# Time-of-flight diffraction (TOFD)

> Time-of-flight diffraction (TOFD) is an ultrasonic weld inspection technique that uses two probes in pitch-catch arrangement and times the weak signals diffracted from flaw tips to size defects accurately through the wall.

- Source: https://amps.global/glossary/time-of-flight-diffraction/
- Type: Glossary
- Published: 2026-09-05
- Tags: NDT, ultrasonic testing, advanced NDT

## Key facts

- Transmitter and receiver straddle the weld; the lateral wave and back-wall echo frame the D-scan image
- Sizing accuracy is largely independent of flaw orientation, unlike amplitude-based UT
- Dead zones near the scanning surface and back wall are usually covered by pulse-echo PAUT
- Codes: ISO 10863 and ASME BPVC Section V Article 4 (TOFD appendix)

Also known as: TOFD.

## How it works

A transmitter sends a wide beam across the weld and a receiver on the other side records everything that arrives: a lateral wave along the surface, the back-wall reflection, and between them the low-amplitude waves diffracted from the upper and lower tips of any flaw. Because the arrival time of a tip signal depends only on its depth, the through-wall height of a flaw can be measured to within about a millimetre.

## Where it fits

TOFD is a screening and sizing tool for welds in thick pressure vessels, pipelines and offshore structures, and is increasingly used for in-service monitoring of known flaws. It is normally combined with pulse-echo PAUT to cover the near-surface dead zones and to help characterise indications.

## TOFD in AMPS

TOFD reports follow the same path as any other method in AMPS: in AMPS, reports are produced from your own Microsoft Word templates through the template engine: job data such as the client, purchase order number, equipment serial numbers, location and dates is filled in automatically, an AI assistant can tidy the wording, the report can be signed in AMPS, and the finished Word file is saved in the job's report folder in your OneDrive, SharePoint or Google Drive.

## Related pages

- [Phased array UT (PAUT)](https://amps.global/glossary/phased-array-ultrasonic-testing/)
- [Ultrasonic testing (UT)](https://amps.global/glossary/ultrasonic-testing/)
- [Using the AMPS reporting system](https://amps.global/case-studies/04-reporting-system/)

## Sources

- [Time-of-flight diffraction ultrasonics on Wikipedia](https://en.wikipedia.org/wiki/Time-of-flight_diffraction_ultrasonics)
- [ASME Boiler and Pressure Vessel Code](https://www.asme.org/codes-standards/bpvc-standards)