, 2017, 53(8): 975-982
doi: 10.11900/0412.1961.2016.00566
不同环境介质中X70钢的交流腐蚀行为及腐蚀产物膜层分析
Investigation on AC-Induced Corrosion Behavior and Product Film of X70 Steel in Aqueous Environment with Various Ions
张慧, 杜艳霞, 李伟, 路民旭
北京科技大学新材料技术研究院腐蚀与防护中心 北京 100083
ZHANG Hui, DU Yanxia, LI Wei, LU Minxu
Corrosion and Protection Center, Institute for Advanced Materials and Technology, University of Science and Technology Beijing, Beijing 100083, China
 Cite this article:
ZHANG Hui, DU Yanxia, LI Wei, LU Minxu. Investigation on AC-Induced Corrosion Behavior and Product Film of X70 Steel in Aqueous Environment with Various Ions. Acta Metallurgica Sinica[J], 2017, 53(8): 975-982 doi:10.11900/0412.1961.2016.00566

摘要:

通过交流腐蚀模拟实验考察了X70钢在4种环境介质中的交流腐蚀行为,获得了X70钢在4种介质中的腐蚀速率Kd。结果表明,腐蚀速率Kd (NaCl)>Kd Na2SO4)>Kd (CaCl2)>Kd (MgCl2)。采用SEM、EDS和XRD对腐蚀产物膜的表面/截面微观形貌、元素和物相成分进行了表征与分析,探讨了X70钢在相同交流电流密度下,不同介质中腐蚀速率差异的原因:在Na2SO4和NaCl介质中,腐蚀产物膜比较疏松,侵蚀性离子SO42-和Cl-的存在会加速X70钢的腐蚀,Na+不会影响腐蚀产物膜的形成;在MgCl2和CaCl2介质中,Ca2+和Mg2+的存在有利于形成保护性好的致密腐蚀产物膜。

关键词: X70钢 ; 交流腐蚀 ; 环境介质 ; 腐蚀速率 ; 腐蚀产物膜

Abstract:

During the past decades, more buried oil or gas pipeline failures have been attributed to alternating current (AC) interference, and finally, those corrosion failures were investigated and the AC current density was identified as the critical influence parameter. There is general agreement on AC current density as a chief factor in determining metal wastage condition or assessing the AC corrosion risk for any type of soil in the presence of AC corrosion. Different degrees of AC corrosion may occurr if long distance pipelines pass through different kinds of soil environments, however, the effect of soil ions on pipeline steel without cathodic protection is still not well understood. Therefore, it is imperative to study the AC corrosion behaviors of pipeline steel in different soil environments. In the AC corrosion simulation experiment, by investigating the AC corrosion behaviors of X70 steel in 4 kinds of environmental media, the corrosion rates (Kd) were obtained, whose order was Kd (NaCl)>Kd Na2SO4)>Kd (CaCl2)>Kd (MgCl2). SEM, EDS and XRD were used to characterize and analyse the microscope morphologies, elements and phase compositions of the corrosion product films surfaces/cross-sections. Under the same AC current density, the reasons of differences of X70 steel's corrosion rate in different media were discussed. The presence of corrosive ions SO42- and Cl- would accelerate the corrosion rate, Na+ would not affect the formation of corrosion product film in NaCl and Na2SO4 solution media, however, the presence of Ca2+ and Mg2+ were helpful to form protective corrosion product films in MgCl2 and CaCl2 solution media.

Key words: X70 steel ; AC corrosion ; environmental media ; corrosion rate ; corrosion product film

随着国民经济水平的不断提高以及城镇化建设步伐的不断加快,社会对能源的需求越来越大,大量的埋地油气管道和高压输电线路相继建设并投入使用。由于地理位置、地理资源等限制,不可避免地出现了埋地管道与高压输电线平行或者交叉运行的情况,并在局部地区形成了“公共走廊”[1]。这种情况下,埋地管道可能遭受来自高压输电线路的交流干扰,严重时可能会发生交流腐蚀。国内外越来越多的埋地管道因遭受交流干扰而发生交流腐蚀,使得管道出现泄漏或失效的问题。

研究者们[2~6]通过对这些管道交流腐蚀案例进行分析,认为交流电流密度是影响交流腐蚀最关键的因素,因此,众多标准把交流电流密度(JAC)作为判别管道能否发生交流腐蚀的关键因素[7~9],这些标准的应用范围对土壤介质没有明确要求。然而,Pourbaix等[10]通过实验证实,交流腐蚀的判别并不完全依赖于交流电流密度的大小。Goidanich等[11]认为,金属的交流腐蚀速率随着交流电流密度的增加而增加,但在不同的腐蚀介质中增长的幅度不一样。长输管道穿越不同类型的土壤时,其发生腐蚀的程度是不一样的[12]

