阴极保护电位对破损环氧涂层阴极剥离的影响

采用电化学阻抗技术(EIS),并结合SEM,EDS和XRD研究了室温、静态模拟海水中不同保护电位对海洋平台研制钢在模拟海水中防腐涂料与阴极保护联合作用效果以及对破损环氧防腐涂层的阴极剥离机理。结果表明:在本实验选择的保护电位中,随着电位的负移,涂层剥离面积逐渐增大。-750 mV (vs SCE,下同)保护电位对于破损涂层的金属基体欠保护。-1050 mV电位极化下发生严重的析氢现象,破坏了钙质沉积层的完整性,界面碱化程度较大,涂层剥离面积最大;-850和-950 mV保护电位均能抑制破损处金属的腐蚀;-950 mV保护电位下生成的CaCO_3和Mg(OH)_2钙质沉积层完整致密,保护效果最佳。     

X65和X80管线钢在大港模拟土壤溶液中的阴极保护参数研究

目的为管道安全运行提供支撑。方法通过搭建室内实验系统,基于极化曲线法和电化学阻抗谱法(Electrochemical Impedance Spectroscopy,EIS),对X65和X80管线钢在大港模拟土壤溶液中的阴极保护参数进行系统的实验及理论研究。结果通过分析X65和X80管线钢的极化曲线,发现在大港模拟土壤溶液中,X65管线钢的阴极保护电位范围为-400~-1200 mV,而X80管线钢的阴极保护电位范围为-400~-1150 mV。基于X65和X80管线钢的EIS结果,通过研究电荷转移电阻Rt随阴极极化电位Ee,c的变化趋势,进一步探明在大港模拟土壤溶液中,X65管线钢的析氢电位为-970 mV,最佳保护电位为-850 mV,而X80管线钢的析氢电位为-960 mV,最佳保护电位为-800 mV,从而明确了在大港模拟土壤溶液中,X65管线钢析氢电位小于X80管线钢的析氢电位。结论探明了X65和X80管线钢在大港模拟土壤溶液中的阴极保护参数,发现X65管线钢的析氢电位及最佳保护电位均小于X80管线钢,为X65和X80管线钢的阴极保护提供了一定理论依据。     

外加电位对X80管线钢在轮南土壤模拟溶液中应力腐蚀行为的影响

采用慢应变速率拉伸(SSRT)实验、SEM观察和动电位极化曲线测量等方法,研究了外加电位对X80管线钢母材及焊缝在轮南土壤模拟溶液中的应力腐蚀开裂(SCC)行为。结果表明,X80钢母材及焊缝在轮南土壤模拟溶液中均具有一定的应力腐蚀敏感性。在同一外加电位下,X80钢焊缝的SCC敏感性高于母材的;X80钢SCC敏感性及开裂机理受外加电位影响显著,在-500 mV外加阳极电位下,X80钢的SCC机理为裂尖阳极溶解-膜破裂机制,在-800 mV阴极电位以下(-850,-1000和-1500 mV),氢脆作用在SCC过程中的影响明显增强,阴极析氢反应促进了钢的氢致开裂,导致X80钢SCC敏感性显著增加。     

阴极保护下X65钢在模拟海水中的氢脆敏感性研究

采用阴极极化条件下的氢渗透实验和慢应变速率拉伸实验研究了X65钢在模拟海水中的氢渗透行为及其对断裂机理的影响。氢渗透实验结果表明,阴极极化过程中试样表面的钙镁沉积层能显著地降低氢扩散系数,采用Fourier方程、Laplace方程以及时间滞后法计算得出的有效氢扩散系数平均值为1.49×10-7cm2·s-1。结合变电位极化氢渗透测试结果、拉伸试样断口分析以及极化曲线测试,对阴极极化条件下X65钢的氢脆敏感性进行评估。结果显示,随着极化电位的降低,X65钢中的吸附氢浓度呈指数规律上升。当极化电位较高时,X65钢的裂纹扩展受阳极溶解和阴极析氢的双重作用控制。当极化电位较低,如-1200 mV时,钢中的吸附氢浓度急剧增加,脆性断裂区域的比例上升,X65钢发生氢致脆化失效。     

低温低溶解氧海水环境中X70钢阴极极化行为研究

采用动电位极化曲线及恒电位极化法研究了X70管线钢在低温低溶解氧海水中的阴极极化行为,线性极化测试和表面分析技术分析了阴极保护后钙镁沉积层的形成情况.结果表明,8℃、1.5 mg/L溶解氧海水中X70管线钢的析氢电位最正,4℃、3.0 mg/L溶解氧海水中析氢电流密度最小.在低温低溶解氧海水中钙质层难以形成,要得到致密良好的钙质层需要较高的保护电位.低温低溶解氧海水条件有利于Mg（OH）₂沉积,对CaCO₃形成不利.     

