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DIGITAL COMPUTED RADIOGRAPHYComputed radiography (CR) uses phosphor-imaging plates instead of film to store radiographic inspection results. The plates are exposed as per standard radiographic testing, but the images are laser scanned from the plates into a computer system. Using powerful software one can then analyze, manipulate, print and store the images for future review. The remaining wall thickness can then be determined for corrosion evaluations and ASME code radiograph interpretations. ASME Code Case 2476 now allows the use of CR for all ASME work.
Fuji DynamIX Scanner
CR image
Computed radiography can be performed on the same materials and in the same situations as standard radiography.
The use of CR results in a reduction of exposure times from 50 to 70% when using Ir 192. Similar, or better, results are obtained when utilizing Se 75, Co 60 and X-rays. CR is well suited for low curie strength sources or SCAR (Small Contained Area Radiography) devices that require less area to be roped off. The much greater dynamic range of the imaging plates practically eliminates re-shots by providing a much greater range over which exposures can be practically done.
CR is performed in the same manner as standard radiography. A qualified radiography technician requires minimal training when implementing CR field applications. However, unlike standard radiographic testing, the CR film does not require development chemicals and water.
CR has some of the same requirements and limitations as standard radiography. Images obtained by CR show discontinuities in two dimensions only, and require access to both sides of the subject material.
The component thickness limitations are the same as for standard radiography. The practical limit for carbon steel gamma radiography is approximately 2.5" for Iridium 192 and 9" for Cobalt 60. With x-rays, the x-ray generator energy determines the maximum thickness penetrated.
Radiation safety considerations are as fundamental for CR as they are for standard radiography. Large areas adjacent to the component tested must be cleared from persons or items that may be affected by radiation.
Two limitations must be considered when using CR:
- The equipment reading station is required to scan the imaging plates. Consequently, physical space and on-site electrical power are required to set-up the equipment. In some projects, the imaging plates can be transported from the job site to the reading station, but this is not often the case.
- Some additional costs may be associated with using CR.
IRISNDT uses Fuji DynamIX software to report CR data; the software allows detailed image analyses. The data is then burned to a CD or DVD with the Fuji Image Share software; this allows the customer to view the CR images and perform some image manipulation. Bulky film is replaced with DVD's or CD's that store many images per disc. Test results are interpreted in accordance with relevant specifications or customer requirements. DVD's or CD's are given to the customer with findings/ comments on the actual images. A second report detailing complete inspection results is also submitted.
