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Sources have been described of corrosively hazardous electric fields and methods of determination of the corrosion hazard to metal structures caused by electrolytic corrosion. Results of potential and impedance investigations in the field of stray currents flowing out of a tram traction and in the presence of a defined electric field of low frequency have been presented. Uncertainties have been indicated relating to the generally accepted interpretation principles of measurement results in the presence of electric fields. The possibility has been indicated of incorporating the impedance spectroscopy technique to potential‐voltage investigations, allowing estimation of the real corrosion interaction of stray currents on underground structures.

The purpose of this paper is to present the investigation of aluminum alloy by means of dynamic electrochemical impedance spectroscopy (DEIS), which is simultaneous method of AC impedance and DC polarization measurements.

A method of DEIS has been applied. Changes in equivalent circuit (EC) parameters versus potential for both investigated aluminium alloys are evaluated.

On the basis of obtained results, it is unambiguously demonstrated that the addition of 4.5 percent magnesium degraded the anticorrosive properties of the test alloys. It is difficult to define unequivocally the range of passive state and a moment of passive layer breakdown on the basis of current/voltage dependencies. However, application of the DEIS method and analysis of the evolution of particular elements of an electrical EC allowed identification of the instant of corrosion process initiation.

The presented method is only suitable for laboratory evaluation of metal alloys because it requires sophisticated measuring equipment and is a difficult and time‐consuming way to obtain final results.

In one experiment, both polarization (DC) data and impedance (AC) measurements can be obtained. This allows the electrochemical properties of very similar aluminum alloys to be compared precisely with one other.

Performed investigations by cyclic thermometry in a solution containing 1 per cent H₂SO₄ by weight admixed with chloride ions in 0.2 per cent quantity by weight at 553K have shown that 654SMO steel is not susceptible to pitting, while 316L steel is intensively attacked in investigation conditions. On cyclic thermograms for 316L steel three temperature zones can be distinguished. The first zone is the zone of resistance to pitting. In the third temperature zone rapid development of pits is observed. The second intermediate temperature range includes the process of initiation and formation of pits. The temperature of pitting corrosion of 316L steel depends linearly on the applied polarisation. The temperature determined by extrapolation for a polarisation equal to zero is the measure of resistance to pitting corrosion. The pitting corrosion temperature determined in this way is related to stationary conditions, with no polarisation.

A new method of spectral analysis has been proposed for non‐stationary harmonic analysis of corrosion processes. The current of a model circuit has been considered which would simulate a first‐order electrode reaction proceeding in conditions of a linearly changing electrode potential with a superimposed sinusoid signal. It has been shown that the Fourier transformation approach does not reflect the amplitude changes of harmonic components as a function of constant potential. In addition, it has been shown mathematically that application of Gabor transformation in spectral analysis is a means of obtaining the correct frequency components. The Gabor transform correctly reflects amplitude changes of harmonic components as a function of potential. Digital analysis of current changes by Gabor transformation unequivocally confirmed the usability of this method for harmonic analysis of corrosion processes.

The results of the electrochemical noise observations in 0H18N9 steel are presented. Current noise was obtained by potentiostatic measurements in aqueous solution of 0.1M H₂SO₄ and 0.06M Cl⁻. The recorded noise had an evident trend and peaks that are typically observed during pitting corrosion. The trend was removed by means of the third order polynomial approximation. The statistical hypothesis, i.e. the difference between the approximation and the observed noise, was tested. The results confirmed that current noise caused by pitting corrosion has nonstationary or weakly stationary character. The recorded noise was analysed using the Joint Time‐Frequency Analysis method, which is appropriate for nonstationary signals. The derived results confirmed the presence of pitting corrosion. It was usual for a few pits to form on the surface of the electrodes in distinct phases, and these were observed as peaks in current fluctuations.

