Application of Computed Radiography in Pressure Vessel Welds: ASME Sec V Requirements and Recommendations of ASTM E2007

Computed radiography or CR has been used in the Radiography NDT industry for quite a long time. Use of CR in the pressure vessel welds has not been so popular or common industry practice, particularly in this region, may be because of cost and to some extent acceptance by the client. However ASME BPV Code has already approved use of CR and DR techniques in pressure vessel welds in place of film Radiography. The latest edition of ASME BPV Code Sec V has added some new requirements for qualification and certification of NDT personnel in Computed Radiography (ASME Sec V: 2015 Article I; Mandatory Appendix II). Typically, as we all know, CR or computed radiography uses a storage phosphor imaging plates, known as SPIP, which emits photo-stimulable luminescence in place of Silver Bromide coated films, that luminescence or light radiation is amplified by photomultiplier tubes and passes through A/D converter and several filters which produce an image on the suitable computer monitor. Most of the requirements of ASME Sec V for CR are similar to that of film radiography except in some cases as resolution, brightness and contrast in place of density and contrast used for film radiography. Although it requires expertise for processing the images, but the technique is very useful in replacing film radiography particularly in terms of chemical hazards and environmental issues of film processing, exposed film archiving and computer assisted image enhancement. But more than in traditional radiography, the use of digital images is a trade-off between the speed and the required quality. Better image quality is obtained by longer exposure times, slower phosphor screens and higher scan resolutions. Therefore, different kinds of storage phosphor screens are needed in order to cover every application. ASTM E2007 & E2033 provide excellent information and guidance of the process and application of computed radiography. Here in this presentation, we have described our understanding and experience of using computed radiography in lieu of film radiography for a pressure vessel meeting all the requirements of ASME Code.