Abstract
The term “naphthenic acids” is a collective name for organic acids present in various crudes. It has been proved that while minor quantities of other organic acids are included, the main acids from naphthenic base crudes are saturated ring structures containing acid groups.
The circumstances under which naphthenic acid corrosion occurs are analogous to those of sulfur corrosion. A practical differentiation between naphthenic acid and sulfur corrosion is possible on the basis of different corrosion phenomena. It would appear that the rate of naphthenic acid corrosion is dependent on the concentration of the naphthenic acids in the oil, operating temperature, fluid velocity and activity of the naphthenic acids. Of these factors fluid velocity seems to be the most important. Unfortunately the critical velocity values below which the corrosion rates become negligible are not yet known.
Data are given to show the relationship between temperature and corrosion rates at selected locations in a high vacuum column of a distilling plant. Corrosion of mild steel by naphthenic acids becomes apparent at operating temperatures in excess of 220 C (430 F) with a maximum at approximately 280 C (540 F). Above 400 C no evidence of this type of corrosion has ever been found.
Naphthenic acid corrosion can be counteracted by removal or neutralization of the naphthenic acids by modifying fluid velocity conditions where possible and by proper selection of the constructional ma terials. Some hints on the suitability of various materials of construction are given. 4.4.2
