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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.

Anodic protection (A.P.) for corrosion control is based on the principle of protecting a metal or alloy from corrosion by raising the electrochemical potential of its surface to a value at which a protective oxide film (passive film) is formed and maintained. The principles of design of anodic protection systems are not very well developed. This paper discusses several important basic design concepts and describes several equations which can be used for the design and optimization of anodic protection systems for corrosion control.

Evidence of corrosion of reinforncing steel in concrete has become a familiar sight on United States highways and parking structures. Decks and substructures expected to provide maintenance‐free service for 40 years often require major repair within 5 to 10 years, and frequently have to be replaced after only 15 years of service. At first, poor construction practice and excessive loading were the primary factors blamed by most highway engineers. However, a geographical distribution of the problem pointed to a relationship with salt used to melt snow and ice, or present in seawater and salt spray. Only recently, as research has continued and as field evaluation tools were developed, has corrosion of reinforcing steel been understood as the major cause of this problem.

When the electrical potential criterion for cathodic protection has been determined the engineer is faced with the problem of achieving this at every part of the structure. Lack of spread of protection is caused by a change in potential of either or both the metal and the electrolyte. This change may be attributed to three factors: cathode control where the metal potential varies, electrolyte control where the electrolyte potential varies by virtue of the cathode shape and positional control where the anode proximity controls the spread. These factors can be analysed and models made to reproduce the conditions so that an economical design may be achieved.

The purpose of this paper is to study the effect of cyclic hydrostatic pressure on the protective performance of cathodic protection (CP) system consisting of Zn‐Bi sacrificial anode and Ni‐Cr‐Mo‐V steel.

The anode and cathode polarization curves of the driving potential and current for CP were investigated in case of cyclic hydrostatic pressure (0‐3.5 MPa) and compared with that at atmospheric pressure. The morphologies of the anode material with and without corrosion products were observed by scanning electron microscopy.

The experimental results revealed that the cyclic hydrostatic pressure had significant influence on the CP system. The anode potential instantaneously responded to the cyclic hydrostatic pressure and the discharge performance decreased due to the deposition of corrosion product. Also, the CP system exhibited higher slope parameter under cyclic hydrostatic pressure, indicating that the CP system cannot provide adequate protection for Ni‐Cr‐Mo‐V steel.

The results presented in this paper clearly show the effect of cyclic hydrostatic pressure on the sacrificial anode CP system, and present a foundation for further research on the practical application of sacrificial anode under cyclic hydrostatic pressure environment.

To study the corrosion behavior of pipeline steel in coastal areas, a tidal seawater macro-cell corrosion device was built using a cycle soaking tank and a macro-cell corrosion facility to simulate the corrosion behavior of pipeline steel in a simulated coastal environment (dry and wet alternations during seawater-soil corrosion macro-cell processes).

The corrosion behaviors were studied via the weight loss method, electrochemical methods and morphological observations on corrosion.

The results show that during the initial stage of tidal seawater/soil macro-cell corrosion process of the X65 steel, the working electrode on the seawater side is the anode of the macro-battery. As corrosion progresses, the anode and the cathode of the macro-battery become inverted. As the area ratio and the dry – wet ratio increase, the time of anode and cathode inversion shortens. Galvanic current density decreases as the dry – wet ratio increases and increases as the area ratio increases. The corrosion process of macro-cell is affected by the reversal of anode and cathode. After the reversal of anode and cathode, the corrosion rate is mainly controlled by dry – wet alternating corrosion.

The corrosion behavior of a pipeline steel in a coastal environment was studied using a tidal seawater macro-cell corrosion device. The synergism effect between the tidal seawater and seawater-soil macro-cell on corrosion behavior was clarified.

It is often difficult to decide whether a value is a cathodic or an anodic potential, and the method of identification is described in some detail in this concluding article. In another section the author deals with interference to cathodic protection systems caused by stray currents, and provides some very interesting practical data regarding problems he has investigated. Other subjects covered include a detailed description of the ground wire method of taking potential measurements, and the use of solution potential measurements for plotting the direction of stray currents.

Introduction Cathodic protection is used to prevent corrosion of buried or immersed steel structures. Current is made to enter the surface of the structure via a system of anodes, and the structure is the cathode, hence the name cathodic protection.

The dock gate cable seen in the photograph below is submerged in sea‐water for 12 hours out of every 24. Nine years ago an inspection showed the appearance of rust on the same cable and a replacement was considered. However, it was decided to try an application of the anti‐corrosive lubricant Voler V 200 R, a graphited compound made by Revol Ltd. The cable was ‘unlocked’ and impregnated with the compound. In the nine years since, no further trouble has been experienced. Another example of the protection afforded by V 200 R in the marine field is its use on the cables of Arctic survey ships. After treatment with the compound it is claimed that the life of these cables has been quadrupled.

In recent years, the demand for oil and gas pipelines has increased rapidly. Due to the restrictions of the pipeline routing, pipelines are generally laid in parallel or in the same trench, which results in stray-current interference between the independent cathodic protection (CP) systems. The purpose of this paper is to study the interference between the long-distance parallel pipelines and to obtain the optimized operation for the CP systems.

In this study, first, the numerical model of parallel pipelines was established using the boundary element analysis software (BEASY). Second, the effects of horizontal distance between parallel pipelines, coating damage rate, soil conductivity and anode output current on the interference of parallel pipelines were studied. Finally, by varying the layout or the output currents of CP stations, an optimized operation scheme osf long-distance parallel pipelines was put forward.

Simulation results showed that with a decrease in soil conductivity or coating damage rate, the interference increased. Moreover, the interference decreased with an increase in horizontal distance between two parallel pipelines or a decrease in anode output current. It was found that there are three methods to reduce the interference between long-distance parallel pipelines: to reduce the output currents of CP stations, combined protection and to close part of the CP stations. Among them, to close part of CP stations was the optimized scheme because of the lowest operating and maintenance cost.

The optimized operation scheme proposed in this study can not only solve the interference between parallel pipelines but also provide guidance for the parallel pipelines to be built in the future. Reasonably arranging the cathodic protection stations using numerical simulation can avoid the interference in the cathodic protection systems, and reduce the construction cost.