Inspection and Non-Destructive Examination Methods
What you must know
Understand visual inspection as the primary method, then the volumetric and surface techniques: radiography, ultrasonic testing, magnetic particle, liquid penetrant, and eddy current. For each, know what it detects, its limitations, surface preparation needs, and typical applications. Know the difference between surface and subsurface detection, and how orientation affects detectability. Understand the sequence: examination after sufficient cooling, after any required heat treatment, and before final coating. Know that NDE methods complement rather than replace visual and dimensional checks.
Traps in questions
- Expecting radiography to reliably detect tight lack-of-fusion planar defects oriented parallel to the beam.
- Using magnetic particle on austenitic stainless steel or non-ferrous metals.
- Forgetting that penetrant requires a clean, dry surface and dwell times.
- Assuming ultrasonic testing needs no couplant or surface condition control.
- Confusing sensitivity with resolution.
Worked example
A planar, tightly closed crack lies perpendicular to the surface in a ferritic butt weld. Radiography may miss it because there is little thickness change; ultrasonic testing with a suitable angle beam is far more likely to detect it. Rule of thumb: volumetric methods find volumetric defects; surface methods find surface-breaking defects; orientation decides which beam or field works.
Inspection link
Record technique, equipment, calibration status, and acceptance criteria; an undocumented examination has little evidentiary value.