ASTM D6224-23

Standard Practice for In-Service Monitoring of Lubricating Oil for Auxiliary Power Plant Equipment

SIGNIFICANCE AND USE
4.1 This practice is intended to help users, particularly power plant operators, maintain effective control over their mineral lubricating oils and lubrication monitoring program. This practice may be used to perform oil changes based on oil condition and test results rather than on the basis of service time or calendar time. It is intended to save operating and maintenance expenses.  
4.2 This practice is also intended to help users monitor the condition of mineral lubricating oils and guard against excessive component wear, oil degradation, or contamination, thereby minimizing the potential of catastrophic machine problems that are more likely to occur in the absence of such an oil condition monitoring program.  
4.3 This practice does not necessarily reference all of the current oil testing technologies and is not meant to preclude the use of alternative instrumentation or test methods that provide meaningful or trendable test data, or both. Some oil testing devices and sensors (typically used for screening oils that will be tested according to standard methods) provide trendable indicators that correlate to water, particulates, and other contaminants but do not directly measure these.  
4.4 This practice is intended for mineral oil products, and not for synthetic type of products, with the exception of phosphate esters fluids typically used in power plant control systems.
SCOPE
1.1 This practice covers the requirements for the effective monitoring of mineral oil and phosphate ester fluid lubricating oils in service auxiliary (non-turbine) equipment used for power generation. Auxiliary equipment covered includes gears, hydraulic systems, diesel engines, pumps, compressors, and electrohydraulic control (EHC) systems. It includes sampling and testing schedules and recommended action steps, as well as information on how oils degrade.
Note 1: Other types of synthetic lubricants are sometimes used but are not addressed in this practice because they represent only a small fraction of the fluids in use. Users of these fluids should consult the manufacturer to determine recommended monitoring practices.  
1.2 This practice does not cover the monitoring of lubricating oil for steam and gas turbines. Rather, it is intended to complement Practice D4378.  
1.3 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.  
1.4 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety, health, and environmental practices and determine the applicability of regulatory limitations prior to use.  
1.5 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.

General Information

• Status: Published
• Publication Date: 31-Oct-2023
• ICS: 29.160.40 - Generating sets
• ICS: 75.100 - Lubricants, industrial oils and related products
• Technical Committee: D02 - Petroleum Products, Liquid Fuels, and Lubricants
• Drafting Committee: D02.C0.01 - Turbine Oil Monitoring, Problems and Systems

Relations

• Replaces: ASTM D6224-22 - Standard Practice for In-Service Monitoring of Lubricating Oil for Auxiliary Power Plant Equipment
• Effective Date: 01-Nov-2023
• Refers: ASTM D445-24 - Standard Test Method for Kinematic Viscosity of Transparent and Opaque Liquids (and Calculation of Dynamic Viscosity)
• Effective Date: 01-Apr-2024
• Refers: ASTM D1500-24 - Standard Test Method for ASTM Color of Petroleum Products (ASTM Color Scale)
• Effective Date: 01-Mar-2024
• Refers: ASTM D4378-24 - Standard Practice for In-Service Monitoring of Mineral Turbine Oils for Steam, Gas, and Combined Cycle Turbines
• Effective Date: 01-Mar-2024
• Refers: ASTM D7546-24 - Standard Test Method for Determination of Moisture in New and In-Service Lubricating Oils and Additives by Relative Humidity Sensor
• Effective Date: 01-Feb-2024
• Refers: ASTM D7647-24 - Standard Test Method for Automatic Particle Counting of Lubricating and Hydraulic Fluids Using Dilution Techniques to Eliminate the Contribution of Water and Interfering Soft Particles by Light Extinction
• Effective Date: 01-Feb-2024
• Refers: ASTM E1064-24 - Standard Test Method for Water in Organic Liquids by Coulometric Karl Fischer Titration
• Effective Date: 01-Jan-2024
• Refers: ASTM D4175-23a - Standard Terminology Relating to Petroleum Products, Liquid Fuels, and Lubricants
• Effective Date: 15-Dec-2023
• Refers: ASTM D665-23 - Standard Test Method for Rust-Preventing Characteristics of Inhibited Mineral Oil in the Presence of Water
• Effective Date: 01-Dec-2023
• Refers: ASTM D445-23 - Standard Test Method for Kinematic Viscosity of Transparent and Opaque Liquids (and Calculation of Dynamic Viscosity)
• Effective Date: 01-Nov-2023
• Refers: ASTM D892-23 - Standard Test Method for Foaming Characteristics of Lubricating Oils
• Effective Date: 01-Oct-2023
• Refers: ASTM D95-23 - Standard Test Method for Water in Petroleum Products and Bituminous Materials by Distillation
• Effective Date: 01-Oct-2023
• Refers: ASTM E1064-23 - Standard Test Method for Water in Organic Liquids by Coulometric Karl Fischer Titration
• Effective Date: 15-Jul-2023
• Refers: ASTM D4175-23e1 - Standard Terminology Relating to Petroleum Products, Liquid Fuels, and Lubricants
• Effective Date: 01-Jul-2023
• Refers: ASTM D4175-23 - Standard Terminology Relating to Petroleum Products, Liquid Fuels, and Lubricants
• Effective Date: 01-Jul-2023

Overview

ASTM D6224-23 - Standard Practice for In-Service Monitoring of Lubricating Oil for Auxiliary Power Plant Equipment provides comprehensive guidelines for power plant operators and maintenance personnel on effective monitoring of mineral oil and phosphate ester lubricants used in auxiliary (non-turbine) power generation equipment. This standard supports condition-based maintenance by shifting oil change intervals from fixed schedules to data-driven decisions based on oil analysis results and performance trends, aiming to enhance equipment reliability, extend lubricant life, and minimize maintenance expenses.

Key Topics

• Lubricating Oil Monitoring: Focuses on sampling, testing, and analysis strategies for various auxiliary equipment-including gears, hydraulic systems, diesel engines, pumps, compressors, and electrohydraulic control (EHC) systems.
• Condition-Based Maintenance: Encourages oil changes based on lubricant condition rather than time or usage intervals, helping reduce unnecessary oil consumption and operating costs.
• Contamination & Degradation Control: Addresses risks such as component wear, oil degradation, and contamination (particulates, water, external and internal sources), providing guidance to prevent catastrophic equipment failures.
• Sampling Procedures: Recommends best practices for oil sample collection, handling, labeling, frequency, and representative sampling locations to ensure data accuracy and repeatability.
• Oil Type Coverage: Applies to mineral lubricating oils and phosphate ester fluids (commonly used in EHC systems), with limited scope for synthetic lubricants.

