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TOEIC Link Vocabulary — Time-of-Flight Diffraction (TOFD) and Weld Flaw Sizing Cluster: The Send-Diffract-Time Terminology Behind Every Weld-Sizing Passage

A new pipeline weld looks perfect on the surface, but inside it there may be a crack, a lack of fusion, or a pocket of slag that no amount of polishing will reveal. Time-of-flight diffraction listens to the faint waves that flaw edges scatter and turns their arrival times into a picture of exactly how tall and how deep the defect is. That single idea — send a pulse across the weld, catch the waves the flaw tips diffract, and read the depth from the time they take to arrive — is why TOFD carries its own vocabulary of sending, diffracting, and timing, and it recurs across the TOEIC Link modules as a self-contained setting. This guide builds the cluster as a connected path so the weld-sizing register decodes at reading speed.

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TOEIC Link Vocabulary — Time-of-Flight Diffraction (TOFD) and Weld Flaw Sizing Cluster: The Send-Diffract-Time Terminology Behind Every Weld-Sizing Passage

A brand-new girth weld on a high-pressure pipeline can look flawless when you grind it smooth and run a magnet over it, and still hide, buried in the fusion line, a crack or a strip of unfused metal that will open the moment the line goes into service. The surface tells you nothing about the flaw's true height, and height is what decides whether the weld is acceptable or has to be cut out. Time-of-flight diffraction, or TOFD, is the technique built to answer that one question. Two probes straddle the weld, one sending a broad ultrasonic pulse and the other catching it; when the pulse hits the top and bottom edges of a flaw, those edges act as tiny sources that diffract faint waves in all directions, and the exact time each diffracted wave takes to arrive tells the machine how deep that edge sits. The whole discipline rests on that single move: send the pulse across the weld, catch the waves the flaw tips diffract, and turn their arrival times into a height and a depth. It has three beats — send the beam across the joint, diffract off the flaw edges, and time the returns into a sizing — and each carries its own vocabulary. Because a TOFD job is therefore a sending problem, a diffracting problem, and a timing problem all at once, it turns up often as a setting in TOEIC Link passages — a scan plan that couples two probes over a new weld, and a sizing report that hands over a flaw height and an accept-or-repair call.

A field message that reads "the technician coupled the transmit and receive probes across the weld cap, ran the encoder along the seam, captured the lateral wave and backwall, and sized the flaw between the tip diffractions at 4 mm through-wall" is dense with cluster terms — transmit, receive, lateral wave, backwall, diffraction, through-wall — and a candidate decoding each in isolation has already spent the reserve a fluent reader keeps in hand. The failure pattern is the familiar one: a candidate meets diffraction or through-wall in a single practice item, half-learns it, and never links it to the terms it always travels with. Learn them grouped by the path from sending the beam to reporting the height and recognition becomes anticipatory rather than reactive. This is the same interrogate-the-weld logic behind the phased array ultrasonic testing and weld inspection cluster and the radiographic testing and weld film interpretation cluster — all three exist to find and measure what is hidden inside a joint, and a weld-integrity passage will often move between shooting a film, steering a beam, and timing the diffractions to pin the flaw's true size.

Component 1 — The send

Setting up the two probes and launching the pulse across the joint. Concrete setup terms that cue the whole passage.

  • Transmit / receive / probe pair / straddle — the two transducers set either side of the weld.
  • Coupling / couplant / contact / wedge — how sound is passed from probe into steel.
  • Probe centre spacing / PCS / beam angle / spread — the geometry that aims the pulse across the joint.
  • Encoder / scanner / index / raster — the device that tracks probe position along the weld.
  • Lateral wave / near-surface / dead zone / cap — the first wave skimming the surface that marks the top of the scan.

Component 2 — The diffraction

Catching the faint waves the flaw edges scatter. This is where the technique hides the detail a question depends on.

  • Diffraction / tip signal / upper tip / lower tip — the weak waves from the top and bottom of a flaw.
  • Backwall / backwall echo / far surface / mode conversion — the reflection from the opposite wall of the pipe.
  • Amplitude / phase / grey scale / D-scan — how the diffracted signals appear on the display.
  • Lack of fusion / porosity / slag / crack — the flaw types the diffractions reveal.
  • Non-relevant / geometry / root / misfit — signals that mimic flaws but come from the weld shape.

Component 3 — The timing and the deliverable

Turning arrival times into a height and a verdict. The terms that carry the whole result of the job.

  • Time-of-flight / arrival time / depth / through-wall — how deep each flaw edge sits from the timing.
  • Flaw height / vertical extent / sizing / length — the measured size the acceptance decision rests on.
  • Acceptance criteria / code / fitness-for-service / reject — the standard the sized flaw is judged against.
  • Repair / excavate / re-weld / re-inspect — what happens to a weld that fails the sizing.
  • Report / scan record / traceability / archive — the documented result handed to the client.

Why the cluster holds together

The three components are one motion, not three topics. A TOFD scan begins by sending the pulse across the joint, lives in the faint waves the flaw edges diffract, and ends by timing those returns into a through-wall height. Every term above belongs to one of those beats, which is why they co-occur so reliably: a passage that mentions tip diffraction will almost certainly mention through-wall and acceptance criteria, because that is the arc of the work. A candidate who has stored the words as a path reads the second and third terms as confirmations of the first; a candidate who stored them as isolated flashcards has to solve each one cold.

That is the difference the cluster buys. In a timed section, diffraction decoded in isolation costs you a beat; diffraction recognised as the middle of send-diffract-time costs you nothing, because you already expect the height and the verdict to follow. The vocabulary stops being a list of hard words and becomes the shape of a job you can see coming.

How this shows up in TOEIC Link

The setting is a new-construction weld or an in-service inspection: a technician couples a probe pair across a girth weld, runs an encoded scan along the seam, and reports a flaw height against a code. A reading item might pair a scan plan email with a sizing report and ask which weld exceeded the acceptance criteria; a listening item might play a lead technician explaining why a tip diffraction was called non-relevant. The reason the register feels dense is that it packs the send, the diffraction, and the timing into a few lines — but that is exactly the arc the cluster trains.

This is the same measure-what-is-hidden logic that runs through the ultrasonic thickness testing and pipe corrosion monitoring cluster: both use sound to read a dimension the eye cannot reach, one the remaining wall of a corroding pipe and the other the height of a flaw inside a weld. Learn the send-diffract-time path once and both passages decode at speed, because they share the underlying move — send a pulse, catch what comes back, and turn the timing into a number that decides whether the metal stays in service.