PREPRODUCTION INITIATIVE-NELP DIGITAL RADIOGRAPHIC SYSTEM (NONDESTRUCTIVE INSPECTION APPLICATION) FINAL REPORT NAS JRB FORT WORTH, TX

Transcription

1 PREPRODUCTION INITIATIVE-NELP DIGITAL RADIOGRAPHIC SYSTEM (NONDESTRUCTIVE INSPECTION APPLICATION) FINAL REPORT 1.0 INTRODUCTION NAS JRB FORT WORTH, TX The U.S. Navy has adopted a proactive and progressive position toward protecting the environment and complying with environmental laws and regulations. Rather than merely controlling and treating hazardous waste by end-of-the-pipe measures, the Navy has instituted a program for pollution prevention (P2) to reduce or eliminate the volume and toxicity of waste, air emissions, and effluent discharges. P2 allows the Navy to meet or exceed current and future regulatory mandates and to achieve Navy-established goals for reducing hazardous waste generation and toxic chemical usage. P2 measures are implemented in a manner that maintains or enhances Navy readiness. Additional benefits include increased operational efficiency, reduced costs, and increased worker safety. The Navy has truly set the standard for the procurement and implementation of P2 equipment. The Chief of Naval Operations (CNO), Environmental Protection, Safety, and Occupational Health Division (N45), established the P2 Equipment Program (PPEP), through which both the Naval Air Warfare Center Lakehurst (NAWCADLKE) and the Naval Facilities Engineering Service Center (NFESC) serve as procurement agents under the direction of N45. P2 equipment is specified and procured under two complementary initiatives: the Preproduction Initiative (i.e., technology demonstration) and the Competitive Procurement Initiative. The Preproduction Initiative directly supports both the Navy Environmental Leadership Program (NELP) for P2 shore applications and the P2 Afloat program, which prototypes and procures P2 equipment specific to the needs of ships. This report provides an analysis of the procurement, installation, and operation of P2 equipment under the Preproduction Initiative. Technology demonstrations and evaluations are primarily performed under NELP at two designated NELP sites Naval Air Station (NAS) North Island and Naval Station (NS) Mayport. Additional sites, including Naval Air Station Joint Reserve Base (NAS JRB) Fort Worth, have been added as required to meet specific mission goals. The program involves defining requirements, performing site surveys, procuring and installing equipment, training operators, and collecting data during an operational test period. The equipment is assessed for environmental benefits, labor and cost savings, and ability to interface with site operations.

2 2.0 BACKGROUND 2.1 Nondestructive Inspection at NAS JRB Fort Worth, TX The nondestructive inspection (NDI) technicians at the Aircraft Intermediate Maintenance Department (AIMD) Laboratory at NAS JRB Fort Worth are responsible for the radiographic examination of aircraft components and support equipment (SE) at the intermediate I level. The technicians use NDI techniques to examine various aircraft components and SE that have sustained damage due to accidents, catastrophic failure, and normal wear. Approximately 10% of these inspections are performed as part of unscheduled maintenance, while the rest are performed during regularly scheduled maintenance activities. NDI examination of aircraft components is used to inspect for foreign object damage (FOD), corrosion, and moisture entrapment. NDI technicians also inspect for cracks, discontinuity defects, and internal part positioning. The NAS JRB Fort Worth AIMD originally used an Agfa D4 auto film processor to perform conventional radiography (x-ray film) examinations of aircraft components and SE. Because the facility performs AIMD level NDI inspections on a daily basis, NAS JRB Fort Worth was selected as the digital radiography NDI prototype site. Site personnel analyze a substantial number of aircraft components and pieces of SE using conventional radiography. The quality of the x-ray images is sufficient for the site s requirements, but the conventional radiography process uses hazardous materials, including developers and fixers. These chemicals, together with the hazardous waste that results from their use, require proper handling, storage, and disposal by NAS JRB Fort Worth AIMD and Environmental Hazmat personnel. A digital radiography system was recommended for evaluation in an effort to eliminate hazardous waste generation, reduce hazardous material usage, provide a safer workplace, and minimize costs related to the NDI application. For any radiographic system to be effective in NDI operations, it must be able to produce high-quality images with sufficient contrast and resolution. One standard for measuring image quality is the 2T rating (short for 2-2T). In this rating, the first 2 refers to contrast, the second 2 refers to detail, and the T stands for thickness. The rating is used throughout the military and commercial nondestructive testing (NDT) communities as a standard measure of radiographic image quality. To determine a system s rating, a steel test plaque is placed in a non-vital portion of the area being x-rayed. On the plaque are three holes with diameters equal to one, two, and four percent of the thickness of the object being x-rayed. If the image of a test plaque with a thickness equal to 2% of the total thickness of the object being examined can be seen, then the system receives a 2 rating for contrast. If it is possible to resolve the 2% hole on the aforementioned test plaque, the system is rated 2 for detail. The Navy was seeking a technology that would realize 2T resolution.