Applications

ASTM D6224-23 is tailored for in-service monitoring of lubricating oils in non-turbine auxiliary equipment within power generation facilities. Key applications include:

• Optimized Lubrication Management: Implementing systematic oil monitoring programs to base maintenance actions on actual lubricant condition, extending service life and reducing downtime.
• Early Detection of Equipment Issues: Identifying trends and deviations in oil analysis parameters to catch wear, contamination, or degradation before they lead to equipment failure.
• Quality Control of New Oil Deliveries: Standardizing procedures for sampling, examining, and acceptance of incoming lubricant supplies to avoid the use of off-spec or contaminated oils.
• Regulatory and Environmental Compliance: Supporting adherence to good safety, health, and environmental practices in line with international standards and local regulations.
• Cost Reduction: Lowering overall maintenance expenses by reducing unnecessary oil changes, labor, and waste disposal.
• Safety and Reliability Enhancement: Minimizing operational risks and ensuring the continuous, reliable operation of auxiliary power plant systems.

Related Standards

ASTM D6224-23 is part of a suite of international standards related to lubricating oil monitoring, some of which include:

• ASTM D4057 – Practice for Manual Sampling of Petroleum and Petroleum Products
• ASTM D4378 – Practice for In-Service Monitoring of Mineral Turbine Oils for Steam, Gas, and Combined Cycle Turbines
• ASTM D445 – Test Method for Kinematic Viscosity of Transparent and Opaque Liquids
• ISO 3448 – Industrial Liquid Lubricants – ISO Viscosity Classification
• ISO 4406 – Hydraulic Fluid Power – Methods for Coding the Level of Contamination by Solid Particles
• SAE J300 – Engine Oil Viscosity Classification
• SAE J306 – Automotive Gear Lubricant Viscosity Classification

These related standards provide additional methods and reference points for oil testing, terminology, and data interpretation, supporting a holistic approach to lubricant health monitoring and condition-based equipment maintenance.

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Keywords: ASTM D6224-23, lubricating oil monitoring, auxiliary power plant equipment, condition-based maintenance, lubricant contamination, oil degradation, mineral oils, phosphate ester lubricants, oil sampling, power generation standards.

