Table of Content
- What is Digital Radiography?
- Technical Advantages of Digital Radiography
- Performance Metrics in Digital Radiography
- Digital Radiography in Ongoing Aerospace Maintenance
- DR in the Service of the US Air Force
- Comparative Analysis – DR v/s Film X-Ray
- Advancements in DR in Aerospace
- Key Takeaways
- FAQs
Aerospace is an industry that has experienced great growth in recent decades. Non-Destructive Testing in aerospace has a special driver of its own due to the high levels of human traffic involved; the crash of a civil or military airliner can cause loss of life reaching catastrophic proportions.
Therefore, strict NDT specifications have been set to detect minute cracks and defects in engine turbo discs, blades, and airframe structures in production and ongoing maintenance.
What is Digital Radiography?
Radiography is a technique that involves the use of X-rays to create images of the internal composition of components, allowing for the detection of defects or deformities without damaging the object. Digital Radiography (DR) is a modern iteration of traditional radiography, employing digital detectors instead of photographic film to capture X-ray images. These digital detectors convert X-ray radiation into electronic signals, which are then processed and displayed on a computer monitor.
By utilising digital detectors, DR enables immediate capture and analysis of internal component structures. DR allows thorough inspection, revealing imperfections like misaligned parts, welding defects, and contaminants such as dirt. DR can also uncover structural flaws like impurities, pores, and voids within components. It's capable of detecting cracks invisible to the naked eye, offering proactive identification of potential issues before component installation.
Technical Advantages of Digital Radiography
The Aerospace Industry prioritises precision and accuracy to ensure safety and durability. Producing components through investment casting is common for systems such as interiors, landing gear, braking, cargo, and hydraulic fluids, necessitating rigorous testing.
Digital Radiography ensures these aerospace parts meet the highest standards of safety and precision. While investment casting is effective for complex components, it can introduce defects due to various factors affecting mould quality and process.
The Technical Advantages of Digital Radiography include:
Image Quality and Precision
The use of Digital Detector Arrays (DDAs) significantly enhances the Probability of Detection (POD) of defects.
- Modern digital detectors provide high-resolution images with pixel sizes ranging from 25 to 200 µm, allowing for detailed inspections of critical aircraft components.
- This level of detail is crucial for identifying small cracks and other defects that could compromise the safety and integrity of aircraft structures.
- Additionally, DR provides immediate imaging results, enabling real-time analysis and quicker decision-making processes.
Portability and Environmental Impact
Unlike traditional film-based radiography, digital systems are compact and lightweight, facilitating easy transportation and deployment in various inspection scenarios, including remote or difficult-to-access areas of aircraft.
- This portability is particularly advantageous for maintenance operations that require flexibility and rapid response.
- Traditional X-ray inspection methods in aerospace involve chemical processing for film development, which generates hazardous waste.
- DR eliminates the need for these chemicals, significantly reducing the environmental footprint of radiographic inspection processes.
- This also simplifies the overall workflow, as there is no need for chemical handling and disposal.
Cost Efficiency and Time Savings
The immediate availability of digital images leads to quicker diagnostics and shorter downtime for aircraft, which is crucial in maintaining operational schedules and reducing costs associated with prolonged aircraft grounding.
DR enables businesses to detect sub-surface defects in aerospace metals, providing a reliable non-destructive testing method. Digital radiography offers significant benefits over traditional film processing, including shorter exposure times and eliminating the need for a darkroom.
Performance Metrics in Digital Radiography
By leveraging advanced digital imaging technology, digital radiography enables the detection of defects and abnormalities that may compromise the integrity of aircraft structures. To assess the performance of digital radiography systems effectively, several key metrics are considered, each contributing to the overall quality of radiographic images.
These Key Metrics include:
Spatial Resolution (SRb):
- Spatial resolution is vital for evaluating the performance of digital radiography.
- Digital detectors (DDA) and scintillators play a key role in determining resolution.
- Resolution is measured using a double-wire Image Quality Indicator (IQI), assessing the smallest discernible details in an image.
Contrast Noise Ratio (CNR):
- CNR is measured using single wire or hole type IQI.
- It is crucial for achieving high-contrast images, allowing for better detection of defects.
Signal to Noise Ratio (SNR):
- SNR is significant for producing clear images in digital radiography.
- It is calculated by dividing the mean grey value by the standard deviation in a defined range.
- Increasing image integration improves SNR, enhancing the visibility of defects in aerospace radiographs.
Digital Radiography in Ongoing Aerospace Maintenance
Digital Radiography (DR) has existed in various forms (for example, CCD and amorphous Silicon imagers) in the security X-ray inspection field for over 20 years and is rapidly replacing the use of film for inspection X-rays in the Security and NDT fields.
DR has opened a window of opportunity for the aerospace NDT industry due to several key advantages including excellent image quality, high POD, portability, environmental friendliness, and immediate imaging.
Israel Aircraft Industries (IAI) NDT lab provides NDT services for both production and maintenance of aircraft.
- It uses a digital flat imager in a wide range of maintenance applications: In one case, a nitrogen pressure tank was malfunctioning and exploding during pressure testing.
- Eight shots of each tank using an Image Intensifier with a flat-panel, portable DR system revealed tiny cracks 0.05 mm wide and 0.4 mm long in the weld.
- An attempt was made to use film X-ray but without any success until the DR system was introduced.
A table put together by Mr. David Belo, (see above) IAI Radiography Level III Expert at the recent ISR ASNT Section, compares the advantages of DR X-ray as compared to film X-ray. The numbers speak for themselves; significant savings of time and money (annual savings of over $64,000 for a scope of 7,250 images) have been achieved.
