Guided ultrasonic waves are widely used for long range inspection. Higher Order Modes Cluster (HOMC), discovered at the author's research group [1-3] consist of multiple higher order guided wave modes that travel together as a single wave-packet and without appreciable dispersion for distances in the range of meters. These waves not only propagate along the length of the structure but also cover the entire thickness, and in view of the higher frequencies, they can offer improved resolution over conventional low-frequency guided waves. This paper studies the sensitivity of axial plate HOMC to notch-like defects, evaluated by calculating wave reflection co-efficient. The studies are carried out using finite element models validated by experiments. Analysis is presented for better understanding of wave-defect interaction. Advantages and limitations for practical realization of the above approach are also discussed. © 2017 Author(s).

Prabhu Rajagopal

Department of Mechanical Engineering

Krishnan Balasubramaniam

K. Sri Harsha Reddy

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IIT Madras is a public technical and research university located in Chennai, Tamil Nadu. Founded in 1959, it is recognised as an Institute of National Importance.

IIT Madras has been ranked as the top engineering institute in India for four years in a row by the National Institutional Ranking Framework of the MHRD

It currently offers undergraduate, postgraduate and research degrees across 16 disciplines in Engineering, Sciences, Humanities and Management. About 596 faculty belonging to science and engineering departments and centres of the Institute are engaged in teaching, research and industrial consultancy.

IIT Madras

Interaction of Higher Order Modes Cluster (HOMC) guided waves with notch-like defects in plates

AIP Conference Proceedings

The authors have recently reported on the attractive properties of shear-horizontal type feature guided (SHB) waves for the inspection of 90° plate bends. Further to this, here the interaction of the SHB mode with transverse and longitudinal defects in the bend region is studied using 3D finite element simulations validated by experiments. Trends are discussed in light of the underlying wave mechanics principles. The results show that the SHB mode yields improved through-thickness defect resolution capabilities as compared to regular plate guided SH waves in view of mode confinement and higher frequencies used. © 2015 Elsevier Ltd. Allrightsreserved.

NDT and E International

Interaction of shear horizontal bend (SHB) guided mode with defects

This paper reports on a new means of generating higher-order mode clusters of guided waves (HOMC-GW) using a meander-coil (MC) electromagnetic acoustic transducer (EMAT) in plates at frequencies significantly higher than the lower-order plate modes. These wave modes are considerably less dispersive and they occur at much higher frequency¿thickness (f x d) products. Our studies cover the f x d range of 13 to 20 MHzmm. Experimental measurements were carried out on Al plate samples of different thicknesses using three different EMAT coil periods. To understand the generation and propagation characteristics of HOMC-GW with EMATs, several simulations were carried out using 2-D finite element models at different f x d products. These simulations captured all features observed in the experiments. The time¿frequency smoothed pseudo Wigner-Ville distribution (SPWVD) was used to analyze the HOMC-GW modes. Defect detection measurements using HOMC-GW generated using EMATs were made on Al plates with machined defects. © 2012 IEEE.

IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control

Generation and detection of higher-order mode clusters of guided waves (HOMC-GW) using meander-coil EMATs

Corrosion detection in the annular plate region of above- ground storage tanks is a critical needfor tank farm operators in the oil and gas industry. The critical zone between the tank shell wall and the first few inches of the annular plate is difficult to inspect with conventional floor scanning methods due to the presence of coatings, uneven surfaces and a lack of access due to the presence of the weld toe. This region, however, is prone to accelerated corrosion due to the additional stresses caused by the weight of the tank wall and the increased possibility of water entrapment under the annular plate. Repairs in this region demand replacement of the entire annular plate and this leads to long shutdown of the tank, and often failures occur without any warning. A new method using the Higher Order Modes Cluster Guided Waves (HOMC*) to detect and screen defects in the critical inaccessible zones in the annular plate is discussed. This testing can be carried out online while the tank is in operation using HOMC guided waves generated on the outer exposed region of the annular plate. Robotic scanners allow for the inspection to be carried out in relatively short periods of time. Data collected in the laboratory as well as from the field trials are presented. The HOMC technique has potential for non-destructive inspection of inaccessible regions in structures for medium-range applications (2 to 3 m).

Insight: Non-Destructive Testing and Condition Monitoring

Higher order modes cluster (HOMC) guided waves for online defect detection in annular plate region of above-ground storage tanks

The non-dispersive propagation of ultrasonic guided wave higher order modes cluster (HOMC) traveling along the circumferential direction in a hollow cylinder and its interaction with defects in pipe support regions is reported. These circumferential guided waves were generated in mild steel (MS) pipe specimens containing artificially created axial notches (simulating axial cracks) and pinholes (simulating pinhole-like defects) of different sizes in order to simulate conditions such as cracking and corrosion under pipe supports. The characteristics of these guided waves were also studied as a function of parameters related to how they were generated; namely, using: (a) 2.25 MHz linear phased array transducer, (b) 2.25 MHz conventional circular transducer and (c) 1 MHz conventional circular transducer. These higher frequency modes were explored for their ability to detect and size defects. Because of access limitations to the pipe support region in actual field testing, the transducer was always placed at a fixed circumferential position and moved axially along the length of the pipe. The defect position along the circumference was ascertained from the time of flight while the defect size was estimated using the amplitude data. The signals obtained for all three transducer configurations are compared for their ability to locate, detect and size the above-mentioned defects. It was shown that at these relatively higher frequencies, the guided wave modes exhibit small dispersion and have the ability to provide improved imaging of small size defects throughout the cross-section of the pipe. © 2007 Elsevier Ltd. All rights reserved.

Journal	Data powered by TypesetAIP Conference Proceedings
Publisher	Data powered by TypesetAmerican Institute of Physics Inc.
ISSN	0094243X
Open Access	Yes