Scope of the Literature Review

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The American Petroleum Institute (API) published in 2002 an Executive Summary and Literature Review titled Impact of Gasoline Blended with Ethanol on the Long-Term Structural Integrity of Liquid Petroleum Storage Systems and Components. This document consolidates the available scientific and engineering data regarding the interaction of ethanol‑gasoline blends (typically E5 to E85) with the materials commonly used in underground storage tanks (USTs), piping, dispensers, and ancillary equipment.

Although not a consensus standard or a recommended practice, the review provides essential background for operators, regulators, and engineers who must assess the compatibility of existing storage infrastructure with oxygenated fuels. This article distills the key findings of the API review and translates them into actionable technical considerations.

Scope of the Literature Review

The API Executive Summary was commissioned in response to the growing use of ethanol as a gasoline oxygenate after the phase‑out of methyl tert‑butyl ether (MTBE). The review addresses the following aspects:

• Metallic corrosion – including general, pitting, galvanic, and stress corrosion cracking (SCC) of carbon steel, stainless steel, and aluminum alloys.
• Non‑metallic swelling, softening, and degradation – elastomers (gaskets, O‑rings, hoses) and thermoplastics (pipe liners, tank sumps).
• Fuel properties alteration – changes in electrical conductivity, water carrying capacity, and vapor pressure due to ethanol.

The literature survey covered studies from the 1970s through 2001, including work by ASTM, EPA, and independent research groups. The scope explicitly excludes surface storage tanks, but the material compatibility data are often transferable.

Technical Findings on Material Compatibility

The review identifies three major risk areas when switching from conventional gasoline to ethanol‑blended gasoline (E‑gasoline).

1. Corrosion of Metallic Components

Ethanol can increase the corrosion rate of carbon steel in several ways:

• Water pickup: Ethanol is hygroscopic; water content above ~0.3 % begins to form a separate phase that accelerates galvanic corrosion and microbiologically influenced corrosion (MIC).
• Acidic by‑products: Oxidation of ethanol in the fuel phase produces acetic acid, which lowers pH and promotes pitting.
• Stress corrosion cracking (SCC): Carbon steel in fuel‑grade ethanol (FGE) with oxygen and trace chlorides has been shown to crack under tensile stress. The review notes that SCC thresholds are lower at higher ethanol concentrations.

2. Degradation of Non‑Metallic Materials

Elastomers and thermoplastics can swell, harden, or crack when exposed to ethanol‑gasoline blends. The review groups materials by their volume swell percentage:

• Nitrile rubber (NBR): Volume swell increases from ~5 % in gasoline to 15–25 % in E10, causing extrusion and seal failure.
• Fluoroelastomers (FKM, Viton^®): Limited swell (2–5 %) in E10; acceptable for most applications, though some compounds degrade in high‑ethanol blends.
• Polyethylene and polypropylene: Generally resistant, but stress cracking can occur if the material is not properly stress‑relieved.
• Polyurethane: Not recommended for ethanol service due to rapid hydrolysis and loss of mechanical properties.

3. Changes in Fuel Properties

The review also highlights how ethanol addition alters gasoline characteristics relevant to storage system operation:

• Electrical conductivity increases, raising the risk of static discharge during fueling if equipment is not properly bonded and grounded.
• Reid Vapor Pressure (RVP) increases by 1–2 psi for low‑level blends, affecting vapor recovery system performance.
• Water solubility increases dramatically; phase separation can occur at water contents as low as 0.5 % for E10, leading to tank bottom water accumulation.

Implementation Recommendations

Based on the literature review, the API Executive Summary does not prescribe mitigation actions but implies several best practices for operators who introduce ethanol‑gasoline blends:

• Material verification: Confirm that all wetted components – tank internal lining, drop tube, sump liners, gaskets, hoses, and dispenser seals – are rated for the maximum ethanol concentration expected.
• Water management: Increase frequency of water detection and removal; install electronic tank gauges with water sensing; empty loose water before the fuel becomes saturated.
• Corrosion monitoring: Implement a periodic internal inspection program (e.g., API 653 for aboveground, but adapt for USTs) to check for pits, cracks, and coating disbondment.
• Electrical bonding: Verify that all metallic components are bonded and that conductive hoses are used to dissipate static charge.

Compliance Notes

While the API 2002 literature review is not a regulatory document, it informs compliance with several U.S. and international regulations:

• EPA Underground Storage Tank regulations (40 CFR 280): Operators must ensure that UST systems are compatible with the fuel stored. The API review provides evidence that many older systems designed for conventional gasoline are not compatible with ethanol blends without retrofitting.
• UL listing requirements: UL 971 (piping), UL 58 (tanks), and UL 2245 (submersible pumps) now include ethanol compatibility tests. The review data support the parameter changes adopted in later editions of these standards.
• International codes (e.g., EN 13160, PEI RP100): European and Canadian codes reference the same body of literature regarding ethanol impacts. The API review is often cited in guidance documents for countries that have introduced E5/E10 mandates.

Regulators and owners should be aware that the review’s conclusions – though several decades old – remain valid for moderate ethanol blends (E10–E15). For higher blends (E20–E85) or anhydrous ethanol, more recent data from ASTM D4806 and the Coordinating Research Council (CRC) projects should be used.

Note: This article reflects the content of the API Executive Summary and Literature Review published in 2002. Readers are encouraged to consult the original document for complete references and the most up‑to‑date technical data.

Last reviewed: 2026