Corrosive naphthenic acids and sulfur compounds in crude oils present a major challenge for refineries which are struggling in a profit-diminishing business. Although it was accepted that some sulfur compounds may lay protective FeS scales on the metal surface and deter the corrosion attempting to correlate the characteristics of FeS scale with its protective properties was not successful. Given the complex chemical compositions in real crudes model sulfur compound (n-dodecyl sulfide or DDS) and naphthenic acids were used to mimic the corrosion by crude fractions. The scale formed in the model compound and/or naphthenic acids was challenged to examine its protectiveness against naphthenic acid corrosion. Moreover the scale was analyzed with TEM/EDS technique and a layer of iron oxide was found when naphthenic acids present in the solution. The iron oxide layer appeared to be protective against naphthenic acid corrosion and further analysis revealed that it was composed of magnetite.Key words: naphthenic acids iron sulfide scales iron oxide high temperature corrosion crude fractions model sulfur compounds