Effect of dynamic DC stray current on corrosion behavior of X70 steel

Corrosion behavior of X70 steel under the application of dynamic DC stray current was investigated in simulated soil solution by immersion tests and electrochemical measurements. Experimental results indicated that the corrosion rate of X70 steel under dynamic DC stray current was strongly influenced by the dynamic period. When the dynamic period was <80 s, the corrosion rate was only approximately 1–7% of that caused by an equivalent amount of steady direct current. However, as the dynamic period became >80 s, the corrosion rate increased significantly with the dynamic period. And finally when the dynamic period was >1 hr, the corrosion rate was nearly equal to 100% of that caused by an equivalent amount of steady direct current. Meanwhile, the surface examination showed that the specimens experienced uniform corrosion under the experimental conditions. On the basis of the experiment results, the dynamic DC stray current corrosion mechanism of X70 steel under the experimental conditions was discussed, which was closely related to the electric double-layer structure at the electrode/solution interface and dynamic electrochemical reactions under dynamic stray current.     

Experimental study of dynamic DC stray current corrosion of X70 steel

In this paper, an experimental investigation on X70 steel was performed with respect to dynamic DC stray current interference in a soil-simulated solution and in quartz sand. The results showed that the interference period had a huge impact on the corrosion rate. When the interference period was less than 100 s, corrosion rates in the two testing conditions were less than 12% of that induced by steady DC corrosion with an equivalent current. When the interference period was longer than 100 s, the corrosion rate in the soil-simulated solution increased more significantly than that in quartz sand. Also, when the interference period was longer than 1 h, the corrosion rate in the soil-simulated solution was approximately equal to the Faraday theory corrosion rate. However, the corrosion rate in quartz sand was still less than 81% of the Faraday theory corrosion rate, even though the interference period had been increased to 16 h. The difference of the corrosion rates in the two testing conditions was probably because of the different capacities of charge consumption by the capacitance effect of the electric double layer as well as the different charge consumption due to the extra reaction of species other than iron.     

地铁干扰下管道阴极保护有效性测试方法的探究

近年来,随着对动态直流杂散电流干扰研究的不断深入,如何准确地测试埋地管道在动态直流杂散电流干扰下的阴极保护数据并评价其有效性已成为阴极保护工程师亟待解决的问题.本文通过比较极化试片法和GPS同步中断法采集的两种阴极保护数据结果,得到了简化日常测试过程和优化测试结果的方法,给管道阴极保护日常维护减负、专业化测试调查提供了...     

Mathematical modeling on the corrosion of unprotected structure due to stray current resulting from cathodic protection system

Mathematical modeling on the corrosion of unprotected structures due to a stray current resulting from a nearby cathodic protection system was carried out using the boundary element method. The model consists Laplace’s equation with non-linear boundary conditions (Tafel equations) and the iterative technique to determine the mixed potential of the unprotected structure. The model is applied to an unprotected bare structure as well as a coated structure with several defects. The amount and the location of corrosion along the unprotected structure correlate strongly with experimental results within the experimental conditions studied.     

Experimental study on the corrosion behavior of X70 steel under asymmetric dynamic DC interference

The corrosion behavior of X70 steel in simulated soil environment under asymmetric dynamic direct current (DC) interference was studied by immersion tests. The experimental results showed that the negatively asymmetric dynamic DC interference would induce localized corrosion. Under the same dynamic period of 160 ±80 s, when the negative half-wave current density remained stable at −10 mA/cm² and the positive half-wave one decreased from 7 to 1 mA/cm², the equivalent diameters of the localized corrosion zones became smaller and the steel samples demonstrated typical pitting corrosion morphologies. To further explore the effect of asymmetric dynamic DC interference on the localized corrosion behavior of carbon steel, a variety of experimental measurements were carried out including real-time DC potential monitoring, in-situ near-surface pH measurements, cyclic voltammetry, and Mott–Schottky tests. It was found that the localized corrosion behavior was probably related to the breakdown of passive film formed on the metal surface exposed to negatively asymmetric DC current generated high pH conditions.     

Measuring the corrosion rate of steel in concrete – effect of measurement technique,polarisation time and current

Both on‐site investigations and laboratory studies have shown that different corrosion rates are obtained when different commercially available corrosion rate instruments are used. The different electrochemical techniques and the measurement parameters used, i.e. polarisation current and time, are in some studies considered the main reasons for the variations. This paper presents an experimental study on the quantitative effect of polarisation time and current on the measured polarisation resistance – and thus the corrosion current density – of passively and actively corroding steel. Two electrochemical techniques often used in instruments for on‐site corrosion rate measurements are investigated. On passively corroding reinforcement the measured polarisation resistance was for both techniques found to be highly affected by the polarisation time and current and no plateaus at either short or long polarisation times, or low or high polarisation currents were identified. On actively corroding reinforcement a large effect of the polarisation time was also found, but only a minor effect of the polarisation current. The effect of the polarisation time was, however, practically independent of the corrosion rate for actively corroding steel. For both techniques guidelines for polarisation times and currents are given for (on‐site) non‐destructive corrosion rate measurements on reinforcement steel in concrete.     

