Spatial variability of soil resistivity and rational sampling for corrosion assessment of carbon steel in Daqing area

Soil resistivity is one of the key indicators of the corrosive classification assessment on metal materials in soil environment. This paper presents variance characters of various quantity of soil resistivity samples data based on the semi-variance function methods of Geo-statistical Analysis by analyzing the regional soil resistivity sampling data in Daqing area. Furthermore, the variance of the soil resistivity as well as entire soil circumstance due to different sampling amounts are also analyzed and compared by means of using the characteristic parameters of the semi-variance function. In addition, this work also studied the rational sampling quantities according to various measurement errors required and evaluated the local soil corrosivity on carbon steel based on the actual measuring data in this area.

Effects of bentonite content on the corrosion evolution of low carbon steel in simulated geological disposal environment

The effects of bentonite content on the corrosion behavior of low carbon steel in 5 mM NaHCO3+ 1 mM NaCl + 1 mM Na2SO4 solution were investigated by electrochemical measurements combined with X-ray diffraction(XRD) and scanning electron microscopy(SEM). In the initial immersion stage, the cathodic process of low carbon steel corrosion was dominated by the reduction of dissolved oxygen, while it transformed to the reduction of ferric corrosion products with the immersion time. The presence of bentonite colloids could suppress the cathodic reduction of oxygen due to their barrier effect on the diffusion of oxygen. However, the barrier performance of bentonite layer was gradually deteriorated due to the coagulation and separation of bentonite colloids caused by the charge neutralization of iron corrosion products dissolved from the steel substrate. More bentonite colloids could maintain the barrier effect for a long time before it was deteriorated by the accumulation of corrosion products. Conversely,it could lose the performance completely, and the corrosion behavior of low carbon steel reverted to the same as that in the blank solution.

Effect of chloride ion on corrosion behavior of low carbon steel in 0.1 M NaHCO_3 solution with different dissolved oxygen concentrations

The corrosion behavior of low carbon steel in 0.1 M NaHCO_3+ 0.1 M NaCl solution with different dissolved oxygen concentrations was investigated with gravimetric tests and electrochemical measurements.Results show that the corrosion mass loss of steel is remarkably increased with the addition of chloride ion. In the initial stage, the carbon steel tends to active dissolution due to the dissolution effect of chloride ion on the oxide film; as a result, the corrosion potential maintains as low values. With the immersion time going by, the corrosion potential of the steel is promoted as a result of the accumulation of the corrosion products. However, the rust layer is loose and porous due to the deteriorating effect of chloride ion, which decreases the reduction resistance of oxygen. Meanwhile, the porous rust layer could be repaired by the depolarization of oxygen. Under the synergistic effect of chloride ion and oxygen, the corrosion of the steel is accelerated during the repeated process of dissolution and reparation of the oxide film.

Corrosion Measurements of Reinforcing Steel by Different Electrochemical Techniques

Electrochemical techniques of the corrosion measurements of reinforcing steeI in concrete have been evaluated. These techniques include half-cell potential measurements, impressed voltage method, impressed current method and potentiostatic polarization technique. The results of corrosion behaviour of the steel in both 5%NaCl and 5%MgSO4 show that each electrochemical technique provides some information about the condition of the steel bar or the corrosivity of the environment being evaluated, yet none provides a complete data regarding the corrosion resistance of reinforcing steel in aggressive media

Corrosion behavior of low-carbon Cr micro-alloyed steel for grounding grids in simulated acidic soil

To improve the corrosion resistance of steels for grounding grids, a low-carbon Cr micro-alloyed steel was developed （C 1 steel）, and corrosion behavior of Q235 steel and newly developed C1 steel in simulated acidic soil was investigated. The corrosion rate was evaluated with the mass loss measurements, while the corrosion morphology of surface and cross section of rust layer was observed by scanning electron microscopy. The corrosion products were analyzed by energy- dispersive X-ray spectrometry, X-ray diffraction and X-ray photoelectron spectroscopy, and the polarization curve was measured using potentiodynamic polarization method. Results indicated that C 1 steel displayed good corrosion resistance in the simulated acidic soil, of which the corrosion rate was only 30% of that of Q235 steel after corrosion for 360 h. The analysis of rust layer showed that lower carbon content in steel could reduce the tendency of micro cell corrosion and appropriate amount of chromium could improve the corrosion potential of metal matrix. Moreover, the analysis of X-ray photoelectron spectroscopy revealed that the chromium enriched in inner rust layer of C1 steel existed mainly in the form of Fe2CrO4, which facilitated the formation of Cr-goethite and improved the protection of corrosion products.