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: D6224 − 23
Standard Practice for
In-Service Monitoring of Lubricating Oil for Auxiliary Power
Plant Equipment
This standard is issued under the fixed designation D6224; 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.
INTRODUCTION
A more systematic approach to monitoring auxiliary power plant equipment can help to minimize
the high cost of oil changes and unplanned shutdowns. These avoided costs must be balanced against
the cost of sampling and laboratory testing.
This practice is designed to help the user evaluate the condition of the lubricant through its life cycle
by carrying out a meaningful program of sampling and testing of oils in use. This practice is performed
in order to collect data and monitor trends which suggest any signs of lubricant deterioration and to
ensure a safe, reliable, and cost-effective operation of the monitored plant equipment.
1. Scope* ization established in the Decision on Principles for the
Development of International Standards, Guides and Recom-
1.1 This practice covers the requirements for the effective
mendations issued by the World Trade Organization Technical
monitoring of mineral oil and phosphate ester fluid lubricating
Barriers to Trade (TBT) Committee.
oils in service auxiliary (non-turbine) equipment used for
power generation. Auxiliary equipment covered includes gears,
2. Referenced Documents
hydraulic systems, diesel engines, pumps, compressors, and
electrohydraulic control (EHC) systems. It includes sampling 2.1 ASTM Standards:
and testing schedules and recommended action steps, as well as D92 Test Method for Flash and Fire Points by Cleveland
information on how oils degrade. Open Cup Tester
NOTE 1—Other types of synthetic lubricants are sometimes used but are
D95 Test Method for Water in Petroleum Products and
not addressed in this practice because they represent only a small fraction
Bituminous Materials by Distillation
of the fluids in use. Users of these fluids should consult the manufacturer
D257 Test Methods for DC Resistance or Conductance of
to determine recommended monitoring practices.
Insulating Materials
1.2 This practice does not cover the monitoring of lubricat-
D445 Test Method for Kinematic Viscosity of Transparent
ing oil for steam and gas turbines. Rather, it is intended to
and Opaque Liquids (and Calculation of Dynamic Viscos-
complement Practice D4378.
ity)
1.3 The values stated in SI units are to be regarded as D664 Test Method for Acid Number of Petroleum Products
standard. No other units of measurement are included in this by Potentiometric Titration
standard. D665 Test Method for Rust-Preventing Characteristics of
Inhibited Mineral Oil in the Presence of Water
1.4 This standard does not purport to address all of the
D892 Test Method for Foaming Characteristics of Lubricat-
safety concerns, if any, associated with its use. It is the
ing Oils
responsibility of the user of this standard to establish appro-
D893 Test Method for Insolubles in Used Lubricating Oils
priate safety, health, and environmental practices and deter-
D943 Test Method for Oxidation Characteristics of Inhibited
mine the applicability of regulatory limitations prior to use.
Mineral Oils
1.5 This international standard was developed in accor-
D974 Test Method for Acid and Base Number by Color-
dance with internationally recognized principles on standard-
Indicator Titration
This practice is under the jurisdiction of ASTM Committee D02 on Petroleum
Products, Liquid Fuels, and Lubricantsand is the direct responsibility of Subcom-
mittee D02.C0.01 on Turbine Oil Monitoring, Problems and Systems. For referenced ASTM standards, visit the ASTM website, www.astm.org, or
Current edition approved Nov. 1, 2023. Published November 2023. Originally contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM
approved in 1998. Last previous edition approved in 2022 as D6224 – 22. DOI: Standards volume information, refer to the standard’s Document Summary page on
10.1520/D6224-23. the ASTM website.
*A Summary of Changes section appears at the end of this standard
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
D6224 − 23
D1169 Test Method for Specific Resistance (Resistivity) of cants by Trend Analysis Using Fourier Transform Infrared
Electrical Insulating Liquids (FT-IR) Spectrometry
D1298 Test Method for Density, Relative Density, or API D7546 Test Method for Determination of Moisture in New
Gravity of Crude Petroleum and Liquid Petroleum Prod- and In-Service Lubricating Oils and Additives by Relative
ucts by Hydrometer Method Humidity Sensor
D1401 Test Method for Water Separability of Petroleum Oils D7464 Practice for Manual Sampling of Liquid Fuels, As-
and Synthetic Fluids sociated Materials and Fuel System Components for
D1500 Test Method for ASTM Color of Petroleum Products Microbiological Testing
(ASTM Color Scale) D7647 Test Method for Automatic Particle Counting of
D1533 Test Method for Water in Insulating Liquids by Lubricating and Hydraulic Fluids Using Dilution Tech-
Coulometric Karl Fischer Titration niques to Eliminate the Contribution of Water and Inter-
D2272 Test Method for Oxidation Stability of Steam Tur- fering Soft Particles by Light Extinction
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
D2422 Classification of Industrial Fluid Lubricants by Vis- Triphosphate in Fuel and Fuel-associated Water With
cosity System Sample Concentration by Filtration
D2668 Test Method for 2,6-di-tert-Butyl- p-Cresol and 2,6- D7720 Guide for Statistically Evaluating Measurand Alarm
di-tert-Butyl Phenol in Electrical Insulating Oil by Infra- Limits when Using Oil Analysis to Monitor Equipment
red Absorption and Oil for Fitness and Contamination
D2896 Test Method for Base Number of Petroleum Products D7843 Test Method for Measurement of Lubricant Gener-
by Potentiometric Perchloric Acid Titration ated Insoluble Color Bodies in In-Service Turbine Oils
D2982 Test Methods for Detecting Glycol-Base Antifreeze using Membrane Patch Colorimetry
in Used Lubricating Oils D7978 Test Method for Determination of the Viable Aerobic
D3427 Test Method for Air Release Properties of Hydrocar- Microbial Content of Fuels and Associated Water—
bon Based Oils Thixotropic Gel Culture Method
D3524 Test Method for Diesel Fuel Diluent in Used Diesel D8506 Guide for Microbial Contamination and Biodeterio-
Engine Oils by Gas Chromatography ration in Turbine Oils and Turbine Oil Systems
D4052 Test Method for Density, Relative Density, and API E1064 Test Method for Water in Organic Liquids by Coulo-
Gravity of Liquids by Digital Density Meter metric Karl Fischer Titration
D4057 Practice for Manual Sampling of Petroleum and F311 Practice for Processing Aerospace Liquid Samples for
Petroleum Products Particulate Contamination Analysis Using Membrane Fil-
D4175 Terminology Relating to Petroleum Products, Liquid ters
Fuels, and Lubricants F312 Test Methods for Microscopical Sizing and Counting
D4378 Practice for In-Service Monitoring of Mineral Tur- Particles from Aerospace Fluids on Membrane Filters
bine Oils for Steam, Gas, and Combined Cycle Turbines 2.2 ISO Standard:
D4739 Test Method for Base Number Determination by
ISO 3448:1992 Industrial liquid lubricants—ISO viscosity
Potentiometric Hydrochloric Acid Titration classification
D5185 Test Method for Multielement Determination of ISO 4406:1999 Hydraulic fluid power—Fluids—Method for
Used and Unused Lubricating Oils and Base Oils by coding the level of contamination by solid particles
Inductively Coupled Plasma Atomic Emission Spectrom-
2.3 SAE Standards:
etry (ICP-AES) J300 Engine Oil Viscosity Classification
D6304 Test Method for Determination of Water in Petro- J306 Automotive Gear Lubricant Viscosity Classification
leum Products, Lubricating Oils, and Additives by Cou-
3. Terminology
lometric Karl Fischer Titration
D6810 Test Method for Measurement of Hindered Phenolic 3.1 Definitions:
Antioxidant Content in Non-Zinc Turbine Oils by Linear
3.1.1 For definitions of terms used in this practice, refer to
Sweep Voltammetry Terminology D4175.
D6971 Test Method for Measurement of Hindered Phenolic
4. Significance and Use
and Aromatic Amine Antioxidant Content in Non-zinc
Turbine Oils by Linear Sweep Voltammetry
4.1 This practice is intended to help users, particularly
D7155 Practice for Evaluating Compatibility of Mixtures of
power plant operators, maintain effective control over their
Turbine Lubricating Oils
mineral lubricating oils and lubrication monitoring program.
D7414 Test Method for Condition Monitoring of Oxidation
This practice may be used to perform oil changes based on oil
in In-Service Petroleum and Hydrocarbon Based Lubri-
Available from American National Standards Institute (ANSI), 25 W. 43rd St.,
