# Guided wave testing (long-range UT)

> Guided wave testing (GWT, also long-range ultrasonic testing) sends low-frequency torsional or longitudinal waves along a pipe from a collar of transducers and detects changes in cross-section, screening tens of metres in each direction from a single location.

- Source: https://amps.global/glossary/guided-wave-testing/
- Type: Glossary
- Published: 2026-09-05
- Tags: NDT, ultrasonic testing, advanced NDT, pipelines

## Key facts

- Frequencies in the tens of kHz; range from a few metres to over 100 m depending on coating, contents and geometry
- A screening method: it locates features with cross-section change, then conventional UT quantifies them
- Ideal for insulated, buried, elevated or road-crossing pipe where access is expensive
- Results are sensitivity-limited by welds, supports and attenuation, which the report must state

Also known as: GWT, LRUT, long-range ultrasonic testing, guided wave ultrasonics.

## How it works

A ring of transducers clamped around the pipe launches a wave that fills the whole wall and travels along it. Every change in cross-section (welds, supports, corrosion patches) reflects part of the energy back. Welds and features are used as reference reflectors, so corrosion appears as an unexplained signal at a known distance.

## Where it is used

Corrosion under insulation programs, buried and cased pipelines at crossings, offshore risers, and screening long runs of piping before targeted excavation or scaffolding.

## Guided wave in AMPS

Guided wave results point to locations that need follow-up; in AMPS those follow-up jobs are created against the same asset so the screening report, the follow-up UT and the repair record share one history.

## Related pages

- [Ultrasonic thickness gauging](https://amps.global/glossary/ultrasonic-thickness-gauging/)
- [Corrosion mapping](https://amps.global/glossary/corrosion-mapping/)
- [Asset register](https://amps.global/glossary/asset-register/)

## Sources

- [Guided wave testing on Wikipedia](https://en.wikipedia.org/wiki/Guided_wave_testing)