长输管道会穿越各种类型的土壤环境,如:盐碱地环境、高pH环境、酸性土壤等,不同环境中各离子的含量也大为不同。周围环境中的离子也会对交流腐蚀产生一定的影响,这些离子有些可以通过直接或间接参与电极反应影响电化学过程,另一些可以生成致密腐蚀产物膜覆盖金属表面影响电极反应的传质过程[13,14]。近年来,国内外已有学者围绕不同离子(SO42-、Cl-、碱土金属离子、CO32-/HCO3-)对交流腐蚀的影响开展了研究工作。Prinz[15]和Helm等[16]指出,NaHCO3和CaCO3的存在会加速腐蚀,而NaCl则会抑制交流腐蚀的发生。而且交流腐蚀在流体中比在静止液体中更加严重,这可能是由于流体使得表面Ca2+和HCO3-供应量增多引起的。Fu等[17]发现,Cl-会向金属缺陷处迁移,并加快金属的溶解速率,从而提高腐蚀速率。尹可华等[18]研究发现,Ca2+和Mg2+会在金属附近形成碳酸盐薄膜,从而提高整个体系的电阻率,并降低腐蚀速率。杨燕[19]研究了X70管线钢在不同电解液中的腐蚀规律后发现,Cl-、SO42-以及HCO3-均对金属有侵蚀性,但当Cl-与SO42-共存时,SO42-具有缓蚀性,可以代替电极表面薄膜吸收Cl-,减弱其对金属的点蚀。Gummow等[3]将他人的实验结果进行了对比,指出在3.5%NaCl溶液中的交流腐蚀速率大于中性土壤中的交流腐蚀速率。Jüttner等[20]研究了交流电流密度为200 A/m2时,圆盘电极在硫酸盐、碳酸盐和氯化物水溶液中的交流腐蚀情况,实验结果显示,并没有明显的证据表明交流电流的存在改变了阴、极阳极反应。

可见,尽管国内外学者围绕离子对交流腐蚀的影响开展了部分研究,但目前尚未形成统一的认识,同时对不同离子环境下交流腐蚀的发展机制尚缺乏深入的研究,围绕离子对交流腐蚀产物膜的形成及其成分影响的研究较少,且多数交流腐蚀研究是在单一介质中进行,很少有将多种介质中的腐蚀行为进行对比分析,同时,多数研究将去离子水作为腐蚀介质的载体,该类型腐蚀介质不能较好地反映土壤结构对腐蚀产物膜的影响。因此,本工作选用石英砂(纯度99%,主要成分为SiO2)和土壤模拟液作为腐蚀媒介,通过失重测试实验,及对腐蚀产物膜进行分析,研究了300 A/m2交流干扰下X70钢在4种不同腐蚀介质中的交流腐蚀行为及腐蚀产物膜层特点。

1 实验方法

实验装置如图1所示。实验装置回路包括沃森BP6005交流电源(电流频率50 Hz)、滑动变阻器、10 Ω电阻、MMO辅助电极(CE)、参比电极(RE)以及工作电极(WE),工作电极与辅助电极之间的交流电流密度可通过调节滑动电阻器阻值来调节,参比电极采用饱和甘汞电极(SCE),将RE放入盐桥中,保持盐桥末端距试样表面1 mm。交流电为正弦波形,保持交流电流密度为300 A/m2不变,交流干扰时间(即腐蚀浸泡时间)为168 h。


图1

实验装置图

Fig.1

Diagram of experiment setup equivalent circuit (RE—reference electrode, WE—working electrode, CE—counter electrode)

工作电极材质为X70钢,其主要化学成分(质量分数,%)为:C 0.061,Si 0.24,Mn 1.53,P 0.011,S 0.0009,Fe 余量。尺寸为20 mm×20 mm×8 mm。

X70钢试样实验前处理流程:首先,将试样的6个面使用水磨砂纸逐级打磨至800号,直至表面光滑、无明显划痕。然后依次使用去离子水、无水乙醇等清洗并吹干。其次,采用FA2004B电子天平(精度为0.1 mg)称重并记录,用绝缘胶将工作面密封,将试样的非工作面用导电铜胶与导线粘在一起。最后,将试样用石蜡封入PVC管中,保留1个4 cm2的工作面,确保封装后工作面表面没有气泡和凹槽。实验所用4种模拟环境介质参数如表1所示。

