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Calculation of Anode Life

According to Faraday's law of electrolysis, the service life of a sacrificial anode can be calculated using Equation (5-7), with an anode utilization rate of 0.85.

In the equation, T is the working life of the anode, in years; m is the mass of the anode, in kg; I is the output current of the anode, in A; ω is the actual consumption rate of the anode, in kg/(A·year) (which can be found in Tables 5-3 to 5-5 or converted). In practical engineering, the design life of sacrificial anodes can be selected as 10 to 15 years.

Sacrificial Anode Groundbed

(1) Structure of the Groundbed

To ensure the stable performance of sacrificial anodes in soil, the anode should be surrounded by appropriate chemical backfill. The functions of the backfill are: to keep the anode adjacent to the backfill, improving the anode's working environment; to reduce the anode's grounding resistance and increase its output current; the chemical composition of the backfill facilitates the dissolution of anode products, preventing scaling and reducing unnecessary anode polarization; and to maintain long-term moisture in the anode groundbed.

Cathodic Protection

1.Introduction to Cathodic Protection Technology

Cathodic protection is one of the important anti-corrosion measures for offshore oil and gas fields in the eastern South China Sea, and it is also the most widely used protection method in seawater and sub-mud sections. Currently, cathodic protection methods include impressed current and sacrificial anode methods, with the sacrificial anode method being the most widely applied in offshore oil and gas fields in the eastern South China Sea.

Cathodic protection is an electrochemical protection technique used to prevent metal corrosion in electrolytes (such as seawater, freshwater, and soil). The basic principle of this technology is to make the metal structure act as a cathode and apply a certain direct current to it, causing cathodic polarization. When the metal's potential is more negative than a certain value, the electrochemical heterogeneity on the metal surface is eliminated, and the cathodic dissolution process of corrosion is effectively inhibited, achieving the purpose of protection.

According to the principle of metal electrochemical corrosion, if iron with a more negative potential and copper with a more positive potential are connected and immersed in seawater, the iron with the more negative potential will corrode, while the copper with the more positive potential will be protected. To prevent both iron and copper from corroding, a piece of metal zinc with a potential more negative than both copper and iron needs to be connected.

Due to the strong electrochemical activity of the zinc plate, after connection, a large number of excess electrons from the zinc plate flow along the wire into the copper and iron plates.

In the equation, ------ number of electrons flowing from the zinc plate to the iron plate.

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