Zinc alloy sacrificial anode implementation standard
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Sacrificial Anode Cathodic Protection
The basic principle of sacrificial anode cathodic protection is to use a metal or alloy with a more negative potential than the protected pipeline metal, connecting it to the protected metal. Relying on the current generated by the potential difference between them, the protected metal is cathodically polarized and thus protected, as shown in Figure 5-1. The underground metal pipeline has a higher electrode potential and acts as the cathode of the battery, where the reaction Fe2++2e-
→
Fe occurs, or in acidic media, the reaction 2H++2e-H2 takes place, or in neutral or alkaline media, the reaction O2+2H2O+4e-4OH- occurs; the sacrificial anode has a more negative potential and undergoes the reaction MMn++ne-. In this way, the sacrificial anode is continuously corroded, and the generated electrons are transferred to the underground pipeline, protecting it from soil corrosion. According to the above principle, the sacrificial anode must have a sufficiently low potential to generate sufficient current; in addition, the medium must be an electrolyte, meaning it must conduct electricity, so that metal M can be corroded to form Mn+, and the soil medium can also quickly diffuse Mn+ into the soil, preventing polarization on the surface of the metal anode and ensuring that the metal can release electrons. However, the sacrificial anode should not be consumed too quickly, as this could lead to overprotection and even increase the frequency of anode replacement, raising protection costs. How to achieve effective sacrificial anode protection with low cost? This involves the selection of anode materials, calculation of the protection range of sacrificial anodes, modification of soil electrical
conductivity, depolarization of the anode surface, and other issues.
Figure 5-1 Working Principle of Sacrificial Anode
There are many types of sacrificial anode materials available, such as magnesium and magnesium alloys, zinc and zinc alloys, aluminum alloys, etc. Among them, magnesium sacrificial anode materials can provide a potential of about -1.75V, zinc about -1.1V, and industrial pure aluminum about -0.8V. In practical operation, the selection of sacrificial anodes should be comprehensively considered based on the potential provided by each material, the surrounding environment in contact with the metal, and the required protection current.
I. Soil Medium Requirements for Sacrificial Anodes
II. Soil is a complex system composed of gaseous, liquid, and solid substances. The composition of these three states changes with factors such as temperature, climate, and season, leading to variations in soil resistivity, redox potential, pH value, salt content, etc., making the assessment of soil corrosiveness extremely complex. As a commonly used reference indicator, Table 5-1 provides the standard for assessing soil corrosiveness based on soil resistivity.
The grounding resistance of the anode is related to soil resistivity, and it changes annually. To avoid such changes and reduce grounding resistance, the anode in the soil should be surrounded by backfill. This backfill not only limits the formation of surface films and prevents electro-osmotic dehydration but also ensures uniform current output and uniform consumption of the material. The latter is mainly because the backfill contains gypsum, while bentonite and diatomaceous earth retain moisture. Adding sodium sulfate can reduce the resistivity of the backfill. The composition includes: gypsum powder, bentonite, diatomaceous earth, sodium sulfate.
Pei Yingying 186258 79268
| Industry Category | Minerals-Metallurgy |
|---|---|
| Product Category | |
| Brand: | 立博防腐 |
| Spec: | 400*100*40mm |
| Stock: | 11111 |
| Manufacturer: | |
| Origin: | China / Henan / Jiaozuoshi |