4th Floor, New York, NY 10036, http://www.ansi.org.
3 5
The last approved version of this historical standard is referenced on Available from SAE International (SAE), 400 Commonwealth Dr., Warrendale,
www.astm.org. PA 15096, http://www.sae.org.
D6224 − 23
condition and test results rather than on the basis of service protection properties will assist in keeping system metals in
time or calendar time. It is intended to save operating and satisfactory condition.
maintenance expenses.
5.4 Diesel Engine Oils—In addition to the typical role of
4.2 This practice is also intended to help users monitor the lubricating oils which is to lubricate, clean, cool and seal,
condition of mineral lubricating oils and guard against exces- diesel engine oils are formulated to provide protection from
sive component wear, oil degradation, or contamination, acids and disperse soot particles that are created during the
thereby minimizing the potential of catastrophic machine combustion process. Diesel engine oils are compounded with
problems that are more likely to occur in the absence of such alkaline additives to neutralize the sulfuric acids that are
an oil condition monitoring program. produced when the diesel fuel is combusted. They are also
compounded with dispersant/detergents to keep the engine
4.3 This practice does not necessarily reference all of the
clean and the by-products of combustion (fuel soot) suspended.
current oil testing technologies and is not meant to preclude the
The combination of wear regimes found in the diesel engine
use of alternative instrumentation or test methods that provide
require the lubricants to have high levels of anti-wear additives
meaningful or trendable test data, or both. Some oil testing
to protect the engine from wear during the most severe
devices and sensors (typically used for screening oils that will
condition. Multi-grade lubricants (high viscosity index) are
be tested according to standard methods) provide trendable
often employed in diesel engine lubricants that are required to
indicators that correlate to water, particulates, and other con-
operate over a wide temperature range.
taminants but do not directly measure these.
5.5 Turbine Oils or Circulating Oils, or Both—These oils
4.4 This practice is intended for mineral oil products, and
provide satisfactory lubrication and cooling of bearings and
not for synthetic type of products, with the exception of
gears (for example, in auxiliary turbines, pumps and gearboxes
phosphate esters fluids typically used in power plant control
as circulating oils). They also can function as a governor
systems.
hydraulic fluid. The oil must have a viscosity high enough to
maintain a sufficiently thick film of oil on load-bearing
5. General Properties of Lubricating Oils
surfaces, but low enough to minimize energy losses while
5.1 In general, lubricating oils are designed to reduce providing adequate cooling. These oils are recommended
friction and wear, provide cooling, control deposits, and where the degree of loading on bearings and gears is less than
combat the effects of contamination. A base oil’s lubricating in gear oil applications. Turbine or circulating oils, or both,
properties are enhanced by selected additives. Different ma- have excellent oxidation resistance and contain rust inhibitors;
chines have different lubricant additive requirements, some of they are often referred to as rust and oxidation inhibited (R&O)
which are described in this section. Proper lubrication mini- oils. They can also contain additives to improve water separa-
mizes or precludes contact between metal surfaces and reduces bility and decrease foaming tendency.
component wear.
5.6 Compressor Oils—In addition to possessing the correct
5.2 Gear Oils—The primary requirement of gear oils is that viscosity for satisfactory bearing and cylinder lubrication,
they prevent wear and minimize other forms of damage such as particularly for air compressors, very good oxidation resistance
pitting and scuffing by maintaining a lubricant film between the is required to avoid degradation of the lubricant in the presence
moving surfaces. of heated air. This is particularly important for mineral oils
where discharge temperatures are high, since carbon and
5.3 Hydraulic Oils—A hydraulic fluid is required to transmit
oxidized oil deposits may autoignite if exposed continuously to
hydraulic pressure and energy, minimize friction and wear in
temperatures above 148 °C. The fire potential that exists under
pumps, valves, and cylinders, and protect metal surfaces
these conditions make low volatility and high auto-ignition
against corrosion. To obtain optimum efficiency of machine
values equally or more important than high-flash or fire points.
operation and control, the viscosity of the oil should be low
In compressor lubrication, condensed water is present fre-
enough to minimize frictional and pressure losses in piping.
quently. For this reason, the oil must possess properties that
However, it also is necessary to have a sufficiently high
ensure that the oil rather than water wets the metal surfaces.
viscosity to provide satisfactory wear protection and minimize
Also, to avoid the accumulation of water-in-oil emulsions in
leakage of the fluid. High-viscosity index fluids help to
the after coolers, the water should separate out rather than form
maintain a satisfactory viscosity over a wide temperature
an emulsion.
range. The anti-wear properties of high-quality hydraulic oils
usually are improved by suitable additives. Since the clear- 5.7 Electrohydraulic Control (EHC) Fluids—Triaryl phos-
ances in pumps and valves tend to be critical, it is important to phate ester EHC fluids are inherently fire-resistant and main-
provide adequate filtration equipment (full flow or bypass, or tain this property throughout their service life. The very low
both) to maintain a minimum particle content and thus mini- vapor pressure and chemical nature of these fluids result in
mize wear. The antioxidant additives in the hydraulic oil high flash point, fire point, and autoignition temperature. EHC
should give the oil good oxidation stability to avoid the fluids should be continuously purified using bypass systems to
formation of insoluble gums or sludges; the oil should have maintain acid number, moisture, and particulates at low levels.
good water separation properties, and, because air may be Moisture can cause hydrolysis of EHC fluids which results in
entrained in the system, the oil should have good air-release elevated acid number. Components constructed of copper and
properties and resistance to foaming. Similarly, good rust lead alloys should be avoided. These fluids are chemically
D6224 − 23
different from mineral oils; consequently, the interpretation of be avoided. When oils must be mixed, testing should be
test results will be significantly different. The fluid supplier performed in an attempt to determine compatibility in accor-
should be consulted if there is a question about interpretation of dance with Practice D7155. Consideration should be given to
analytical results. consulting the lubricant supplier(s) and equipment manufac-
turer prior to mixing oils.
6. Operational Factors Affecting the Service Life of Oils
6.2 Deterioration of Oils in Service—Air (oxygen), elevated
6.1 New Oil Quality and Suitability for Intended Use—Use temperatures, metals, and water (moisture) are present to some
extent in lubricating systems. Record these factors that pro-
of high-quality oils that meet recognized standards (such as
manufacturer military specifications and OEM specifications) mote lubricant degradation. Lubricant deterioration occurs by
one or more of the following processes:
is the best assurance of potentially long service life. Careful oil
storage is important to prevent the degradation of the lubricant
6.2.1 Oxidative Degradation—This process occurs as the
while in storage or being dispensed. Accurate labeling of result of chemical changes brought about by oxygen in the
lubricant containers is vital to ensure proper identification.
atmosphere and proceeds by a chain reaction that is with the
6.1.1 Viscosity is the most important characteristic of an oil. presence of water, heat, and certain metals. The results of
Oil load bearing and lubricating properties are related to its oxidation can consist of AN increase, viscosity (KV) increase),
viscosity. The use of oil with incorrect viscosity can increase or sludge and varnish deposits, or a combination thereof as
wear rates, heat build-up, and lube degradation. In extreme end-products within the lubricating system.
cases, the use of oils with incorrect viscosities can result in
6.2.2 Thermal Degradation—This process occurs in the