阴极极化下X80钢在鹰潭土壤模拟溶液中应力腐蚀行为研究

采用电化学阻抗和慢应变速率方法,结合扫描电子显微镜,研究了不同阴极极化电位下X80钢在鹰潭土壤模拟溶液中的应力腐蚀行为。结果表明：鹰潭土壤模拟溶液中,X80钢/溶液界面处电荷转移电阻随阴极极化程度增加先升后降。在自腐蚀电位条件下开裂机理为阳极溶解,当外加电位为-1000 mV (vs SCE),应力腐蚀敏感性最低,此电位为最佳保护电位;继续增大阴极极化程度,应力腐蚀敏感性增加,此时开裂机制为氢和应力协同作用下的氢致开裂。     

海水环境中组合电位极化对铁氧化菌腐蚀的影响

采用电化学测试、扫描电镜、激光共聚焦显微镜、Raman光谱等手段研究了-850 mV (vs.SCE,下同)转-1050 mV和-1050 mV转-850 mV组合电位阴极极化对X65钢在含铁氧化菌(IOB)的海水中腐蚀的影响.结果 表明:两种组合电位极化都对IOB腐蚀有一定抑制作用;极化与开路电位下X65钢腐蚀产物种...     

海水流速对DH36平台钢阴极保护的影响

利用自行设计的管流式海水循环实验装置模拟在0.20~2.00 m/s流速范围内的阴极保护情况,采用恒电流极化法进行阴极保护,通过电位的变化、电极宏观形貌和钙质沉积层的生成情况评价阴极保护效果。结果表明,流速越大,电位达到保护电位-800 m V(vs Ag/Ag Cl海水)时所需的电流密度越大;而且当流速大于1.20 m/s时,即使电位达到了保护电位仍可能发生明显的冲刷腐蚀;生成的钙质沉积层主要是单层的富镁层,只有电流密度较大时,才会在富镁层上进一步沉积富钙层。     

外加电流法对Q235A钢在模拟浪花飞溅区的保护效果

在模拟浪花飞溅区环境中采用外加电流法对Q235A钢实施阴极保护,通过保护电流密度、电化学性能试验,腐蚀形貌观察和保护效率计算研究了保护电位对Q235A钢保护效果的影响。结果表明:在恒电位控制下,保护电流密度在初期较大,之后急速下降并逐级稳定在100mA/m2以下;不同保护电位下,由于表面形成钙镁沉积物,试验钢的极化电阻急剧增大;随着保护电位的负移,阻抗弧直径变大,膜的保护性能加强;恒电位控制在-850mV(vs.SCE)及析氢电位之间时,保护效率可以达到98%以上。     

硫酸盐还原菌附着对阴极保护条件下钙质沉积层形成及其对金属保护性能的影响

通过扫描电镜(SEM)、能谱(EDS)、电化学阻抗谱(EIS)等方法研究了硫酸盐还原菌的附着对阴极保护条件下钙质沉积层形成及其对金属保护性能的影响。结果表明:硫酸盐还原菌附着后,施加阴极保护的碳钢表面依然能形成钙质沉积层,无论硫酸盐还原菌附着时间长短,生物膜的形成都导致金属表面钙质沉积层量减少,使其对金属的保护性减弱,硫酸盐还原菌局部腐蚀加速。     

外加电位下X80双相管线钢在模拟沿海土壤环境中的应力腐蚀行为

采用交流阻抗谱、极化试验、慢应变拉伸试验研究了不同外加电位下在模拟沿海土壤环境中X80双相管线钢的应力腐蚀行为,对拉伸断口和极化后试样进行SEM表面形貌及能谱分析。结果表明,与慢扫极化(模拟的非裂尖区域)相比,X80双相管线钢快扫极化模拟的裂尖腐蚀电位较负且腐蚀电流较大。-750 mV外加阴极电位处于裂尖自腐蚀电位范围,不足以起到阴极保护的作用,对应力腐蚀仍十分敏感。外加电位为-1050 mV时,阴极反应速率显著大于阳极反应,阴极反应产生的氢被金属吸收且扩散,慢应变拉伸未经颈缩即发生断裂,为准解理断裂。外加阴极电位为-900 mV,阴极电流有效抑制了阳极溶解反应,因此管线钢在模拟沿海土壤溶液中慢应变拉伸抗拉强度和断面收缩率都最高,断口表现为韧性断裂,侧面裂纹细小,阻抗模值最大,应力腐蚀敏感性最小。     

