Underground Tanks Cathodic Protection Solutions
Underground storage tanks for gas (gasholders), oil, and petroleum products are usually equipped with anti-corrosion coatings. However, the coating cannot completely prevent natural corrosion or protect against the effects of stray currents, which are caused by the proximity of rail transport or high-voltage power lines. Corrosion significantly reduces the service life of the underground tank and can become a determining factor in the occurrence of an accident.
Underground tanks require reliable corrosion protection. Such tanks must be protected with paint coatings. Nevertheless, for example, during earthworks, if the coating is damaged, corrosion spots may subsequently form. For metal underground tanks used at sites with special safety requirements, solutions based on cathodic protection (CP) have been developed.
There are two methods of cathodic protection: active protection using impressed current and the method of sacrificial anode protection.
Impressed Current Cathodic Protection for Underground Tanks
The active method consists of directing impressed current to the protected tank. This method is used upon the requirement of the technical inspection service or other regulatory documents at critical facilities. The entire process is managed by a cathodic protection power supply, which receives data from sensors, a corrosion rate indicator plate block, and a reference electrode, and which requires connection to a power source. Due to the cost of the first option, gasholders and other underground tanks are mainly protected by sacrificial anode protection.
Sacrificial Anode Cathodic Protection for Underground Tanks
Sacrificial anode protection provides for the installation of metal elements (anodes) with a more negative electrochemical potential and their connection to the underground tank via cable. During operation, the sacrificial anode degrades: its metal oxidizes, thereby reducing the corrosion of the tank’s steel. The most common are magnesium anodes PM, which are supplied pre-packaged in bags with an anode backfill activator; this package allows for stable conditions for efficient anode performance. This protection method does not require electricity.
The protection system also serves as a grounding device. This is necessary when refueling the gasholder, as strong static electricity is generated during gas flow through the hose. Steel grounding in such a case may lead to a decrease in the anti-corrosion properties of the tank, while using an anode in activator as the grounding element significantly improves the corrosion resistance of the tank.
Advantages of the sacrificial anode protection kit:
- Magnetic contacts are used to connect to the tank. This eliminates unnecessary welding work
- For ease of use and data acquisition, the components of the system are connected at a test station
- The installation of equipment for the anode-cathode protection of the underground tank fully complies with the requirements of regulatory documents
