Tank Floor & Tank Bottom Corrosion Problems - Microbially Influenced Corrosion

Since the introduction of steel tanks in the late 19th century corrosion has been an archenemy. Each year thousands of aboveground and underground steel tanks develop corrosion permeations that allow their contained liquids to escape into the environment. Depending on the product and where it ends up, the outcome can have disastrous consequences. The vast majority of these tank problems develop at or near the bottom of these tanks.

(PRWEB) September 20, 2004 -- We caught up with Jeff Colner of Armor Shield Tank Lining & Repair, a national network of specially trained tank repair, lining and coating professionals. The network, around since the late 1960s, has lined thousands of fuel, water and chemical storage tanks for such companies as ExxonMobil, Chevron, Shell and Texaco as well as hundreds of municipalities, water districts and private companies.

Jeff had been a good source of information in the past for such topics as compatibility of new gasoline blends with older tanks, and the plight of aged fuel oil storage tanks located under big buildings in our cities. When we spoke with him he had just returned from visiting a site in the southwest where one of Armor Shields crews were lining the bottom of three large aboveground tanks used to store fuel oil for a power plant. The first question he was asked was Why do fuel oil and gasoline storage tanks corrode mostly on the bottom?"

His initial answer was quick and to the point, Because thats where the water is". Then he quickly added, And in many cases, also the sludge where water and bugs get together to wreak havoc on the steel." When we asked him to elaborate, he continued, I dont want to over simplify the dynamics of what goes on inside a steel petroleum storage tank, but one of the basic enemies of the steel materials used to construct atmospheric storage tanks (aboveground) and underground storage tanks is water. When water gets into a petroleum tank it eventually sinks to the bottom because its heavier than the stored product, and it stays there until its either purposely removed or gobbled up by some additive like isopropyl alcohol, pumped out with the petroleum product as it is dispensed or transferred, or leaked out through a corrosion permeation."

We asked him to go back to the bugs", and he said, Over the last decade or so the phenomenon of MIC, or microbially influenced corrosion has entered the limelight for popular reasons why steel tanks corrode and leak. These bacterium mix in with water at tank bottoms and create sludge, acids and a whole bunch of nasty stuff that leads to corrosion. These critters actual feed on the hydrocarbons in the fuel product. When we enter a steel petroleum storage tank, we often can see a built up area of sludge at the bottom. In many cases, after the tank is cleaned and the sludge is removed, we can see a defined area of corrosion exactly where the sludge had been. You dont have to be a rocket scientist to know somethings happening there."

We were curious about how water and bugs would get into the tanks to begin with. Jeff told us, Water may be delivered mixed with product coming into the tank, it also may be leaked in through piping attached to the tank, or dripped through a poorly sealed fill cap. The bugs can get in hitching a ride in water, fuel product or they come in airborne through vents. Anyway they get there, once they make themselves at home with the water and hydrocarbons, they can double in number every twenty minutes."

We next asked why, after so many decades of gasoline and oil storage in steel tanks, is MIC suddenly a problem. Well, MIC was first identified in 1891, over 100 years ago, so its been around for a long time. I believe that changes in the formulation of fuel products and even economic factors have contributed to its current rise", he answered, and continued, When they removed lead from gasoline products years back, to help clean the air, these microbes were given a free ride because the lead in the gas had been a natural biocide. For years the lead had helped keep the microbes in check. Then the addition of oxygenates to help keep the air clean was also a source of food for them. This coupled with the reduction of aromatics, another bug inhibitor, from both gasoline and diesel fuels, gave them another leg up."

When we asked what were the economic factors he had referred to, he responded, When environmental regulations tightened up, it hit storage tank owners in the wallet in many ways. One of which was that the fuel oil or gasoline distributor or gas station owner could no longer just pump the water out from the bottom of their tanks and dump it. The water coming out of the tanks was now hazardous waste" and it cost serious money to be manifested and transported away for proper disposal. This led to water being left to accumulate for longer periods on the tank bottoms".

As I said earlier", Jeff added, I dont want to over simplify the problems found in these steel tanks, because there are many other influences that can cause corrosion problems. Some of these are electrolysis from dissimilar metals used in a tanks construction, welding materials used to build some tanks, backfill materials the tanks are sitting in or on, as well as stray currents and other close steel structures causing cathodic and anodic influences on a tanks exterior shell or soil side".

It was near the end of the interview and we wanted Jeff to tell us what the answer was to fixing the problem that now existed in tanks. He commented, Well, we can treat fuel tanks with special biocides that kill the existing organisms, but the existing internal corrosion and corrosion pitting should be dealt with by having bottom lining systems applied, In cases where there is critical steel loss, tank bottom laminated lining systems can be used for additional floor strength. Both will help protect the tanks steel from further corrosion".

We ended by asking if the biocides he referred to would stop the corrosion that had begun as well as do in the microbes. He thought for a moment and said, That would be some biocide. But no, if the corrosion cycle has begun, it's going to continue on its own until stopped by direct intervention."

To get more information on Armor Shield Tank services log on to www.armorshieldlining.com, or call their customer service hotline toll-free 1-888-839-0373. Email to info@armorshieldlining.com.

Interview conducted by C.R. Manning & Lynn Cooper

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