Though it’s a relatively new technique in the field of industrial NDT, PCI demonstrates enormous potential to solve many of the current challenges that inspectors are facing. The intention of providing these examples is to show the types of applications where PCI can be advantageous compared with amplitude-based ultrasonic techniques. Sizing cracks in welds is also eased when using PCI for the same reasons mentioned for SCC. It’s so effective that you can clearly distinguish the individual pores (see Figure 4 on the left). PCI is also a big help when trying to identify porosity, due to its high sensitivity to small defects. Additionally, sizing a LOF is faster and easier since you can use the tips diffractions as reference points, and you no longer need to adjust the gain or find the 6 dB drop like with amplitude-based techniques (see Figure 4 on the right). As previously mentioned, the problem of signal saturation is eliminated with PCI. Signal saturation is a common issue when evaluating lack of fusion (LOF) in a weld using amplitude-based ultrasonic techniques, which can make sizing the LOF time consuming. Image of porosity pores (left) lack of fusion in a weld (right) using PCI. Note that T-T and TT-TT pulse-echo propagation modes typically provide excellent PCI results for SCC detection. When detecting SCC with PCI, fewer groups can be used to achieve high-quality images and using fewer groups improves the efficiency of your setup and data collection. The tip diffractions enable you to easily identify the shape and direction of the crack, and you can use the hot spots to accurately size them.
#Mean phase coherence crack#
For a crack of any orientation, the tip diffractions from its sharp directional changes provide highly coherent phase responses, which generate “hot spots” in the PCI image. PCI, on the other hand, reliably detects vertical, irregular defects and they stand out clearly on the display. This makes it more difficult to characterize defects in applications such as sizing and analyzing stress corrosion cracking (SCC). Self-tandem wave sets are sometimes successful, but the top and bottom of the defect are usually split between two groups. Vertical defects are also an imaging challenge for conventional TFM, because the crack orientation results in a weak and inconsistent amplitude response. PCI rendering of hydrogen sulfide (H 2S) induced blistering. Despite a weak signal amplitude, PCI can still evaluate the phase information, revealing this hidden but essential information (see Figure 3).įigure 3. This is an inherent limitation, which is due to insufficient amplitude or the sound being unable to access the surface connection.
#Mean phase coherence full#
With amplitude-based techniques, it is possible to detect hydrogen blistering using a 0° inspection, but it’s difficult to determine the full extent of the damage. Wet Hydrogen Sulfide DamageĪnother challenge when using conventional PA and TFM is determining whether hydrogen sulfide (H 2S) induced blisters have propagated to the surface-for example, the internal diameter of process piping. Since each tiny edge of the defect emits a diffraction signal, the direction and orientation can easily be seen, regardless of the orientation. With PCI, however, the tip diffraction response from these small reflectors is highly coherent compared to large specular reflectors such as the back wall (see Figure 2). The orientation of HTHA defects, their size, and their proximity to the back wall are all contributing factors.
In its early stages, high-temperature hydrogen attack (HTHA) damage can be difficult to detect using amplitude-based ultrasonic techniques. This means there is less risk that small defects located in proximity to large reflectors, such as the back wall, are lost in their strong echoes. Furthermore, because amplitude is irrelevant with PCI, gain no longer needs to be adjusted. Because the PCI data is phase based, small defects are easy to distinguish in the final image. PCI is especially sensitive to small defects and crack tips that typically have a highly coherent response yet weak amplitude. Individual HTHA pockets stand out with high contrast when imaged using PCI.
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