The Advantages of Digital Radiography over Film

Roughly twenty years after the introduction of industrial digital technology, film still exists, but the investment into digital gives better returns every day.  The initial cost of converting to digital is expensive, but recurring expenses are virtually gone and the price of film and film processing is increasing. Yes, the capital expenditure approval process can be challenging but the return on investment has been proven by even small volume film users. In addition to decreasing costs, switching to digital increases speed of technology, improves image quality and manipulation and saves time and labour.

When millions of pounds are spent each year on consumables such as; film, processing equipment, processing chemicals, water, and disposal fees. Reducing cost at X-ray is a key target area for cost reduction. Another large variable for cost reduction is associated with labour. A company moving into digital radiography is normally unsure of the labour savings based on finding the correct equipment to increase throughput and production needs. For example, in castings, a digital system with CNC motion is key for cost savings. A midsized casting of around 20” cubed went from 2 hours on film, exposed to reaching the film interpreter, to 20 minutes with digital. A different casting, 3 to 4 times larger, took about 6 hours from exposure to interpreter compared to 1 hour and 15 minutes on digital.

Digital technology allows for easy measurement, reporting, software analysis, and visualization not available in an analog system.  With the Digital Detector Array (flat panel detector) as the imaging medium, the drawbacks of film have now been eliminated. In the digital era, we now have significant choices, both in terms of X-ray tubes and detectors. You may choose a system with lower spatial resolution with the minimum magnification required to allow for maximum part coverage.  You also have a choice of higher resolution with less part coverage per image, or a system with multiple tubes or detectors for both.  When tubing welds were reviewed on film, they were the same size (1 to 1) if in contact with the film. This made review slow to interpret due to size and need for an optical magnifier. With digital radiography we use geometric magnification to enlarge the tube weld image, and increase spatial resolution to find small indications. This speeds the interpretation portion, making the correct accept or reject decision easier.

Another important consideration between film and digital is the archival requirement.  In many industries image data must be held for an extended period of time such as the life of an aircraft, service of a pressure vessel, etc. Some companies have warehouses full of exposed film costing tens to hundreds of thousands of pounds per year. Liability on such storage is high, as a strong storm or power loss could destroy years of records. Of course there is a cost associated with digital storage as well, but those costs are no longer comparable.  In addition, a piece of film cannot be sent via email in moments like a digital image can, but the value is much more. Viewing a ten year old image takes a few mouse clicks and fidelity is not a factor.

There are obvious advantages of switching from film to digital technology but ultimately, digital radiography still has some hurdles to overcome when we review the issue of indications in the 2D perspective. With a 2D image we’re only able to measure the lengths, widths, or diameters. We need a 3D perspective in order to truly and accurately know all aspects of the indication and its orientation within a product.  Computed Tomography (CT) technology allows you to focus on seeing the true indication and its location.  CT is simply a collection of 2D radiographs while rotating the part normally 360 degrees. Proprietary algorithms are then used to reconstruct the 2D projections into a 3D CT volume, which will allow you to view and slice the part at any angle.  3D CT virtually eliminates interpretation errors and opens the door to many capabilities; some not available with any other technology.

North Star Imaging’s facility in High Wycombe, UK houses NSI’s most versatile system, the X5000 series, capable of digital radiography and computed tomography with a scanning envelope of 0.8m x 1.2m.  The system has both 225kV and 450kV capabilities and hence can cover a very wide range of applications. The company offers advice and support to customers wanting to develop application specific solutions and supply inspection services.

Typical inspection service requests are for internal and external measurements, visualisation of internal defects such as voids and/or porosity, surface reconstructions for reverse-engineering and the ability to perform failure analysis in a non-destructive manner.

To see a demonstration of the capabilities of NSI’s Digital X-ray and Computed Tomography equipment, contact Guy Tolley at gtolley@4nsi.com or 07557 034195.

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