pH值对海水中TMCP X80钢氢脆敏感性影响

采用氢渗透实验法、动电位极化法研究TMCP X80管线钢在不同pH值海水中的氢渗透行为,结合扫描电镜 (SEM) 观察研究显微组织及氢渗透行为对氢脆敏感性的影响。结果表明,随着海水pH值的减小,析氢电位发生正移。天然海水和酸性海水中氢扩散系数随着极化电位负移而增加;极化电流密度越大,氢扩散系数和氢浓度越大。在负于析氢电位时,显微形貌显示出明显的蚀坑和氢鼓泡,酸性海水中更严重。随着海水pH值的减小及外加阴极极化电位负移,氢扩散到材料内部的量更大;充氢电流密度增加也促进氢的扩散,X80钢氢脆敏感性增加。     

杂散电流干扰和阴极保护作用下碳钢腐蚀规律研究

目的探讨杂散电流和阴极保护二者共同作用对碳钢腐蚀的影响。方法在碳钢管表面手工涂刷涂层并制造小块破损点,研究Q235碳钢在涂层破损后,受单纯直流杂散电流干扰、单纯阴极保护以及二者共同作用时随时间变化的电化学交流阻抗图谱(EIS),通过图谱信息以及图谱数据拟合进行分析。结果所有条件下,Bode图低频阻抗和Nyquist图容抗弧半径都随时间延长而逐渐增加。通过图谱和数据拟合发现,单纯杂散电流条件下,杂散电流越大,电化学阻抗越小,浸泡15天时,20 m A杂散电流条件下的极化电阻达到200 m A条件下的4倍。阴极保护对杂散电流腐蚀具有防护作用,无论是单独施加阴保,还是杂散+阴保共同作用,-1000 m V(vs.CSE)与-850 m V(vs.CSE)横向对比,总是-1000 m V条件下的极化电阻更高。一定程度上,阴保电位越负,极化电阻越大,保护效果越好。结论在一定范围内,不论是单独施加,还是共同作用,总是杂散电流越小,阴极保护电位越负,对碳钢的保护效果越好,腐蚀程度越轻。利用电化学交流阻抗技术监测管道腐蚀状况是可行的。     

Hydrogen uptake by structural steels at cathodic protection in sea water inoculated with sulfate reducing bacteria

The effect of sulfate reducing bacteria (SRB) on the hydrogen permeation rate through ferrite‐pearlite and sorbite steels of quite similar chemical composition was studied using a specially designed facility. Tests were carried out in synthetic sea water, sterile or inoculated with bacteria, at potentials corresponding to cathodic protection (? 800 mV to ? 1400 mV_NCE). Cathodic polarization within the studied potential range did not stop the metabolism of SRB. Presence of SRB was found to increase the hydrogen permeation rate, to form S^2? ions, to increase the polarization current, to modify the impedance spectrum and to change the appearance of cathodic deposits in comparison with sterile conditions. The promoting effect of SRB on the hydrogen uptake was concluded to be the result of the increase in polarization current due to the formation of the less protective layer of cathodic deposits on the steel surface, the presence of S^2? ions and the possible decrease in pH. Despite the similar tendencies, the effect of SRB on hydrogen uptake was more pronounced in the case of sorbite steel. The bacteria action can cause hydrogen deterioration of steel at potentials, recognized as safe ones at cathodic protection.     

CREVICE CORROSION BEHAVIOR OF X70 STEEL IN HCO_3~- SOLUTION UNDER CATHODIC POLARIZATION

The crevice corrosion behavior of XTO steel was investigated with a wedge-shaped crevice assembly under -1000 m V （SCE） cathodic polarization in the solutions with various HCO3 concentrations. The potential, current, pH and the oxygen content within the crevice were measured with or without outside coupled specimen. The results indicated that the polarization potential of XTO steel in the crevice dropped with the increase of time under the cathodic polarization. There was a remarkable influence of HCO3 concentration on the potential of XTO steel in the crevice. When HCO3 concentration was up to 0.125%, the surface of the metal was covered with the corrosion products that resulted in the polarization extent of XTO steel decreased. The pH value in the crevice rose and it dropped gradually from the crevice mouth to the bottom under the cathodic polarization. With the increasing of HCO3 concentration, the hydrolyzation reaction of metal in the crevice bottom aggravated. Most of the dissolved oxygen in the crevice was consumed by the cathodic current. The maximum cathodic current on the metal surface was at the crevice mouth and it was much more than that at the crevice bottom.     