Effects of alternating current interference on cathodic protection potential and its effectiveness for corrosion protection of pipelines

In this work, the effect of alternating current (AC) interference on cathodic protection (CP) potential on a X65 steel in a near-neutral pH bicarbonate solution was investigated, and the CP performance under AC was evaluated by weight-loss measurements. The CP potential applied on the steel cannot be maintained in the presence of AC interference. The shift of the CP potential depends on the applied CP level and AC current density. No matter if the direct current potential of the steel is shifted negatively or positively upon application of AC, the steel suffers from increased corrosion. The AC decreases the effectiveness of CP for corrosion protection. The CP standard at ?0.850?V (copper sulphate electrode) that does not consider the AC interference is not appropriate for AC corrosion protection.     

Effect of current density on corrosion resistance of micro-arc oxide coatings on magnesium alloy

Oxide coatings were prepared on magnesium alloys in electrolyte solution of Na2SiO3 at different current densities (3, 4 and 5 A/cm2) with micro-arc oxidation process. X-ray diffractometry (XRD) results show that the oxide coatings formed on magnesium alloys are mainly composed of MgO and MgAl2O4 phases; in addition, the content of MgO increases with increasing the current density. The morphology and surface roughness of the coatings were characterized by confocal laser scanning microscopy (CLSM). The results show that the surface roughness (Ra) decreases with increasing the current density. Moreover, the electrochemical corrosion results prove that the MgO coating produced in the electrolyte Na2SiO3 at current density of 5 A/cm2 shows the best corrosion resistance.     

Assessment of cathodic protection effect on long-distance gas transportation pipelines based on buried steel specimens

Different severe corrosions are found at the damaged point of anticorrosive coating on natural gas pipelines, even though the cathodic protection (CP) potential is between −0.85 and −1.15 V. Therefore, there are totally 168 buried steel specimens (BSSs) and 28 soil samples at 28 buried points that are taken out in situ and then analyzed in the lab to assess the CP effectiveness. First, the CP status is simulated by BSSs at the damaged points, and the corrosion products on BSSs are analyzed microscopically. Second, the corrosion rates of the testing BSSs are calculated by the weight-loss method to perform the quantitative assessment. Third, the specific reasons for external corrosion are explored via analyzing the CP potential attenuation tendency and the corrosiveness of soil. The corrosion growth trend is also investigated by comparing the test results among three test cycles within 8 years. Finally, the control measures for external corrosion of pipelines are put forward. The study is beneficial to evaluate the CP system and determine the causes of external corrosion of pipelines, thereby formulating corresponding protective measures.     

Influence of electric current on the corrosion behavior of Cu for the electric contact in the isolation switch

The flow of electric current through the conductor has a far‐reaching effect on its corrosion behavior. In this paper, the effect of current on the corrosion behavior of Cu is investigated. The accelerated corrosion test of Cu with various external currents from 1 A to 5 A are carried out in 5% NaCl neutral salt spray environment. The results show that the samples with external current exhibit a faster corrosion rate than those without current. The corrosion kinetics and underlying mechanism are also discussed in this paper.     

交流杂散电流对X70管线钢3PE防腐层下腐蚀及剥离行为的影响

目的 明确交流杂散电流对埋地管线防腐层剥离和破损处防腐层下腐蚀的影响规律及其导致防腐层剥离的作用机理。方法 通过基于COMSOL Multiphysics有限元仿真、交流阻抗谱分析及三维体式显微镜观测等方法,研究在格尔木土壤模拟溶液中,交流杂散电流干扰下,X70钢表面3PE防腐层剥离处的防腐层下腐蚀及剥离机理。结果 由于防腐层破损点和剥离区域的存在,使得防腐层的防护性能明显降低,交流杂散电流在初始预留剥离处的X70钢表面呈不均匀分布,破损点处所分布电流密度明显高于剥离区边缘处。杂散电流引起的腐蚀反应主要集中在防腐层破损点处,而处于预留剥离区域下方的X70钢表现出缝隙腐蚀的现象。防腐层破损点处的腐蚀坑深度随电流密度的增加而逐渐变深,而当交流电流密度由0 A/m2增加到100 A/m2时,防腐层剥离面积明显增大,此后,当电流密度继续增大,剥离面积基本保持不变。当施加的交流电流密度相同时,随着防腐层剥离面积的减小,杂散电流造成的防腐层剥离面积增大,X70钢试样上的最大腐蚀坑略微加深。结论 造成防腐层剥离的交流杂散电流存在临界电流密度值,使得防腐层剥离面积达到最大且之后保持不变。防腐层初始剥离面积较小时,交流电所造成的X70钢腐蚀及防腐层剥离行为更为严重。     

