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The characteristics of aluminum alloy anodes are: large theoretical power generation, small specific gravity, can be designed as long-life anodes with light weight, convenient manufacturing, simple manufacturing process, ample material sources, excellent electrochemical performance, and the function of initially regulating current and potential. They are widely used for protection inside marine petroleum equipment, outside submarine pipelines, platform jackets, etc. However, aluminum anodes have the disadvantages of lower current efficiency than zinc anodes, poorer dissolution performance than zinc anodes, and are not suitable for high resistivity media.

Currently, the development of aluminum alloy anodes is moving towards improving current efficiency, enhancing dissolution performance, and adapting to high resistivity media as well as high and low-temperature seawater environments. For example, to effectively protect offshore oil pipelines, bracelet-type sacrificial anodes are widely used in the eastern South China Sea, making aluminum sacrificial anodes more suitable for installation, with the generated current meeting pipeline requirements as much as possible to achieve the desired protection lifespan.

(3) Sacrificial Anode Protection Design

The effectiveness of sacrificial anode protection mainly depends on the sacrificial anode material and reasonable sacrificial anode protection design. The basic steps are as follows:

1) Collect design parameters.

Gather information on material, surface condition, geometric shape, and relevant environmental conditions; set the protection current density; understand the protection area and structural characteristics; calculate the total protection current required based on the protection lifespan.

2) Select sacrificial anode material and specifications.

Based on the protection lifespan and requirements, select the sacrificial anode material (such as zinc anode or aluminum anode); based on installation and structural conditions and protection current, select the anode's protection distance to determine the anode's size and specifications.

3) Calculate the number of anodes and verify.

Based on the total anti-corrosion area and anti-corrosion current, the number of anodes required can be calculated and then verified.

The relationship for anode design and installation should satisfy:

Where I------- total protection current required, A;

LA----- protection current per anode, A;

a---- number of anodes

IC---- average protection current density on the protected area SC per anode

The verification formula for anode service life is:

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