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The presence of alternating current (AC) causes serious damage on buried pipelines even when the off potential matches the −0.85 V/CSE criterion. The optimum cathodic protection potential (OCPP) is more accurate for cathodic protection. The paper aims to study how to get the optimum cathodic protection by electrochemical impedance spectroscopy (EIS) and the effects of AC on the OCPP.

This paper describes the application of EIS to investigate the OCPP of X70 steel in a soil simulating solution with different AC interferences.

The experimental results indicate that AC interference makes the OCPP decrease and the −0.85 V/CSE criterion is not reasonable when there is AC interference. When the AC voltage is less than 6 V, the OCPP is approximately −900 mV/SCE, and when AC voltage is more than 7 V, the OCPP is roughly −1,000 mV/SCE.

There have been some researches on the OCPP, and the paper is the first one to study the AC effects on the OCPP and found that the OCPP changed when there was AC interference.

The presence of alternating current (AC) causes serious damage on buried pipelines, even when the off potential meets the −0.85 V/CSE criterion. The optimum cathodic protection potential (OCPP) is more reliable for cathodic protection. The purpose of this paper is to study the effects of AC on the OCPP and, using electrochemical impedance spectroscopy (EIS), to investigate how to get the optimum cathodic protection.

The paper describes the application of EIS to investigate the OCPP of X70 steel in a soil simulating solution with different AC interferences.

The experimental results indicate that AC interference makes the OCPP decrease. It was determined that the −0.85 V/CSE criterion is not appropriate when there is AC interference. When the AC voltage was less than 6 V, the OCPP was approximately −900 mV/SCE, whereas when the AC voltage was more than 7 V, the OCPP was approximately −1,000 mV/SCE.

Although there have been previous research studies on the OCPP, this paper is the first to study the effects of AC interference on the OCPP and it has been confirmed that the OCPP changed when AC interference is present.

The purpose of this paper is to investigate the application of electrochemical impedance spectroscopy (EIS) as a tool for determining the optimum protection potential (OPP) of brass in impressed current cathodic protection (ICCP) for a given environment.

The electrochemical measurements (EIS, polarization curves) were applied to study the electrode processes of brass in fresh water at different pH values.

The paper finds that the depolarizer in the electrode process of brass corrosion is different in solutions with different pH values, and has different key steps in the electrode processes. Hence, EIS is a better tool for the determination of the optimum polarization potential for brass in fresh water when the depolarizer of the cathodic half‐cell reaction in corrosion reaction is the dissolved oxygen. However, when the depolarizer in solution is changed, and especially if the reduction reaction of depolarization is not controlled by the mass transport, the EIS method may be not suitable to determine the OPP.

There have been few reports on the effect of pH on the applicability of EIS as a tool for determining the OPP. In this paper, it is clearly shown that the EIS method be suitable only to determine the OPP when the critical step in the electrochemical process is diffusion of the depolarizer. This research can offer theoretical guidelines for the application of EIS to determine the OPP in ICCP.

Reliable grounding is an important condition for the stable operation of substations and cathodic protection is one of the electrochemical protection technologies for substation grounding grids. The purpose of this paper is to consider the design proposal, installation, construction requirements and monitoring methods for Hunan 220 kV substation grounding grid.

This paper treated Hunan 220 kV substation grounding grid as a research object. The physical and chemical data of three soil samples were measured, German DIN50929 evaluation criteria were used to assess its corrosion and a sacrificial anode cathodic protection design was selected, based on advanced concepts.

The design proposal, installation, construction requirements and monitoring methods for the 220 kV substation grounding grid were clearly explained and recommended for implementation.

This paper has some guidance on design ideas and the selection method for substation sacrificial anode cathodic protection.

The purpose of this paper is to study the damage evolution (DE) of coated API5L-X52 steel pipe with cathodic protection (CP) in nature soil. Also, different coating conditions, intact coating and coating with artificial holiday defect are considered to study the electrochemical behavior combined with soil properties and CP potential. An approach of electrochemical impedance spectroscopy (EIS) analysis is also developed.

This work developed a laboratory experimental set-up of coated pipeline under CP in nature soil. The electrochemical behavior has been investigated using EIS. The CP potential provided by a DC power supplier has been adjusted and recorded to maintain the protective potential of pipe at −850 mV vs Cu/CuSO₄.

Various parameters were derived from the EIS fitting data by equivalent circuit models to illustrate the three DE stages of coated carbon steel in soil. Each stage changes faster for the artificial defect coating system compared to intact coating, especially at the initial water uptake and ion transport stage. The CP potential has been proved to be correlated to the soil properties, coating conditions and DE stages of pipeline samples.

