Abstract:
This chapter contains sections titled: Sacrificial Anode Cathodic Protection Systems Impressed Current Cathodic Protection Systems Cathodic Protection Current Need Effect of Coatings on Cathodic Protection Effect of Passivation on Cathodic Protection Automated Cathodic Protection Systems Cathodic Protection Criteria Reliability of Cathodic Protection Criteria Interference Effects of Cathodic Protection Systems Criteria for Cathodic Protection Projects Cost of Cathodic Protection Comparison of Cathodic Protection SystemsKeywords:
Passivation
Galvanic anode
The protection effect of a novel Zn-based sacrificial anode(ZLR) for steel in soil was studied by measuring constant current and protection potential. Results show that the ZLR anode has a low polarization and steady potential in soil,recording a current efficiency of over 70%. When ZLR anode,conventional Zn anode and conventional Mg anode were separately coupled with steel in soil,the lowest potential and the best protection effect were obtained for the steel coupled with ZLR anode. Besides,the humidity of soil had little effect on the potential of steel coupled with ZLR anode. The ZLR anode was comparable to Mg anode in terms of long-term cathodic protection of steel in soil.
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In this work, the thermal spraying sacrificial anode was investigated as reinforced concrete structure cathodic protection method. During our experiment, the performance of the thermal spraying sacrificial anode was studied using electrochemical method, metallographic microscopy method and simulation tests. And the results show that the thermal spraying sacrificial anodes are better than traditional sacrificial anodes. The method of thermal spraying applied in sacrificial anode field is successful, which solve the problem of insufficient driving initial potential of traditional sacrificial anode in the concrete structure.
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Passivation
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Voltage drop
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This chapter contains sections titled: Anodic Potentials and Anodic Polarization Galvanic Cathodic Protection Current Need Anodic Current Capacity and Anodic Current Efficiency Service Life of an Anode Minimum Number of Galvanic Anodes Commonly Used Galvanic Anodes Performance Measurements of Galvanic Anodes Galvanic Anodic Beds Sacrificial Anode Cathodic Protection Projects Maintenance of Sacrificial Anode Cathodic Protection Systems
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An updated version of sacrificial anodes for cathodic protection of structures immersed in seawater was recently patented. The anode, constructed in two anodic materials (aluminum alloy on the inside and magnesium alloy on the surface), offers significant reductions in weight and cost. These reductions are due to the highly protective calcareous deposit that forms on the immersed structure when these anodes are used. Characteristics of the deposit and anode performance are reported.
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The performance of different sizes of zinc, and aluminium galvanic anodes on the cathodic protection of mild steel in seawater and 0.2 M sulphuric acid was evaluated at ambient temperature. The magnitude of corrosion protection by the galvanic anodes was observed by weight loss method,corrosion rate calculation and potential measurement technique. It was observed that the aluminium
anodes proved more effective as sacrificial anode for mild steel in seawater environment. In sulphuric acid environment, the zinc anode gave a more protective performance than aluminium anode. Potential measurement results obtained were found to correspond with the results obtained from weight loss method. For both environments, the effects of a varying cross-sectional area and the anode material on the cathodic protection of mild steel were examined
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The experiments of cathodic protection have been performed using Daiichi-Tetsuei Maru and four other ships during about one year. The used anode materials were magnesium and zinc plates. Then, following consideration were resulted.(1) In the magnesium anode system it was difficult to control anode current and occured frequently over current, therefoe it was possible to damage the paint of ship and make faster consumption of magnesium anode.(2) But in the zinc anode system current was less than that of magnesium. so it was necessary to have a number of zinc plates but easy to use. And from these performance a basis of cathodic protection and its methods were clear.
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There are two cases when the life of a sacrificial anode is shortened from the designed life: one case results from self-corrosion of the anode due to contamination by sea water in the other case, however, electrical current to protect some given steel piles overflows to protect other, adjacent non-protected steel piles. In this study, the variation of polarization potential of nine steel piles, being protected cathodically and with anode-producing current between anode and steel piles, was investigated. Parameters were varied, such as the eighth and ninth steel piles either connected electrically or not, and whether the ninth steel pile was protected by another sacrificial anode or not. The current produced by the sacrificial anode decreased when the ninth steel pile was cathodically protected by the anode of another pile. However, produced current increased when the ninth steel pile was not connected to another anode. The study concludes that the life of a sacrificial anode can be prolonged or shortened depending on whether adjacent steel piles are cathodically protected or not.
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Cathodic protection of concrete structure is gaining more and more importance. Though the impressed current system is being widely used, sacrificial anode system is also gaining ground. It is well known that alloys of zinc, aluminium and magnesium are the candidate materials for use as sacrificial anodes. However, very little work has been done for evaluating their utility as compared with that done for utilizing impressed current system. In the present work cathodic protection of embedded steel reinforcement bars has been achieved by utilizing a suitable magnesium alloy anode, which is manufactured based on indigenous technology (CECRI know-how). The potential of the embedded steel and the current flowing between the anode and the embedded steel were monitored over a period of one year, in conventional M20 (1:2:4 WIC 0.5) concrete. The results indicated that there is a considerable shift in potential in the presence of chloride. The steel was found to be well protected from corrosion, noticed after breaking open the tested concrete. The anode characteristics were evaluated at the end of the test period and the data obtained prove that the cathodic protection system utilizing magnesium alloy sacrificial anode is suitable under specific conditions.
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