Crack characterisation using invariable feature extraction in stainless steel specimen used for absorber tubes of CSP applications via EMAT

Abstract

Absorber tubes are one of the most critical components of parabolic trough Concentrated Solar Plants. Due to the high temperatures where these tubes perform at with concentration of sunlight, it is very likely to get damaged such as crack etc and lose functionality. Therefore, the monitoring via NDT techniques is essential for preventing them from being significantly defective and reducing maintenance cost. Non-contact method is one of the best inspection candidates, which is more reliable to the tubes at high temperature through a review and the access to the absorber tubes is limited. In this paper, the crack detection and quantification for stainless steel specimen used for absorber tube using Electromagnetic Acoustic Transducers is presented. Through numerical and experimental studies, features are extracted to quantify the crack. Among these features, the ratio between the first edge echo and the second crack echo (Ac2/Ae1) is investigated as invariable feature to factors such as electromagnetic coupling, lift-off distance between EMATs and the specimen etc. In addition, the feature Ac2/Ae1 has linear relationship with the depth of the crack when the depth is more than 0.75mm, which proves the feature Ac2/Ae1 is invariable for crack quantification via both numerical modelling and experimental studies.

Investigating the Influence of Design Frequency on the Ultrasonic Signal of PFSV-EMATs

“…The NDT&E methods include ultrasonic testing (UT), magnetic flux leaking (MFL), alternating current field measurement (ACMF), eddy current testing (ECT), etc. [1][2][3][4][5]. Among the NDT&E methods mentioned above, electromagnetic ultrasonic transducer (EMAT) as a nonconduct UT approach is widely used for thickness measurement and material characterization due to its ability to generate and receive ultrasonic waves without physical contact or coupling with the surface of the workpiece being inspected.…”

Single SH guided wave mode generation method for PPM EMATs*

“…Being nondispersive and having the particle motion in the plane of the plate, the SH0 mode is sensitive to defects that are either perpendicular or parallel to the wave vector. [1][2][3] These good characteristics enable SH guided waves to be applied to increasing applications such as crack detection, [2][3][4] corrosion detection, [5,6] weld detection, [7][8][9] and the evaluation of interfacial adhesion. [10] SH guided waves can be generated by piezoelectric transducers, but piezoelectric transducers need to be specially designed and attached to plates by a very viscous or solid couplant, [11] making it difficult to apply to online detection.…”

Measurement System of Metal Magnetic Memory Method Signals around Rectangular Defects of a Ferromagnetic Pipe

“…Nevertheless, this technique presents limitations such as radiation hazard and highly expensive equipment, and it requires operators with high skill level [10][11][12]. Finally, Eddy current testing is employed for inspection of defects based on electromagnetic induction [12,13]. However, this technique needs an external magnetic field source to induce Eddy currents.…”