Total Hemispherical Emissivity of SS 316L with Simulated Very High Temperature Reactor Surface Conditions

Type 316L stainless steel (SS 316L) is a candidate material for the reactor core barrel and selected internal components for high (and very high) temperature gas reactors. An apparatus constructed in accordance with the standard ASTM C835-06 was used for measuring total hemispherical emissivity of this material for the following surface conditions: (1) “as-received” from the manufacturer, (2) sandblasted with alumina beads, (3) sandblasted and coated with IG-11 nuclear-grade graphite powder, and (4) oxidized in air at 973 K for different durations. The emissivity of the as-received samples increased from 0.25 at 436 K to 0.36 at 1166 K. Sandblasting with 60-grit–sized alumina beads increased the emissivity from 0.32 to 0.44 in the temperature range from 561 to 1095 K. The emissivity continued to increase with sandblasting with 120- and 220-grit alumina beads, despite decrease in surface area associated with the more finely sized alumina beads. The coating of IG-11 graphite powder further increased the emissivity of the sandblasted surfaces. Following a similar trend, the IG-11–coated surfaces sandblasted by 120- and 220-grit alumina had an emissivity from 0.42 at 540 K to 0.57 at 1075 K. Electron micrographs showed more deposition of IG-11 powder on the 120- and 220-grit sandblasted surfaces. Oxidation in air at 973 K for 5 min also increased the emissivity of SS 316 L. Oxidations for 10 and 15 min provided an additional increase, but it was not as significant. Analysis indicates that spallation of oxide layer occurred between 10 and 15 min oxidation. This is consistent with studies on the time variation of total normal emissivity of SS 316L for oxidation at similar temperature.