数值模拟长输管道线性辅助阳极的阴极保护

通过建立数学模型,确定边界条件,采用基于边界元的数值模拟软件BEASY,对长输埋地钢质管道采用线性辅助阳极时的阴极保护效果进行了模拟。总结了土壤电阻率、线性辅助阳极轴向电阻和输出电流变化时,线性辅助阳极输出电流的衰减规律。研究了线性辅助阳极与管道的间距、管道防腐层绝缘电阻率、土壤电阻率、线性辅助阳极初始输出电流和管径大小变化时,60km长管道的阴极保护电位分布。研究结果可为后续线性辅助阳极在长输管道阴极保护中的应用提供理论参考和依据。     

固溶态Al-Mg-Si合金的电阻变化研究

通过电阻法研究了完全固溶态和退火态的Al-Mg-Si合金,分析了空位、溶质原子和析出相对合金固溶体电阻率的影响,在此基础上补充并修定了Matthissen定律,对低浓度固溶体电阻率偏离Matthissen定律这一现象作出了合理的解释,得到了合金电阻率与成分和固溶温度的关系式。经验证,合金电阻率的计算值与实验测得值比较接近。     

酸性土壤中接地网牺牲阳极阴极保护法研究

目的提高牺牲阳极的阴极保护法在酸性土壤中对接地网的防腐能力,分析牺牲阳极阴极保护法在酸性土壤中应用的技术要点,总结保护效果优化措施。方法设计牺牲阳极模拟系统,模拟地网面积为3.52 m2,保护电流设计为35.2 m A,对Q235碳钢和镀锌钢两种常用接地材料的接地电阻、保护电位及保护电流进行研究。结果该方法对镀锌钢保护较好,保护电位均低于-0.95 V;对Q235碳钢保护较差,保护电位部分高于-750 m V,且波动较大,最大波幅可达201 m V。系统运行中,计算得出保护电流在降雨量较大时最高可达30.75 m A,降雨量较小时最低为11.89 m A,均低于设计值。结论由于阳极处砂石较多、土壤电阻率高,阳极不能完全释放电流。其次,土壤保水性差,电阻率波动大,系统运行不稳定也抑制了保护效果。酸性土壤盐基性离子大量淋失,土壤电阻率普遍较高,且受降雨扰动较大,牺牲阳极工作效率较低且稳定性差。需采用适当提高保护电流、降低阳极区土壤电阻率、优化阳极设计工艺参数等措施以达到良好的保护效果。     

雷击高压输电线路对临近埋地油气管道电磁干扰的案例分析

为研究雷击高压输电线路对临近埋地油气管道的电磁影响,利用SES CDEGS数值模拟软件建立了国内某现场案例的输电线路和临近埋地油气管道电磁干扰模型,计算预测了雷电流对管道造成的干扰情况。基于国内外相关标准和研究成果的调研,从人身安全、管道防腐蚀层击穿风险和管壁电弧熔伤风险三方面建立了雷电流对管道电磁影响的风险评价指标,对现场案例的干扰风险进行了评价,同时计算分析了土壤电阻率和杆塔接地网类型对管道过电压和接地网导体泄漏电流的影响。结果表明：现场案例中雷电流导致的管道安全风险低;土壤电阻率对管道过电压和接地网导体泄漏电流有明显影响,其随土壤电阻率升高而增大;采用水平接地网时,在接地网表面积相同的前提下,接地网结构对管道过电压和接地网导体泄漏电流的影响较小;垂直接地体的引入可缓解管道过电压,但其数量不宜过多。     

土壤环境对埋地金属管道所受高压直流干扰的影响

利用数值模拟技术研究了高压直流(HVDC)输电系统接地极对长输管道干扰受土壤环境的影响规律,并通过现场监测数据对模拟结果进行了验证。结果表明:当表层土壤厚度超过9km时,深层土壤电阻率的影响可以忽略;干扰程度受直流接地极附近土壤以及距离直流接地极最近处管道附近土壤影响很大;如果直流接地极不可避免在埋地管道附近时,应尽可能选择埋设在土壤电阻率较低的区域;模拟计算所得管道沿线电位分布情况与现场监测数据基本一致,因此该数值模拟方法可以准确预测土壤环境对埋地金属管线受高压直流接地极干扰的影响。     

