Chakra If you have processed crude mix with TAN above 0.5 without any kind of inhibition is much probable that your corrosion was due to NAC. Your corrosion situation is being worsened by the fact that your feed has a low sulphur content. If your intention in the near future, is to process Naphtenic crude you have to consider or a metallurgy up grade or a chemical treating. The naphtenic corrosion aspect is known by %E2%80%9Corange skin%E2%80%9D surface with large and smooth pits normally found in places with turbulence and changes of velocity. Best Regards Luis marques