Corrosion is the primary threat to Above Ground Storage Tank (AST) integrity, accounting for over 60% of tank failures globally. Understanding corrosion mechanisms is essential for implementing effective mitigation strategies that extend tank service life and prevent catastrophic failures.

Common Corrosion Types

• Uniform Corrosion: General surface degradation across tank surfaces
• Pitting Corrosion: Localized attack creating deep cavities
• Crevice Corrosion: Occurs in confined spaces and gaps
• Galvanic Corrosion: Results from dissimilar metal contact
• Microbiologically Influenced Corrosion (MIC): Bacterial activity accelerates degradation

Impressed Current Systems

Impressed current cathodic protection (ICCP) uses an external power source to provide corrosion protection. This system is ideal for large tanks and facilities with multiple structures requiring protection.

Key Components:

• DC power source (rectifier)
• Anode groundbed system
• Reference electrodes for monitoring
• Electrical connections and cabling

Sacrificial Anode Systems

Galvanic (sacrificial) anodes provide passive protection without external power. Magnesium, zinc, or aluminum anodes corrode preferentially, protecting the tank structure.

External Coating Systems

Epoxy Coatings: High-performance protection for shell exteriors, offering excellent chemical resistance and durability in harsh environments.

Polyurethane Topcoats: UV-resistant finish coatings that maintain color and gloss while providing weathering protection.

Zinc-Rich Primers: Sacrificial protection at the coating level, ideal for areas prone to mechanical damage.

Internal Coating Systems

Internal coatings must withstand product contact, temperature variations, and chemical exposure:

• Phenolic epoxy for crude oil and refined products
• Novolac epoxy for high-temperature applications
• Glass flake epoxy for enhanced chemical resistance
• Polyurethane for potable water storage

Ultrasonic Thickness Monitoring

Permanent or semi-permanent ultrasonic sensors provide continuous thickness monitoring at critical locations, enabling real-time corrosion rate calculations and predictive maintenance.

Corrosion Coupons

Metal coupons installed in tanks provide direct measurement of corrosion rates under actual service conditions. Weight loss analysis reveals corrosion mechanisms and validates protection strategies.

Electrochemical Monitoring

Linear polarization resistance (LPR) and electrical resistance (ER) probes offer instantaneous corrosion rate measurements, allowing rapid response to changing conditions.

  Regular Inspections: Scheduled visual and instrumental examinations

  Coating Maintenance: Touch-up and repair of damaged coating areas

  Cathodic Protection Testing: Annual verification of protection levels

  Water Management: Removal of water bottoms to prevent MIC

  Biocide Treatment: Control of microbial growth in susceptible systems

A major refinery implemented a comprehensive corrosion mitigation program combining impressed current cathodic protection, high-performance coating systems, and continuous monitoring. Results after 5 years:

• 85% reduction in corrosion-related failures
• Extended inspection intervals from 5 to 10 years
• $2.3 million in avoided repair costs
• Zero environmental incidents related to corrosion