… alloy groupings has been expanded to 37 to accommodate the 14% silicon cast irons, which had been dropped from the fifth … and nickel-chromium-molybdenum group. There are nearly 1,000 corrosive environments represented in the metals … < 0.05 mm/y ( < 2 mpy), < 0.508 mm/y ( < 20 mpy), 0.0508-1.27 mm/y (20-50 mpy), and > 1.27 mm/y (> 50 mpy). …