Mistras Group
Advantageous Applications for Phase Coherence Imaging (PCI)
Source: Evident
The introduction of phase coherence imaging (PCI) in the OmniScan™ X3 64 flaw detector has vastly improved the visualization and characterization capabilities for some of most difficult-to-detect defects using today’s conventional ultrasound techniques. PCI’s imaging enhancements offer improvements not only for these challenging use cases, but also for common use cases such as weld inspections and crack sizing.

Unlike current ultrasonic testing technologies—including conventional phased array (PA) and total focusing method (TFM) techniques—PCI’s signal processing does not consider the amplitude when generating TFM images. It detects defects using only the phase information of the signal by measuring the phase coherence of the elementary A-scans for each point in the TFM zone.

Challenges That PCI Helps Overcome

Sound attenuative and coarse-grained materials Relying on the signal’s phase rather than the amplitude means that even in materials with high attenuation or background noise, the coherence of the signal can still be evaluated since the frequency distribution can be found even with low signal amplitude.

In fact, the noisier the background noise is, the easier it is for PCI to distinguish between the phase coherence of the flaw signal and the incoherence of the chaotic noise. This is why the results are better in coarse-grained materials such as austenitic steels.

Detecting small defects, especially those near large reflectors For example, compare this conventional TFM image versus the PCI mode image of creep damage (see image).

The back ground noise and the back wall echo in the amplitude-based TFM image (blue background) obscur the creep damage that is clearly visable in the PCI mode image (gray background). Both images were acquired using a 10 MHz, 64-element Dual Linear Array™ (DLA) probe and the L-L wave set.

Because amplitude is no longer a factor, gain adjustments and signal saturation are also eliminated. This helps mitigate problems such as strong echoes from the back wall or other larger reflectors obscuring smaller defects in their proximity.

Read the full article to see the 4 use cases where PCI is particularly powerful, and more at Olympus-IMS.com.

Sensor Networks