Detection of wall thinning in tube to tubesheet welds of steam generator by microfocal radiography

Abstract

The tube to tube sheet (TTS) welds of steam generator of Prototype Fast Breeder Reactor (PFBR). This is because, sodium flows on shell side and water on tube side. Any failure would thus be catastrophic. The specifications for the evaluation of such welds are thus highly stringent. The maximum permissible value for internal concavity and convexity of TTS welds is 0.2 mm. It is easy to determine the external convexity and concavity due to availability of access by replica measurement. In the case of internal concavity and convexity, the technique of replica using dental compounds is quite difficult. Replication using silicon rubber compound and special hardware has been carried out by the authors. However, the cost of making one replica is more than Rs. 10,000 thus making this a highly unviable solution for shopfloor inspection of all joints. Earlier the authors have successfully developed procedures and adopted the same in shopfloor for the evaluation of these welds for defects by microfocal radiography. This paper presents the experimental results of procedure developed for quantitative evaluation of concavity in the tube to tubesheet welds by microfocal radiography.