电化学氢通量法用于油气管线在线腐蚀监测

通过恒电位阳极极化和失重法考察了不同pH、温度和H₂S浓度下Q235A钢在弱酸性介质中的氢渗透电流密度与腐蚀速率的变化情况,着重探讨了各影响因素下氢渗透电流与失重腐蚀速率之间的相关性,为氢通量技术用于油气管道非侵入式腐蚀监测提供依据。研究发现：随着pH降低或介质温度升高,Q235A钢的腐蚀速率与氢渗透电流均逐步增大,且二者之间具有良好的线性相关性。随着H₂S浓度增加,Q235A钢的腐蚀速率呈现先增大后降低的趋势,但氢渗透电流则先增大而后趋于稳定;当H₂S浓度在5～200 mg·L^-1范围内,腐蚀速率与氢电流符合二阶多项式函数关系。通过自制的氢通量探针监测实验管道内腐蚀时,发现过厚的管壁降低了氢电流测量灵敏度,但采用恒电位阶跃法得到的氢渗透电量（氢通量）则与失重腐蚀速率之间具有良好相关性,表明渗氢电量法可用于测量油气管道的内腐蚀速率。     

A model for the corrosion of steel subjected to synthetic produced water containing sulfate, chloride and hydrogen sulfide

A model was developed for the prediction of corrosion rates associated with steel subjected to synthetic produced water. The corrosive species included in the model, identified through water analysis conducted in the field, are sulfate, chloride and hydrogen sulfide. The effect on corrosion of these species was examined through polarization experimentation using a three electrode glass corrosion cell and potentiostat. Samples of carbon steel, used in sub-sea pipeline systems, were used at the working electrode and the experiments were carried out at similar physicochemical conditions observed in pipeline systems in the field. The model was based on heterogeneous reactions at the metal surface, with electrochemical parameters determined through experimentation employed in the model to describe the anodic and cathodic processes involved in the corrosion of steel. The model consists of a system of equations with Butler–Volmer kinetics describing the charge transfer and the Nernst diffusion model the mass transfer processes occurring in the corrosion system. The solution is based on a charge balance between the reduction and the oxidation processes which occur at the steel surface. Current density convergence criteria were used in the model to solve the system of equations for corrosion potential, surface species concentration and component current densities. The corrosion rate is determined as the rate of oxidation of iron at the surface and model results have been validated using experimental data. The model demonstrates a reasonable qualitative match with corrosion data collected in the potential region close to the corrosion potential in general, with good qualitative match in the anodic region near the corrosion potential. Some deviation occurs between model and experimental values where overpotentials become large but the model is shown to respond well to changes in input parameter values and predicts the corrosion potential and corrosion rate for each system within experimental variability and the accepted standards of accuracy.     

埋地管道点蚀生长的三维元胞自动机模拟

采用一个三维元胞自动机模型对土壤腐蚀环境中管道金属基体坑点的生长、演化过程进行研究。模拟结果得到了不同条件下管道腐蚀损伤过程的瞬像,并提出了蚀坑宽径比、蚀坑深度比及蚀坑形状参数等一系列腐蚀损伤参数,对管道腐蚀损伤程度进行了定量描述。     

直流和交流混流杂散电流对埋地燃气管道失效影响的实验室研究

把埋地燃气管道受到直流和交流影响的现场环境通过相似原理搬到实验室。首先介绍了直交流混流杂散电流的概念、来源、危害以及腐蚀作用机理,接着分析了实验所用土壤的理化性质,介绍实验原理,然后进行了直流和交流杂散电流共同作用下腐蚀影响的实验研究。研究表明,在直流和交流共同作用下,埋地燃气管道的腐蚀破坏比单一种类杂散电流的腐蚀影响要严重得多。     

基于合作博弈的管道外腐蚀多层次灰色动态评价

对管道进行外腐蚀评价可以为管道检维修方案的优化提供依据。考虑到埋地管道外腐蚀影响因素的复杂性、不确定性和时效性，将灰关联分析法引入管道安全评价领域，提出了一种基于合作博弈的管道外腐蚀多层次灰色动态评价方法。首先建立包含土壤腐蚀性、防腐层性能、阴极保护有效性和杂散电流干扰强度4个方面的腐蚀综合评价指标体系，再基于群决策的改进层次分析法确定指标主观权重，综合实时检测客观数据信息得到指标客观权重，两种权重通过基于合作博弈的组合赋权确定指标组合权重，在此基础上构建动态的多层次灰色评价方法模型。以某地区埋地管道检测数据验证了所建方法和模型的有效性和合理性。     

