Analysis of different factors affecting cathodic protection for deep well casings

This paper introduces a comparative theoretical investigation of the conventional cathodic protection (CP) and the pulse cathodic protection (PCP) systems to show how both of them behave under different operating conditions. The effectiveness of the PCP system is also highlighted for a typical large‐scale configuration as well as some field measurements have been carried out. The performance of PCP system has been analyzed in the light of getting better protection‐current distribution along the protected well casing at reduced anode current together with reducing the stray current (corrosion) at any nearby unprotected structure(s). Many factors have been investigated to show their effects on the performance of the CP system, namely, soil resistivity, voltage pulse waveform and frequency, and multi‐layer soil. In addition, the performance of both the conventional CP and the PCP systems has been compared to that when utilizing unused/abandoned well casing as anode energized by the conventional CP system. The PCP system shows better performance than that of the conventional CP, and a similar performance at high soil resistivity to that when using unused/abandoned well casing. On the other hand, the utilization of the unused/abandoned well casing gives superior performance, especially at low soil resistivities, where the protection‐current profiles of both the conventional CP and the PCP systems decay sharply.     

Impressed current cathodic protection

Development of optimum system configurations for ships using scale models (physical scale modelling) The purpose of this fundamental study was to establish optimum cathodic corrosion protection system configurations for ship hulls. Comprehensive surveys were conducted in order to develop a better understanding of the electrochemical processes occurring on a ship hull in a seawater electrolyte. The results obtained show that the performance of a system can only be evaluated when it is installed on a real object. However, once installed the location of the impressed current anodes and the reference electrodes cannot be changed if the potential distribution over the underwater hull is not optimal. Hence, a procedure had to be established that permits the development and optimisation of system configurations for future objects. A validated, experimental laboratory technique using scale ship models was established to determine the fundamentals of cathodic corrosion protection and to develop a theoretical understanding of the underlying mechanisms. The findings obtained in practice could be applied to the models. The model studies were conducted in a systematic manner and under defined conditions in German standard (DIN) artificial seawater and in a natural electrolyte. The experiments clearly showed the functional correlation between the geometric configuration of the reference electrodes on the hull and the locations of the anodes. The results reflect the interrelationships between the electrochemically more positive bronze propeller and the steel. The configuration developed in the course of the experiments provided an optimum distribution of the protection current over the entire hull model. The data from the model study were applied to the design features of the Class 123 Frigate. Subsequently, the efficiency of this procedure was evaluated on a real object in a real electrolyte. The results obtained clearly demonstrate that physical scale modelling is a rational, scientific method for the evaluation and design of impressed current cathodic protection systems.     

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.     

Stray current-induced corrosion in cathodic protection installations of steel-reinforced concrete structures: FEM study of the critical parameters

A wide range of parameters was investigated by numerical calculations concerning their impact on DC stray current corrosion of reinforced concrete (RC) structures. A simplified model geometry was used to extract the relevant parameters and their interaction in terms of stray current-affected structures. This study mainly focuses on RC structures that are fitted with cathodic protection installations. The findings reveal a complex interaction between the investigated parameters. The possible relevance of further parameters, which is not the subject of this study, was emphasised.     

Electrochemical characteristics of stainless steel using impressed current cathodic protection in seawater

Stainless steels such as STS 304, 316 and 630 are frequently used as shaft materials in small fiber reinforced polymer (FRP) fishing boats. If the shaft material is exposed to a severely corrosive environment such as seawater, it should be protected using appropriate methods. The impressed current cathodic protection was used to inhibit corrosion in shaft materials. In anodic polarization, passivity was remarkably more evident in STS 316 stainless steel than in STS 304 and STS 630. The pitting potentials of STS 304, 316, and 630 stainless steels were 0.30, 0.323, and 0.260 V, respectively. The concentration polarization due to oxygen reduction and activation polarization due to hydrogen generation were evident in the cathodic polarization trends of all three stainless steeds. STS 316 had the lowest current densities in all potential ranges, and STS 630 had the highest. Tafel analysis showed that STS 316 was the most noble in the three. In addition, the corrosion current density was the lowest for STS 316.     

