ASME SA209 Grade T1a Carbon Steel Boiler Tube Superheater Tube Seamless Steel Tube ASME SA209 Grade T1a is a seamless carbon-molybdenum (C-Mo) alloy steel tube manufactured specifically for high-temperature boiler and superheater service. The "T1a" designation means it has strictly controlled residual elements (copper, nickel, and chromium) to ensure stable creep resistance and structural integrity under prolonged exposure to elevated temperatures and internal steam pressure.