4. Experiment results
Austenitic stainless steel weld pads of 25 mm thick, 200 mm
length and 200 mm width fabricated by Shielded Metal Arc Welding
(SMAW) method were used for experimentation. The grain size
of Austenitic stainless steel weld used was 100–150 lm. Ultrasonic
wavelength used was 1.5 mm (for 4 MHz longitudinal wave).
Hence the grain size to the wavelength ratio is about 1:10 which
falls in the Rayleigh scattering regime. This regime is commonly
used in ultrasonic testing since attenuation due to scattering is
least significant in this regime.
Slag inclusions of length 35 and 40 mm were intentionally
introduced in the welds. The weld pads have been scanned by
TOFD technique. The transducers used were 4 MHz, 45 longitudinal
angle. Experiment was conducted at room temperature and the
equipment used was MICROPLUS from AEA Technology, UK. The channel gain was set to 80 dB while scanning. TOFD signals were acquired using a digital storage oscilloscope . Fig. 3 shows the complete set-up. The major sources of noise present in the signal are the instrumental noise and the structural noise from the weld. The native signal obtained from the TOFD equipment is subjected to averaging in the digital storage oscilloscope with a weighing value 8. Weighing