An EIS study of the effect of the pedant group in imidazolines as corrosion inhibitors for carbon steel in CO2 environments

Electrochemical impedance spectroscopy (EIS) measurements were carried out to study the corrosion inhibition of carbon steel in 3 % NaCl with and without diesel saturated with CO₂ at 50 °C. The inhibitors examined were hydroxyethyl (HEI‐18), amino ethyl (AEI‐18), and amide ethyl imidazolines (AMEI‐18). When the oily phase, i.e diesel, is absent, the inhibition efficiency of the imidazolines is low, around 80 %. It was found, however, that the inhibition dramatically increased with the presence of the oily phase, because the imidazolines are able to act as both emulsifiers and corrosion inhibitors. Experimental results showed an increase in the film resistance (R_f), charge transfer resistance (R_ct), capacitance of the film and the capacitance of the double layer values with the addition of inhibitor in presence of the oily phase also in several orders of magnitude. The most effective inhibitor in presence of diesel is a solution of AMEI‐18, as the oily phase is carried to the surface also. This is due to the presence of two large alkyl groups than the only chain present in the HEI‐18 and AEI‐18 imidazolines with better hydrophobic properties associated with the formation of a protective film that reduces drastically the corrosion process. The effects of the interaction of inhibitors with hydrocarbons and the correlation on the performance of inhibitor films have been examined.     

The inhibition of CO2 corrosion of N80 mild steel in single liquid phase and liquid/particle two-phase flow by aminoethyl imidazoline derivatives

The inhibitory behaviour of 2-undecyl-1-aminoethyl imidazoline (AEI-11) and 2-undecyl-1-aminoethyl-1-hydroxyethyl quaternary imidazoline (AQI-11) on CO₂ corrosion of N80 mild steel in single liquid phase and liquid/particle two-phase flow was investigated using weight loss, linear polarization, potentiodynamic polarization, EIS methods and SEM observations. The two compounds inhibited the CO₂ corrosion of N80 steel and the extent of inhibition was dependent on the flow conditions and particulate content. In both phases, AQI-11 exhibited better inhibition ability than AEI-11 due to the polycentric adsorption sites on its structure. Theoretical calculation on the inhibition abilities of the compounds and their modes of adsorption are reported.     

Computational simulations of the molecular structure and corrosion properties of amidoethyl, aminoethyl and hydroxyethyl imidazolines inhibitors

To proof the corrosion efficiency of hydroxyethyl, aminoethyl and amidoethyl imidazolines, they were evaluated by linear polarization resistance and polarization curves in deaerated 3% NaCl + Diesel + inhibitors saturated with CO₂ at 50 °C. The most efficient inhibitor was the amido ethyl imidazoline, with an efficiency of 97.88% whereas the least efficient was the hydroxyethyl imidazoline, with an efficiency of 88.8%. A theoretical study of the corrosion inhibition efficiency of these imidazoline derivatives, was carried out using density functional theory (DFT). The computational calculations were used to obtain information about their molecular structure and those properties related with the inhibition efficiency of these inhibitors. The obtained correlations and theoretical conclusions agree well with the experimental results.     

咪唑啉型缓蚀剂中疏水基团对N80钢在CO2饱和的3%NaCl溶液中的缓蚀性能影响

合成了四种含有不同疏水基团的咪唑啉型缓蚀剂,即正丁基咪唑啉(IM-4)、壬基咪唑啉(IM-9)、十一烷基咪唑啉(IM-11)和十七烷基咪唑啉(IM-17),产物经红外,紫外光谱等进行表征.在静态及动态条件下,用失重法、电化学等方法研究各缓蚀剂对N80钢在CO2饱和的3%NaCl溶液中的缓蚀性能.结果表明,静态条件下,缓蚀剂的缓蚀性能与疏水基团的碳链长度、空间位阻及其水溶性有关;在介质流速为5 m/s的动态条件下,缓蚀剂的缓蚀效率显著降低,对缓蚀剂的疏水和屏障作用要求更高.     

