| The corrosion behavior of super15Cr martensitic stainless steel in mud acid is studied by the corrosion test of fresh acid and subsequent conditions combine with electrochemical analysis test and SEM, confocal laser scanning, XPS and XRD methods. The results show that:Inhibition of corrosion inhibitor for super15Cr martensitic stainless steel in fresh acid (mud acid) at the rage of60℃-140℃is in the primary standard criteria, with temperature increased, the average corrosion rate, maximum pit depth, average corrosion depth and the average corrosion rate are all increased. Although the uniform corrosion rate of super15Cr martensitic stainless steel in fresh acid is up to9.1269mm/a, uniform corrosion rate is far less than the required standard of oil and gas field that can be accepted. Therefore, in the view of uniform corrosion rate of super15Cr martensitic stainless steel, there is a excellent matching between corrosion inhibitor and super15Cr martensitic stainless steel.Electrochemical properties of the super15Cr martensitic stainless steel in different temperature fresh acid solution is studied by electrochemical analysis,results show that reaction rate of H+in the cathodic is increased as temperature increasing, which causes corrosion potential is increased;the corrosion inhibitor decreases corrosion current density by the way of inhibiting cathodic and anodic reaction, corrosion inhibition efficiency is more than90%that shows a good corrosion inhibition performance;the inhibitor can significantly improve the Tafel slope of cathodic and anodic and can inhibit cathodic and anodic reaction, so the type of the corrosion inhibitor is a mixed control of anode reaction inhibitor;AC impedance analysis shows that the capacitive arc is appeared when the temperature is30℃, potential rise can promote the adsorption process of inhibitor particles, but the inductance is appeared in low end when the temperature at45℃-70℃, potential increase promotes adsorption desorption process of corrosion inhibitor particle, which explains the mechanism of inhibitor has been changed at more than45℃.Super15Cr martensitic stainless steel with a very high corrosion rate in the corrosion conditions of fresh acid, in contrast, uniform corrosion of super15Cr martensitic stainless steel under the condition of the acid residue and conditions of CO2corrosion is mild, corrosion rate is low, thus, in terms of uniform corrosion severity, corrosion of fresh acid is the most serious in the conditions of corrosion simulation test.Super15Cr martensitic stainless steel with120℃fresh acid-170℃residual acid-170℃CO2corrosion of formation water, pitting density increased significantly, compared to the phenomenon of obvious pitting in the independent residual acid corrosion and CO2corrosion of independent formation water is not appeared, the reason may be due to the formation of the adsorption film (or corrosion product film) in the process of fresh acid corrosion is incomplete coverage in the process of residual acid corrosion and conditions of CO2corrosion, which promotes the initiation of pitting corrosion. |
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