Self Linear Polarization Resistance-Theory and Examples

Measuring the corrosion rate of a corroding metal is of interest in many situations, including monitoring industrial processes and undertaking fundamental research. The corrosion rate of a metal can be measured electrochemically by determining its polarization resistance, which is inversely proportional to the corrosion rate. What is described in this article is a technique for mathematically extracting from electrochemical noise (EN) data the polarization resistance as well as a measure of the frequency of anodic and cathodic transients. The theoretical framework for self-linear polarization resistance is based on a time-domain analysis of an electrical circuit model of an EN experiment. The analysis indicates that the polarization resistance for one electrode can be interpreted only if the second electrode alone is generating current transients during a given time record. One advantage of this approach, compared with other techniques for obtaining a polarization resistance from EN data, is that short time records, i.e. less than one minute, can be assessed. The self-consistency of the polarization resistance can be assessed with a correlation coefficient. Another advantage is that the nature of localized corrosion events can be attributed to either anodic or cathodic current transients from one of the electrodes.     

The Influence of Heat Treatment and Process Parameters Optimization on Hardness and Corrosion Properties of Laser Alloyed X12CrNiMo Steel

Martensitic stainless steels are used in the production of steam turbine blades but their application is limited due to low hardness and poor corrosion resistance. Laser surface alloying and heat treatment of X12CrNiMo Martensitic stainless steel was conducted with the aim of enhancing hardness and corrosion properties. A Rofin Sinar Continuous Wave Nd: YAG solid-state laser was used to alloy the specimens. The electrochemical and hardness properties were studied using potentiodynamic polarization technique and Vickers micro hardness tester. The microstructures of the as-received, post-heated and pre-heated specimens were investigated by a Scanning Electron Microscope (SEM) and Optical Micrograph (OM) respectively. From the experimental results, the post-heated specimens exhibited the highest hardness property as compared to all other specimens. There was also significant improvement in the corrosion resistance of the post heated specimen compared to all other specimens and the substrate as evidenced by higher polarization resistance and lower corrosion rates. From the analysis of grey relational grade model, the significant laser processing parameters were identified. The results showed the influence of laser power and scanning speed on the corrosion rate, hardness and alloyed depth. The predicted results were found to be in good agreement with the experimental results.     

Calibration of LEACHN model using LH-OAT sensitivity analysis

LEACHN model is useful to describe the nitrogen transport and transformation in soil but requires many input parameters. A sensitivity analysis can help to sort out the sensitive ones among many input parameters. A global sensitivity analysis technique, Latin Hypercube One factor At a Time (LH-OAT) method, was applied to LEACHN model in this study. Only a few parameters were found to be sensitive compared to many input parameters of the model from the sensitivity analysis. Using the results from the sensitivity analysis, calibration and validation of LEACHN model for nitrate leaching was performed for the experimental results from pot experiments that consisted of six types with different soil depth in mini-lysimeters and different fertilizer additions. The results indicated that the use of LH-OAT method could help the facile field application of LEACHN model. Model fitting could be improved by adopting current values in yearly crop parameters in validation.     

Corrosion and Corrosion Inhibition of Steel Pipelines in Montmorillonitic Soil Filling Material

Silicon - Buried steel pipelines pass through different soils therefore; it could be subjected to dissimilar soil corrosion. A possible way to overcome this problem is using one kind of soil as...     

垂直分布双金属管线阴极保护交互影响分析

阴极保护是金属管线最有效的腐蚀防护措施之一,但埋地金属管线强制电流阴极保护系统之间可以产生强烈的交互影响。本文采用ANSYS有限元分析软件,对垂直分布的双金属管线强制电流阴极保护系统的电势、电流密度、电场强度进行了有限元分析,研究了其分布规律、大小等交互影响关系,能为金属管线的强制电流阴极保护设计、施工、维护提供一定的理论和技术支持。     

Electrochemical state conversion model for occurrence of pitting corrosion on a cathodically polarized carbon steel in a near-neutral pH solution

Pitting corrosion occurs frequently on oil/gas pipelines which are protected by both coating and cathodic protection (CP). Since the steel is in an active state, the classic theories attributing pitting to the passive film breakdown do not apply. This work is anticipated to advance the understanding of the fundamentals of pitting corrosion of carbon steel pipelines occurring in an active system. In this work, a square wave polarization method was used to simulate the CP fluctuation and its effect on pipeline steel pitting in a near-neutral pH solution. Moreover, an electrochemical state conversion model was developed to illustrate the pit initiation and growth on the cathodically polarized steel. According to ESCM, when a potential fluctuation is generated on the steel electrode, the local double-charge layer structure is disturbed. The defect area undergoes a temporary anodic potential field, resulting in the local anodic dissolution to nucleate pits. Thus, local anodic dissolution (pitting) of steel would occur under an unstable cathodic polarization. Furthermore, it is found that the potential shifting range plays an important role in pitting initiation and growth. Pits nucleate in high-density under square wave polarization if the polarization potential range is relative narrow and the upper potential is not so negative, i.e., close to OCP. When under a wide potential range and a relatively negative upper potential, pits tend to grow into big size with a low density. Therefore, although the pipeline is protected by CP, the CP fluctuation could occur during service, which would introduce the polarization fluctuation on the steel, resulting in pitting corrosion.     

