Radiography has been an integral part of the NDT landscape for decades, being used to examine everything from small welds to long lengths of oil and gas pipelines and other mission critical structures and components. The practices and equipment haven’t changed much over the last several decades, but as we head towards industry 4.0 there is a need to transition to more modern work practices using computed radiography (CR) and digital radiography (DR).
Conventional Radiography
Conventional radiography has been around for decades and the workflows are well understood and well-practiced by many professionals out in industry. Basically, the sample to be imaged is placed between an X-ray source or tube head and X-ray film. Following a suitable exposure, the film needs to be developed in a darkroom using a film processor and chemicals, typically located centrally in a laboratory.
The most recent development for film-based radiography are digitisers that, like slide scanners, they convert film into a digital format. This solution overcomes the degradation of film over time.
Computed Radiography
Like conventional radiography, CR is also an indirect imaging technology. It differs from conventional radiography in that it uses an imaging plate, negating the need for X-ray film, film processors and chemicals. The reusable imaging plate is coated with a photostimulable phosphor that functions similarly to film, capturing a latent image.
Following exposure, the image plate is read by a CR scanner. It uses a laser to stimulate the phosphor, releasing the image as light that is detected and converted to a digital signal that can be processed into a radiographic image displayed on a computer screen. The imaging plate can then be reset by exposure to white light.
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Advantages of Computed Radiography CR
Advantages of computed radiography include:
- Faster processing – reduces time to image
- Improved image quality – CR offers wider dynamic range and higher sensitivity compared to film, making it easier to detect subtle variations
- Elimination of consumables – no need to keep stock or order film and chemicals
- More environmentally friendly – no chemicals to dispose of
- Versatility – Flexible image plates can be used in a wide variety of applications and scenarios
- Reduced radiation exposure – CR typically requires lower exposure levels
- Digital data – no need to store and archive exposed film, and data is easier to share
- Cost effectiveness – despite the initial outlay for CR hardware, these typically pay themselves off by elimination of consumables, convenience of always being ready to go and more efficient workflows
Digital Radiography
Digital radiography is a direct imaging technology. This time the image is captured on a Digital Detector Array (DDA), often referred to as a flat panel detector in place of film or an imaging plate.
The DDA detects the radiation passing through the sample and sends the information to a computer which can display the image on the screen immediately. Real-time imaging allows for immediate analysis and adjustment if required.
Advantages of Digital Radiography DR
Advantages of digital radiography include:
- Faster inspection – Significantly faster than CR and analogue radiography
- Improved image quality – DR provides a wider dynamic range and better signal to noise, resulting in clearer images, better able to reveal small defects
- Reduced radiation exposure – provides similar quality imaging with less exposure than film
- Digital data storage – digital data storage is simpler than film and easier to share
- Cost-effective – initial outlay typically pays back through improved throughput and elimination of film and consumables
The disadvantage of DR is the DDA is rigid and can be fragile.
Summary
CR and DR are modern alternatives to conventional film-based radiography. All modes have a place in modern NDT, but with advantages such as:
- Faster and more efficient workflows
- No need for consumables
- Digital data which is easier to store and share and will not degrade over time
- Cost effectiveness
Combined with lower costs with increased popularity, CR and DR are beginning to make a charge. Furthermore, with increasingly modernised work practices, automated and semi automated X-ray inspection, along with computed tomography are also gaining momentum.