ASTM D8506-23
(Guide)Standard Guide for Microbial Contamination and Biodeterioration in Turbine Oils and Turbine Oil Systems
Standard Guide for Microbial Contamination and Biodeterioration in Turbine Oils and Turbine Oil Systems
SIGNIFICANCE AND USE
5.1 This guide provides information addressing the conditions that lead to turbine oil microbial contamination and biodeterioration, the general characteristics of and strategies for controlling microbial contamination. It compliments and amplifies information provided in Practices D4378 and D6224 on condition monitoring of lubricating oils.
5.2 This guide focuses on microbial contamination in turbine oils and power generation turbine oil systems. Uncontrolled microbial contamination in turbine oils and lubrication systems remains a largely unrecognized but potentially costly problem in power generation systems.
5.2.1 Examples of turbine oil and system biodeterioration include, but are not limited to:
5.2.1.1 Filter plugging,
5.2.1.2 Oil line and orifice fouling,
5.2.1.3 Increased oil acidity,
5.2.1.4 Increased oil corrosivity,
5.2.1.5 Oil additive depletion,
5.2.1.6 Water emulsification,
5.2.1.7 Lubricity loss, and
5.2.1.8 Decreased oxidative stability and increased sludge generation.
5.3 This guide introduces the fundamental concepts of turbine oil microbiology and biodeterioration control.
5.4 This guide provides personnel who are responsible for turbine oil 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.
SCOPE
1.1 This guide provides personnel who have a limited microbiological background with an understanding of the symptoms, occurrence, and consequences of chronic microbial contamination. The guide also suggests means for detection and control of microbial contamination in turbine oils and turbine oil systems. This guide applies primarily to turbine lubricants (see Specifications D4293 and D4304) and turbine oil systems. However, the principles discussed herein also apply generally to lubricating oils with viscosities 2/s (for example, see Specification D6158).
1.2 This guide focuses on turbine system and turbine oil microbiology. Despite considerable differences in turbine systems (for example, gas and steam driven turbines; power generation and propulsion; etc.) as ecosystems for microbial communities – with the exception of temperature – these differences are largely irrelevant. Ambient temperatures are typically similar. Recirculating turbine oil temperatures are commonly >40 °C. However, generally speaking, all systems in which accumulations of free water can develop, share properties that are considered in this guide.
1.2.1 Steam turbines, and to a greater extent hydro turbines, are continuously exposed to water ingression. Diligence is needed to ensure seals and bearings are in good condition to prevent water ingression or conditions that are conducive to biodeterioration. However, due to the risk of the accumulation of condensation, all equipment can become susceptible when shut down for extended periods.
1.3 This guide complements Energy Institute’s Guidelines on detecting, controlling, and mitigating microbial growth in oils and fuels used at power generation facilities (2.2). The Energy Institute’s guidance document provides greater detail than the overview provided in this guide.
1.4 Microbial contamination in turbine oil systems shares common features with microbial contamination in fuel systems (See Guide D6469). However, there are also relevant differences. Although the chemistry of the fluids is different, this Guide draws heavily on D6469 but highlights unique aspects of turbine oil and turbine oil system biodeterioration and microbial contamination.
1.5 This guide is not a compilation of all of the concepts and terminology used by microbiologists. It provides basic explanations of microbial contamination and biodeterioration in turbine oils and turbine oil systems.
1.6 The values in SI units are to be regarded as the standard.
1.7 This standard does not purport to address all ...
General Information
- Status
- Published
- Publication Date
- 14-Jun-2023
- Technical Committee
- D02 - Petroleum Products, Liquid Fuels, and Lubricants
- Drafting Committee
- D02.C0.01 - Turbine Oil Monitoring, Problems and Systems
Relations
- Effective Date
- 01-Apr-2024
- Effective Date
- 01-Apr-2024
- Effective Date
- 01-Apr-2024
- Effective Date
- 01-Apr-2024
- Effective Date
- 01-Mar-2024
- Effective Date
- 01-Mar-2024
- Effective Date
- 01-Mar-2024
- Refers
ASTM D4175-23a - Standard Terminology Relating to Petroleum Products, Liquid Fuels, and Lubricants - Effective Date
- 15-Dec-2023
- Effective Date
- 01-Dec-2023
- Effective Date
- 01-Dec-2023
- Effective Date
- 01-Nov-2023
- Effective Date
- 01-Nov-2023
- Effective Date
- 01-Nov-2023
- Effective Date
- 01-Oct-2023
- Refers
ASTM D4175-23e1 - Standard Terminology Relating to Petroleum Products, Liquid Fuels, and Lubricants - Effective Date
- 01-Jul-2023
Overview
ASTM D8506-23: Standard Guide for Microbial Contamination and Biodeterioration in Turbine Oils and Turbine Oil Systems provides essential guidance for identifying, understanding, and managing the risks associated with microbial contamination in turbine oils. Developed by ASTM International, this standard supports maintenance and reliability professionals, engineers, and plant operators in power generation facilities by offering foundational knowledge on the symptoms, origins, and consequences of microbial growth and oil biodeterioration. The guide is especially valuable for those with limited microbiological expertise responsible for turbine oil system stewardship.
Key Topics
- Microbial Contamination in Turbine Oils: The guide explains how bacteria and fungi can enter and thrive in turbine oil systems, primarily due to the presence of water, nutrients, and favorable temperatures. Contaminants may be introduced via open reservoirs, venting systems, or during oil processing.
- Consequences of Biodeterioration: Uncontrolled microbial contamination can lead to costly and often underestimated issues, such as:
- Filter plugging, impacting oil flow and overall efficiency
- Oil line and orifice fouling, causing blockages
- Increased oil acidity and corrosivity, accelerating system wear
- Oil additive depletion, reducing lubricant protection
- Water emulsification, leading to decreased lubrication
- Loss of lubricity and oxidative stability, causing premature equipment failure
- Increased generation of sludge and deposits, complicating maintenance
- Detection and Monitoring: The guide offers strategies for recognizing microbial contamination, including recommended approaches to sampling, testing, and monitoring the overall health of turbine oils. It highlights the importance of sampling interface zones, such as the oil/water interface, where microbial activity is typically highest.
- Control and Mitigation Strategies: Practical advice on system design, routine monitoring, water management, and biocide treatments is provided to minimize contamination risks. The importance of preventive maintenance, regular cleaning, and effective system remediation is emphasized.
- Comparison with Related Systems: The guide notes similarities and differences between microbial contamination in turbine oil systems and fuel systems, drawing from both ASTM and Energy Institute practices.
Applications
- Power Generation Facilities: Especially relevant for gas, steam, and hydroelectric turbines where continuous water exposure and temperature fluctuations create environments conducive to microbial growth.
- Maintenance Planning: Helps reliability engineers and maintenance personnel develop targeted inspection, sampling, and intervention programs for turbine oil systems.
- Condition Monitoring Programs: Supports integration of microbial contamination checks with standard oil condition monitoring practices, enhancing early detection and preventing unexpected equipment failures.
- Troubleshooting and Failure Analysis: Aids in identifying the root causes of lubricant- and system-related problems, differentiating between biological and non-biological sources of oil degradation.
