DC Stray Currents Research Articles

A new hybrid approach for the prediction of corrosion due to DC stray currents emitted by electrical traction and nonlinear dynamic process monitoring

A new hybrid approach for the prediction of corrosion due to DC stray currents emitted by electrical traction and nonlinear dynamic process monitoring

Investigating the impacts of high voltage powerlines on ground current fields

Stray currents are a typical problem of areas crossed by electric railways. This well-known phenomenon can cause significant damage to all underground metallic installations, especially in case of DC stray currents. In areas close to the railway, the presence of stray currents is expected, and protective measures are applied to all sensitive installations like pipelines. However, field measurements have shown that the presence of high voltage power lines can significantly affect the ground current field due to the well-grounded ground wire representing an excellent alternative path for ground currents. This way, stray currents can appear in areas where the presence of ground current field from DC traction is normally not expected. Preliminary simulations have confirmed that high voltage power lines are a significant element affecting the spreading of ground current and the presence of high voltage power lines must be considered when investigating the ground current field of an area. However, these simulations were performed only for a limited area with a very simplified geometry of railway truck and a single power line. This paper presents results of a more complex simulation involving a large area crossed by a DC railway traction system and a complex high voltage network. The simulation is based on real topology representing an area around the town of Zilina, an industrial area with a complex high voltage network and an important railway hub.

Effect of straight bolt corrosion on mechanical properties of shield tunnel under DC stray current

The strength of straight bolt is an important index affected the mechanical properties of shield tunnel, at present most studies only focus on the effect of bolt corrosion on local structure performance under DC stray current, but the performance change of local structure cannot reflect the stiffness degradation of the whole ring tunnel structure. The purpose of the research is to study the influence mechanism of bolt corrosion on mechanical properties of shield tunnel under DC stray current. Combined with numerical and experimental analysis methods, the coupling calculation of electric, chemical and mechanical fields is realized based on the theory of electrochemical and structural mechanic, the deformation and internal force of shield tunnel contained corroded bolt are also presented. The major conclusions include: the effect of straight bolt corrosion on the deformation and internal force of shield tunnel understraightjointassembling is greater than that understaggered joint assembly. When the number of DC stray current input point is equal, the effect of bolt corrosion on tunnel deformation and internal force under current bilateral input mode is greater than unilateral input mode and hypotenuse input mode.

Effect of Soil Salt Content on Stray Current Corrosion of Buried Metal

In order to study the effect of soil salt content on the corrosion of buried metal by the stray current in urban rail transit, a small experimental platform for the buried metal corrosion is built. The corrosion rate and mass loss of buried carbon steel specimens in soil samples with or without DC stray current are measured and calculated when different content of NaCl is added into the soil samples, respectively. The experimental results show that the corrosion rate and mass loss of the buried metal increase with the increase of soil salt content. DC stray current will aggravate the corrosion of the buried metal. The corrosion degree of buried metal will be seriously aggravated under the coupling action of DC stray current and salt. When there is no DC stray curren, the corrosion degree of buried metal is relatively small, and the influence of soil salt content on the buried metal corrosion is also relatively small. Finally, a multiphysics simulation model corresponding to the experiment is established to verify the experimental results. The simulation results are basically consistent with the experimental results, which proves the accuracy of the experimental results. The research results can provide a theoretical basis for the corrosion protection design of subway stray current.

Effect of DC Currents and Strain on Corrosion of X80 Steel in a Near-Neutral Environment

The corrosion behavior of X80 steel in a near-neutral soil-simulated solution under various DC stray currents and applied strains was investigated using electrochemical measurements (open circuit potential, linear polarization, and electrochemical impedance spectroscopy) and surface analysis techniques. Our results show that a DC stray current has a substantially greater effect on steel corrosion compared to applied strain. However, strain could slow down the corrosion rate in specific conditions by affecting the composition of corrosion products and the structure of the corrosion scale on the surface of the steel. Although the porosity of the corrosion scale of steel without an applied strain will increase with increasing DC currents, once strain is applied, the corrosion scale will become denser. Furthermore, both DC currents and strain can promote steel pitting, and the number and size of pitting holes will increase significantly with an increase in current densities.

Effects of non-stationary stray current on carbon steel buried pipelines under cathodic protection

DC stray currents may cause severe corrosion on buried carbon steel pipelines even if in cathodic protection. According to international standard anodic interference is unacceptable if the IR-free potential is more positive than the protection potential (−0.85 V CSE). But, duration and magnitude of the anodic peak is not defined. The criterion appears to be too restrictive if short periods of anodic interference are established. This paper deals with the study of the effects of anodic interference on carbon steel in cathodic protection in soil-simulating environment in the presence of DC interference at varying peak current density and duration.

