Influence of pH on corrosion behavior of carbon steel in simulated cooling water containing scale and corrosion inhibitors

In this paper, the influence of pH on the corrosion behavior of AISI 1020 carbon steel in simulated cooling water was investigated by using electrochemical and surface analysis methods. The results of polarization showed that the corrosion resistance of carbon steel increased with an increase in pH of the simulated water, and the corrosion control process changed from cathodic polarization to anode polarization control. The scale and corrosion inhibitor 2-phosphonobutane-1,2,4-tricarboxylic acid (PBTCA) had a certain anodic corrosion inhibition effect on carbon steel, whereas Zn²⁺ acted as a cathodic inhibitor for carbon steel in simulated water with pH 7–9. In simulated water containing both PBTCA and Zn²⁺, a good synergistic corrosion inhibition was found between PBTCA and Zn²⁺, and their corrosion inhibition effect on carbon steel was the best at pH 8. This was attributed to the formation of Zn(OH)₂ precipitate film in the cathode region and the formation of Zn–PBTCA complex film in the anode region at this pH.     

Theoretical considerations on the supposed linear relationship between concrete resistivity and corrosion rate of steel reinforcement

Traditionally, the assessment of service life of steel reinforced concrete structures has been focused on the prediction of the time required to achieve a transition from passive to active corrosion rather than to accurately estimate the subsequent corrosion rates. However, the propagation period, i.e. the time during which the reinforcing steel is actively corroding, may add significantly to the service life. Consequently, ignoring the propagation period may prove to be a conservative approach. On the other hand the prediction of the corrosion rate may result in a very complex task in view of the electrochemical nature of corrosion and the numerous parameters involved. In order to account for the various influences an essentially empirical model has been introduced in which the electrolytic resistivity of the concrete environment serves as the major parameter. This model will be discussed for carbonation‐induced corrosion based on the commonly accepted theory of aqueous corrosion. An alternative model for microcell corrosion is proposed which is based on the commonly accepted view that anodic and cathodic sites are microscopic and their locations change randomly with time. In line with this view electrolytic resistivity can be incorporated and thus may play a significant role in the kinetics of the corrosion process. For a wide range of corrosion current densities the relationship between corrosion current density, log(i_corr), and concrete resistance, log(R_con), can then be approximated by an almost ideal linear relationship. Assuming a fixed geometrical arrangement of anodic and cathodic sites on the steel surface, this linear relationship is also valid for concrete resistivity, ρ_con. However, from the theoretical treatment of the electrochemical processes underlying reinforcement corrosion it becomes evident that a linear relationship between corrosion current density and concrete resistivity does not necessarily imply that concrete resistance is dominating the overall corrosion cell resistance. In most cases a significant portion of the driving voltage of the corrosion cell will be consumed by the transfer of electrical charge involved in cathodic reactions, i.e. cathodic activation control will dominate.     

Corrosion and Stress Corrosion Cracking Behavior of X70 Pipeline Steel in a CO2-Containing Solution

The electrochemical corrosion and stress corrosion cracking (SCC) behaviors of X70 pipeline steel in CO₂-containing solution were studied by electrochemical measurements, slow strain rate tensile tests, and surface characterization. The results found that the electrochemical corrosion of X70 steel in aerated, alkaline solution is an activation-controlled process, and a stable passivity cannot develop on steel. Corrosion rate of the steel increases with the CO₂ partial pressure. The enhanced anodic dissolution due to the additional cathodic reaction in the presence of CO₂, rather than the film-formation reaction, dominates the corrosion process. The mass-transfer step through FeCO₃ deposit is the rate-controlling step in corrosion of the steel. The susceptibility of steel to SCC and the fracture brittleness increase with the CO₂ partial pressure. The enhanced fracture brittleness is attributed to the evolution and penetration of hydrogen atoms into the steel, contributing to crack propagation. The formed deposit layer is not effective in reducing hydrogen permeation due to the loose, porous structure.     