3 2.2 Digital Radiography Technology Description This prototype study explored the applicability of digital radiography to Navy NDI applications. Digital radiography was first implemented commercially in hospitals during the early 1980s. Since then, advances in microprocessing performance have progressively allowed the design and construction of smaller and more efficient systems. When digital radiography is used to view an object, the variations in the object s features and density are mapped onto phosphor-coated plates based on differences in radiation absorption. The different features and densities of the object being inspected permit different amounts of radiation to pass through to the phosphor plate. The radiation that reaches the plate excites the electrons in the phosphor layer in a way that is somewhat analogous to light activating the silver halide grains in conventional film, with the number of excited electrons in proportion to the amount of radiation that reaches the plate. As a result of the electron excitation, a temporary latent image is stored on the phosphor plates. To read the image, the exposed plate is scanned with a laser. The light from the laser reveals the latent image by causing the phosphor layer to luminesce, with the intensity of the luminescence proportional to the number of electrons that were excited by the original radiation exposure. The emitted light is then captured by a light sensor and converted into a digital image that is displayed on a computer workstation. From this workstation, the image can be transferred and thermally printed onto digital radiography film. Digital radiography film is similar to conventional x-ray film in size, appearance, and its ability to be viewed through backlighting; however, it contains no silver. The manufacturer has stated that once an image is read and digitized, the phosphor plate can be erased and reused more than 5,000 times. The erasure process is accomplished by exposing the plate to radiation (e.g., bright light, infrared light). While this removes the latent image from the plate, it has previously been found that the process does leave a fog on the plate that can affect subsequent image quality. To minimize the effects of this fog, various combinations of radiation sources have been tried in the erasure process. Two that have been used with a measure of success in the past are bright white light and a combination of sodium vapor light followed by infrared light. One of the key advantages of digital radiography is that it allows the electronic storage, retrieval, enhancement, and transfer of images. During scanning/reading of an image plate, a digital file is created. This digital file, containing the originally scanned image, is write-protected by the system and cannot be altered. The file is then transferred and archived on an optical disk or it can be reviewed on a computer workstation. Once displayed, the image can be manipulated (e.g., changes to gray scale, contrast, density, etc.), but the digital file containing the originally scanned image will remain unaltered. Files can be electronically transferred, thus enabling multiple personnel to view and access the image file. Also, because phosphor image plates can record more information than film, greater in-depth analysis and manipulation of an image can be performed from a single shot; conventional radiography sometimes requires multiple shots to be taken of the same object. Consumables are minimized because the image plate can be used