- Training and Decision-Making: Equips those with limited microbiological backgrounds with the knowledge needed to assess potential economic and safety implications of microbial contamination in lubricant systems.
Related Standards
- ASTM D4378 & D6224: Practices for monitoring lubricating oil condition in turbine systems, complementing the guidance provided by D8506.
- ASTM D6469: Guide for microbial contamination in fuels and fuel systems, referenced for techniques applicable to turbine oils.
- ASTM D4293 & D4304: Specifications for turbine lubricants addressed by this guide.
- Energy Institute Guidance (IP 613): Offers detailed refinery and power generation facility protocols for microbial detection and control.
- Relevant ISO Standards: ISO 3722, ISO 4406, ISO 4407, ISO 11500, and ISO 11171 cover fluid sample procedures, contamination codes, and particle counting needed for comprehensive oil system monitoring.
By incorporating the recommendations of ASTM D8506-23, power generation facilities and industrial plants can improve turbine oil reliability, manage contamination risks more effectively, and prevent unexpected downtime and maintenance costs associated with microbial biodeterioration.
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Frequently Asked Questions
ASTM D8506-23 is a guide published by ASTM International. Its full title is "Standard Guide for Microbial Contamination and Biodeterioration in Turbine Oils and Turbine Oil Systems". This standard covers: SIGNIFICANCE AND USE 5.1 This guide provides information addressing the conditions that lead to turbine oil microbial contamination and biodeterioration, the general characteristics of and strategies for controlling microbial contamination. It compliments and amplifies information provided in Practices D4378 and D6224 on condition monitoring of lubricating oils. 5.2 This guide focuses on microbial contamination in turbine oils and power generation turbine oil systems. Uncontrolled microbial contamination in turbine oils and lubrication systems remains a largely unrecognized but potentially costly problem in power generation systems. 5.2.1 Examples of turbine oil and system biodeterioration include, but are not limited to: 5.2.1.1 Filter plugging, 5.2.1.2 Oil line and orifice fouling, 5.2.1.3 Increased oil acidity, 5.2.1.4 Increased oil corrosivity, 5.2.1.5 Oil additive depletion, 5.2.1.6 Water emulsification, 5.2.1.7 Lubricity loss, and 5.2.1.8 Decreased oxidative stability and increased sludge generation. 5.3 This guide introduces the fundamental concepts of turbine oil microbiology and biodeterioration control. 5.4 This guide provides personnel who are responsible for turbine oil 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. SCOPE 1.1 This guide provides personnel who have a limited microbiological background with an understanding of the symptoms, occurrence, and consequences of chronic microbial contamination. The guide also suggests means for detection and control of microbial contamination in turbine oils and turbine oil systems. This guide applies primarily to turbine lubricants (see Specifications D4293 and D4304) and turbine oil systems. However, the principles discussed herein also apply generally to lubricating oils with viscosities 2/s (for example, see Specification D6158). 1.2 This guide focuses on turbine system and turbine oil microbiology. Despite considerable differences in turbine systems (for example, gas and steam driven turbines; power generation and propulsion; etc.) as ecosystems for microbial communities – with the exception of temperature – these differences are largely irrelevant. Ambient temperatures are typically similar. Recirculating turbine oil temperatures are commonly >40 °C. However, generally speaking, all systems in which accumulations of free water can develop, share properties that are considered in this guide. 1.2.1 Steam turbines, and to a greater extent hydro turbines, are continuously exposed to water ingression. Diligence is needed to ensure seals and bearings are in good condition to prevent water ingression or conditions that are conducive to biodeterioration. However, due to the risk of the accumulation of condensation, all equipment can become susceptible when shut down for extended periods. 1.3 This guide complements Energy Institute’s Guidelines on detecting, controlling, and mitigating microbial growth in oils and fuels used at power generation facilities (2.2). The Energy Institute’s guidance document provides greater detail than the overview provided in this guide. 1.4 Microbial contamination in turbine oil systems shares common features with microbial contamination in fuel systems (See Guide D6469). However, there are also relevant differences. Although the chemistry of the fluids is different, this Guide draws heavily on D6469 but highlights unique aspects of turbine oil and turbine oil system biodeterioration and microbial contamination. 1.5 This guide is not a compilation of all of the concepts and terminology used by microbiologists. It provides basic explanations of microbial contamination and biodeterioration in turbine oils and turbine oil systems. 1.6 The values in SI units are to be regarded as the standard. 1.7 This standard does not purport to address all ...
SIGNIFICANCE AND USE 5.1 This guide provides information addressing the conditions that lead to turbine oil microbial contamination and biodeterioration, the general characteristics of and strategies for controlling microbial contamination. It compliments and amplifies information provided in Practices D4378 and D6224 on condition monitoring of lubricating oils. 5.2 This guide focuses on microbial contamination in turbine oils and power generation turbine oil systems. Uncontrolled microbial contamination in turbine oils and lubrication systems remains a largely unrecognized but potentially costly problem in power generation systems. 5.2.1 Examples of turbine oil and system biodeterioration include, but are not limited to: 5.2.1.1 Filter plugging, 5.2.1.2 Oil line and orifice fouling, 5.2.1.3 Increased oil acidity, 5.2.1.4 Increased oil corrosivity, 5.2.1.5 Oil additive depletion, 5.2.1.6 Water emulsification, 5.2.1.7 Lubricity loss, and 5.2.1.8 Decreased oxidative stability and increased sludge generation. 5.3 This guide introduces the fundamental concepts of turbine oil microbiology and biodeterioration control. 5.4 This guide provides personnel who are responsible for turbine oil 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. SCOPE 1.1 This guide provides personnel who have a limited microbiological background with an understanding of the symptoms, occurrence, and consequences of chronic microbial contamination. The guide also suggests means for detection and control of microbial contamination in turbine oils and turbine oil systems. This guide applies primarily to turbine lubricants (see Specifications D4293 and D4304) and turbine oil systems. However, the principles discussed herein also apply generally to lubricating oils with viscosities 2/s (for example, see Specification D6158). 1.2 This guide focuses on turbine system and turbine oil microbiology. Despite considerable differences in turbine systems (for example, gas and steam driven turbines; power generation and propulsion; etc.) as ecosystems for microbial communities – with the exception of temperature – these differences are largely irrelevant. Ambient temperatures are typically similar. Recirculating turbine oil temperatures are commonly >40 °C. However, generally speaking, all systems in which accumulations of free water can develop, share properties that are considered in this guide. 1.2.1 Steam turbines, and to a greater extent hydro turbines, are continuously exposed to water ingression. Diligence is needed to ensure seals and bearings are in good condition to prevent water ingression or conditions that are conducive to biodeterioration. However, due to the risk of the accumulation of condensation, all equipment can become susceptible when shut down for extended periods. 1.3 This guide complements Energy Institute’s Guidelines on detecting, controlling, and mitigating microbial growth in oils and fuels used at power generation facilities (2.2). The Energy Institute’s guidance document provides greater detail than the overview provided in this guide. 1.4 Microbial contamination in turbine oil systems shares common features with microbial contamination in fuel systems (See Guide D6469). However, there are also relevant differences. Although the chemistry of the fluids is different, this Guide draws heavily on D6469 but highlights unique aspects of turbine oil and turbine oil system biodeterioration and microbial contamination. 1.5 This guide is not a compilation of all of the concepts and terminology used by microbiologists. It provides basic explanations of microbial contamination and biodeterioration in turbine oils and turbine oil systems. 1.6 The values in SI units are to be regarded as the standard. 1.7 This standard does not purport to address all ...
