Research and Application Development

• Initial technique development using BeamTool
• Initial proof of concept using CIVA Models for probe, wedge and technique optimization
• Preparation of Inspection Qualification Plan document outlining required tests and sample test for full Probability of Detection (PoD) study
• Preparation of Factory Acceptance Tests (FAT) for initial evaluation of the manufactured tool based on PAUT inspection capabilities
• Performing full probability of Detection (PoD) and sizing accuracy study and preparation of Technical Justification (TJ) Document for CIQB qualification
• Technical justification and inspection technique was successfully delivered

Development of Phased Array Inspection system for Weld Inspection and corrosion mapping at Elevated Temperatures up to 350 Celsius.

Research and Applications Development in partnership with Eclipse Scientific developed a phased array inspection system to be used for inspections at elevated temperatures. The inspection system includes wedges designed for use at elevated temperatures and build from plastics resistant to high temperature degradation and equipped with a cooling jacket around the array. Temperature effects on generated ultrasonic beams at elevated temperatures have been fully studied and compensated for.

• A model of the ultrasonic beam skew pattern due to thermal gradient inside a wedge is developed
• Model results are used to obtain transmission and reception time delays on individual elements for generation of a plane waves or focused beams in a hot test piece while compensating for thermal gradient inside the wedge.
• BeamTool high temperature module has been prepared for exporting the custom transmission-reception time delays in law file format readable by conventional phased array instruments.
• Performance of the developed phased array inspection system has been fully validated including the effect of using the custom law files in proper positioning of defects detected at elevated temperatures
• The Inspection system is currently being successfully used widely in industrial sites for inspection of engineering components at elevated temperatures.

Inspection of Near Surface Delamination and Forging Defects using Focused Linear Scanning and Rayleigh Waves

We recently concluded a project in which the first 10 mm of a forged component was to be inspected for small de-laminations (~ 0.5 mm). Using a combination of high frequency, highly focused linear scans as well as relatively low frequency Rayleigh wave inspection, full coverage of the inspection range was demonstrated. Machined targets as small as 0.5 mm in a range of 1-10 mm from the component’s surface were repeatably detected using the proposed PAUT technique, while targets as small as 0.5 mm in the first 3 mm from the surface were reliably detected using Rayleigh wave inspection. A 1 mm target located 2 mm below the component’s surface, detected by both the PAUT and Rayleigh wave techniques is shown in the figure below.

The technique was developed using an OmniScan MX 1, off the shelf probes and a custom profiled wedge which was designed and manufactured by the Research and Applications Development group.

PAUT Scanning with Custom Pitch/Catch Focal Laws – Application to Root Erosion Monitoring and Stress-Corrosion Crack Depth Estimation

In an effort to strike a balance between the improved resolution achievable with FMC/TFM and the cost effectiveness/scanning speed/deployability of traditional phased array systems, we have been working to develop custom focal laws which produce highly focused images of narrow regions of interest. These laws can be imported into common phased array acquisition units. This approach has been found to be very promising for two particular applications: monitoring/sizing of weld root erosion and depth estimation of stress corrosion cracking (SCC).

For the case of weld root erosion monitoring a pitch/catch PAUT arrangement is used with focal laws designed to focus shear waves along the nominal centerline of the weld, which allows regions of root erosion to be easily detected and the extent of erosion readily estimated, as seen in the figure below.

A similar focal law has been used in an attempt to focus shear waves along the face of surface breaking cracks, with the ultimate goal of estimating the extent of SCC cracks (as shown in the figure below).

Using a 3D printed inspection jig (made in house), the technique has been used to accurately size surface breaking notches, as shown in the image below:

The way that the resulting focal law is plotted in standard PAUT analysis software (Zetec’s Ultravision Software) shows the vertical extent of the notches along the horizontal axis. Further work is underway to determine the precise sizing accuracy of the proposed technique. In addition, the possibility of including a second group using a different focal law which involves another backwall skip is being investigated by the Research and Applications Development group.

Advanced Phased Array Processing

FMC/TFM technology provides ultrasonic images with much higher resolution as compared to standard phased array images. Accordingly, FMC/TFM offers clear benefits in terms of flaw interpretation and sizing. FMC/TFM based inspections have 3 major limitations: 1. processing speed, 2. storage requirements and 3. limited pulsing energy (only a single element is used at a time in transmission). All of these shortcomings can limit the practical inspection range, which is particularly problematic as FMC/TFM is becoming commonly used for HTHA inspections of thick reactor walls. The Research and Applications Development group has developed a novel algorithm which processes standard phased array sectorial sweeps into high resolution images which rival those obtained by applying the TFM to FMC data. The following images compare the resolution of angled holes on a Harfang block obtained using FMC/TFM and the advanced PAUT processing algorithm (2 groups of 32 elements used in the sectorial sweep, +/- 60 degrees, 1 degree increment).

A major advantage of the proposed algorithm is that it can be run using standard acquisition units (OmniScan, Topaz, etc.). In addition, scan files are only slightly larger than for a typical PAUT sweep which allows for the possibility of rendering the higher resolution images live for large inspection ranges (data transfer and rendering algorithm can be fast enough). In addition, the fact that a large aperture is used in transmission allows more energy to be generated in the piece, which can help penetrate deeper, specifically in noisy materials.

Bounce Path Attenuation and Attenuation Rate Tomography for Imaging Microstructural Damage

Many defect types do not reflect ultrasound with appreciable energy and thus cannot be imaged using traditional UT techniques. Such types of defects, which can be microstructural in nature can manifest as inhomogeneity in the ultrasonic attenuation (or the frequency dependence thereof) within a component. The Research and Applications Development group has developed a technique capable of mapping subtle changes in attenuation to produce cross-sectional images of pieces suspected of localized microstructural damage. The technique is a straightforward adaptation of computed tomography (CT) scanning, commonly used in medical ultrasound to image soft tissue, where projection data are instead obtained by looking at the back-wall response between element pairs on a phased array probe (operating in Full Matrix Capture mode) with respect to a healthy reference sample. The technique has been used successfully to image small clusters of microporosity (10 micron pores) introduced into a small aluminium sample, as shown below.

The hope is that this technique will prove effective for imaging other types of microstructural damage such as HTHA and early stage creep, as well as other types of non-reflecting defects, such as poor fusion of plastic pipe welds and defects in friction stir welds. Additionally, this technique has been found to be a promising new approach for imaging/sizing surface connected cracks. The image below shows the ability of attenuation tomography to accurately size, tight, surface connected notches.

An obvious application for surface connected crack sizing is the depth estimation of SCC crack colonies, which the Research and Applications Development group is actively investigating at the present moment.

Through Cap PAUT Inspection of Fillet Welds with Flexible Polymer Wedges

Currently no commonly accepted technique exists for inspecting fillet welds for lack of fusion or volumetric defects. To that end, we have developed a technique which uses wedges made of flexible polymers to scan directly through the weld cap, focusing along the nominal fusion face or the center of the weld volume, depending on what type of weld defect is to be inspected. Coupling is achieved using a thin ethanol film which when pressed between the weld cap and the flexible wedge material achieves acceptable acoustic transmission. The following image shows the detection of incomplete weld penetration and crack like defects found in a FlawTech T-weld sample.

Further work is currently underway to establish and evaluate an appropriate sizing technique.