Effect of aluminum on the corrosion resistance of low‐alloy steel in 10 wt% sulfuric acid solution

The aqueous corrosion behavior of low‐alloy steel with aluminum contents was examined in a 10 wt% H₂SO₄ (pH 0.13) solution using electrochemical techniques and surface analyses. The corrosion resistance of the new alloy steel was evaluated in terms of electrochemical parameters, such as passive current density, film, and charge transfer resistances. The results showed that a high Al content in the steel imparted better passivation behavior resulting in a lower corrosion rate. It related to the enrichment of iron carbonate and hydrocarbon by the dissolution of the carbide phase.     

Q235钢在库尔勒地区土壤腐蚀性的影响因素分析

通过模糊聚类确定了影响Q235钢腐蚀速率的主要土壤因素,利用灰关联和层次分析等方法探讨了各主要影响因素对腐蚀速率的影响顺序和权重大小.结果表明,影响Q235钢在库尔勒地区土壤腐蚀性的主要因素的权重依次为:全盐(0.4050)电导率(0.2517)含水量(0.1493)Cl-(0.0868)pH(0.0501)SO42(0.0291)HCO3-(0.0173)NO-(0.0107),这些结果为土壤腐蚀性评价方法的制定提供了一些新的数据参考.     

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.     

20#钢和球墨铸铁材质燃气管道的土壤腐蚀行为比较研究

采用正交试验设计方法，以含水量、孔隙度、pH值等9种影响因素作为试验因素进行土壤腐蚀模拟试验，对20#钢和球墨铸铁的腐蚀形貌和腐蚀产物进行比较分析，探讨其腐蚀行为和腐蚀机理。分析表明：在相同环境下球墨铸铁比20#钢更容易腐蚀，它们的土壤腐蚀环境因素重要度排序呈现较大的差异，但两者对Cl^-都比较敏感，在20#钢的腐蚀产物中检出了球墨铸铁腐蚀产物中没有的磷酸铁族物质Fe₂PO₅。含碳量少、含有抗腐蚀元素Cr、腐蚀产物中含有抗腐蚀作用的磷酸铁族物质以及晶界少是20#钢比球墨铸铁耐腐蚀性好的主要原因。     

Corrosion and Prevention '95

The corrosion behaviour of duplex stainless steel 2101 exposed to 0.1?wt-%NaOH, 5.0?wt-%H₂SO₄ and 6.0?wt-%FeCl₃ solutions was investigated with an electrochemical noise technique. The time records revealed salient features of the steel in the three solutions, and the corresponding corrosion morphologies were shown. The slopes of the power spectral density plots of current and potential noises were associated with the nature of corrosion attack. The corrosion rates in the three media were reflected by the noise resistance, presenting good correlation with the results from linear polarisation and electrochemical impedance spectroscopy.     

Nitrogen-based corrosion inhibitor film study using weight loss and electrochemical methods in static and turbulent conditions

There is an increasing demand from oil and gas industry to ensure the integrity of assets and the enviroment in the critical conditions found in presalt wells. This study evaluates new formulations of corrosion inhibitors with different types and alkoxylation degrees of nitrogen-based inhibitors to assess corrosion behavior of carbon steel (API X65). For these studies, corrosion rates were determined through measurements of weight loss and linear polarization resistance (LPR). In the case of electrochemical measurements, experiments were carried out in a laminar flow and in a turbulent flow regime. All data were collected in the presence of CO₂ and CO₂/H₂S mixtures. The results revealed that corrosion protection of carbon steel critically depends on the nitrogen-based inhibitor's alkoxylation type and degree as well as the condition to which they are exposed. It was possible to notice that an ethoxylated amine whose inhibition efficiency in the presence of CO₂ was about 10%, when exposed to H₂S environment at the same temperature showed an efficiency of 86%. It was also observed that the inhibitor with a higher ethoxylation degree presented better efficiencies than the one with a lower degree.     

Effect of Immersion Time and Cooling Mode on the Electrochemical Behavior of Hot-Dip Galvanized Steel in Sulfuric Acid Medium

In this work, we investigated the influence of galvanizing immersion time and cooling modes environments on the electrochemical corrosion behavior of hot-dip galvanized steel, in 1 M sulfuric acid electrolyte at room temperature using potentiodynamic polarization technique. In addition, the evolution of thickness, structure and microstructure of zinc coatings for different immersion times and two cooling modes (air and water) is characterized, respectively, by using of Elcometer scan probe, x-ray diffraction and metallography analysis. The analysis of the behavior of steel and galvanized steel, vis-a-vis corrosion, by means of corrosion characteristic parameters as anodic (β _a) and cathodic (β _c) Tafel slopes, corrosion potential (E _corr), corrosion current density (i _corr), corrosion rate (CR) and polarization resistance (R _p), reveals that the galvanized steel has anticorrosion properties much better than that of steel. More the immersion time increases, more the zinc coatings thickness increases, and more these properties become better. The comparison between the two cooling modes shows that the coatings of zinc produced by hot-dip galvanization and air-cooled provides a much better protection to steel against corrosion than those cooled by quenching in water which exhibit a brittle corrosive behavior due to the presence of cracks.     

