酸性氯化钠溶液中硫脲基咪唑啉缓蚀剂对X70钢孔蚀行为的影响

发布时间：2018-01-11 03:21

本文关键词：酸性氯化钠溶液中硫脲基咪唑啉缓蚀剂对X70钢孔蚀行为的影响　出处：《北京化工大学》2015年硕士论文　论文类型：学位论文

【摘要】：X70钢在油气田集输系统中常处于酸性环境(pH 3～6),由于环境中含有Cl-等侵蚀性离子,X70钢表面容易产生孔蚀,从而造成严重的经济损失。虽然相关学者针对该环境中使用的缓蚀剂进行了部分研究,缓蚀剂的开发也比较成熟,但有机类缓蚀剂针对钢材孔蚀的缓蚀机理仍不明确,需要进一步的研究。为此,研究有机类缓蚀剂对酸性体系中X70钢孔蚀的影响,可以进一步揭示缓蚀机理,指导缓蚀剂的开发与实际应用。本文采用了慢速动电位扫描、电化学阻抗测试、Mott-Schottky曲线、扫描电镜和能谱分析(SEM-EDS)和X射线光电子能谱(XPS)等方法研究在含0.2 mol/L NaCl+0.0mol/L NaNO2的体系(pH=5.5)中分别加入硫脲和硫脲基咪唑啉(TAI)后X70钢的腐蚀行为,通过改变两种缓蚀剂的浓度和浸泡时间等方法探讨缓蚀剂对X70钢小孔腐蚀的影响及缓蚀机理。通过对电化学参数(自腐蚀电流密度icorr、稳定孔蚀电位Eb)分析,讨论两种缓蚀剂对X70钢均匀腐蚀和孔蚀的缓蚀影响；通过Mott-Schottky、电化学阻抗谱、XPS等测试手段,对X70钢在不同浓度的两种缓蚀剂中、不同浸泡时间后表面吸附膜的形貌、元素成分和含量进行分析,探讨表面吸附膜层结构以及膜层完整性等状态变化的,研究两种缓蚀剂对X70钢孔蚀的缓蚀机理,主要得出以下结论：(1)X70钢在0.2 mol/L NaCl+0.05 mol/L NaNO2的体系(pH=5.5)中添加适量(90～300 ppm)的硫脲作为缓蚀剂,硫脲可以抑制X70钢的均匀腐蚀,但促进孔蚀。体系中硫脲对X70钢的缓蚀率随着硫脲的加入量增大呈先增加后减小的趋势,当加入量为90 ppm时缓蚀率最高。将X70钢置于加入90 ppm硫脲缓蚀剂的体系中预钝化24h,缓蚀率上升到98%。但硫脲在X70钢表面形成的膜层结构疏松,能够促进孔蚀的发生,在经过浸泡和不浸泡两种情况下硫脲缓蚀剂都会增大X70钢的孔蚀敏感性,促进孔蚀的发生。(2)X70钢在0.2 mol/L NaCl+0.05 mol/L NaNO2的体系(pH=5.5)中,添加适量的硫脲基咪唑啉(TAI)缓蚀剂可以抑制均匀腐蚀,但促进孔蚀的发生。当TAI的添加浓度为40 ppm-110 ppm时,TAI能够促进X70钢的均匀腐蚀；添加浓度达到160 ppm时可以有效抑制均匀腐蚀,缓蚀率达到99%,自腐蚀电流密度降低4个数量级,TAI可以促进试样表面膜层中的Fe2+转化为Fe3+,可以有效抑制X70钢均匀腐蚀；TAI浓度增大至240 ppm时,,缓蚀率开始下降,缓蚀效果减弱。孔蚀电位随着咪唑啉用量的增加逐渐下降,是因为X70钢表面吸附膜疏松导致Cl-等侵蚀性离子侵入。(3)X70钢在TAI中的浸泡时间对缓蚀效果有显著影响,X70钢在含Cl-酸性体系中加入160 ppm TAI,延长浸泡时间至24h,此时TAI针对X70钢均匀腐蚀具有很好效果,同时也使X70钢在体系中的孔蚀电位大幅上升,这是由于吸附膜可以有效阻隔Cl-的侵入,降低X70钢的孔蚀敏感性耐孔蚀性,有效抑制孔蚀萌生。(4)X70钢在TAI中浸泡24h后,膜层表面主要以咪唑啉分子为主；膜层中更深的位置硫脲分子含量增加,这是由于硫脲分子具有更小的相对分子质量,优先吸附在基体表面。硫脲分子为主的膜层结构疏松,促进孔蚀的发生；随着浸泡时间的增加,咪唑啉分子包覆在硫脲分子之上,生成Fe-N配位键,形成致密的吸附膜,提高X70钢在腐蚀介质中的阳极活化能,降低阳极腐蚀速率；同时,吸附膜外层的咪唑啉分子形成的疏水膜,可以有效阻隔侵蚀性离子的侵入,有效抑制均匀腐蚀和孔蚀。
[Abstract]:X70 steel in acidic environment and transportation system in oil and gas (pH 3 ~ 6), in the environment containing Cl- and other corrosive ions, the surface of X70 steel is prone to pitting, resulting in serious economic losses. Although scholars in the use of corrosion inhibitors in the environment are part of the research, development the inhibitor is mature, but the organic corrosion inhibitor for the corrosion mechanism of steel pitting are still not clear and need further research. Therefore, study on the effect of inhibitors on organic acid system in X70 steel pitting, can reveal the inhibition mechanism, guide the development and application of corrosion inhibitor agent. This paper uses the slow potentiodynamic scanning, electrochemical impedance test, Mott-Schottky curve, scanning electron microscopy and energy spectrum analysis (SEM-EDS) and X ray photoelectron spectroscopy (XPS) method in NaCl+0.0mol/L containing 0.2 mol/L NaNO2 system (pH=5.5) were added Thiourea and thiourea imidazoline (TAI) corrosion behavior of X70 steel after two, by changing the concentration of corrosion inhibitor and soaking time of corrosion inhibitors and inhibition mechanism of influence on the pitting corrosion of X70 steel. The electrochemical parameters (corrosion current density icorr, stable pitting potential Eb analysis) two, discuss the corrosion inhibition effect on X70 steel corrosion and pitting; by Mott-Schottky, electrochemical impedance spectroscopy, XPS spectroscopy of X70 steel in different concentrations of two kinds of corrosion inhibitors, the surface morphology of adsorption film after different immersion time, element composition