The highest corrosion risk is for emergency backup generators, and their storage tanks. The fuel in emergency generator storage tanks is turned over very slowly; generators are typically tested on a monthly schedule for an hour or two. At this rate of fuel consumption, the fuel is effectively never replaced, just topped off a few times a year. While NFPA 110 recommends the complete replacement the fuel on a regular basis, in reality this is rarely followed. Water is continually absorbed and bonded to the ULSD biodiesel blend, and microbial growth continues unabated, acidifying the fuel, and corroding the tank and generator components.
The risk extends from the tank to the emergency backup generator itself, acidified fuel corrodes the micron size injector tips, greatly increasing the risk of generator failure during an emergency. In addition, excess water in the fuel flashes into steam at the injector tips, thereby increasing the damage to the injectors. During a real emergency, generators run 7/24, placing great stress on weakened injectors. A single injector failure will shut the generator down.
Biofilms provide a new threat to emergency generators. An engineer wrote this about the biofilm he found: “WOW. Never saw anything like this, check out the last picture. This was the consistency of boiled pig skin. It was lining the bottom of the tank. Super bugs.”
Biofilm can cause emergency generator failures by:
1 – corrosion of injectors and tanks components
2 – biofilm separates when fuel added, plug fuel pipes
3 – biofilm disintegrates, plugs filters
Most generator manufacturers have a 200 ppm warranty water limit, and have tightened up biodiesel warranty requirements. The amount of bonded water that is delivered by diesel delivery trucks to emergency generator storage tanks can be well above 200 ppm, voiding the generator warranty from the first day of operations.
A key point is that in order to identify the presence of bonded water, a Karl Fisher titration (ASTM D6304) must be used. Traditional test methods will not pick up the presence of bonded water. For example, the visual “clear and bright” test will continue to be “clear and bright” with substantial bonded water, and no visible free water present. Water paste will not indicate bonded water.