Cathodic protection and DC non-stationary anodic interference

DC stray currents may induce corrosion on buried carbon steel pipelines transporting methane even if in cathodic protection. According to international standard, anodic interference is unacceptable if the IR-free potential is more positive than the protection potential (−0.85 V CSE). But, duration and magnitude of the anodic peak is not defined. This paper describes results of laboratory tests performed in soil-simulating environment on cathodically protected carbon steel specimens suffering DC interference at varying peak current density, anodic potential and duration. Measured corrosion rate is always lower than the theoretical value predicted by Faraday Law. Consequently, it is possible to conclude that cathodic protection has a positive effect towards DC interference. A parameter Time Out of Protection has been defined as the period of time during interference where the potential is more positive than −0.85 V CSE; this factor has been correlated to the measured potential during DC interference.

Effect of dynamic DC stray current on corrosion behavior of X70 steel

AbstractCorrosion behavior of X70 steel under the application of dynamic DC stray current was investigated in simulated soil solution by immersion tests and electrochemical measurements. Experimental results indicated that the corrosion rate of X70 steel under dynamic DC stray current was strongly influenced by the dynamic period. When the dynamic period was <80 s, the corrosion rate was only approximately 1–7% of that caused by an equivalent amount of steady direct current. However, as the dynamic period became >80 s, the corrosion rate increased significantly with the dynamic period. And finally when the dynamic period was >1 hr, the corrosion rate was nearly equal to 100% of that caused by an equivalent amount of steady direct current. Meanwhile, the surface examination showed that the specimens experienced uniform corrosion under the experimental conditions. On the basis of the experiment results, the dynamic DC stray current corrosion mechanism of X70 steel under the experimental conditions was discussed, which was closely related to the electric double‐layer structure at the electrode/solution interface and dynamic electrochemical reactions under dynamic stray current.

Analysis of the Monitoring Data of UHVDC Grounding Current Interference in a Buried Pipeline

The transmission power and rated current of the ±800 kV ultrahigh-voltage direct current (UHVDC) project is so high that the grounding current aggravate the corrosion of buried pipelines during the monopole operation period, which is a critical issue that needs to be studied. The stray current and the pipe-soil potentials (PSPs) synchronous monitors have been installed on a buried pipeline near the receiving end of the Zhalute-Qingzhou ±800 kV UHVDC transmission project and the monitoring experiment for the effect of the grounding current of the receiving ground electrode is carried out. The monitoring data of stray current and PSP offset in relation to the grounding current of the ground electrode are obtained for the first time all over the world, during the UHVDC project commissioning in October 10th and December 24th, 2017. The results of data analysis show that the pipeline 150 km away from the ground electrode is also affected by the UHVDC project, its PSP offset exceed the limit value required by the national standard for discharge measures and the dc stray current is produced in the pipeline. According to the data and calculation, the characteristics and rules of the influence of UHVDC grounding current on pipelines are acquired.

Numerical modelling of buried pipelines under DC stray current corrosion

Corrosion of buried pipelines caused by stray currents is becoming a serious industrial and environmental problem. It is therefore necessary to study corrosion mechanisms of buried pipelines under DC stray currents in order to propose effective anti-corrosion measures. Since measurement of the potential is one of important ways to identify stray current intensity, the COMSOL Multiphysics software was used to simulate stray current corrosion dynamics of buried pipelines. It was also used to calculate the distribution and intensity changes of electrolyte potential in the cathodic protected system by solving Laplace’s three-dimensional equation. The obtained results showed that increased applied voltage leads to more positive shift of a pipeline potential, resulting in acceleration of stray current corrosion. On the contrary, increased soil resistivity can retard the corrosion process. The protected pipeline with a sacrificial anode suffers less corrosion interference than unprotected pipeline. Two crossed arrangement of pipelines makes no difference in corrosion of protected pipeline, but affects greatly on unprotected pipeline.

Optimization of the Amount of Coke Filling Usage in Cathodic Protection Systems for an Anode Grounding Model in the form of a Hemisphere

In this work, we calculated the optimal amount according to “annualized costs” criteria on the basis of model representations for anodic grounding of the cathodic protection system in the form of a single hemisphere, which is located on the surface of the ground and contains coke backfilling. At the same time, calculations were made for a similar grounding, but without the use of coke filling, which allowed comparative analysis and calculation of their comparative economic efficiency, depending on the specific resistance of the soil. As a result of these calculations, we proposed a modernized anodic grounding with a normalized amount of coke filling that has increased safety in comparison with the traditional product, since it allows reducing risks, caused by generation of positive DC stray currents of cathodic protection system, to other underground metal constructions. This quality of the proposed anode grounding is especially important in urban areas and at the territories of large industrial facilities characterized by an increased density of underground metal structures.

