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Synopsis A brief introduction is given to the theory of cathodic protection. Principles and design procedures are described for both sacrificial anode and impressed current cathodic protection with a comparative assessment of both systems and the anodes used in them.

The purpose of this investigation was to study these problems and design regional cathodic protection, using numerical simulation. Regional cathodic protection technology is immature at home and abroad. This is reflected in the fact that in gas stations, there are many underground pipelines, which can lead to serious interference and shielding phenomena, and there are many grounding networks that can cause substantial loss of the cathodic protection current.

Based on the above, in this article, first of all, the mathematical model of the buried pipeline cathodic protection potential distribution was established and the control equations solved using the boundary element method. Second, the cathodic shielding effect in pipeline concentration areas, the effect of instrument equipment grounding systems on cathodic protection and the influence of DC stray current on the interference of pipeline corrosion were studied separately using BEASY software. Finally, the BEASY software was used for a regional cathodic protection design for a real gas station.

It was concluded that impressed current used in combination with sacrificial anodes for regional cathodic protection design is often the most economic and effective approach. However, the output current of the auxiliary anode is large with high energy consumption. In consequence, it may be recommended that the station pipelines should be laid on the ground, rather than under it.

It is considered that the results can guide regional cathodic protection design for real-life installations very well.

Impressed‐current cathodic protection techniques can be used to provide automatically the right amount of current at all times and, with the use of one or other of the systems described here, protection can be provided for the largest and the smallest vessel with any steelwork under water. This full range of equipment gives protection under the most varying conditions, and is considered by the manufacturers as being the most advanced system of cathodic protection in the world.

The operation of impressed current cathodic protection devices on ships frequently results in some destruction of the paint coating on the rest of the structure. The reasons why these devices are more aggressive to paints than laboratory work suggests are explored and the operational parameters of practical systems described. The use of a conductive paint to simulate an anode is introduced as well as tests which have shown that a conducting paint film may be used as a cathodic protection anode with significant improvement in corrosion protection in high resistivity environments.

The purpose of the paper was to design an anti-corrosion system that combined conductive coatings with cathodic protection for a 500-kV substation ground grid, and provide a basis for the anti-corrosion construction of the installation.

The study took the Shaoguan 500-kV substation grounding grid as the research object. The anti-corrosion performance of KV conductive coatings on grounding metal was researched. In parallel, the alkalinity of substation soil was evaluated according to the German DIN50929 Standard, and the combined protection system comprising conductive coatings and impressed current cathodic protection was designed.

KV conductive coatings, that have resistance to acids, alkalis and salts, can effectively slow down the corrosion rate of the grounding grid. The investigation also provided the outline design, installation, construction requirements and monitoring methods for the 500-kV substation grounding grid.

This report contains some guiding significance for anti-corrosion engineering of 500-kV substation grounding grids.

Probably the first use of electricity to protect ships' hulls was Edison's trailing anode technique. It was an economic failure because of the cost of the electricity and also because of misinterpretation of the rate of corrosion of the hull in moving from laboratory to full‐scale experiment. Where Davy had succeeded dramatically with sacrificial anodes Edison failed economically with impressed current. Has the situation changed today with our tremendous advances in electrical power and control techniques?

3. Unsolved problems and future developments The previous sections may indicate that cathodic protection, at least if installed to the best standard practice, will solve all immersed corrosion problems offshore. This would be incorrect. However, the history of those structures in the North Sea with complete records of effective cathodic protection indicates that the existing techniques do largely result in safe structures for long periods.

ENGELHARD INDUSTRIES have, for the past 15 years, been particularly interested in the subject of impressed current cathodic protection of ships' hulls. A study we made convinced us of the advantages of platinum as an anode material, since even under high current density (500 A/sq.ft.) the dissolution rate of this metal was only 6 mg./A‐yr. in sea‐water. The noble metals are manufactured by the industry, and so it followed that the cathodic protection of ships became an active project.

The radical mitigation of corrosion on external or internal surfaces of pipelines, tank farms, storage tanks, pylon footings and of gasholders, ship's ballast tanks, ship's hulls, condenser end‐boxes, heat exchangers and pasteurisers, has been successfully accomplished by the application of cathodic protection both by galvanic anodes and by the use of the impressed‐current method. The scope of cathodic protection is thus comprehensive. This paper describes in a general way the properties, uses and limitations of the principal materials used as anodes in impressed‐current cathodic protection systems, together with some indication of the effects of different environments upon the various materials. In this first part, graphite, silicone iron and scrap steel are discussed.

The basic aspects and mechanism of corrosion of steel piles in sea water are briefly discussed. The effects of parameters viz. pH, salinity, dissolved oxygen, temperature and wind velocity responsible for the corrosion of steel piles have been presented. The methods used for corrosion control and the impressed current cathodic protection technique in particular, with its merits, when applied to under‐water marine structures are outlined. The values and importance of potential required at the surface under protection, surface current density requirement and its distribution for the protection of steel structures under different service conditions useful for the design of cathodic protection systems are presented. The characteristics of various types of anode materials with a special reference to the latest platinized (Platinum‐Niobium) niobium anodes, with their merits, over other types of anodes are tabulated. The basic considerations required for the design of cathodic protection and the design of the system have been presented.