Measuring the wall thickness of tubes and closed hollow objects is a difficult subject in the art.
Normally, to measure a thickness, one have to be able to access 2 faces of the wall to be measured. In the case of a closed object, this is impossible.
In addition, in the case of tubes, the surface to be measured is not flat, which adds a difficulty.
There are some techniques to measure the thickness of a wall non-destructively, i.e. from the outside, without having to open the object:
- Ultrasound: An ultrasound beam is sent through the surface of the wall to be measured. Once it has touched the opposite side, a part of the sound comes back. By measuring the time of the return trip, knowing the propagation characteristics of ultrasound in the material of the wall, one can deduce the thickness. The disadvantage of this method is that it is necessary to put a gel on the probe to ease the transmission of ultrasound, which requires a significant preparation time. In addition, the probe must be positioned as vertically as possible to the surface, which is difficult for manual operations on curved surfaces.
The ultrasound method does not allow to measure very thin thicknesses: indeed, when the wall to be measured is thin, the echo of the sound comes back too quickly. The measurement electronics are not able to measure this very short return time with great precision.
- X-rays or Gamma-rays: these systems are very versatile and allow to measure the thickness of very complex objects. They use ionizing rays that are able to cross the opaque materials. By making a series of 360 ° images around the object to be measured, it is possible to reconstruct the object by mathematical calculations, giving access to the measurement of the thickness of the walls. However, these systems are dangerous for health, their implementation is very expensive. They are also not effective for all cases: in highly granular materials as formed by 3D printing (additive manufacturing), the density variation makes the interpretation of the image complicated and harms the obtained precision.
- Eddy Currents: This method has many advantages over the previous methods. This is Sciensoria’s specialty. It uses an alternating magnetic field to penetrate the material of the object to be measured. This magnetic field creates induced electric currents that circulate in the volume thus “illuminated” and reports information. It is thus possible to determine the electrical conductivity, the thickness, the presence of defects in the volume, the distance between the probe and the surface of the object, etc.
Sciensoria has introduced key innovations in the sensor structure, the excitation field injection method, the signal processing in order to make possible the multi-parameter measurement of the object. With these innovations, it is possible to measure the wall thickness of a curved object such as a tube or box, with a tolerance on the grade of the metal, the angle or height of the probe relative to the surface of the object. No coupling is necessary: the probe can remain without any contact with this surface. The mesurement system can do up to tens of measurements per second. The eddy current method is thus well suited to measurement on production lines, dangerous installations (chemical or nuclear), uncleaned or dirty surfaces, etc.
Prestigious companies around the world have used Sciensoria’s non-destructive thickness measurement technology: General Electric Power, which measures the thickness of these 3D printed turbine blades, or the German supplier Mahle, which controls 100 % of auto parts with 2 Sciensoria equipments.