影响舰船外加电流阴极保护电位因素分析及仿真

舰船都会使用外加电流阴极保护的方法进行船体防腐保护,保护电位是进行外加电流阴极保护方法的核心参数,如何设定保护电位的数值将会决定舰船的防腐效果。文章首先建立舰艇外加电流阴极保护电位计算模型,然后从阳极与被保护体的距离,腐蚀介质电阻率变化对电流分布的影响,涂层对电位电流分布影响三个方面讨论影响外加电流阴极保护电位的因素。通过仿真,确定了以上因素如何影响外加电流阴极保护电位,为合理设计外加电流阴极保护电位参数提供了理论依据。     

外部结构对储罐底板外壁阴极保护电位分布影响的数值模拟计算

利用有限元和有限差分法,建立了储罐底板外壁阴极保护电位分布的数学模型,利用BEASY软件模拟计算外部结构对罐底外壁的阴极保护电位分布影响,包括接地类型、砂土层、阳极形式等。探讨了采用深井阳极对储罐底板外壁进行阴极保护时,输出电流较大、保护效果不理想的主要原因。     

沈阳中科腐蚀控制工程技术中心

正技术支持:常守文研究员[现场测试及腐蚀研究]□环境介质(土壤、水介质)综合腐蚀性能测量评定(介质电阻率、介质pH值、氧化还原电位和管地电位的测量)□阴极保护效果的评价及故障诊断□管道防腐层性能评价与管道定位□腐蚀调查、交直流干扰、杂散电流腐蚀的原因分析和防护[设计和现场安装服务]□阴极保护系统设计,包括牺牲阳极法和外加电流法。保护参数的选取、材料设备的选择和施工图设计等□阴极保护系统现场施工及安装     

阴极保护防止绝缘覆盖层下金属的缝隙腐蚀

对阴极保护防止绝缘覆盖层下金属缝隙腐蚀国内外的研究动态进行了综述,总结了有关阴极保护下缝隙内的电位、电流分布和传质过程及其数学模型等方面的研究成果,分析了阴极保护防止缝隙腐蚀的机理。     

沈阳中科腐蚀控制工程技术中心

正技术支持:常守文研究员【现场测试及腐蚀研究】□环境介质(土壤、水介质)综合腐蚀性能测量评定(介质电阻率、介质PH值、氧化还原电位和管地电位的测量)□阴极保护效果的评价及故障诊断□管道防腐层性能评价与管道定位□腐蚀调查、交直流干扰、杂散电流腐蚀的原因分析和防护【设计和现场安装服务】□阴极保护系统设计,包括牺牲阳极法和外加电流法。保护参数的选取、材料设备的选择和施工图设计等     

深井套管阴极保护的计算与分析

对江汉油田3000多米深的王59井套管的阴极保护电位的分布进行了计算，计算结果与实测结果的相对误差均小于8%.尽管如此，在阴极保护电流从5 A增大到20 A的情况下，仍然无法使该井套管的保护电位完全达到最小保护电位的标准.     

电化学阴极保护系统中的电位和电流分布

电化学阴极保护系统中的电位和电流分布邱枫(中国科学院上海冶金研究所九五届硕士研究生,上海200050)受电化学阴极保护的金属结构物表面的电位只有在一定的范围内才能受到有效的保护。因而,了解电位分布的规律是合理地设计阴极保护系统的必要条件。本文作者首先探讨了适用于阴极保护系统中电位和电流分布计算的有限元算法的应用范围,并提出了改善迭代收敛性的一种特殊的网格划分方法:在沿第二类边界面法向方向上适当细密地划分,....     

用带状牺牲阳极对埋地钢管实施阴极保护时的电位和电流分布

用带状牺牲阳极对埋地长输钢管实施阴极保护时,沿着轴线方向的电位分布一定是均匀的。本文通过有限元法计算,进一步研究沿着管道圆周上的电位和电流分布的规律。结果表明,在研究的参数范围以内,沿着管道圆周的电位分布也是相当均匀的。土壤电阻率越低,电位极化值越大,但所需的保护电流也增大。防护性能好的涂层总是有利于阴极保护。阳极距离和管道外径对电位和电流分布没有什么影响。这些结果可以供工程上参考,同时说明用带状牺牲阳极对埋地长输钢管实施阴极保护是十分理想的。     

边界元法在导管架外加电流阴极保护系统设计中的应用

本文提出了一种基于边界元法的导管架外加电流阴极保护系统设计方法。该方法不仅可以预测导管架结构表面保护电位和电流密度分布状态,而且可以得到外加电流阴极保护系统所需的保护电流值和参比电极点的电位值。为验证该方法的有效性,将使用该方法得到的设计方案应用于实验室导管架模型外加电流阴极保护试验,最终得到的试验结果与计算结果吻合良好。该方法可作为导管架外加电流阴极保护系统设计的有效工具。     

反电位法阴极保护的电力线分布研究

通过外加电流阴极保护的模拟实验,绘制了反电位法阴极保护的电力线分布,并与同条件下不加反电位法的和一般外加电流阴极保护的电力线分布进行了对比分析,探讨了反电位法阴极保护电力线的特征及管地电位的分布情况,为长距离的阴极保护设计提供了可靠的工程依据。     

剥离涂层下管线钢腐蚀研究进展

综述了在有阴极保护的条件时剥离涂层下缝隙内电位电流的分布和化学环境的变化、阴极保护防止缝隙腐蚀的机理、微生物腐蚀的机理以及前人提出的关于剥离涂层下微生物腐蚀与阴极保护相互作用的规律，并展望了对于解决剥离涂层下微生物腐蚀难题需进一步的实验研究.     

