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Micro-CT Examination of a Rusty Screw Point

Figure 1: Rusty screw imaged in this study

Corrosion in metals can affect a wide array of man-made materials, from reinforced steel in concrete to historic monuments and implanted medical devices. Corrosion causes a loss of strength that can lead to safety hazards in bridges, buildings, and pipelines, as well as in medical devices. The annual direct cost of metallic corrosion worldwide is estimated at over $2.2 trillion USD, and the annual cost of corrosion in the US is estimated at $423 billion, the equivalent of 3.1% of the Gross Domestic Product (GDP). Micro-CT is an excellent tool that allows scientists to non-destructively visualize the progression and effects of corrosion on metal products.

This month we chose to highlight our SkyScan 1272 high resolution desktop micro-CT to examine the point of a rusty screw.

Micro-CT Scan of a Rusty Screw Point

Our micro-CT examination of this rusty screw point allows us to examine the effects of oxidation on the metallic surface of the screw, leading to the formation and propagation of rust. As can be seen in Figure 1 above, the sample has undergone significant oxidation prior to analysis.

Figure 2: Two-dimensional views through the screw point with the metal in yellow and the rust in red

As can be seen in Figure 2, there is a generally thin but near uniform coating of rust over the region of the screw which we examined. In addition to the surface rust, we can see the loss of metallic volume, especially in the threads of the screw point. The regions with the greatest loss of volume can be seen in red in the image. The red color indicates regions with lower X-ray attenuation which would be consistent with a loss in metallic strength. 

Figure 3: Clipped volumetric rendering of a rusty screw point showing the calculated rust thickness

In addition to just visualizing the rust layer on the surface and interior of the screw point, a volumetric analysis of the rust layer was completed and a sphere fitting model was used to calculate the thickness of the rust layer throughout the scan results. The results of that analysis are visually depicted in Figure 3. The screw is rendered in standard grey while the rust layer is shown in color scales ranging from yellow to red with yellow being thicker, orange being middle thickness, and red being the thickest. In agreement with what we observed from the 2-dimensional images in Figure 2, the thickest areas of rust were calculated to be present on the screw threads and represent areas where the metal has been compromised by the rusting oxidation process.

Conclusion

Micro-CT is particularly useful in non-destructive examination of metallic samples to examine for the effects of oxidation. We hope you found this Image of the Month informative. If you have an Image of the Month sample that you would like us to scan, please contact us by calling Seth Hogg at 610-366-7103 or e-mailing seth.hogg@microphotonics.com

Scan Specifications

Sample

Rusty Screw Point

Voltage (kV)

100

Current (µA)

100

Pixel Size (µm)

10

Rotation Step

0.4

Scan Time (HH:MM:SS)

02:00:35

This scan was completed on our high resolution desktop SkyScan 1272 system at the Micro Photonics Imaging Laboratory in Allentown, PA. Reconstructions were completed using NRecon and visualization of 2D and 3D results were completed using DataViewer and CTVox.

 

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