4 numerous times and can bend to the shape of the object. Furthermore, because the system replaces conventional film, the hazardous materials and hazardous waste associated with film development are eliminated. Finally, worker exposure to x-rays is decreased since fewer shots are required and each shot uses lower radiation levels than conventional radiography. 3.0 EQUIPMENT DESCRIPTION 3.1 Vendor Selection During the digital radiography prototype test period for inspecting ordnance material at NSWC Indian Head, Maryland, it was determined that Fuji s digital radiography system could be applied to NDI applications. An agreement was subsequently established with Fuji to lease a digital radiography system for a 6-month test period at NAS JRB Fort Worth. The selection of the Fuji system was based primarily on its past performance (the ordnance application), high throughput, and ability to meet the 2T image quality requirements. In addition to the Fuji equipment lease, a separate agreement was established with Virtual Media Integration (VMI) to lease its storage transmission and remote reproduction system for 5 months. While the Fuji system is used to capture and print the original digital radiography image, the VMI system aids with managing and archiving image files, provides image analysis and enhancement tools, and allows electronic image transmission. Originally, the digital radiography NDI application prototype test period was to be divided between two bases (three months at NAS JRB Fort Worth, followed by 3 months at NAS North Island). However, during the first stage of the testing, NAS JRB Fort Worth provided a large amount of data using the Fuji system, and it was decided that relocating the equipment was unnecessary. It was decided that it would be more costeffective to have Navy officials from NAS North Island observe and critique the system s performance during a site visit to NAS JRB Fort Worth. The primary reasons for this decision were the elimination of training costs for NAS North Island personnel and equipment shipping costs. 3.2 Fuji Digital Radiography System and Virtual Media Integration The Fuji Digital Radiography System and the VMI equipment and software have been integrated to provide a system that allows the widespread use of digital radiography. Fuji hardware allows the digital imaging system to read the images from exposed phosphor imaging plates and display the images on a computer workstation. VMI software allows the images from the Fuji system to be enhanced, stored, and transmitted electronically. NAS JRB Fort Worth was provided with the following components for this study:

5 Fuji Digital Radiography System AC-3 image plate reader/erasure unit Image plates and cassettes Fuji HI-C654 workstation to display imagery; the unit has hard-copy and system image storage capabilities when used with VMI STARR software Laser printer. Virtual Media Integration VMI workstation and high resolution monitor STARR software program, which enhances the digital images and can be used to download, manipulate, and electronically transmit Fuji image files Fuji Digital Radiography AC-3 Image Plate Reader/Erasure Unit The AC-3 Image Plate Reader/Erasure Unit is the main component of Fuji s hardware system. The AC-3 scans the captured images from the exposed phosphor plates into the system before erasing the plates by exposing them to a very bright white light. The AC-3 also includes a data entry terminal that enables inspection personnel to select various read routines. Digital enhancements are applied to the image data as it is being extracted and compiled. Data specific to the particular piece of equipment being x-rayed is input into the AC-3 system via one of the included data entry devices (programmable menu drive, manual keyboard, and/or magnetic card reader). When using the programmable menu drive, for instance, the technician can input information that is pertinent to a particular x-ray (date, name of part, and description of the type of inspection performed) to a series of data entry fields. This information can then be used to recall current and previous x-rays and transferred to a file stored in the HI-C654 (see Section 3.2.2). The information is also transferred to the Fuji laser printer where the image is printed out. The AC-3 can be used to correct for underexposed or overexposed phosphor plate images. This correction is done through the system s constant density control, which enables the user to display image files at preselected gray-scale levels, regardless of the exposure parameters used when the image was created. Other features and advantages of the AC-3 system include the following: Computer-processed image data produce workable images for inspection. Wide, dynamic range of the imaging plate provides images with high quality, resulting in fewer reshoots. System s high sensitivity allows a significant reduction in exposure time. Digitized image data allow electronic image transmission, manipulation, enhancement, and storage. Easy operation of the system yields greater image consistency and less potential for user error. Scan time of approximately 45 seconds. Ability to preprogram specific inspection parameters.

6 Ability to consistently provide a 4.0 line pairs per millimeter (lp/mm) or better resolution in all directions (horizontally and vertically) The Fuji Digital Radiography CRT Image Console HI-C654 and Laser Printer Fuji s HI-C654 Image Console displays images on a high resolution, 21-inch monitor and can provide additional image processing capabilities, if necessary. The HI-C654 has a proprietary operating system. The images can be displayed or printed individually or in groups of two, three or four to a screen. This allows faster inspection and side-by-side comparison of images. Hard copies of the images can be generated with the use of the system s laser printer. The HI-C654 workstation provides the following features and advantages: Displays high quality images on a high resolution CRT monitor. Automatically stores incoming images on built-in hard disk for quicker retrieval of individual images. Writes images to the hard disk without interrupting the processing of currently displayed data, allowing the user to manipulate images while the newest images are being transferred and stored. Allows images with tonal, magnification, and/or spatial frequency modifications to be sent to the system s laser printer to be printed as hard copies on digital radiography film. The Fuji digital radiography system s laser printer provides the following features and advantages: Uses a transparent recording media that is similar in appearance to conventional wet processed radiographs (x-ray film). Hard-copy printing technology uses no wet chemistry and does not produce hazardous waste. Laser copies are thermally processed with typical spatial resolution of 2K x 2K pixels/scene. User can select printing format (e.g., single or multiple images per hard copy) Virtual Media Integration The VMI software package, called STARR, has been integrated and is compatible with the Fuji system. It converts and compresses existing imaging files for electronic transmission, and makes the files compatible with most computers so the recipient can view the image file without special software. However, to view the image clearly after it has been sent electronically, a high quality monitor is recommended. The STARR software converts a 10-bit Fuji image to a TIFF or other 8-bit file format, thereby facilitating communications protocol and recordkeeping.

