hydrogen has been used for over 75 yrs as a coolant for large electrical generators ,typically over 250MWe rating. If you use the GE design guidelines issued to every engineering firm that builds the connecting pipng , valves and pressure vessels that connect to the hydrogen cooling systems, I think you will find that extraordinary metallurgical materials are not required. If you are certain of the temperature limits you listed above, you will find economical materials are permtted, but special care is needed to prevent corrosion if underground UG piping is used. Please note that the NASA hydrogen safety guidelines prohibit the use of UG routing of hydrogen piping, but it is routed underground for most large combined cycle power plants that I am aware of, with the consequent requirement to use cathodic protection of the piping and double wall piping when in the vicinity of a building or other person-accessible containment. IMHO the most likely failure mode for older combined cycle plants may be the failure of these cathodic protection systems over time.
"...when logic, and proportion, have fallen, sloppy dead..." Grace Slick