Buried Metallic Structures Research Articles

Dynamic Diffusion Model of Stray Current in DC Traction Power Supply System

The dynamic fluctuation of stray current is the main characteristic of the metro causing harm to surrounding buried metal structures. While establishing the equivalent circuit model of the return system, not only mainline but also metro depot should be considered. The diffusion models of the dynamic stray current of the DC traction power supply system (DTS) in multi-layer soil medium and massive texture soil medium are established. They are co-simulated with the DC traction power supply return system. The massive texture model (MTSM) is verified by an on-site experiment of ground potential distribution. In the case study, the direct grounding of the rail in the depot will deteriorate the ground potential gradient and stray current. When considering the impact of the river or lake, the stray current easily flows to the low resistivity texture soil, the maximum ground potential gradient increases.

Synergistic effect of alternating current and sulfate-reducing bacteria on corrosion behavior of X80 steel in coastal saline soil

With the development of electrified railways and high-voltage transmission lines, it is often inevitable that buried metal structures are subjected to interference from the alternating current (AC) induced by the neighboring power facilities. Commonly found in soil, sulfate-reducing bacteria (SRB) have the capability to accelerate metal corrosion. In this paper, with electrochemical methods, surface analysis techniques, and weight-loss test, the influence of AC and SRB on the X80 steel corrosion behavior was explored in coastal saline soil. The results revealed that the 100 A m−2 AC inhibited the growth of the sessile and planktonic SRB cell. Under the action of 100 A m−2 AC, the metabolic activity of viable bacteria was enhanced, and the process of extracellular electron transfer was accelerated. When both AC and SRB were introduced, the maximum pit depth (76.2 μm) increased significantly to be 15 times higher than in the control condition (4.9 μm). Both SRB and AC played a role in enhancing corrosion. The corrosion rate of the AC-influenced specimen was far higher than that of the SRB-influenced specimen, while SRB and AC produced a synergistic effect on the enhanced corrosion of the specimen.

Stray Current Protection and Monitoring Systems: Characteristic Quantities, Assessment of Performance and Verification.

Electrified transportation systems (ETSs) are affected by stray current problems impacting within and outside the right of way on reinforcement, buried metal structures and foundations. Stray current protection systems have recently been integrated in the track structure. Track electrical quantities are, thus, usually measured to assess track insulation and protection efficiency but should be backed up by additional measurements at the affected structures and installations, in order to assess their exposure and risk of corrosion. Ideally, a stray current monitoring system proceeds from the measurement of these quantities, to data collection and archival, to data presentation, analysis and prediction. Feasible sensors and probes, the impact of environmental conditions and uncertainty are considered for the measurement at the physical level. Data analysis is critically reviewed considering the variability of operating conditions and the effectiveness of each quantity as indicator of track insulation and protection efficiency. Given the normal spread of values, for data presentation and interpretation, suitable techniques are considered based on averaging, curve similarity and feature extraction, and also for the task of assessing compliance to limits or reference values and establishing a trend that may drive informed maintenance decision.

Prediction Model of Corrosion Current Density Induced by Stray Current Based on QPSO‐Driven Neural Network

The buried pipelines and metallic structures in subway systems are subjected to electrochemical corrosion under the stray current interference. The corrosion current density determines the degree and the speed of stray current corrosion. A method combining electrochemical experiment with the machine learning algorithm was utilized in this research to study the corrosion current density under the coupling action of stray current and chloride ion. In this study, a quantum particle swarm optimization‐neural network (QPSO‐NN) model was built up to predict the corrosion current density in the process of stray current corrosion. The QPSO algorithm was employed to optimize the updating process of weights and biases in the artificial neural network (ANN). The results show that the accuracy of the proposed QPSO‐NN model is better than the model based on backpropagation neural network (BPNN) and particle swarm optimization‐neural network (PSO‐NN). The accuracy distribution of the QPSO‐NN model is more stable than that of the BPNN model and the PSO‐NN model. The presented model can be used for the prediction of corrosion current density and provides the possibility to monitor the stray current corrosion in subway system through an intelligent learning algorithm.