Electrochemical corrosion of liquid phase sintered silicon carbide ceramics

Liquid‐phase sintered silicon carbide (LPS‐SiC) is silicon carbide ceramic which contains sintering additives forming a liquid phase during sintering. These additives segregate in the grain boundary phase during cooling. The usually used Al₂O₃ dissolves partially in the SiC‐grains and therefore changing the conductivity of the SiC (core rim structure). This study is focused on the electrochemical properties of LPS‐SiC with yttria and alumina as sintering additives. Electrochemical corrosion behaviour of LPS‐SiC has been determined by linear and cyclic voltammetry in acidic and alkaline solution. The effect of anodic oxidation on the material has been monitored by field emission scanning electron microscopy (FESEM) and energy dispersive X‐ray spectroscopy (EDX) as well as by atomic force microscopy (AFM). The core‐rim structure of the investigated materials plays a decisive role in the vulnerability towards corrosion. If oxidative attack was found to occur under anodic polarization, it happened preferentially in the rim region of the SiC‐grains, while the core of the SiC‐grains remained basically unaffected.     

Corrosion inhibition of mild steel by ethylamino imidazoline derivative in CO2-saturated solution

The corrosion inhibition and adsorption behaviour of 2-undecyl-1-ethylamino imidazoline (2UEI) on N80 mild steel in CO₂-saturated 3% NaCl solutions was investigated using potentiodynamic polarization, electrochemical impedance spectroscopy techniques and SEM observation. Inhibitor efficiency increased with increase in 2UEI concentration. Temperature studies revealed an increase in inhibition efficiency with rise in temperature and corrosion activation energies decreased in the presence of 2UEI. A mechanism of chemical adsorption of 2UEI on the metal’s surface is proposed. The adsorption characteristics of the inhibitor were approximated by Temkin isotherm. The inhibition efficiency of 2UEI was enhanced in the presence of iodide ions.     

Interaction of inhibitors with corrosion scale formed on N80 steel in CO2‐saturated NaCl solution

The performance of the selected inhibitors, including thioglycolic acid (TGA), diethylenetriamine (DETA), and naphthene acid imidazolines (IM), on the bare surface of N80 steel and its scaled surface pre‐corroded in CO₂‐saturated 1%NaCl solution was investigated by weight‐loss method, electrochemical measurements using rotating cylinder electrode and surface analytical methods (SEM, XRD, and EPMA). The results indicate that there is a remarkable difference in inhibition efficiency of inhibitors on the N80 steel with and without pre‐corrosion scale. The synergistic effect between inhibitors and corrosion scale not only depends on the size of inhibitor molecules, but also depends on the interaction of the inhibitor with the corrosion scale. It shows that IM and DETA have a good positive synergistic effect with the corrosion scale formed on N80 steel, although DETA has no inhibition efficiency for bare N80 steel, which can easily enter into the apertures of the corrosion scale, and block the active sites on the metal surface and the diffusion routeways of the reactant so as to depress the corrosion of the substrate metal. While TGA shows excellent inhibition efficiency on bare N80 steel, but it has an antagonistic effect with the corrosion scale although it has a small molecular weight as well as DETA, because TGA can dissolve corrosion scale and break its integrality and protectiveness performance.     

Corrosion inhibition approach of oil production systems in offshore oilfields

Synthesis and modification of imidazoline were carried out based on review of the corrosion inhibitor development and application for oilfields. A series of imidazoline compounds were synthesised through the solvent dewatering and vacuum dewatering methods. After reaction of imidazoline with ethane oxide, the produced compound was used to react with halogen hydrocarbon and polyphosphoric acid respectively. Finally an agent with performance of corrosion‐inhibition, sterilisation and anti‐scaling was obtained. The structures of the compounds were characterised by the Fourier transformation infrared spectrum. The relationships between corrosion inhibition effectiveness of the compounds and their structures were investigated so as to determine the structure of a novel corrosion inhibitor. The selected corrosion inhibitor was evaluated by a series of experiments to understand the characteristics of imidazoline derivative and some major factors associated with oil production in the oilfields of China. The experimental results showed that this corrosion inhibitor has outstanding performance of corrosion inhibition and sterilization, and is suitable for corrosion inhibition of the oil abstraction systems with high water‐content in the offshore oilfields.     