ASTM D8506-23 is classified under the following ICS (International Classification for Standards) categories: 75.100 - Lubricants, industrial oils and related products. The ICS classification helps identify the subject area and facilitates finding related standards.
ASTM D8506-23 has the following relationships with other standards: It is inter standard links to ASTM D445-24, ASTM D4412-19(2024), ASTM D5392-24, ASTM D3326-07(2024), ASTM D1500-24, ASTM D4378-24, ASTM D8112-24, ASTM D4175-23a, ASTM D665-23, ASTM D4898-23, ASTM D445-23, ASTM D6158-23, ASTM D6224-23, ASTM D892-23, ASTM D4175-23e1. Understanding these relationships helps ensure you are using the most current and applicable version of the standard.
ASTM D8506-23 is available in PDF format for immediate download after purchase. The document can be added to your cart and obtained through the secure checkout process. Digital delivery ensures instant access to the complete standard document.
Standards Content (Sample)
This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the
Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
Designation: D8506 − 23
Standard Guide for
Microbial Contamination and Biodeterioration in Turbine
Oils and Turbine Oil Systems
This standard is issued under the fixed designation D8506; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope ences. Although the chemistry of the fluids is different, this
Guide draws heavily on D6469 but highlights unique aspects of
1.1 This guide provides personnel who have a limited
turbine oil and turbine oil system biodeterioration and micro-
microbiological background with an understanding of the
bial contamination.
symptoms, occurrence, and consequences of chronic microbial
contamination. The guide also suggests means for detection 1.5 This guide is not a compilation of all of the concepts and
and control of microbial contamination in turbine oils and terminology used by microbiologists. It provides basic expla-
turbine oil systems. This guide applies primarily to turbine nations of microbial contamination and biodeterioration in
lubricants (see Specifications D4293 and D4304) and turbine turbine oils and turbine oil systems.
oil systems. However, the principles discussed herein also
1.6 The values in SI units are to be regarded as the standard.
apply generally to lubricating oils with viscosities <100 mm /s
1.7 This standard does not purport to address all of the
(for example, see Specification D6158).
safety concerns, if any, associated with its use. It is the
1.2 This guide focuses on turbine system and turbine oil
responsibility of the user of this standard to establish appro-
microbiology. Despite considerable differences in turbine sys-
priate safety, health, and environmental practices and deter-
tems (for example, gas and steam driven turbines; power
mine the applicability of regulatory limitations prior to use.
generation and propulsion; etc.) as ecosystems for microbial
1.8 This international standard was developed in accor-
communities – with the exception of temperature – these dif-
dance with internationally recognized principles on standard-
ferences are largely irrelevant. Ambient temperatures are
ization established in the Decision on Principles for the
typically similar. Recirculating turbine oil temperatures are
Development of International Standards, Guides and Recom-
commonly >40 °C. However, generally speaking, all systems
mendations issued by the World Trade Organization Technical
in which accumulations of free water can develop, share
Barriers to Trade (TBT) Committee.
properties that are considered in this guide.
1.2.1 Steam turbines, and to a greater extent hydro turbines, 2. Referenced Documents
are continuously exposed to water ingression. Diligence is 2
2.1 ASTM Standards:
needed to ensure seals and bearings are in good condition to
D130 Test Method for Corrosiveness to Copper from Petro-
prevent water ingression or conditions that are conducive to
leum Products by Copper Strip Test
biodeterioration. However, due to the risk of the accumulation
D445 Test Method for Kinematic Viscosity of Transparent
of condensation, all equipment can become susceptible when
and Opaque Liquids (and Calculation of Dynamic Viscos-
shut down for extended periods.
ity)
1.3 This guide complements Energy Institute’s Guidelines D664 Test Method for Acid Number of Petroleum Products
on detecting, controlling, and mitigating microbial growth in by Potentiometric Titration
oils and fuels used at power generation facilities (2.2). The D665 Test Method for Rust-Preventing Characteristics of
Energy Institute’s guidance document provides greater detail Inhibited Mineral Oil in the Presence of Water
than the overview provided in this guide. D888 Test Methods for Dissolved Oxygen in Water
D892 Test Method for Foaming Characteristics of Lubricat-
1.4 Microbial contamination in turbine oil systems shares
ing Oils
common features with microbial contamination in fuel systems
D943 Test Method for Oxidation Characteristics of Inhibited
(See Guide D6469). However, there are also relevant differ-
Mineral Oils
This guide is under the jurisdiction of ASTM Committee D02 on Petroleum
Products, Liquid Fuels, and Lubricants and is the direct responsibility of Subcom- For referenced ASTM standards, visit the ASTM website, www.astm.org, or
mittee D02.C0.01 on Turbine Oil Monitoring, Problems and Systems. contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
Current edition approved June 15, 2023. Published July 2023. DOI: 10.1520/ Standards volume information, refer to the standard’s Document Summary page on
D8506-23. the ASTM website.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
D8506 − 23
D974 Test Method for Acid and Base Number by Color- D5392 Test Method for Isolation and Enumeration of Es-
Indicator Titration cherichia coli in Water by the Two-Step Membrane Filter
D1067 Test Methods for Acidity or Alkalinity of Water Procedure
D1293 Test Methods for pH of Water D6158 Specification for Mineral Hydraulic Oils
D1331 Test Methods for Surface and Interfacial Tension of
D6224 Practice for In-Service Monitoring of Lubricating Oil
Solutions of Paints, Solvents, Solutions of Surface-Active for Auxiliary Power Plant Equipment
Agents, and Related Materials
D6304 Test Method for Determination of Water in Petro-
D1401 Test Method for Water Separability of Petroleum Oils leum Products, Lubricating Oils, and Additives by Cou-
and Synthetic Fluids
lometric Karl Fischer Titration
D1500 Test Method for ASTM Color of Petroleum Products
D6439 Guide for Cleaning, Flushing, and Purification of
(ASTM Color Scale)
Steam, Gas, and Hydroelectric Turbine Lubrication Sys-
D1744 Test Method for Determination of Water in Liquid
tems
Petroleum Products by Karl Fischer Reagent (Withdrawn
D6469 Guide for Microbial Contamination in Fuels and Fuel
2016)
Systems
