Showing papers by "Anish Kumar published in 2021"

Comparative Study on Using Ultrasonic Array-Based Techniques for Detection of Flaws in Thick and Attenuating Materials

Abstract: This paper reports the influence of thickness and material attenuation on volumetric inspection using conventional and advanced ultrasonic array-based techniques through suitable examples. The sensitivity achieved in conventional phased array ultrasonic testing technique with focusing at specific depth using delay laws and advanced array-based techniques for simultaneous focusing at all depths such as Full Matrix Capture-Total Focusing Method and plane wave imaging-TFM are compared in the present study. Finally, experimental results are discussed for advanced ultrasonic array-based techniques for detection and characterization of a 4 mm through wall dimension vertical planar defect (simulating a lack of side wall fusion in a thick narrow gap weld) in a nickel base alloy forging having fine and coarse grains. The sensitivities and signal-to-noise ratio achieved in the different techniques are discussed in detail.

Influence of thermal expansion bend and tubesheet geometry on guided wave inspection of steam generator tubes of a fast breeder reactor

Abstract: Periodic assessment of steam generator tubes of a sodium-cooled nuclear reactor is very crucial for smooth operation of steam generators. To examine the integrity, an in-bore magnetostrictive trans...

Optimization of Geometrical Parameters of a Magnetostrictive Ultrasonic Guided Wave Probe for Tube Inspection

Abstract: Non-destructive examination of steam generator (SG) tubes of Fast Breeder Reactors is of paramount importance. The inspection needs to be carried out from the inner side of an SG tube due to the constraint in accessibility. Recently, the magnetostrictive ultrasonic guided wave (MUGW) technique has been proposed as an alternative for the inspection of SG tubes. As a commercial MUGW probe for small-diameter ferromagnetic tubes is not available, it needs to be designed and developed with optimum parameters. This paper proposes a three-step optimization approach for the development of a MUGW probe, namely optimization of the diameter and length of a permanent magnet (for bias) finite element modeling based, optimization of the width of the transmitter and receiver coils of the probe by empirical modeling and the optimization of the number of turns of the transmitter and receiver coils by equivalent circuit models. A MUGW probe is fabricated and tested experimentally to validate the optimized parameters. Experiments show the validity of the approach in terms of generation, long-range propagation (47.6 m) of L(0,2) mode at 300 kHz, and the required sensitivity (multiple 10% wall thickness deep uniform wall loss circumferential grooves) in SG tubes.

EMAT-Phased Array Inspection of Thick Austenitic Stainless Steel and Dissimilar Metal Welds

Abstract: Non-destructive testing (NDT) of austenitic stainless steel and dissimilar metal welds is important for inspection of main vessel in prototype fast breeder reactor (PFBR). The strong material anisotropy and coarse grain make these welds very difficult to inspect using conventional ultrasonic techniques (UT) employed with piezoelectric transducers. It is well known that the shear horizontal (SH) wave is very well suited for this inspection, and electromagnetic acoustic transducers (EMAT) are the best for generating this wave mode. In order to overcome the low-efficiency sound generation due to low conductivity and strong attenuation, an 8-channel EMAT-phased array (PA) sensor has been used in tandem mode to enhance the power level and to improve the signal-to-noise ratio. It generates bulk SH waves with almost uniform amplitude for beam angles from 0° to 90° and can cover the entire volume of the weld including the heat affected zone by scanning from one probe position. In this paper, the EMAT PA probe was used for detection of defects in thick austenitic stainless steel and dissimilar metal mock-up weldments at 600 kHz. It has been successfully demonstrated that the EMAT PA probe can detect 3 mm deep notches and 2 mm diameter side-drilled hole in 30 and 25 mm thick weld pads. The large active aperture allows the use of highly focused beams for good defect detection and high-resolution imaging of weld defects. The results obtained from the mock-up samples with artificial defects demonstrate the potential of this EMAT PA probe in laboratory settings and recommendations to transit to the actual field are also explained in this paper. Though the exciting frequency of the EMAT PA probe is very low, it offers good defect detection sensitivity in thick austenitic stainless steel and dissimilar metal welds in main vessel of PFBR.

Total focusing method-based ultrasonic phased array imaging in thick structures

Abstract: Ultrasonic nondestructive testing traditionally uses a conventional monolithic transducer. An approach similar to this comprising of independent single transmissions but with reception performed by all the elements in phased array ultrasonics is known as full matrix capture (FMC). The acquired data are processed by total focusing method (TFM). Conventional FMC-TFM has limitations in the inspection at large depth in attenuating materials due to single element transmission. To improve the beam forming process, coherent recombination of the plane wave with specific angles is utilized in transmission and the same aperture is used for the reception in plane wave imaging (PWI). A new methodology called angle beam virtual source FMC-TFM (ABVSFMC-TFM) is proposed to inspect thick attenuating materials such as nickel-base alloys. The ABVSFMC method leads to improved signal-to-noise ratio (SNR) as compared to the conventional FMC due to increased energy with directivity during transmission using a group of elements and improved divergence as compared to the PWI due to a small virtual source near the sample surface. In the present paper, FMC-TFM, PWI-TFM, and ABVSFMC-TFM methods are compared for the inspection of thick nickel-base superalloy (Alloy 617) with slots at various depths in the range of 25–200 mm. Optimization of the incidence angle has been performed by beam computation in CIVA software. Results obtained by CIVA simulations are discussed and also compared for the three methods.

Parametric study on resolution achieved using FMC-TFM-based phased array ultrasonic imaging

Abstract: Full Matrix Capture-Total Focusing Method (FMC-TFM) is an advanced mode offered by phased array technology for defect detection and characterization. Imaging using the FMC-TFM provides simultaneous focusing at all the depths and also offers various modes of imaging by post-processing the same acquired data. In FMC, each element acts as a transmitter, and all elements act as receivers. The TFM involves the extraction of the maximum amount of possible information from the specimen. The present work aims to study the influence of various parameters such as aperture size, frequency, and depth of the defects on resolution achieved using the FMC-TFM technique. The experimental results of FMC-TFM have been compared with those of Synthetic Focusing using Linear Array (SFLA) technique, which is similar to the conventional Synthetic Aperture Focusing Technique (SAFT) in which a single element is utilized for both transmission and reception. The study revealed that the lateral resolution decreases with increase in the defect depth, decrease in the wave frequency, and decrease in the aperture size.