Simulation Software of NDT Techniques

NDT.net • June 2006 • Vol. 11 No.6

Simulation Software of NDT Techniques

Fabrice Foucher*, Cedrat SA; Laurent Le Ber, Steve Mahaut, Commissariat à l'Energie Atomique.
*Email: software@cedrat.com

ABSTRACT

Simulation and data processing in Non Destructive Testing p lays an increasing role for analysing results (improve the identification, location and characterization of defects) or p erformance demonstration (evaluation of the capability of a given method and identification of the limitations). Another very common application, particularly for phased-array methods, is the design and optimization of inspection methods. Large work for over ten years has led to CIVA^nde software to fulfill the requirement of computation times compatible with practical use in industrial context, a twofold strategy was put forward: the choice of semi- a nalytical methods and the development of models integrated into software modules usable by operators who are not simulation specialists. The application fields have become increasingly diverse: nuclear industry, aircraft industry or petrochemical, railways,...

Ultrasonic tools in CIVA^nde

• Nozzle inspection:
We can see in figure 1 an example of ultrasonic simulation performed in CIVA^nde concerning a nozzle inspection. The nozzle is specified by a few parameters (diameter, depth and orientation of the two pipes) and automatically a CAD designed nozzle is built. A wedge coupled transducer has been located outside the secondary pipe and the field computation module has been executed. The display is a cartography of the magnitude of the velocity potential within the component. It can be noticed that, on this example, the field computation accounts for reflections on the internal surface of the nozzle.

Figure 1: Ultrasonic field transmitted by a wedge coupled probe within a nozzle.

• Phased Array & Electronic commutation:
Ultrasonic NDT techniques based on phased array transducers rely on the application of delay and amplitude laws to groups of elements of an array. Within the CIVA^nde software are included a set of tools specifically developed for phased array applications. The electronic commutation technique is one of the most usual application for phased array probes: it consists in using a limited number of active elements (at transmission and reception) multiplexed over a large array. This technique is classically applied to reach very high acquisition rates with a simplified mechanical device, since one of the displacement direction can be replaced by an electronic commutation.

• Highly Bended composite inspection:
As shown in figure 2, a semicircular linear array transducer has been developed to assess a highly bended component. Electronic commutation with a 8*64 sequence is used to keep L0°-wave on the entire bend.

Figure 2: Transmitted beam in a highly bended component.

It means that 8 elements are fired over an overall aperture of 64 channels. The first 8 elements are used at transmission and reception, then this aperture of 8 elements is successively translated to cover the whole array.

The efficiency of this technique can be evaluated and qualified in the echo computation module of CIVA^nde First, six flaws have been aligned along the curved part, then another simulation has been performed with several misaligned flaws (see figure 3). On the first simulation, thanks to the normal incidence of the longitudinal waves hold all along the curved part, the echoes are clearly separated , there is neither distortion neither attenuation between the different ones. On the second simulation, echoes are still clearly separated but signal distortion and attenuation appears for misaligned defects.

Flaws aligned along the curved part Tilted/misaligned flaws Figure 3: Echo computation.

• Tandem Technique:
Figure 4 deals with another a pplication of electronic commutation. The aim here is to benefit from the phased array skills to improved flexibility in terms of tandem applications. It relies on the selection of different groups of elements over an array, some elements being in transmission mode, other elements in reception mode.

Figure 4 : Component inspected with phased array probe settled for tandem technique

Such inspection techniques may be carried out to detect mid wall defects in noisy materials, as they provide a way to assess flaws in specular reflection (as a contrary a pulse echo inspection with one single probe cannot be used for an optimal corner echo as soon as the defect is not emerging at back wall or front wall). As the elements may be arbitrarily selected, and, in addition, with arbitrary delay laws applied, phased array allows a flexible tool for tandem inspections. In this example, three mid wall defects have been inserted in a cylindrical component at different depths. A contact phased array made of 48 elements is used with separate elements at transmission and reception. Inspections have been simulated for three different settings of the phased array probe, each setting being designed to optimise the inspection of one particular defect.

The delay laws are computed to focus shear waves at the selected defect depth, in direct mode for elements used at reception, and focusing after back wall reception for elements used at reception. We can see on the echo dynamic curves that, for each set of delay laws, the echoes of the different defects are clearly separated (figure 5).

Figure 5: Echodynamic curves obtained for 3 different set of delay laws.

Figure 6: EC signals for a bobbin coil in a tube with a 3D flaw.

Eddy Current simulation tools in CIVA^nde

The main problem in Eddy Current Non Destructive Evaluation consists in predicting the effects due to the interaction of eddy currents with defects within a conducting material. For many applications, the surface curvature is low and can be locally considered as planar. The response of a surface riding coil to a 3D flaw in a slab can be computed with great time efficiency and accuracy with the semi-analytical model. CIVA^nde also offers the possibility to simulate the response of an encircling coil or a bobbin coil for any configuration of tubes with axisymmetrical flaws such as grooves or 3D flaws. An example of a signal obtained with a differential bobbin coil at 100 kHz with a longitudinal notch is given in figure 6. This flaw is a 54% tw outer notch of 10 mm length and of 0.1 mm opening. The agreement is excellent between simulation and experimental data.

Conclusions

In this paper we have briefly presented the capabilities of the CIVA^nde software. Emphasis has been put on the major ultrasonics and Eddy Current simulation tools existing in the plat-form. For both techniques, the semi-analytical modeling approach has been chosen to minimize numerical costs for an industrial use of the codes. With successive versions of CIVA^nde, the last results of research are integrated in order to improve the software capability and to widen the fields of applications.