A D V A N C E D M A T E R I A L S & P R O C E S S E S | S E P T E M B E R 2 0 2 2 2 8 the algorithm to differentiate what is coherent and what is noncoherent. A third advantage of the PCI technique is that sound attenuation has less of an impact in thick parts. As ultrasound travels through a medium, the amplitude of the signal decreases over time. In Fig. 4a, which shows a typical Fig. 1 — (a) Carbon steel sample with induced high-temperature hydrogen attack (HTHA) microfissures; (b) TFM (amplitude-based technique) detecting two reflectors; and (c) PCI detecting the two reflectors and additional microfissures undetected by TFM. (a) (b) (c) amplitude A-scan, the amplitude of the first signal representing an indication in the material is much higher closer to the surface (0) and diminishes over time or as the sound continues to travel through the part. Figure 4b represents the phase information of the A-scan, showing that neither time nor distance have an impact on the signal strength. This phenomenon has an influence on the detection results because the amplitude of sound reflected from a defect that is large and critical but deeper in a component may not return with the same intensity to the sensor as that of a smaller yet closer defect. The images in Fig. 5 show an ultrasonic probe on a carbon steel component containing several side-drilled hole (SDH) reflectors at increasing depths. Even though all the Fig. 2 — (a) PCI/TFM ultrasonic equipment with a creep damage sample and a phased array probe; (b) conventional TFM imaging of the creep damage sample; and (c) PCI detecting the creep damage while removing the excessive background noise. (a) (b) (c)
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