and content analysis. To investigate the adsorption film structure and film integrity status change, on two kinds of corrosion inhibition mechanism of pitting corrosion of X70 steel, the main draw the following conclusions: (1) system of X70 steel in 0.2 mol/L NaCl+0.05 mol/L NaNO2 (pH=5.5) add amount (90 ~ 300 ppm) The thiourea as a corrosion inhibitor, thiourea can inhibit the uniform corrosion of X70 steel, but promotes pitting. In the system thiourea on X70 steel corrosion rate with thiourea added amount increased first and then decreases, when the dosage is 90 ppm. The highest inhibition rate of X70 steel in 90 ppm urea sulfur corrosion inhibitor system prepassive 24h inhibition rate rose to 98%. in the film but thiourea loose structure formed on the surface of X70 steel, can promote the occurrence of pitting, the pitting susceptibility after soaking and soaking in two cases of thiourea inhibitors will increase X70 steel, promote pitting happened. (2) system of X70 steel in 0.2 mol/L NaCl+0.05 mol/L NaNO2 (pH=5.5), adding proper amount of imidazoline (TAI) inhibitor can inhibit corrosion, but promote the occurrence of pitting. When the TAI concentration was 40 ppm-110 ppm, TAI can promote the corrosion of X70 steel Tim; And when the concentration reached 160 ppm can effectively inhibit the corrosion, the corrosion rate reached 99%, the corrosion current density decreased 4 orders, TAI can promote the film layer in the conversion of Fe2+ to Fe3+, can effectively inhibit the X70 steel uniform corrosion; the concentration of TAI increased to 240 ppm, and the inhibition rate began to decline and the inhibition effect was weakened. The pitting potential gradually decreased with increasing dosage of imidazoline because X70, adsorption film on the surface of Cl- steel lead to loose aggressive ion invasion. (3) soaking time of X70 steel in TAI has a significant effect on the inhibition effect of X70 steel with 160 ppm TAI in acid system with Cl- the immersion time, to 24h, the TAI for X70 steel corrosion has good effect, and the X70 steel pitting potential in the system increased sharply, this is because the adsorption film can effectively block the invasion of Cl-, reduce the X70 steel Kong Shimin emotional pitting resistance , effectively inhibit the pitting initiation. (4) X70 steel immersed in TAI 24h, the film surface mainly in the imidazoline molecule; increasing the molecular content in the film deeper position thiourea, this is due to the relative molecular mass of thiourea molecules with smaller, preferentially adsorbed on the surface of the substrate. The film structure of loose thiourea molecules mainly, promote occurrence of pitting; with the increase of immersion time, imidazoline molecule coated on the thiourea molecules on the formation of Fe-N coordination bond, forming dense membrane adsorption, improve the anode of X70 steel in corrosive medium activation energy, reduce the corrosion rate of anode; at the same time, the hydrophobic membrane imidazoline molecule adsorption film formed by the outer layer, can invade effectively the barrier of erosive ions, effectively inhibit the uniform corrosion and pitting corrosion.

【学位授予单位】：北京化工大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TG174.42

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