Inspection, Testing, and Quality Control
What the exam expects
Inspection questions reward precision about what is measured and when. Know surface profile measurement methods (comparator, replica tape, stylus), DFT measurement (magnetic/eddy-current gauges, Type 1 vs. Type 2), and the statistics of DFT sampling (spot vs. average, per SSPC-PA 2). Understand holiday detection (low-voltage wet sponge for thin films, high-voltage spark testing for thick linings) and the risk of over-voltage damaging sound film.
Know adhesion tests: pull-off (ASTM D4541), cross-cut/tape, and knife tests, and when each applies. Recognize environmental instruments: sling psychrometer, dew point meter, surface thermometer. Understand hold points and inspection reports as records of conformity.
Traps
- Using a high-voltage holiday test on a thin film and creating a false defect - or missing a real one with too low a voltage.
- Reporting a single DFT reading as the coat thickness when the standard requires a minimum and maximum across a defined area.
- Confusing pull-off adhesion values with cohesive vs. adhesive failure modes.
- Forgetting gauge calibration and zeroing on the substrate.
Rule of thumb
For DFT, follow the specified sampling pattern and evaluate both the minimum individual reading and the average against limits; one low spot does not necessarily fail the area, but a low average or below-minimum reading can.
Worked example
A 350 µm epoxy lining is spark-tested. The inspector must select voltage per the product/standard rather than defaulting to the highest setting, because excessive voltage can perforate a sound film and produce a false holiday.