Organic molecules showing the characteristics of localised corrosion aggravation and inhibition

The behaviour of imidazoline and an acid functionalised resorcinarene as steel corrosion inhibitors in carbon dioxide (CO₂)-saturated brine solutions has been studied using an electrochemically integrated multi-electrode array namely the wire beam electrode (WBE). Both imidazoline and resorcinarene acid provided excellent inhibition to general CO₂ corrosion; however imidazoline was found to aggravate localised corrosion by creating a small number of major anodes that focused on a small area of the WBE surface, leading to highly concentrated anodic dissolution. The resorcinarene acid showed distinctively different behaviour by generating a large number of minor anodes randomly distributing over the WBE surface, leading to insignificant general anodic dissolution. These results indicate that resorcinarene acid provided effective localised corrosion inhibition by promoting a random distribution of insignificant anodic currents.     

咪唑啉类缓蚀剂对 P110 钢在 CO2 注入井环空环境中应力腐蚀行为的影响

目的研究咪唑啉类缓蚀剂对P110钢在CO2注入井环空环境中的应力腐蚀(SCC)行为的影响,为CO2注入井环空环境腐蚀防护方法的建立提供参考和依据。方法在实验室模拟的CO2驱注井环空环境中进行应力腐蚀试验、电化学测试和腐蚀形貌分析。根据现场提取的CO2注入井环空介质的成分分析结果配制模拟溶液,选用咪唑啉类缓蚀剂,调节模拟液p H至4。通入高纯N2进行除氧,以防止硫化物氧化。应力腐蚀试样采用三点弯试样,通过将试样的挠度控制为设定值来控制加载载荷。应力腐蚀试验和电化学试验均在密闭高压釜内进行。实验结束后,采用扫描电镜对腐蚀形貌进行观察。结果在CO2注入井环空环境下,咪唑啉缓蚀剂的浓度对P110钢的SCC行为有重要影响。在拉应力载荷存在时,添加足量的缓蚀剂对均匀腐蚀和SCC均具有较好的抑制效果,但当用量不足时,缓蚀剂的添加会增大P110钢的SCC敏感性,其SCC机制为氢脆与局部阳极溶解的混合机制。因此,P110钢在模拟CO2注入井的环空环境中会发生SCC,其机制为AD+HE机制。结论咪唑啉缓蚀剂的浓度对P110钢的SCC行为有重要影响,足量的缓蚀剂对均匀腐蚀和SCC均具有较好的抑制效果,但浓度不足时反而会增大SCC敏感性。     

Effect of flow velocity and entrained sand on inhibition performances of two inhibitors for CO2 corrosion of N80 steel in 3% NaCl solution

Inhibition for CO₂ corrosion of N80 steel by quaternary alkynoxymethyl amine (IMC-80-Q) and imidazoline in 3% NaCl solution was investigated under static and flowing conditions by using modified rotating disk apparatus. The effects of flow velocity, concentration of inhibitor as well as entrained sand on inhibition performances were studied through weight loss test, scanning electron microscope (SEM) observation and electrochemical techniques including electrochemical impedance spectroscopy (EIS), linear polarization resistance. Electrochemical parameters such as R_t and C_d for IMC-80-Q exhibited peak-value-phenomenon at inhibitor concentration of 150 mg/L when flow rate was below 5 m/s, in contrast with 300 mg/L when flow rate was beyond 5 m/s. The optimum concentration was further enhanced by the entrained sand in the medium containing IMC-80-Q. The adsorption of IMC-80-Q under static condition obeyed Langmuir isotherm when inhibitor concentration was below 150 mg/L, but it changed into Freundlich isotherm as inhibitor concentration was beyond 150 mg/L. The optimum inhibitor concentration of imidazoline under static condition was 100 mg/L, but it increased to 200 mg/L at 5 m/s. Under static condition imidazoline exhibited better inhibition than IMC-80-Q did; in contrast, at 5 m/s IMC-80-Q exhibited better inhibition than imidazoline did. The critical flow velocity was a function of both inhibitor type (IMC-80-Q or imidazoline) and inhibitor concentration.     

