| During high acid crude oil refining, naphthenic acid corrosion?NAC? is a common form of corrosion, which has a huge threat on the equipment safety and service life. During high acid crude oil processing, refining companies have taken some methods to counteract naphthenic acid corrosion, such as upgrade of the materials, addition of corrosion inhibitors and mixing refining with low acid crude oil. But in high turbulence region,naphthenic acid corrosion is still serious. The naphthenic acid corrosion can be moderately inhibited, but cannot be completely eliminated. Therefore, to ensure the safety of equipment,the corrosion law clarity of naphthenic acid corrosion, the construction of corrosion prediction model could be valuable for acid oil processing .In this paper, corrosion law of typical materials under high flow rate and high turbulence was researched firstly. The influence of temperature, flow rate, turbulence and the content of active sulfides was quantified respectively and expressed by corresponding factor. Subsequently combining with the scaled reference corrosion data, the max corrosion depth and average corrosion depth were selected as the corrosion indicators to construct the naphthenic acid corrosion predication model under high flow rate and high turbulence.Then the predication software was programmed. The main research results were listed as below:?1? Base on the analysis of available corrosion data, the relationship between temperature and naphthenic acid corrosion rate was confirmed, which could be expressed by linear relationship between lnv and ?- 1/T?. Combining with the reference corrosion rate of v240? calibrated at 240 ?, the influence of temperature on corrosion rate could be expressed by It=vT/v240?..?2? As active sulfides existed in the high acid crude oil, the active sulfides were involved in naphthenic acid corrosion. Protective sulfide film could be formed on the metal substrate when the active sulfides content was appropriate. The sulfide film maybe inhibit naphthenic acid corrosion to some extent, but too high sulfide could lead to serious sulfide attack. Therefore, the influence of sulfide content on naphthenic acid corrosion was quite complicated which could not be directly expressed in mathematical formula. However, the effect of sulfide on naphthenic acid corrosion rate could be expressed in isotherms. Based on the isotherms, the active sulfide influencing factor could be expressed by Is=si,c/si,0(si,c:the corrosion rate at any sulfide content, si,0:the corrosion rate when the content of sulfide is zero).?3? Turbulence intensity and flow rate mainly influenced the max corrosion depth and the average corrosion depth respectively. With the increase of turbulence, the max corrosion depth increased. The influencing factor of turbulence on maximum corrosion depth can be expressed by Iu=Dmax,u%/Dmax,0%, and the influence of flow rate on average corrosion rate could be expressed by Ir =Df/D0.?4? Available corrosion tests and corrosion data indicated that no interaction existed between the influencing factors above, thus the cumulative effect of the factors can be expressed in the maximum corrosion depth Dm, the naphthenic acid corrosion model can be expressed as Dm= Db · It · Is · Iu. |
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