牺牲阳极技术在埋地管道中的应用

深圳机场埋地管道经过20年地下杂散电流,各种土壤微生物和电解介质的腐蚀,容易发生电化学及穿孔。但在活泼阳极优先腐蚀溶解和释放出的电子与被保护体表面发生阴极还原反应,抑阻了阳极溶解进程。2006年进行检测维护,增加部分阳极,保证正常的电流电位。2011年在开挖埋地管道回收中,发现埋地管道及设施免受其电化学腐蚀。     

Engineering behaviour of soil materials on the corrosion of mild steel

Underground pipelines and steel structures are usually expected to have a long working life. The risk of corrosion should be estimated before installing such pipelines so this paper is aiming at the investigation of the surrounding and incorporating medium (soil filling materials).Many problems related to soil application are due to the unfavorable interaction between water and soil. Underground corrosion is primarily influenced by the following factors: the presence of soil moisture, the supply of oxygen, the redox potential, the pH value, the soil resistivity, and also by microbial activity.From engineering aspects an increase in soil water content has a number of disadvantages e.g. swelling, shrinkage and cohesion decreases which affect directly on the interaction of pipelines, causing deterioration of pipeline materials “corrosion” and also cause damage of infrastructure above this soil due to the occurrence of general and localized corrosion (pitting formation) which is present in different sites of steel structures. The presence of water is a prerequisite for the functioning of corrosion cells. Corrosion of mild steel is affected by grain size, swelling, shrinkage and clay mineral content. The finer soil particles, owing to the increase in swelling, shrinkage, and plasticity, are considered as corrosive medium for underground pipelines and steel structures. The clay mineral contents are also the main quality control to the mild steel corrosion for example montmorillonite and illite absorbed water more than kaolinite clay minerals so it is highly effective in the deterioration of metals.     

Evaluation of cysteine as environmentally friendly corrosion inhibitor for copper in neutral and acidic chloride solutions

The efficiency of cysteine as a non-toxic corrosion inhibitor for copper metal in 0.6 M NaCl and 1.0 M HCl has been investigated by electrochemical studies. Potentiodynamic polarization measurements and electrochemical impedance spectroscopy “EIS” were used to study the effect of cysteine on the corrosion inhibition of copper. Inhibition efficiency of about 84% could be achieved in chloride solutions. The presence of Cu²⁺ ions increases the inhibition efficiency to 90%. Potentiodynamic polarization measurements showed that the presence of cysteine in acidic and neutral chloride solutions affects mainly the cathodic process and decreases the corrosion current to a great extent and shifts the corrosion potential towards more negative values. The experimental impedance data were analyzed according to a proposed equivalent circuit model for the electrode/electrolyte interface. Results obtained from potentiodynamic polarization and impedance measurements are in good agreement. Adsorption of cysteine on the surface of Cu, in neutral and acidic chloride solutions, follows the Langmuir adsorption isotherm. The adsorption free energy of cysteine on Cu (−25 kJ mol⁻¹) reveals a strong physical adsorption of the inhibitor on the metal surface.     

DY-1酸洗缓蚀剂的研制与机理研究

通过正交试验设计方法研制了DY - 1新型酸洗缓蚀剂。该缓蚀剂缓蚀率高达 98.4%,加入量少 ,在 5 0℃以下的HCl溶液中对A3钢具有良好的缓蚀作用。通过化学失重法、电化学法及物理测试对DY - 1的缓蚀率、极化电阻和交流阻抗等电化学性能及缓蚀机理进行了研究 ,结果表明DY- 1是以物理吸附的方式吸附于金属表面而起作用。     

埋地油气管道腐蚀机理研究及防护

埋地油气管道的腐蚀一直是油气储运及集输工程的一个重要问题.分析了埋地油气输送管道腐蚀的各种形式及主要腐蚀机理.针对输油管道的腐蚀问题,从土壤微生物、理化性质以及交流电对管道的腐蚀影响等方面进行了分析.介绍了埋地油气混输管道腐蚀防护的方法:加缓蚀剂、外涂层、内涂层和衬里保护、阴极保护法、杂散电流排流保护等.提出要提高油气...     