rapid catastrophic failures. absence of oxygen and at much higher temperatures. Typically,
6.1.2 Oils that meet the equipment manufacturers’ require- temperatures of more than 300 °C may cause the hydrocarbon
ments should be used. For situations where the manufacturer molecule to crack and produce various degradation species.
simply offers a generic viscosity classification without specific Some of these species are low molecular weight by-products
performance criteria, the user should consult the equipment that evaporate or burn (producing a noticeable “burnt” smell in
manufacturer, lubricant suppliers, and experts in the field of the oil) and other degradation species are high molecular
lubrication. weight by-products that form sludge and varnish.
6.1.3 When fresh, unused lubricants are received, it is 6.2.3 Lubricant Deposits and Sludge (Lacquering/
advisable to obtain typical test data from the oil supplier. Upon Varnishing)—As lubricants degrade either through thermal and
receipt of the first oil charge, take a sample of oil to confirm the mechanical forces, they may produce submicron, high molecu-
typical test data. lar weight, polar insoluble particles. These particles may
agglomerate, become insoluble in the oil, as it is non-polar in
6.1.3.1 Because systems usually contain some residual oil,
(whether from a previous charge or a flush) the baseline sample nature, and adsorb onto the metal parts of a lubricating system.
Some highly refined base oils used in the manufacturing of
to be used for condition monitoring comparisons should be
taken after the new oil is charged and circulated for up to 24 h lubricants (API Group II and above) may be less tolerant to the
presence of these degradation by-products due to their high
(depending on the size of the reservoir and turnover time).
purity and lower solvency. Base oils with proper formulation
6.1.3.2 This baseline should be the reference sample for the
can result in low deposit tendency oils. Deposits (such as
physical and chemical properties of the fluid, and for future
varnish) could be very costly to an equipment operator, as they
comparisons with in-service oil information. This is most
may deposit on bearing and turning gear surfaces increasing
important! Recommended tests for new oil are given in the
wear, settle in servo-valves causing valves to stick and seize,
schedules of this practice. (Warning—Physical and chemical
coat heat exchangers lowering their performance and form in
properties of lubricants after installation may not match results
reservoirs acting as a catalyst to further degradation. If deposits
obtained for new oil as received from the supplier.)
are found in the system, analysis can be performed on the
(Warning—Storage conditions affect the shelf life of lubri-
deposit to identify possible root causes. The insoluble polar
cants. Manufacturing shelf life recommendations should be
compounds (soft contaminants) may be removed by the use of
followed. If no shelf life guidance information is available and
varnish separation technologies and through carefully per-
the lubricants is greater than two years old, the lubricant
formed high velocity flushes.
manufacturer should be consulted to confirm suitability for
6.2.3.1 When these conditions of lubricants deposits and
use.)
sludge occur, dramatic reductions in the viscosity of the oil are
6.1.4 Manufacturer shelf life recommendations should be
possible and the flash point of the resulting fluid can also
observed. Oils should be stored to preserve their original
change.
quality and prevent contamination. Stored oils may be tested to
ensure and document their quality, cleanliness, and continued 6.2.4 Hydrolysis—Hydrolysis is a mode of degradation in
the presence of moisture. This is very important for phosphates
suitability for their intended use. It is suggested that oil
manufacturers’ recommendations be followed when storing (and other esters) and may also have an effect on additive
systems in oil-based products. The major characteristic of
lubricants to ensure maximum product life.
hydrolysis is the generation of corrosive acids in the fluids.
6.1.5 Make-up oils should normally be of the same type,
quality, and manufacturer. Available formulations may change 6.2.5 Loss of Additives—Additives are used to protect the oil
over a period of time. Lubricant incompatibility can arise from and enhance its performance abilities. When these additives are
mixing differing base stocks and additive packages and should depleted as a result of service, the performance of the oil will
D6224 − 23
be reduced as a consequence of oil oxidation, foaming, 7.1.1 Microbiological Testing—When sampling in order to
excessive wear, or premature rusting. perform microbiological testing, refer to Practice D7464 and
6.2.6 New Oil Make-up Rate—Addition of new oil is Guide D8506 for guidance on sample collection and handling.
required in nearly every system to make up for losses due to
7.2 Representative Sampling—A representative sampling
leakage, filter changes, or other maintenance. Monitor the
location is a sampling location that supports repeatable and
amount and frequency of added make-up oil, since they play a
representative lubricant sampling to monitor the health of the
very significant part in determining the life of a system oil
equipment and the properties of the lubricant. Collect oil
charge.
samples when machines or equipment are running at normal
6.3 Contamination—Contamination of lubricating oils oc-
operating temperatures, loads, pressures and speeds. To ensure
curs both from outside and from within the system. Common
that insoluble material is suspended evenly throughout the
types of contamination are: debris introduced at initial startup
system. A fluid sample is probably not representative if: (1) the
or after an overhaul, lubricant degradation byproducts, com-
system fluid is hot while the sample is cold, (2) the fluid in the
ponent wear debris, airborne particulates, and water (moisture).
system is one color or clarity in an in-line sight glass while the
Contamination is often the most significant factor affecting oil
sample is a different color or clarity, and (3) the fluid viscosity
service life. Contamination of oil is a valid reason to change oil
of the reservoir fluid is different from that of the sample when
and flush to restore system cleanliness.
both are at the same temperature. Samples should be taken in
6.3.1 Condition of Equipment on Start-up—Oil system con-
the same manner each time to allow reliable trending of oil
tamination prior to start-up usually consists of preservatives,
properties.
paint, moisture, rust particles, and construction debris such as
7.2.1 It should be noted that on occasion a sample may be
dust, dirt, or welding spatter. Whenever practical, flushing the
requested which will not be representative. At that time,
system before starting operation is recommended. Fluid clean-
sampling instructions, as specified by the requestor, must be
liness should be brought to a level of one to two ISO FDIS
followed. For example, a sample might be taken off the top or
4406.2 classes below warning levels before beginning opera-
the bottom of a tank to check for contamination. In all cases,
tion. If flushing is not performed, oils should be tested soon
the sample point should be marked on the sample container.
after startup or repair to verify their cleanliness.
7.3 Sampling Location—Assign sample location upstream
6.3.2 External Contamination-Solids—Solid contamination
of filters and downstream of machine components such as
consists of any material small enough to pass through bearing
bearings and gears to obtain the best data. The sampling
seals and vents or which can be introduced with make-up oil.
downstream of the filters is only advised to determine the
From whatever source, contamination must be dealt with by
efficiency (beta-ratio) of filters or filtration systems.
monitoring oil condition and using purification devices such as
filters and centrifuges on a regular basis.
7.4 Flushing Procedures—Always flush a sample line be-
6.3.3 External Contamination-Liquid—Coolant leaks, mois-
fore a sample is taken and flushing will be achieved by flushing
ture or steam condensation, or introduction of improper lubri-
properly the sampling valves, devices, and hardware thor-
cating oils can compromise the oil. Accumulated water pro-
oughly prior to taking oil samples.
motes oil degradation as well as interfering with lubrication.
7.4.1 The flushing is usually accomplished using a spare
Contamination with an improper lubricant is not easily cor-
container/bottle to catch the purged fluid. It is important to
rected without a complete oil change. An oil monitoring
flush 5 to 10 times the dead space volume before obtaining the
