Cathodic Protection of Aboveground Petroleum Storage Tanks

API RP 651: Essential Guidance for Cathodic Protection of Aboveground Petroleum Storage Tanks

Ensuring the long-term integrity and safety of aboveground petroleum storage tanks is paramount in the oil and gas industry. Corrosion poses a significant threat, potentially leading to leaks, environmental damage, and costly downtime. API RP 651 provides industry-leading, proven practices for mitigating this risk through effective cathodic protection. This comprehensive standard is an essential resource for engineers and asset managers responsible for safeguarding these critical infrastructure assets.

What is API RP 651?

API Recommended Practice 651 (RP 651) is an authoritative document developed by the American Petroleum Institute. It offers detailed guidelines and proven methodologies for applying cathodic protection to the external surfaces of aboveground steel storage tanks. The primary purpose of RP 651 is to prevent or mitigate corrosion on the tank bottom and associated structures, thereby extending their service life and ensuring operational safety.

Scope & Purpose

This recommended practice governs the design, installation, and maintenance of cathodic protection systems specifically for the external surfaces of aboveground steel storage tanks containing petroleum products. It addresses various aspects, including determining the need for cathodic protection based on tank history and site conditions, selecting appropriate cathodic protection methods (galvanic and impressed current), and establishing criteria for effective protection. The standard focuses on preventing corrosion of the tank bottom and its immediate surroundings, and does not extend to internal corrosion control or other components of tank maintenance beyond cathodic protection.

Who Must Comply?

• • Primary audience: Corrosion Engineers, Asset Integrity Engineers, Maintenance Engineers, Storage Tank Inspectors, and Design Engineers.
• • Industries affected: Oil and Gas (upstream, midstream, and downstream), Petrochemical, Chemical Storage, and any facility storing petroleum products in aboveground tanks.
• • Compliance nature: While API RP 651 is a recommended practice, compliance is often mandated by regulatory bodies, industry insurance providers, and company-specific integrity management programs, making it de facto mandatory for responsible operators.
• • Enforcement: Compliance is typically verified through internal audits, third-party inspections, regulatory agency reviews, and insurance audits.

Key Requirements Overview

The standard requires a thorough assessment of tank conditions and environmental factors to determine the necessity and design of a cathodic protection system. Professionals must ensure that the chosen cathodic protection method—either galvanic anodes or impressed current systems—is appropriately designed to provide adequate current distribution and protection levels. Key provisions include the establishment and monitoring of specific protection criteria, such as voltage potential measurements, to confirm ongoing effectiveness. Furthermore, the standard emphasizes proper installation techniques and regular monitoring to maintain system performance and address any potential interference issues.

Related Standards & References

API RP 651 works in conjunction with other essential API standards. API 650 (Welded Tanks for Oil Storage) provides the foundational requirements for tank design and construction, while API 653 (Tank Inspection, Repair, Alteration, and Reconstruction) outlines inspection protocols that can inform the need for and effectiveness of cathodic protection systems. Together, these standards form a robust framework for managing the integrity of aboveground petroleum storage tanks.