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ADVanced Inspection of Complex StructurEs

Periodic Reporting for period 3 - ADVISE (ADVanced Inspection of Complex StructurEs)

Reporting period: 2020-09-01 to 2022-02-28

Material choices for components in nuclear reactors are mostly dictated by mechanical and operational requirements, in particular corrosion resistance and high mechanical strength and creep resistance at elevated temperatures. These requirements often prime over considerations of inspectability, and therefore the ultrasonic inspection of corrosion resistant alloys used in nuclear power plants is a long-standing issue. For materials such as austenitic welds and cast austenitic steels, a complex microstructure is responsible for both structural noise and attenuation, thus degrading the performance of ultrasonic testing.
The global objective of ADVISE was to improve the ultrasonic inspection of complex structured materials used in Generation II and III European reactors, by optimising the performance of existing ultrasonic inspections, where better signal-to-noise ratio, deeper penetration depth and more reliable diagnostics are required and by applying ultrasound to cases where the industry must resort to radiography, which is highly disruptive and has certain imminent dangers due to the radiation used.
The main technical objectives were to increase the comprehension and modelling of complex structures for accurate prediction; develop new tools for material characterisation and input data; provide advanced inspection methods; provide defect evaluation methods and assisted diagnostics and harmonise and share knowledge about ultrasonic inspection of complex structured materials while ensuring results uptake by the industry.
The results confirm a key premise of the project: No single technological advancement is likely to solve the issue at hand. Rather than looking for the proverbial silver bullet, the project aimed to improve the inspection capability of these materials by a number of incremental improvements in different fields.
Major ADVISE achievements (TRL):
-Fast FE Solution for 3D simulation in welded components (8)
-Anisotropic generalised point source synthesis (7)
-Weld formation modelling (3)
-Weld map inversion (4)
-Bulk material characterisation (4)
-Multilayer Transducer (7)
-TRL-Phased Array (9)
-EMAT array (7)
-Adaptive TFM Image optimisation (7)
-CIVA Lab framework (9)
-FMC post processing plug-in: Scattering Matrix (7)
-Effective material calculation (7)
-Multimodal TFM guidance (SEE estimator) (9)
-Heterogeneous structural noise reduction (CORUS) (8)
-Embedded algorithms on acquisition system (8)

ADVISE’s incremental improvements in the following topics:
- Understanding the underlying propagation phenomena is essential for an informed choice of the best compromise in terms of transducer configuration, wave mode and frequency, and is best served with computer models capable to take a complex microstructure into account and to predict performance for a given inspection setup.
- Knowledge of a weld’s macrostructure is necessary for precise ultrasound imaging, to take beam deviations into account, while local variations of the microstructure can cause large spatial variations of scattering and attenuation. For bulk materials, larger variations of grain sizes are often encountered, which may also include specific local features such as stratified layers. Material characterization is thus an important building block towards improved inspection capability. For welds, model-based approaches can provide good estimates, provided that the welding parameters are known.
- Inspection Technique optimisation refers to the choice of the optimum combination of inspection parameters such as transducer setup, mode, frequency, focusing. ADVISE pursued a model-based approach to the optimisation problem. Evaluation and demonstration of novel techniques, such as EMAT transducers and their unique ability to generate horizontally polarized shear waves, reputed to be less affected by beam skewing, and signal processing techniques to reduce backscatter noise were also performed.
- Model based defect analysis refers to different strategies to enhance defect characterization. An essential first step consists in taking into account knowledge about the macrostructure under inspection, to account for local variations of wave velocity, thus removing the traditional assumption of constant wave velocity when relating travel time-based information in ultrasound acquisitions to spatial locations within a component. The combination of relevant information from multiple images using different inspection modes relies on a model to discriminate defects from artefacts and geometry-induced indications, in order to combine only relevant modes. Adaptive imaging accounts for perturbations of local characteristics and corrects these for an accurate imaging of defects. Inversion techniques exploit forward models iteratively to converge towards a reliable defect characterization.
- Integration is a prerequisite for successful deployment of any inspection technique. ADVISE responded to this challenge in three ways. The principal receptacle for all developments is the well established CIVA platform, widely accepted in the industry. For algorithms which lend themselves to an actual integration into an acquisition system (e.g. with real-time or close to real-time performance), this was done, benefitting of the flexibility of the Panther acquisition system developed by Eddyfi.
ADVISE specifically addresses technology gaps for the inspection of cast austenitic stainless steel components and austenitic welds by providing incremental improvements in several areas, including transducers and imaging, which are necessary to achieve the performance step change required for the ultrasonic inspection of complex structured materials. ADVISE has demonstrated the feasibility to take a component’s microstructure into account in ultrasound imaging and thus correct for its impact on the ultrasound beam. With the integration of this capability in an upcoming commercial version of the CIVA platform, this will have a lasting impact on the way TFM and TFM-derived imaging is done. Weld formation modelling is a rapidly maturing technology, and ADVISE contributed to increasing awareness of this technology as a means to obtain information about a weld’s microstructure and to study the impact of influential parameters on ultrasound inspection. In terms of transducer technology, ADVISE prototyped an impedance matched transducer, which has potential applications in highly attenuating media, and demonstrated the potential of shear-horizontal wave mode inspection using EMATs, although both require further work to become deployable in the field. However, ADVISE also demonstrated the added value of combining TRL wedges with phased array transducers, which is rapidly becoming the method of choice for the inspection of heterogeneous structures with significant backscatter, in conjunction with TFM- and TFM-derived imaging. Another development which is already seeing deployment is the CORUS noise reduction algorithm. The availability of fast computer modelling of ultrasound inspection in complex structured components is already making an impact on the development of new inspection procedures and their subsequent qualification. Finally, the consistent use of an open data, documented and efficient interchange format (MFMC) and its adoption in tools already deployed in the industry has spawned interest in pursuing the further development, refinement and ultimately the standardisation of this format.
Ultrasonic Inspection of an austenitic stainless steel mockup using angle wedge contact transducer
SEE map in Capture – Illustration with TTTT and TTT examples
CIVA Software platform for integrating ADVISE results (Simulation, Imaging, Data processing and ML)