Parametric Study of Soil Characteristics on Pipeline AC Interference

The technology available for monitoring induced alternating current (AC) levels and additional corrosion risk factors for AC corrosion risk has continuously evolved along with the recognition of AC as a significant factor in pipeline corrosion. This paper covers the current state of the art regarding monitoring AC levels and AC corrosion risk on buried structures as well as monitoring the effectiveness of AC mitigation deployed to alleviate the risk of corrosion due to AC interference. Significant topics include induced AC interference, AC and DC current density factors, AC voltage for safe touch and as the driving force for elevated current density, and AC drain to ground and grounding efficiency. Cost-effective and best practices monitoring strategies are discussed as well as the value of continual assessment of AC and DC values relating to ongoing corrosion risk.

PurposeThe purpose of this paper is to quantify the influence of alternating current (AC) interference on hydrogen evolution reaction of X80 steel.Design/methodology/approachThe hydrogen evolution potential was obtained by cathodic potentiodynamic polarization curve. The instantaneous potential under AC interference was obtained by high-frequency acquisition with three-electrode system. Electrochemical impedance spectroscopy and Tafel polarization curves were used to study the influence mechanism of AC interference on instantaneous potential.FindingsIt was concluded that the hydrogen evolution reaction could occur on X80 steel under AC interference. There were critical AC current densities of about 100 to 200 A/m2, beyond which the cathode reaction of X80 steel changed from oxygen absorption to hydrogen evolution. Besides the pH value, the initial polarization potential EZ and impedance module of the steel/electrolyte interface under AC interference were also the factors that affected the critical AC densities in different solutions.Originality/valueThis research quantified the hydrogen evolution capacity of X80 steel under AC interference, which could be applied to clear the effect of AC interference on hydrogen evolution reaction.

The traditional cathodic protection (CP) criteria of “-850mV CSE” is no longer effective when pipelines are exposed to alternating current (AC) interference. Unfortunately, the CP criteria for buried pipelines in the presence of AC interference have not reached a consensus so far. In this work, weight loss tests on mild steel in the simulating soil solution of 4 g/L Na2SO4 were conducted to explore the reasonable CP potential for mild steel under AC interference. The experimental results show that the corrosion rates of mild steel under different CP potentials were affected significantly by AC current and the effects depended on the applied CP current density. In addition, AC induced corrosion can be controlled by increasing CP level when AC current density was below 300A·m-2. However, the corrosion of mild steel would be accelerated when the CP potentials were too negative. Finally, a reasonable CP potential range for mild steel in the presence of AC interference was proposed basing on the experimental results.

An alternating current (AC) corrosion on buried pipeline under cathodic protection with impressed current system has been studied using coupon and ER probe. Coupons and ER probes were applied to the sites after the survey of AC voltages on buried gas transmission pipeline over the country. Parameters such as AC current density of coupon, AC voltage, cathodic protection potential, soil resistivity and frequency were monitored continually. Where pipeline was cathodically protected below -1.0V (CSE, on-potential), AC corrosion rate was affected not by AC voltage but by both of frequency and AC current density. An experimental corrosion rate relation could be obtained according to effective AC current density, in which AC corrosion rate increased linearly with effective AC current density, and slope was 0.619 in coupon method and 0.885 in ER probe.

Electrochemical studies on the alternating current corrosion of mild steel under cathodic protection condition in marine environments

This paper discusses case studies of high voltage direct current (HVDC) & high voltage alternating current (HVAC) crossing Pipelines right of way (RoW) showcasing the effects of alternating current (AC) interference with respect to AC corrosion and Safety Hazards while running parallel and crossing at different angles to the same pipeline at multiple locations in a short span of length and restricting the AC current & safe voltage within maximum tolerable limits through deployment of mitigation measures as per industry code of practice, globally. The paper discusses effects of both powerline fault conditions as well as induced steady state on underground pipelines, AC interference modelling for enhancing effectiveness of Cathodic protection and analysis of AC interference mitigation measures. A comprehensive technical analysis involving collection of baseline information on both the pipeline and powerline and determining powerline fault current effects adjacent to each tower, on the pipe wall, the pipe coating, and the resulting safety hazard for pipeline personnel.

