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by Andrea Koetz

Managing image data from nondestructive testing (NDT), especially radiographic inspection data, has always been a labor- and space-intensive operation. Expert opinion has often been required at the point of inspection, even for simple tasks, and film storage in large organizations has often required many thousands of dedicated square feet. However, with the implementation of digital radiography and the introduction of sophisticated image processing, reviewing, and archiving software, even the very largest of tasks, such as inspecting and keeping track of the results associated with maintaining aircraft fleets, can be effectively and efficiently handled.

Traditionally, radiography systems have been based upon wet-film technology. However, traditional wet-film radiography has its drawbacks. It has accompanying operational costs, such as cost of consumables and the costs of chemical disposal. Film storage is space-intensive, retrieval of archived film is time-consuming, and results-sharing is only possible by copying film or reshooting. Moreover, extremely accurate results are difficult to achieve, as flaw sizes must be measured manually, and reference points such as visible edges are, in fact, optical illusions. Consequently, equipment manufacturers have for many years carried out development programs to produce systems that provide radiography inspection solutions incorporating all the benefits of wet-film systems with none of the disadvantages. The result of all these endeavors has seen the birth of a new generation of radiography—digital radiography, which is divided into two technologies: digital X-ray and computed radiography.

Digital radiography
With digital X-ray, a flat panel is covered with a cesium iodide scintillation material that converts the X-rays into light. This light is then converted into electronic charges in a low-noise, photodiode/transistor array, where each photodiode represents a pixel or picture element. The charged electrons then pass to read-out electronics for digitizing and immediate display on a suitable monitor.

This is instant X-radiography, with no film and, hence, no wait for film to be developed. Moreover, because they’re based on digital technology, the images can be viewed on a local review station, a remote station, or shared among a number of stations. Images can also be enhanced to focus on particular areas of interest. They can then be filed and archived for future reference and traceability.

Digital radiography offers equal and often greater probability of detection compared with film, and it also offers significant operational productivity. There are fewer process steps with digital radiography, and so the cycle times are reduced by more than 50 percent. This means more than 50-percent better throughput.

The technology is currently restricted to the laboratory and manufacturing environments, although developments are underway to extend the areas of application of digital radiography.

Computed radiography
Computed radiography, on the other hand, is very much field-applicable and is spearheading the conversion from film to digital technology in X-ray.

Computed radiography (CR), which uses an imaging plate instead of film, is fast replacing conventional radiography in many applications and will be covered by an American Society of Mechanical Engineers code in the near future. The imaging plate of a CR system contains phosphors that retain a latent image produced by means of a conventional X-ray source. When the plate is scanned with a laser beam in a digitizer or scanner, the latent image is released as visible light. This light is then captured and converted into a digital stream to create the digital image, which can then be viewed on an image review station. Once used, the imaging plates can be wiped clean and reused, typically up to 1,000 times.

Greatly reduced costs of consumables and the absence of darkroom or processing chemicals are just a few of the many benefits offered by computed radiography. Because the phosphors on the imaging plate have an extremely wide dynamic range, there is greater tolerance for varying exposure conditions. This results in fewer retakes, which means a substantial reduction in X-ray dose. There is also no development time because images are available for viewing as soon as the plates are scanned, with the result that productivity can be two times that of film systems.

Although flexible phosphor plates, with suitable protective pouches, are finding wide application, the majority of inspections are carried out with specially developed NDT cassettes. These are much more robust than flexible plates and are scanned using purpose-designed scanners.

The benefits of digitization
Basically, a computed radiography system consists of a radiation source (X-ray or isotope), an imaging plate, a scanner, a high-resolution monitor, a personal computer (PC) workstation, and the associated imaging and review software. The radiation source, the PC, and the monitor are standard hardware. What differentiates one computed radiography system from another is the quality of the imaging plate, the scanner, and the power and flexibility of the software.

The early development of software to process and transfer radiographic images was carried out in the medical field. This resulted in the creation of the standard for digital imaging and communication in medicine (DICOM). Much of the pioneering work was carried out by GE Healthcare during the past 12 years, and DICOM is now used by virtually every medical profession that utilizes images. It is the accepted image- and data-transfer protocol.

The industrial sector has benefited from this pioneering work with the development of digital imaging and communication in nondestructive evaluation (DICONDE). This relies very much on the DICOM protocol but incorporates many features that are focused on nondestructive evaluation. The first version of the DICONDE standard was released by the American Society for Testing and Materials in 2003.

Essentially, DICONDE is a dictionary that describes all the necessary syntax, attributes, and data elements to allow users to acquire, store, archive, transmit, and receive image data in a way that’s universally compatible. It’s a system that allows images to be saved with context, in that all the technical information and information on location, date, time, and inspector is saved along with the image. Such information can then be included in any report, while its inclusion with the image into databases means that database searches can be carried out on a variety of criteria.

