Total Hemispherical Emissivity of Grade 91 Ferritic Alloy with Various Surface Conditions

For very-high-temperature reactors (VHTRs), the ability of structural components, specifically the reactor pressure vessel, to dissipate heat by radiation is an important design criterion. Thus, in selecting components for VHTR applications, it is necessary to measure the emissivity of all structural materials being considered. With the standard ASTM C835-06 test method, the total hemispherical emissivity of A387 Grade 91 steel, a leading candidate alloy for VHTR structural applications, was measured under four distinct surface conditions: (1) mild abrasion following electrical discharge machining, (2) increased surface roughness via sandblasting, (3) coating with NBG-18 graphite powder, and (4) oxidization in air. A detailed account of experimental methods and procedures, as well as the results of the total hemispherical emissivity measurements, are presented.