Computed Tomography (CT) for performing Non-Destructive testing

Since its origin, the imaging/inspection approach has seen significant development and is currently utilized across numerous industries for a wide range of product kinds. First of all, realize that CT is an x-ray-based imaging technique that is only used once all the usual x-ray safety precautions and concerns have been taken care of. However, it is not an ordinary conventional x-ray. In a traditional x-ray, an object is targeted, the x-rays pass through it with varying degrees of absorption, and then they are finally caught on a film, imaging plate, or digital detector. A two-dimensional image of the object under test is the outcome. A doctor or an industrial technician will interpret this image to decide whether everything is normal or if there are any problems.

With CT, rotation and occasionally exact vertical movement are accomplished in addition to the x-rays still traveling through the object with varying degrees of absorption and being captured at the detector. The x-ray source and detector are spun around the target when used for medical CT and a few other specialized industrial applications. The item is rotated while the x-ray source and detector are static in the majority of Industrial CT and NDT operations. For the hardware and data collection, there are a variety of configurations and methods.  There are either mini focus or microfocus sources on the x-ray side, and bigger area detectors and linear diode arrays are available on the detector side (LDAs). The big area detectors essentially work the same way as the digital x-ray detectors in that they collect the entire scan in a volumetric way. The LDAs are very dissimilar. A single “slice” of the x-rays is captured by the LDA, a narrow band detector, at a specific Z height.

Three-dimensional information about the thing being tested is gathered using either method. The entire subject is often scanned at once by volumetric devices. The entire subject, various portions, or a 2-D slice will be scanned using LDAs. Each system type has benefits and drawbacks, but each application will have particular requirements that will determine which system is selected.

Beyond hardware, there is software, and there are many different solutions available based on the required examination. There are specialist third-party packages created especially for CT, as well as several system makers’ own unique software solutions. The choice of which option to utilize will depend on the requirements, preferences, and intended results for each inspection. Both alternatives can produce reliable inspection results. Cross-sectional photographs and complete 3-dimensional files are the two main outputs. The cross-sectional photos are simply combined with volume rendered processing to create the 3-dimensional files. These results can all be applied to various inspections.

Additionally, there are a few additional crucial elements of CT inspection that can be very specific to the different parts. I won’t get into all the specifics, but I will talk about a couple of them, including filtering and tools. The x-ray beam and occasionally the detector will need various filters manufactured of particular materials for filtering. These filters function to enhance the contrast of metallic components and the imaging of the subjects. To maximize the x-ray spectrum in various applications, the x-ray beam must pass through these filters. These filters are chosen for each application depending on the requirements that must be fulfilled. In terms of tooling, this is also important for guaranteeing a precise scan. It is important to think about how to place the individuals so that the CT scan is optimized and that they are in the proper position. Additionally, tooling is the most effective approach to guarantee that the x-rays’ route through various subjects is constrained.

Although CT systems need to be calibrated, tailored for particular purposes, and frequently operated and interpreted by a team of highly skilled inspectors, when all of this is done right, they can yield data that no other inspection can. A fantastic tool is the ability to “look” into a subject’s interior in ways that are blind to all other inspections.

Particularly for NDT, CT data sets are frequently utilized for inspection requirements such as defect identification, wall thickness measurements, geometrical verification, and others. In industries where internal geometry and integrity are crucial, such as additive manufacturing, gas turbine component production, and others, these examinations are frequently used. When it comes to essential components with internal geometries that cannot be properly inspected by any other NDT approach, CT is the preferred instrument. High-pressure turbine blades are depicted in the example photographs. Due of their intricate external and internal geometry, they are frequently examined using CT. Even with CT, these are challenging to inspect, but without CT, there is a significant chance that many of these might malfunction while in use.

How does an industrial CT scan work?

Industrial CT scanning functions similarly to digital radiography in that the test object is exposed to X-rays, which are absorbed to variable degrees based on the density and thickness of the material. A detector is struck by the leftover radiation, creating a grayscale image.

The test object is rotated 360 degrees during a CT scan to create hundreds of pictures. These photos are used to create a 3D model, which can then be analyzed using analysis software or processed using CAD software.

Which materials are suitable for scanning?

The resolution of CT scans ranges from a few micrometers to a few millimeters, depending on the material and size of the test object. Nearly all materials are acceptable for industrial CT scanning, which is especially beneficial for:

• Plastics
• carbon fiber reinforced plastics (CFRP)
• glass fiber reinforced plastics (GFRP)
• aluminum
• magnesium.

Various non-destructive testing techniques, such as the following, can be used to more thoroughly analyze other materials for flaws:

• Radiography
• Ultrasonic testing
• Eddy current testing
• Dye penetrant testing
• Magnetic particle inspection
• Dimensional inspection

Application of industrial CT scans

Industrial computed tomography’s high-resolution and three-dimensional imaging of items has several potential applications.

DEFECT ANALYSIS

Industrial computed tomography aids in the improvement of operational processes by locating and analyzing faults like pores, cavities, and inclusions.

• production start-up
• tool optimization
• production control and optimization
• quality assurance  
• failure analysis

3D MEASUREMENT AND METROLOGY

Metrological applications are made possible by precise 3D measurement of internal and external components.

• target/actual comparisons and actual/actual comparisons
• wall thickness measurement
• surface determination

ASSEMBLY AND JOINING INSPECTION

Industrial CT can discover assembly flaws non-destructively and without requiring the assembly to be disassembled:

• final assembly inspection
• incorrectly inserted or forgotten components
• position of seals
• analysis of soldering points
• visualization of leaks and corrosion

REVERSE ENGINEERING

CT scans of existing components enable the creation of drawings or CAD data sets, e.g. for the 

• digitization of handmade prototypes
• digitization of spare parts that are no longer available 

Conclusion

In conclusion, computed tomography has been used as an NDT technique for 50 years. It is utilised throughout numerous applications and industries. There is no other way to inspect the things that are inspected using CT. Although it differs significantly from traditional x-rays, the technology still uses x-rays and should only be used after all standard x-ray safety measures and concerns have been taken care of. The technique has a wide range of applications and is crucial to manufacturing, research, and quality control. New uses for CT will keep emerging as new manufacturing and maintenance techniques are developed.