The NDT Decoder

Plain-English meanings of the trade words in our jokes, so family, friends and newcomers get the joke too. In any joke, tap an underlined word to see its meaning.

A-Scan: A graph of echo strength against time or depth. Peaks on the screen show where sound bounced back from inside the part.
Acceptance Criteria: The written limits that say how big a discontinuity can be before the part is rejected. The code or customer sets them.
Acoustic Emission: Listening with sensors for the tiny sounds a part makes when a crack grows or metal strains under load. It finds trouble while the part is working.
Acoustic Impedance: How strongly a material resists sound passing through it. When two materials have very different impedances, such as steel and air, most sound bounces back.
Alternating Current Field Measurement: A method that induces a current in the surface of a part and measures its magnetic field. Cracks bend the current and change the field, even through coatings.
Angle Beam: Sound sent into a part at a slant instead of straight down. It lets inspectors check welds from the flat surface beside the weld.
Back Wall: The far surface of a part, which reflects sound back to the probe. A steady back wall echo means the sound made the whole trip.
Barricade: The rope or tape and signs that keep people out of a radiation area. Everyone stays outside it during an exposure.
Beam: The path and spread of sound or radiation traveling from a probe or source. Where the beam goes decides what the inspector can see.
Black Light: A lamp giving ultraviolet light (UV-A) that makes fluorescent materials glow. Inspectors use it in a darkened booth or room to see small cracks.
Bond Testing: Checking that layers glued together are still stuck. Sound, vibration or tapping reveals loose spots, common in aircraft panels and honeycomb parts.
Borescope: A thin camera on a tube or flexible cable that goes into tight places, like inside an engine or pipe, so inspectors can look around.
C-Scan: A top-down picture of a part built from many ultrasonic readings. Colors show where echoes changed, as on a map.
Calibration: Setting and checking an instrument against a known standard before use. It proves the readings can be trusted.
Calibration Block: A piece of metal with known thickness and known built-in reflectors. Inspectors set up and check their instruments on it before testing real parts.
Cassette: A light-tight holder for film or a digital plate. Technicians place it behind the part before the exposure.
Certification: Written proof from an employer that a person has the training, experience and test results to perform a method at a given level.
Code Book: A published set of rules for how something must be built and inspected. Inspectors keep one nearby to check what is allowed.
Coil: A loop of wire that carries electric current and makes a magnetic field. It is the working part of most Eddy Current Testing probes.
Confined Space: A tight area, such as the inside of a tank, with limited ways in and out. Special permits and safety checks are required before anyone enters.
Corrosion: Metal slowly wearing away from chemical reaction, such as rust. It thins walls and is a main reason pipes and tanks are inspected.
Couplant: A gel, oil or water layer between an ultrasonic probe and the part. Sound barely crosses air, so couplant fills the gap and lets the sound in.
Crack: A thin break in a part. It is usually the most serious kind of discontinuity because it can grow.
Darkroom: A room with no ordinary light where radiographic film is loaded and developed. Light would spoil the pictures.
Data File: The saved electronic record of an inspection, kept by the instrument. It can be reviewed later.
Dead Zone: The area just under the probe where the instrument cannot see flaws, because it is still recovering from sending the pulse. Very thin parts can fit inside it.
Defect: A discontinuity that is too big or serious to pass the acceptance criteria. All defects are discontinuities, but most discontinuities are not defects.
Demagnetization: Removing the leftover magnetism from a part after Magnetic Particle Testing. Leftover magnetism can attract metal chips, disturb instruments, or cause trouble in later work.
Developer: In Penetrant Testing, a thin white powder coating that pulls penetrant out of cracks so they show as bright lines. In film work, it is the chemical that makes the picture appear.
Digital Radiography: Radiographic Testing that records pictures on a reusable plate or detector instead of film. Results appear on a computer screen.
Discontinuity: Any break or irregularity in a part, such as a crack or void. It only becomes a defect if it fails the acceptance rules.
Dosimeter: A small badge or pocket device that keeps track of the radiation a person has received. Radiographers wear one all day.
Dwell Time: The waiting time that lets penetrant soak into cracks, or lets developer pull it back out. Rushing it can hide a crack, so inspectors watch the clock.
Echo: Sound that bounces off a surface or flaw and returns to the probe. The time it takes tells how far away the reflector is.
Eddy Current Testing: A method where a coil makes small swirling electric currents in a metal part. A crack or thickness change disturbs those currents, and the instrument shows the change.
Experience Hours: The logged time a person must spend doing a method before being certified. More hours are needed for higher levels.
Exposure: In radiography, the timed period when radiation reaches the film or detector. Everyone stays clear of the area while it runs.
Eye Exam: A required vision check for inspectors, including reading small print up close. It shows they can see fine detail.
Fillet Weld: A triangle-shaped weld joining two pieces that meet at an angle, like the corner of a T.
Film: The light-sensitive sheet that records a radiograph. It turns dark where more radiation reaches it, then is developed like a photograph.
Firmware: The built-in software that runs an instrument. Updates can add features, and sometimes also move every menu to a new place.
