There’s something very special about Cygnus’ Multiple-Echo technology; it allows ALL our gauges, for surface and subsea ultrasonic thickness gauging, to measure through coatings!
Measuring through coatings has a significant value to inspectors, saving them the time-consuming task of removing coatings on the test area, as well as the cost of doing so.
Read on to learn more about how this technology works.
Where It All Started
In the 1970s, the periodic inspection of ships (as demanded by IACS and all the major Classification Societies) was conducted using what we would now consider to be very heavy and outdated equipment. The founder of Cygnus was himself a ship surveyor and realised there was a better way. He set about digitising the ultrasonic equipment, based out of small offices in Dorchester in the southwest of the UK.
The idea of the Cygnus-pioneered “Multiple-Echo” UT technique was born at the same time; IACS and Class Societies immediately saw the value of a gauge that could read reliably and repeatedly “through” marine anti-fouling paint. And as such, the Multiple-Echo technique is still specified by IACS today – and is still at the forefront of every Cygnus ultrasonic thickness gauge. A real testament to a true innovation that has stood the test of time.
How Multiple-Echo Technique Works
A Multiple-Echo Cygnus gauge can “see through” and ignore surface coatings (up to 20mm thick in Deep Coat mode).
To do this, the probe generates 3 back wall echoes. The first back wall echo which goes through the coating, is ignored. The gauge measures the time between the 1st and 2nd echo signal, and the 2nd and 3rd echo signal. If these times are equal, the gauge verifies and provides a valid thickness measurement.
There is no need to remove the paint to take a measurement, making it highly cost effective and time efficient. This also prevents the risk of exposing the substrate material to corrosion.
Another principal advantage of this is that users with very little training can obtain highly accurate measurements.
The Multiple Echo measurement uses a single element (or single crystal) probe there are no errors due to the V-path of the ultrasound beam found in all twin element probes. This makes it simple to calibrate – two-point calibrations are not required.
This method is excellent for use on curved surfaces, like pipes, as the probe can be rotated 180° without effecting readings. However, because it requires three echoes to take a measurement, in heavily corroded steels there is often an insufficient number of echoes so measurements may not be possible.
Measuring Through Thick Coatings
Cygnus’ Deep-Coat feature allows the gauge to leap from measuring through the standard 3mm (0.12”) coatings up to 20mm (0.8”) thick coatings.
Measuring through thick coatings is ultimately limited by how well the coating material allows the ultrasound to pass through. For example, soft coatings like rubber or bitumen don’t transmit ultrasound very successfully. Whereas, most protective coatings up to 3mm thick, like paint, anti-foul, hard plastics and epoxy, should present no problems using Multiple-Echo (ME) mode, as long as they have not de-laminated/de-bonded from the metal surface.
Probe Capabilities
To complement the Multiple-Echo measurement, Cygnus offers a range of single crystal probes to suit different coated materials and applications. This table can be used as a guide to select the most appropriate probe for your inspection.
| Probe Type |
Size |
Frequency |
Range in Steel |
Typical Uses |
| S2C |
13mm
0.5″ |
2.25 MHz |
3-250mm
0.12 to 10” |
General purpose probe suitable for most applications that can use Multiple Echo measurement.
Coated metals |
| S3C |
13mm
0.5″ |
3.5 MHz |
2-150mm
0.08 to 6” |
Coated metals |
| S5C |
13mm
0.5″ |
5.0 MHz |
1-50mm
0.04 to 2” |
Coated metals |
| S5A |
6mm
0.25″ |
5.0 MHz |
1-50mm
0.04 to 2” |
Small diameter tubes
Thin metals
Coated metals |
To learn more about the Cygnus multi-mode Surface Thickness Gauges, visit the Cygnus Surface UT Testers page.