The US Air Force (USAF) primarily requires NDT inspection for ongoing maintenance purposes, to inspect different parts of its aircraft for fatigue, corrosion, and aging (including wing sections, rotors, and more).
- In 2000, the USAF carried out a study comparing DR to film X-ray methods.
- Since deployment for NDT inspection purposes involves moving vast equipment and aircraft, the USAF sought a cost-effective and compact mechanism to perform its NDT maintenance inspections.
DR in the Service of the US Air Force
The US Air Force (USAF) primarily requires NDT inspection for ongoing maintenance purposes, to inspect different parts of its aircraft for fatigue, corrosion, and ageing (including wing sections, rotors and more). In 2000, the USAF conducted a study comparing DR to film X-ray methods.
Because deployment for NDT inspections involves moving a vast amount of equipment and aircraft, the USAF sought a cost-effective and compact mechanism to perform its NDT maintenance inspections.
- It was discovered that flat panel, battery-operated digital X-ray systems were cheaper and faster, with a much smaller footprint (space required for shipping) than traditional film equipment (a 65% to 97% reduction).
- DR flat-panel-based X-ray systems required only 84 minutes for deployment, while film-based X-ray equipment required several hours.
- Thus, DR featured 43% savings as compared to the film-based technology in the same amount of time required to perform the inspection.
- Even more important was that DR-based NDT inspections offered a unique battery-operated, portable solution at unparalleled lower prices.
- According to the USAF, cost assessment showed that economically the Air Force could realize a return on its investment in only 3 months.
- The conclusion was quite clear – DR meets the needs of Expeditionary Air Force (EAF) technical orders.
These advantages can be observed in practical terms when considering another maintenance case:
The rear rotor of an Apache broke off as the aircraft was taxiing on the runway before take-off. According to the procedure, the entire Apache fleet was grounded until each aircraft underwent NDT inspection.
- Due to the use of a portable DR X-ray system, the entire inspection was conducted in 2 days.
- If a film-based system had been used for this purpose, the process would have taken at least a week or more.
This grounding procedure also applies when a civil aircraft malfunctions.
Here, too, a portable DR system can save many man-hours of inspection work, thus reducing economic consequences for the airline while ensuring top-rate inspection and preserving ultimate human safety without any compromise.
Read More - The Importance of Radiographic Testing in the Aerospace Industry
Comparative Analysis – DR v/s Film X-Ray
Digital radiography (DR) and traditional film X-rays are both used in aerospace industries for NDT and radiographic inspection of aircraft components. However, there are some key changes. The differences between the two methods are as follows:
DR v/s Film X-Ray
Performance Metrics
- Detection Capability - DR offers higher resolution and better image quality, enhancing defect detection in aerospace components.
- Deployment Time - DR systems have faster deployment times, providing immediate imaging results and reducing inspection times.
- Operational Costs - While the initial investment for DR may be higher, long-term operational costs are lower due to the elimination of film processing chemicals and reduced maintenance requirements.
Cost-Benefit Analysis
- Long-Term Financial Benefits - Adopting DR in aerospace radiography results in significant cost savings over time, including reduced chemical costs and maintenance expenses, as well as increased productivity and decreased aircraft downtime.
Advancements in DR in Aerospace
Recent years have witnessed notable enhancements in DR, including the introduction of innovative products such as CR scanners, phosphor imaging plates, and sophisticated software applications. These advancements enable higher levels of precision and efficiency in radiographic inspection processes of aerospace components, ensuring their safety and reliability.
With the availability of cylinder or flat panel type scanners and software offering a wide range of capabilities from 14-bit logarithmic to 16-bit linear, the versatility and performance of DR systems continue to improve. Additionally, advancements in minimum pixel sizes ranging from 12.5μ to 100μ and scanning resolutions as low as 12.5μ promise unparalleled detail and accuracy in defect detection.
Key Takeaways
- Digital radiography (DR) revolutionises non-destructive testing (NDT) in aerospace by offering high-resolution imaging, immediate analysis, and proactive defect detection, ensuring heightened safety and precision in critical components.
- The adoption of DR results in substantial cost savings and improved operational efficiency in aerospace maintenance. Its portability, environmental friendliness, and quicker diagnostics reduce downtime and associated costs, making it a cost-effective solution in the long run.
- Recent advancements in DR technology, including CR scanners, phosphor imaging plates, and sophisticated software applications, continually improve the performance and efficiency of radiographic inspection processes, promising unparalleled detail and accuracy in defect detection.
FAQs
1. Is Digital Radiography (DR) more environmentally friendly compared to traditional film-based radiography?
A: Yes, DR eliminates the need for hazardous chemicals used in film processing, significantly reducing the environmental footprint of radiographic inspection processes in aerospace industries.
2. What are the key performance metrics used to evaluate digital radiography systems?
A: The key performance metrics in digital radiography include spatial resolution (SRb), contrast noise ratio (CNR), and signal-to-noise ratio (SNR). These metrics assess image quality, contrast, and clarity, crucial for defect detection in aerospace components.
References
- Daniel MITCHARD, T. L. (n.d.). Advances in Digital Radiography.
- FujiFilm. (n.d.). How Does CR/DDA Assist the Aerospace Industry?
- Imaging, A. (n.d.). CT AND X-RAY INSPECTION FOR AEROSPACE APPLICATIONS.
- Imaging, N. S. (n.d.). Aerospace Suppliers Entering the World of Digital Radiography.
- Schulenburg, L. (n.d.). Digital Radiography in Aerospace.
- Systema, V. P. (n.d.). Aircraft Industries using NDT Inspection.
- Topias Tyystjärvi, I. V. (n.d.). Automated defect detection in digital radiography of aerospace welds using deep learning
