PSI - Issue 14

Altaf Ali et al. / Procedia Structural Integrity 14 (2019) 273–281

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Author name / Structural Integrity Procedia 00 (2018) 000–000

region. For 45 0 refracted shear wave (bc), time taken to travel comes out to be 0.261 µs. Thus, beam travel time in half skip and full skip modes are about 0.522 µs and 1.044 µs, respectively. UT experiments on prepared samples (same as those were used in RT) have been carried out on experimental set up consisted of an underwater B and C scan system having 5 axis manipulator controlled by LabVIEW software (Fig. 4 (a)). The specimen was kept in immersion tank filled with water over two V blocks to arrest the necessary degree of freedom and probe was oriented at 18.78 0 incidence angle. A 20 MHz computer controlled pulser-receiver was used at 6 dB gain. 7000 data points were acquired at a sampling rate of 625 MS/s to digitize the wave form by using PCI based digitizer card and were stored using a LabVIEW program. A spherically focused 20 broadband immersion transducer with 12.5 mm focal length in water and 0.25 inch element dia. has been chosen which is having a spot diameter of 0.2 mm at - 6 dB drop. The water path of 10.636 mm was adjusted such that the ultrasonic beam gets focused at the tube ID.

Fig. 4. (a) Schematic representation of different components of UT experimental set up;(b) UT rays in the end plug weld zone with scanning direction; (c)&(d) histogram for I and II weld dimensions respectively

Fig. 5. (a) UT B-scan response from 45 µm deep inverted V notch; (b) Corresponding A-scan signal showing surface and notch echoes

However, the target sensitivity was set to 10% of tube wall thickness. So, an inverted V notch of 45 µm depth located at tube ID was prepared as per the ASTM standard and was taken as reference for system calibration. B-scan image (without angle correction) and corresponding A-scan signal from this notch are shown in Fig. 5 (a) and (b), respectively. As can be noticed, amplitude of about 100 points is obtained from the notch against the noise of about 10 points, giving a signal to noise ratio (SNR) of 10 that is quite good.