Modelling and testing of optimum soil moisture levels in the corrosion of underground pipelines

Corrosion is one of the major factors leading to the failure of buried pipelines. Soil properties such as aeration, moisture content and level of compaction are known to cause variations in the level of corrosion of buried metallic structures. It is known that, at a particular soil moisture content, the corrosion rate reaches a maximum value. While this phenomenon is generally understood, an explanation from a soil mechanics perspective with mechanisms for soil water continuity and mass transport processes is currently lacking. This work fills this void by modelling the moisture-controlled diffusion transport and electrical conductivity in soil coupled to the electrochemical activity on the buried metal surface. Variations in the electrical conductivity and oxygen diffusion in sand at different degrees of saturation were determined experimentally. The results were used as input parameters in a finite element model. Results from the coupled finite element model were compared with experimental results from electrochemical corrosion tests. The tests were conducted on cast iron specimen buried in sand and the corrosion behaviour under various aeration regimes were studied. The presence of an optimum moisture/aeration regime, where the corrosion rate becomes a maximum was demonstrated and the mechanisms behind this phenomenological behaviour are discussed in this paper. The modelling and experimental results are expected to be useful in developing non-intrusive testing methods for underground corrosion.

Proposed methodology for coating defect and location in buried pipelines from frequency signal data applied in field conditions

PurposeThe purpose of this paper is to develop a real-time methodology to detect damages in coating and metallic structure in buried pipelines by using DC bias added to AC signal under field operation conditions, including cathodic protection.Design/methodology/approachImpedance measurements were performed on buried pipeline for different field conditions, to develop a methodology to detect and locate damages by impedance distribution along the metallic structure.FindingsField condition measurements were conducted as a pilot test on a buried steel pipeline segment with a diameter of 16 inches and length of 20 km. The frequency-based technology shows some differences but overall good behavior between impedance magnitudes vs localization of the interface changes at the soil-coating-steel interface at different frequencies using DC bias added to AC signal under field operation conditions, including cathodic protection.Research limitations/implicationsThe methodology is not applicable to highly resistive soil or high degradation coatings.Practical implicationsIn this work, we depict a methodology that describes real time monitoring technology for buried metallic structures using AC signal. This monitoring is capable to detect and locate real time damage occurrences on the pipe surface (coating break). Field measurements include different conditions, such as temperature, soil resistivity and soil physical structure and chemical composition.Social implicationsIn consideration of the satisfied application in the field of the methodology, it is believed that it can be used for the monitoring of damages in pipes in areas with high consequences and hence pipe integrity can be increased.Originality/valueThis real-time methodology is based on the impedance distribution signal and the differential changes along the pipeline under operating conditions. The results showed good agreement with the proposed methodology, which is able to discriminate some situations inherent of field conditions by using different impedance measurements performed along ±10 km of buried steel pipeline and assuming the reference location as the cathodic protection set up.

Efficiency and Cost Analysis of Power Sources in Impressed Current Cathodic Protection System for Corrosion Prevention in Buried Pipelines of Balochistan, Pakistan

Corrosion is the physical deterioration of metals, including buried metal structures and gas pipelines, resulting from chemical reactions between metals and the surrounding environment. Cathodic protection of these underground metal structures & pipelines can be achieved either by the Impressed Current method or by the sacrificial anodes method. This research paper focuses on the corrosion prevention of buried metal structures in general and gas pipelines in particular, by the novel method of Impressed Current Cathodic Protection (ICCP) which uses electrical current from an external DC power source for its operation. Three major DC power sources i.e. Transformer Rectifier, Thermoelectric Generator and the Solar System are selected for this purpose and are projected over a period of time in a pre-designed ICCP for high transmission underground gas pipeline in Balochistan province of Pakistan. The efficiencies of these three power sources are then analysed and compared according to the climate effects, the versatility effects, the intensity of power output, their operational limitations and their initial, running and maintenance costs. The measured results will aid the selection of efficient and robust DC power source for ICCP design and will contribute to mitigating and controlling the corrosion rate in underground pipelines. Based on analysis of the measured results for the three available DC sources, the Solar System was found as the most efficient DC power source for Impressed Current Cathodic Protection of buried gas pipelines. The selection of efficient corrosion protection system will result in a smooth flow of oil and gas products through these buried pipelines which may otherwise lead to huge monetary and accidental losses when get corroded.

