Nondestructive testing of brazed graphite/molybdenum joints by radiographic examination

Brazed molybdenum/graphite joints are frequently adopted for plasma facing components in fusion experiments. In particular, the RFX (Reversed Field Pinch Experiment) first wall tiles are fastened onto the vacuum vessel by molybdenum retaining keys having a graphite cap brazed onto the top. The possibility of testing graphite-molybdenum brazed joints by means of radiographic examination has been demonstrated by means of a comparison with the results of destructive methods (metallographies and mechanical tests). The good correlation that was obtained among the three different methods allowed the adoption of this test procedure for the final quality control of approximately 3000 brazed pieces to be exposed to the plasma in the RFX experiment; the tests proceeded very quickly and 100% of the pieces were accepted. The installation of the tiles with their clamps inside the vacuum vessel was then accomplished in four weeks without any major difficulty