| ABSTRACT: | SIZING OF CRACKS EMBEDDED IN SUB-CLADDING USING ULTRASONIC SYNTHETIC
APERTURE FOCUSING TECHNIQUE (SAFT)
S.Baby1, T. Balasubramanian1, R. J. Pardikar2, K.V. Rajkumar3 , T. Jayakumar3 and Baldev Raj3
1Department of Physics, National Institute of Technology, Tiruchirappalli, Tamil Nadu, India; 2 NDTL,
Bharat Heavy Electricals Limited, Tiruchirappalli, Tamil Nadu, India; 3 Indira Gandhi Centre for Atomic
Research, Kalpakam, Tamil Nadu, India
This paper deals with the experimental work carried out to demonstrate the feasibility of ultrasonic Synthetic
Aperture Focusing Technique (SAFT) to obtain improved detection and sizing of vertical/inclined simulated
cracks underneath different claddings. Pressure vessels, heat exchangers and many other components used in
many applications such as nuclear reactors, petrochemical and power plants etc., are typically fabricated
from thick carbon steel covered with austenitic stainless steel cladding. Clad is applied by welding using
either an automated or manual process. These clads pose problem for the ultrasonic inspection during the
routine in service inspection. The most commonly used NDE method for these applications is ultrasonic
testing. To obtain accurate defect sizes using conventional ultrasonic NDT equipment, considerable skill is
required because, there are many factors, which affect the accuracy and sizing ability of the ultrasonic
inspection. In order to overcome the limitations i.e. to get better detection sensitivity, and sizing ultrasonic
SAFT is employed. A PC based version of the SAFT in the time domain along with longitudinal angle beam
probe of 45¡- 4MHz was used. Automated scan and digital recording of ultrasonic data was carried out with
Line SAFT manufactured by M/s IZFP, Germany. The experimental study was confined to simulated cracks
(machined slits). The steel test blocks used for the study contained 0.5mm wide vertical/inclined cracks
(machined slits) of 10¡ and 15¡ inclination. Crack heights ranging from 1.68mm to 19.04mm underneath
stainless steel, Inconel and ferritic steel cladding could be sized with an accuracy of ±0.1 to ±0.3 mm. The
problem encountered in TOFD with regard to sizing of near surface cracks was successfully overcome by
SAFT.
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