耐候钢新型表面锈层稳定剂处理及其耐3.5％NaCl溶液周浸腐蚀性能

目的解决耐候钢裸露使用初期锈液流挂与飞散的问题。方法制备了新型耐候钢表面锈层稳定剂,通过周期浸润循环腐蚀试验、锈层微观分析和电化学测试等方法研究了在模拟海洋大气环境下,锈层稳定剂对耐候钢锈层结构及耐腐蚀性能的影响。结果表面锈层稳定化处理后,耐候钢表面生成的锈层区分为致密且连续的内锈层和外锈层。室内加速腐蚀168 h后,耐候钢的失重腐蚀速率由未处理的5.71 g/(m~2×h)降低到表面处理后的3.31 g/(m~2×h),失重腐蚀速率降低了约42%。耐候钢的锈层电阻由未处理的96?·cm~2提高到表面处理后的167.7?·cm~2,锈层电阻提高了约75%。表面处理后的耐候钢锈层中,Cr元素以α-(Fe_(1-x)Cr_x)OOH的形式存在于基体与锈层的界面处,Cr元素在内锈层与基体结合处发生聚集。结论新型锈层稳定剂可以明显改善耐候钢锈层结构,细化锈层晶粒,阻碍Cl~-的渗透,有助于耐候钢表面快速生成致密、连续且稳定的保护性锈层。     

储罐底板外侧阴极保护电位分布的数值模拟

建立了储罐底板外侧阴极保护电位分布的数学模型,利用FLUENT软件模拟了罐底外侧的阴极保护电位分布;研究了土壤电阻率、罐底的极化特性、阳极的埋深、与罐距离及数量等因素对罐底外侧阴极保护电位分布的影响,并将模拟结果与实测数据进行了对比。结果吻合较好。     

稀土铝合金Miedema模型计算中的参数φ*

研究修改计算式中电负性参数φ*,考虑合金化过程中不同元胞边界上电子化学势差会对合金形成能产生负的贡献,提出Miedema模型中参数φ*的计算表达式.结果表明:参数φ*的计算值与功函数值比较接近,与功函数值相比,其最大相对误差在12.0%以内,平均误差低于5.0%,计算得到的稀土铝合金系统混合焓与实验值更接近.     

浅埋高硅铸铁阳极地床降阻技术在库鄯输油管线阴极保护工程中的应用

通过模拟试验,筛选出了由聚丙烯酰胺、三乙醇胺、工业细盐、缓蚀剂及水组成的降阻剂及其最佳配比.接着,在鄯善末站开展浅埋式阳极地床工业性试验.经一年的多次测试结果表明,单根(?)150mm×1500mm的高硅铸铁阳极的接地电阻力3.9～8.4Ω,为不用降阻剂时的1/5～1/8.阳极地床由浅埋20根阳极组成,阳极间距5m,接地电阻稳定在1.3～1.8Ω之间,能满足≤2Ω的技术要求,具有工程实用价值.在此基础上,及时更改了设计,在库鄯管线需采用外加电流法实施阴极保护的约276km长的管段,4处辅助阳极地床施工均采用了浅埋阳极降阻技术.     

AgMg合金丝材的内氧化

本文用光学显微镜、电阻、硬度测量等方法研究了AgMg_(0.12),AgMg_(0.24),AgMg_(0.47)合金丝材在2—8kg/cm~2氧压下,500——800℃范围内的氧化动力学、组织和性能,研究结果表明:内氧化深度的平方与氧压力的平方根成正比;与Mg含量成反比;内氧化深度平方的对数与绝对温度的倒数成线性关系。丝材的氧化区面积与氧化时间成抛物线关系,电阻率随氧化温度的增加而降低,电阻率及显微硬度不随氧压力变化。上述结果还表明,提高内氧化速度可以改善合金的性能。     