program may be used to monitor and identify contaminants
sample.
likely to be encountered in service.
7.4.2 All hardware that the oil comes into contact with is
6.3.4 Internal Contamination—Contaminants include wear
considered dead space and must be flushed, including, system
debris, oil degradation products, and microbial growth. The
dead-legs, sampling ports, valves and adapters, probe on
types of internal contaminants will vary by equipment type and
sampling devices, adapters for using vacuum sample extraction
oil type; the rate of generation will be highly dependent on the
pumps, as well plastic tubing used for vacuum pumps (this
equipment operating conditions. The analysis methods em-
tubing should not be reused to avoid cross-contamination
ployed must be able to identify expected wear debris and
between oils).
degradation products. Testing frequencies should be sufficient
7.4.3 After opening the sample port and flushing, fill the
to account for operating conditions.
sample container/bottle to approximately 50 % of its capacity
with the oil—leave enough void to allow shaking of the sample
7. Sampling
prior to testing. In case of flash point testing, for most accurate
7.1 General—When taking lubricant samples from storage
testing, reduce the head space volume.
tanks or equipment in service, it is important that the extracted
sample is representative and is taken from a specified loca- 7.5 Documenting Sampling Procedures—To ensure that
tion(s) to monitor the properties of the lubricant. The following each sample is taken in the same manner and from the same
are some suggested guidelines for proper sampling technique point, the operator defines and documents oil sampling proce-
and sample handling techniques. (See also Practice D4057.) dures for each system such as: (1) tools needed, (2) line
The user should have written procedures to insure that samples flushing requirements, (3) sampling locations, (4) sampling
are taken consistently according to good maintenance prac- methods, (5) safety requirements, and (6) sample bottle label-
tices. ing.
D6224 − 23
7.5.1 It should be noted that on occasion a sample may be 7.8.7 Type of fluid sampled,
requested which will not be representative. At that time,
7.8.8 Sampling point,
sampling procedures, as specified by the requestor, must be
7.8.9 System operating temperature and temperature of oil
followed. For example, a sample might be taken off the top or
at sampling point,
the bottom of a tank to check for contamination. In all cases,
7.8.10 Type of purification system (filters, centrifuge, and so
the sample point should be marked on the sample container/
forth),
bottle.
7.8.11 Make-up (volume) since last sample was taken, and
7.6 Oil Sampling Frequency—Take oil samples at a speci- 7.8.12 Coolant additives.
fied frequency; this will ensure that any problems are identified
7.9 Sampling of New Oil Deliveries—Thoroughly clean all
early. Sampling frequencies will be set specifically for each
sampling devices before use to avoid cross-contamination.
machine or piece of equipment, since each is unique in its
7.9.1 Take samples representative of the fluid being exam-
intended performance, condition, locality, operating
ined but obtained from the point(s) most indicative of gross
environment, and maintenance schedule.
contamination by debris and water, that is, just above the
7.7 Oil Sample Container/Bottles—Take oil samples in oil
bottom of the drum or tanker compartment bottom.
sample containers or bottles which should be:
7.9.2 When consignments of oil are in drums, sample them
7.7.1 Clean—If in doubt about its cleanliness, use another
in accordance with Practice D4057.
sample container/bottle. If this is not possible, flush it out with
7.9.3 In cases where the product is suspected of being
the fluid to be sampled. Take special care to ensure that sample
non-uniform, sample a larger number of drums. Where con-
containers/bottles for water separability, particle count, and
tamination is suspected, there may be no alternative to sam-
wear debris testing are clean.
pling every drum.
7.7.2 Resistance to the Material Being Sampled—For
7.9.4 For bulk consignments, sample each tanker compart-
example, fire-resistant phosphate ester fluids will dissolve
ment. If these are clear of debris and water, then the samples
certain plastics. (This includes the liner in bottle caps.) To
can be combined for subsequent laboratory analysis of the
verify the sample container/bottle’s resistance, if time permits,
consignment. The user may decide to perform a limited
allow the sample to stand in the sample container/bottle and
number of tests on individual compartment samples; a com-
observe its effects. Aluminum foil or polytetrafluoroethylene
posite sample may be tested for other properties.
(PTFE) make good, resistant cap liners.
7.9.5 From tanker deliveries, sample individual tanker com-
7.7.3 Appropriate for Required Handling—Sample
partments. The sample should be taken preferably from the
containers/bottles with leaking tops and glass sample
outlet of the flexible pipework or at least from the tanker
containers/bottles improperly protected are not suitable for
bottom valve manifold. This is important because the tanker
shipment. Stringent packaging requirements must be followed
contents can become contaminated by residual material left in
if shipment is to be made by air.
the bottom valve manifold. This can occur particularly when
7.7.4 Appropriate for the Analyses Required—As an
different products are being carried in separate compartments
example, some plastic sample containers/bottles may not be
or previous deliveries of a different product have been made to
acceptable for flash point testing (per Test Method D92)
other locations without subsequent adequate cleaning and
because volatile materials may leak through the container/
flushing. Dead leg piping should always be drained and flushed
bottle walls. Use sample containers/bottles of either glass or
prior to sampling.
polyethylene for wear debris analysis samples (to avoid mate-
7.9.6 Bottom samples (if desired) must be collected by
rial leaching).
either a tube or thief sampler (for example, Bacon bomb).
These samplers permit collection of settlings on the bottom of
NOTE 2—Some lubricant suppliers and commercial testing laboratories
provide sample containers/bottles that meet all these requirements. Use the containers without introducing false contamination by
these whenever possible. If frequent samples are taken, an adequate
scraping the container lining or wall.
supply of containers/bottles should be kept.
7.10 Preservation of Sample and Analysis of Oil
NOTE 3—For samples intended for microbiological testing, see Practice
D7464. Although the guidance provided in Practice D7464 is nominally
Samples—It is generally advised to ship the oil samples
for fuel sample collection, the procedures provided are equally applicable
immediately to the oil analysis laboratory, as ideally, oil should
to turbine oils.
be analyzed within as soon as reasonably achievable after
7.8 Sample Labeling—Properly label a sample container/
being sampled. If oil samples are stored for an extended period
bottle in order to track the history of a particular piece of
of time, this may result in a non-representative sample.
equipment. The equipment must be identified uniquely. Labels
7.10.1 If the samples are to be retained for extended periods
should include the following information as appropriate:
of time, special arrangements should be made in agreement
7.8.1 Customer name,
with the oil analysis laboratory to ensure that the integrity of
7.8.2 Site (or plant name),
the sample is not compromised. The special arrangement may
7.8.3 Location (unit number, tank number, compartment
include storing in dark amber glass bottles in an ambient
number, and so forth),
temperature area as the longer an oil sample is stored in the
7.8.4 Equipment serial number (or other ID), container/bottle, the more oxidation products will be generated.
7.8.5 Oil and machine service hours,
7.10.2 Store the sample(s) away from strong light and as
7.8.6 Date sample taken, close to room temperature as possible.
D6224 − 23
8. Examination of New Oil on Delivery nation can also be a problem when the lubricant comes in
contact with dirty or poorly maintained equipment. Final
8.1 Experience has shown the need for standardizing pro-
filtration while filling equipment may be used in lieu of or in
cedures and acceptance criteria for the sampling, examination,
addition to particle counting. The final filter should be as fine
and acceptance of incoming supplies of lubricating oil. It is
or finer than the lubrication system filter of the equipment
essential that personnel responsible for sampling and testing
