Rampant Diesel Corrosion in Underground Storage Tanks Containing Ultra-low Sulfur Diesel
Posted / Last update: 20-03-2017
When the United States Environmental Protection Agency (EPA) recently revealed the results of its study on the increasing presence of substantial corrosion in diesel fuel tanks throughout the U.S., it proved that the problem is much larger than anyone realized.
The facts are astonishing:
- 83% of the diesel tank systems exhibited moderate-to-severe corrosion.
- 75% of the owner/operators of those diesel tanks had no idea it was happening.
- The corrosion is developing in both steel and fiberglass tank systems.
Even more staggering is the severity of the corrosion.
I have been an engineer in the petroleum industry for my entire career, first with Exxon and for the last 23 years, with Tanknology. I have never in my life seen corrosion of this magnitude in a fueling system. The fact it was found in moderate-to-severe states in 83 percent of the systems points to a major industry problem.
Tanknology partnered with Battelle and performed all the fieldwork for this EPA study, which the agency termed the “largest field research of this issue to date.” Our fieldwork consisted of inspecting and sampling each of the 42 tanks in the survey. The sites were from all over the country, covering widespread geography.
Our work consisted of collecting fuel, water, and vapor samples, and inspecting fuel filters and the tank system access points for signs of corrosion. We also used our TankCam® remote internal video system to record the conditions inside the tanks. The images you see here are representative of the extreme conditions we discovered.
In this article I’ll address a little more about what we found, why it might be happening, and what an owner/operator can do to mitigate the potential for severe corrosion degradation of their diesel system.
During our fieldwork for this study last year, as well as subsequent studies performed for our clients, we have observed and documented what I consider to be unique, rapidly accelerated corrosion on the metal components of USTs storing diesel. Virtually all on-road diesel for sale today in the U.S. is Ultra Low Sulfur Diesel, or ULSD, which has been in use since 2006.
Unlike the mild orange-colored oxidation that would be typical for corrosion in this environment, we have seen large tubercles and nodules that can vary in color from yellow to orange to reddish brown and even black. The metal components in the vapor space of both steel and fiberglass tanks, including bungs, risers, caps, plugs, STP shafts, ball float assemblies, and flapper valves have all exhibited this unusual form of aggressive corrosion.
It has not been uncommon to find a severely corroded ball float assembly or bungs completely covered in tubercles, some of which can be up to an inch long. On one occasion, the top of a riser pipe broke completely in half as a result of the corrosion.
We have pulled completely corroded STP shafts from tanks, and in some cases are not even able to remove them due to the excessive corrosion in the riser. Layers of corrosion and tubercles have built up so severely that the inside of the riser is no longer wide enough for the STP motor to be removed or serviced.
We have seen the same problem with ATG probes; corrosion build up in the riser pipe can make it impossible to remove the ATG floats. Consequently, the probes and STP’s remain in the corrosive environment of the upper vapor space, either unable to be serviced, or in some cases replaced with smaller diameter ATG floats once the original floats are knocked off and left to fall down into the tank.
As the study concluded, 83 percent of the tanks exhibited moderate to severe corrosion. This large percentage of such a diverse experimental group indicates that this issue is not limited by geographic conditions. It can, and is, happening everywhere.
This corrosion can, and in some cases did, compromise the functionality and structural integrity of the UST systems, leaving even the most responsible of UST owners unaware of the problem and potentially exposed to significant environmental impact.
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