Flashlight: A hand light, the main tool of Visual Testing. Aiming it at a low angle makes surface flaws stand out.
Flaw: A general word for an imperfection in a part. It might be harmless or serious, depending on the rules.
Fluorescent: Glowing brightly under ultraviolet light. Fluorescent penetrant and powder show cracks as glowing lines in a darkened area.
Frequency: How many wave cycles happen each second. Higher frequency sound sees smaller flaws but does not travel as deep.
Gain: How much the instrument turns up the echoes on the screen, like a volume knob. Too much gain shows noise, and too little hides small flaws.
Gate: A marked window on the instrument screen. Echoes inside the window are measured or sound an alarm.
Gauss: A unit for how strong a magnetic field is. A gauss meter checks that a part has been magnetized enough.
Guided Wave Testing: A method that sends sound waves along a pipe or rail instead of through it. One probe position can check many feet of length for wall loss.
Half-Life: The time a radioactive source takes to lose half its strength. Each source material has its own half-life.
Heat Exchanger: A device with many small tubes that move heat from one fluid to another. Tubes are inspected for thinning and cracks.
Honeycomb: A light, stiff sandwich panel with a core of small hollow cells between thin skins. Aircraft use it, and bond testing checks that the skins are still glued on.
Image Quality Indicator: A small plate or set of wires placed on the part before a radiograph. Its visible details prove the picture is sharp enough to show small flaws.
Impedance Plane: An Eddy Current Testing display that plots the signal as a moving dot. The direction and shape of the dot's path tell what kind of change was found.
Incomplete Fusion: A weld flaw where the weld metal did not melt together with the metal beside it or the weld below. It acts like a hidden seam.
Indication: A sign on the screen, film or surface that something may be there. It must be evaluated before anyone knows what it means.
Infrared Thermography: Using a heat camera to see temperature differences on a surface. Hidden flaws often change how fast heat moves, so they show up as warm or cool spots.
Inverse Square Law: The rule that radiation gets weaker fast with distance. Double the distance, and the strength drops to one quarter.
Iridium-192: A radioactive material used as a gamma ray source. It loses half its strength about every 74 days, so sources are replaced often.
Lamination: A flat layer split inside rolled metal plate, like the pages of a book coming apart. It lies parallel to the surface.
Leak Testing: Checking whether a tank, pipe or part holds in liquid or gas. Methods include watching for bubbles, using pressure change, and sniffing for a tracer gas.
Level I: The entry certification level. A Level I performs tests and records results, working under the direction of a Level II or III.
Level II: The certification level for people who set up equipment, perform tests, and evaluate results under a written procedure. Most working technicians hold this level.
Level III: The most senior certification level in NDT. A Level III writes procedures, trains others, and decides how methods and codes apply.
Lift-Off: In Eddy Current Testing, the gap between the probe and the part. Even a small gap changes the signal, so paint or dirt can matter.
Loss of Back Wall: The back wall echo gets weaker or vanishes. Something in the sound path, such as a large flaw, blocked or scattered the sound.
Magnetic Field: The invisible area of magnetic force around a magnet or a wire carrying current. Flux means the lines of that force.
Magnetic Flux Leakage: A method that magnetizes steel and senses where the magnetic field spills out. Spilled field means metal is missing, as with corrosion pits in a tank floor or pipe.
Magnetic Particle Testing: A method that magnetizes a steel part and sprinkles fine iron powder on it. The powder gathers where a crack interrupts the magnetic field.
Mirror: A small angled mirror on a handle that lets an inspector see around corners and behind parts.
Noise: Unwanted small signals on the screen, often from the grain of the metal. Inspectors nickname it grass because it looks like a lawn on the display.
Nondestructive Testing: Ways of checking a part for hidden problems without damaging it. The part goes back into service afterward, like a doctor's scan for metal.
Nonrelevant Indication: An indication caused by something harmless, like a sharp corner, a change in shape or a stray mark. It does not count against the part.
Outage: A planned period when a power plant or unit stops running so it can be inspected and maintained.
Penetrant: The special liquid that seeps into surface cracks in Penetrant Testing. It is either bright red or glows under black light.
Penetrant Testing: A method that finds cracks open to the surface. Colored or glowing liquid seeps into them, and a powder coating draws it back out so it can be seen.
Per Diem: A fixed daily payment to cover meals and lodging when traveling for work. Latin for "per day."
Permit: A signed paper that gives permission to start work and lists the safety steps required. No permit, no work.
Phased Array Ultrasonic Testing: Ultrasonic Testing with a probe made of many small elements fired in timed patterns. The sound beam can be steered and swept to build a picture.
Piezoelectric: A material that makes a small voltage when squeezed and changes shape when given a voltage. That is how an ultrasonic probe makes and senses sound.
Pig: A device pushed through a pipeline by the flow, sometimes carrying sensors. It cleans or inspects the pipe from inside.
Pipeline: A long run of welded pipe that carries oil, gas or water over great distances. Its girth welds are often inspected by radiography.
Pit: A small hole eaten into a metal surface by corrosion. Many pits together can seriously thin a wall.