表1

模拟环境介质参数

Table 1

Parameters of simulation corrosion media

待168 h的腐蚀实验结束以后,立即将工作电极取出。然后,使用Rigaku Dmax-RB型X射线衍射仪(XRD)进行物相分析(参数:40 kV,150 mA,Cu靶,扫描范围10°~90°,步宽0.02°),采用附带能谱(EDS)的GSM-6510A型扫描电子显微镜(SEM)对腐蚀产物膜进行微观形貌观察和元素分析。采用酸洗液(500 mL盐酸+500 mL去离子水+3.5 g六次甲基四胺)将试样表面的腐蚀产物去除干净,并在丙酮中超声波清洗干净,清洗5 min。最后,待试样清洗后冷风快速吹干,用电子天平测量其失重,利用下式计算其腐蚀速率:

K d = 8.76 × W 0 - W Stρ × 10 4 (1)

式中,Kd为腐蚀速率,mm/a;W0为试样腐蚀前质量,g;W为试样腐蚀后质量,g;S为试样暴露的面积,cm2;t为测试时间,h;ρ为试样的密度,g/cm3

2 实验结果
2.1 腐蚀速率

图2为300 A/m2交流干扰下X70钢在4种介质中腐蚀168 h后的腐蚀速率。可以看出,300 A/m2交流干扰下,X70钢在不同介质中的腐蚀速率差异较大。X70钢在Na2SO4和NaCl介质中腐蚀速率较高,分别为0.93和0.98 mm/a,在MgCl2和CaCl2介质中的腐蚀速率相对较低,分别为0.41和0.54 mm/a。


图2

300 A/m2交流干扰下X70钢在4种介质中腐蚀168 h后的腐蚀速率

Fig.2

Corrosion rates of X70 steel under alternating current (AC) interference density of 300 A/m2 in 4 kinds of simulated media exposed for 168 h

2.2 腐蚀产物膜成分

图3为300 A/m2交流干扰下X70钢在4种介质中腐蚀产物的XRD谱。可以看出,在Na2SO4介质中,腐蚀产物主要为γ-FeO(OH)、α-FeO(OH)、Fe(OH)3、Fe2O3H2O和Fe3O4;在MgCl2介质中,腐蚀产物中主要为β-FeO(OH)和Fe(OH)3;在CaCl2介质中,腐蚀产物中主要为β-FeO(OH);在NaCl介质中,腐蚀产物中主要为γ-FeO(OH)、α-FeO(OH)、β-FeO(OH)、Fe(OH)3、Fe2O3H2O和Fe3O4


图3

300 A/m2交流干扰下X70钢在4种介质中腐蚀产物的XRD谱

Fig.3

XRD spectra of the corrosion product films on X70 under AC interference density of 300 A/m2 in simulated media of Na2SO4 (a), MgCl2 (b), CaCl2 (c) and NaCl (d)

2.3 腐蚀产物膜微观形貌

图4和5分别为X70钢在4种介质中腐蚀产物膜表面与截面微观形貌的SEM像。可以看出,X70钢在4种介质中生成的腐蚀产物膜均存在分层现象,分为内层膜和外层膜,其截面形貌疏密程度与其表面腐蚀产物的疏密程度相对应。4种介质中的内层膜均比外层膜更为致密,在Na2SO4和NaCl介质中的内层膜相对疏松,并存在微小孔洞和微观裂纹等微观缺陷,而在MgCl2和CaCl2介质中内层膜整体更为致密,无明显微观缺陷。在NaCl介质中生成的腐蚀产物膜最厚,达97 μm,在Na2SO4和CaCl2介质中生成的腐蚀产物膜厚度分别约为79和73 μm,在MgCl2介质中生成的腐蚀产物膜最薄,约为32 μm。


图4

X70钢腐蚀产物膜表面微观形貌的SEM像

Fig.4

Low (a, c, e, g) and high (b, d, f, h) magnified surface SEM images of corrosion product films on X70 steel in simulated media of Na2SO4 (a, b), MgCl2 (c, d), CaCl2 (e, f) and NaCl (g, h)


图5

X70钢腐蚀产物膜截面微观形貌的SEM像

Fig.5

Low (a, c, e, g) and high (b, d, f, h) magnified cross-sectional SEM images of corrosion product films on X70 steel in simulated media of Na2SO4 (a, b), MgCl2 (c, d), CaCl2 (e, f) and NaCl (g, h)