电流密度对海水淡化用铝合金微弧氧化陶瓷膜层耐蚀性的影响

在硅酸盐体系中研究了双极性脉冲电源的电流密度对6061铝合金微弧氧化的影响。结果表明,电流密度对膜层的生长、形貌及耐蚀性具有明显的影响;电流密度为15.0 A/dm2时,起弧时间最短为86 s,且膜层形貌均匀、致密,腐蚀电位E0和腐蚀电流密度Icorr分别达到-0.526 72 V和5.287×10-8A/cm2,表现出良好的耐蚀性能。用高浓度海水喷淋腐蚀试验表明来自海水中的Cl-阴离子只能进入MAO膜层的疏松表层,生成可溶性的Al-O-Cl络合物,造成表面出现大量"海绵絮状"孔洞,但Cl-、SO24-等阴离子无法进到膜层内部致密层,从而基体不被腐蚀。     

Effects of Tafel slope,exchange current density and electrode potential on the corrosion of steel in concrete

A parametric study is carried out to investigate the effect of variations in anodic and cathodic Tafel slopes, exchange current densities and electrode potentials on the rate of steel corrosion in concrete. The main goal of this investigation is to identify the parameters that have significant influence on steel corrosion rate. Since there is a degree of uncertainty associated with the selection of these parameters, particularly during modelling exercises, it is intended that the results of this study will provide valuable information to engineers and researchers who simulate steel corrosion in concrete. To achieve this goal, the effect of a parameter on the corrosion rate of steel is studied while all other parameters are kept constant at a predefined base case. For each parameter, two extreme cases of anode‐to‐cathode ratio are studied. The investigation revealed that the variations in the anodic electrode potential have the greatest impact on the corrosion rate, followed by the variations in the cathodic Tafel slope.     

涂层破损时杂散电流对Q235、16Mn、X70钢腐蚀的影响

通过腐蚀速率测定、腐蚀形貌观察、腐蚀坑深度测量及分形维数计算等方法,研究了杂散电流作用下涂层破损率对Q235、16Mn和X70钢腐蚀的影响.结果表明,杂散电流作用下,Q235钢腐蚀程度最严重,16Mn次之,X70最小;随杂散电流增大和涂层破损率减小,腐蚀速率和腐蚀坑深度均相应增大,腐蚀程度加剧;根据"盒子"维法测定杂散电流腐蚀形貌的分形维数,反映的腐蚀规律与实测腐蚀速率吻合,分形维数可定量表征杂散电流腐蚀形貌.     

中国南海油气井隔水导管腐蚀规律研究

目的 针对我国南海海域使用过的六种材质隔水导管,系统性地分析其在60、90、180 d三个腐蚀周期及在大气区、飞溅区、潮差区、全浸区四个区带的腐蚀行为与腐蚀规律,为我国南海隔水导管材质优选提供理论依据。方法 首先,开展室内实验模拟海洋腐蚀环境,通过SEM扫描分析隔水导管在大气区、飞溅区、潮差区及全浸区的腐蚀特点,并针对六种材质挂片在四个区带的腐蚀速率开展研究,最后基于动电位极化与电化学阻抗技术分析隔水导管的抗腐蚀性能。结果 飞溅区与潮差区的腐蚀程度相比大气区及全浸区更严重,且飞溅区、潮差区及全浸区三个区带的腐蚀产物主要为γ-FeO(OH);180 d时大气区平均腐蚀速率约0.0651~0.0976 mm/a,飞溅区约0.3924~0.4857 mm/a,潮差区约0.3482~0.4281 mm/a,全浸区约0.1714~ 0.2109 mm/a。六种材料容抗弧大小为X80< X70< X65< X60相似文献   

Effect of current density on micro‐arc oxidation of Q235 steel and corrosion resistance in liquid Pb‐Bi

An attempt has been made to improve the corrosion resistance in liquid Pb‐Bi by micro‐arc oxidation (MAO), and the effects under different current densities on the corrosion resistance of the coatings were discussed. Scanning electron microscope, energy dispersive spectrometer, and X‐ray diffraction were used to analyze the surface morphology and phase constituents of the MAO coatings produced under different current densities. The corrosion resistance of the coatings was evaluated by studying the element changes and morphology evolution. The results show that the compactness of the ceramic coating decreases with the current density increasing. In contrast to the performance of matrix metal, the ceramic coating exhibited a much better corrosion resistance in liquid Pb‐Bi. Moreover, the ceramic coating produced under current density of 10 A/dm ² shows the best corrosion resistance.