Corrosion behavior of API 5L X‐60 pipeline steel exposed to near‐neutral pH soil simulating solution

Steel gas pipelines are exposed externally to damage by surface corrosion and cracking phenomena. They are the main deterioration mechanism under coating failure and cathodic protection (CP) that can reduce the structural integrity of buried gas transmission pipelines where the soil aggressiveness and bacterial activity appear. Corrosion phenomenon is accentuated by the soil parameters influence such resistivity, pH, temperature, moisture content and chemical composition of electrolytes contained in the soil. Soil parameters influence on pipeline steel corrosion behaviour exposed in near‐neutral pH soil simulating solution has been investigated by potentiodynamic polarisation and EIS method. Results showed that the steel corrosion increases, corrosion current density increases with temperature in the range from 20 to 60 °C. The associated activation energy has been determined. Impedance curves showed that the charge transfer resistance (R_t) increases with increasing immersion duration. Parameters such as corrosion current density (I_corr), polarization resistance (R_p), and soil resistivity (ρ) can serve as the parameters for evaluation of soil corrosivity.     

Fe3C influence on the corrosion rate of mild steel in aqueous CO2 systems under turbulent flow conditions

The corrosion and corrosion inhibition of mild steel in CO₂ saturated solutions were studied under turbulent flow conditions at different pH. Electrochemical measurements using a.c. and d.c. techniques in uninhibited solutions of pH 3.8 indicated the formation of protective surface films (FeCO₃) in short immersion times. However, as the exposure time was increased the corrosion rate always increased, an effect attributed to the increased surface area of Fe₃C residue from corrosion of the steel. At pH 5.5, the corrosion rate always increased with time, behaviour also associated with the presence of Fe₃C surface film. The huge cathodic area of Fe₃C seems to have a more important impact on the electrochemical behaviour than the poorly formed FeCO₃ products. The effect of Fe₃C on inhibition by a quaternary amine inhibitor at pH 3.8 is to increase the corrosion rate as the pre-corrosion time is increased. The Fe₃C causes either (a) a cathodic area increase reflected in the corrosion rate increase with time or (b) a potential gradient in the pores of the Fe₃C layer that prevents positively charge amine ions from reaching all anodic sites.     

基于电化学方法5Cr钢熔化焊接头CO2腐蚀行为

为了获得5Cr钢熔化焊焊接接头的动态腐蚀特性,采用基于电极电位的电化学方法进行5Cr钢焊接接头耐CO₂腐蚀行为的研究,建立了基于极化曲线下的腐蚀模型,研究了不同填充材料的焊接接头的耐腐蚀性. 研究发现,在温度为40 ℃,CO₂分压为10个大气压等加速腐蚀条件下,低铬焊丝的焊缝区域的自腐蚀电位最正,腐蚀速率最小,高铬焊丝的焊缝区域的自腐蚀电位较正,腐蚀速率较小,无铬焊丝的焊缝自腐蚀电位最负,腐蚀速率最大. 对比只反应腐蚀前后质量变化的失重法,电化学方法反映了腐蚀周期任一时刻的动态腐蚀速率,基于电化学腐蚀模型下的腐蚀速率与失重法测量结果相吻合. 验证了电化学腐蚀模型的正确性. 结果表明,低铬钢匹配适当的低铬焊丝可使得焊接接头具有较强的耐CO₂腐蚀性能.     

Study on localized corrosion mechanism of 2195 Al‐Li alloy in 4.0% NaCl solution (pH 6.5) using a three‐electrode coupling system

Localized corrosion morphologies of 2195 Al‐Li alloy with various heat treatment in 4.0% NaCl solution (pH 6.5) were investigated, and its corrosion mechanism was studied using a three‐electrode coupling system of α (Al) substituting for the precipitate‐free zone (PFZ), simulated bulk θ′ (Al₂Cu) and T1 (Al₂CuLi). θ′ acts as cathodic zone in the alloy. At the initial stage, T1 phase is active with respect to θ′ and α (Al), and endures the main anodic current, indicating that anodic dissolution occurs on T1. However, its potential moves to positive direction with immersion time, due to dealloying of Li from T1. As a result, the main anodic dissolution occurs on α (Al) at a later stage. At this stage, as only T1 and α (Al) are coupled, T1 is cathodic to α (Al). In real 2195 alloy, T1 phase is very tiny, and anodic dissolution of T1 and PFZ occurs alternately. These results show that its intergranular corrosion or intersubgranular corrosion is caused by alternate anodic dissolution of T1 phase and PFZ along grain and subgrain boundaries.     

热浸镀锌层上钼酸盐转化膜的腐蚀电化学性能

    将热镀锌钢在含10 g/L Na₂MoO₄·2H₂O、pH为5的溶液中60℃下处理10~300秒,获得了钼酸盐转化膜试样.应用极化曲线和电化学交流阻抗谱(EIS)研究了转化膜层在5% NaCl水溶液的耐蚀性能.结果表明,经钼酸盐转化处理后的镀锌钢板,其腐蚀电流密度下降,极化电阻升高,阴极极化作用明显增强,腐蚀保护效率显著提高,电化学阻抗值提高了一个数量级;低频扩散阻抗值随处理时间的增加先增大后减小,表明腐蚀电解质在转化膜层孔隙中扩散的难易程度先增加后下降.     