being filled.
have the necessary experience and skills, and that scrupulous
attention to detail be applied at all times to avoid erroneous
8.3 Sampling of incoming supplies should be in accordance
results.
with proper sampling procedures (see Section 7).
8.2 It is equally essential that all incoming supplies of oil be
8.4 All samples should be immediately examined for ap-
adequately monitored to guard against incorrect or contami-
pearance.
nated material being delivered. This information can be used
from quality control of in-coming fluid as well as future fluid
8.5 Testing schedule guidelines for various types of new oils
reference data. The cleanliness of the delivery container should
are provided in Table 1. With drums, tests should be completed
be noted; if the container is dirty on the outside, there may be
on a composite (or bulked) sample before the oil is used in
particulate contamination of the oil inside. Particulate contami-
A
TABLE 1 Guidelines for Sampling and Testing New Oils
NOTE 1—Legend–R = Recommended; O = Optional.
NOTE 2—An infrared spectrum may be obtained for new oil to ensure that the oil is not contaminated and to provide a baseline for comparison to spectra
of in-service oil.
Diesel Air EHC EHC
Common Hydraulic Turbine/
Test Gear Oils Engine Compressor (PO (Mineral
Methods Oils Circulating Oils
B
Oils Oils Esters) Oils)
C
Appearance Visual R R R R R R
D
Viscosity, (40 °C) D445 R R O R R R R
Viscosity (100 °C) D445 R
Acid number D664 R R R R R R
D974
E F F F F F F
Water D6304 O O R O O R O
D95/D7546
Antioxidants/Oxidation inhibitor D2668 O O
G G G
D6971 O O
Oxidation stability (RPVOT) D2272 O O
API gravity or density D1298 O
D4052
Flash point (COC) D92 O
Water separability D1401 O O
Particle counts Equipment R O O
Manufacturer’s
Method
Base number D974 R
D2896
D4739
Electrical resistivity D257/D1169 R
H
Elemental Analysis D5185 O O O O O O O
A
Tests which are performed on in-service oils for trending purposes should also be performed on new oils for baseline information.
B
Does not include refrigeration (chiller) oils.
C
Appearance includes observations such as color, clarity, odor, and sediment.
D
A diesel engine oil must be tested at 40 °C and 100 °C if it is necessary to determine whether it is the proper multi-grade oil.
E
Test Method D6304 Procedure C is recommended for lube oils.
F
Recommended if oil is not clear and bright.
G
Test Method D6971 is not recommended for zinc-based lubricating oils.
H
Another spectrochemical method such as rotating disk electrode (RDE), atomic absorption (AA), or x-ray fluorescence (XRF) may be substituted for the ICP method.
D6224 − 23
service. Individual samples should be retained until the bulk increase in acid number above the value for new oil indicates
sample is passed as satisfactory. the presence of acidic oxidation products or, less likely,
contamination with acidic substances. The acid numbers deter-
8.6 With tanker deliveries, the additional tests to be com-
mined by these two test methods are not identical and only
pleted before the tanker is discharged can only be judged from
loosely correlate; a single method should be used consistently.
the risk involved by the acceptance of non-specification
The use of Test Method D974 on aged phosphate ester fluids
product. That is, can the charge be readily recovered and
which have significantly darkened in color, and especially
corrected before passing into service if the subsequent tests
those which have been dyed prior to use, is not recommended.
indicate this is necessary.
9.4 Water Content—If a mineral oil is clear and bright, the
8.7 Handling and dispensing methods contribute to the
amount of dissolved water present is of little significance. Most
required health and cleanliness specifications of the lubricant.
mineral oils will remain clear with up to 75 μg ⁄g water at room
All sources and opportunities of contamination must be
temperature. Phosphate ester fluids can hold more than
avoided.
1000 μg ⁄g water at ambient temperature and still be clear and
8.8 The product specifications for new oils should be clearly
bright. The presence of water determined by screening meth-
communicated between the user and supplier. If a sample of oil
ods (such as the hot plate splatter test for mineral oils) may be
fails to meet the product specifications agreed upon by user and
confirmed using a standard test method. Adequate lubrication
supplier, the sample should be retested to verify the initial test
cannot be maintained by an oil which contains a significant
result. A resample should be taken and tested if needed to
quantity of water. The analytical range for Test Method D95 is
verify that the sample is representative of the shipment. If the
0.05 % to 25 % and the range for Test Method D6304 is
retest or resample still fails to meet product specification, an
50 μg ⁄g to 1000 μg ⁄g. Other methods (such as Test Methods
investigation should be made to determine whether the prob-
D1533 and E1064) are available for measuring the water
lem is due to transportation, handling, or product formulation.
content in oils.
The user must recognize that typical values are not the same as
9.5 Antioxidants Level—The measurement of antioxidant
purchase specifications.
concentration is important for monitoring the oxidation of
9. Significance of Tests
industrial lubricants and their remaining useful life. Existing
practices for measuring the concentration of phenolic (or
9.1 In determining the condition of the oil and equipment
amine) antioxidants include infrared spectrometry Test Method
for continued service, important properties of in-service oils
D2668 and linear sweep voltammetry Test Method D6971 or
include:
D6810.
9.2 Viscosity—Most commercial turbine oils are sold under
9.5.1 FTIR—The Fourier Transform Infrared (FTIR) by Test
ISO (International Standards Organization) viscosity classifi-
Method D7414 is a refined infrared spectroscopy method,
cation system. Typical turbine fluids fall into ISO VG-32,
which can be used to monitor the remaining antioxidants
VG-46, VG-68 and higher viscosity grades corresponding to
2 2 2
blended into the oil. It can also be used to monitor the increase
32 mm /s, 46 mm /s, 68 mm /s at 40 °C (Classification
in oxidation products as the oil degrades. Each antioxidant is a
D2422). The viscosity of gear oils is classified using either
specific chemical substance and will absorb infrared light at
ISO 3448 or D2422 viscosity classification for industrial gear
particular wavelengths and absorptivities; some antioxidants
oils or SAE J306 for automotive gear oils. The viscosity of
may not be detectable by infrared spectroscopy. (Test Method
diesel engine oils is classified according to SAE J300. The
D2668 may be used for antioxidants if the wavelengths and
viscosity (for example, for multi-grade oils) can be measured at
absorptivities are known.)
40 °C and 100 °C in order to calculate the viscosity index and
9.5.2 Linear Sweep Voltammetry—Voltammetry is an elec-
determine that the correct oil has been used. The main purpose
trochemical test technique, which can be used for measuring
for checking the viscosity of in-service oil is to determine if the
many antioxidant additives. The technique applies a voltage
correct oil is being used and to detect contamination. In
ramp through a 3 electrode sensing system and measures the
extreme cases, in-service oils will experience a significant
current flow that occurs when the applied voltage equals the
increase in viscosity due to thermal or oxidative degradation.
oxidation potential of the antioxidant. The potential at peak
Contamination can cause the viscosity to either increase or
current is diagnostic for the antioxidant, and the amplitude of
decrease, depending on the contaminant. Emulsified water and
the peak is proportional to the concentration of the antioxidant.
diesel fuel soot will increase the viscosity, while diesel fuel,
Antioxidants such as hindered phenols and amines can be
Freon, or solvents will decrease the viscosity. Dissolved water
measured by Test Method D6971 or D6810.
in phosphate ester fluids can reduce the fluid viscosity slightly.
Contamination from a different lubricant can change the
9.6 Oxidation Stability (Rotary Pressure Vessel Oxidation
viscosity of the oil in either direction. The method normally
Test, RPVOT)—One of the most important properties of new
used for viscosity determinations is Test Method D445.
oil containing oxidation inhibitor is its ability to resist oxida-
9.3 Acid Number—The test most used to indicate the extent tion while in service. This is accomplished by the addition of
of oxidation is the acid number (Test Method D664 or D974). antioxidants. Measuring the concentration of the antioxidant
Wi
...

