Instead of timing the journey from the probe to the back wall, the stretch between two successive back-wall echoes is timed. The coating stays out of the count, and the paint no longer needs to be removed.
- ✓ Measurement of the metal alone, with the coating in place
- ✓ No grinding of the point and no restoration of the protection
- ✓ Noticeably faster inspection times on large structures
- ✓ On Dakota NDT the function is identified as Echo-Echo ThruPaint™
When a pulse reaches the opposite surface it does not come back only once: part of the reflected energy, back inside the material, is sent back by the upper surface and makes a second journey, generating a second back-wall echo, then a third and so on. Echo-Echo mode exploits precisely this succession.
By measuring the time interval between two consecutive back-wall echoes, rather than between emission and the first echo, one obtains the time of a path entirely contained in the metal. The coating, crossed only once on the way in and out, leaves the count: the reading returns the thickness of the metal substrate alone.
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On the operational level the advantage is concrete. On a tank, a bridge or a ship’s hull plating the anti-corrosion protection is part of the integrity of the structure: having to remove it at every measurement point means adding a grinding and a restoration for each reading, with a cost that becomes decisive over hundreds of points.
Pulse-Echo and Echo-Echo compared
| Aspect | Behaviour |
|---|---|
| What Pulse-Echo measures | The path from the probe to the opposite surface, coating included |
| What Echo-Echo measures | The interval between two back-wall echoes, i.e. the metal alone |
| Painted surface | In Pulse-Echo the paint is counted, in Echo-Echo it is not |
| Energy required | Echo-Echo works on subsequent echoes, of lower amplitude |
| Typical use | Protected structures, inspections repeated over time |
When the mode may fail
Echo-Echo works on echoes after the first, hence on signals of lower amplitude. On strongly attenuating materials, large thicknesses or very irregular inner surfaces the second echo may be too weak for the instrument to recognise, and the measurement fails.
In these cases one goes back to Pulse-Echo, accepting that the coating is counted, or the coating is removed at the measurement point. Instruments with an A-Scan make it possible to understand which of the two situations one is facing, instead of proceeding by trial and error.
Instruments with Echo-Echo ThruPaint™
| Instrument | Typical use |
|---|---|
| Dakota CX4 | Measurement through coatings on painted pipes and structures |
| Dakota CX8-DL | Extensive campaigns with data logger and B-Scan |
| Dakota ZX6-DL | Multi-Echo with data logger for epoxy coatings |
| Dakota MX2-DL | A-Scan and B-Scan to validate the reading in difficult cases |
Frequently asked questions
Because it measures the time interval between two consecutive back-wall echoes, i.e. a path that takes place entirely inside the metal. The coating stays outside the timed stretch.
Not in every condition. The method requires the second back-wall echo to return with sufficient amplitude: on very thick coatings, attenuating materials or irregular inner surfaces the measurement may fail.
ThruPaint™ is the name by which Dakota NDT identifies its own Echo-Echo mode for measuring through the coating. The operating principle is the one described on this page.
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Further information and contacts
Systems division and sensor integration partner : www.roder.it
More information about RODER SRL : about us
Contact for general information : info@roder.it
Contact for information about these products : info@roder.it
The information contained on this web page is provided for information purposes only. Although it has been compiled with the utmost care, it does not constitute a contractual offer or a binding commitment to supply. It may contain transcription, translation or typographical errors. For precise and up-to-date information, please contact our company directly.
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