Steel cathodic protection afforded by zinc, aluminium and zinc/aluminium alloy coatings in the atmosphere

Zinc has traditionally been the metallic material most widely used to protect steel against atmospheric corrosion due to its ability to afford cathodic protection to steel in all types of natural atmospheres. In recent decades, aluminium and zinc/aluminium alloy coatings have been used instead of zinc in certain atmospheric applications. Although these coatings present some advantages over zinc, they are not able to cathodically protect steel substrates in all types of natural atmospheres. The present paper assesses the cathodic protection afforded by Al (flame spraying), Al/13 Si (hot dipping), 55Al/Zn (hot dipping), Zn/15Al (flame spraying), Zn/5Al (hot dipping), Zn (hot dipping), Zn (discontinuous hot dipping) and Zn (electroplating). Aluminium and aluminium-rich alloy coatings (55%Al/Zn) provide cathodic protection to the steel substrate only in atmospheres that are highly contaminated with chloride ions (>100 mg Cl⁻ m⁻² day⁻¹) where these coatings become active.     

高铁动态交流干扰下管道钢的腐蚀行为试验研究

利用电化学测试、表面分析及失重分析技术,研究了模拟高铁动态交流干扰下管道钢的腐蚀行为和规律及阴极保护的有效性.结果 表明,动态交流干扰下,阴极保护电位向负方向偏移,交流干扰增大管道的阴极保护电流密度;动态交流干扰下,随干扰水平增加,管道钢腐蚀程度增加,点蚀坑明显加深.阴极保护明显减缓交流干扰试样的腐蚀程度,腐蚀速率降为...     

Disbonding of underwater-cured epoxy coating caused by cathodic protection current

Cathodic disbonding of the underwater-applied, ultra-thick, solvent free epoxy coating subjected to various levels of cathodic protection was investigated during the period of the coating cure. The results indicate that the partially cured coating was of low resistivity, between 10³ and 10⁵ Ω cm² for the cathodic polarization of on-potentials between −0.98 and −1.4 V_Ag/AgCl/sw. The coating was shown to be capable of withstanding normal levels of cathodic protection between off-potentials of −0.8 and −1.1 V_Ag/AgCl/sw while the IR drop, introduced by the coating in the same potential range, increased from 0.06 to 0.1 V and has to be taken into account at the design stage of the cathodic protection system. Beneficial influence of calcareous deposit formation on the cathodic protection current was confirmed, particularly for the failed coating. The initial period (1 week) of coating cure was shown as the most critical for disbonding processes caused by the excessive cathodic polarization.     

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 AC interference on cathodic protection monitoring

Abstract

Cathodic protection (CP) monitoring in the presence of simultaneous AC and DC interference could lead to erroneous measurements, since IR drop contribution due to both DC and AC could heavily affect potential readings. Therefore, to know the true potential (or true polarisation level), the ohmic drop contribution has to be eliminated. In literature, there is lack of agreement about the proper procedure to measure the true potential in the presence of AC. Laboratory tests on carbon steel specimens in soil simulating conditions were carried out focusing on potential measurement problem in the presence of AC through standard potential measurement procedure and the use of a potential probe. Results suggest the need of a proper methodology for potential measurement to determine reliably CP conditions.     

Influence of irregularities in the electrolyte on the cathodic protection of steel: A numerical and experimental study

This paper shows how the last algebraic matricial form can be obtained when the finite element method is used to approximate the potential distribution of a cathodic protection system that includes low conductivity irregularities in the electrolyte away from, close to and directly on the cathode. In order to study the influence of the resistivity of these irregularities on the possibilities of steel protection, five conductivities were analysed. The numerical results, validated with COMSOL® Multiphysics, show the importance of considering irregularities in the domain in order to prevent systems from becoming unprotected. The experimental data agrees with the theoretical data.     