7 The STARR software includes the following features and advantages: STARR software eliminates the use of film and allows the image files to be accessed more readily and sent electronically to multiple personnel. Converting from the Fuji format to the STARR program increases accuracy, allows more images to be read, and reduces the time it takes to evaluate images. Image enhancement tools include: image threshold contrast/brightness stretching 90-degree image rotation image flip and mirror image crop image pan and scowl image zoom up to pixel resolution image annotation ability to display density values along a line at arbitrary angles ability to measure the distance between any two arbitrary chosen points, with the measured distance remaining unchanged during zoom or minimize ability to measure area as a function of density histogram masking high pass, low pass, and median filtration magnification and a floating magnification glass customizable image processing kernels of 3 x 3, 5 x 5, 7 x 7, 9 x 9 sizing, allowing for varied edge enhancement and other kernels positive/negative switching false color true optical density with varied backlighting colors densitometer functions density graphing and histogram functions within a region of interest. 3.3 Implementation Requirements and Specifications AC-3 Image Plate/Erasure Unit Operational specifications and requirements for the Fuji AC-3 unit include: Dimensions: 27-15/16 W x 26-13/16 D x 41-1/8 H Weight: 81.7 lb. Electrical: 110-V outlet AC 50/60Hz 1kVA Capable of processing 70 to 90 imaging plates per hour, depending on the size of the imaging plate Imaging Plates and Cassette Operational specifications for the Fuji digital radiography imaging plates include: Imaging plates are flexible and reusable.

8 Standard type imaging plates come in four standard sizes: 14 x 17, 14 x 14, 10 x 12, and 8 x 10. High image quality (HQ) plate available in 14 x 17 and 8 x 10 sizes. Approximately 50 seconds required to feed and load the image plate. Vinyl pouch that prevents surface scratching when the phosphor image plate is removed from its cassette VMI Workstation The VMI workstation uses a small computer systems interface (SCSI) bus to store data on a PC platform. The workstation subassemblies include: Pentium III 450 PC platform with 256 MB RAM, 15.1-GB hard drive, CD-RW (CD ROM burner), and a network card SCSI communications port for high data transfer rates 21 high resolution monitor with a 16-MB high resolution video card to power the monitor STARR software to enhance and digitally process images exported from digital radiography image files. 3.4 Benefits Technical Benefits The Fuji System and the VMI hardware/software provide several technical benefits compared to conventional radiography, including: Imaging plates have a wide dynamic range and a linear exposure response, which means that one exposure can cover a wide range of part thicknesses while maintaining target densities. Automatic density controls compensate for either overexposure or underexposure. Images are stored on optical disks to facilitate retrieval and review. Radiographic data stored on a disk is preserved for a long, usable life. Minimal archival storage space is required. Digital radiography expands the viewable density range by three to four times over conventional film. Images can be electronically transferred to remote viewing sites for instant consultation and analysis. Image analysis is improved by reducing interpreter subjectivity Environmental and Cost Benefits Using the Fuji System and the VMI hardware/software provides several environmental and cost benefits compared to conventional radiography, including the following:

9 Reduces the volume of hazardous waste and the cost of disposal. Eliminates costs associated with procuring conventional x-ray film. Provides a healthier work environment by reducing exposure to radiation since a smaller dose is required for plate exposure. Eliminates the use, storage, and disposal of the hazardous photographic chemicals associated with film processing. Eliminates the precleaning of conventional radiography equipment and the associated use of hazardous materials. Reduces labor hours required for NDI inspections. Expands the capabilities of NDI field personnel. Facilitates the electronic transfer of images from the field or between experts for consultation and analysis. Imaging plates can be reused, thereby eliminating the costs associated with conventional film. Eliminates labor and waste associated with reshooting multiple exposures by allowing the images to be manipulated electronically. 4.0 DATA ANALYSIS 4.1 Quantitative Analysis The digital radiography system described herein costs approximately $252,000 (including the VMI software) and has a projected useful life of approximately 20 years. Fuji has stated that an improved version of the current digital radiography system will be available in the near future for an estimated cost (including the VMI software) of approximately $192,000. The projected lifespan of the existing conventional system, when new, is 7 to 10 years, which means that while the existing system is currently in working order, it will most likely require replacement at least once before the end of the digital system s projected useful life. The shorter lifespan of the conventional system is largely due to the corrosive effects of the fixer used to develop exposed film. While the cost of a replacement conventional unit is approximately $20,000, this cost was not used in the 10- year return on investment (ROI) and break-even analyses because of uncertainty regarding the remaining usability of the existing unit. The annual operating costs of the digital radiography system are projected to be approximately one-sixth those of the conventional system ($8,994 versus $54,814). These cost reductions are largely due to the reduced labor and film costs associated with the digital system and the elimination of hazardous waste generated by the conventional system. Compared to the conventional radiography system, the Fuji/VMI digital radiography system that is currently available has a 10-year ROI of approximately $206,202 per unit, with a break-even point of 5.5 years. Recalculating these analyses with the projected price of the forthcoming version of the Fuji system, the 10-year ROI changes to $266,202, and the break-even point is 4.2 years. With conventional radiography, NAS JRB Fort Worth uses approximately 300 gallons of developer and fixer per year. NAS JRB Fort Worth Environmental personnel must handle

10 and dispose of approximately 240 gallons of these materials each year as hazardous waste. The digital radiography system uses no chemicals to process its x-rays and therefore generates no hazardous waste. Complete data on disposal amounts and costs are presented in the Cost Analysis for this project. 4.2 Qualitative Analysis Installation and Training Fuji System The Fuji system was easily installed at NAS JRB Fort Worth. Fuji representatives installed the AC-3 system, HI-C654 workstation, image plates and cassettes, and the printer, and gave a brief introduction to the technicians who would handle the equipment daily. During the training session, Fuji provided technicians and computed radiography specialists to properly train the Fort Worth NDI technicians in the use of the AC-3 digital radiography system. The training, which took approximately one day, encompassed how to use the image plates, program the AC-3 system, and use the HI-C654 workstation. Within that day, the Fort Worth technicians were able to familiarize themselves with the complex functions of the AC-3 system and HI-C654 workstation. The Fuji system was then incorporated into the technicians regular work schedule. VMI Workstation The installation and training sessions for the VMI workstation took place on a different date. VMI sent its director of digital radiography and the designer of the STARR software program to train the technicians. The workstation was installed and made compatible with the Fuji system. Installation and training took approximately one day. Training included taking x-ray images of aircraft parts, processing images through the Fuji system, sending images to the VMI system, and reviewing specific functions available on the workstation. The training was accomplished by working with x-ray images taken during Fuji s training session and sending images electronically. Throughout the training, explanations were provided on the proper procedures to manipulate images to see the various defects associated with aircraft parts. In addition, explanations of the software s advanced features were provided. After training, the VMI workstation was then incorporated into the technicians regular work schedule Maintainability Fuji System During the 6-month test period the Fuji unit experienced no problems with maintainability and did not require repairs. Standard upkeep consists of a basic preventive maintenance program. Fuji has a customer support program with a toll-free