Porosity: Tiny gas bubbles trapped in a weld or casting. They look like pinholes or a scatter of small round dots.
Probe: The hand-held sensor an inspector moves over a part. It sends energy in, listens for what comes back, and connects to the instrument by a cable.
Procedure: The step-by-step written instructions for how to do a specific inspection. Inspectors are expected to follow it.
Prods: Two hand-held contacts that push electric current through a small area of a part. The current makes a circular magnetic field around its path for Magnetic Particle Testing.
Radiation: Energy given off by X-ray machines and radioactive sources. It cannot be seen or felt, so people use meters and barricades to stay safe.
Radiograph: The picture made by Radiographic Testing. Thinner or flawed areas look darker because more radiation got through.
Radiographer: A technician trained and licensed to take radiographs with X-rays or gamma rays. Radiographers also manage radiation safety at the work site.
Radiographic Testing: A method that sends X-rays or gamma rays through a part onto film or a digital detector. Thinner or flawed spots let more rays through and show up darker.
Refraction: The bending of a wave when it passes into a new material at a slant. Like a straw that looks bent in water, but with sound.
Relevant Indication: An indication caused by a real discontinuity that must be evaluated against the acceptance criteria. It is not just a false signal from the shape of the part.
Report: The written record of what was inspected, how, and what was found. Clients rely on it, and it is often needed before work can move on.
Residual Magnetism: Magnetism a steel part keeps after the magnet or current is turned off. It can cling to metal chips and make later steps harder.
Rope Access: A way to reach high or awkward places by working on ropes with a harness and a backup line. It is used instead of scaffolding on tall structures.
Scaffold: A temporary frame of pipes and boards that gives workers a place to stand at height. Inspectors often climb them to reach a weld.
Shearography: A laser method that compares a surface before and after a gentle stress, such as a little heat or vacuum. Hidden flaws make the surface bulge slightly and show up.
Shielding: Dense material, like lead or thick concrete, that blocks radiation. It protects people nearby.
Shutdown: A planned stop of a plant or unit so maintenance and inspection can happen safely. Crews often come in from out of town.
Signal: A response the instrument displays, such as an echo peak or a change in a coil reading. Inspectors decide whether a signal is a flaw or just noise.
Sketch: A hand-drawn picture of a part or weld that shows where each indication was found. Reports include it so others can find the spot.
Skin Depth: How far eddy currents reach into a metal. They are strongest at the surface and get weaker the deeper you go.
Slag Inclusion: Bits of leftover coating from the welding process trapped inside a weld. It shows up as irregular lumps.
Snell's Law: The rule for how a wave bends when it crosses from one material to another at a slant. It sets the angle of sound in the part.
Source: The material or machine that gives off radiation for Radiographic Testing. It is handled carefully and kept locked away when not in use.
Survey Meter: A hand-held detector that shows how much radiation is present in an area. Radiographers use it to confirm the area is safe.
Tailgate: A short safety meeting held before work starts. The crew goes over the plan and its hazards.
Tank: A large container for liquid or gas. Tank floors and walls are checked for corrosion.
Thickness Gauge: A handheld instrument that measures how thick a wall is, usually by timing sound echoes. Corrosion shows up as thinner readings.
Time-of-Flight Diffraction: An ultrasonic method that uses sound scattered from the tips of a crack. The travel time of that sound tells how tall the crack is.
Trainee: A person still learning the trade who works under a certified person. Trainees log hours of experience toward certification.
Transducer: The part inside an ultrasonic probe that turns electricity into sound and sound back into electricity. It is usually a small slice of special crystal or ceramic.
Tube: A hollow metal cylinder, often in groups inside a boiler or heat exchanger. Eddy Current Testing is widely used on tubes.
Turnaround: A planned shutdown of a plant for repairs and inspections. Many crews work long hours to finish before it restarts.
Ultrasonic Testing: A method that sends high-pitched sound into a part and listens for echoes. Echoes from the far side or from a flaw show what is inside.
Undercut: A groove melted into the metal along the edge of a weld and left unfilled. It makes the metal thinner at that spot.
Velocity: How fast sound travels in a material. The instrument needs the right velocity to turn echo time into a correct thickness reading.
Vessel: A closed tank built to hold liquid or gas under pressure. Its welds and walls are inspected on a schedule.
Visual Testing: Looking closely at a part, often with a flashlight, mirror or camera. It is the oldest method, and every other method still depends on good eyes.
Wavelength: The distance covered by one full wave cycle. A flaw much smaller than the wavelength is hard to see.
Wedge: A small plastic block that tilts an ultrasonic probe so its sound enters the part at an angle. Different wedges give different beam angles.
Weld Bead: The ridge of metal one weld pass leaves behind.
Weld Gauge: A small metal measuring tool with cutouts. It checks the size and shape of a weld, such as how tall or wide it is.
Wind Turbine: A tall tower with big blades that spin to make electricity. Blades, bolts and welds are inspected.
Yoke: A hand-held U-shaped magnet with two legs. It magnetizes the part between its legs so magnetic powder can show cracks.