Microbiologically influenced corrosion of X60 carbon steel in CO2‐saturated oilfield flooding water

The corrosion behavior of X60 carbon steel in CO₂‐saturated oilfield flooding water inoculated with sulfate‐reducing bacteria (SRB) was investigated using polarization curves and electrochemical impedance spectroscopy (EIS). With the propagation of SRB in the flooding water, the pH values of flooding water increased quickly in the initial 2 days and remained relatively steady during the later stage. Polarization curves showed that the corrosion current density decreased during the first 10 days due to the protection of corrosion products and SRB‐biofilms, and then increased possibly due to the partial detachment of the corrosion products and the biofilms. EIS analysis also showed that the charge transfer resistance increased initially and then decreased with exposure time. In the beginning of corrosion, the anodic dissolution of X60 steel was dominated by CO₂. After the formation of SRB‐biofilms, part of FeCO₃ corrosion products was converted to incompact FeS precipitates by SRB bio‐mineralization. Thus, the dispersed iron sulfide in SRB‐biofilms and X60 steel base may constitute a galvanic couple, accelerating the localized corrosion of the steel base in the flooding water.     

Electroplating of nickel from acetate based bath – Hull Cell studies

Abstract

Electroplating of nickel onto steel substrates from an electroplating bath containing nickel acetate, nickel chloride, boric acid and acetic acid has been investigated under different levels of operating conditions such as bath composition, current density and temperature. A detailed study has been made on the influence of these variables by measuring cathodic current efficiency and throwing power for various baths. Deposition parameters have been optimised using Hull Cell experiments. From potentiodynamic polarisation studies on Ni deposits it was revealed that E _corr moved towards the more negative direction. It is inferred from this fact that there is cathodic control of the corrosion reaction. The R _t value increases with increasing deposit thickness and the corresponding C _dl value is decreased.     

Effect of heat treatment on corrosion properties of CuAlNi shape memory alloy

The effect of heat treatment on corrosion properties of CuAlNi shape memory alloy was investigated in 0.9% NaCl solution at pH 7.4 and 37 °C by open circuit potential measurements, polarisation techniques, and electrochemical impedance spectroscopy. Investigations were performed on CuAlNi alloy samples in as-cast state and after heat treatment procedure containing annealing at 850, 885 and 920 °C followed by water quenching. Electrochemical impedance measurement results indicate that heat treatment of CuAlNi alloy leads to the increase in charge transfer resistance and surface layer resistance and the decrease in values of capacitance of the double and surface layers, indicating higher corrosion resistance compared with the as-cast CuAlNi alloy. The increase in polarisation resistance and the decrease in corrosion current density of heat-treated CuAlNi alloy also suggest beneficial influence of heat treatment on corrosion resistance of CuAlNi alloy. Optical microscopy, SEM/EDX and XRD analysis of samples surface after polarisation measurements show the occurrence of pitting corrosion on the electrode surfaces, with the existence of CuCl₂, AlCl₃ and Cu₂Cl(OH)₃ compounds as the surface corrosion products.     

辽河油田土壤中溶解氧对X70管线钢腐蚀的影响

目的 降低腐蚀对油气管线运行的危害。方法 通过控制溶液中不同通氮时间,获得不同溶解氧浓度的辽河油田土壤模拟溶液,利用交流阻抗技术和动电位极化技术研究不同的溶解氧浓度对X70管线钢在模拟溶液中电化学腐蚀行为的影响,并结合金相显微镜对管线钢表面的腐蚀形貌进行表征,以阐明该条件下不同浓度溶解氧对管线钢腐蚀行为的作用机制。结果 在该环境下,X70钢的腐蚀机理为阳极溶解机制。随着溶解氧含量的不断降低,电极极化电阻变大,腐蚀电流密度明显减小,此时,电极表面点蚀坑数量也变少,点蚀坑的直径变小,金属腐蚀速率显著下降。当溶解氧质量浓度为10.0 mg/L时,试件的腐蚀速率最大,腐蚀现象最明显。当溶解氧质量浓度从10.0 mg/L降低至0.3 mg/L时,金属电极表面生成了一层以FeCO3为主的腐蚀产物膜,产物膜明显抑制了腐蚀反应的进行,对X70钢起到保护作用,此时试样腐蚀现象最不明显。结论 溶解氧浓度的不同导致了X70管线钢电极表面产物膜形态的不同,从而影响了该环境下金属的电化学腐蚀行为。     