11 number to call if any problems arise. Troubleshooting advice is given over the phone and, if repair is required, a Fuji technician would be dispatched. VMI Workstation The VMI software also had a maintenance-free record. No problems occurred while the system was onsite. Similar to Fuji, VMI offers troubleshooting advice over the phone, with a VMI technician dispatched if repair is needed Interface with Site Operations Site personnel readily and eagerly integrated the equipment into operating procedures. During initial testing of the unit, both conventional and digital radiography methods were used and the results compared. Eventually, the workers switched to digital radiography exclusively in the interest of saving time and because there was no longer a need for redundant testing. However, in the event that a user or part verification discrepancy involving a difficult aircraft component arose, conventional radiography was implemented and compared to the digital radiography output. The quality of the digital radiography images was judged to be better than or equal to conventional x-ray film images Overall Performance The Fuji and VMI equipment has performed very well. The Fuji system reached its maximum resolution potential of 2-2T. Fuji and Navy officials observed the system operations and results and verified this 2-2T resolution capability. The digital radiography process required less time during the developing and manipulation stages than the traditional wet chemistry process. The developing stage of digital radiography involves scanning the exposed image plate and downloading the image into the Fuji AC-3. During the manipulation stage, the original scanned image is saved on the hard drive of the computer and cannot be changed. This image can then be manipulated on the computer workstation until an acceptable picture appears on the screen. The overall time to prepare the unit, expose plates, and scan and manipulate images was reduced from 134 hours per month with conventional radiography to 33.5 hours per month with digital radiography (a 75% reduction in overall labor time). Digital radiography does not require chemicals when developing the image, while traditional wet chemistry images require hazardous chemicals for development. Complex objects sometimes required that multiple shots be taken using traditional wet chemistry, while with digital radiography only one exposure was needed. These advantages and the test results showed that the Fuji system s performance is superior to that of conventional x-ray methods.

12 5.0 LESSONS LEARNED During the test period at Fort Worth, it was noted that Fuji did not provide the highest resolution monitor currently available. This caused some resolution issues when the aircraft components and SE were viewed for defects and discontinuities. For a small percentage of the images, it was difficult to determine whether or not cracks were the observed lengths or continued further. Fuji does sell high-resolution monitors, and its system has a high-resolution setting that allows it to scan the image at a higher rate. With a skilled technician, a high-resolution monitor, and the processor set at a high resolution, NDI personnel believe that cracks and other problems associated with aircraft components and SE will be easily analyzed. It was also noted that images downloaded from the Fuji AC-3 system to the VMI system and then electronically transferred from the VMI system to another workstation could be difficult to interpret unless the recipient s workstation monitor has a sufficiently high resolution. It is necessary to ensure that a high quality monitor is used to view the originally stored image from the Fuji and VMI workstation. The Fuji laser printer is used for printing the images downloaded into the AC-3 system. Jeff Mason (Fort Worth technician) observed that the Fuji laser printer might not be needed. When an image is being viewed on the HI-C654 workstation, it also can be manipulated on the monitor, allowing the technician to view electronic copies of the x- rayed items. Therefore, by analyzing the electronic images on the monitor, one could reduce the number of hard copies printed on the laser printer. This would result in reduced costs associated with purchasing film for the laser printer, as well as reducing the purchase and upkeep costs of the digital radiography equipment. The phosphor image plates provided by Fuji are reusable and flexible. Two types of cassettes are used to hold the plates during the digital radiography process: a hard cassette and a soft cassette. The hard cassette is used for most applications. The flexible soft cassette can be used where part geometry necessitates wrapping the plate around the item to get the clearest image. During the test period, Fort Worth technicians used both types of cassettes. After scanning images into the AC-3 system from plates exposed using soft cassettes, technicians noted that while the produced images were clearly visible on the HI-C654 workstation, a slight distortion was apparent. Images from plates exposed using hard cassettes showed no distortion or changes in sensitivity or contrast. 6.0 CONCLUSIONS Compared to conventional radiography, digital radiography eliminates the generation of hazardous waste in this NDI application and saves time and money. In addition, the technology is superior to film for applications that require sensitivity to very small changes in subject contrast. This is especially true for instances where part thickness varies over a wide range. By providing a side-by-side comparison of conventional versus digital radiography, Fort Worth radiologists were able to compare data from the two methods and agree that the digital system provided high quality usable images. When the system was integrated into the daily routine at NAS JRB Fort Worth, it quickly gained

13 acceptance with NDI technicians, and the technicians felt it made radiography an easier process. Digital radiography is an excellent alternative to, or replacement for, conventional radiography. Its advantages, as outlined above, outweigh those of conventional x-ray procedures, but because of the payback period observed (greater than 3 years), it is recommended that high usage NDI labs be outfitted before those with less need for radiographic inspection.