A New Generation of X-ray Inspection Technology
Traditional X-ray technology plays a key role in metrology and quality inspections in a wide range of manufacturing sectors – wherever there is a need to check the internal structures of components, pipes and vessels reliably and accurately.
But a new generation of X-ray technology holds the promise of a faster, more cost-effective approach to meet the demands of modern engineering, particularly with the growing use of composite materials.
Digital X-ray film (DXF) is a flexible digital gamma and X-ray detector technology, designed specifically to be used as a fully digital alternative to radiographic film or digital radiography (DR) panels. Combining the flexibility of film with the digital image generation of digital X-ray detectors, DXF offers a new approach to the inspection of welds, complex shaped castings or shaped composite materials (see Fig 1).
Until now, traditional radiography has been a popular inspection technology, with a track record of reliability and accuracy. The flexibility of radiographic film makes it ideal for the inspection of things with complex geometries involving curved surfaces and tight spaces. When metal parts are joined by welding during manufacture, X-ray inspection can also highlight defects, such as cracks, porosity, inclusions or incomplete fusion, that could compromise structural integrity.
However, using radiographic film is a time-consuming and labour-intensive process. It involves loading the film into light-proof envelopes, exposing it to X-rays, developing the image in a dark room and then analysing the results. The overhead costs are also high – ranging from the cost of the chemicals, dark rooms and development equipment to the cost of digitising the film for storage or physically storing the film for up to 60 years.
DR overcomes many of the drawbacks of traditional X-ray technology as images can be captured and analysed almost instantaneously – enabling faster decision making and reduced downtime during the manufacturing process – and costs are lower as there is no need for film or chemical processing and digital images can be stored electronically.
Another advantage is that digital images can be enhanced and manipulated using software tools – improving defect detection and analysis. Advanced algorithms and artificial intelligence (AI) can further enhance image quality and help automate the detection of potential issues during production.
But one of the main challenges is that DR panels are rigid, square, thick and heavy. Unlike radiographic film, they can’t be bent around curved components or squeezed into tight spaces. This limits their use to mainly flat objects that have sufficient space around them to accommodate the rigid panels.
DR panels are also typically indirect conversion X-ray detectors – they use a scintillator material that converts X-rays or gamma rays into visible light. The higher the X-ray or gamma ray energy, the thicker the scintillator has to be. It then has a pixelated backplane with a photo diode per pixel which converts the visible light into an electrical signal. These electrical signals are then analysed partly in the hardware world and partly in software to produce a digital image.
Indirect conversion detectors are a tried and tested DR detector technology – and the most common technology used in medical X-ray imaging – but they have drawbacks. There are conversion losses in converting X-rays to visible light and then again to an electrical signal – limiting its sensitivity. In addition, as soon as the X-rays are converted to visible light, the light scatters from one pixel to the next. In the case of detectors with thick scintillators, the light can scatter across multiple pixels – causing blurring of the image (see Fig 2.1).
In the last decade, there have been massive improvements in the flexible semiconductor industry, with foldable screens on mobile phones and a range of curved computer monitors and television screens on the market today. The pixelated backplane technology used in these products is essentially the same as that used in DR flat panel detectors.
Combining one of these flexible pixelated backplane technologies with an X-ray sensitive semiconductor ink layer paves the way to a truly flexible digital equivalent to X-ray film. Incoming X-rays are attenuated within the nanoparticle-based X-ray conversion material – the semiconductor ink – and directly generate charge carriers, which are then transported to the underlying pixel array where they produce an electrical current response according to the energy of the detected X-ray photon (see Fig 2.2).
The flexible pixelated backplane, coated with the direct conversion semiconductor ink and sandwiched between two layers of carbon fibre, is likely to be less than 1mm thick. The carbon fibre makes it significantly more scratch and kink resistant than radiographic film – but with similar flexibility.
Since DXF is a direct conversion X-ray detector, it offers higher spatial resolution and sensitivity – enabling accurate measurement and the detection of fine cracks and other critical defects with precision. And the resulting digital images can be quickly analysed using advanced software tools. This reduces inspection time and allows for immediate identification of potential issues.
Although the initial cost of DXF detectors is higher than that of radiographic film, they significantly reduce the labour and overhead cost associated with radiographic film – resulting in a lower total cost of ownership.
DXF is also potentially well suited for inspecting the more complex shapes possible with composite materials, which are proving popular because of their superior strength-to-weight ratio, corrosion resistance and design flexibility (see Fig 3).
These materials – such as carbon fibre reinforced polymers and glass fibre reinforced polymers – present unique challenges for inspection because of their layered structures and potential for hidden defects, such as delamination and voids. But the flexibility and high resolution of DXF offers the potential of detecting defects that might be missed by traditional methods.
As well as the potential benefits of improved safety, reduced downtime and lower overall costs, the integration of DXF with existing digital systems in manufacturing is set to streamline workflows and improve data management. Digital images can be easily shared between departments and locations, for example, for faster and more effective collaborative analysis and decision making.
By combining the proven reliability of traditional methods with the speed, efficiency and enhanced capabilities of DR, DXF detectors could play a pivotal role in taking metrology and quality inspections to the next level – and meeting the evolving needs of modern manufacturers.
For more information: www.silveray.co.uk
Author: Norman Stapelberg, Silveray Products and Marketing Director