Galvanic Corrosion Behavior of Copper-Drawn Steel for Grounding Grids in the Acidic Red Soil Simulated Solution

The influence of pH and metallographic structure on the corrosion behavior of copper-drawn steel is studied with the simulated system.The effect of pH on the corrosion behavior of copper-drawn steel has been investigated using open-circuit potential,potentiodynamic polarization,galvanic current measurement,scanning electron microscopy and scanning vibrating electrode technique techniques.The steel is corroded as anode,while the corrosion of copper plate is protected as cathode.All the results revealed that pH and metallographic structure had a significant influence on the corrosion behavior of copper-drawn steel.With the decrease in pH value from 6 to 2.4,the corrosion rate of copper-drawn steel galvanic couple(Cu-Fe GC)obviously increased in the simulated solution of acidic red soil.The electric field formed by the Cu-Fe GC changes the direction of ion migration between the copper and drawn steel electrodes,which impacts the composition and microstructure of corrosion products formed on the electrode surface.

低碳钢在库尔勒土壤中腐蚀行为的室内研究

利用埋设试样的方法和SEM、EDS、XRD等分析以及失重法和电化学方法研究了低碳钢在库尔勒水饱和土壤中腐蚀 .结果表明 ,在 1 6℃下腐蚀速率随时间增加变化不大 ,而在 32℃和 4 5℃时 ,80天后的腐蚀速率要远大于 32天的 .电化学测量表明自然腐蚀电位在 2 0天时达到稳定 ,腐蚀速率随温度的升高而增加 .埋设 32天后 ,试样表面产生的氧化膜阻碍了腐蚀的进行 ,而随着埋设时间延长 ,温度效应仍占主导地位 。

碳钢在华南酸性土壤中的腐蚀行为研究

根据 12年来对华南酸性土壤腐蚀试验站与土壤腐蚀性有关的性能数据测试结果 ,分析了华南站酸性土壤的基本情况 ;在华南酸性土壤中 ,用埋设试样的方法测试了经过 1.4年、3.4年、6.4年及 8.6年 4个试验周期后的腐蚀数据 ,并在近两年对碳钢埋样作连续原位测试 ,探讨腐蚀数据变化规律 .结果表明 ,碳钢在华南地区酸性土壤中的腐蚀严重 ,主要为局部腐蚀 .

用极化曲线评价钢铁材料土壤腐蚀行为的研究

在后插参比电极测量法的基础上，运用极化曲线测试技术测出的累加平均腐蚀速度普遍高于实际腐蚀速度，两者之间具有很好的线性相关性．依此制定了一项电化学评价方法，对钢铁材料在不同土壤腐蚀体系中的腐蚀行为进行了研究和评估，通过室内试验，表明土壤湿度、含气率和盐分含量三个因素共同影响着土壤腐蚀行为．

碳钢的不均匀性和土壤中阴离子对腐蚀的影响

对埋藏在土壤中２０年以上的碳钢腐蚀进行了分析，扫描电镜、能谱和金相分析结果表明，钢中夹杂物．焊缝区域易产生点蚀，土壤中存在硫酸根和氨离子也是产生点蚀的重要因素．

土壤腐蚀体系后插参比测量法研究

通过后插参比电极的方法有效地消除了试验／参比电极之间的土壤介质电阻上ＩＲ降的影响，从而得到在高阻抗的土壤介质中真实反映金属电极极化行为的曲线，为运用电化学技术研究土壤腐蚀提供了一种新的手段．

温度对不同含水率土壤中碳钢腐蚀行为的影响

中原油田气举管网的土壤腐蚀十分严重。为此,采用极化曲线测试技术和电化学阻抗谱,研究了20碳钢在25,55,85℃的正常含水率(21%WHC)和高含水率(45%WHC)的中原油田土壤(较高盐含量)中的腐蚀行为。结果表明,在同一温度下,正常含水率的土壤中碳钢腐蚀速率均大于高含水率土壤时的腐蚀速率。温度对碳钢腐蚀的作用与土壤含水率有关,85℃时在正常含水率的土壤中碳钢的自腐蚀电流增大到68.42μA/cm2,而此时在高含水率的土壤中碳钢自腐蚀电流变化较小(13.06μA/cm2),这与阻抗结果相符。正常含水率的土壤中温度对土壤腐蚀的影响大于对高含水率时的影响。