Techniques for testing and monitoring the cathodic disbondment of organic coatings: An overview of major obstacles and innovations

Abstract Coatings in conjunction with cathodic protection (CP) have been widely used for protecting buried metallic structures such as steel pipelines against corrosion. A drawback of the combined use of these two techniques is cathodic disbondment of coatings, i.e. the loss of adhesion between a coating and its metal substrate due to the products of cathodic reactions that take place at the coating and metal interface. Disbonded coatings provide easy lateral paths for corrosive species to reach the metal surface while simultaneously shielding cathodic protection currents from reaching the metal substrate. Currently, corrosion under disbonded coatings remains as a major issue affecting the integrity of civil and industrial infrastructures such as buried pipelines; therefore the ability of testing and monitoring coating disbondment is important for ensuring the durability of these infrastructures. This paper provides an overview of major innovative efforts made over the past several decades to overcome technical obstacles in testing and monitoring the cathodic disbondment of coatings. The limitations of various techniques including the standard cathodic disbondment test (CD test), electrochemical impedance spectroscopy (EIS), localized electrochemical spectroscopy (LEIS), scanning Kelvin probe (SKP) and scanning acoustic microscopy (SAM), have been critically reviewed. The recent application of multi-electrode array method has been discussed to illustrate an innovative approach aimed at addressing major difficulties in the in situ measurement and monitoring of cathodic disbondment of coatings.

Estimating stray current interference from DC traction lines on buried pipelines by means of a Monte Carlo algorithm

The paper presents a non-deterministic approach to the study of stray current effects generated by direct current railway or tramway lines on buried pipelines which are located in the nearby area. The potential shift induced (via conductive coupling) on the latter ones by the stray current dispersed in the soil is evaluated by means of a suitable equivalent circuit combined with a Monte Carlo procedure. The algorithm proposed has to be intended as a tool for the estimation of the corrosion risk for a pipeline (or, more in general, for long buried metallic structures) due to the stray current generated by electrified railway/tramway lines. Different from the existing models present in literature, which are based on a deterministic approach, a method based on the random and statistical aspects of stray current, which are captured by Monte Carlo approach, is proposed. This is the novelty of the method.

Analysis of the harmful effects to buried oil pipeline from power line short-circuit fault

Based on the transmission line theory of the buried metallic structures, the concerned harmful effects to the buried oil and natural gas pipelines caused by the power line short-circuit fault are further discussed. A closed-form expression of the induced voltage caused by the short-circuit fault of the ultra-high voltage power (UHVAC) transmission line is given. The transmission line model of the buried pipeline is set up and a set of formulas for calculating induced voltage on the pipeline and the parameters of the buried pipeline in actual environment condition are given. At last, the characteristic of the harmful effects on the buried pipeline from the power line short-circuit fault are discussed.

Electromagnetic field model for the numerical computation of voltages induced on buried pipelines by high voltage overhead power lines

This paper proposes an innovative, generally applicable numerical model for the calculation of the three-dimensional (3D) electromagnetic field generated by high voltage (HV) overhead power transmission lines (OHL) on the buried metallic structures (e.g., pipeline networks). The numerical analysis is based on a coupled finite element-boundary element model (FEM-BEM) designed to calculate the induced potential on buried pipelines for complex geometrical structures of HV OHL networks working on normal or fault conditions. The one-dimensional (1D) FEM technique based on pipe elements is used to discretize the mathematical model that describes the interior of the pipe and is coupled with the mathematical model that describes the exterior of the pipe using 3D-BEM integral equations. The full electromagnetic field model gives the flexibility to calculate the potential distribution in any point of the soil, providing useful information for the step and touching voltages. The computation accuracy of the numerical algorithm implemented is verified through two test problems by comparing the numerical results with those obtained using a software package based on the Transmission Line Method (TLM) and CIGRE formulae. Last part of the paper presents calculations of the induced potential on buried pipeline in the vicinity of a complex HV OHL working on normal and fault condition. The influence of the currents’ direction and magnitude flowing on the HV OHL on the induced pipeline potential distribution is analyzed.

