Prevention of steel corrosion in concrete exposed to seawater with submerged sacrificial anodes

This paper presents the results of a study of the effectiveness of submerged sacrificial anodes in preventing the onset of pitting corrosion in the emerged part of marine piles. Experimental tests were carried out on reinforced concrete columns with steel embedded both in chloride free concrete and chloride contaminated concrete in order to compare the effects of sacrificial anodes on passive steel and on corroding steel. Results have shown, at least under the present testing conditions, that sacrificial anodes may be more effective in preventing corrosion initiation (i.e. in providing cathodic prevention) than in controlling ongoing pitting corrosion (i.e. in guaranteeing cathodic protection). Monitoring criteria for this type of prevention are also discussed.     

Cathodic protection of steel in concrete using magnesium alloy anode

Corrosion of steel embedded in concrete structures and bridges is prevented using cathodic protection. Majority of the structures protected employ impressed current system. Use of sacrificial system for the protection of steel in concrete is not as widely employed. The use of magnesium anodes for the above purpose is very limited. This study has been carried out with a view to analyse the use of magnesium alloy anode for the cathodic protection of steel embedded in concrete.Magnesium alloy anode, designed for three years life, was installed at the center of reinforced concrete slab, containing 3.5% sodium chloride with respect to weight of cement, for cathodic protection. Potential of the embedded steel and the current flowing between the anode and the steel were monitored, plotted and analyzed. Chloride concentration of concrete at different locations, for different timings, were also determined and analyzed.The magnesium anode was found to shift the potential of the steel to more negative potentials initially, at all distances and later towards less negative potentials. The chloride concentration was found to decrease at all the locations with increase in time. The mechanism of cathodic protection with the sacrificial anode could be correlated to the removal of corrosive ions such as chloride from the vicinity of steel.     

Electrochemical measurements of cathodic protection for reinforced concrete piles in a marine environment using embedded corrosion monitoring sensors

This study developed a sensor to monitor the corrosion of reinforced concrete structures. Concrete pile specimens with embedded sensors were used to obtain data on corrosion and cathodic protection for bridge columns in a real marine environment. Corrosion potential, cathodic protection current density, concrete resistivity, and the degree of depolarization potential were measured with the embedded sensors in concrete pile specimens. The cathodic protection (CP) state was accurately monitored by sensors installed in underwater, tidal, splash, and atmospheric zones. The protection potential measurements confirmed that the CP by Zn-mesh sacrificial anode was fairly effective in the marine pile environment. The protection current densities in the tidal, splash zones were 2–3 times higher than those in underwater and atmospheric zones. The concrete resistivity in the tidal and splash zones was decreased through the installation of both mortar-embedded Zn-mesh (sacrificial anode) and outside an FRP jacket (cover). Considering the CP, the cathodic prevention was more effective than cathodic protection.     

复合式牺牲阳极保护钢管桩的试验研究

本文报道在淡水环境中采用铝合金和镁合金复合式牺牲阳极对钢管桩进行阴极保护的可行性研究。分别检测了安装3组、4组或5组复合牺牲阳极后,钢管桩1天和7天的极化电位,评估了该方案的实际保护效果,确定了较为合理的镁合金与铝合金牺牲阳极的用量和比例。     

冷却消声器牺牲阳极保护的模拟试验研究

海水冷却消声器选用316L不锈钢制造,并采用牺牲阳极的阴极保护方法.为验证牺牲阳极保护设计的合理性和检验保护效果,在1:1模拟样器上模拟实际工况测定了冷却器水套的电极电位分布和牺牲阳极块的失重.结果表明防蚀方案可行,设计合理,保护充分     

Polarisation behaviour of steel bar samples in concrete in seawater. Part 2: A polarisation model for corrosion evaluation of steel in concrete

In the companion paper [Z.T. Chang, B. Cherry, M. Marosszeky, Polarisation behaviour of steel bar samples in concrete in seawater, Part 1: Experimental measurement of polarisation curves of steel in concrete, Corrosion Science 50(2) (2008) 357-364], influences of the experimental procedure on measured polarisation curves of steel in concrete in seawater were investigated. It was found that an undistorted full polarisation curve of a steel sample in concrete can be obtained by the two-test procedure to conduct separate anodic and cathodic polarisation tests and combine the two partial curves into one curve. However, polarisation curves of steel samples in concrete in seawater were found not to fit with the theoretical curves based on the kinetics of charge transfer reactions. This was considered to be due in the main to the influence of a passive film on the steel surface in concrete. This paper proposes an empirical model for the polarisation behaviour of steel in concrete based on the assumption of two major electrochemical processes taking place at the interfaces of steel/passive-film/concrete: one is the active corrosion process and the other is the passive film growth or dissolution process. Typical curve-fit results are presented using the proposed model to simulate the polarisation behaviour and to evaluate the corrosion rate and Tafel parameters of three types of steel corrosion in seawater: steel bars in concrete, new steel bars and corroded steel bars.     