Development of a real-time AC/DC data acquisition technique for studies of AC corrosion of pipelines

Extracting reliable corrosion kinetic parameters from polarization curves is particularly challenging for X70 steel under the synergistic effect of microbiologically influenced corrosion (MIC) and alternating current (AC) interference, as both factors significantly distort the electrochemical response. To address this, a novel fitting strategy was developed. In this approach, the overall polarization curve is reconstructed by combining separately modeled anodic and cathodic branches. To preserve the shape of the polarization curve, a slope-consistency constraint was enforced through dynamic penalty factors that balance fitting accuracy with shape preservation during optimization, which was performed using an intelligent algorithm. The results demonstrate the robustness of the proposed strategy, demonstrating low sensitivity to initial guesses and algorithmic parameters. Evaluation confirms that accuracy is maintained even when the data density is reduced by half. Among the parameters extracted, the Tafel slopes and corrosion current density show higher reliability than others. This work provides a robust and effective tool for the kinetic analysis of complex corrosion systems involving MIC and AC.

Buried carbon steel pipe are provided with corrosion prevention systems, namely an insulating coating and a cathodic protection system which reduces (or halts) corrosion rate as a result of soil corrosiveness. The presence of alternating current (AC) interference may cause serious corrosion damages on metallic structures corresponding to coating defects, even if the −0.850 VCSE protection criterion is matched. Nowadays, the AC corrosion mechanism, as well as the protection criteria in the presence of AC, is still controversial and debated. In this paper, a two-step AC corrosion mechanism of carbon steel under cathodic protection condition is proposed: (1) AC causes the electromechanical breakdown of the passive film formed on carbon steel under overprotection condition, and (2) after passive film breakdown, high-pH chemical corrosion takes place. In order to investigate AC effects on passive condition (Step 1), experimental tests have been performed on stainless steels in neutral solution, as a result of its passive behavior: AC has harmful effects on passive condition, reducing anodic overpotential, and causing film breakdown over a critical AC interference level. The electromechanical oxide breakdown mechanism resulting from high alternating electric fields (of the order of 106 V/cm) within the passive film is proposed. Electrostriction stresses are a possible explanation. After film breakdown, corrosion can occur if the pH inside the crack is close to 14; this strong alkalization can be reached in overprotection condition (high cathodic current density) and in the presence of AC.

As a continuing effort to understand the mechanisms of alternating current (AC) transdermal iontophoresis and the iontophoretic transport pathways in the stratum corneum (SC), the objectives of the present study were to determine the interplay of AC frequency, AC voltage, and iontophoretic transport of ionic and neutral permeants across human epidermal membrane (HEM) and use AC as a means to characterize the transport pathways. Constant AC voltage iontophoresis experiments were conducted with HEM in 0.10 M tetraethyl ammonium pivalate (TEAP). AC frequencies ranging from 0.0001 to 25 Hz and AC applied voltages of 0.5 and 2.5 V were investigated. Tetraethyl ammonium (TEA) and arabinose (ARA) were the ionic and neutral model permeants, respectively. In data analysis, the logarithm of the permeability coefficients of HEM for the model permeants was plotted against the logarithm of the HEM electrical resistance for each AC condition. As expected, linear correlations between the logarithms of permeability coefficients and the logarithms of resistances of HEM were observed, and the permeability data were first normalized and then compared at the same HEM electrical resistance using these correlations. Transport enhancement of the ionic permeant was significantly larger than that of the neutral permeant during AC iontophoresis. The fluxes of the ionic permeant during AC iontophoresis of 2.5 V in the frequency range from 5 to 1,000 Hz were relatively constant and were approximately 4 times over those of passive transport. When the AC frequency decreased from 5 to 0.001 Hz at 2.5 V, flux enhancement increased to around 50 times over passive transport. While the AC frequency for achieving the full effect of iontophoretic enhancement at low AC frequency was lower than anticipated, the frequency for approaching passive diffusion transport at high frequency was higher than expected from the HEM morphology. These observations are consistent with a transport model of multiple barriers in series and the previous hypothesis that the iontophoresis pathways across HEM under AC behave like a series of reservoirs interconnected by short pore pathways.