图4还可以看出,在Na2SO4和NaCl介质中,腐蚀产物膜表面高低不平,外层膜为一层疏松多孔的絮状物,堆积在内层膜表面,使得膜表面的均匀性和致密性较差,该结构对内层膜构不成保护作用。在MgCl2和CaCl2介质中,产物膜表面形貌单一的颗粒状物质堆积在一起,彼此之间紧密结合在一起,结构致密,可以较好地保护内层膜。

2.4 腐蚀产物膜截面EDS分析

图6为X70钢在4种介质中腐蚀产物膜截面成分的EDS分析。可以看出,腐蚀产物膜主要包含Fe、O和Si元素,说明产物膜成分以Fe的混合氧化物为主。Si来源于石英砂,其主要成分为SiO2,腐蚀过程中小的SiO2颗粒进入膜层之中所致。


图6

X70钢在4种介质中腐蚀产物膜截面成分的EDS分析

Fig.6

EDS analyses of inner corrosion product films (a, c, e, g) and outer corrosion produt films (b, d, f, h) on X70 steel in simulated media of Na2SO4 (a, b), MgCl2 (c, d), CaCl2 (e, f) and NaCl (g, h)

在Na2SO4和NaCl介质中的腐蚀产物膜中分别存在S和Cl元素,未发现Na元素,表明腐蚀过程中SO42-和Cl-能够穿透腐蚀产物膜,进入到基体/膜界面,从而加剧X70钢的腐蚀。在Na2SO4和NaCl介质中,与金属接触的内层膜Fe:O原子比约为1:3,结合XRD谱(图3a和d),表明该内层膜主要成分为混合有Fe2+、Fe3+γ-Fe2O3γ-FeO(OH)以及Fe(OH)3,最外面的锈层成分主要是α-FeO(OH)和α-Fe2O3[19]γ-FeOOH是一种针状物质,为热力学的亚稳态FeOOH,α-FeOOH是一种短棒状物质,为热力学稳态FeOOH[21~23],外膜层的α-FeO(OH)由内膜层的γ-FeO(OH)转化而来[24]

在MgCl2介质中内层膜Fe:O原子比约为1:3,表明内层膜成分主要为Fe(OH)3;外层膜Fe:O原子比约为1:2,结合XRD结果(图3b)表明外层膜成分主要为β-FeO(OH)。在CaCl2介质中,内部与外部的产物膜Fe:O原子比均约为1:2,结合XRD谱(图3c),表明内、外层膜成分主要均为β-FeO(OH)。同时,在MgCl2和CaCl2介质中的产物膜中分别存在Mg和Ca元素,并没有发现含有Mg2+和Ca2+的化合物,表明Mg2+和Ca2+的存在影响了膜层的生成过程,使得膜层比较致密,对基体具有较好的保护性。

3 分析讨论

图1可以看出,在300 A/m2的交流干扰下,X70钢在不同环境中的腐蚀速率差异较大。X70钢在Na2SO4和NaCl介质中的腐蚀速率较高,在MgCl2和CaCl2介质中腐蚀速率较低,表明环境介质对管线钢的交流腐蚀过程有着重要的影响。图3所示的XRD谱表明,X70钢在4种介质中的腐蚀产物膜的成分不尽相同,X70钢在4种介质中均发生了电化学腐蚀。

图4和5可以看出,X70钢在Na2SO4和NaCl介质中生成的腐蚀产物膜表面疏松多孔,介质中侵蚀性离子SO42-和Cl-容易在腐蚀产物膜表面活性较大的位置发生吸附,容易引起膜的不均匀性溶解[25],从而为侵蚀性离子不断进入内层膜提供更多的离子通道。SO42-对X70钢的腐蚀影响较大,在SO42-存在时Fe会发生如下反应:

Fe + S O 4 2 - FeS O 4 + 2 e - (2)

2 FeS O 4 + 2 NaOH + O 2 F e 2 O 3 · H 2 O + N a 2 S O 4 (3)

由于Na2SO4能够再生,使得X70钢基体不断被腐蚀[26]

