# Engineers use ultrasound waves to inspect metal pipelines for internal cracks without cutting the pipes open. Explain how ultrasound waves can be used to detect a crack inside a metal pipeline, and why ultrasound rather than audible sound is chosen for this purpose.

> OCR A-Level Physics A (H556) — 5.3 Astrophysics and cosmology · Explain · 5 marks

> Industrial pipelines carry high-pressure gases and must be regularly inspected for internal cracks. Engineers use a non-invasive technique that involves directing waves into the metal from outside the pipe and analysing the reflected signals.

## Mark scheme (5 marks)

1. Ultrasound waves are emitted into the metal pipeline from outside
2. When the waves reach a boundary (e.g. a crack), they are partially reflected back
3. A receiver detects the reflected waves and the time between emission and detection is measured
4. A crack reflects waves earlier / after a shorter time than the far wall of the pipe, so its position can be located
5. Ultrasound has a frequency above 20 kHz (above the upper limit of human hearing) giving a shorter wavelength, which allows smaller cracks to be detected / gives better resolution than audible sound

## Key terms

- [ultrasound waves](https://www.gradenine.co.uk/glossary/ultrasound-waves)

## Related

- [Revision notes for OCR A-Level Physics A (H556)](https://www.gradenine.co.uk/learn)
- [How to answer "Explain" questions](https://www.gradenine.co.uk/tools/command-word-cheatsheet)
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Source: [GradeNine](https://www.gradenine.co.uk/q/engineers-use-ultrasound-waves-to-inspect-d809e900) · Published by Druglandscape Ltd.