Digital radiography and Computed radiography for Enhancing the Quality and Productivity of Weldments in Boiler components

This paper presents a detailed performance anal ysis and comparison of Conventional film radiography, Real Time Radioscopy with Digital Radiography (DR) using Flat Panel and Computed Radiography (CR) using Flexible Phosphor Imaging Plates, in the case of Quality evaluation of weldments in Boiler Components. Conventional Film Radiography is a slow, expensive and hazardous method, particularly for mass pr oduction. Eventhough Real Time Radioscopy (RTR) with Image Intensifiers is an altern ative to film radiography, conventional RTR systems are compared unfavorably with film radiography in two aspects viz.low contrast sensitivity and limited resolution. The new digital detector arrays (Flat Pan el Detector) have the potential to substitute the X-Ray films as they have considerably higher image qualit y than the conventional Image Intensifiers. They allow fast acquisition of radiography images with high dynamic range, and high signal to noise ratio. Computed Radiography is one of the Digital Rad iographic Techniques used in lieu of conventional film radiography. The Phosphor Imaging plates (IP) are used as digital detectors in place of photographic X-Ray films. The experimental results revealed that D R can successfully replace Real Time Radioscopy with X-Rays and Image Intensifier, for Tubular Steel welds up to Single wall thickness 12mm. Using the Flat Panels with 200 microns pixe l pitch, it was possible to achieve more than 3 line pairs / mm, at an MTF of over 20%. On the other hand CR has been found to be suitable for Radiography of thick wall welds (Steel thickne ss up to 140 mm) in Boiler components using Gamma Ray Isotopic Sources like Ir-192, Co-60 and X-Ray sources including Linear Accelerators (up to 6 MeV) with spatial resolution better than 25mico meter, meeting the 2 % Radiographic sensitivity requirements as per ASME code.