在Na2SO4和NaCl介质中,腐蚀产物膜均含有γ-FeO(OH)、α-FeO(OH)和Fe2O3H2O,γ-FeO(OH)能够参与阴极反应从而促进了膜下金属的腐蚀,α-FeO(OH)为多孔结构,并具有较高的阴极反应活性,腐蚀过程受电解质在多孔膜中的扩散过程控制,也参与了腐蚀反应[27]。同时,α-Fe2O3的溶解度很低且结构疏松多孔,会进一步生成Fe2O3H2O,促进反应的进行,随着Fe2O3的增多,Fe溶解量也随之增加[28]。疏松的产物膜及膜内的缺陷容易造成侵蚀性离子吸附和滞留在微观缺陷内,成为了腐蚀介质的流通通道[29],这样的腐蚀产物膜并不能有效地阻止SO42-和Cl-与X70钢表面的直接接触,使得X70钢基体腐蚀较为严重。

在MgCl2和CaCl2介质中,腐蚀产物膜均含有β-FeO(OH),与α-FeO(OH)一样,β-FeO(OH)的化学性质相对稳定,不易与其它物质发生反应。产物膜中微孔、裂纹等缺陷较少,致密性较好,使得介质中的Cl-很难通过产物膜进入膜/基体界面处,因此在MgCl2和CaCl2介质中,Cl-对腐蚀过程的影响大大减小,腐蚀速率较低。

4 结论

(1) 在300 A/m2的交流干扰下,X70钢在4种不同介质中腐蚀168 h后的腐蚀速率差异较大,腐蚀速率 K d ( NaCl ) > K d N a 2 S O 4 ) > K d ( CaC l 2 ) > K d ( MgC l 2 ) ,表明交流腐蚀速率不仅与交流电流密度有关,还与环境相关。

(2) X70钢在Na2SO4和NaCl介质中生成的腐蚀产物膜比较疏松,对基体无保护作用;Na+不会影响腐蚀产物膜的形成,侵蚀性离子SO42-和Cl-的存在会加速X70钢的腐蚀。X70钢在MgCl2和CaCl2介质中生成的腐蚀产物膜比较致密,对基体有保护作用;Mg2+和Ca2+的存在影响腐蚀产物膜的形成,有利于在X70钢表面形成致密的保护膜,降低腐蚀速率。

The authors have declared that no competing interests exist.