Assessment of d.c. traction stray currents effects on nearby pipelines

Purpose – dc electrified traction systems are a potential source of stray currents. The purpose of this paper is to evaluate the harmful effects (electrolytic corrosion) that an electrified railway has on nearby earth return circuits (e.g. pipelines). Design/methodology/approach – The electric circuit approach, based on the earth return circuit theory, to model stray currents interference on extended structures is presented. An exact method of calculation is applicable to any dc railway system in which tracks can be represented by a single earth-return circuit (equivalent rail) with current energization. In the approximate method, the equivalent rail with current energization is modeled as a large multinode electrical equivalent circuit with lumped parameters. The circuit is a chain of basic circuits, which are equivalents of homogenous sections of the rail. The electrode kinetics (polarization phenomenon) is taken into account in the model developed. Findings – Formulas in partially closed forms are derived applicable to the analysis of currents and potentials along a pipeline laid in the proximity with railway tracks. The attempt is undertaken, to incorporate the electrode kinetics into the simulation model in which the polarization phenomenon (Tafel equation) is modeled by a non-linear voltage source with source voltage being iteratively calculated. The polarization potential along the affected pipeline can be determined. Originality/value – The pipeline electrochemical response (polarization behavior – non-linear phenomenon on the interface metal-soil electrolyte) to the dc stray currents interference is innovative incorporated into the simulation model with lumped parameters using the iterative process.

The influence of DC stray current on pipeline corrosion

DC stray current can cause severe corrosion on buried pipelines. In this study, firstly, we deduced the equation of DC stray current interference on pipelines. Next, the cathode boundary condition was discretized with pipe elements, and corresponding experiments were designed to validate the mathematical model. Finally, the numerical simulation program BEASY was used to study the corrosion effect of DC stray current that an auxiliary anode bed generated in an impressed current cathodic protection system. The effects of crossing angle, crossing distance, distance of the two pipelines, anode output current, depth, and soil resistivity were investigated. Our results indicate that pipeline crossing substantially affects the corrosion potential of both protected and unprotected pipelines. Pipeline crossing angles, crossing distances, and anode depths, our results suggest, have no significant influence. Decreasing anode output current or soil resistivity reduces pipeline corrosion gradually. A reduction of corrosion also occurs when the distance between two parallel pipelines increases.

Impact of Photovoltaic-Oriented DC Stray Current Corrosion on Large-Scale Solar Farms' Grounding and Third-Party Infrastructure: Modeling and Assessment

This paper discusses the impact of photovoltaic (PV)-oriented dc stray current corrosion on large-scale solar farms' grounding and third-party infrastructure. The dc stray current may result from a fault or may be facilitated by buried cables' condition that allows dc leakage to flow into the earth. In particular, such abnormal conditions can impact the grounding electrodes of the PV plants as well as third-party metallic infrastructures (e.g., natural gas pipelines) that are laid in the nearby vicinity of a solar plant. This paper unfolds by thoroughly addressing three specific objectives: 1) defining the origin of the problem; 2) modeling the problem in commercially available software; and 3) discussing the arising implications.

Stray Currents on Direct - Current Railways in Slovenia

DC stray currents are currents which do not flow through designed conductors but along the path of least resistance. These currents are very harmful to various metallic structures and lead to corrosion in the long term. The most significant sources of DC stray currents in Slovenia can be found in electrified railways using the direct current system of 3000 V. Not all the return current can flow back to the rectifier substation through the rails but a high percentage of this current is dispersed in the earth, depending on conductive arteries. In some cases, these stray currents even cross a very winding railway line. The Slovenian Railways have electrified a substantial part of their railway lines using the direct current system of 3000 V. The complete 3000 V direct current overhead line system in Slovenia is being fed by 18 rectifier substations (ENP).

Boundary element simulation of DC stray currents in oil industry due to cathodic protection interference

AbstractThis paper presents a 3D theoretical simulation and analysis of DC stray current corrosion (SCC) in oil fields that could contribute to oil leak and finally oil deferment of electric submersible pump (ESP) systems. Application of the boundary element analysis system (BEASY) allowed cathodic protection (CP) interference to be assessed in terms of the normal current density, which is directly proportional to the corrosion rate, rather than using the qualitative approach of measuring the potential shift of the soil. Different real structures consisting of pipelines and/or well casings with different arrangements and interference conditions are simulated. The results reveal that the application of impressed current cathodic protection (ICCP) systems creates DC SCC on other nearby unprotected structures. This is an inherent potential problem with the application of such systems which dominates with decreasing soil conductivity, and/or increasing the anode current density and its proximity to the protected structures. On the contrary, SCC can be reduced by using multi‐groundbed anodes. Copyright © 2006 John Wiley & Sons, Ltd.

CVケーブル活線絶縁測定における1Hzの信号電流検出メカニズム(脈動検出法)

Detection signals obtained under the application of commercial AC voltage can be explained by two kinds of current mode, namely generation mode which is correspond to void discharge and transmission mode which is composed of conductive path and signal source contained in the line voltage of the operating cables. By the circuit restrictions of cable shielding layer capacitor earthing and also to avoid the effect of DC stray current, detection frequency for in-service measurement needed to select lower than AC frequency and also higher than DC. At the water tree deteriorated cable specimen, 1Hz (lower than commercial AC voltage) signal was obtained by transmission mode under the operating voltage stress. Furthermore, existence of the generation mode was suggested by the dried water tree deteriorated cables, because the micro discharge seemed to be existed in the non-conductive dried micro void of deteriorated cables.