Effect of oil in multiphase flow on corrosion product film in large horizontal pipeline

The properties of corrosion product film formed on carbon steel pipelines under saltwater‐oil‐CO₂ multiphase flow are examined by AC impedance methods. Experiments are performed in a 101.6 cm I.D., 10 m long pipeline. Experimental results show that there are two reactions on the steel surface in saltwater‐oil mixture. One is charge transfer, and the other is diffusion. By calculation of charge transfer resistance, R_t, and Warburg impedance coefficient, σ, it is found that, R_t in saltwater‐oil mixture is much higher than that in saltwater. In saltwater‐oil mixture, R_t and σ increase with immersion time. It is suggested that the porous corrosion film occurs on the surface of the steel, and that the film becomes compact when the immersion time increases. The longer the exposure time, the more compact the film, resulting in that the corrosion rate becomes lower.     

Optimization of deposition conditions for bright Zn-Fe coatings and its characterization

Sulfate bath having ZnSO₄ · 7H₂O, Fe₂(SO₄)₃ · H₂O and thiamine hydrochloride (THC) and citric acid (CA) in combination, represented as (THC + CA) was optimized for deposition of bright Zn-Fe alloy coating on mild steel. Bath constituents and operating parameters were optimized by standard Hull cell method, for peak performance of the coating against corrosion. The effect of current density (c.d.), pH and temperature on deposit characters, such as corrosion resistance, hardness and glossiness were studied and discussed. Potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) methods were used to assess the corrosion behaviors. Surface morphology, and composition of the coatings were examined using Scanning Electron Microscopy (SEM), interfaced with EDXA facility, respectively. The Zn-Fe alloy, with intense peaks corresponding to Zn(100) and Zn(101) phases, showed highest corrosion resistance, evidenced by X-ray diffraction (XRD) study. A new and cheap sulfate bath, for bright Zn-Fe alloy coating on mild steel has been proposed, and results are discussed.     

The use of electrochemical techniques for the investigation and monitoring of microbiologically influenced corrosion and its inhibition – a review

The background of several electrochemical techniques – recording of the corrosion potential E_corr, electrochemical impedance spectroscopy (EIS), electrochemical noise analysis (ENA) and recording of potentiodynamic polarization curves – has been discussed and examples of the use of these techniques in studies of microbiologically influenced corrosion (MIC) and MIC inhibition have been presented. These examples range from the use of the polarization resistance R_p and the noise resistance R_n in corrosion monitoring in a sewer environment and a gas production field, respectively, to the application of EIS and ENA in the evaluation of the interaction of bacteria with protective coatings on steel exposed to natural seawater (NS). A more detailed analysis based on EIS and ENA of Corrosion protection of Al 2024, mild steel and brass in artificial seawater (AS) by bacteria such as B. subtilis, B. licheniformis, E. coli and Shewanella has been presented. Determination of the changes of R_p and R_n as well as E_corr allows to propose appropriate mechanisms of MIC inhibition. These mechanisms have been confirmed in the case of S. algae by recording of anodic and cathodic potentiodynamic polarization curves after exposure to AS containing the bacteria for extended time periods.     

埋地钢质管道交流干扰腐蚀影响因素实验分析

参照埋地管道服役环境,搭建钢质管道交流干扰腐蚀实验平台。采用腐蚀试片失重法,测试钢质管道在土壤模拟溶液中的腐蚀速率,研究交流杂散电流干扰环境下杂散电流大小、土壤电导率以及土壤酸碱度对钢质管道腐蚀速率的影响。实验结果表明:杂散电流对钢质管道的腐蚀速率影响最大,土壤酸碱度和土壤电导率对钢质管道的腐蚀速率影响规律复杂。     

Evaluation of localized corrosion phenomena with electrochemical impedance spectroscopy (EIS) and electrochemical noise analysis (ANA)

The use of electrochemical impedance spectroscopy (EIS) and electrochemical noise analysis (ENA) for non-destructive evaluation of corrosion processes is illustrated for three model systems. EIS can be used to detect and monitor localized corrosion of Al alloys and determine pit growth laws which can be used for lifetime prediction purposes. Electrochemical potential and current noise data can be analyzed in the time and the frequency domain. A comparison of noise data obtained for Pt and an Al 2009/SiC metal matrix composite (MMC) exposed to 0.5 N NaCl has shown that the use of potential noise data alone can lead to erroneous conclusions concerning corrosion kinetics and mechanisms. The electrochemical noise data have been evaluated using power spectral density (PSD) plots in an attempt to obtain mechanistic information. The system Fe/NaCl has been used to determine the relationship between the polarization resistance R_p obtained from EIS data and the noise resistance R_n determined by statistical analysis of potential and current noise data. Potential and current noise can be recorded simultaneously allowing construction of noise spectra from which the spectral noise resistance R can be obtained as the limit for zero frequency. Good agreement between R_P, R_n and R has been observed for iron exposed to NaCl solutions of different corrosivity. For polymer coated steel exposed to 0.5 N NaCl for five months analysis of EIS data allows to draw conclusions concerning the degree of disbonding of the coating and the decrease of the coating resistivity with exposure time. R_n and R obtained from electrochemical noise data for an alkyd coating on cold rolled steel agree with each other and show the same time dependence as R_p and the pore resistance R_po determined from EIS data, but are significantly lower than R_p and R_po. The relationships of derived noise parameters such as R_n and R to coating properties and to the remaining lifetime of a polymer coating are not clear at present.     