This work is the first one to study DE of coated pipeline system under CP in soil. It introduces an electrochemical method to study coating defects which can promote to design the deterministic model to detect coating defects of buried pipe using AC impedance technique.

This paper aims to research the corrosion behavior of the metal under the disbonded coatings interfered with AC through electrochemical method.

The corrosion behavior of the metal under disbond coating interfered with alternate stray current (AC) was studied by electrochemical methods using the rectangular coating disbonded simulator. The obtained data from electrode potential test, electrochemical impedance spectroscopy (EIS) and polarization curves in simulated soil solution indicated that under the natural corrosion condition, the self-corrosion potential and the corrosion current density of the metal at different depths under disbond coating had obviously changed if there was AC interference.

The self-corrosion potential of the metal at the same depths under disbond coating shifted negatively with the rising of the AC voltage. Under the condition of cathode polarization, there was still obvious potential gradient with the extension of the deep peeling of the coating gap, and the corrosion current density of the test points was minimum, and the protection effect was best when the cathode protection potential was −1.0 V. When the metal was applied with over-protection, the corrosion rate of the metal increased as AC stray current flowing through it increased.

This paper used the rectangular aperture device to study the corrosion behavior of X80 steel under the disbonded coatings through electrochemical methods when the AC stray current interference voltage was 0V, 1V, 5V or 10V and the protection potential was 0V, −0.9V, −1.0V, −1.2V or −1.3V, respectively. There is great significance to the safe operation and long-term service of pipeline steel in soil environment.

Irrespective of the type of cathodic protection system applied to an offshore platform or pipeline the longevity and effectiveness of that system, and therefore the safety and continued revenue earning capacity of the platform or pipeline, can be assured only if adequate monitoring and surveying of the performance is undertaken.

This study aims to evaluate the influence of pulsed cathodic protection on calcareous deposit formation on structures submerged in the synthetic sea water.

Chronoamperometric and C_HF methods have been used to evaluate the influence of pulsed cathodic protection on decreasing the required cathodic current for protection and also decreasing the surface coverage. The morphology of the formed deposits was evaluated using scanning electron microscopy. Chemical analyses of the formed deposits were performed using energy dispersive X‐ray spectrometer and X‐ray diffraction.

It was observed that pulse frequency influenced both the structure and the composition of the deposits. The most compact aragonite layer was obtained at high frequencies and at a high off‐time. It was clearly shown that by applying currents with less than 100 Hz frequency, the deposits formed on the sample involved CaCO₃ (aragonite) and Mg(OH)₂ (brucite). However, the kinetics of deposits formed when applying pulse current have been improved, compared to deposits formed by conventional cathodic protection. The reason is that large electrode overpotential favors nucleation through a decrease in the energy of nucleus formation. On the other hand, by intensive decrease of surface potential, repulsion of aggressive anions such as SO₄²⁻ and Cl⁻ occurs. These anions inhibit the formation of aragonite deposits.

In order to have a better investigation of electrodeposition processes in the shorter time, the use of more advanced techniques and analysis methods such as XPS is recommended. Furthermore, EHD techniques could be used for measurements of thickness of the layers.

The pulsed cathodic protection method is a relatively new method for the protection of buried and submerged structures. Recently, many researches have investigated that the influence of this technique on increasing the throwing power, decreasing interference effects on neighboring structures and increasing the uniformity of current distribution under cathodic protection.

Very little attention has been paid in the past to the effect of pulsed CP on deposit formation. The present paper, therefore, contributes useful understanding of the mechanism and advantages of such deposits in improving the effectiveness and lowering the operational cost of cathodic protection in use on offshore structures.

Underground corrosion of steel pipe has been estimated to cost $600 million (approximately £200 million) annually, in the United States. Efforts to reduce this toll have been stimulated since 1941 by heavy defence requirements for steel and other metals. Workers in the field have learned that underground corrosion can be greatly reduced by cathodic protection techniques, in which the structure is maintained at a suitable negative electrical potential.

The aim of this fieldwork was the study of the effect of 50Hz AC, induced by high‐voltage power lines, on the cathodic protection system of a natural gas pipeline. The effectiveness of cathodic protection was checked through in situ long‐term monitoring and analysis of pipeline electrical parameters. The results gave an insight into the problems of the cathodic protection system operation, caused by AC interference. An AC and DC potential interdependence was observed, that previously has hardly been reported, and was scrutinized in relation to cathodically protected pipelines. The effects of the AC‐interference and low frequency DC potential fluctuations, as well as the potential deviations from the protection potential, are examined. These phenomena are associated with corrosion susceptibility and difficulties in obtaining reliable cathodic protection measurements.