Results of investigations on a working cathodic protection installation of two underground LPG tanks are presented. The efficiency of anodes and buried reference electrodes were evaluated using electrochemical impedance measurements. On the basis of the impedance spectra obtained it can be shown how one of the anodes attached to the long anode line works inefficiently. In addition, the potential distribution map for the protected tanks is presented. On the basis of this information, an electric connection was revealed from the tanks to the neighbouring reinforced concrete structures, this being inconsistent with the technical guidelines for the cathodic protection installation. The inspection performed on the installation yielded some recommendations concerning the operational parameters and the identification and replacement of defective components.

Industrial chimneys are a great part of environmental protection in industrial countries. In recent years many of them have been used to carrying away very aggressive gases from boilers and flue gas desulphurisation (FGD) units below acid dew‐point temperature. It is opf very important to modernize the old stacks and protect them against corrosion. The proper anti‐corrosion protection of modern high stacks is also an important technical and economical problem. In this paper the mechanism of acid dew‐point corrosion, as well as construction of industrial chimneys, methods of their anti‐corrosion protection and modernisation are described.

This paper sets out to detect and characterize electric fields in the ground (such as stray current fields) using a tandem time/frequency method of signal analysis.

Results were obtained from investigations performed in the presence of a generated electric field with controlled variable characteristics, and in the presence of an electric field generated by a tramline. The analysis of measurement registers was performed using Short‐Time Fourier Transformation. The results were presented in the form of spectrograms, which illustrate changes in the spectral power density of the measured signal versus time.

Tandem time/frequency analysis reveals the random or deterministic character of the electric field, enabling its complete time/frequency characteristics to be obtained. Such information is inaccessible using exclusively the frequency analysis methods that utilize classical Fourier transformations. Moreover, an analysis of the spectral power density distribution of the signals in three directions on the ground surface makes it possible to define the localization of the field source.

Analysis methods for electric fields in the ground should be adapted to the evaluation of non‐stationary signals because the stray currents are of this type. Such a possibility is given by combined analysis in the domains of time and frequency. This method can be used as complementary to applied measurement techniques of stray current interference.

The method of electric field detection and characterization, as related to stray currents, previously has not been presented in the literature. This method of signal analysis may be adopted for other investigations that are reliant on the registration of voltages or potentials characterized by arbitrary frequencies.

The purpose of this paper is to investigate whether the sedimentation of calcareous deposits occurs on cathodically protected steel in Baltic sea water.

Steel electrodes were cathodically polarized in natural Baltic sea water at potential +0.150 V vs Zn electrode in potentiostatic mode. During exposure chronoamperometric measurements were carried out. After the exposure, the electrode's surface was examined by scanning atomic force microscope (AFM) and by scanning electron microscope (SEM). Deposit composition was examined by energy‐dispersive X‐ray spectroscopy (EDX). Comparative investigation was carried out in 1 percent NaCl solution (comparable to the salinity of Baltic sea water).

During cathodic polarization in Baltic sea water, non‐conducting calcareous deposits developed on steel surface. These deposits significantly lowered the cathodic current demand. Morphology and EDX spectroscopy of the deposit indicated that it was built mainly of aragonite (polymorph of CaCO3). No non‐conducting deposits on cathodically protected steel electrodes developed in 1 percent NaCl solution.

Composition of Baltic sea water favours the formation of calcareous deposits on cathodically protected steel. Sedimentation is a beneficial and desired phenomenon from the point of view of cathodic protection system of maritime construction as it facilitates polarization. Evolution of calcareous deposits should be taken into account as one of the environmental factors when designing a cathodic protection system.

The purpose of this paper is to analyze and estimate the stray current corrosion hazard of a buried metallic pipeline using a predictive model for stray current density.

A predictive model for stray current density of the buried metallic pipeline was built, using a back propagation (BP) neural network method and experimental data. The accuracy of the model was tested using test samples. The single sensitivity analysis predictive method was used to establish the relationship between stray current density with the soil resistivity. The effects of buried depth and the pipe‐to‐ground voltage offset were researched using this network model.

The feasibility of the BP neural network to forecast stray current effects from the buried metallic pipeline was confirmed.

The paper provides a new method to analyze and estimate the stray current corrosion hazard of buried metallic pipelines.