Cathodic protection of steel in concrete

Cathodic protection of reinforced concrete has been developed by a combination of trial and error, fundamental research, applied research and transfer of technology from related fields. These developments have been underway for 35 years and have been progressed by civil engineers, concrete technologists, corrosion scientists and cathodic protection engineers. In the past 6 years in the U.K. the investment in repairs to reinforced concrete structures incorporating cathodic protection has grown from a minimal £100,000 p.a. to some £20 million p.a. This paper reviews the developments in cathodic protection of reinforced concrete during the last 35 years with particular emphasis on developments during the last decade. The critical areas of this multi-discipline technology in respect of system performance and future development are anode systems, anode overlays and assessment of cathodic protection performance. These critical areas are addressed in detail and some requirements for future work are highlighted.     

Cathodic protection of new and old reinforced concrete structures

Current and potential distributions measured on concrete slabs and simulated by computer modelling are discussed in relation with the application of cathodic protection to new reinforced structures as a corrosion preventive method. The results show high penetration of cathodic protection over the depth of uncontaminated concrete, so that even a rebar relatively distant from the anode can be polarized, whereas the penetration is limited to the rebars near to the anode in chloride contaminated slabs with corroding rebars. The great throwing power and the wide range of protection potentials for uncorroding concrete structure enable safe application of the cathodic protection even to new prestressed structures.     

Cathodic protection of steel in concrete using magnesium alloy anode

Corrosion of steel embedded in concrete structures and bridges is prevented using cathodic protection. Majority of the structures protected employ impressed current system. Use of sacrificial system for the protection of steel in concrete is not as widely employed. The use of magnesium anodes for the above purpose is very limited. This study has been carried out with a view to analyse the use of magnesium alloy anode for the cathodic protection of steel embedded in concrete.Magnesium alloy anode, designed for three years life, was installed at the center of reinforced concrete slab, containing 3.5% sodium chloride with respect to weight of cement, for cathodic protection. Potential of the embedded steel and the current flowing between the anode and the steel were monitored, plotted and analyzed. Chloride concentration of concrete at different locations, for different timings, were also determined and analyzed.The magnesium anode was found to shift the potential of the steel to more negative potentials initially, at all distances and later towards less negative potentials. The chloride concentration was found to decrease at all the locations with increase in time. The mechanism of cathodic protection with the sacrificial anode could be correlated to the removal of corrosive ions such as chloride from the vicinity of steel.     

Cathodic protection of cargo/ballast tanks of crude oil tankers

Unless a special protection is provided pitting corrosion may occur on top and at the bottom of ballast tanks. Usually a partial coating (horizontal areas) is used in connection with cathodic protection by sacrificial anodes. More than two years' observation of coated and uncoated, cathodically protected containers has shown, that anode efficiency is generally better than 90%, and in many cases as high as 100%. The current densities measured depend from the point of measurement and are higher at the bottom, in particular when the latter is coated. On the basis of the measurement results it is possible to assess the protective current requirements for horizontal anc vertical surfaces.     

浅析东临复线输油管道阴极保护距离缩短的原因

通过多种测试方法对东临复线输油管道阴极保护系统的检测,发现防腐层老化、漏电点多是该管线阴极保护距离缩短的主要原因.为此,提出了处理方法和预防措施,建议对管道腐蚀与防护系统的技术现状和管道整体安全性进行科学评价.     

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.     

阴极保护法在电力 电缆防腐蚀中的应用分析

在电力系统中,电力电缆作为其中比较重要的一项设施,同时也在当前我国基础设施中占据一定的应用地位,就此本文分别从恒电位仪、科学选用阳极材料以及其他方面三个角度来分析阴极保护法在电力电缆防腐蚀中的应用,以供参考.     

阴极保护电化学场的有限元仿真及电位扫描测量系统研究

阴极保护的有限元仿真计算是一种有效的数值计算方法。三维计算时为了解LAPLACE方程,采用8节点立体单元剖分场域、构造插值函数,通过每个单元的分析和整体合成建立了三维有限元模型,并给出了电流电位分布等值线图。最后设计了一套全自动钢表面电位扫描验证系统,将三维情况下模型计算值和实验验证测量值进行了比较。     

Cathodic protection of XL 52 steel under the influence of sulfate reducing bacteria

