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Application: crude oil storage tanks, wastewater treatment tanks, sewage tanks.
A tank is a large container used to store crude oil or other liquids, consisting of tank walls, tank roof, tank bottom, and accessories. The tank's cathodic protection includes internal cathodic protection and external cathodic protection. Internal cathodic protection can usually be used in tanks, and external cathodic protection can also be used for tanks with longer protection life requirements. The bottom of the tank is usually protected by external cathodic protection due to the difficulty of replacing sacrificial anodes and the requirement for a longer service life.
Cathodic Protection of Tank Interiors
For the corrosion of crude oil storage tanks and sewage tanks, the main causes of corrosion on the inner wall of the tank bottom are electrochemical corrosion caused by crude oil deposits and sewage, as well as bacterial corrosion. The crude oil deposits and sewage in the tank bottom have high salt content and high temperature, so their corrosiveness is stronger. At present, the general method of using sacrificial anode for tank bottom plate inner wall protection is adopted. This method is safe and reliable for tanks and does not require special management. The protection effect is good. Aluminum alloy sacrificial anode and zinc alloy sacrificial anode are commonly used as sacrificial anodes. The sacrificial anode blocks are uniformly arranged on the inner bottom plate of the tank, and the sacrificial anode blocks are welded directly to the steel plate. Our company can calculate the number of sacrificial anodes required based on the protection area, protection period, and medium resistivity, and select the specifications and shapes of the sacrificial anodes.
Cathodic Protection of Tank Bottoms
The main reasons for the corrosion of the tank bottom plate are due to the aging and cracking of the asphalt sand layer under the tank base, which allows water in the foundation to penetrate to the tank bottom plate through the cracks, causing corrosion of the tank outer wall bottom plate; rainwater may penetrate into the tank bottom plate through the gap between the tank bottom plate and the asphalt sand, creating an oxygen concentration cell with varying permeability, forming a large cathode and a small anode, causing local corrosion to occur at a very fast rate. A self-catalytic effect of pitting corrosion may also occur in the gap. The corrosion caused by stray currents; the presence of sulfate-reducing bacteria; and construction quality issues can also cause corrosion of the tank outer wall bottom plate. Currently, the most common method of protecting the tank bottom plate outer wall is to use external current protection, which can use MMO anodes, mesh anodes, etc. Small tanks can use sacrificial anode protection, which can use magnesium alloy sacrificial anodes and zinc alloy sacrificial anodes.
Cathodic Protection of Underground Storage Tanks
The external cathodic protection of underground storage tanks is adopted according to the different soil resistivity, and different methods are used in environments with low soil resistivity. In such environments, sacrificial anode cathodic protection can be used, which can use magnesium alloy sacrificial anodes or zinc alloy sacrificial anodes. When the soil resistivity is high, external current cathodic protection should be used, which can use MMO anodes or mesh anodes.
