American Society for Testing and Materials (ASTM). Current edition approved March 1, 2006. Published April 2006. Originally approved in 1954. Last previous edition approved in 2004 as A376/A376M – 04. 7 p. 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 service.