The effect of sulfate reducing bacteria (SRB) upon the cathodic protection of XL 52 steel was determined, in order to identify if the potential value of ?0.950 V versus copper/copper sulfate electrode is good enough to protect the metal surface. During the experiments, different operational parameters were monitored: hydrogen sulfide production, iron concentration, electrolyte alkalinity, microorganisms' population, as well as the metal surface damage. At the same time, the corrosion rate was determined using two electrochemical techniques: polarization resistance (PR) and electrochemical impedance spectroscopy (EIS). According to the results, it was observed that the protection potential of ?0.950 V versus copper/copper sulfate electrode is not enough to control the microbiologically induced corrosion. This situation is reinforced by the fact that significant iron concentration was found in the electrolyte. The microbiological activity is not affected by the protection potential. On the contrary, the population growth is slightly strengthened. The alkalinity generated by the applied potential did not stop the SRB growth. A type of localized corrosion was developed during the experiments with microorganisms, even when the protection potential was applied to the system.     

外加电流系统在天然气管道阴极保护工程实例

本文主要讲述了外加电流系统在新建6.4km城市天然气管道阴极保护的应用实例。本工程外加电流系统采用浅埋式高硅铸铁阳极地床作为辅助阳极,采用高频开关恒电位仪为系统电源,采用长效硫酸铜参比电极作为信号反馈电极,沿线设置6个测试桩用于监测阴极保护效果,阴极保护投产运行后,整条天然气管道阴极保护效果良好。     

Cathodic protection monitoring of buried carbon steel pipeline: measurement and interpretation of instant-off potential

The criterion used to verify the cathodic protection condition of a structure is based on structure-to-electrolyte potential measurement, which can include an ohmic drop contribution. Among the available techniques, the use of potential probes with internal reference electrode and of corrosion coupons with a so-called soil-access tube represents the most appropriate way to measure the IR-free potential, eliminating the ohmic drop contribution. An alternative is represented by on-off technique if equalising, galvanic or stray currents are not present. Laboratory tests have been carried out in soil-simulating solution on cathodically protected carbon steel in order to evaluate the effectiveness of off-potential for the assessment of cathodic protection. Instant-off potential is not reliable in overprotection condition; moreover, the accuracy of the measurement is strongly influenced by the presence of external current as galvanic or equalising currents. The effect of low-pass filter in the data acquisition system on the potential reading is discussed.     

Cathodic protection of UNS C71500 heat exchanger tubes in sulphide polluted Arabian Gulf sea water

Abstract

A laboratory investigation using a specially designed circulating test rig has been undertaken to study the feasibility of achieving complete cathodic protection of UNS C71500 heat exchanger tubes in sea water applications by means of sacrificial carbon steel anodes. The results have indicated that the galvanic current distribution covered the entire 6 m length of the tube. However, the presence of sulphide ions as pollutants in the sea water shifted the galvanic potentials of the tubes to less active potentials and affected the development of the protective films that normally form.     

Corrosion protection of commercial steel using stainless steel coatings deposited by Cathodic Arc Plasma Deposition technique

The commercial steel AISI 1010 was coated with AISI 316L steel using Cathodic Arc Plasma Deposition (CAPD) technique. The coatings were deposited in vacuum and in the presence of nitrogen, acetylene and mixture of the two as reactive gases. The coatings were deposited as a function of time while other parameters remained constant. The coatings 0.75 to 1.3 μm thick were adherent and amorphous. The aqueous corrosion properties of the coated samples in 3.5 wt % NaCl solution were studied by Tafel, cyclic and potentiodynamic polarization measurements. The derived corrosion parameters were then compared among the various uncoated and coated samples. The study revealed that the coated samples were more corrosion resistant than the uncoated one. Similarly, the samples coated in the nitrogen + acetylene mixture atmosphere were more corrosion resistant than the samples coated in only nitrogen and acetylene atmospheres. The corrosion parameters were also compared as a function of coating time to ascertain best coating thickness.     

Cathodic protection requirements for high strength steel in sea water assessed by potentiostatic weight loss measurements

Abstract

A potentiostatic weight loss technique has been used to compare the corrosion rates of Weldox 700 high strength low alloy steel exposed to both natural and sterile sea water at potentials ranging from the free corrosion condition to - 1000 mV (SCE). Anodic polarisation curves with Tafel constants of 54 and 64 mV per decade were fitted to the data and the minimum levels of protection required to limit the corrosion rate to 0·001 mm per year were found to be - 770 and - 790 mV (SCE) in natural and sterile sea water, respectively. Lower corrosion rates occurred in filtered natural sea water than in sterile sea water but the highest rates were recorded on specimens ex posed to a seabed sediment. The reasons for this behaviour are discussed in terms of the biofilms and the numbers of sulphate reducing bacteria present on the surfaces.