This article reports simulation studies of ultrasonic wave generation and reception using the sector scan feature of a phased array transducer to image and size crack-like defects in large pipes, elbows, and tee sections. The simulations were based on a two-dimensional implementation of the Finite Difference Time Domain (FDTD) method. Experiments were conducted to validate modeling results for pulse-echo simulations of the phased array transducer on pipe samples with notches of three different sizes. The defects were imaged using the sector scan mode of the phased array and sized using the Absolute Arrival Time Technique (AATT). A 64 element, 5 MHz linear phased array transducer with the ultrasonic beam swept over an angular range of 10°-75° (refracted angles), directly in contact with the specimen, was used. Simulation and experimental studies were also conducted to image and size cracks in elbow and tee section pipes.

Krishnan Balasubramaniam

Department of Mechanical Engineering

C V Krishnamurthy

Department Of Physics

Computer simulation

Crack detection

finite difference time domain method

pipe

Scanning

Ultrasonic waves

CIRCUMFERENTIAL SURFACE CRACKS

PULSE-ECHO SIMULATIONS

ULTRASONIC PHASED ARRAY

Ultrasonic transducers

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

Finite Difference Time Domain Simulation of Ultrasonic Phased Array Sector Scan for Imaging Cracks in Large Pipes, Elbows, and Tee Sections

Research in Nondestructive Evaluation

The suitability of the synthetic aperture imaging of defects using a matched filter approach on finite aperture transducers was investigated. The first part of the study involved the use a finite-difference time-domain (FDTD) algorithm to simulate the phased array ultrasonic wave propagation in an aluminum block and its interaction with side-drilled hole-like defects. B-scans were generated using the FDTD method for three active aperture transducer configurations of the phased array (a) single element and (b) 16-element linear scan mode, and (c) 16-element steering mode. A matched filter algorithm (MFA) was developed using the delay laws and the spatial impulse response of a finite size rectangular phased array transducer. The conventional synthetic aperture focusing technique (SAFT) algorithm and the MFA were independently applied on the FDTD signals simulated with the probe operating at a center frequency of 5 MHz and the processed B-scans were compared. The second part of the study investigated the capability of the MFA approach to improve the SNR. Gaussian white noise was added to the FDTD generated defect signals. The noisy B-scans were then processed using the SAFT and the MFA and the improvements in the SNR were estimated. The third part of the study investigated the application of the MFA to image and size surface-crack-like defects in pipe specimens obtained using a 45 steered beam from a phased array probe. These studies confirm that MFA is an alternative to SAFT with little additional computational burden. It can also be applied blindly, like SAFT, to effect synthetic focusing with distinct advantages in treating finite transducer effects, and in handling steered beam inspections. Finally, limitations of the MFA in dealing with larger-sized transducers are discussed. © 2006 IEEE.

IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control

Application of a matched filter approach for finite aperture transducers for the synthetic aperture imaging of defects

New techniques developed using the array transducer, to image and size the bottom-surface and near-through-wall crack-like defects in thick carbon steel components are discussed. Three studies are reported here including (a) Optimal beam steering angle for focused and unfocused inspection using phased array method for bottom-surface crack sizing. (b) A front wall correction algorithm for sizing of near-through-wall crack-like defects. (c) A small aperture technique for sizing of near-through-wall crack-like defects. A Finite Difference Time Domain (FDTD) based simulation was used to study and verify the experimental observations. The application of time domain scheme relative arrival time technique (RATT), to measure the size of the near-through wall crack-like defects for the leak before break (LBB) criterion, was also investigated and found to be insufficient. A conventional SAFT algorithm was used for improving the sizing using the small aperture technique. © 2009 Springer Science+Business Media, LLC.

Journal of Nondestructive Evaluation

Sizing cracks in power plant components using array based ultrasonic techniques

Finite difference time domain simulation of ultrasonic phased array sector scan for imaging cracks in large pipes, elbows, and tee sections

Phased array ultrasonics can be used as a rapid tool for imaging and sizing crack-like defects. This paper reports the simulation of phased array ultrasonic wave interaction with the defects using the finite-difference time domain (FDTD) method. Experiments were conducted to validate modeling results for pulse-echo simulations of the phased array transducer on a mild-steel (MS) pipe sample with circumferential internal surface notches of three different sizes. Experiments were carried out on the MS pipe specimen using a conventional ultrasonic technique with a 5 MHz transducer at 45° refracted angle within the specimen and the defects were imaged and sized using the relative arrival time technique (RATT). The experimental B-scans obtained using the conventional ultrasonic techniques were compared with the experimental B-scans obtained using the phased array instrument. Simulation studies were also carried out by steering the beam to the requisite angles by the phased array transducer to study the effect of various angles of incidence on the defect definition, i.e., with respect to imaging and sizing, using the RATT. © 2007 Elsevier Ltd. All rights reserved.

International Journal of Pressure Vessels and Piping

Simulation of ultrasonic phased array technique for imaging and sizing of defects using longitudinal waves

This paper reports on the numerical simulations of the Time-of-Flight Diffraction (TOFD) technique to image and size cracks in plate specimens, using the Finite Difference Time Domain (FDTD) method for modelling the ultrasonic wave propagation. Experiments were conducted to validate modelling results for pitch-catch simulations of transducers on samples with calibrated defects of different configurations and sizes in aluminium plate sections. Defects were imaged and sized taking into consideration the velocity of the wave and the times of arrival of the diffracted echoes. Experiments were carried out using a 5 MHz transmitter-receiver transducer pair mounted on suitable wedges to generate a beam of 50° refracted angle within the specimen to image and size cracks and hence validate the simulations. A front/back-wall correction algorithm coupled with a synthetic aperture focusing of the TOFD signals was also demonstrated for improved sizing of defects.

Insight: Non-Destructive Testing and Condition Monitoring

Finite difference time domain simulation of the time-of-flight diffraction technique for imaging and sizing cracks

This paper reports experimental sizing of fatigue crack profiles that are initiated from artificially made circumferential starter notches in stainless steel pipes of 169 mm outer diameter and 14.33 mm thickness, which were subjected to cyclic bending loads in a four point bending load arrangement using two nondestructive evaluation (NDE) methods: (a) phased array ultrasonic technique and (b) alternating current potential drop technique. The crack growth estimated using the two NDE techniques were compared with the beach marks that were present in the fracture surface. A simulation study using the ray tracing method was carried out to model the ultrasonic wave propagation in the test specimen, and the results were compared with the experimental results. Copyright © 2007 by ASME.

Journal of Pressure Vessel Technology, Transactions of the ASME

Phased array ultrasonic measurement of fatigue crack growth profiles in stainless steel pipes

Ultrasonics

Finite-difference and finite-volume methods for nonlinear standing ultrasonic waves in fluid media

Ultrasonic Nondestructive Evaluation for Material Science and Industries

Guided Wave Focusing Mechanics in Pipe

Journal	Research in Nondestructive Evaluation
ISSN	09349847
Open Access	No