Cathodic Protection Insulated Flange

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Hydraulic and Hydroelectric Expansion Joints

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Product Structure Features:

Insulated flanges achieve electrical insulation between the two sides of the flange by leveraging the dielectric properties of the insulating gasket and the high‑strength insulating sleeve. The primary insulating materials include polytetrafluoroethylene, oil‑resistant rubber‑asbestos sheets, chloroprene rubber, and other such materials. Compared to the designed service life of the project, the service life of insulating materials is relatively short, requiring multiple inspections and replacements within the pipeline’s intended service life.
Principle of Cathodic Protection:
The principle of cathodic protection is to supply a large number of electrons to the metal, placing the entire protected metal in a state of electron excess, so that all points on the metal surface reach the same negative potential. As a result, metal atoms are less likely to lose electrons and become ions that dissolve into the solution. There are two methods to achieve this: sacrificial anode cathodic protection and impressed current cathodic protection.
1. Sacrificial anode cathodic protection involves connecting a metal with a more negative electrode potential to the metal being protected, placing them in the same electrolyte. This causes electrons from the sacrificial anode to transfer to the protected metal, bringing the entire protected metal to a uniformly more negative potential. This method is simple and easy to implement, requires no external power source, generates minimal corrosion interference, and is widely used to protect small metallic structures—typically those with currents less than 1 ampere—or structures located in environments with low soil resistivity (soil resistivity less than 100 ohm-meters), such as urban pipeline networks and small storage tanks. According to reports in domestic literature, there have been numerous instances of failure in the use of sacrificial anodes; it is generally believed that the service life of a sacrificial anode rarely exceeds 3 years, at most 5 years. The primary cause of cathodic protection failure with sacrificial anodes is the formation of a non‑conductive, hard crust on the anode surface, which restricts the anode’s current output. In my view, the main reason for this issue is that the anode composition fails to meet regulatory requirements; secondarily, it is often due to excessively high soil resistivity at the anode’s installation site. Therefore, when designing a sacrificial anode cathodic protection system, in addition to strictly controlling the anode composition, it is essential to select an anode bed location with low soil resistivity.
2. Impressed current cathodic protection uses an external DC power source and auxiliary anodes to force current to flow from the soil into the protected metal, thereby lowering the electrical potential of the protected metal structure relative to its surrounding environment. This method is primarily used to protect large metal structures or those located in soils with high resistivity, such as long-distance buried pipelines and large tank farms.

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