Q. Explain about Napthenic Acid Corrosion?

Some crude oils contain napthenic acids, which, at elevated temperatures, may contribute to more active corrosion with or without the presence of water. The critical temperature at which severe corrosion may occur is significantly lower than if only sulphur was present. Type 316 stainless steel and Inconel 600 show the best degree of corrosion resistance. Type 502 (5% Cr) low alloy steel is useful where there is increased fluid velocity, except in furnace and heat exchanger parts. Stainless steel types 304, 321, and 347 may also be unreliable in these services.

There is some indication that napthenic acid corrosion may be mitigated by passivation of the surfaces with a thiazoline / phosphite mixture at temperatures of 550° - 660°F (200° - 316°C).