For carbon steel - it is simply that 'NACE' pipe contains less than 1 mass % Ni and has been hardness tested and verified as meeting the requirements of ISO 15156-2/NACE MR0175. Get this - if 'non-NACE' pipe also contains less than 1 mass % Ni and has been hardness tested it too could also be called 'NACE' pipe if it was within the hardness limits and somebody wished to change the name! If one is talking about stainless steels and nickel alloys, then it's a whole different story and I'm not writing an essay on that. Upshot: try to avoid using the term 'NACE pipe'; try "ISO 15156 pipe" for a pleasant change.
NACE pipe is not a grade of Carbon Steel. Is a terms sometime used, wrongly, to state that a Carbon Steel follow all the requirements of NACE MR 0175 / ISO 15156.
It's a common mistake, in my opinion, that needs to be avoided and eliminated 'cause someone, not introduced in Materials and COrrosion, could think that NACE means only Sour Service and not other thousand of Standard, Materials Requisition and so on..