Mathematical model for iron corrosion that eliminates chemical potential parameters

Iron corrosion in acidic media is a natural phenomenon that converts elemental iron to a more chemically-stable form, i.e. its oxide and hydroxide. In this study, the iron corrosion process is modeled as a completely implicit problem, solved by a novel finite difference model to provide insight into the ionic aspects of corrosion behavior. This new mathematical model eliminates the chemical potential parameters from the corrosion process equations, thereby reducing the need for experimental determination of chemical potentials. The eliminatedchemical-potential-parameters model predicts and quantifies key parameters (concentrations of conjugate base ion, iron (II) ion, hydrogen ion, anodic and cathodic potentials, and the electrical current density) associated with the iron corrosion process in acidic solutions. The rigorous derivation and novel application of the eliminated-chemical-potential-parameters model and its results provide new insights into the iron corrosion process. The present model is also applicable in any industrial process which is associated with metal corrosion. The model helps to guide the design of future corrosion resistant systems, and various experimental studies pertaining to corrosion inhibition techniques.     

Model for corrosion of metals covered with thin electrolyte layers: Pseudo-steady state diffusion of oxygen

A one-dimensional mathematical model is presented for the free corrosion of a bare metal surface (devoid of any oxide film) under a thin electrolyte layer using mixed potential theory where anodic metal dissolution is controlled by oxygen diffusion through the electrolyte layer and by the oxygen reduction at the metal surface. A pseudo-steady state is considered wherein the oxygen diffusion is at steady state while the metal and hydroxyl ions keep accumulating in the thin electrolyte layer due to a decoupling arising from the assumed Tafel laws for corrosion kinetics. Under free corrosion the oxygen diffusion is shown to depend on a non-linear boundary condition with a non-integer power on oxygen concentration at the metal surface which makes the model non-trivial. Analytical and numerical results for the oxygen concentration at the metal surface, corrosion potential, and corrosion current density are reported which depend on several kinetic, thermodynamic and transport parameters in the system. The model is applied to iron and zinc systems with input data taken from the literature. The experimental utility of the model for gathering thin-film corrosion parameters from a study of the corrosion current and potential as a function of the thickness of the electrolyte layer is discussed. Precipitation and passivity, though not the main object of study in this work, are briefly discussed.     

The relationship between the impedance of corroding electrode and its polarization resistance determined by a linear voltage sweep technique

The polarization resistance of metallic materials in contact with an electrolyte is largely used for the evaluation of its corrosion rate. The experimental value of polarization resistance is very often determined by plotting the polarization curves at the vicinity of the rest potential by a triangular voltage sweep technique. It is found that, for materials having high resistivity against corrosion, the value of polarization resistance is largely dependent on the sweep rate or the period of sweep cycle. If an equivalent circuit of a corroding electrode is to be presented by a parallel connexion of a resistance and a capacitance, such dependence of the polarization resistance cannot be explained at all. In fact, though the impedance of corroding electrode measured within a large frequency range shows one capacitive arc in the complex plane in accordance with parallel R—C circuit, the values of R and C both depend on frequency. The current response to a triangular voltage sweep signal is calculated numerically by Heaviside operational calculus using experimentally determined electrode impedance. A fairly good agreement was found between the experimental and calculated current—voltage cycles for different periods of a triangular voltage sweep signal.     

Unified approach to localized and general corrosion of stainless steels

Localized and general corrosion of stainless steels is considered. In the case of localized corrosion, statistical parameters are deduced from the comparison of the distributions of breakdown and corrosion potential values to rank different materials, environments and designs. Cumulative frequency F is considered for breakdown (E_b) and corrosion (E_c) potential, and both are represented on a logarithm plot as E=E(log F). An extrapolated value of F (the risk H) corresponding to E_b=E_c is related to the field behavior of the material. The risk H is formally related to the corrosion current density (i) of the general corrosion approach. An analogy between the formalism of the probabilistic treatment of localized corrosion of stainless steels and that of uniform corrosion is highlighted through Monte Carlo simulation. Introducing a discretization model of the general corrosion, the time evolution of the surface roughness during general corrosion of stainless steels is reproduced in agreement with the experimental results. According to this model, the general corrosion can be treated on a similar basis of the localized corrosion in terms of discretization of corroding areas, and vice-versa localized corrosion can be treated on a similar basis of the general corrosion in terms of statistical distributions of the potential values.