ASTM D6469 standard guide for microbial contamination in fuels and fuel systems
4. Summary
4.1 Microbes may be introduced into fuels as products cool in refinery tanks. Bacteria and fungi are carried along with dust particles and water droplets through tank vents. In seawater ballasted tanks, microbes are transported with the ballast. Vessel compartments ballasted with fresh, brackish, or seawater, all of which may contain substantial numbers of microbes, may easily become contaminated with the microbes transported with the ballast water. See Section 6 for more a detailed discussion.
4.2 After arriving in fuel tanks, microbes may either stick to overhead surfaces or settle through the product. Some microbes will adhere to tank walls, whereas others will settle to the fuel/water interface. Most growth and activity takes place where fuel and water meet. The tank bottom fuel/water interface is the most obvious fuel/water boundary. However, there is also a considerable area of fuel/water interface on the interior surface of tank-shells. Typically, fuel and system deterioration is caused by the net activity of complex microbial communities living within slimy layers called biofilms. Biofilms may be found on tank roofs, shells, at the fuel/water interface, and within bottom sludge/sediment. Section 7 provides greater detail.
4.3 Obtaining representative samples may be challenging. For best results, samples should be collected from the interface zones, especially the fuel/water interface, described in 4.2. Refer to Section 8 for more details.
4.4 Sample analysis includes gross observations as well as a battery of physical, chemical, and microbiological tests. Because biodeterioration shares symptoms with other fuel and fuel-system degradation processes, it is critical to subject samples to a sufficient range of appropriate tests to permit accurate root-cause diagnosis. Section 9 provides more information on examining and testing samples.
4.5 Microbial contamination control requires a well designed strategy that considers system design, sampling and analysis, and preventive and remedial treatment. See Section 11 for details.
4.5.1 Good system design minimizes contaminant entry and provides for adequate sampling, water removal, and periodic cleaning and inspection.
4.5.2 Effective monitoring programs cost-effectively balance biodeterioration risks with sampling and analytical costs.
4.5.3 Remedial efforts may include fuel filtration, reconditioning, disposal, biocide treatment, or tank/system cleaning, or combination thereof. Health, safety, and environmental considerations are critical to proper tank remediation.
5. Significance and Use
5.1 This guide provides information addressing the conditions that lead to fuel microbial contamination and biodegradation and the general characteristics of and strategies for controlling microbial contamination. It compliments and amplifies information provided in Practice D4418 on handling gas-turbine fuels. More detailed information may be found in the IP Guidelines.
5.2 This guide focuses on microbial contamination in refined petroleum products and product handling systems. Uncontrolled microbial contamination in fuels and fuel systems remains a largely unrecognized but costly problem at all stages of the petroleum industry from crude oil production through fleet operations and consumer use. This guide introduces the fundamental concepts of fuel microbiology and biodeterioration control.
5.3 This guide provides personnel who are responsible for fuel and fuel system stewardship with the background necessary to make informed decisions regarding the possible economic or safety, or both, impact of microbial contamination in their products or systems.
