mm before falling 6 dB from that maximum. The plausible mistake is recording the length as the full distance over which any echo at all is visible, because the probe beam spreads beyond the flaw edges and inflates the figure. The better decision is to maximise the echo, mark the probe positions where the echo has dropped by 6 dB from that maximum, and record those endpoints as the flaw length, stating that the dB drop method was used. It matters because the two habits give different lengths on the same flaw, and inconsistent figures make the report impossible to compare against acceptance criteria.
DAC serves a different purpose: it tells you how an indication's amplitude compares to calibrated reference reflectors at the same sound path, supporting classification and evaluation decisions. In study scenarios, always state which question you are answering before choosing the technique: amplitude relative to a reference, or extent along the weld. Check these observations during practice: your endpoint marks sit at the stated amplitude loss, not where the echo merely flickers or vanishes, and your report names the sizing method explicitly. If a procedure prescribes a specific technique, that prescription governs, whatever your personal preference.
Building a weld scan plan that covers what matters
A defensible plan states probe angles, scanning directions, ranges, coupling and coverage of root, fusion faces and heat-affected zones, plus how deviations from the written procedure are handled and recorded.
Write scan plans for standard joints before touching a scenario question. For a single-V butt weld, that means lacing scans from both sides where access allows, covering the full volume including root and fusion faces, and selecting probe angles so vertical fusion faces are interrogated near perpendicular. State the range calibration mode, the reference technique, and the transfer correction basis. A plan that cannot say which zones a given angle cannot reach is incomplete, because uncovered regions are as reportable as findings.
Use the decision table below during scenario practice to structure each indication evaluation the same way an examiner's reasoning runs. After every practice weld scenario, score yourself against it: did you check geometry before classification, apply the transfer correction before amplitude comparison, and name the sizing method? Repeating the same table on paper scenarios builds the habit of ordered decisions, which is precisely what the applied-practice side of this subject rewards.
| Observation | First check | Likely explanation | Record and decide |
|---|---|---|---|
| Echo at expected root or toe position | Plot beam path on the joint design | Geometric reflector from weld profile or backing | Note as geometric; verify from opposite side |
| High amplitude on a fusion face projection | Scan with a second probe angle | Possible planar flaw such as lack of fusion | Evaluate against reference; size per procedure |
| Echo moves smoothly with full probe travel | Check 6 dB drop endpoints from maximum | Elongated reflector along the weld | Record length and stated sizing method |
| No echo where coverage was assumed | Re-check calibration and range mode | Calibration drift or unplanned coverage gap | Recalibrate; report any coverage limitation |
Reporting and professional conduct you must demonstrate
A report must let another qualified person retrace every decision: equipment, calibration, technique, indication data and evaluation method. BINDT certification carries published ethical obligations, including working within your certified scope.
Treat every practice answer as a report draft. A traceable report identifies the instrument and probes used, the calibration basis including reference technique and transfer correction, the scan plan actually followed, each indication with its position, amplitude basis and length, and the sizing and evaluation methods by name. Compare two of your own scenario reports: if a colleague could not redraw the indication's position on the cross-section from your text alone, the report has failed its purpose regardless of how correct the interpretation was.
Professional standards are part of the subject, not decoration. BINDT, which administers PCN certification, publishes a Statement of Ethical Principles and Code of Conduct and operates certificate verification, so holders are accountable to defined standards of integrity and competence. In written scenarios, practise the honest-path decisions: recording an indication exactly as displayed even when it is inconvenient, stating coverage limitations rather than implying complete examination, and recognising when a decision sits outside the scope your certification supports. These judgements belong in your answers alongside the physics.
A four-phase sequence with a self-check rubric
Sequence preparation from physics fluency through block calibration, geometry plotting and sizing decisions to full written weld scenarios. Judge readiness with a written rubric of reasoning milestones, not with feelings or predicted scores.
Phase one: decibel fluency and calibration theory, including annotated gain chains and range calibration modes. Phase two: hands-on or simulated calibration work on standard reference blocks, confirming beam-path and surface-distance readouts. Phase three: geometry plotting, drawing cross-sections with skip zones and expected geometric echo positions for the joint types in your syllabus. Phase four: full paper weld scenarios evaluated end to end with the decision table, then written up as reports and self-scored. Each phase feeds the next, so do not start scenarios before your plotting is reliable.
Adapt the pace to your available weeks by compressing or expanding phase durations, not by skipping phases. Self-check rubric for phase four, scored per scenario, these are learning milestones rather than pass predictions: skip distance computed correctly for the given thickness and angle without notes; geometric reflectors identified before any defect is named; transfer correction applied before every amplitude comparison; sizing method named and its endpoints marked correctly; report complete enough for an independent redraw. A practical exercise to run once per week: pick one joint, write the scan plan, evaluate three paper indications through the decision table, and compare this week's written reasoning with last week's. Expected observation: your decision chain shortens while your written trace stays complete, which is exactly the fluency this subject asks of a Level 2 inspector.
- Phase 1: dB chains and calibration theory with annotated worked examples.
- Phase 2: block calibration drills confirming beam path versus surface distance.
- Phase 3: plotted cross-sections with skip zones and geometric echo predictions.
- Phase 4: full scenarios through the decision table, written up and self-scored.
References and further reading
Use these references to explore the concepts and check the latest information from the relevant organizations.