Effects of SRB on cathodic protection of Q235 steel in soils

The effects of sulfate reducing bacteria (SRB) on cathodic protection (CP) of the Q235 steel in the soils have been studied by bacterial analyses, electrochemical impedance spectroscopy (EIS), scanning electron microscopy (SEM) and energy‐dispersive X‐ray analysis (EDX). The results showed that the pH value of the soil around the steel gradually increased, the number of SRB and the corrosion rate of the steel decreased, and the CP efficiency increased with the increasing of applied cathodic potential. At the cathodic polarization potential of ?1050 mV, SRB still survived in the soils. At the same potential, the CP efficiency in the soil without SRB was higher than that with SRB, and the corrosion rate of the steel in the soil with SRB was much higher than that without SRB. The cathodic current density applied for the steel in the soil with SRB was bigger than that without SRB at the same cathodic potential.     

埋地钢质管道交流干扰及排流研究

结合某埋地钢质输油管道的交流干扰测量及排流过程,对交流杂散电流的危害、标准和排流工作进行了探讨。在调查中,发现本段输油管道受直流干扰较小,但是,由于电气化铁路和高压电线路的影响,存在着严重交流杂散电流干扰。根据调查的结果提出了采用嵌位式排流技术解决交流干扰的技术方案。在排流方案实施后,排流效果总体较好,但在局部未达到预...     

Erosion-corrosion behavior and cathodic protection of alloys in seawater-sand slurries

An experimental study was conducted on the erosion-corrosion behavior of three alloys in seawater-sand slurries. The idea explored was to select a steel, a copper alloy, and a titanium alloy, which should have good resistance to abrasive wear because of high hardness (within their alloy classes). Then cathodic pro-tection would be used to protect them from corrosion. The alloys studied were 4340 steel, silicon bronze, and titanium alloy Ti-6V-4Al. Limiting conditions for cathodic protection were derived from electro-chemical polarization measurements. From erosion-corrosion tests, it was found that erosive wear by sand dominated the metal loss rates of both silicon bronze and Ti-6V-4Al. For the 4340 steel, which was the hardest material, cathodic protection provided good erosion-corrosion resistance. Supplementary measurements showed that ductility loss due to cathodically charged hydrogen in the 4340 steel was neg-ligible under the experimental conditions.     

Application of nickel-coated carbon fibre material in cathodic protection of underground-buried steel structures

The present paper reports the results of a preliminary study on potential suitability of a chopped nickel-coated carbon fibre (NiCCF) material to an impressed current, cathodic protection (CP) system, for an underground-buried steel structure. A primary role of a conductive NiCCF filler (Toho-Tenax^®-J MC HTA-12K A302 fibre) was to enhance distribution of a protective current, by significantly lowering the corrosion environment’s resistivity.Initially, the resistivity of sand-based soil (with humidity of ca. 20%) was optimized through addition of small amounts of chopped (15 ± 3 mm long) pieces of Toho-Tenax fibre. An operational efficiency for two laboratory CP setups (in the presence and absence of NiCCF soil modifier) was then monitored, over a period of 30 days. Each cathodic protection setup consisted of a protected structure (simulated by a steel rebar:  = 10 mm and length 0.5 m) and a DSA (Ti/MMO: _a = 95 mm) anode. Obtained results demonstrated a continuous increase of the soil resistivity parameter during a preliminary, 30-day cathodic polarization cycle, for the NiCCF-modified CP setup.     

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.     

Physical scale modelling of stray current interference to shipboard ICCP system

Cathodic protection is commonly used for corrosion protection of the underwater hull structures of naval platforms. Cathodic protection works by establishing an electrostatic field that provides the desired potential and current distributions in the seawater surrounding the structures to be protected. Interference to a ship’s cathodic protection system may occur when the ship is alongside a jetty or another naval ship due to the influence of the electrostatic field associated with the cathodic protection system employed on the jetty or another naval ship. The interference may alter the electrostatic field surrounding the ship and, therefore, the level of corrosion protection to the ship hull. In the current study, a physical scale modelling technique is used to evaluate how, and to what extent, the level of cathodic protection on a ship hull could be affected by an external current source. A 1/100 scale ship model with two-zone four-anode impressed current cathodic protection (ICCP) system is used in the study. The modelling results indicate that the presence of stray current may affect the potential distribution along the ship hull. The extent of stray current effect depends on a number of factors including the relative position and layout of stray current source, the magnitude and direction of the stray current flow and the operating mode of the shipboard ICCP system.