NDT terms glossary: UT, MT and PT terms explained
The General exams for UT, MT and PT reward a clear picture of why each method behaves the way it does. This glossary groups twenty terms that candidates search for most, with a one-line meaning for each and a full page behind it. Every page has an original drawing, the formula or mechanism, the mix-ups that cost points, and where the term sits in the General exam topics.
Everything here is in our own words. The formulas are plain physics, such as Snell's law and the near field relation. Limits, times and acceptance values come from the written procedure or specification that governs a job, so none are given here. The topic names used on each page are ASNT's published headings.
Ultrasonic beam and geometry
How the beam is shaped, how far it travels along a plate and how it spreads.
| Term | In one line | Full page |
|---|---|---|
| Skip distance | Surface distance for one leg (half skip) or a round trip (full skip) of an angle beam | Skip distance |
| Near field | The zone where on-axis pressure swings up and down, ending at N = D² / 4λ | Near field |
| Beam spread | How the beam widens in the far field, set by wavelength over diameter | Beam spread |
| Dead zone | Depth near the surface lost in the initial pulse and ring-down | Dead zone |
| Critical angles | The incident angles where the refracted longitudinal and then the shear wave reach 90 degrees | Critical angles |
The beam geometry formulas are worked step by step in the UT formulas guide, and the UT beam calculator and skip distance calculator check your answers.
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Discontinuity Detection
A planar reflector gives its highest echo amplitude when the beam strikes it
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Ultrasonic waves, losses and calibration
What the sound does inside the material and how echo height is judged.
| Term | In one line | Full page |
|---|---|---|
| Shear wave vs longitudinal wave | Particles move across or along the travel direction, at different velocities | Shear vs longitudinal |
| Acoustic impedance | Density times velocity, which sets reflection at a boundary | Acoustic impedance |
| Couplant | The liquid film that removes the air gap under a contact probe | Couplant |
| Attenuation | Energy lost to scattering and absorption along the path | Attenuation |
| DAC curve | A curve through echoes from equal reflectors at different depths | DAC curve |
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Magnetic particle testing
Field direction first, then particles, then what is left behind.
| Term | In one line | Full page |
|---|---|---|
| Longitudinal vs circular magnetization | Field along the part from a coil or yoke, or in rings around a current path | Longitudinal vs circular |
| Leakage field | Flux forced out of the surface by a flaw, where particles collect | Leakage field |
| Wet vs dry particles | Powder dusted on, or particles carried in oil or water | Wet vs dry particles |
| Yoke vs prods | A magnet on the surface, or current pushed through the part | Yoke vs prods |
| Demagnetization | Removing the residual field with a reversing, shrinking field | Demagnetization |
The MT field direction and technique guide turns these into a sketch routine, and the magnetic particle testing quiz gives drawn setups to practice on.
Liquid penetrant testing
The process in order: entry, removal, development and viewing.
| Term | In one line | Full page |
|---|---|---|
| Capillary action | The pull that draws penetrant into a narrow surface opening | Capillary action |
| Dwell time | How long penetrant sits on the part before removal starts | Dwell time |
| Removal methods | Water-washable, two emulsifier routes, or solvent wipe | Removal methods |
| Developer types | Dry powder, two water-based forms, or a solvent suspension | Developer types |
| Visible vs fluorescent | A red dye in white light, or a dye that glows under UV-A | Visible vs fluorescent |
The PT process control and indications guide shows how these steps are reviewed, and the penetrant testing quiz drills them.
How these terms show up on the exams
For UT the terms sit mostly under the weldment, technique and general evaluation topics, and many of them are calculations. For MT they sit under principles, flux fields, magnetization methods, demagnetization and equipment. For PT they sit under principles, method selection and procedures. ASNT publishes no topic weights, so every topic needs some coverage. Each page lists the topic it falls under.
If you are studying for more than one method, the ASNT Level 2 study guide lays out UT, MT and PT in study order, and the NDT methods compared page shows what each method can and cannot find.
Know the words? Check the rest of the General topics
Each method has its own free 10-question check: UT, MT and PT. Each needs no signup and explains every answer, so you see which topic costs you the most before you decide what to study. The course then adds timed practice exams and a study plan built from your exam date.
Sources
Show the list
Background reading: ASNT's published topic headings, Evident's published UT material and ASNT's Level II PT self-study collection. Outline checked 25 October 2026.
- ASNT NDT Level II examinations, published topic headings.
- Evident, ultrasonic flaw detection tutorial
- Level II PT self-study collection, ASNT.
Not affiliated with or endorsed by ASNT.
Facts checked 25 October 2026 against the sources listed above. If something has changed, tell us and we will correct it within 2 business days.
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