PCN NDT Radiographic Testing Level 2 Exam common mistakes
PCN NDT Radiographic Testing Level 2 Exam · Understand the traps and how to avoid them.
Calculates a new dose rate or exposure time by scaling linearly with distance (for example, doubling distance halves the dose rate) instead of applying the inverse-square law, and forgets radioactive decay when using a stored gamma-source output.
Formulas are memorized as isolated equations, so the candidate does not build the physical chain from source activity to dose rate at the detector.
What to do instead
Write the full chain every time: A = A0 e^(-λt), dose rate varies as A/d², then apply shielding and convert units explicitly. Check the result by dimensional analysis and a rough order-of-magnitude estimate.
Uses 20 mSv as the annual dose limit for a member of the public, or treats 1 mSv and 20 mSv as interchangeable when setting a controlled-area boundary.
Occupational and public dose limits are learned as a list, and the exam question hides which exposed population applies.
What to do instead
Before calculating, label the exposed group as classified radiation worker, non-classified worker or member of the public, and write the applicable limit. Convert all doses to the same unit (µSv or mSv) before comparing.
Uses the X-ray focal-spot size in Ug = F × t / d for a gamma exposure, or ignores source size altogether because 'gamma has no focal spot'.
Focal spot is taught with X-ray tubes, and the physical dimensions of a sealed source are not connected in the candidate's mind to geometric unsharpness.
What to do instead
For gamma radiography, F is the active source dimension projected in the exposure direction. Take the larger dimension from the source certificate, calculate Ug, and compare it with the limit in the applicable standard or procedure.
Adjusts development time by feel when developer temperature drifts, or develops every film for the same time regardless of chemistry age, without processing a control strip.
Manual processing is treated as routine labour rather than a controlled process, and the manufacturer's temperature-time chart is not used.
What to do instead
Use the manufacturer's temperature-time chart, process a pre-exposed control strip or film with each batch, and record developer temperature, time and replenishment. Reject or retake films when density or contrast drifts outside the control limits.
Places the IQI on the film side in a single-wall exposure because it is easier, then reports the result as if source-side sensitivity had been demonstrated.
The IQI is treated as a density or 'box-ticking' check rather than as a measure of technique sensitivity, so the standard's placement rules are skipped.
What to do instead
Place the IQI on the source side whenever it is accessible. If source-side placement is impossible, use the film-side IQI and its permitted sensitivity from the standard, mark the placement on the technique sheet and report it.
Accepts a radiograph because film density is within the specified range even though the required IQI wire or hole is not visible and a scratch or processing artifact lies over the weld.
Density is easy to measure and becomes a proxy for overall image quality; IQI evaluation and artifact assessment take more time and judgement.
What to do instead
Evaluate three separate gates: density, required IQI essential wire or hole for the film system and technique, and artifact/coverage. Only then interpret the image for discontinuities.
Records a short, sharp linear indication as slag or acceptable porosity because it is small, without considering orientation, density profile and end conditions.
Classification is based on size rather than morphology, and candidates are reluctant to reject a weld on a single small indication.
What to do instead
Classify by shape, orientation and sharpness. Treat any crack-like indication as rejectable under most acceptance standards; when uncertain, compare with reference radiographs and escalate to a higher-level review.
Writes a technique sheet that lists kV/mA or source activity but omits source-to-object distance, object-to-film distance, IQI type and placement, film system class, collimation and an exposure-geometry sketch.
The technique sheet is treated as a recipe for the operator rather than as a traceable record that another Level 2 or Level 3 can reproduce.
What to do instead
Use an essential-variables checklist from the applicable radiography procedure or standard, and include geometry, consumables, processing conditions, IQI details and acceptance-standard revision.
Sets the controlled-area boundary by measuring dose rate at the source or collimator exit, then applies an occupancy factor guessed from memory rather than from the site survey.
Source output is confused with boundary dose rate, and distance, shielding and occupancy factors are mixed together without a dose-chain calculation.
What to do instead
Calculate the dose rate at the actual boundary distance after shielding, multiply by occupancy and exposure time, and compare it with the site or legal limit. Confirm with a calibrated survey meter and document the result.
Reads films on a wall-mounted light box with room lights on, or scans only the weld cap and misses undercut, root erosion or film artifacts near the edges and identification markers.
Viewing conditions and a systematic scan pattern are not drilled as part of interpretation, so attention is drawn to the most obvious weld area.
What to do instead
Use a masked, adjustable-luminance viewer in a darkened room. Scan in a fixed pattern covering root, cap, heat-affected zone, film edges and markers, and record the viewing conditions.