One of 14 vertical radiant tubes (RA 333 alloy) in a heat-treating furnace failed when a hole about 5 x 12.5 cm (2 x 5 in.) corroded completely through the tube wall. The tube measured 183 cm (72 in.) in length and 8.9 cm (3 in.) in OD and had a wall thickness of about 3 mm (0.120 in.). Failure occurred where the tube passed through the refractory hearth (floor) of the furnace. Although the furnace atmosphere was neutral with respect to the work, it had a carburizing potential relative to the radiant tubes. Analysis (visual inspection, 250x spectroscopic...