Corrosion of copper armor caused by induced current in a 500 kV alternating current submarine cable

Purpose Pipelines are seriously corroded due to the close distance between pipelines and high voltage transmission lines. The purpose of this paper is to study the influence of alternating current (AC) on corrosion behavior of X80 pipeline steel in coastal soil solution. Design/methodology/approach The corrosion behavior of X80 steel under different AC densities in coastal soil solution was investigated by electrochemical measurements and image processing technology. Furthermore, a quantitative description model of AC corrosion through fractal dimension of corrosion image was established. Findings The results show that under low AC density the X80 steel is mainly uniform corrosion, and once AC density reaches 150 A/m2, the corrosion morphology gradually turns to pitting corrosion with irregular circle. For another aspect, the fractal dimension of corrosion images shows that the two/three-dimensional fractal dimension increase with the increase of AC density, presenting a linear and an exponential relationship respectively. In addition, the variation of the three-dimensional fractal dimension is the same as that of average corrosion rate. The threshold of the increasing trend of fractal dimension as well as corrosion type is 150 A/m2. Originality/value The investigation provides a quantitative method to describe AC corrosion morphology through fractal dimension. Furthermore, the method is of benefit to process corrosion images automatically.

As mentioned earlier, a LD is an electrical device that needs a source of electrical energy with the output characteristic of a CCS or CPS for power. This chapter examines the types of available sources. There are a variety of devices designed to produce and supply electricity to consumers. They transform carriers of nonelectric energy, e.g., from oil, gas, chemical reactions, water, wind, sunlight, etc., into electrical energy (the technical literature refers to them as the "primary sources of electrical energy"). This transformed energy is either direct current (DC) or alternating current (AC). Most applications of this energy use two types of primary sources: electric batteries (used in mobile objects such as vehicles and flashlights) and AC generators with an associated AC grid (in which the energy from many primary sources is combined to power stationary equipment). There are also mobile generators, which generate electricity with parameters that match an AC grid. The primary sources of electrical energy can only directly power limited types of electrical devices, such as the incandescent bulbs in flashlights powered by batteries. Some AC motors and incandescent lamps are powered directly from an AC line. Most electrical devices (electrical loads) require either AC sources with a different AC voltage and/or frequency, or DC sources with an output characteristic of a CVS, CCS, or CPS. This arrangement involves an intermediate device connected between the primary electric source and the load that converts electrical energy from the primary source into electrical energy that has the characteristics needed by the load. These devices are called "secondary sources of electrical energy." In the American technical literature, they are usually called power supplies (PSs). In relation to powering LDs, secondary sources are identified as LDDs. An understanding of the characteristics of electrical sources and electrical loads, as well as the interaction between them, is necessary for competent LDD design. One of the primary goals of this book is to present the design principles and characteristics of the secondary sources of electrical energy devoted to powering LDs. The following section considers the characteristics of primary sources.

The risks of alternating current (AC) corrosion, overprotection, and stray direct current (DC) corrosion are increasing on cathodically protected buried steel pipelines due to the recent changes in factors such as burial conditions, the characteristics of coatings, and pipe material. In the present study, field tests as well as a review of the literature on these risks were conducted. As a result, it has been revealed that there is a certain limitation to assess these risks with respect to conventional cathodic protection (CP) criteria based on pipe-to-soil potential. Therefore, new CP criteria for the elimination of these risks have been developed based on DC and AC current density measurements on coupons. The effectiveness of the new CP criteria was evaluated through the design of CP systems on newly constructed pipelines subject to the risks of AC corrosion, overprotection, and stray DC corrosion. Using these new CP criteria, the design and installation of CP systems as well as the elimination of these risks were completed successfully. The risks of overprotection as well as stray DC corrosion were eliminated by providing an appropriate level of DC current from CP rectifiers. The elimination of the AC corrosion risk was accomplished using distributed magnesium anodes and solid-state DC decoupling devices. Finally, the new CP criteria were proven to be effective in eliminating the risks of AC corrosion, overprotection, and stray DC corrosion on buried steel pipelines.

The transport processes of the dissolved chemicals in stratified or layered soils have been studied for several decades. In case of the solute transport through stratified layers, interface condition plays an important role in determining appropriate transport parameters. First- type and third- type interface conditions are generally used in the literature. A first-type interface condition will result in a continuous concentration profile across the interface at the expense of solute mass balance. On the other hand, a discontinuity in concentration develops when a third- type interface condition is used. To overcome this problem, a combined first- and third- type condition at the interface has been widely employed which yields second- type condition. This results in a similar break-through curve irrespective of the layering order, which is non-physical. In this work, an interface condition is proposed which satisfies the mass balance implicitly and brings the distinction between the breakthrough curves for different layering sequence corroborating with the experimental observations. This is in disagreement with the earlier work by H. M. Selim and co-workers but, well agreement with the hypothetical result by Bosma and van der Zee; and Van der Zee.