不同湿度土壤中硫酸盐还原菌对碳钢腐蚀的影响

利用微生物分析、失重法、交流阻抗测试技术、扫描电镜及表面能谱等方法 ,研究了在不同湿度的同一种土壤中 ,硫酸盐还原菌对碳钢腐蚀的影响规律 .结果表明 ,土壤湿度对菌类生长的影响是显著的 ,硫酸盐还原菌随着湿度的提高呈递增趋势 ;在相同的湿度下 ,接菌土壤中A3钢腐蚀速率和点蚀深度都明显大于灭菌土壤 ,说明硫酸盐还原菌加速了A3钢在土壤的中的腐蚀 ;随着含水量的增大 ,A3钢腐蚀速率首先增大 ,当土壤含水量增大到 15 %～ 2 0 %时 ,腐蚀速率达到最大 ,然后腐蚀速率随着湿度增大而趋于减小 ;最大腐蚀深度出现在土壤含水量为 15

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位和土壤的电阻率、氧化还原电位及温度等参数。经实验室和野外现场试验 ,并对测得的数据进行分析表明 。

油田腐蚀实例及腐蚀机理解析与控制技术

对赵州桥油田生产设备的腐蚀状况进行了全面的调查和事例分析,通过腐蚀介质化学成分分析和腐蚀试验初步研究了油田污水介质中碳钢的腐蚀机理,确定了其主要腐蚀因素为高含量的Cl-和微生物的活动。室内试验和现场试验的结果表明,这些因素导致了强烈的点蚀倾向,是构成油田设备腐蚀穿孔的主要原因。基于腐蚀事例分析和腐蚀机理研究的结果,针对油田的不同生产设备和生产环境,提出并实施了相应的腐蚀控制措施。

湿度对钢铁材料在中性土壤中腐蚀行为的影响

应用弱极化曲线技术和电化学阻抗谱研究了湿度对中性土壤中钢铁材料腐蚀行为的影响 .结果表明 ,各种湿度的土壤中碳钢的腐蚀速度和腐蚀电位均随着腐蚀的持续进行而趋于一个稳定值 ;碳钢的稳定腐蚀电流密度随湿度变化存在最大值 .碳钢土壤腐蚀过程与土壤湿度密切相关 .

X70管线钢在CO_3^(2-)/HCO_3^-溶液中的电化学行为研究

采用动电位扫描技术研究了X70管线钢在CO3 2 -/HCO3 -溶液中的电化学行为 .通过分析X70管线钢在Na2 CO3 /NaHCO3 溶液中的极化曲线 ,讨论了HCO3 -的浓度对阳极极化行为的影响 .采用快扫描与慢扫描得到的结果 ,分别利用Parkins边界条件和应力腐蚀破裂 (SCC)参数Pi,预测出X70管线钢在 1mol/LNaHCO3 +0 5mol/LNa2 CO3 溶液中的SCC敏感性电位区间 。

钢筋在模拟碳化渐变条件下的腐蚀过程研究

采用电化学阻抗谱(EIS)和极化曲线研究了供货状态和打磨光滑钢筋在模拟孔隙液中碳化渐变条件下的腐蚀行为.采用扫描电镜结合能谱(SEM/EDX)和X射线衍射(XRD)对钢筋表面形貌和组成结构进行了分析.结果表明:碳化过程中钢筋表面的电化学行为可分为2个过程,即钝化膜形成或修复过程以及钙沉积过程.在混凝土碳化的过程中,并不是随着pH值降低随即就发生腐蚀,而是随着时间的进一步推移,当CaCO_3转化为Ca(HCO_3)_2,沉积层破坏时才发生腐蚀.另外,供货状态和打磨光滑钢筋在此过程中的响应时间有一定差异.

温度对土壤中碳钢腐蚀行为的影响

利用极化曲线、电化学阻抗谱(EIS)和X射线衍射(XRD)等方法,研究了温度对试验土壤中碳钢腐蚀行为的影响。结果表明,在25～75℃试验温度范围内,随着土壤温度的升高,碳钢的腐蚀速率增加。碳钢的电化学阻抗谱由高频容抗弧和低频感抗弧组成,表现为两个时间常数,电荷转移电阻R_1随温度升高而减小,腐蚀过程受活化极化控制。碳钢表面的腐蚀产物主要由Fe_2O_3、Fe_3O_4、SiO_2和Al_2O_3组成。

同种金属在异种土壤中的腐蚀行为研究

研究了电连接的20无缝钢管试件在穿过两种相邻但理化性质迥然不同的土壤时的腐蚀行为,在粘土中部分表现为阳极,有较严重的腐蚀,在沙土中部分表现为阴极,腐蚀较轻。