You don't give any idea what type of pressures or temperatures you are talking about. If this is cryogenic temperatures or very high pressure, the following won't apply.
Nitrogen is commonly used within refineries as a purge gas to remove hydrocarbons from equipment before it is turned over to maintenance and to remove air from equipment before returning it to service. Steam can also be used to hydrocarbon free equipment.
The nitrogen piping specifications I've seen have been just plain carbon steel good for nitrogen at ambient temperatures and up to a few hundred psig. Essentially, they've been the same as our specs for light, sweet hydrocarbons. If you have a compressed air piping spec (not instrument air as this typically calls for galvanized piping), that should work since air is already 79% nitrogen by volume.
