Corrosion is the gradual deterioration of metals due to environmental, chemical, or electrochemical reactions. In storage tanks—especially those used for industrial purposes—corrosion can compromise structural integrity, create environmental hazards, and lead to costly repairs or shutdowns.
Understanding the causes and types of corrosion is crucial for implementing effective protection strategies.
Types of Corrosion in Storage Tanks
Corrosion can occur due to multiple mechanisms:
Chemical Corrosion
Occurs without the involvement of electrical current, usually due to direct reaction with aggressive chemicals in the tank.
Electrochemical Corrosion
Happens when a corrosion current flows between different areas of the metal in the presence of an electrolyte, like water or brine.
Mechanical-Chemical Corrosion
Caused by the combined effect of mechanical stress and chemical exposure, especially in high-pressure environments.
External Corrosion
Affects the outer surface of the tank due to atmospheric conditions, humidity, acid rain, and industrial pollutants.
Internal Corrosion
More aggressive than external corrosion. Influenced by product type, frequency of tank loading, and the presence of water or sediment inside the tank.
External Tank Surface Protection: Coating & Maintenance
For above-ground tanks, maintaining the external surface is critical for long-term durability. Regulatory standards often require routine inspections and protective coatings.
Steps for External Surface Protection:
Surface Preparation
Old paint, rust, and dirt are removed using wire brushes or sandblasting tools. A degreasing agent is applied, followed by hot water washing to remove corrosion residue.
Drying and Cleaning
The cleaned surface is thoroughly dried to avoid trapping moisture under the new coating.
Priming and Painting
An industrial-grade primer is applied using a pneumatic spray gun, ensuring smooth application without drips. Multiple layers of UV-resistant paint are used. Reflectivity is considered—light-colored coatings help reduce heat absorption.
Tank Bottom Protection: Preventing Soil Corrosion
The bottom of a storage tank is particularly vulnerable to moisture-driven corrosion due to its direct contact with the soil.
Best Practices for Tank Bottom Protection:
Install a waterproof barrier between the tank base and the soil.
Implement cathodic protection systems, which use sacrificial anodes or impressed current systems to prevent oxidation.
Design the foundation to allow drainage of groundwater and precipitation.
Always adhere to environmental protection and safety standards, such as those from the EPA or API 653.
Electrochemical Corrosion Control
Electrochemical (or cathodic) protection uses direct current to suppress the metal’s tendency to corrode. It’s especially effective in environments with saltwater exposure or high soil conductivity.
Important Note: Over-protection can lead to hydrogen evolution, which may damage coatings and compromise tank safety. Monitoring systems should be in place.
Internal Coating of Storage Tanks
Coating the inside of a storage tank is labor-intensive but essential for protecting the tank from stored chemicals and water.
Internal Coating Process:
Surface Prep
Interior walls are cleaned of residues and dried thoroughly.
Application of Primer
A corrosion-resistant primer is applied using airless spray equipment. Avoiding drips is critical.
Top Coats
2–4 layers of protective coating (epoxy, polyurethane, or lacquer-based) are applied and dried individually. Each layer enhances chemical resistance and structural durability.
Final Thoughts & Recommendations
Effective corrosion protection is a combination of proper material selection, regular inspection, and the right application of protective systems. Whether dealing with atmospheric exposure or soil-based corrosion, each layer of protection—from primers to cathodic systems—plays a vital role.