Frederick J. Passman, Ph.D., Biodeterioration Control Associates, Inc.
My last article discussed the opportunity costs caused by dispenser flow-rate reduction. I’ll open today’s article with a few photos that I’ve selected from my collection of thousands of dirty, fuel-system photos.
Going clockwise from the top left: slime-coated fuel dispenser filter next to its corroded canister; corrosion covered submerged turbine pump (STP) riser adapter; badly degraded, dispenser flow-control valve diaphragm; and automatic tank gauge (ATG) water-float, covered with microbial slime. Each of the first three photos illustrate damage that affects fuel dispensing. The ATG float photo shows how water accumulating in tank bottoms can go undetected. More on why below.
Most operators recognize reduced flow when dispensers are delivering 20% of their designed flow, but commonly make three mistakes. The first mistake is to ignore reduced flow when you are still getting 60% or 80% (6 – 8 gpm from retail dispensers, 24 – 32 gpm from commercial dispensers) flow. I hope that my first article in this series convinced you that even 20% flow-rate reduction can be expensive in terms of opportunity cost.
The second mistake is to assume that filter plugging is the only cause of slow-flow. Sure, most often, filter plugging does cause flow rate to fall. However, there are at least three other fuel system sites where bugs can block flow: pre-filter screen, leak detector screen and STP inlet screen. Too often, operators never check flow-rates immediately after replacing dispenser filters, and therefore fail to notice that changing the filter did not fix the flow-rate problem.
The third mistake is to assume that slow flow is an early symptom of fuel system contamination. In reality, slow flow is similar to a heart attack. Just as heart attacks are typically late symptoms of chronic heart disease, premature slow flow is a late symptom of system contamination.
Fouling can affect ATG readings within a month after they have been cleaned and recalibrated. Microbes (bugs) produce a slime layer that helps them to control their living conditions in otherwise hostile environments. In addition to an active bug community, this slime layer (biofilm—can be home to more than 100 different types of bugs), traps gas (air) bubbles, dispersed water, rust particles and lots of other stuff that helps the biofilm bugs thrive.
When an ATG’s water float slime has lots of air bubbles, the air can lift the float off the tank bottom and give a false indication of water that is not actually there. More often, trapped rust particles weigh the float down so that it becomes heavier than water and fails to detect bottom water that is present.
Both filter plugging and biofilm accumulation on ATG water-floats are examples of fouling. The problems reflect just the physical presence of the bugs. As I’ll discuss in a future article, both symptoms are relatively easy to prevent through condition monitoring. However, microbiologically influenced corrosion (MIC)—material damage that bugs cause directly or indirectly—is more difficult to monitor.
Recall that during their 2014 ultra-low-sulphur diesel (ULSD) system survey, the Environmental Protection Agency (EPA) found that 80% of operators, whose fuel systems have moderate to heavy corrosion, were unaware of the damage. Bugs are not responsible for all fuel system corrosion. Moreover, MIC shares symptoms with other corrosion processes.
Finally, there’s a reason that the “I” in MIC stands for influenced. Most often, bugs contribute to corrosion indirectly. Slime on system surfaces causes electrical current to flow between covered surfaces and uncovered surfaces. This flow causes Galvanic corrosion. Active microbes produce a variety of acidic molecules. Acids are corrosive and MIC can drill holes in tank walls, or destroy metallic pumps and lines, in a matter of months. Fortunately, MIC-caused tank failures have become increasingly rare since the late 1990s, after the leaking underground storage tank (UST) regulations went into effect. Still, component damage causes system down time and considerable corrective maintenance costs.
Bugs can attack the elastomer directly or chemicals that the bugs excrete as wastes can degrade the elastomer. Either way, the valve fails; resulting in dispenser failure (leakage, degraded flow-control and, potentially, fuel spillage).
Coated tanks can be attacked when water and bugs find their way through invisibly narrow openings (“holidays“) in the coating, and grow between the coating and tank shell. When this happens, the coating peels away from the tank wall in sheets.
Microbes can damage fleet and retail systems in a variety of ways. Too often we remain unaware of the damage until it disrupts our operations. In my next article, I’ll begin to discuss how to do effective, predictive maintenance-based condition monitoring inexpensively and without much technical know-how.
Fred Passman is a Ph.D. Microbiologist with more than 40 years’ experience studying damage that microbes cause to industrial systems. Fred is Founder and President of Biodeterioration Control Associates, Inc. (www.Biodeterioration-Control.com) and can be reached at FredP@Biodeterioration-Control.com.