API RP 651-2014 PDF

Full title and description

API RP 651-2014 — Cathodic Protection of Aboveground Petroleum Storage Tanks. This recommended practice provides procedures and practices for achieving effective corrosion control of carbon‑steel tank bottoms in aboveground petroleum storage tanks using cathodic protection methods (galvanic and impressed‑current) and associated design, installation, testing and maintenance practices.

Abstract

API RP 651-2014 describes how to determine the need for cathodic protection for aboveground tank bottoms, acceptable protection criteria, design approaches (distributed buried anodes, perimeter anodes, sacrificial anodes, impressed current systems), installation practices, methods to measure tank‑to‑soil potentials, interference issues, and operation & maintenance practices to sustain protection over the life of the tank. The RP is intended to reduce tank‑bottom corrosion risks and guide owners and engineers in implementing corrosion control programs.

General information

• Status: Superseded (replaced by API RP 651:2024).
• Publication date: May 9, 2014 (2014 edition).
• Publisher: American Petroleum Institute (API).
• ICS / categories: Petroleum and storage tanks (ICS 75.080); Corrosion / metallurgy (ICS group 77 — corrosion/metal products).
• Edition / version: API RP 651 — 2014 (this record represents the 2014 RP edition).
• Number of pages: 56 pages (2014 edition).

Scope

Provides guidance for assessing the need for cathodic protection of aboveground carbon‑steel tank bottoms in contact with soil or tank pad material, selecting appropriate cathodic protection systems, sizing and locating anodes and rectifiers, setting protection criteria (potentials and currents), installing reference electrodes and test stations, managing stray and interference currents, and establishing inspection, monitoring and maintenance procedures for long‑term protection of tank bottoms. It is intended for new and existing atmospheric aboveground tanks and addresses special considerations such as release prevention barriers and tank bottom repairs.

Key topics and requirements

• Assessment of soil and pad corrosivity and methods to determine the need for cathodic protection (soil resistivity, contamination, oxygen cells).
• Comparison of cathodic protection methods: distributed buried anodes, perimeter anodes, galvanic (sacrificial) systems, and impressed‑current systems.
• Design guidance: anode selection and placement, backfill, anode life estimation, rectifier sizing, and conductor routing.
• Protection criteria and measurement: tank‑to‑soil potential measurement techniques, instant‑off testing, IR drop considerations, and target polarizations.
• Installation and commissioning practices: reference electrode installation, test station placement, wiring and grounding, and avoiding pad undermining during directional boring.
• Interference and stray current management: identification, mitigation, and coordination when external sources exist.
• Operation, monitoring and maintenance: periodic surveys, rectifier maintenance, record keeping, and actions after tank repairs or bottom replacements.

Typical use and users

Used by tank owners/operators, corrosion engineers, cathodic protection designers and contractors, facilities engineers, inspection and maintenance teams, and regulators. Typical applications include new tank design, evaluation of existing tanks for corrosion risk, retrofitting cathodic protection systems, commissioning and routine monitoring of protection effectiveness.

Related standards

Commonly used with other API and industry documents such as API 650 (welded tanks for oil storage), API 652 (linings of aboveground storage tank bottoms), API 653 (tank inspection, repair and alteration), NACE/AMPP standards and test methods related to cathodic protection and corrosion measurement, UL 142, and national/regulatory guidance for fuel storage facilities.

Keywords

cathodic protection; aboveground storage tanks; tank bottom corrosion; impressed current; galvanic anode; reference electrode; tank‑to‑soil potential; rectifier; interference currents; tank pad; API RP 651.

FAQ

Q: What is this standard?

A: API RP 651-2014 is an American Petroleum Institute recommended practice that provides guidance on cathodic protection methods and practices for carbon‑steel aboveground petroleum storage tank bottoms.

Q: What does it cover?

A: It covers how to determine the need for cathodic protection, suitable protection techniques (galvanic and impressed‑current), design and installation details, measurement and acceptance criteria, interference issues, and operation and maintenance of cathodic protection systems for aboveground tank bottoms.

Q: Who typically uses it?

A: Corrosion and mechanical engineers, tank owners/operators, cathodic protection contractors, inspection and maintenance personnel, and regulatory compliance staff involved with aboveground tank integrity.

Q: Is it current or superseded?

A: The 2014 edition is superseded; API RP 651:2024 is the newer edition that replaces the 2014 RP. Users implementing or referencing cathodic protection requirements should consult the 2024 edition for the latest requirements.

Q: Is it part of a series?

A: Yes — API RP 651 is part of the API family of tank and corrosion documents and is commonly used alongside API 650, API 652, API 653 and related NACE/AMPP standards addressing linings, inspection, and corrosion control.

Q: What are the key keywords?

A: cathodic protection, tank bottom, impressed current, sacrificial anode, reference electrode, tank‑to‑soil potential, interference, rectifier, operation and maintenance.