Corrosion of underground storage tanks

Underground storage tanks are generally in contact with materials such as soil and sand. The electrochemical reaction between the tank and the surrounding soil (electrolyte) leads to tank corrosion. The small voltage difference on the steel surface causes a current to flow from one part of the tank to another. Corrosion occurs where current flows into the soil (electrolyte). This part in the galvanic cell is called the anode. Where the flow from the soil enters the reservoir is the cathode and corrosion does not occur.

Prevention of tank corrosion (cathodic protection of underground storage tanks)

An outer cover as well as a cathodic protection system are used to protect the underground tanks from corrosion. A suitable outer cover can protect more than 99% of the tank surface. But since there is no complete cover, in addition to the outer cover, a cathodic protection system must be used to protect the tank from corrosion. The cathodic protection system converts the tank into a cathode by applying an external current and protects it from corrosion. In cases where the amount of current required to protect the structure is small, sacrificial anodes are used. For large structures such as large diameter pipelines, an impressed current system is used.

Magnesium sacrificial anode for cathodic protection of underground storage tanks

Magnesium sacrificial anode is the most common sacrificial anode used in cathodic protection of underground tanks. Magnesium anode can protect underground tanks in any soil. To reduce the electrical resistance of the anode to soil, a magnesium anode is usually used inside a linen bag with backfill material that is a combination of gypsum plaster, bentonite and sodium sulfate. Magnesium anode is produced in two types of standard and high potential. High potential magnesium anode is used in soils with a resistance of about 10,000 ohm-cm. Based on the dimensions of the tank and the soil resistance in which the tank is located, the number and dimensions of the required anodes are determined. The two most common sizes of magnesium anodes to protect underground reservoirs are 17-pound and 32-pound anodes. The anodes are installed at a suitable distance and depth from the tank. The anode wire is connected to the top of the tank with a low-resistance electrical connection. All connections are covered with waterproofing.

In terms of cathodic protection of underground storage tanks, the technical and engineering department of Tavanazob Sana’ati Kavir Company is ready to provide consulting services for which you can contact us.