缓蚀剂咪唑啉季铵盐与烷基磷酸酯用作在饱和CO2模拟盐水体系中的协同效应

    应用电化学方法评价了在饱和CO₂模拟盐水中对咪唑啉季铵盐和烷基磷酸酯抑制 A3碳钢腐蚀的效果,并考察了二者复配使用时的协同效应.结果表明,当二者比例为 1∶〖KG-*2〗1时,缓蚀率比单独使用时提高了20%以上.咪唑啉季铵盐主要抑制由于阴极反应引起的腐蚀,烷基磷酸酯主要抑制阳极反应引起的腐蚀,复配使用可同时抑制阴、阳极反应引起的腐蚀,缓蚀效果更好.     

H2S水溶液中的腐蚀与缓蚀作用机理的研究——Ⅶ.H2S溶液中咪唑啉衍生物对碳钢腐蚀电极过程的影响

利用电化学测试技术，在H2S溶液中分别研究了14种咪唑啉衍生物浓度的变化对其缓蚀性能以及碳钢腐蚀电化学过程的影响，并对其缓蚀作用过程、缓蚀类型进行了分析探讨。结果表明，随药剂浓度升高，体系的自腐蚀电流和电极表面电容迅速减少，极化电阻增大，表明缓蚀剂分子在电极表面的吸附随药剂浓度的增加而增加，屏蔽效应增强；咪唑啉分子结构中憎水支链的长短对其缓蚀作用类型有重要影响，随支链中碳原子增加，化合物的缓蚀作用类型逐渐由阴极型向阳极型转变；按其对电极过程作用性质的不同，所研究的14种咪唑啉衍生物可分为阳极阴极缓蚀剂两组，其缓蚀作用主要是由于咪唑啉分子在电极表面的化学吸附所至。     

Influence of the alkyl chain length of 2 amino 5 alkyl 1,3,4 thiadiazole compounds on the corrosion inhibition of steel immersed in sulfuric acid solutions

The corrosion inhibition efficiency of 2 amino 5 alkyl 1,3,4 thiadiazole compounds with different alkyl chain lengths, namely: 2 ethyl, 3 n propyl, 5 n penthyl, 7 hepthyl, 11 undecyl and 13 tridecyl, was evaluated in the system steel/1 M H₂SO₄. These compounds were synthesized, characterized by FT-IR and NMR spectroscopy analysis and evaluated using electrochemical impedance spectroscopy and SEM analysis. The results showed that the inhibition mechanism involves blockage of the steel surface by the inhibitor molecules by a Langmuir-type adsorption process and that the alkyl chain length plays an important role in the inhibition efficiency of the synthesized inhibitors.     

咪唑啉缓蚀剂对减粘塔塔顶流出系统的缓蚀作用

通过对腐蚀介质的气相色谱分析和腐蚀产物的XRD分析,研究了辽河某炼油厂稠油加工减粘塔塔顶系统的腐蚀机理;采用电化学法和静态挂片法研究了20钢在加入咪唑啉缓蚀剂的腐蚀介质中的缓蚀作用。结果表明,20钢试样在减粘塔顶水介质中发生了显著的低温HCl+H2S+H2O腐蚀;A1缓蚀剂主要成分为咪唑啉,属阳极吸附性缓蚀剂,可在20号钢表面形成一层高阻值疏水性保护膜,最佳缓蚀剂添加浓度为100mg/L时,缓蚀率最大为84%。     

A new solid‐state mode of hot corrosion at temperatures below 700°C

Preliminary results on a single‐crystal nickel‐based superalloy indicated that hot corrosion can occur at temperatures as low as 550°C, where liquid formation, generally believed to be responsible for Type II hot corrosion, is not predicted. Additional tests were conducted on pure‐nickel samples at 650°C and below to more clearly elucidate the mechanism of this very low‐temperature hot corrosion. Environments in dry air and O₂‐(2.5, 10, 100, and 1000) ppm SO₂ were studied. Based on the results obtained, a solid‐state corrosion mechanism was inferred. The mechanism relies on the formation of a previously unreported compound phase, which was identified using transmission electron microscope analysis that indicated the stoichiometry of Na₂Ni₂SO₅. Furthermore, it was nanocrystalline in structure and metastable. It was deduced that the Na₂Ni₂SO₅ formation was responsible for the rapid nickel transport required for the observed accelerated corrosion process. Moreover, its eventual decomposition resulted in a mixed product of porous NiO with embedded particles of Na₂SO₄. Application of the proposed mechanism to nickel‐based alloys is discussed.     