Localised corrosion of cathodically protected pipeline steel under the effects of cyclic potential transients

Cathodic protection (CP) may lose its effectiveness for protecting buried steel pipeline from soil corrosion due to the effects of potential excursions caused by stray currents. In this work, dynamic localised corrosion processes of buried steel due to the effects of cyclic potential transients have been visualised using an electrochemically integrated multi-electrode array, often referred to as the wire beam electrode (WBE). The focus has been on the understanding of the effect of cathodic transients. The WBE maps suggest that the amplitude of cathodic transient, as well as the ratio of anodic cyclic to cathodic cyclic, can significantly affect the corrosion rates and patterns. In particular, if the cathodic transient leads to a very negative potential, e.g. ?1350?mV_vs.CSE, rapid corrosion would occur on buried steel surface. These results have implications for CP parameter selection for preventing stray current-affected buried steel pipelines.     

Effect of pulse cathodic protection on corrosion mitigation and electrochemical conditions under a simulated coating disbondment on pipeline steel

Coating disbondments on pipeline steels are regions with high resistivity where conventional cathodic protection (CP) could not fully protect. Therefore, in an attempt to mitigate this challenge, this study investigates the effect of pulse CP on corrosion mitigation and electrochemical conditions under a simulated coating disbondment on X-52 pipeline steel. In this regard, conventional and pulse CP of ?870 mV_SCE were applied to the open mouth of a simulated coating disbondment. For pulse CP, frequencies of 1, 5, and 10 kHz were used. Results showed while the conventional CP was not able to fully protect the 20 cm simulated coating disbondment, for the pulse CP with increase in frequency from 1 to 5 kHz, and from 5 to 10 kHz, improve in CP potential protection under the simulated coating disbondment was achieved. This was accompanied by considerably lower corrosion and a more uniform pH distribution under the simulated coating disbondment.     

Korrosionsschutzmaßnahmen bei erdverlegten Rohrleitungen und ihre Überwachung

Measures for corrosion protection of buried pipelines and their control Corrosion protection of buried pipelines involves a combination of proper coating and electrochemical protective measures. The cathodic protection is based on the potential dependence of corrosion rates of steel in water. The theory is easy to understand. But problems in service arise with respect to questions on current distribution as well as the control by pipe-to-soil potential measurements. Proper coating is an essential requirement for an adequate current distribution. In the neighbourhood of large holidays disturbances of the current distribution can occur which can go undetected by normal potential control in steps of 1 to 2 km depending on the soil conditions. For a better control the intensive measuring technique was employed. By this method pipe-to-soil potentials and potential gradients for both “on” and “off” conditions of the polarisation current are measured in steps of 5 m. The values are evaluated through a computer assisted programme. Pipe sections with large holidays and with insufficient polarisation can thus be detected. In special cases that are characterized by high cell currents caused by contact with foreign structures or by stray currents from foreign dc sources it is difficult to measure IR-free potentials. In this case external measuring probes are installed which simulate holidays of the object to be protected. The potential of these probes can be measured without IR-drops with the aid of capillaries. The probes inform on proper cathodic protection, provided the holidays of the object to be protected are smaller than the testing area of the probe. With the aid of the intensive measuring technique as well as the application of the measuring probes it is possible to control the total object to be protected. But in the case of very high ac densities difficulties cannot be excluded. Diversion of these current is a protective measure. Questions occur as to possible corrosion danger beneath disbonded coatings and the occurrence of stress corrosion cracking. Experiments have shown that corrosion resistance is not restricted provided the construction and the service conditions of the pipeline comply with the standards.     

Modeling pipeline crevice corrosion under a disbonded coating with or without cathodic protection under transient and steady state conditions

Underground steel pipelines are protected by coatings and cathodic protection (CP). The pipeline corrosion occurs when the coating is disbonded away from a defect or holiday to form a crevice and the corrosion rate varies temporally and spatially in the crevice. In the presence of dissolved oxygen (O₂) in soil ground water, a differential O₂ concentration cell may develop in the crevice because O₂ diffuses more readily into the crevice through the holiday than through the disbonded coating. CP can decrease or eliminate the O₂ concentration cell depending on the potential applied at the holiday. Since the coatings are usually non-conductive, CP is unable to protect the steel surface deep inside the crevice. The transport of dissolved O₂, and that of dissolved carbon dioxide (CO₂) if present, into the crevice through holiday can be key to determining the crevice corrosion rate. In this work, the transient and steady state behavior of the corrosion process is investigated. The effect of the cathodic portion of iron vs. ferrous ion redox reaction on the crevice corrosion rate, which is often neglected traditionally, is further studied. At steady state, the effect of dissolved O₂ on the crevice corrosion rate and the added effect of dissolved CO₂ are mathematically modeled.     

