High energy tomography : in-situ inspection of massive parts

CyXplus, subsidiary of Cybernetix and Technip Energies group, is a French company that is specialized in design and manufacture of non-destructive testing equipment based on radiography and tomography for the manufacturing industries.

It developed a high energy CT system to inspect massive parts : material integrity (detection of cracks, porosities, contaminants and inclusions…), assembly conformity, dimensional measurements… This system can be adjusted to the special needs of each industry, both in terms of energy (and therefore of penetrating capability) of the X-Ray source and in terms of the size of the parts to be inspected. The inspection of steel risers in the petroleum industry is a use case of high energy tomography. CyXplus and Cybernetix started in 2020 a collaboration with the PRCI (Pipeline Research Council International) for the design of a control and expertise system on submarine flexible pipes.

The work consists in performing onshore tests that are as realistic as possible for the acquisition and analysis of tomographic data on flexible pipes containing artificial calibrated defects in order to qualify the future system, byproduct from the BeamView equipment jointly developed by CyXplus and PMB-Alcen.

Thus, the X-ray source is a 6 MeV energy linear accelerator whose reduced focal spot allows getting radiographs without geometric blur while keeping a reduced focal length compatible with the required compactness of the equipment. By shifting the axis of rotation laterally from the main beam emission axis, samples larger in diameter than the size of the active area of the detector can be acquired in a single pass, saving inspection time. The performance of the imaging system was evaluated radiographically on a steel step wedge with IQI. In particular, the image spatial resolution is evaluated at 270 μm.

The main challenge of this study lies in the fact that this system is intended for in-situ use in an underwater environment. Aquariums have been specifically designed so that all open spaces around the inspected samples are filled with seawater and that the samples themselves are filled with oil to figure the passage of oil during testing.

The high energy of the source, combined with its high dose rate and fine adjustments to the image capture parameters, made it possible to compensate for the absorption of the various fluids and to obtain results comparable to those of the tests carried out in air. Indeed, a very slight degradation of the spatial resolution and of the contrast-to-noise ratio between the steps of the wedge was observed.

Flexible pipes have a complex structure made up of different concentric layers of steel and polymer accumulating several centimeters of steel in a single wall. Localized losses of thickness as well as cracks were introduced into each metal layer in order to assess the detectability of anomalies in these structures. Indications whose size is in the order of mm can thus be viewed and measured, regardless of their radial position in the inspected parts, despite the presence of water in the inspection field of view. Extracting cylindrical sections in each layer makes it easier to analyze the volume data.

The analysis of the quality of flexible pipes in an underwater environment by tomography therefore has a bright future ahead, although many technical challenges remain to be overcome before the system is launched. Beyond this application example, high energy tomography can make it possible to overcome the limitations linked to the absorption of the parts to be inspected or of the surrounding environment in the context of inspection under stress, which is particularly interesting in the fields of aeronautics or defense.

www.cyxplus.fr / www.cybernetix.fr / www.prci.org