The petroleum acid is the general name for all the acidic compounds in crude oil, and over 90% of them are RCOOH, the rest are organic acidic compounds such as fatty acids, phenols and sulphide. The crude oil of the naphthenic acid corrosion under 220 ℃ is very weak, and it is an excellent surfactant, but when high temperature (> 350 ℃), especially when coexist with H2S, it will have very strong chemical activity. There is an insoluble protective film formed by the reaction of the H2S to the S and Fe at high temperature, and it reacts with the naphthenic acid and then produces the naphthenate, which is also formed and soluble in oil. The resulting H2S also accelerated corrosion with Fe reaction.
In addition, the crude oil in naphthenic acid molecules is not identical also, part of the boiling range of 232-288 ℃; Another part of the boiling point range is 350-400 ℃. As the temperature rises, the naphthenic acid gradually vaporizes, it will accumulate in the vapor phase, and the concentration increases, and corrosion occurs in these two temperature segments. With the flow of the medium, the metal surface is continuously scoured, exposed and subjected to naphthenic acid corrosion. The equation is as follows: 2RCOOH+Fe→Fe(COOH)2+H2
Based on the above factors, to avoid and control the erosion of sulfur-naphthenic acid, the equipment and pipelines are useless, the following measures should be taken: the anti-naphthenic acid material should be selected, such as 316L; In the design, the liquid velocity in the pipeline should be calculated, and the corrosion can be controlled effectively by low flow velocity; Avoid simultaneously processing high sulfur and naphthenic acid crude oil.