Possibility of High Phosphorus Pig Iron as Sacrificial Anode

Cathodic protection is an effective method to control the corrosion of underground pipelines and submerged structures. In the present work, high phosphorus containing pig iron was utilized as sacrificial anode for cathodic protection of underground mild steel plates and the results were compared with that of a commercially pure magnesium sacrificial anode. Driving potential and current between the galvanically coupled sacrificial anodes and mild steel plates were continuously monitored in real time for one month. Microstructure and morphology of the corrosion products formed on the surface of pig iron, magnesium sacrificial anodes and mild steel plates were observed with the help of optical microscope and scanning electron microscopy, and phase identification were performed using x-ray diffraction, Raman spectroscopy and Fourier transform infrared spectroscopy. The distribution of phosphorus in the pig iron matrix and soluble rust formation on the surface of pig iron under buried condition were critical from the point of sacrificial effect, indicating the possible scientific reasons for high phosphorous pig iron to be used as sacrificial anode.     

Development of nano cerium oxide incorporated aluminium alloy sacrificial anode for marine applications

Aluminium-zinc alloy sacrificial anodes are extensively used for cathodic protection. The performance of the sacrificial anodes can be significantly improved by incorporation of microalloying elements in the aluminium matrix. In the present work nano cerium oxide particles of different concentrations, ranging from 0 to 1 wt% were incorporated for activating and improving the performance of the anode. The electrochemical test results revealed the increased efficiency of the anode. The electrochemical impedance spectroscopy revealed the information that the presence of nano cerium oxide in the anode matrix caused effective destruction of the passive alumina film, which facilitated enhancement of galvanic performance of the anode. Moreover, the biocidal activity of cerium oxide prevented the bio accumulation considerably which enables the anodes to be used in aggressive marine conditions.     

格形板桩码头牺牲阳极阴极保护效果检测与评估

对华南某港口5万吨级码头格形板桩牺牲阳极阴极保护效果的检测,详细介绍了检测的内容和方法.本工作采用修正的计算公式,准确计算了阳极的剩余寿命,分析了码头端部钢桩保护电位偏低的原因,并提出了一些维修建议.     

用带状牺牲阳极对埋地钢管实施阴极保护时的电位和电流分布

用带状牺牲阳极对埋地长输钢管实施阴极保护时,沿着轴线方向的电位分布一定是均匀的。本文通过有限元法计算,进一步研究沿着管道圆周上的电位和电流分布的规律。结果表明,在研究的参数范围以内,沿着管道圆周的电位分布也是相当均匀的。土壤电阻率越低,电位极化值越大,但所需的保护电流也增大。防护性能好的涂层总是有利于阴极保护。阳极距离和管道外径对电位和电流分布没有什么影响。这些结果可以供工程上参考,同时说明用带状牺牲阳极对埋地长输钢管实施阴极保护是十分理想的。     

Responsive behaviour of galvanic anodes in concrete and the basis for its utilisation

In this study, a unique concrete specimen was used to analyse the response of embedded sacrificial zinc and steel anodes to rainfall and fluctuations in temperature. Current from the zinc and steel anodes increased when the environment was aggressive, showing that the required protection current depends on the present level of corrosion risk. A basis for using the ‘responsive behaviour’ of galvanic anodes is provided by the protective effects of pit re-alkalisation and pH maintenance. By contrast, protection based on achieving adequate polarisation inhibits the use of responsive behaviour and galvanic anodes might only deliver adequate polarisation in aggressive environments.     

中碳钢在海水中阴极保护紫铜的二维有限元法计算研究

对于中碳钢在海水中作为牺牲阳极阴极保护紫铜而建立了6个二维物理模型.对Laplace方程进行了弱形式推导以便于有限元法计算.用有限元法模拟计算了各物理模型阴极保护体系的电位分布,并进行实验验证.结果表明,二维有限元法能很好地模拟该阴极保护体系的电位分布.在小范围内中碳钢和紫铜电偶对的距离远近对电位分布影响不大.各模型中具有代表性的X轴、Y轴方向的电位模拟计算值与实测值接近.中碳钢阴极保护紫铜具有可行性,有限元法计算能够为其阴极保护设计提供依据.     

国产铁基牺牲阳极在冷却器上的应用

依据阴极保护的理论分析了铁基牺牲阳极保护铜冷却器的可行性;收集了几种典型的国产铁基牺牲阳极材料与俄罗斯的铁基牺牲阳极材料进行了室内电化学保护性能对比,并且选取了国产Q235B材质的铁基牺牲阳极与俄罗斯的CT3nc材质铁基牺牲阳极,在实船冷却器上进行了对比应用试验。结果表明,国产铁基牺牲阳极材料的电化学性能与俄罗斯的阳极材料相当,工作电位处于船用铜合金的保护电位范围,电流效率略高于俄罗斯铁基牺牲阳极;实船试验选用的国产Q235B材质铁基牺牲阳极,其活化性能略优于俄罗斯的CT3nc材质铁基牺牲阳极,其保护期效远长于传统的锌合金牺牲阳极。     

