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.

Krishnan Balasubramaniam

Department of Mechanical Engineering

C V Krishnamurthy

Department Of Physics

ARRAY TRANSDUCERS

Arrival time

CORRECTION ALGORITHMS

Experimental observation

FINITE DIFFERENCE TIME DOMAINS

FRONT WALLS

LEAK BEFORE BREAKS

OPTIMAL BEAMS

phased array

PHASED ARRAYS

POWER PLANT COMPONENTS

SMALL APERTURE

Surface cracks

Through-wall crack

Time domain

ULTRASONIC TECHNIQUES

ANTENNA PHASED ARRAYS

Carbon steel

finite difference time domain method

Martensitic Stainless Steel

Surface defects

Ultrasonic testing

Cracks

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

Journal of Nondestructive Evaluation

A new phased array inspection scheme, called Technique to Image using Virtual Array Sources (TIVAS), is proposed to image defects at deeper locations with good lateral resolution. An array of virtual focal spots using electronic beam forming and the expanded aperture through electronic linear scanning was employed to achieve significant increase in the focal depths, with improved SNR, when compared to single element array imaging or the conventional phased array focusing technique. The image reconstruction was performed using the well known synthetic focusing approach. In this paper, the role of the depth of focus and the focal spot size on the performance of TIVAS were studied semi-analytically and through FDTD simulations. It was observed smaller virtual focal spot size provides improved lateral resolution and there is an optimum depth of focus for the smallest focal spot size achievable for a array transducer. Experiments were carried out to validate these findings. © 2011 American Institute of Physics.

AIP Conference Proceedings

Technique for imaging using virtual array of sources (TIVAS)

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 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.

Research in Nondestructive Evaluation

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 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

NDT & E International

Thickness and grain size monitoring in seamless tube-making process using laser ultrasonics

Insight - Non-Destructive Testing and Condition Monitoring

Advanced echo-dynamic measures for the characterisation of multiple ultrasonic signals in aircraft structures

Sizing cracks in power plant components using array based ultrasonic techniques

Journal	Journal of Nondestructive Evaluation
ISSN	01959298
Open Access	No