Steel Grade: T91,T23, T22,T12,T11,T5,T2 etc; Standard: ... 16~168.3, Thickness 1~15 Seamless Ferritic and Austenitic Alloy Steel Boiler Super heater and Heat Exchanger TubesSteel Grade: T91,T23, T22,T12,T11 ... applies to high temperature service such as for super-heaters and reheaters. And the features are precise dimension.