DICONDE compliancy ensures that operators are not constricted by current proprietary formats, eliminates the need for future data conversion, and simplifies data integration from other NDT information sources, such as pipe management databases. Moreover, DICONDE images can be exported in other file formats, such as JPG, BMP, and TIF. A copy of the DICONDE viewer can be included on a CD or DVD to allow the content to be displayed on any standard PC.

One software platform based on the DICONDE standard is Rhythm, from GE Inspection Technologies. The platform is broken down into four separate modules, each focused on driving inspection and data-management productivity to users. At the moment, it is available as a platform for radiographic testing and visual inspection, with future modules planned for ultrasonic testing and eddy current testing.

Rhythm Acquire takes pixel information from computed radiography sources, digital radiography sources, or from film digitizers. These data are converted into a DICONDE file and can be displayed on the monitor of a standard PC.

Rhythm Reporting offers standardized reporting with DICONDE-tagged images. The software allows fast historical comparison and meaningful comparison of reports from different inspectors. Reporting is achieved in just a few clicks of a mouse, which can provide inspection time savings of up to 70 percent. The tagging of inspection images ensures that they correlate precisely to specific assets and also allows ease of any subsequent database searching. Inspectors can add their own notes to images within reports, either by entering information into a laptop while saving the image at the time of inspection or by saving a number of images for entry at a later date. CAD drawings can also be imported to assist in inspection site identification and to aid image interpretation.

Once an image is acquired, it can be sent to Rhythm Review for in-depth data analysis and data management. Data analysis is provided by a wide range of application tools, designed to increase inspection efficiency. These include:

A wall-thickness measurement tool offers two methods of accurately establishing wall thickness. First, it can use a computed tomographic simulation to calculate the position of the inner and outer edge of the pipe. A highly accurate, proprietary algorithm eliminates guesswork and inconsistency between operators. Second, it can use penetrating radiation, where an intensity reference, such as a local reference body or the nominal thickness of the double pipe wall, is taken in the image.

An area measurement and calculation tool allows users to select an area around a porosity indication and automatically calculate the loss of material or the two-dimensional size of the defect.

A defect and material loss tool allows users to measure material loss in the radiographic beam direction. This is similar to wall-thickness penetration measurement but shows material loss instead.

A reference radiograph comparison tool allows comparison with reference radiographs, such as the ASTM radiographs for A1 castings. The radiographs are loaded side-by-side, and the images can be locked together at the same display level so that all image enhancements are synchronized to both displays.

 

Images can be shared between networked workstations, so that inspection data can be sent to remote quality control locations for expert assessment. Unlike many Internet-based solutions, there is no limit to the file size that can be transmitted over a network. In addition, images can be stored on hard disc or to CD/DVD.

For users who generate large volumes of inspection data that need to be safely stored over long periods, there is software specifically designed for archiving large images. Review Archive, for instance, can accept nearly 300 million images from any number of LAN-connected, remote workstations, and stores these using various compression techniques to save storage space without sacrificing image quality. Furthermore, the software not only stores the raw inspection data but also any enhanced images developed at a workstation. The archive software provides a foundation for inspection data management by storing images and data, and by allowing users to connect multiple inspectors around the globe, who can send images to one central archive. This archive can be accessed by multiple review stations for analysis, or provide query functionality to improve inspection planning or asset management.

Aircraft inspection is a key NDT application and one of many applications where this type of software saves money and time. Aircraft inspections are carried out for a number of reasons, ranging from the detection of cracks and corrosion to the location of foreign objects within aircraft systems and components. Radiography is often the only inspection technique that can be applied for certain examinations, although eddy current and ultrasonic inspection are also used where relevant.

Whatever the technique, these inspections generate large amounts of data, much of which needs to be archived to allow traceability. This is as important in the military sector as it is in the civil sector, which is strictly controlled by regulation and legislation.

With the latest DICONDE-based inspection software, inspection data are acquired by a workstation, where they are reviewed and a report generated, detailing the current status of the inspected area, including any inspection notes relating to anticipated, future remedial work. The DICONDE file is then transferred to archiving software so that records are maintained to aid in traceability and to assist in future inspection programs.

Conclusion
For many years, imaging applications have been proprietary, in that they have been built around a specific X-ray solution and focused only on image analysis. There has never been a good way to share rich inspection data and automate archiving. With today’s new breed of inspection management software, there’s a platform to manage the entire inspection process and unlock the value of digital inspection data.

About the author
Andrea Koetz currently serves as business manager for GE Inspection Technologies’ Software Solutions group. Prior to this role, she was product manager for Small Systems. Koetz joined GE Aviation in 2000 on the operations management leadership program and has held various operations and business-development roles. She received a bachelor’s degree in engineering from the University of Florida and holds an MBA from Ohio State University.