Corrosion protection is a critical element in the long-term performance and safety of steel field erected storage tanks. Preventing corrosion not only safeguards the tank’s structural integrity but also extends its service life and reduces maintenance costs. A comprehensive protection strategy typically includes coatings and cathodic protection systems.
Protective Coatings
Coatings act as a barrier between the steel surface and corrosive elements such as moisture, chemicals, and oxygen. These coatings are applied in three primary areas:
- Tank Exterior: Exposed to environmental conditions, the exterior coating must resist the detrimental effects of UV exposure, rain, and temperature fluctuations, and potential effects from other chemicals stored nearby.
- Tank Interior: In some cases, the product stored may react with the material that the tank is constructed of, or there are concerns that contamination or water may enter the tank. To address these concerns, some tank interiors are lined with an appropriate coating. Interior coatings must be selected for compatibility with the contents.
Proper selection, surface preparation, and skilled application of the coating system are essential to ensure optimal performance and longevity.
Proper Foundation Construction
The tank foundation serves several purposes. In addition to supporting the tank, a properly constructed tank foundation helps isolate the tank bottom from exposure to water. The tank bottom is particularly vulnerable to soil moisture, and the tank bottom must be carefully protected, especially if in direct contact with the ground. Protection is generally achieved by careful preparation of the tank foundation using granular material that will support the tank and promote the movement of water away from the tank bottom.
Cathodic Protection Systems
When coating alone is insufficient—such as when the tank bottom is in direct contact with the ground—cathodic protection becomes necessary to halt electrochemical corrosion. Two main methods are commonly used:
Sacrificial Anode Systems
This passive system works by attaching an anode made of a more reactive metal (typically zinc or magnesium) to the tank. The anode corrodes preferentially, protecting the steel structure. As the name implies, the sacrificial anode is consumed over time and must be replaced periodically.
Impressed Current Cathodic Protection (ICCP)
This active method uses an external power source to drive a protective current to the tank shell. ICCP offers continuous, adjustable protection and is ideal for larger tanks or environments where passive systems are inadequate.
System Monitoring and Maintenance
Regardless of the method used, corrosion protection systems are not set-and-forget solutions. Ongoing maintenance is essential:
- Monitor system performance regularly through testing and inspections.
- Replace consumed sacrificial anodes in passive systems.
- Adjust current levels in ICCP systems to adapt to changing environmental or operational conditions.
Proper Tank Maintenance
After the tank is built, it is important that the tank system be properly maintained:
- It is important that the material being stored in the tank is protected from outside contamination, like water, that can cause it to react with the tank shell
- Keep the containment area clear of water, debris, and organic material. It is important that the containment area around the tank be kept free of standing water and organic material that can allow moisture to contact the tank shell and increase the risk of corrosion.
Conclusion
A robust corrosion protection strategy—integrating coatings with passive or active cathodic systems, control of water in the area, stored product quality control, and proper maintenance of all the tank systems—ensures the reliability and durability of steel storage tanks. Proper design, installation, and ongoing maintenance are key to maximizing the investment and preventing costly failures in the future.