CREVICE CORROSION BEHAVIOR OF THE STEEL X70 UNDER CATHODIC POLARIZATION

采用矩形缝隙装置, 测量了模拟剥离涂层下不同位置X70钢的电位、溶液pH值及氧含量随时间的变化曲线. 研究了外加阴极极化电位、涂层破损尺寸和缝隙厚度对X70钢在Na2SO4溶液中的缝隙腐蚀行为的影响. 结果表明, 缝隙内氧气迅速耗尽并使溶液pH值升高, 氧耗尽与外加阴极极化电位无关. 随着缝口阴极极化程度加大, 缝隙内各点电位负移, 有效保护距离增加. 溶液介质电位(IR)降集中在缝口. 极化程度过高会导致氢气的析出. 减小缝隙厚度和破损点尺寸使缝隙内极化程度降低.     

Potentialabhängigkeit der Schwingungsrißkorrosion von höherfestem Dalbenstahl in Salzwässern

Potential dependence of the corrosion fatigue of high strength sheet piling steel in salt water Cathodic protection of high strength steel, grade X 65, against corrosion fatigue (25 Hz) is not effective in seawater. An influence of hydrogen is assumed because hydrogen embrittlement occurs at slow strain-rates (not a constant load) under the condition of cathodic hydrogen evolution. The potential dependency of corrosion fatigue at 5 Hz was investigated with notched and smooth electropolished tensile specimens. The notched specimens showed a slight decrease of the number of cycles to failure with decreasing potential. The polished smooth specimens displayed cathodic protection. The results of the investigation can be explained by recent publications as an participation of hydrogen embrittlement, which happens only at critical strain rates and is dependent on the amount of straining, the frequency and the surface of the specimen.     

Relationship between electrochemical characteristics and SCC of X70 pipeline steel in an acidic soil simulated solution

Stress corrosion cracking (SCC) of X70 pipeline steel in simulated solution of the acidic soil in Yingtan in China was investigated using slow strain rate test (SSRT), SEM and potentiodynamic polarization technique. Experiment results indicate that X70 steel is highly susceptible to SCC as applied potential reduces, which is manifested in loss of toughness and brittle fracture. Constant polarization current can detect the occurrence of SCC. The lower the polarization current is the sooner stress corrosion cracking occurs. The SCC mechanisms are different at varying potentials. When potential is higher than open circuit potential, anodic process controls SCC, whereas when potential is far lower than open circuit potential, cathodic process controls SCC, and between these two potential regions, a combined electrochemical process controls the SCC. Stress or strain has a synergistic effect with electrochemical reactions to accelerate the cathodic hydrogen evolution process, which makes the X70 pipeline steel to be more susceptible to SCC.     

The effect of cathodic polarization on the corrosion behavior of X65 steel in seawater containing sulfate-reducing bacteria

Sulfate-reducing bacteria (SRB) are one of the main reasons for the accelerated corrosion of steel. Cathodic polarization has been reported as an effective and economic method against marine corrosion, including microbiologically induced corrosion. However, the interaction between cathodic polarization and microbial activity has not been well defined. In this study, a fluorine-doped tin oxide electrode is used to study the effect of cathodic current on SRB cells. Fluorescence microscopy results clearly show that the attachment degree of SRB is dependent on the electric quantity and current intensity. The large electric quantity and high cathodic current (400 mA/m² × 30 h) can effectively inhibit bacterial attachment and subsequent biofilm formation. Furthermore, the effect of cathodic potential on the corrosion behavior of X65 steel in the presence of SRB is systematically investigated. Results show that the impressed charges, the increase of pH, and the formation of calcareous deposits on the electrode surface at the cathodic potential of −1,050 mV/SCE inhibit the attachment of SRB. In turn, the presence of SRB also interferes with the electrochemical reactions that occur during the polarization process, thus increasing the cathodic current. The interaction between SRB-induced corrosion and the process of preventing corrosion by various cathodic potentials is discussed.