D1976 Test Method for Elements in Water by Inductively-
D7155 Practice for Evaluating Compatibility of Mixtures of
Coupled Plasma Atomic Emission Spectroscopy
Turbine Lubricating Oils
D2068 Test Method for Determining Filter Blocking Ten-
D7464 Practice for Manual Sampling of Liquid Fuels, As-
dency
sociated Materials and Fuel System Components for
D2272 Test Method for Oxidation Stability of Steam Tur-
Microbiological Testing
bine Oils by Rotating Pressure Vessel
D7669 Guide for Practical Lubricant Condition Data Trend
D2273 Test Method for Trace Sediment in Lubricating Oils
Analysis
(Withdrawn 2022)
D7687 Test Method for Measurement of Cellular Adenosine
D2896 Test Method for Base Number of Petroleum Products
Triphosphate in Fuel and Fuel-associated Water With
by Potentiometric Perchloric Acid Titration
Sample Concentration by Filtration
D3326 Practice for Preparation of Samples for Identification
D7720 Guide for Statistically Evaluating Measurand Alarm
of Waterborne Oils
Limits when Using Oil Analysis to Monitor Equipment
D3328 Test Methods for Comparison of Waterborne Petro-
and Oil for Fitness and Contamination
leum Oils by Gas Chromatography
D7843 Test Method for Measurement of Lubricant Gener-
D3339 Test Method for Acid Number of Petroleum Products
ated Insoluble Color Bodies in In-Service Turbine Oils
by Semi-Micro Color Indicator Titration
using Membrane Patch Colorimetry
D3870 Practice for Establishing Performance Characteristics
D7847 Guide for Interlaboratory Studies for Microbiological
for Colony Counting Methods in Microbiology (With-
Test Methods
drawn 2000)
D7978 Test Method for Determination of the Viable Aerobic
D4175 Terminology Relating to Petroleum Products, Liquid
Microbial Content of Fuels and Associated Water—
Fuels, and Lubricants
Thixotropic Gel Culture Method
D4293 Specification for Phosphate Ester-Based Fluids for
D8112 Guide for Obtaining In-Service Samples of Turbine
Turbine Lubrication and Steam Turbine Electro-Hydraulic
Operation Related Lubricating Fluid
Control (EHC) Applications
E177 Practice for Use of the Terms Precision and Bias in
D4304 Specification for Mineral and Synthetic Lubricating
ASTM Test Methods
Oil Used in Steam or Gas Turbines
E1326 Guide for Evaluating Non-culture Microbiological
D4310 Test Method for Determination of Sludging and
Tests
Corrosion Tendencies of Inhibited Mineral Oils
E1542 Terminology Relating to Occupational Health and
D4378 Practice for In-Service Monitoring of Mineral Tur-
Safety
bine Oils for Steam, Gas, and Combined Cycle Turbines
E2551 Test Methods for Humidity Calibration (or Confor-
D4412 Test Methods for Sulfate-Reducing Bacteria in Water
mation) of Humidity Generators for Use with Thermogra-
and Water-Formed Deposits
vimetric Analyzers
D4454 Test Method for Simultaneous Enumeration of Total
E2756 Terminology Relating to Antimicrobial and Antiviral
and Respiring Bacteria in Aquatic Systems by Microscopy
Agents
(Withdrawn 2015)
2.2 Energy Institute Standards:
D4840 Guide for Sample Chain-of-Custody Procedures
IP 613 Determination of the viable aerobic microbial content
D4898 Test Method for Insoluble Contamination of Hydrau-
of fuels and associated water - Thixotropic Gel Culture
lic Fluids by Gravimetric Analysis
Method Guidelines on detecting, controlling, and mitigat-
D5185 Test Method for Multielement Determination of
ing microbial growth in oils and fuels used at power
Used and Unused Lubricating Oils and Base Oils by
generation facilities.
Inductively Coupled Plasma Atomic Emission Spectrom-
etry (ICP-AES)
3 4
The last approved version of this historical standard is referenced on Available from Energy Institute, 61 New Cavendish St., London, WIG 7AR,
www.astm.org. U.K. https://publishing.energyinst.org/ip-test-methods.
D8506 − 23
2.3 Government Standards: the presence of oxygen, anaerobic growth typically occurs only
40 CFR 152 Pesticide Registration and Classification Proce- in an oxygen depleted environment.
dures
3.1.5 anoxic, adj—oxygen free.
EU Biocides Regulation (528/2012)
3.1.6 antimicrobial, n—see biocide.
2.4 ISO Standards:
3.1.7 bacterium (pl. bacteria), n—a single cell microorgan-
ISO 3722 Hydraulic fluid power – Fluid sample containers
ism characterized by the absence of defined intracellular
— Qualifying and controlling cleaning methods
membranes that define all higher life forms.
ISO 4406 Hydraulic fluid power – Fluids – Method for cod-
3.1.7.1 Discussion—All bacteria are members of the bio-
ing the level of contamination by solid particles, Second
logically diverse kingdoms Prokaryota and Archaebacteriota.
Edition, 1999
Individual taxa within these kingdoms are able to thrive in
ISO 4407 Hydraulic Fluid Power – Fluid Contamina-
environments ranging from sub-zero temperatures, such as in
tion – Determination of Particulate Contamination by
frozen foods and polar ice, to superheated waters in deep-sea
Counting Method Using an Optical Microscope, Second
thermal vents, and over the pH range < 2.0 to > 13.0. Potential
Edition, 2002
food sources range from single carbon molecules (carbon
ISO 11500 Hydraulic fluid power – Determination of the
dioxide and methane) to complex polymers, including plastics.
particulate contamination level of a liquid sample by
Oxygen requirements range from obligate anaerobes, which
automatic particle counting using the light extinction,
die on contact with oxygen, to obligate aerobes, which die if
Second Edition, 2008
oxygen pressure falls below a species-specific threshold.
ISO 11171 Hydraulic Fluid Power – Calibration of auto-
3.1.8 bioburden, n—the level of microbial contamination
matic particle counters for liquids
(biomass) in a system.
3. Terminology
3.1.8.1 Discussion—Typically, bioburden is defined in terms
3.1 Definitions:
of either biomass or numbers of cells per unit volume or mass
3.1.1 For definitions and terms relating to this guide, refer to
or surface area material tested (g biomass / mL; g biomass / g;
Terminologies D4175, E1542, and E2756. Selected terms from
cells / mL sample, and so forth). The specific parameter used to
these Terminology Standards are included for the benefit of
define bioburden depends on critical properties of the system
readers who are unfamiliar with microbiology terms.
evaluated and the investigator’s preferences.
3.1.2 aerobe, n—an organism that requires oxygen to re-
3.1.9 biocide, n—a physical or chemical agent that kills
main metabolically active.
living organisms.
3.1.2.1 Discussion—Aerobes use oxygen as their terminal
3.1.9.1 Discussion—Biocides are further classified as bac-
electron acceptor in their primary energy-generating metabolic
tericides (kill bacteria), fungicides (kill fungi), and microbi-
pathways. Aerobes require oxygen for survival, using aerobic
cides (kill both bacterial and fungi). They are also referred to
metabolic processes to generate energy for growth and sur-
as antimicrobials.
vival.