Synergistic inhibition behaviour of methylbenzyl quaternary imidazoline derivative and iodide ions on mild steel in H2SO4 solutions

The inhibition behaviour of 2-undecyl-1-ethylamino-1-methylbenzyl quaternary imidazoline (2UMQI) and KI on mild steel in 1.0 M H₂SO₄ solutions was investigated at 25 °C using electrochemical methods. The results indicated that 2UMQI inhibited the corrosion of mild steel and the extent of inhibition increased with 2UMQI concentrations. The inhibition action in the presence of 2UMQI is due to physical adsorption of 2UMQI. A mixed-inhibition mechanism is proposed for the inhibitive effects of 2UMQI. Inhibition efficiency of 2UMQI was enhanced by the addition of iodide ions. In the presence of KI, the potentials of unpolarization, E_u was observed and increased with KI concentration.     

CO2环境下油酸咪唑啉对X65钢异种金属焊缝电偶腐蚀的抑制作用研究

研究了X65管线钢与316L不锈钢、Inconel 625双金属复合管的异种金属焊缝在CO2环境下的电偶腐蚀行为,以及油酸咪唑啉的缓蚀作用。结果表明,随着电偶电位差的增大,异种金属焊缝的腐蚀速率明显升高,并且都显著高于母材。添加油酸基咪唑啉缓蚀剂能降低异种金属焊缝在CO2环境下的均匀腐蚀速率。但是,当缓蚀剂浓度添加较低时,异种金属焊接试样的碳钢一侧出现了严重的沟槽腐蚀或密集的点蚀坑;进一步增加缓蚀剂浓度才能消除沟槽腐蚀现象。讨论了缓蚀剂对异种金属焊缝电偶腐蚀的抑制机理,该项研究可为异金属焊接接头处的腐蚀防护提供借鉴。     

注空气驱油环境中缓蚀剂的合成及性能评价

在实验室合成咪唑啉缓蚀剂BMIA的基础上,与效果良好的除氧剂联氨进行复配,得到新型缓蚀体系BMIA-H。应用高温高压动态挂片法找出缓蚀剂BMIA与除氧剂联氨的最佳配比,然后采用动电位极化曲线和电化学阻抗谱评价了其对Q235钢的缓蚀性能。结果表明,缓蚀剂BMIA与除氧剂联氨的最佳配比为2∶3;按此比例进行复配形成的新型缓蚀体系BMIA-H,在模拟某油田水中。当其使用质量浓度为500 mg/L时,缓蚀率能达到98.32%;动电位极化曲线表明BMIA-H是混合型缓蚀剂。     

Electrochemistry and XPS study of an imidazoline as corrosion inhibitor of mild steel in an acidic environment

The effect of 2‐(2‐heptadec‐8‐enyl‐4,5‐dihydro‐imidazol‐1‐yl)‐ethylamine on the corrosion behavior of mild steel in aqueous hydrochloric acid was investigated using weight loss measurements, polarization scans, electrochemical impedance, and X‐ray photoelectron spectroscopy (XPS). The inhibition efficiencies and coverage degrees increased with the concentration of inhibitor but decreased proportionally with temperature. It appears that the steric hindrance of the aliphatic chain on the imidazoline ring adsorption may affect inhibitor efficiency. Polarization curves showed that the oleic imidazoline (OI) acted essentially as a mixed type inhibitor, in which the blocking of active sites occurred. As a result of film formation, impedance spectra revealed a considerable increase in the charge transfer resistance as indicated by the second capacitive loop. XPS depth profile analysis observed the presence of nitrogen and carbon species on the inhibitor film, which were associated to the OI.