Investigation of Soil Aggressiveness towards Underground Fuel Storage Tanks and Water Pipelines in Parts of Bayelsa State, Southern Nigeria

Structural failure of buried cast/ductile iron water mains and tanks due to corrosion attacks manifests in leaks and is common in most cities throughout Nigeria. The appropriate corrective action, which aims to restore pipe/tank integrity is usually based on proper understanding of the degree of corrosiveness of the soil. In an attempt to determine the potential corrosiveness of the soil to buried metallic structures in Bayelsa State, surface geoelectrical sounding was carried out. Twenty-five Schlumberger Vertical Electrical Soundings (VES) was carried out in the freshwater and meander belt geomorphic zone and the salt water mangrove swamp and estuary complex of the state using a maximum current electrode separation ranging from 200 - 400 m. The data obtained was interpreted by computer iterative modeling using a 1D inversion technique software (1X1D, Interpex, USA). The results show a high degree of heterogeneity, both laterally and vertically, which is typical of a complex depositional environment. Generally, the sub-soil condition within the expected depth of installation of water mains and storage tanks (0 - 10 m) is slightly or moderately aggressive (effective aggressivity) in the freshwater and meander belt geomorphic zone but is very strongly aggressive in the salt water mangrove swamp and estuary complex. Corrosion cells which may lead to significant corrosion failures may occur in the vicinities of strongly aggressive stations. This poses a significant corrosion risk to metallic water pipes and storage tanks. Current day design should therefore either mandate the use of a non-metallic piping product (water mains) or cathodic protection system. Prediction of potential corrosiveness of a soil and thus the application of proper corrosion control measures will not only protect the environment from spillages but will also avert cost of repair, clean-up and replacement.

Impedance based method for non-contact determination of the corrosion rate in buried metallic structures

ABSTRACT The electrochemical impedance spectroscopy has been employed in the present investigation to assess the polarisation resistance of carbon steel rebars in different electrolytes. The measurements have been performed using the classical 3-electrode arrangement, where the element under test is the working electrode of the potentiostat, and a new 4-electrode arrangement where the element under test is floating from the electrical point of view (e.g. contact-less technique). The polarisation resistance values obtained using the contact-less technique are very close to those obtained using the traditional 3-electrode arrangement. The measurements, performed in a wide range of electrolyte resistivity values (including mortar) have thus demonstrated the applicability of this new technique for on-site corrosion rate assessment.

Impedance based method for non-contact determination of the corrosion rate in buried metallic structures

ABSTRACT The electrochemical impedance spectroscopy has been employed in the present investigation to assess the polarisation resistance of carbon steel rebars in different electrolytes. The measurements have been performed using the classical 3-electrode arrangement, where the element under test is the working electrode of the potentiostat, and a new 4-electrode arrangement where the element under test is floating from the electrical point of view (e.g. contact-less technique). The polarisation resistance values obtained using the contact-less technique are very close to those obtained using the traditional 3-electrode arrangement. The measurements, performed in a wide range of electrolyte resistivity values (including mortar) have thus demonstrated the applicability of this new technique for on-site corrosion rate assessment.