Cathodic protection of buried steel structures: Processes occurring at the steel/soil interface during wet/dry cycles

The behavior of steel coupons buried in soil under cathodic protection (CP) was studied during wet/dry cycles using electrochemical impedance spectroscopy and voltammetry. The coupons were left at open circuit potential for 7 days before applying CP for 51 days at potentials of −0.8 and −1.0 V versus Cu/CuSO₄ on coupons 1 and 2, respectively. Wet/dry cycling was achieved by first saturating the soil with an electrolyte inside a sealed electrochemical cell and by allowing the soil to dry by opening the top lid of the cell for various periods in the experiment. Surface analysis was performed after the experiments by X-ray diffraction and Raman spectroscopy. The soil electrolyte resistance R_s depended mainly on the variations of soil moisture for coupon 1 but was strongly affected by the effects induced by CP for coupon 2. Residual corrosion rates of 17–18 and 7–10 µm/year for coupons 1 and 2, respectively, were estimated via voltammetry. The kinetic parameters vary with the polarization level so that the data obtained with a coupon polarized at a given potential cannot be used to predict the residual corrosion rate of a coupon polarized at another potential.     

变电站接地网的焊缝腐蚀分析

为了给接地网焊缝的腐蚀防护提供基础,通过电化学噪声和埋片模拟方法,研究了接地网焊缝与母材腐蚀的差别.结果发现在陕西省孝义变电站土壤中,Q235钢接地网焊缝出现了较多暂态峰,母材的暂态峰较少,焊缝腐蚀对接地网泄流的电压更敏感;腐蚀过程中母材噪声阻值R_n=3.38×104Ω/cm2,焊缝噪声阻值R_n=1.44×104Ω/cm2;母材的腐蚀速率为0.067 mm/a,含有焊缝的焊接接头腐蚀速率为0.077 mm/a,母材为均匀腐蚀,焊缝主要为局部腐蚀.     

大庆油田油水井套管侧挂串状阳极防腐模拟实验研究

针对大庆油田油水井浅表层套管腐蚀外漏逐年加剧的问题，对于正常生产的油水井套管的防腐保护提出套管外壁侧埋深井牺牲阳极串的防腐蚀技术.通过室内模拟实验，发现在水电阻率和阴-阳极面积比近似相同的情况下，深埋阳极对套管的保护效果明显优于浅埋阳极，阳极以串、并联组合方式连接有较大的电流输出和较好的电位分布.结果表明，阳极以深埋方式为宜，阳极埋入深度在3000 cm～5000 cm左右为最佳位置，阴阳极间最佳距离为900 cm.     

The effects of a CeO2 coating on the corrosion parameters of type 304 stainless steel

Coatings of CeO₂ derived from inorganic sol-gel dispersions were applied to type 304 bright annealed stainless steel (British Standard 1449 type 304S31) coupons and subjected to heat treatments at 450 and 550 °C. The coatings, 0.5 μm thick, were transparent, adherent, and stable. The aqueous corrosion properties of the coated coupons in 1 molar NaCl were then studied by potentiodynamic polarization measurements and electrochemical impedance spectroscopy. The derived corrosion parameters were then compared with similarly heat-treated, uncoated 304SS coupons. The results indicate that the application of a CeO₂ coating, heat treated at 550 °C, improves the corrosion rate as compared to an uncoated heat-treated coupon. The polarization curve for the 450 °C heat-treated, coated coupon showed passive behavior compared to transpassive for the uncoated specimen. The impedance spectrum data for the uncoated, as-received coupon could be modeled using a resistor in series with a parallel capacitor resistor combination “Randles” equivalent circuit. A coated coupon, heat treated at 550 °C, could be modeled using a more complex equivalent circuit involving a constant phase element, due to the CeO₂ coating. Modeling of the impedance characteristics for the oxidized coupons required the addition of a second series element consisting of a parallel resistor capacitor combination to give a Chi square statistic fit of X² < 5 X 10^-4.     