参考文献

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Jiang Z T, Du Y X, Dong L, et al.Effect of AC current on corrosion potential of Q235 steel[J]. Acta Metall. Sin., 2011, 47: 997
URL
利用室内模拟实验研究了交流电密度、电解质组分以及交流电频率对Q235钢腐蚀电位的影响规律.研究结果表明,交流电会使Q235钢腐蚀电位发生正向或负向偏移,偏移方向与Q235钢在不同电解质中阴、阳极极化速率有一定的相关性;偏移量随交流电密度增大而增大,随交流电频率增大而减小.结合金属界面双电层模型和腐蚀产物分析,对交流电引起Q235钢腐蚀电位偏移的机理进行了探讨.
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Abstract The corrosion rates of low alloy steel and carbon steel in 0.1 N NaCI were accelerated by factors of 4 to 6 when an alternating current density of 30 mA/cm2 (60 cps) was applied in dilute salt solutions purged with nitrogen. Tests with low frequency alternating anodic and cathodic current showed that both steels polarized more rapidly in the cathodic direction than in the anodic. Thus, the anodic half-cycle of AC did not have time to restore the potential to its original value after the preceding cathodic half-cycle. The result is a net cathodic polarization which accelerates or “depolarizes” the anodic metal-dissolution reaction by lowering the anodic Tafel slope. Depolarization of the anodic reaction was confirmed by polarization measurements in the presence of AC. Depolarization of the anodic reaction by AC was also observed in aerated solutions, but the corrosion rate was controlled by diffusion of dissolved oxygen, and no increase in corrosion rate was measured. Possible mechanisms of anodic...
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Pookote S R, Chin D T.Effect of alternating current on the underground corrosion of steels[J]. Mater. Perform., 1978, 17(3): 9
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Results of tests involving imposition of 60 Hz AC at various densities in an oxygen concentration corrosion cell on DC between 2 electrodes are reported. AC imposed on DC increases the corrosion rate of steel in soil with high initial and then steady state attack following after a time interval. High densities increased attack rate and if sufficiently high, pitting. Corrosion products from AC-DC were friable. Temperature increases in the soil had negligible effect on corrosion rate. It is postulated that AC acts as a depolarizer and that reversible potential characteristics may be significant.
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Collet E, Delores B, Gabillard M, et al.Corrosion due to AC influence of very high voltage power lines on polyethylene-coated steel pipelines: Evaluation of risks-preventive measures[J]. Anti-Corros. Methods Mater., 2001, 48(4): 221
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Shows how observations (1993-1999) and on-site and laboratory measurements (1993-1996) have made it possible to define certain prevalent parameters concerning AC corrosion risks. These are from the evaluation and prevention of AC corrosion risks as practised by Gaz de France.
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Pourbaix A, Carpentiers P, Gregoor R.Detection and assessment of alternating current corrosion[J]. Mater. Perform., 2000, 39(3): 34
DOI:10.1016/S1044-5803(99)00072-8 URL
A measuring system to determine the rue peak potential, without ohmic drop error, is described. There is no alternating current (AC)-induced corrosion when the true max. peak potential is below the potential for cathodic protection (CP). Methods are studied to determine the importance of AC corrosion when the potential is higher than the critical potential for CP during a part of the AC period.
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Pipelines and AC power transmission lines frequently share corridors leading to AC interference corrosion problems, as documented by pipeline failures that have occurred in the USA, Canada and Europe, even when cathodic protection is applied. In order to investigate these phenomena, weight loss tests on carbon steel samples were performed in soil-simulating conditions (aerated and de-aerated sulphate solutions) at various AC current densities from 10 to about 900聽A/m. Tests on freely corroding samples showed that the corrosion rate increased as AC current density increased; the effect of AC on corrosion rate was also detected at current densities lower than 30聽A/m. The results obtained are analyzed and discussed together with polarization test results, which were presented in a previous paper by Goidanich et al. (submitted for publication) [1].
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URL
ABSTRACT Overhead power lines are often placed in the same right of way as buried pipelines. Long term AC interference on a buried pipeline may cause corrosion due to an exchange of AC-induced current between the exposed bare metal at unavoidable coating defects in the structure and the surrounding soil. The exchange of current depends on the AC voltage whose amplitude is related to various parameters. The mechanism of the AC corrosion is not very well understood, particularly as it applies to corrosion in soils. The objective of this paper is to present the application of the model based on the conventional (DC) treatment of the corrosion processes to the case of cathodically protected pipeline. The adopted model suggests that the AC currents cause positive polarization shifts during the positive half period of the imposed AC sinwave along with negative polarization shifts in the negative half period. It is shown on an example, that during the cathodic (negative) semi-cycle, the current exhibits shifts to considerable magnitudes, much greater then the protective current. During the anodic semi-cycle the reduction current decreases, but not to the same degree as the increase during the cathodic semi-cycle. Therefore, the complete AC cycle results in a net increase in the reduction current.
