藤壶附着对低合金高强度钢牺牲阳极保护效果的影响

蔡凡帆, 黄彦良, 邢少华, 许勇, 王秀通

表面技术 ›› 2023, Vol. 52 ›› Issue (8) : 226-236.

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表面技术 ›› 2023, Vol. 52 ›› Issue (8) : 226-236. DOI: 10.16490/j.cnki.issn.1001-3660.2023.08.017
腐蚀与防护

藤壶附着对低合金高强度钢牺牲阳极保护效果的影响

  • 蔡凡帆1, 许勇1, 黄彦良2, 王秀通2, 邢少华3
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Effect of Barnacle Adhesion on Cathodic Protection of Low Alloy High Strength Steel by Sacrificial Anode

  • CAI Fan-fan1, XU Yong1, HUANG Yan-liang2, WANG Xiu-tong2, XING Shao-hua3
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摘要

目的 探索藤壶附着对低合金高强度钢阴极保护效果的影响,研究海洋中大型污损生物附着下金属材料的腐蚀规律。方法 在青岛胶州湾进行腐蚀挂板实海暴露实验,运用纱网箱隔离藤壶幼虫作为对照组。在暴露6个月和12个月后回收腐蚀挂板,研究藤壶附着后挂板腐蚀形貌、腐蚀产物和阴极保护效率的变化。在室内进行模拟实验,研究牺牲阳极对存在藤壶附着的钢的保护效果。结果 在施加牺牲阳极保护后,藤壶附着下的钢表面具有更明显的局部腐蚀坑,且多位于藤壶附着的边缘位置。藤壶附着对牺牲阳极保护效率的影响有限,藤壶附着钢的极化电位相较于无藤壶附着钢的极化电位更负,保护电流密度更小。藤壶附着钢的未附着区域的保护电流密度(63.9 μA/cm2)比无藤壶附着钢(46.3 μA/cm2)的保护电流密度高。XRD谱、拉曼光谱和SEM图表明,藤壶附着不影响腐蚀产物或沉积物的组成。结论 在牺牲阳极保护下,处于藤壶附着边缘和中心位置的钢,可作为氧浓差电池的阳极,在自催化的协同作用下,腐蚀过程加速,形成了严重的局部腐蚀。同时,藤壶附着可使钢的有效工作面积下降,导致藤壶附着下钢试样的无藤壶附着区域与不存在藤壶附着的钢试样相比,具有更高的保护电流密度和更负的极化电位。

Abstract

In order to study the effect of barnacle adhesion on the cathodic protection of low alloy high strength steel with sacrificial anode, comparative experiments were set up in the field site. The low alloy high strength steel used in this study was AISI 4135 steel and the sacrificial anode used in this study was 99.9% pure zinc. The steel was machined into corrosion coupons with two specifications of 350 mm×250 mm×4 mm and 60 mm×15 mm×4 mm respectively. Part of the small corrosion coupons were placed in a cage with plankton-filter of porosity 74 μm to prevent barnacle larva from contacting the surface of the corrosion coupons. Based on past long-term observational experiences, adhered barnacles were fairly abundant at the mid-tide level. Accordingly, the corrosion coupons were fixed at the mid-tide level. After being exposed for 6 and 12 months, the corrosion coupons were analyzed by advanced test techniques, such as X-ray diffraction, Raman spectra, confocal laser scanning microscope and electrochemical tests. Meanwhile, simulating experiments were conducted. The protection current and polarization potential of the low-alloy steel with barnacle adhesion under the protection of sacrificial anodes were monitored. After the experiments, the steel surface deposits were analyzed by scanning electron microscope (SEM) and energy dispersive spectrum (EDS). In the corrosion morphology analysis, the barnacle adhesion area was selected as the observation site of the corrosion coupons with barnacle adhesion, and the observation site of the corrosion coupons without barnacle adhesion was randomly selected. The corrosion morphology results demonstrated that localized corrosion pits formed on the steel substrate regardless of the presence or absence of barnacle adhesion. Meanwhile, it could be found that the steel with barnacle adhesion had larger localized corrosion pits, and tended to form at the edges of the barnacle adhesion. Near-circular raised corrosion morphology was formed in the barnacle adhesion area, while local corrosion pits similar to crevice corrosion were formed at the adhesion edge. The adhesion of barnacle did not affect the composition of corrosion products and deposits. Meanwhile, the content of calcite in the corrosion coupons with barnacle adhesion was higher, mainly from the barnacle shells. Mg2+ could inhibit the formation of calcite, accordingly, the corrosion products on the surface of the corrosion coupons without barnacle adhesion were mainly aragonite. Iron oxides in corrosion products were in the form of Fe3O4, γ-FeOOH, β-FeOOH and Fe5HO8.4H2O. The adhesion of barnacles had no apparent effects on the average corrosion rate of steel under cathodic protection state. Accordingly, the adhesion of barnacles had no apparent effects on the protection efficiency of sacrificial anodes. Polarization curves and current/potential-time curves under sacrificial anode protection suggested that the steel with barnacle adhesion required small polarization current only to reach the required protective potential. The area of the steel affected by the shielding effect of barnacle and the area where localized corrosion occurred were blocked from coming into contact with the external corrosive environment. Accordingly, barnacle adhesion could decrease the effective working area of the steel. Under the condition that the physical properties of the sacrificial anode remained unchanged, the smaller the area of the protected steel, the greater the current on the steel surface, and the closer the potential of the steel was to that of the sacrificial anode. Accordingly, the barnacle-free area of the steel with barnacle adhesion had a higher cathodic protection current (63.9 μA/cm2) than the steel without barnacle adhesion (46.3 μA/cm2), while, the barnacle adhesion area and the localized corrosion area were not effectively protected by cathodic protection. Excessively negative cathodic protection potential promoted hydrogen permeation behavior of the steel. The effects of barnacle adhesion on the hydrogen permeation behavior of steels under sacrificial anode protection are of important research interests both theoretically and practically.

关键词

藤壶;低合金高强度钢;牺牲阳极;局部腐蚀;保护效率;遮蔽作用

Key words

barnacle; low alloy high strength steel; sacrificial anode; localized corrosion; protection efficiency; shielding effect

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蔡凡帆, 黄彦良, 邢少华, 许勇, 王秀通. 藤壶附着对低合金高强度钢牺牲阳极保护效果的影响[J]. 表面技术. 2023, 52(8): 226-236
CAI Fan-fan, HUANG Yan-liang, XING Shao-hua, XU Yong, WANG Xiu-tong. Effect of Barnacle Adhesion on Cathodic Protection of Low Alloy High Strength Steel by Sacrificial Anode[J]. Surface Technology. 2023, 52(8): 226-236

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国家自然科学基金(41976033)

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