3.1.10 biodeterioration, n—the loss of commercial value or
3.1.3 aggressiveness index (A.I.), n—the value computed
performance characteristics, or both, of a product or material
from the sum of the pH + log alkalinity + log hardness of water
through biological processes.
sample where both alkalinity and hardness are reported as
-1
3.1.10.1 Discussion—In turbine oil systems, turbine oil is
milligram CaCO L .
the product and turbine oil system components such as filter
3.1.3.1 Discussion—As A.I. decreases, water becomes more
media, transfer lines, heat exchangers, reservoirs, etc. are the
corrosive. At A.I. ≥ 12, water is noncorrosive. At 10 ≤ A.I. <
materials.
12, water is moderately corrosive. At A.I. < 10, water is
3.1.11 biofilm, n—a film or layer of microorganisms,
strongly corrosive.
biopolymers, water, and entrained organic and inorganic debris
3.1.4 anaerobe, n—an organism that cannot grow or prolif-
that forms as a result of microbial growth and proliferation at
erate in the presence of oxygen.
phase interfaces (liquid-liquid, liquid-solid, liquid-gas, and so
forth) (synonym: skinnogen layer).
3.1.4.1 Discussion—Anaerobes use molecules other than
oxygen in their primary energy-generating metabolic
3.1.12 biomass, n—biological material including any mate-
pathways, such as sulfate, nitrate, ketones, and other high-
rial other than fossil fuels which is or was a living organism or
energy organic molecules. Although anaerobes may survive in
component or product of a living organism.
3.1.12.1 Discussion—In biology and environmental science,
biomass is typically expressed as density of biological material
Available from U.S. Government Printing Office, Superintendent of
per unit sample volume, area, or mass (g biomass/g (or /mL or
Documents, 732 N. Capitol St., NW, Mail Stop: SDE, Washington, DC 20401.
/cm ) sample); when used for products derived from organisms
https://ecfr.io/Title-40/Part-152.
Available from
biomass is typically expressed in terms of mass (kg, MT, etc.)
http://eur-lex.europa.eu/JOHtml.do?uri=OJ:L:2012:167:SOM:EN:HTML.
or volume (L, m , bbl, etc.).
Available from International Standards Organization, ISO Central Secretariat,
3.1.13 biosurfactant, n—a biologically produced molecule
Chemin de Blandonnet 8, CP 401, 1214 Vernier, Geneva Switzerland https://
www.iso.org/standards.html. that acts as a soap or detergent.
D8506 − 23
3.1.14 consortium (pl. consortia), n—microbial community magnitude) reductions in number of living microbes in a fluid
comprised of more than one species that exhibits properties not or system receiving that concentration.
shown by individual community members.
3.1.27 skinnogen, n—synonymous with biofilm.
3.1.14.1 Discussion—Consortia often mediate biodeteriora-
3.1.27.1 Discussion—Generally applied to a biofilm formed
tion processes that individual taxa cannot.
at the turbine oil-water interface.
3.1.15 depacifying, adj—the process of removing hydrogen
3.1.28 sour, v—to increase the concentration of hydrogen
ions (protons) from the cathodic surface of an electrolytic cell,
sulfide.
thereby promoting continued electrolytic corrosion.
3.1.29 sulfate reducing bacteria (SRB), pl., n—any bacteria
3.1.16 deplasticize, v—the process of breaking down poly-
with the capability of reducing sulfate to sulfide.
mers in plastics and similar materials, resulting in loss of the
3.1.29.1 Discussion—The term SRB applies to representa-
material’s structural integrity.
tives from a variety of bacterial taxa that share the common
3.1.17 facultative anaerobe, n—a microorganism capable of
= =
feature of sulfate reduction (SO to S ). SRB are major
growing in both oxic and anoxic environments.
contributors to MIC.
3.1.30 taxa, pl., n—the units of classification of organisms,
3.1.17.1 Discussion—Facultative anaerobes use oxygen
when it is present and use either organic or inorganic energy based on their relative similarities.
sources (nitrate, sulfate, and so forth) when oxygen is depleted
3.1.30.1 Discussion—Each taxonomic unit (group of organ-
or absent.
isms with greatest number of similarities) is assigned, begin-
3.1.18 fungus (pl. fungi), n—single cell (yeasts) or filamen-
ning with the most inclusive to kingdom, division, class, order,
tous (molds) microorganisms that share the property of having
family, genus, and species. Bacteria and fungi are often further
the true intracellular membranes (organelles) that characterize
classified by strain and biovariation.
all higher life forms (Eukaryotes).
3.1.31 viable titer, n—the number of living microbes present
3.1.19 metabolite, n—a chemical substance produced by
per unit volume, mass, or area.
any of the many complex chemical and physical processes
3.1.31.1 Discussion—Viable titer is reported in terms of
involved in the maintenance of life.
either colony forming units (CFU) or most probable number
3.1.20 microbial activity test, n—any analytical procedure
(MPN) per milliliter, milligram, or centimeter squared.
designed to measure the rate or results of one or more
3.1.32 water activity, a , n—the ratio of actual partial
w
microorganism processes.
pressure of water to the saturated water vapor pressure at the
same temperature, expressed as a decimal fraction. E2551
3.1.20.1 Discussion—Examples of microbial activity tests
include loss or appearance of specific molecules or measuring 3.1.32.1 Discussion—water activity is also known as rela-
tive pressure in some applications areas.
the rate of change of parameters, such as acid number,
molecular weight distribution (carbon number distribution), 3.1.32.2 Discussion—For example, if a specimen’s a = 0.8,
w
then the partial pressure of water in the specimen is 80 % of
and specific gravity.
what the pressure of water would be under identical conditions.
3.1.21 microbially induced corrosion (MIC), n—corrosion
3.1.32.3 Discussion—In the context of oil systems, there
that is enhanced by the action of microorganisms in the local
may be two considerations for water activity; firstly, the
environment.
amount of free water (moisture) in the oil itself and secondly,
3.1.22 mold, n—form of fungal growth, characterized by
the water activity of any discrete free water phase, which will
long strands of filaments (hyphae) and, under appropriate
be influenced by the amount of dissolved chemicals in it (for
growth conditions, aerial, spore-bearing structures.
example, salts, polar solvents, and water-soluble oil additives).
3.1.22.1 Discussion—In fluids, mold colonies typically ap-
4. Summary
pear as soft spheres; termed fisheyes.
3.1.23 obligate aerobe, n—microorganism with an absolute
4.1 Although free water in turbine oil systems is typically
requirement for atmospheric oxygen in order to function. restricted to quiescent zones in reservoirs and lines, microbes
proliferating in these zones can be dispersed within water
3.1.23.1 Discussion—Obligate aerobes may survive periods
droplets and degrade lubricants. Moreover, once dispersed into
in anoxic environments but will remain dormant until sufficient
oil, microbially-contaminated water has an extraordinary sur-
oxygen is present to support their activity.
face area to mass ratio. This ratio facilitates oil biodeteriora-
3.1.24 obligate anaerobe, n—microorganism that cannot
tion. Microbes can contaminate turbine oils through sumps and
function when atmospheric oxygen is present.
ventilation systems, or through inadequate housekeeping that
promotes dirt ingress. Bacteria and fungi are also carried along
3.1.24.1 Discussion—Obligate anaerobes may survive peri-
ods in oxic environments but remain dormant until conditions with dust particles and water droplets through tank vents. See
Section 6 for more a detailed discussion.
become anoxic.
