1.1 This specification covers seamless austenitic steel pipe intended for high-temperature central-station service. Among the grades covered are five H grades and two nitrogen grades (304N and 316N) that are specifically intended for high-temperature s This specification covers seamless austenitic steel pipe intended for high-temperature central-station service. The grades covered are five H grades and two nitrogen grades. Pipe may be either hot finished or cold finished, with a suitable finishing tr