Electron-Microprobe Study of Scale Formations on Cr-Mo Superheater Tubing After Long-Time Exposure to 2000 Psi Steam of 1100 F and 1200 F

Abstract

Metallographically polished sections through the steam-scaled inside surface of 2-in-od × 0.50-in-wall superheater tubing used in ASME High Temperature Steam Research Tests were subjected to electron-microprobe analyses and the concentrations of iron, manganese, silicon, chromium, and molybdenum determined at intervals of 8 to 15 microns (0.3 to 0.6 mil) across the scale thicknesses and in the adjacent tube metal. The relationships between base-metal composition, scale composition, and scale thickness were examined as a function of temperature and time of exposure. The suitability and value of the electron-microprobe as a research tool for studying mechanisms of scaling behavior and scale formations are outlined.