3.1.25 oxic, adj—an environment with a sufficient partial
4.2 A detailed discussion of the various types of damage
pressure of oxygen to support aerobic growth.
that microbes can cause or to which they can contribute is
3.1.26 shock treatment, n—the addition of an antimicrobial beyond the scope of this Guide. The Energy Institute’s Guide-
agent sufficient to cause rapid and substantial (several orders of lines on detecting, controlling, and mitigating microbial growth
D8506 − 23
in oils and fuels used at power generation facilities describes 5. Significance and Use
these various types of damage in considerable detail.
5.1 This guide provides information addressing the condi-
4.3 After arriving in reservoirs, filter housings, etc., mi- tions that lead to turbine oil microbial contamination and
crobes can attach to surfaces on which they subsequently form biodeterioration, the general characteristics of and strategies
biofilm communities. Most growth and activity occurs where for controlling microbial contamination. It compliments and
oil and water meet. The oil-water interface is the most obvious amplifies information provided in Practices D4378 and D6224
boundary. However, there is also a considerable area of on condition monitoring of lubricating oils.
oil-water interface on the interior surface of reservoir walls.
5.2 This guide focuses on microbial contamination in tur-
4.3.1 Microorganisms require water for growth. Although
bine oils and power generation turbine oil systems. Uncon-
bacteria and fungi can be present in the oil phase, their growth
trolled microbial contamination in turbine oils and lubrication
and activity are restricted to the water phase of lubricant
systems remains a largely unrecognized but potentially costly
systems—recognizing that micelles dispersed in oil can repre-
problem in power generation systems.
sent percentage of the total water volume.
5.2.1 Examples of turbine oil and system biodeterioration
4.3.2 The water phase includes volumes ranging from trace
include, but are not limited to:
(several μL) to bulk (>1 m ) accumulations and water entrained
5.2.1.1 Filter plugging,
within deposits that accumulate on system surfaces.
5.2.1.2 Oil line and orifice fouling,
4.3.3 Typically, lubricant and system deterioration is caused
5.2.1.3 Increased oil acidity,
by the net activity of complex microbial communities living
5.2.1.4 Increased oil corrosivity,
within slimy layers called biofilms. Section 7 provides greater
5.2.1.5 Oil additive depletion,
detail regarding the presence and dynamics of biofilms.
5.2.1.6 Water emulsification,
4.4 Obtaining appropriate samples can be challenging. 5.2.1.7 Lubricity loss, and
Samples collected for microbiological testing are typically 5.2.1.8 Decreased oxidative stability and increased sludge
diagnostic rather than representative. The intention is to detect generation.
microbial contamination if it is present, rather than assess a
5.3 This guide introduces the fundamental concepts of
relatively uniform, turbine oil property. Samples collected from
turbine oil microbiology and biodeterioration control.
the interface zones, especially the oil/water interface are most
5.4 This guide provides personnel who are responsible for
likely to provide indication of whether or not microbial growth
turbine oil system stewardship with the background necessary
is occurring within the system. Refer to Section 8, Practice
to make informed decisions regarding the possible economic or
D7464 Section 7.4.1.3, and of Guide D8112 Section 8.6.3 for
safety, or both, impact of microbial contamination in their
more details.
products or systems.
4.5 Sample analysis includes gross observations as well as a
battery of physical, chemical, and microbiological tests.
6. Origins of Microbial Contamination
4.5.1 Because biodeterioration shares symptoms with other
6.1 Microbes are ubiquitous in soil and airborne dust
turbine oil and turbine oil-system degradation processes, it is
(particulate) and water particles.
critical to subject samples to a sufficient range of appropriate
6.2 Microbial contamination can be introduced into turbine
tests to permit accurate root-cause diagnosis.
oil systems via open reservoirs and vented system components.
4.5.2 Section 9 provides more information on examining
and testing samples.
6.3 Microbial contamination can also be introduced during
turbine oil processing or addition. Unless there is a sufficient
4.6 Microbial contamination control requires a well-
concentration of dispersed water to create water activity (a ≥
w
designed strategy that considers system design, sampling and
0.8), microbes contaminating turbine oil in drum or tank stock
analysis, and preventive and remedial treatment. See Section
are most likely to be dormant—not biologically active (dying
11 for details.
off or waiting for favorable growth conditions).
4.6.1 Good system design minimizes contaminant entry and
provides for adequate sampling, water removal, and periodic
6.4 Polar components of turbine oils and oil additives are
cleaning and inspection.
likely to partition into dispersed water droplets; typically
4.6.2 Effective monitoring programs cost-effectively bal-
providing nutrients for microbes in these droplets. In some
ance biodeterioration risks with sampling and analytical costs.
instances, these organic components can be inhibitory to
4.6.3 Remedial efforts may include oil filtration,
contaminating microbes.
reconditioning, disposal, biocide treatment, or tank/system
6.5 There are several means for categorizing microbes,
cleaning, or combination thereof. Health, safety, and environ-
including physiological properties (that is, the nutrients they
mental considerations are critical to proper system remedia-
can use as food, and the metabolites they produce), genetic
tion.
profiles, respiration pathways (that is, aerobic or anaerobic),
and temperature range—among others.
6.5.1 Psychrophiles are microbes that grow optimally at
Available from Energy Institute, 61 New Cavendish St., London, WIG 7AR,
temperatures <15 °C and will not grow at temperatures >20 °C.
U.K., https://publishing.energyinst.org/topics/power-generation/guidelines-on-
Psychrophiles are unlikely to be recovered from turbine oil
detecting,-controlling-and-mitigating-microbial-growth-in-oils-and-fuels-used-at-
power-generation-facilities, ISBN:9781787251885. systems.
D8506 − 23
6.5.2 Mesophiles are microbes that grow optimally at tem- and wear debris. Although some of these elements can be
peratures between 20 °C and 40 °C. Although many mesophilic limiting in turbine oil systems, compressor oil, and hydraulic
microbes can grow at temperatures <20 °C, most are killed as
fluids can contaminate turbine oil and provide concentrations
temperatures increase above 40 °C. Mesophiles are the sufficient to support microbial activity.
micorbes most commonly recovered from turbine oil systems.
7.1.2.3 Turbine oil systems that provide both the requisite
6.5.3 Thermophiles grow optimally at temperatures ≥40 °C.
water and nutrients will support microbial growth and prolif-
Thermopiles that grow at 122 °C have been recovered from
eration.
deep ocean thermal vents. Thermophiles recovered from tur-
7.1.3 There are several ways in which microbes can be
bine oil systems grow optimally in the 40 °C to 60 °C range.
categorized, including physiological properties (that is, the
6.5.4 Mesophiles and thermophiles can tolerate tempera-
nutrients they can use as food, and the metabolites they
tures cooler than those at which they grow optimally. They
produce), optimal pH range, optimal oxygen concentration,
adapt to cooler temperatures by either growing more slowly or
and optimal temperature range—among others.
becoming dormant (metabolically inactive).