Effect of cathodic protection on macrocell currents: A viable method to monitor and control the efficiency of CP?

Corrosion protection of steel reinforcement in concrete structures by cathodic protection (CP) is a cost effective, reliable, and widely accepted method to stop and prevent the corrosion of the steel reinforcement. The efficiency of CP is usually monitored by the “24 h, 100 mV depolarization criterion,” a purely empirical criterion whose implementation is cost and labor intensive and that does not allow online control of CP. Within an extended research project on CP applied to concrete members of a highway bridge exposed to penetrating moisture, three sets of macrocells (MC), each composed of five MC sensors, were installed in conjunction with concrete resistance sensors and silver/silver chloride reference cells. Chloride profiles were determined from the cored or drilled powder originating from the installation of sensors and from drilling cores. Corrosion currents, steel potentials, and concrete resistance were monitored over a period of 1 year before, after installing the CP systems (which remained switched off for half a year for evaluating the effect of the conductive coating), and after start-up of the CP systems. The CP systems applied consist of a moisture resistant conductive coating. As expected CP has a pronounced effect on local MC currents: Anodic MC currents were reduced or changed into cathodic currents, whereas cathodic currents were only weakly influenced. By adjusting the applied protection current all anodic MC currents may be changed into cathodic MC currents. Results indicate that the 100 mV depolarization criterion is a conservative criterion in atmospherically exposed concrete; it is not reliable in strongly wetted concrete. There was no consistent correlation between the CP induced changes in the local MC currents and 24 h depolarization values indicating that large potential shifts induced by CP do not necessarily imply overprotection. Results show that monitoring MC currents before, during, and after CP operation allows to demonstrate in a transparent way the effect of CP on the corrosion of the steel reinforcement. Online monitoring of MC currents is proposed as a viable and comprehensible method to monitor and control the efficiency of CP.     

埋地管道直流干扰腐蚀研究Ⅱ—地表电位梯度检测

地表电位梯度指标容易检测,但根据现有标准难以获得管道杂散干扰腐蚀的有用信息.本文采用新的方法测量电位梯度,并根据测量数据,解析出二种电流成分:地表干扰电流和流入(出)管道的电流;后者和实际杂散干扰腐蚀有良好相关,电流流出管道的位置代表阴极保护管道的腐蚀活性点.     

Effect of alternating current on cathodic protection on pipelines

In this work, the effects of alternating current (AC) on the performance of cathodic protection (CP) and the CP potential readings were investigated on a 16Mn pipeline steel in a simulated soil solution. The presence of AC interference decreases the CP effectiveness to protect the steel from corrosion. Only when CP potential is sufficiently negative, the steel is under a complete protection even when the AC current density is 400 A/m². Moreover, the AC would shift CP potential from the designed value. The effect of AC on the CP performance depends on the cathodic potential applied on the steel.     

杂散电流对海底管道表面电位影响预测方法研究

目的：外加电流阴极保护技术逐渐应用于船舶和海洋结构物防腐领域,但随之而来的杂散电流很可能使平台附近的海底管道本身或者其牺牲阳极阴极保护系统产生电化学腐蚀,缩短海底管道使用寿命,甚至破坏管道本身结构而造成严重的生产事故,因此需要预测外加电流阴极保护系统对附近海底管道及其牺牲阳极阴极保护系统可能造成的不利影响。方法提出一种基于边界元法的预测海底管道杂散电流影响的数值模拟方法,建立包括域内控制方程和对应的边界条件的数学模型,可以计算得到海底管道受杂散电流影响区域的位置和范围,并且得到受影响区域表面保护电位的分布情况。结果通过实验室海底管道模型杂散电流试验测量结果与数值模拟结果进行比较,验证该方法预测海底管道杂散电流影响的准确性,数值模拟仿真结果与试验测量结果最大误差百分比约为1.7%,平均误差百分比小于0.2%。数值模拟计算结果准确地预测了海底管道模型表面保护电位分布情况,预测了导管架平台模型外加电流阴极保护系统对海底管道模型杂散电流的影响情况。结论使用的边界元阴极保护数值模拟技术可以准确预测海底管道杂散电流的影响情况,为海底管道杂散电流影响预测研究提供了有力工具。     

在役油气管线防腐蚀层老化的评价方法

为研究和评价在役长输油气管线防腐蚀层的质量,建立了反映涂层质量变化的简单数学模型,分析了防腐蚀层过渡电阻与长输油气管线的阴极保护电位分布规律的关系,从理论上了解防腐蚀层的漏失情况。结合工程现场的实测数据,通过标准管地电位(P/S)测试,绘制电位-距离曲线,推算绝缘层特性参数及管线沿线电位的衰减系数,对在役管线的防腐蚀层状况进行评估,从而为管网的维护提供相应依据,指导现场管道的安全运行。