Every time new acidic crude oils are used, the problem of naphthenic acids (NA) arises again. Most investigations concern the corrosiveness of crude oils or gas oil fractions containing NA. In the acidic crude oil “A”, the kerosene fraction was the most corrosive.
The main goal of this work is to investigate the corrosiveness of different petroleum fractions distilled from acidic crude oil “A” at 150 to 370oC (302 to 698oF) and to find effective measures for diminishing the corrosiveness of aggressive fractions.
Corrosiveness of acidic crude oil “A” and petroleum distillates towards pure iron and mild steel (C1010, A 515 Gr 70) was examined in an autoclave and in a specially designed system. It was shown that acidic crude oil “A” at 300oC (572oF) (TAN = 0.4 mg KOH/g) did not have high corrosiveness: corrosion rate of mild steel was 0.05 to 0.1 mm/y (2 to 4 mpy); but that for other fractions of “A” is very high, especially for the kerosene fraction distilled at 150 to 270oC (302 to 518oF) (0.66 mm/y). Five fractions of this “wide” kerosene fraction were cut every 20oC, TAN was measured, and corrosivity of these fractions was determined. Corrosion rate of mild steel as a function of distillate temperature range for various fractions was described with maximum for kerosene distillate 190 to 210oC (374 to 410oF) of crude oil “A” with corrosion rate of 0.97 mm/y (38.8 mpy). The corrosion rate values correlate with TAN (Total Acidity Number). Corrosion kinetics was studied during 1 to 13 days. Blending and corrosion inhibitors were examined for corrosion mitigation in the acidic kerosene. Corrosion inhibitors “P” and “N” based on phosphate esters for the kerosene distillate 190 to 210oC (374 to 410oF) were examined under laboratory and industrial conditions. Inhibitor concentrations of 25 to 75 ppm resulted in efficiency (% reduction in corrosion rate) of 74 to 94%.
Keywords: crude oil, naphthenic acid corrosion, kerosene, mild steel,