7.1.3.1 Within the physiological range (temperature range
6.6 Regardless of the route by which microbes are intro-
within which growth occurs) of a given microorganism, the
duced into turbine oil systems, they are likely to recirculate
growth rate increases with increasing temperature.
with the oil. A percentage of these free-floating (planktonic)
(1) Psychrophiles are microbes that grow optimally at
microbes will adhere onto system surfaces. If those surfaces
temperatures <15 °C and will not grow at temperatures >20 °C.
also have traces of water adhering to them, colonization is
Psychrophiles are unlikely to be recovered from turbine oil
likely to occur.
systems.
6.7 The transition period between microbe attachment to a
(2) Mesophiles are microbes that grow optimally at tem-
pristine surface and the development of a biofilm community
peratures between 20 °C and 40 °C. Although many mesophilic
can occur in ≤24 h, although in practice, periods of weeks or
microbes can grow at temperatures <20 °C, most are killed as
months are likely to pass before biofilm communities within
temperatures increase above 40 °C. Mesophiles are the mi-
turbine oil systems become problematic.
crobes most commonly recovered from turbine oil systems.
(3) Thermophiles grow optimally at temperatures ≥40 °C.
6.8 Biofilms can form on system surfaces where they
Thermopiles that grow at 122 °C have been recovered from
entrain water, inorganic particles, and nutrients to support
deep ocean thermal vents. Thermophiles recovered from tur-
growth. Such growth can slough off and be carried to other
bine oil systems grow optimally in the 40 °C to 60 °C range.
sites within the system.
7.1.3.2 Mesophiles and thermophiles can tolerate tempera-
6.9 Tank materials and configurations are varied, reflecting
tures cooler than those at which they grow optimally. They
use applications that range from small reservoirs (<1 L) on
adapt to cooler temperatures by either growing more slowly or
emergency generators to large (>4000 L) day tanks feeding
becoming dormant (metabolically inactive).
major power generation and propulsion turbines. Turbine oil
reservoirs accumulate water and bioburden that can lead to 7.1.3.3 Within turbine oil systems, thermal regimes vary
failure through bearing or seal failure or filter plugging. considerably.
Moreover, MIC can compromise reservoir integrity, leading to (1) Typical temperatures of oil in circulation are in the
leakage. In steam turbine systems, substantial water volumes
range from approximately ambient in turbine oil service tanks
can be introduced into turbine oil via leaking steam seals. and reservoirs, and 40 °C to 50 °C in recirculating oil transfer
lines or isolated zones where little circulation occurs.
7. Occurrence and Impact
(2) The cooler zones can provide habitats for the prolifera-
tion of microbes that cannot tolerate temperatures >40 °C.
7.1 Microbes require water as well as nutrients.
(3) Biomass from this growth can be dislodged and trans-
Consequently, they concentrate at sites within oil systems,
ported to areas of the system where their optimal growth
where water accumulates, and in dispersed water droplets.
temperature is exceeded. Thus, microbes with temperature
7.1.1 Water is essential for microbial growth and prolifera-
optima in the 20 °C to 35 °C range can cause filter plugging
tion. Miniscule amounts of available water (≥250 mL/m and
and line blockage problems in zones where the turbine oil
a ≥ 0.8) are sufficient to support microbial populations.
w
temperature is >40 °C.
7.1.2 Nutrients are divided into macro-nutrients and micro-
(4) Similarly, acids and biosurfactants, produced by mi-
nutrients. Carbon, hydrogen, oxygen, nitrogen, sulfur, and
crobes can be dispersed into turbine oil, adversely affecting its
phosphorus (CHONSP) comprise the macro-nutrients, and
acidity (9.4.3) and water separability (9.3.2) properties.
most of these are readily available in turbine oils.
(5) Consequently, biodeterioration symptoms such as pre-
7.1.2.1 Although N, P, and S concentrations in base-oil
mature filter plugging, corrosion, and turbine oil degradation,
stocks can be insufficient to support microbial growth, their
can be observed at system positions where no microbes are
concentrations in performance additives are often sufficient to
detected.
overcome this limitation.
7.1.3.4 During outages, when recirculation and heat ex-
7.1.2.2 Microbes require a variety of elements, including
calcium, sodium, potassium, iron, magnesium, manganese, change from bearings is discontinued, mesophilic microbes can
proliferate wherever traces of water (condensation) accumu-
copper, cobalt, nickel, and other metals in trace quantities.
Micronutrient sources include additives, dirt ingress, water, late.
D8506 − 23
7.1.4 Water pH is generally not a controlling factor in oil (6) Biofilm communities are directly involved in MIC that
systems. can result in pinhole leaks in reservoirs and transfer lines. The
problem of MIC is a consequence of several microbial pro-
7.1.4.1 Most contaminant microbes can tolerate pH’s rang-
cesses.
ing from 5.5 to 8.0.
(7) First, the heterogeneity of biofilm accumulation creates
7.1.4.2 As with temperature, there are microbes that prefer
electropotential gradients between zones of covered and un-
acidic environments (some grow in the equivalent of 2N
covered surfaces.
sulfuric acid) and others that grow in alkaline systems with pH
(8) SRB and other anaerobes use the hydrogen ions,
>11.
thereby depacifying the electrolytic cell and accelerating the
7.1.4.3 Turbine oil associated water pH is typically between
corrosion reactions. The hydrogen sulfide generated by bio-
6 and 9.
logical sulfate reduction sours the turbine oil, causing copper
7.2 After free-water zones, water concentrations tend to be
corrosion test (see Test Method D130) failure. Moreover, toxic
greatest at interface zones, this is where microbes are most
hydrogen sulfide trapped within bottom sludge can be a safety
likely to establish communities, or biofilms.
hazard to personnel entering gas-freed tanks.
7.2.1 Numbers of microbes within biofilms are typically (9) Microbes growing anaerobically produce low molecu-
lar weight organic acids (formate, acetate, lactate, pyruvate,
orders of magnitude greater than elsewhere in turbine oil
systems. and others). These acids accelerate the corrosion process by
chemically etching the metal surface. There are data demon-
7.2.2 Biofilms can form on tank overheads, at the bulk-
strating that biofilm communities can deplasticize the polymers
turbine oil, bottom-water interface, and on all system surfaces.
used in fiberglass synthesis. Such activity can result in cata-
7.2.2.1 The biofilm that develops at the turbine oil-water
strophic tank failure and is most likely to occur at turbine
interface (sometimes called the skinnogen layer because of its
oil-water interfaces and low points. In horizontally-oriented
tough membranous characteristics) represents a unique micro-
tanks and pipes, the low point is a line along the longitudinal
environment relative to either the overlying turbine oil or
centerline (the same place of the greatest frequency of MIC
underlying water. Nutrients from both the overlying turbine oil
pinholes).
and underlying water are concentrated in this third phase.