Cathodic protection design optimization of a buried vessel by FEM simulation

Installing linear anode loops around a buried vessel is one of the latest cathodic protection anode arrangements for buried vessels. In this arrangement, besides the physical properties of the environment, for example, soil resistivity and oxygen content, the distance of anode loops to the vessel, number of anode loops, and distance between each loop are three main designing parameters. In the present study, the cathodic protection of a buried vessel (8-m long; 2.5 m in diameter) with complete nonlinear polarization at the protected surface is studied with finite element method simulation. The analyzed variables are the number of anode loops from one to three, the anode-to-vessel distance from 0.2 to 0.6 m, the distance between loops from 0.2 to 1.6 m. Soil resistivity varies from 10 to 500 Ω·m, and oxygen limiting current density changes from 5 to 100 mA/m². Increasing anode-to-vessel distances will reduce the potential differences, and the best condition is the maximum distance, 0.6 m. The optimum number of anode loops is two. Increasing soil resistivity will increase the potential difference, but in an optimum design, its effect is not significant.     

接地极Q235碳钢材料在上海土壤环境中的腐蚀行为

通过电化学阻抗 (EIS)、极化曲线、扫描电镜 (SEM)、能谱分析 (EDS) 和X射线衍射 (XRD) 等技术对接地极Q235碳钢材料在含不同盐分的上海地区土壤中的腐蚀行为进行了研究。结果表明,在不同盐分土壤条件下,Q235碳钢的阻抗均随着浸泡时间的延长出现先升高后平稳的趋势,腐蚀速率随盐分含量增大而增大。由于沿海土壤的侵蚀性阴离子含量较高,使得所产生的锈层失去保护性。Q235碳钢腐蚀主要以全面腐蚀为主,还伴有微生物腐蚀现象,腐蚀产物膜主要由Fe₂O₃组成。根据耐腐蚀性能评价标准,接地极碳钢材料在上海土壤环境中的耐腐蚀性能为良。     

Shape and size effects for marine immersion coupons

Abstract

The conventional wisdom in corrosion testing is that the size of the coupon and its perimeter/area ratio (the surface area of the perimeter expressed as a percentage of the total surface area) are important parameters and that these will have an effect on the results obtained. In order to test this proposition, sets of mild steel coupons of the same exposed areas but having different perimeters were immersed in a marine environment. Corrosion mass loss was observed for area/perimeter ratios in the range 3·52-6·03%. Mass loss observations were taken at various times to 12 months. Sets of rectangular coupons of different sizes (50 × 100 mm and 100 × 200 mm) were also immersed. The results indicate that any variation caused by shape or size falls within the expected variability of corrosion at a test location.     

Research on corrosion rate assessment of buried pipelines under dynamic metro stray current

To provide a reference for the evaluation of corrosion rate under dynamic metro stray current, both simulated experiments in laboratory and coupon tests in the field were conducted to explore the corrosion behavior and the relationship between corrosion rates and dynamic DC interference parameters of buried pipelines. The results show that the dynamic period has a significant influence on the corrosion rate and the ratio of actual corrosion rate to the theoretical corrosion rate. The statistical data of pipe to soil potentials or current densities of coupons electrically connected to pipelines obtained from the field in many cities of China show that the dynamic fluctuation periods under metro stray current are within the range of 0–300 s, among which the majority of fluctuation periods distribute from 50 to 200 s. The dynamic fluctuation of pipe to soil potentials and current densities of coupons exhibits symmetric or asymmetric characteristics. Under the situation of symmetric positive and negative current density, the ratio of the actual corrosion rate to the theoretical corrosion rate ranges from about 4% to 22% under the typical dynamic periods range from 50 to 200 s based on the simulated experiments results in the laboratory. Besides, two corrosion rate assessment methods, including the positive shifting and time ratios of off-potentials and symmetrical or asymmetric characteristics of DC current density of coupons were proposed. In addition, the evaluation of the on-potential criteria to assess the corrosion risk of time-variant anodic interference was also discussed in the paper.     

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.