Back To The Water Injection No < Sub > 2 < / Sub > < Sup > - < / Sup > On The Corrosion Mechanism Of Carbon Steel Secondary Research

The technology, adding nitrate or nitrite in reinjection water, is used in inhibit SRB in oilfield. The technology, which is based on the oilfield sulfur cycle basic rule, takes advantage of the competition of different strata of bacteria to get the effect of suppressing SRB biological activity. It has the advantages which is low cost, high effect and no damage to the formation, while, the nitrite produced a secondary corrosion harm. The corrosion mainly performances for fixed-point corrosion and serious pitting corrosion, what’s more, It caused invalidation of corrosion inhibitors in oil field.At present most of laboratory research for injection process NO2-secondary corrosion are the direct expression and selection through the corrosion rate of. This paper research the mechanism of secondary corrosion of nitrite, the methods and conclusions are as follows:(1)Using the hanging piece weight-loss method to get the environment factors, at which the most serious nitrite making secondary corrosion happens.(2)Observe the surface corrosion form of hanging via the scanning electron microscopy (SEM). Determine the corrosion product components through infrared spectrometry. Adding of nitrite causes the increasing of the product of corrosion. As the analysis of infrared spectrometry, the main products of corrosion are y-FeOOH and β-FeOOH. The structure of γ-FeOOH is loose, that is easy to make active anion go into, form the core of corrosion.(3)Research the Electrochemical behavior of the secondary corrosion via the corrosion potential, electrochemical impedance spectroscopy (EIS), cyclic voltammetry curves and polarization curve method. The conclusions are as follows:1) adding nitrite causes both in two corrosion medium potential into is moved, and the overall corrosion rate drop;2) The prophase of adding nitrite, FeOOH, which is the product of nitrite oxidation Fe2+, adhere to the carbon steel as to form a preservative to stopping the corrosion of large area, which caused the drop of the corrosion rate; the anaphase of adding nitrite, because of the loose structure of β-FeOOH, more and more active anion adhere to it to destroy the passivation layer, form the micro cells and cause some erosion.3) In anaerobic acidic H2S system, nitrite-injection make cathode to polarization enhancement, promote the metal corrosion, time in metal surface anode oxidation reaction, the overall corrosion not affected, but local corrosion increase.4) The zero current potential in two corrosion medium of nitrite-adding, are respectively-745mv and-780mv, which are all lower than zero current potential in have not adding nitrite system. In both medium adding nitrite is easy to cause pitting corrosion.(4)Synthetic a kind of adsorption type corrosion inhibitors, with who have good effect of controlling the corrosion pit, especially for no H2S environment. In the environment of including H2S, there is no significant point corrosion, but low rate of corrosion inhibitor.