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Fu A Q, Cheng Y F.Effects of alternating current on corrosion of a coated pipeline steel in a chloride-containing carbonate/bicarbonate solution[J]. Corros. Sci., 2010, 52: 612
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In this work, the alternating current (AC)-induced corrosion of a coated pipeline steel was studied in a chloride-containing, concentrated carbonate/bicarbonate solution, which simulated the trapped high pH electrolyte under coating, by potentiodynamic polarization measurements, immersion tests and surface characterization technique. It was found that an application of AC resulted in a negative shift of corrosion potential of the steel, caused an oscillation of anodic current density, and degraded the steel passivity developed in the solution. With the increase of AC current density, the corrosion rate of the steel increased. At a low AC current density, a uniform corrosion occurred, while at a high AC current density, pitting corrosion occurred extensively on the steel electrode surface. At individual applied AC, there was a higher electrochemical dissolution activity of the coated steel electrode containing a 1聽mm defect than that of the electrode containing a 10聽mm defect.
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[18]
(尹可华, 唐明华, 熊祥键. 埋地钢构筑物在工频电场作用下的腐蚀[J]. 中国腐蚀与防护学报, 1982, 2(3): 33)
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Magsci URL
本文提出了用电场理论和电化学理论相结合的方法来研究交流腐蚀这一途径。在变化极快,强度甚大的交流干扰电场作用下。金属的电化学腐蚀过程发生变化。此时,电场强度是一个重要的物理量。测量和分析了干扰电压、电位梯度、点电流密度、失重量及腐蚀坑深后,可以看出失重量随平均电流密度而增加,腐蚀坑深随干扰电压而加剧。根据埋片实验结果,初步提出了交流腐蚀临界安全电压指标。
[本文引用: 1]
[19]
(杨燕. X70钢交流腐蚀行为及机理研究 [D]. 青岛: 中国石油大学(华东), 2013)
Yang Y. AC corrosion behavior and mechanism of X70 pipeline steel [D]. Qingdao: China University of Petroleum (East China), 2013
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Jüttner K, Reitz M, Schäfer S, et al. Rotating ring-disk studies on the impact of superimposed large signal AC currents on the cathodic protection of steel [J]. Mater. Sci. Forum, 1998, 289-292: 107
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A method for detecting rotational speeds (n) of an internal combustion engine having a signal wheel having marks (M 1 through M 7 ) for signaling on a crankshaft of the internal combustion engine is described. The marks (M 1 through M 7 ) on the signal wheel are detected with the aid of a sensor and evaluated by a detection and evaluation device. To implement high-precision detection of a rotational speed, the rotational speeds (n) are evaluated using a sector section of approximately 6° to 35° to increase the accuracy on the basis of a reduced sector section of the signal wheel.
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[21]
Smith D C, McEnaney B. The influence of dissolved oxygen concentration on the corrosion of grey cast iron in water at 50 ℃[J]. Corros. Sci., 1979, 19: 391
DOI:10.1016/0010-938X(79)90037-4 URL
The formation of corrosion scales has been studied on grey cast iron in flowing water at 50°C as a function of O 2 concentrations from 0.1 to 3.95 ppm O 2. Below 1.0 ppm O 2, nodular scales form containing Fe 3O 4 and a green rust, GR. At higher O 2 concentrations, a continuous scale eventually forms, consisting of a porous subscale of Fe 2O 4 + GR overlaid with a compact crust of Fe 3O 4 + GR and a thin surface layer of γ-FeOOH. ‘Chimneys’ oriented in the water flow direction grow out of the crust. γ-FeOOH is reduced to Fe 3O 4 which becomes the principal constituent of the scale. Scales on cast iron components from central heating systems closely resemble those found in the present work.
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[22]
Raman A, Nasrazadani S, Sharma L.Morphology of rust phases formed on weathering steels in various laboratory corrosion tests[J]. Metallography, 1989, 22: 79
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The morphology and growth characteristics of rust phases formed on ASTM A-588 weathering steel in three different types of laboratory tests—accelerated atmospheric exposure simulation tests (AAEST), salt fog test, and continuous immersion test in plain as well as salt water—are analyzed using microstructural information obtained from representative exposed specimens studied in a scanning electron microscope (SEM). The ultimate and most dominant phase in the AAEST was α-FeOOH whereas an amorphous phase designated as amorphous bulk (AB) appeared as “cotton bolls” in the adherent, sedimentary layer formed on the steel surface during continuous immersion. Crystalline phases α-, δ-, and γ-FeOOH as well as γ-Fe 2O 3.H 2O were found developed on top of the first-formed sedimentary amorphous layer, containing another amorphous phase designated as amorphous mix (AM). Magnetite was the dominant phase obtained in the salt fog test. It forms in layers and seems to transform to α-FeOOH through formation of whiskers and rods on its surface. Sandy grains of γ-Fe 2O 3.H 2O were also seen in the rusts obtained in this test.