海工钢筋混凝土结构热喷涂牺牲阳极保护研究

本文研究了沿海钢筋混凝土结构阴极保护的热喷涂牺牲阳极,实验通过电化学方法和金相显微等方法以及模拟试验深入研究了热喷涂对牺牲阳极性能的影响,发现热喷涂牺牲阳极较传统牺牲阳极具有更高的综合性能,成功地将热喷涂的方法应用到了牺牲阳极领域,解决了钢筋混凝土结构中牺牲阳极初始驱动电位不足的问题。     

崇启大桥钢管桩使用现状及防腐蚀效果评价

崇启大桥钢管桩投入使用以来,从未对钢管桩防腐蚀进行过系统的检测。通过钢管桩上挂片检测、阳极外观检查、阳极消耗量检测等来评价大桥钢管桩的使用现状及防腐蚀效果。结果表明,服役8年多后,崇启大桥的钢管桩被保护极好,牺牲阳极尚可使用50余年,其余阳极的剩余寿命基本达100年甚至200年以上。     

铁基牺牲阳极性能及其对12Cr钢管的阴极保护

采用恒电流试验测试了铁基材料在海水中的牺牲阳极性能,并结合12Cr钢管的极化和循环伏安曲线测试以及阴极保护的实海试验,分析了铁基阳极用于12Cr钢管牺牲阳极保护的可行性。结果表明,所选铁基阳极中材料C具有良好的牺牲阳极性能,工作电位稳定,电流效率高,溶解均匀,消耗慢;对12Cr钢管进行阴极保护时具有足够的驱动电压;实海阴极保护试验显示铁基阳极材料C对12Cr钢管有良好的保护效果。     

Zn-Al-Cd合金对20#钢牺牲阳极保护行为

以工厂换热器为研究背景,采用极化技术和自放电法,研究了不同温度下Zn-Al-Cd合金牺牲阳极和纯Zn阳极在地下井水和模拟海水中对20#钢的牺牲阳极电化学性能。开路电位、工作电位及极化曲线的测试结果表明：在30~80 ℃范围内,Zn-Al-Cd合金、纯Zn和20#钢在两种介质中均未出现电位极性逆转现象,牺牲阳极具有良好的电化学性能;Zn-Al-Cd合金在地下井水中生成的保护膜比模拟海水中的稳定;牺牲阳极合金成分的优化,可以有效防止电位逆转行为。     

Ten‐year results of galvanic sacrificial anodes in steel reinforced concrete

Zinc sacrificial anodes have been included in patch repairs to steel reinforced concrete structural elements suffering from corrosion since the mid‐1990s. A number of these anode‐containing repairs have been monitored with time. One of the first monitored sites was of a locally repaired cross beam of a bridge structure in Leicester, UK, which has now completed 10 years since its original repair and anode installation. This paper reviews the performance of the anodes installed at the Leicester site in terms of anode current output and steel reinforcement polarisation and corrosion rate over the period. It also presents results of analysis of recovered anodes exposed for 10 years which still show electrolyte continuity, uniform consumption of the zinc and coherent encasing mortar. The knowledge gained from the 10 year results has enabled the development of new, higher current output anodes, which are now trialled in this and other sites.     

舟山某码头钢管桩牺牲阳极阴极保护系统检测

舟山某码头钢管桩采取牺牲阳极阴极保护已10余年。通过检测阳极的表面形貌,计算阳极使用寿命,测量保护电位和检查钢管桩腐蚀状况,对牺牲阳极保护效果进行了评价和分析。结果表明,10年间钢管桩受到了充分有效的保护,阳极剩余寿命在10年以上,实际使用寿命将大于设计寿命。     

Influence of Sn,Cd, and Si addition on the electrochemical performance of Al–Zn–In sacrificial anodes

Overcoming the reduction of current efficiency and stacking of corrosion products on the surface of Al–Zn–In sacrificial anodes after long-term use is of great significance for Al–Zn–In alloy as an anode material for cathodic protection of steel structures in seawater. In this study, four different sacrificial anode materials were prepared based on the Al-6Zn-0.03In (wt%) alloy without and with the addition of alloying elements of Sn, Cd, and Si, respectively. The influence of the addition of Sn, Cd, and Si on the microstructure and electrochemical performance of the Al–Zn–In anode was investigated by optical microscopy and electrochemical measurements. The results show that the introduction of Sn, Cd, and Si changes the microdendrite structure of Al–Zn–In to equiaxed grain. The added Sn, Cd, and Si alloys have more negative and stable working potential and uniformly dissolved morphology. The actual capacity and current efficiency of aluminum alloys increase from 2,000.6 Ah/kg and 70.7% of Al–Zn–In alloy to 2,539.4 Ah/kg and 88.6% of Al–Zn–In–Sn, 2,437.3 Ah/kg and 85.5% of Al–Zn–In–Cd and 2,500.4 Ah/kg and 88.8% of Al–Zn–In–Si alloys, respectively.