西南地区某输油管道外腐蚀分析

目的研究西南地区某输油管道外腐蚀行为。方法现场检测,对土壤理化性质及腐蚀产物成分进行室内分析。结果开挖点A的土壤呈弱碱性,土壤腐蚀性弱,管道发生轻微均匀腐蚀,腐蚀产物主要为FeO(OH),Fe(OH)3和Fe3O4等铁的氧化物,对应的阴极反应为吸氧反应;开挖点B的土壤酸性强,硫酸根离子浓度高,土壤腐蚀性强,管道发生严重坑蚀,腐蚀产物主要成分为FeSO4·7H2O及少量碱式硫酸铁,对应的阴极反应以析氢反应为主。结论开挖点土壤的理化性质差异,导致管道的腐蚀形态、腐蚀产物和腐蚀机理显著不同。     

EIS characterisation of the layer of corrosion products on various substrates in differing atmospheric environments

The layer of corrosion products forming on zinc in atmospheric environments of varying aggressivity have been characterised and compared with previous results obtained for carbon steel. The characteristics of said layers have been linked to the nature of the products found. Likewise, we have found that EIS is a useful tool towards characterising the layers of corrosion products of carbon steel and zinc. The equivalent circuit which gives the best fit of impedance data for both metals is type R(C(R(C(R(CR))))), where the Nyquist diagrams are composed of two time constants. It is observed that the value of the capacitance of the corrosion product layer (C_pc) diminishes as the time of exposure increases, which is directly related with an increase in the thickness of the corrosion product layer. Also, it is observed that when the nature of the corrosion products doesn't vary with the time of exposure, the decrease of the charge transfer resistance is related with the increase in the thickness of the corrosion product layer.     

Effect of deformation temperature on precipitation,microstructural evolution,mechanical and corrosion behavior of 6082 Al alloy

The influence of cryorolling (CR), room temperature rolling (RTR) and post annealing on precipitation, microstructural evolution (recovery, recrystallisation and grain growth), mechanical and corrosion behavior, was investigated in the present work. The precipitation kinetics and microstructural morphology of CR, RTR, and post annealed samples were investigated by differential scanning calorimetry (DSC), transmission electron microscopy (TEM), and electron back scattered diffraction (EBSD) to elucidate the observed mechanical properties. After annealing at 200 °C, UTS and hardness of CR samples (345 MPa and HV 127) were improved as compared to RTR samples (320 MPa and HV 115). The increase in hardness and UTS of CR samples after annealing at 200 °C was due to precipitation of β″ from Al matrix, which imparted higher Zener drag effect as compared to RTR samples. The improvement in corrosion and pitting potentials was observed for CR samples (?1.321 V and ?700 mV) as compared to RTR samples (?1.335 V and ?710 mV). In CR samples, heavy dislocation density and dissolution of Mg₄Al₃Si₄-precipitates in the Al matrix have improved corrosion resistance of the alloy through formation of protective passive layer and suppression of galvanic cell, respectively.     

Novel corrosion experiments using the wire beam electrode: (III) Measuring electrochemical corrosion parameters from both the metallic and electrolytic phases

The wire beam electrode (WBE) and the scanning reference electrode technique (SRET) have been applied in a novel combination to measure, for the first time, electrochemical parameters simultaneously from both the metallic and electrolytic phases of a corroding metal surface. The objective of this work is to demonstrate the application of this combined WBE-SRET method in obtaining unique information on localised corrosion mechanism, by investigating typical corrosion processes occurring over a mild steel WBE surface exposed to the classic Evans solution. The WBE method was used to map current and potential distributions in the metallic phase, and the SRET was used to map current or potential distribution in the electrolytic phase. It has been found that the combined WBE-SRET method is able to gain useful information on macro-cell electrochemical corrosion processes that involve macro-scale separation of anodes and cathodes. In such macro-cell corrosion systems, maps measured using WBE and SRET were found to correlate with each other and both methods were able to detect the locations of anodic sites. However the movement of the scanning probe during SRET measurements was found to affect the SRET detection of cathodic sites. In micro-cell corrosion systems where the separation of anodic and cathodic sites were less distinct, SRET measurement was found to be insensitive in detecting anodic and cathodic sites, while the WBE method was still able to produce results that correlated well with observed corrosion behaviour. Results obtained from this work suggest that the WBE-SRET method is applicable for understanding the initiation, propagation and electrochemical behaviour of localised corrosion anodes and cathodes, and also their dependence on externally controllable variables, such as solution pH changes and the existence of surface coatings.     