7.2.2.2 Whereas a 1 mm thick biofilm on a tank wall might
7.3 Biodeterioration shares many symptoms with nonbio-
seem negligible, it is 100 times the thickness of most fungi, and
logical turbine oil deterioration processes. Without an adequate
500 to 1000 times the longest dimension of most bacteria. This
battery of tests, the root cause of a given turbine oil degrada-
seemingly thin film provides a large reservoir for microbial
tion problem may be misdiagnosed. The following paragraphs
activity. Within the biofilm micro-environment, conditions can
discuss symptoms caused by microorganisms. However, many
be dramatically different from those in the bulk product.
of these symptoms may also be caused by nonbiological
7.2.2.3 The microbial ecology of biofilms is complex. factors.
Microbial consortia (communities) give the biofilm community
7.3.1 Biosurfactants facilitate water transport into the tur-
characteristics that cannot be predicted from analysis of its
bine oil phase and some turbine oil additive partitioning into
individual members.
the water phase. Other metabolites may accelerate turbine oil
7.2.2.4 Biofilms are formed when early colonizers, or polymerization (that is, particle generation as detected by Test
Methods D2068 and D2273).
pioneers, secrete mucous-like biopolymers that protect cells
from otherwise harsh environmental conditions.
7.3.1.1 Metabolites produced at concentrations that are
(1) These biopolymers trap nonpolymer producing
difficult to detect against the complex chemistry of turbine oil
microbes, that then become part of the biofilm community, and
components, can have a significant deleterious effect on turbine
cations that act as ligands that strengthen biofilm structural
oil stability.
integrity.
7.3.1.2 Although most of the change occurs within a few
(2) Aerobes and facultative anaerobes (bacteria that grow
centimeters of the biofilm-turbine oil interface, product mixing
aerobically under oxic conditions and anaerobically under
can distribute metabolites throughout the turbine oil system.
anoxic conditions) scavenge oxygen, creating conditions nec-
7.3.2 After degraded water separability properties and MIC,
essary for obligate anaerobes to grow and proliferate.
the most common symptoms of microbial contamination are
(3) Some bacterial and fungal species produce biosurfac-
filter plugging and fiber coalescer disarming.
tants that create invert emulsions, which in-turn make nonpolar
7.3.2.1 Because all the fluid passes multiple times through
turbine oil components available for use as food.
the system filters, collection of microbes on the filters is a
(4) Microbes able to attack hydrocarbons directly excrete
common event.
waste products that other consortium members use as food.
(1) Once microbes are trapped on or within filter media,
The net effect is a change in pH, oxidation-reduction (or redox)
they can proliferate and produce biopolymers—providing suf-
potential, water activity, and nutrient composition that has little
resemblance to the environment outside the biofilm. ficient water also accumulates.
(5) The biofilm consortium acts like a complex bioreactor, (2) These two activities contribute to rapid filter plugging
which is reflected in increased pressure differentials (ΔP)
causing several types of significant changes to the turbine oil
and turbine oil systems. between a filtration unit’s inlet and outlet.
D8506 − 23
7.3.2.2 During normal function, of coalescer-type filter 8.1.3 Samples of oil in circulation enable assessment of the
elements, water droplets enlarge (coalesce) as they travel along extent to which microbial contamination is active within water
the surface of polar fibers.
suspended in oil and dispersed through the oil system.
(1) When sufficiently large droplets impact hydrophobic
8.1.4 Samples of oil taken from before and after oil purifiers
resin beads within the fiber matrix, the droplets fall out of the
and filters are useful for determining whether these treatments
oil phase and are captured in the filtration unit’s water
are beneficial in reducing numbers of microbial contaminants
reservoir.
in circulated oil.
(2) When microbes attach to hydrophobic beads, they
8.2 Non-fluid samples can also provide useful microbial
create hydrophilic surface characteristics—effectively neutral-
contamination diagnostic information.
izing the beads’ performance properties.
(3) Microbial population densities substantially lower than 8.2.1 Biomass tends to concentrate on filter media.
those needed to measurably increase pressures across the filter
8.2.1.1 Surface swab samples from the internal walls of
are sufficient to disarm coalescers.
filter housing and media can be diagnostic for microbial
contamination (Fig. 1d).
8. Sampling
8.2.1.2 Sections of filter media can be excised and tested for
8.1 Bottom samples, as described in Practice D7464, pro-
microbial contamination.
vide the material most likely to be suitable for evaluating
whether microbial contamination is present in the system.
NOTE 1—Recognizing that filter media concentrate microbes and other
Guide D8112 provides figures of suggested sampling points. turbine oil particulate contaminates, bioburdens recovered from these
samples should be used as a qualitative indicator of microbial contami-
8.1.1 Turbine oil service tank and filter housing bottom
nation in the system rather than as a quantitative indicator of microbial
drains are typically readily accessible for sample collection
bioburdens.
(Fig. 1a and Fig. 1b).
8.1.2 Where water traps are installed (Fig. 1c), accumulated 8.3 Because sample analyses may be performed by more
than one laboratory, good sample chain of custody procedures
water in these traps can be collected for chemical and micro-
biological testing. should be followed (see Guide D4840).
a) Turbine oil reservoir bottom drain;
b) Filter housing bottom drain;
c) In-line water separator;
d) Filter housing wall swab sample collection;
e) Filter with outer casing partially removed;
f) Portion of filter medium removed from filter element.
White circles in 1a and 1b highlight drain outlet locations.
FIG. 1 Sampling Points for Diagnostic Microbiological Contamination Testing
D8506 − 23
8.4 Both biological and nonbiological deterioration pro- exceed criteria levels after biocide treatment, then tests should
cesses continue in a sample during the period between collec- be performed every 1.5 to 2 months. This provides a compro-
tion and analysis. Ideally, all testing should be accomplished at mise between controlling monitoring costs and detecting po-
the sampling site, within a few minutes after a sample is drawn. tential problems before they affect operations. Determination
As this is rarely possible, good practices for preserving and of sampling intervals is discussed in greater detail in ASTM
preparing samples for analysis should be following (see MNL 1, Chapter 8 .
Practice D3326).
9. Examination and Testing
8.5 Samples for pH (Test Methods D1293) and alkalinity/
9.1 Some analytical methods can be performed in the field
acidity determinations (Test Method D1067) of free-water
under less-than-optimal conditions, but many others will re-
samples should be tested within 1 h after sampling, or as soon
quire the services of a laboratory with specialized equipment.
thereafter as practical.
The guidance provided in Practice D4378 is directly applicable
NOTE 2—Oil additives that can partition from the oil into free-water can
to the examination and testing of oils for evidence of microbial
have a buffering effect masking pH change as low molecular weight
contamination and biodeterioration.
organic acids accumulate. These partitioned additives contribute to the
water-phase’s alkalinity. Consequently, a decrease in alkalinity typically
9.2 Gross Observations:
precedes a decrease in pH.
9.2.1 Gross observations, such as color (Method D1500),
8.6 Samples for microbiological testing should be kept on
odor, clarity, and appearance of the turbine oil, are made during
ice for transport to the laboratory. Tests should be performed
routine housekeeping and change over practices. When careful
within 1 h and no later than 36 h after sampling. Samples
records are kept, they can identify changes in operating
stored at higher temperatures, or for longer times, may show
practices and environmental conditions that result in increased
the presence of microbial conta
...
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