The Comparison Analysis of Field Test Cases on Technical Specifications of Electrolytic Corrosion in Urban Railway

DC electricity feeder system operating in the urban railway is typically a feedback circuit consisted of the contact wire and electric railway vehicle via rail. But stray current is flowed on a structure that is not part of the intended electrical circuit with respect to a given structure. This paper presents comparison analysis of field test cases based on criteria of electrolytic corrosion protection of buried metallic structures adjacent to DC traction systems. As a result of it, we confirmed that measurement methods are different from each other about the same tests. Therefore measurement methods to prevent electrolytic corrosion need to establish electrical facilities standards to be applied domestic.

Influence of soil structures on corrosion performance of floating-DC transit systems

The production of stray currents by DC-transit systems leads to the corrosion of nearby buried metallic structures, such as pipelines and cable sheaths. The paper details the corrosion performance of a DC transit system with a floating return rail, for a number of different soil-resistivity structures: uniform, horizontal and vertical-layer models. This builds on previous work carried out in homogenous soils. It is shown that a variation in soil type along the route of a transit system can lead to high local leakage-current densities on buried metallic structures, increasing their vulnerability to corrosion damage.

Blends of maleic-anhydride-grafted polyethylene with polyethylene for improved cathodic disbondment performance

Buried metal structures such as pipes are usually protected by a coating, often in conjunction with cathodic protection (CP). Whilst this minimizes corrosion, it can also lead to the loss of adhesion between the protective coating and metal structure by a phenomenon called cathodic disbondment (CD). In this study, various medium-density polyethylene (MDPE) compositions with maleic-anhydride-grafted-polyethylene (MAH-g-PE) have been formulated to investigate the effect on CD performance, as well as both wet and dry bond strength. The results indicate an improvement in both CD performance and bond strength for all compositions. Differential scanning calorimetry (DSC) and pressure-volume-temperature (PVT) experiments are used to characterize the polymer formulations developed and to aid in the understanding of the reasons for such improvement. Energy dispersive X-ray spectroscopy (EDXS) has been used to obtain surface analysis data on disbonded materials in order to evaluate the failure mode during the CD process. It is found that there may be an optimum loading of the polar functional groups in MDPE necessary for the best CD performance, and that wet adhesion strength (rather than dry) is an important parameter to assess and understand the CD performance of coatings. © 2001 Society of Chemical Industry

Accelerated aging corrosion tests for buried metal structures : Lieberman, P. Pipeline and Gas Journal, Vol. 223, No. 10, pp. 48–52 (Oct. 1996)

It is necessary to identify those measurable soil parameters which dictate the severity of the corrosion problem for coated irons and steels. When this is done, meaningful accelerated aging tests can be designed to validate the reduced corrosion rate for the planned coating. The following discussion introduces the important concepts and measurement parameters in the (a) design of accelerated aging tests, and (b) evaluation of the planned installation site for corrosion potential. Certain combinations of soil oxidation reduction potential (ORP) or electric potential (Eh), acidity (pH), fertilizer, water table, and soil hydraulic conductivity can result in severe corrosion of buried steel/iron vessels. If there are power lines nearby, additional loss of vessel material to the soil will occur. These factors are discussed.

Study of influence of buried metallic structures on soil resistivity measurements

A detailed study of the influence of buried metallic structures on soil resistivity measurements has been carried out. Different measurement methods, various soil structures, and different locations of measurement profiles with respect to metallic structures have been analyzed. It is found that the influence of buried metallic structures on soil resistivity measurements can be significant and that this influence varies in a wide range depending on measurement methods, locations of measurement profiles and soil structure characteristics. This study also shows how to choose measurement locations to minimize the influence of buried metallic structures when soil resistivity measurements must be made in the presence of buried metallic structures.

Magnetic Field Measurement of Corrosion Processes

Localized corrosion rates on buried metallic structures have been quantitatively evaluated by detecting the magnetic fields generated by electrochemical reactions. These results were obtained using electrochemical impedance spectroscopy instrumentation modified to include a SQUID magnetometer as the electrical current sensor. Data from field studies on buried pipes are presented which show that the local corrosion rate of an isolated segment of an extended structure can be measured without local contact to the structure. This permits high activity regions on large structures with spatially varying corrosion rates to be mapped and evaluated.