Localised corrosion of cathodically protected pipeline steel under the effects of cyclic potential transients

Cathodic protection (CP) may lose its effectiveness for protecting buried steel pipeline from soil corrosion due to the effects of potential excursions caused by stray currents. In this work, dynamic localised corrosion processes of buried steel due to the effects of cyclic potential transients have been visualised using an electrochemically integrated multi-electrode array, often referred to as the wire beam electrode (WBE). The focus has been on the understanding of the effect of cathodic transients. The WBE maps suggest that the amplitude of cathodic transient, as well as the ratio of anodic cyclic to cathodic cyclic, can significantly affect the corrosion rates and patterns. In particular, if the cathodic transient leads to a very negative potential, e.g. ?1350?mV_vs.CSE, rapid corrosion would occur on buried steel surface. These results have implications for CP parameter selection for preventing stray current-affected buried steel pipelines.     

Electrochemical evaluation of the corrosion protectiveness and porosity of vacuum annealed CrAlN and TiAlN cathodic arc physical vapor deposited coatings

The corrosion behavior of cathodic arc physical vapor deposited CrAlN and TiAlN coatings were examined in 1 M HCl solution before and after vacuum annealing at 700, 800, 900, and 1000 °C. Electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization (PDP) methods were used to study the corrosion behavior and porosity of the coatings in comparison with the bare steel substrate (304SS). Structural and mechanical characterization of the coatings were also conducted. It is found that with increasing annealing temperature, the mechanical properties of TiAlN increased due to age hardening caused by spinodal decomposition while the hardness of CrAlN decreased as result of relaxation. Similarly, EIS and PDP results revealed that the as‐deposited and annealed coatings offer higher corrosion resistance as compared to the bare 304SS substrate. The coatings susceptibility to corrosion is reduced after annealing as indicated by the increasing nobility of E_corr. Both PDP and EIS tests revealed that CrAlN coating annealed at 1000°C exhibited superior corrosion resistance properties. It is found that the reduced current density for CrAlN coating annealed at 1000°C was due to the reduction in the porosity. Annealed TiAlN coating follows similar behavior until an optimum annealing temperature of 800°C. Beyond this temperature, porosity enlargement and an increase in the number of pores subsequent to structural changes deteriorated the corrosion resistance of TiAlN coating.     

The acid corrosion of Fe-P alloys

The effect of the P-content in iron (0.002-0.12% P) and the stirring rate on the corrosion rate of five Fe-P alloys in H₂SO₄ and HCl solutions (pH = 0) has been investigated. It was assumed that phosphine generated during corrosion process acts as a stimulator of the cathodic process (at low concentrations) or as an inhibitor of both partial electrode processes (at high concentrations). A mechanism of the corrosion of Fe-P alloys, including the transfer of phosphine from the surface into the bulk of the solution by stirring has been discussed.     

基于优化随机森林的H2S腐蚀产物类型及腐蚀速率预测

目的研究H2S环境下碳钢腐蚀产物类型及失重腐蚀速率预测模型,为含硫油气田管道腐蚀防护设计与选材提供依据。方法整合H2S腐蚀模拟实验数据,采用随机森林算法对各腐蚀因素重要性进行排序,一方面以腐蚀产物类型为输出量,通过随机森林分类算法建立硫铁腐蚀产物类别预测模型,另一方面以腐蚀速率为输出量,通过随机森林回归算法建立腐蚀速率预测模型,并与其他模型进行比较。运用网格搜索方法对各类算法的超参数进行优选,以提高预测可靠性。结果随机森林算法得出的影响H2S腐蚀产物类型的因素重要性排序为:H2S分压、温度、pH值、实验周期、总压、CO2分压。基于网格搜索优化的随机森林分类模型交叉验证得分超过0.9,f1得分达到0.96,优于其他三种常用分类模型。采用网格搜索优化的随机森林回归模型预测结果与实际值的均方误差为0.86%。相关系数R值为0.979,优于其他两个回归模型。结论网格搜索优化后的随机森林分类、回归模型对含H2S复杂环境下的碳钢腐蚀产物类型及腐蚀速率预测准确性较高,能够为油气田管道腐蚀防护提供参考。     

