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Simple and Novel Solutions to Countering Uneven Density Variations in Microfocal Radiographs

The tube to tube sheet (TTS) welds of steam generator of Fast Breeder Reactor is the most critical joint. This is because, sodium flows on shell side and water on tube side. Any failure would thus be catastrophic. Microfocal radiography is an established technique that is being used for the evaluation of such welds. Using microfocal radiography pores of the order of 25 microns could be detected. Microfocal radiography of TTS joints is primarily accomplished using a backward throw rod anode. Such an arrangement however is beset with its own problems. The angled beam results in uneven beam intensity across the weld. During actual weld radiography, the trailing edge of the beam where intensity is minimum, traverses a longer distance than the leading edge which compounds the problem of density variation. This results in uneven radiographic density and contrast. It is a well-known fact that sensitivity achievable in radiography is a function of radiographic contrast and definition. Radiographic contrast in turn is affected by subject and film contrast. Uneven radiographic contrasts make interpretation complex and sometimes result in unacceptable density variations. To overcome this problem, the authors devised a novel solution. Using appropriately designed and fabricated filters and image processing techniques, authors have successfully developed procedures for ensuring uniformity in radiographic density. This has also resulted in improved effective sensitivity. A 32 /25 micron wire could be clearly resolved through a wall thickness of 2.3 mm. More than 600 welds have been examined successfully. This paper dwells on the criticality of the problem and the solutions that have been successfully developed and applied in the shop floor.