[23]
Majzlan J, Mazeina L, Navrotsky A.Enthalpy of water adsorption and surface enthalpy of lepidocrocite (γ-FeOOH)[J]. Geochim. Cosmochim. Acta, 2007, 71: 615
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Lepidocrocite (γ-FeOOH) appears to be thermodynamically metastable with respect to goethite (α-FeOOH) and yet the former phase forms and persists both in nature and laboratory. Here we show that the thermodynamic factors relevant to these observations cannot be dismissed, although kinetics undoubtedly plays a significant role in the formation and preservation of metastable phases. To understand the relationships of the FeOOH polymorphs in the bulk and nanoscale, we investigated the energetics of lepidocrocite nanoparticles. We measured enthalpy of water adsorption and enthalpy of formation of lepidocrocite samples with surface area of 42–103 m 2/g. Having both quantities measured allowed us to calculate the surface enthalpy for a water-free surface of this phase as 0.62 ± 0.14 J/m 2 and the energy of a relaxed (hydrated) surface as 0.40 ± 0.16 J/m 2. Our measurements show that a portion of the adsorbed water (6540% under laboratory conditions) is chemisorbed (strongly bound) with enthalpy of adsorption of 6165.8 ± 2.6 kJ/mol of H 2O relative to vapor (or 6121.8 ± 2.6 kJ/mol relative to liquid water). The standard enthalpy of formation from elements for a hypothetical lepidocrocite with nominal composition FeOOH and zero surface area is 61552.0 ± 1.6 kJ/mol. Our results demonstrate that when considering the thermodynamic properties of iron oxides in the environment, a conclusive statement about their stability cannot be made without specifying the particle size of individual phases.
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Misawa T, Asami K, Hashimoto K, et al.The mechanism of atmospheric rusting and the protective amorphous rust on low alloy steel[J]. Corros. Sci., 1974, 14: 279
DOI:10.1002/chin.197420046 URL
Atmospheric rusting of mild and low alloy steels was studied by means of infra-red and far infra-red spectrophotometries, X-ray and electron diffraction methods and scanning electron microscopy. The rusting process can be interpreted on the basis of a previously reported diagram for rust formation in aqueous solution. A large amount of amorphous matter in rust formed in semi-rural atmosphere was identified by infra-red and far infra-red spectra as amorphous ferric oxyhydroxide, FeO x (OH) 8鈥2x. The amorphous ferric oxyhydroxide rust on low alloy steel was dense and uniform, and contained a considerable amount of bound water. From these results it can be concluded that the amorphous ferric oxyhydroxide rust acts as a protective barrier against atmospheric rusting of the steels. Cu, P and Cr in low-alloy steels are inferred to favour the formation of crack-free, uniform rust layer and help to produce uniform amorphous ferric oxyhydroxide.
[本文引用: 1]
[25]
(孙敏, 肖葵, 董超芳. 带腐蚀产物超高强度钢的电化学行为[J]. 金属学报, 2011, 47: 442)
Sun M, Xiao K, Dong C F, et al.Electrochemical behaviors of ultra high strength steels with corrosion products[J]. Acta Metall. Sin., 2011, 47: 442
URL
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[26]
(刘文霞, 孙成. 土壤中阴离子对碳钢腐蚀的影响[J]. 全面腐蚀控制, 2006, 20(6): 10)
Liu W X, Sun C.Effects of different cathodic ions on the corrosion of carbon steel in soils[J]. Total Corros. Control, 2006, 20(6): 10
DOI:10.3969/j.issn.1008-7818.2006.06.005 URL
用弱极化曲线技术和交流阻抗法研究了土壤中Cl^-,SO4^2-。 CO3^2-,NO3^-对碳钢腐蚀的影响。结果表明:阴离子对碳钢腐蚀的影响比较显著。当土壤中分别添加CL^-,CO3^2-,NO3^-时,随着阴 离子质量浓度的增加,碳钢的腐蚀速率增大,在某一离子质量浓度时,腐蚀速率达到最大,然后腐蚀速率随着离子质量浓度的增加而减小。在有SO4^2-的土壤 中随着SO4^2-质量浓度的增大,土壤中碳钢的腐蚀速率增大。在四种阴离子土壤中,阻抗谱均为单容抗弧,且大多在低频区出:见扩散弧。
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[27]
(谢颖, 李瑛, 孙挺. 原位生长的纯γ-FeOOH和α-FeOOH锈膜对Q235钢保护性能的研究[J]. 科学通报, 2008, 53: 2848)
Xie Y, Li Y, Sun T, et al.Study of the protective property of in-situ pure γ-FeOOH and α-FeOOH corrosion product film on Q235 steel[J]. Chin. Sci. Bull., 2008, 53: 2848
URL
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Lin J P, Ellaway M, Adrien R.Study of corrosion material accumulated on the inner wall of steel water pipe[J]. Corros. Sci., 2001, 43: 2065
DOI:10.1016/S0010-938X(01)00016-6 URL
The purpose of this study is to identify the chemical composition of corrosion material accumulated on the inner wall of a mild steel “water pipe”, and the iron species present. It will be shown that the material accumulated is predominantly derived from in situ iron corrosion processes rather than from the sedimentation of particles introduced into the water distribution system. The dominant iron species found was Fe(III) – >90%, with concentrations of Fe(II) and Fe free+amorphous (free and amorphous Fe) being <10%. The results also showed that the accumulated material was composed predominantly of goethite (α-FeOOH – 75.6%), with magnetite (Fe 3O 4 – 21.5%) and lepidocrocite (γ-FeOOH – 2.9%) also being present. It is assumed that FeOOH is derived from amorphous Fe(OH) 3 when it dehydrates.
[本文引用: 1]
[29]
(赵国仙, 陈长风, 路民旭. CO2腐蚀的产物膜及膜中物质交换通道的形成[J]. 中国腐蚀与防护学报, 2002, 22: 363)
Zhao G X, Chen C F, Lu M X, et al.The formation of product scale and mass transfer channels during CO2 corrosion[J]. J. Chin. Soc. Corros. Prot., 2002, 22: 363
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