Steel Tanks and Fuel Compatibility

The National Research Energy Laboratory, NREL, contacted STI staff recently about studies pertaining to another developing fuel additive to gasoline, isobutanol, and the current downstream fueling infrastructure.  Based on what I have read, isobutanol has many parallels to ethanol and is acceptable as an alternative gasoline blend additive in that it increases oxygenates to burn the fuel with few unwanted emissions, while also increasing octane.

Automobile manufacturers are interested in higher octane fuels due to increased efficiency as it burns in motors.  Higher engine efficiency can result in less energy loss as the vehicle consumes the fuel, resulting in higher mileage.  The United States government has set some very hefty goals for vehicle mileage in the years ahead, and auto manufacturers and the US Department of Energy are researching the additives that will be the best fit with gasoline to increase octane, mileage, and its feasibility.

Of course, new fuel additives also raise other questions and issues.  Is the additive compatible with today’s fuel infrastructure?  Is it easily transported?  Will the fuel create new issues downstream at the petroleum marketers’ dispensing systems or with emissions from vehicles?  For example, the downstream market segment has experienced non-anticipated consequences from sulfur removal from diesel in storage.  Refineries produce ULSD to comply with EPA air quality requirements and ASTM fuel quality requirements, yet as the fuel gets transported and stored in other locations, additives are used, water can get absorbed, and microbial activity can occur.  Fugitive emissions from equipment operating in sumps installed atop UST’s with ethanol blended gasoline coupled with condensation, has also created random non-anticipated consequences. 

Engines today require cleaner fuels, less and smaller particulates can be present in fuel.  The tolerance for water in today’s fuel storage has become a more significant issue.  Hence, the insides of tanks have now become a common focus point for petroleum marketers and their service providers.  Maintenance and monitoring and removal of water is paramount to today’s motor vehicle fuel system and back-up power systems. A whole new industry of service providers  that did not exist 10 or 15 years ago have formed – fuel polishers, tank cleaners, biocide treatment providers, and internal inspection contractors.


The steel tank industry tracks performance via third party warranty and environmental impairment insurance required of its technology licensees in the United States. Today’s USLD systems experience random, surface corrosion on internal tank metallic components, such as pumps, fill lines, ball vent valves, etc. It sometimes is seen on the tank ullage space itself, even on metal flanges and manways in non-metallic tanks. Yet claim history of underground steel tank manufacturers has not shown an increase in steel tank failures from this phenomenon. Paid warranty claim rate was 0.044% over STICO Mutual’s first 20 years of providing fabricators (building to STI tank specifications) with warranty insurance or 44 tanks per 100,000 tank population.

States, on the other hand, are also worried about tank performance, but more so with aging tanks.  A recent study by eight states participating in an ASTSWMO study, indicated that over 50% of its UST’s were over 20 years old, and of single wall construction.

The Arizona Department of Environmental Quality has had recent concerns of aging underground tank performance.  They hired Tanknology to use their camera technology to investigate condition of 79 underground storage tanks, 41 diesel and 38 gasoline, located at schools in 21 cities and 7 counties.

Grading the 66 FRP tanks and 13 steel tanks, based on these videos, involved using an A through E grade, similar to grading scales often used in our education system. 

Scores were given based on the fuel stored, and a separate set of scores based on the tank material.

Since the turn of the century, the biodiesel market has developed, and grown into a billion gallon industry.  Since ethanol has been in common use for over 30 years, and even goes back to the days of the Model A, biodiesel remains one of the most significant new additives.  Will isobutane become the next?  In 2008, STI hired Southwest Research Institute to perform a corrosion study on biodiesel, both with and without water, finding steel to be compatible.

Now isobutanol is coming into the marketplace as a fuel enhancement, or as an alternative to ethanol.  Oak Ridge Laboratories, to no surprise, found steel to be compatible with isobutanol.

The full ADEQ presentation from the STI/SPFA Annual Meeting can be found here.

Editors note: This article originally appeared in the May 2018 STI Tank Talk Newsletter. The original article can be found here.