典型飞机管状结构内腔阴极电泳防腐技术

目的以典型直升机主减撑杆为例,优选小内径管状结构内腔阴极电泳防腐工艺。方法应用中性盐雾试验、丝状腐蚀试验、电化学阻抗法等方法,考察不同电泳电压和槽液温度对电泳漆膜防腐蚀性能的影响;采用加速腐蚀试验对比分析防腐措施改进前后涂层的防腐蚀效果。结果 4种电泳漆膜中性盐雾试验480 h后划痕处均出现锈蚀,盐雾试验2000 h后,4~#工艺电泳电压350V、槽液温度34.9℃时,制备的电泳漆膜划痕处锈蚀未见明显变化。4种电泳漆膜耐丝状腐蚀性能满足MIL-PRF-23377J的要求。在3.5%(质量分数)Na Cl溶液中浸泡2000 h后,4~#工艺制备的漆膜电化学阻抗值最大,稳定在6×1010Ω·cm~2左右;3~#工艺电泳电压350 V、槽液温度34.3℃时,制备的漆膜电化学阻抗值最小,从浸泡初期的6×10~(10)Ω·cm~2降至9×10~7Ω·cm~2。各项性能测试表明,4种电泳工艺制备的漆膜均具有优异的防腐性能;4~#工艺制备的漆膜防腐性能最优,4种电泳工艺中最佳管状结构内腔电泳工艺为:电泳电压350 V,槽液温度34.9℃。阴极电泳涂装替代灌涂后,涂层的使用寿命可提高40倍以上。结论阴极电泳防腐技术能够有效解决内腔结构防腐难题,明显改善内腔结构的抗腐蚀品质。     

Pitting corrosion behavior of superferritic stainless steel in waters containing chloride

On a cost-performance basis, superferritic stainless steel (SFSS) grades can now be considered competitive choices for brackish and sea water cooling systems. The pitting corrosion of a SFSS (X2CrNiMoTi 25 3.6 3.5) was tested in a chloride/sulfate solution similar to sea water, as a function of temperature, pH, and salinity. Potentiodynamic polarization techniques and experimental stability diagrams were used to evaluate the pitting conditions. The critical pitting temperature (CPT) was found to be above 50°C, and the re-passivation tendency under critical temperatures was satisfactory even when the pH was less than the depassivation pH, a condition which simulates a propagating occluded cell. The SFSS behavior in the presence of chlorine was evaluated by means of potentiodynamic tests and by studying the cathodic reduction kinetics of Cl₂ and O₂ (air).     

Effect of Nitrogen Partial Pressure on the Electrochemical Evaluation of (Ti-A1)N Coatings Deposited by Reactive Magnetron Sputtering

Titanium aluminium nitride films were deposited on stainless steel substrates by reactive magnetron sputtering under various nitrogen partial pressures, using a composite target consisting of alternate arc segments of titanium and aluminium. Electrochemical evaluation of these coatings, carried out by the potentiodynamic measurement technique in deaerated 1N H₂S0₄ solution at room temperature, has shown that initially there is a rapid increase in corrosion resistance of the coatings with increase in partial pressure of nitrogen; a further increase in nitrogen partial pressure leads to a much lower increase in the corrosion rate. The corrosion potential (E_corr) increased from -339.8 to -268.0 mV with the increase in nitrogen partial pressure from 0.18 to 0.63 mtorr. With further increase in partial pressure of nitrogen to 1.08 mtorr, E_corr decreased to -303.6 mV. The corrosion current density (I_corr) was found to be least 4.6 μA cm^?2 at nitrogen partial pressure of 1.08 mtorr. Coatings were characterized by X-ray diffraction phase analysis, which showed the presence of microcrystalline cubic TiN structure for nitrogen partial pressures of up to 0.88 mtorr. A cubic TiN plus hexagonal AIN structure was present at 0.98 mtorr, while only hexagonal AIN structure was observed at 1.08 mtorr nitrogen partial pressure. Surface hardness measured by microhardness tester using a Knoop indenter showed an increase in surface hardness values with increase in partial pressure of nitrogen. The maximum hardness of 2790 HK₂₅ was observed at a nitrogen partial pressure of 0.98 mtorr. At nitrogen partial pressure of 1.08 mtorr the hardness value decreased drastically to 1746 HK₂₅     

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.