An embedded multi‐parameter corrosion sensor for reinforced concrete structures

A prototype of an embedded corrosion sensor has been developed for assessing the corrosion status of reinforcing steel bar (rebar) in concrete. The integrated sensor unit includes an Ag/AgCl probe, a metallic oxide probe, a multi‐electrode array sensor (MAS), and a four‐pin (Wenner) array stainless steel electrode for chloride content, pH, microcell corrosion current, and localized concrete resistivity measurements, respectively. A stable solid probe was used as the reference probe in this unit to express the potentiometric measurement of chloride content and pH probes. In this study, the chloride and pH probes were calibrated in simulated pore solutions (SPSs) regarding temperature and pH fluctuations. The corrosion current results of the MAS probe in SPSs matched very well with those obtained by the linear polarization resistance technique, which was conducted on companion carbon steel specimens. A sensor prototype was embedded into a paste cylinder for long‐term performance evaluation. Up‐to‐date results show that the sensor probes exhibit excellent sensitivity and reliability through 1 year of monitoring. Continuous monitoring in the laboratory for extended periods is underway.     

The effect of temperature on the corrosion of steel in concrete. Part 1: Simulated polarization resistance tests and model development

The effect of temperature on the corrosion rate of steel corrosion in concrete is investigated through simulated polarization resistance experiments. The simulated experiments are based on the numerical solution of the Laplace’s equation with predefined boundary conditions of the problem and have been designed to establish independent correlations among corrosion rate, temperature, kinetic parameters, concrete resistivity and limiting current density for a wide range of possible anode/cathode (A/C) distributions on the reinforcement. The results, which successfully capture the resistance and diffusion control mechanisms of corrosion as well as the effect of temperature on the kinetic parameters and concrete/pore solution properties, have been used to develop a closed-form regression model for the prediction of the corrosion rate of steel in concrete.     

Schutzmaßnahmen gegen interkristalline Spannungsrißkorrosion von Gashochdruckleitungen aus Stahl bei erhöhter Betriebstemperatur

Protection of high-pressure steel pipelines for the transmission of gas against stress corrosion cracking at high temperature Grade X 60 line pipe sections were capped to pressure vessels and were placed in concrete pits where they were exposed to controlled corrosion conditions. The corrosive conditions were represented by a sand environment containing NaHCO₃, a wall temperature of 70°C and pipe-to-soil potentials of U_H = ? 0.43, ? 0.55 and ? 0.68 V. The pipes were polyethylene coated to DIN Standard 30 670 without prior surface treatment (no mill scale removal) or after the removal of the mill scale by brushing or sandblasting. The coating included holidays of different sizes to allow disbonding. These pressure vessels were tested by pressure cycling. The strain rate for the cycles was 10^?7 sec^?1 whereas strain release was much faster. The test programme included 4800 cycles between 44 and 87% YS, 1390 cycles between 66 and 87% YS and 5000 cycles between 79 and 87% YS. The total duration of the test was 9830 hrs. Following the completion of the pressure cycles, the pipes were examined. No corrosion defects were discovered in the holiday areas. In the cases of the pressure vessels where mill scale had been removed by sandblasting or brushing, no corrosion was found below the disbonded coating, either. Minor crack formation which was not revealed by conventional test methods was, however, established below the disbonded coating of the pressure vessels where the mill scale had not been removed. The scanning electron microscope showed corrosion pitting type strain induced cracking of a depth of up to 0.2 mm. In a limited number of cases these cracks could be considered intercrystalline stress corrosion cracking. The paper discusses what action must be taken to prevent such stress corrosion cracking. It concludes that stress corrosion cracking in West German high-pressure gas transmission pipelines is impossible if the pipelines are designed, built and operated in accordance with existing standards and codes of practice.     

土壤腐蚀性检测器的研制

介绍一种新研制的土壤腐蚀性检测器。它可以检测金属在土壤中的腐蚀电流密度及腐蚀电但和土壤的电阻率、氧化还原位及温度等参数。经实验室和野外现场试验,并对测得的数据进行分析表明,稳态腐蚀电流密度与埋片失重腐蚀速度之间具有较好的相关性。