maryam1979,
There is not such thing as 304NACE and 304, nobody would manufacture NACE / Non-NACE steel....The NACE MR 0175 or 0103 are limiting the use of various type of materials in specific corrosive applications, due to the materials inheritent limitations. The Carbon steel or Stainless steel (and other steel materials) can be manufactured on the basis of range for each componemt (carbon, chromium, nickel, manganese, molibdenum, etc..) The NACE standard would specify the maximum or minimum content of all the relevant chemical components in one particular steel, in order to satisfy the minimum corrosion resistance nominated in the NACE standard. The similar materials in the same group/type (say carbon steel with more than 0.25% carbon content) should not be used in corrosive environment specified in the "NACE", because of the elevated risk to fail.
To reply to your question, there is no difference between the NACE and non-NACE materials because they don't exist with this classification.
cheers,
gr2vessels
