By Sean Gleeson on Wednesday, April 6th, 2011
Almost any time you weld two pieces of metal together using a code or specification, you will almost always be requires to do some sort of non-destructive test on the weld. One of the oldest and most reliable methods is the use of radiography to provide a volumetric view of the weld area. The traditional approach to capturing an image using radiography requires an X-ray tube, film and a dark room. This procedure works remarkably well but has its drawbacks like:
· Many safety precautions for the use of high intensity radiation
· Many hours of technician training prior to use
· Access to both sides of sample required
· Orientation of equipment and flaw can be critical
· Determining flaw depth is impossible without additional angled exposures
· Expensive initial equipment cost
At EWI, we solve many of these problems by using a technique called as Computed Radiography.
Computed Radiography (CR) uses most of the same equipment as conventional radiography but images can be obtained at lower radiation levels and with shorter exposure times. We generate x-rays using a NDI-320-23 X-ray tube (stationary) manufactured by Varian Medical Systems that has the power to penetrate approximately 2.5″ of carbon steel or 1 7/8″ of stainless steel. Once the CR plates are exposed, a Kodak 2000i CR System is used to process our digital images.
The difference between traditional and Computed Radiography is in the film and development process. Computed Radiography CR uses a cassette that houses the imaging plate, similar to traditional film-screen systems. This imaging plate (IP) contains photostimulable storage phosphors, which store the radiation level received at each point in local electron energies. The image is digitized using the Kodak ACR-2000i (CR System) system and then can be printed, enhanced, e-mailed used in a presentation or and number of processes that digital technology allows. The images are erased by simply exposing the imaging plate to room-level fluorescent light, greatly reducing the costs associated with developing film.
In addition to our CR capabilities, we also offer high resolution film scanning utilizing the Kodak LUMISCAN Desk Top Scanner (LSDT). This is a single sheet laser film digitizers designed to digitize x-ray film and measure diffuse optical density. Scanning is achieved with a high intensity spot of light derived from a Helium Neon (HeNe) laser that is scanned across the film plane as the film is moved perpendicular to the beam scan. We use this system to digitize radiographs so that they can be transmitted, archived, or presented.
In industry, CR has attempted to replace film for several years. The generally accepted comparison between CR and traditional film is that CR is good but film is still more sensitive. That being said, there are codes that have been established in the United States that accept CR as an acceptable method for inspection of welds (BS EN 14784, ASME Boiler and Pressure Code Article V Appendix VIII and ASME Code Case 2476: Radiography using phosphor imaging plates).
Computed Radiography…………. gota love it