Since the adoption of ultralow Sulphur diesel back in 2006, authorities such as the U.S.  Environmental Protection Agency (EPA) have documented the increased risk of severe and rapid corrosion of fuel storage tanks. 

What causes this corrosion?

The change in diesel fuel specifications with the allowance of fatty acid methyl esters (FAME), commonly known as biodiesel, combined with the reduction of Sulphur, make the fuel more hygroscopic and, therefore, more susceptible to microbial contamination. There is always some level of water present in the fuel that enters through condensation, rainwater penetration, or adsorption from the air. The combination of nutrients in the water and the carbon in the fuel create a thriving ecosystem for microbes to grow. The speed at which they grow will depend on environmental factors, such as temperature and humidity, but as communities of these microbes breed, they create biomass and biofilms that can block filters; foul equipment; corrode metals; and, ultimately, cause catastrophic engine failure. The hygroscopic nature of biodiesel also means greater potential for the presence of available water molecules to develop and grow microbes. Microbial contamination will increase the risk of injector damage and filter blocking.

Why is this an issue for data centers?

The challenge for data centers is that backup generators may often lie idle for long periods. During this time, with the biodiesel-blended fuel resting in the tank, the microbes have greater opportunity to multiply and form large communities, creating biofilms that will cause fuel system issues. With the use of biodiesel-blended fuel, the potential risk of water content is higher, meaning a better environment for microbes to reproduce is created.

Protecting backup gensets

Modern backup generators are high-pressure common rail (HPCR) models, and higher PSIs mean greater risks of damage or failure. Emulsified water in the fuel enables microbes to multiply, which can create acidic compounds that can cause pitting and corrosion. Alongside the risk of part failures, pitting within the injector system can also cause the engine to become over-fuelled, resulting in temperature rises, increased emissions, and higher fuel consumption. Therefore, minimizing the water content within the fuel is a priority. Filters designed to the latest SAE J1488 Recommended Practice help remove emulsified water from the fuel, which should be kept below 200 parts per million (ppm) of total water content (the usual OEM warranty limit). The fuel should be filtered three times a week, with the complete volume of fuel filtered within an eight-hour period.

Maintenance programs should also check how long fuel has been stored in the generator tanks. Biodiesel blends typically have less shelf life than non-biodiesel diesel fuel, such as ultralow sulphur diesel (ULSD), and are therefore more susceptible to oxidation. Oxidation products combined with higher water content containing fuel will contribute to fuel degradation with greater the risk of microbial contamination.

For these reasons, data centers should implement a fuel testing and tank inspections program to ensure costly failures are avoided. 

Regular visual tank inspections can reveal signs of excessive water bottoms, which can cause tank corrosion. Presence of tank bottom contaminants in the form of dark, slimy matter is indicative of fuel degradation and, most likely, microbial contamination. By taking regular fuel samples from the bottom of various storage tanks (main storage tanks, belly tanks, and day tanks) will provide a qualitative assessment of the fuel. Fuel should be clear and bright at room temperature and should not display persistent haziness nor sediments and/or microbial contamination. If tests show evidence of fuel degradation and microbial contamination, the fuel should be filtered and/or replaced, and the tanks should be cleaned. 

Filtration systems are recommended to reduce particulate or other forms of foreign material contamination. They should be designed with the ability to sample the product both pre- and post-filtration.

Traditionally, storage tank fuel samples are sent to a laboratory for testing. However, regarding microbial contamination, this creates issues, as the community of microbes may change during transit if the sample is not stored correctly. It also means a delay in test results. 

The Standard Guide for Microbial Contamination in Fuels and Fuel Systems, ASTM D6469 – 14, states in Section 8.5 that: “Samples for Microbiological testing should be kept on ice for transport to the laboratory. Tests should be performed within 4 h and no later than 24 h after sampling. Samples stored at higher temperatures, or for longer times, can show the presence of microbial contamination that does not represent actual fuel system conditions.” 

Overall, it makes more sense to carry out testing on-site to avoid these issues altogether. 

Fuel testing carried out at the tank provides quicker and more reliable results. This takes just a matter of minutes without the need for specialist training or skills. On-site testing kits can save thousands in repair costs, protect mainframes from damage due to power outage, and provide data center customers with greater security. 

While the goal is to prevent loss of service, data centers should also avoid unnecessary maintenance costs. Tank cleaning, replacing fuel, and installing higher efficiency fuel polishing systems will help to prevent failures, but they add considerable cost to operations. While there are recommendations about how often such operations should be carried out, different environments mean each site will have different maintenance and testing requirements. Testing fuel at the tank provides a route to predictive maintenance schedules. Over time, results can be recorded to show trends of microbial growth and provide better understanding of maintenance requirements. Tank testing regimes can be adjusted accordingly for optimum frequency.


Backup power is a critical part of data center infrastructure. A genset failure could mean damage to mainframes and other assets, loss of data, and damage to a brand’s reputation. Good fuel management should be an integral part of maintenance operations with visual and at-the-tank inspections at the heart of the regime to avoid corrosion, damage, or blockage of fuel systems and engine failure. Biodiesels are now commonplace and are a good move to help reduce environmental impact, but the change in chemical composition of these fuels should not be ignored, and testing regimes should be adapted accordingly to allow for their increased affinity for water and the more attractive environment they provide for microbes to multiply.