This document is not an ASTM standard and is intended only to provide the user of an ASTM standard an indication of what changes have been made to the previous version. Because
it may not be technically possible to adequately depict all changes accurately, ASTM recommends that users consult prior editions as appropriate. In all cases only the current version
of the standard as published by ASTM is to be considered the official document.
Designation: D6224 − 22 D6224 − 23
Standard Practice for
In-Service Monitoring of Lubricating Oil for Auxiliary Power
Plant Equipment
This standard is issued under the fixed designation D6224; 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.
INTRODUCTION
A more systematic approach to monitoring auxiliary power plant equipment can help to minimize
the high cost of oil changes and unplanned shutdowns. These avoided costs must be balanced against
the cost of sampling and laboratory testing.
This practice is designed to help the user evaluate the condition of the lubricant through its life cycle
by carrying out a meaningful program of sampling and testing of oils in use. This practice is performed
in order to collect data and monitor trends which suggest any signs of lubricant deterioration and to
ensure a safe, reliable, and cost-effective operation of the monitored plant equipment.
1. Scope*
1.1 This practice covers the requirements for the effective monitoring of mineral oil and phosphate ester fluid lubricating oils in
service auxiliary (non-turbine) equipment used for power generation. Auxiliary equipment covered includes gears, hydraulic
systems, diesel engines, pumps, compressors, and electrohydraulic control (EHC) systems. It includes sampling and testing
schedules and recommended action steps, as well as information on how oils degrade.
NOTE 1—Other types of synthetic lubricants are sometimes used but are not addressed in this practice because they represent only a small fraction of the
fluids in use. Users of these fluids should consult the manufacturer to determine recommended monitoring practices.
1.2 This practice does not cover the monitoring of lubricating oil for steam and gas turbines. Rather, it is intended to complement
Practice D4378.
1.3 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.
1.4 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility
of the user of this standard to establish appropriate safety, health, and environmental practices and determine the applicability of
regulatory limitations prior to use.
1.5 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.
This practice is under the jurisdiction of ASTM Committee D02 on Petroleum Products, Liquid Fuels, and Lubricantsand is the direct responsibility of Subcommittee
D02.C0.01 on Turbine Oil Monitoring, Problems and Systems.
Current edition approved April 1, 2022Nov. 1, 2023. Published April 2022November 2023. Originally approved in 1998. Last previous edition approved in 20162022 as
D6224D6224 – 22. – 16. DOI: 10.1520/D6224-22.DOI: 10.1520/D6224-23.
*A Summary of Changes section appears at the end of this standard
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
D6224 − 23
2. Referenced Documents
2.1 ASTM Standards:
D92 Test Method for Flash and Fire Points by Cleveland Open Cup Tester
D95 Test Method for Water in Petroleum Products and Bituminous Materials by Distillation
D257 Test Methods for DC Resistance or Conductance of Insulating Materials
D445 Test Method for Kinematic Viscosity of Transparent and Opaque Liquids (and Calculation of Dynamic Viscosity)
D664 Test Method for Acid Number of Petroleum Products by Potentiometric Titration
D665 Test Method for Rust-Preventing Characteristics of Inhibited Mineral Oil in the Presence of Water
D892 Test Method for Foaming Characteristics of Lubricating Oils
D893 Test Method for Insolubles in Used Lubricating Oils
D943 Test Method for Oxidation Characteristics of Inhibited Mineral Oils
D974 Test Method for Acid and Base Number by Color-Indicator Titration
D1169 Test Method for Specific Resistance (Resistivity) of Electrical Insulating Liquids
D1298 Test Method for Density, Relative Density, or API Gravity of Crude Petroleum and Liquid Petroleum Products by
Hydrometer Method
D1401 Test Method for Water Separability of Petroleum Oils and Synthetic Fluids
D1500 Test Method for ASTM Color of Petroleum Products (ASTM Color Scale)
D1533 Test Method for Water in Insulating Liquids by Coulometric Karl Fischer Titration
D2272 Test Method for Oxidation Stability of Steam Turbine Oils by Rotating Pressure Vessel
D2273 Test Method for Trace Sediment in Lubricating Oils (Withdrawn 2022)
D2422 Classification of Industrial Fluid Lubricants by Viscosity System
D2668 Test Method for 2,6-di-tert-Butyl- p-Cresol and 2,6-di-tert-Butyl Phenol in Electrical Insulating Oil by Infrared
Absorption
D2896 Test Method for Base Number of Petroleum Products by Potentiometric Perchloric Acid Titration
D2982 Test Methods for Detecting Glycol-Base Antifreeze in Used Lubricating Oils
D3427 Test Method for Air Release Properties of Hydrocarbon Based Oils
D3524 Test Method for Diesel Fuel Diluent in Used Diesel Engine Oils by Gas Chromatography
D4052 Test Method for Density, Relative Density, and API Gravity of Liquids by Digital Density Meter
D4057 Practice for Manual Sampling of Petroleum and Petroleum Products
D4175 Terminology Relating to Petroleum Products, Liquid Fuels, and Lubricants
D4378 Practice for In-Service Monitoring of Mineral Turbine Oils for Steam, Gas, and Combined Cycle Turbines
D4739 Test Method for Base Number Determination by Potentiometric Hydrochloric Acid Titration
D5185 Test Method for Multielement Determination of Used and Unused Lubricating Oils and Base Oils by Inductively
Coupled Plasma Atomic Emission Spectrometry (ICP-AES)
D6304 Test Method for Determination of Water in Petroleum Products, Lubricating Oils, and Additives by Coulometric Karl
Fischer Titration
D6810 Test Method for Measurement of Hindered Phenolic Antioxidant Content in Non-Zinc Turbine Oils by Linear Sweep
Voltammetry
D6971 Test Method for Measurement of Hindered Phenolic and Aromatic Amine Antioxidant Content in Non-zinc Turbine Oils
by Linear Sweep Voltammetry
D7155 Practice for Evaluating Compatibility of Mixtures of Turbine Lubricating Oils
D7414 Test Method for Condition Monitoring of Oxidation in In-Service Petroleum and Hydrocarbon Based Lubricants by
Trend Analysis Using Fourier Transform Infrared (FT-IR) Spectrometry
D7546 Test Method for Determination of Moisture in New and In-Service Lubricating Oils and Additives by Relative Humidity
Sensor
D7464 Practice for Manual Sampling of Liquid Fuels, Associated Materials and Fuel System Components for Microbiological
Testing
D7647 Test Method for Automatic Particle Counting of Lubricating and Hydraulic Fluids Using Dilution Techniques to
Eliminate the Contribution of Water and Interfering Soft Particles by Light Extinction
D7669 Guide for Practical Lubricant Condition Data Trend Analysis
D7687 Test Method for Measurement of Cellular Adenosine Triphosphate in Fuel and Fuel-associated Water With Sample
Concentration by Filtration
For referenced ASTM standards, visit the ASTM website, www.astm.org, or contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM Standards
volume information, refer to the standard’s Document Summary page on the ASTM website.
The last approved version of this historical standard is referenced on www.astm.org.
D6224 − 23
D7720 Guide for Statistically Evaluating Measurand Alarm Limits when Using Oil Analysis to Monitor Equipment and Oil for
Fitness and Contamination
D7843 Test Method for Measurement of Lubricant Generated Insoluble Color Bodies in In-Service Turbine Oils using
Membrane Patch Colorimetry
D7978 Test Method for Determination of the Viable Aerobic Microbial Content of Fuels and Associated Water—Thixotropic Gel
Culture Method
D8506 Guide for Microbial Contamination and Biodeterioration in Turbine Oils and Turbine Oil Systems
E1064 Test Method for Water in Organic Liquids by Coulometric Karl Fischer Titration
F311 Practice for Processing Aerospace Liquid Samples for Particulate Contamination Analysis Using Membrane Filters
F312 Test Methods for Microscopical Sizing and Counting Particles from Aerospace Fluids on Membrane Filters
2.2 ISO Standard:
ISO 3448:1992 Industrial liquid lubricants—ISO viscosity classification
ISO 4406:1999 Hydraulic fluid power—Fluids—Method for coding the level of contamination by solid particles
2.3 SAE Standards:
J300 Engine Oil Viscosity Classification
J306 Automotive Gear Lubricant Viscosity Classification
3. Terminology
3.1 Definitions:
3.1.1 For definitions of terms used in this practice, refer to Terminology D4175.
4. Significance and Use
4.1 This practice is intended to help users, particularly power plant operators, maintain effective control over their mineral
lubricating oils and lubrication monitoring program. This practice may be used to perform oil changes based on oil condition and
test results rather than on the basis of service time or calendar time. It is intended to save operating and maintenance expenses.
4.2 This practice is also intended to help users monitor the condition of mineral lubricating oils and guard against excessive
component wear, oil degradation, or contamination, thereby minimizing the potential of catastrophic machine problems that are
more likely to occur in the absence of such an oil condition monitoring program.
4.3 This practice does not necessarily reference all of the current oil testing technologies and is not meant to preclude the use of
alternative instrumentation or test methods that provide meaningful or trendable test data, or both. Some oil testing devices and
sensors (typically used for screening oils that will be tested according to standard methods) provide trendable indicators that
correlate to water, particulates, and other contaminants but do not directly measure these.
4.4 This practice is intended for mineral oil products, and not for synthetic type of products, with the exception of phosphate esters
fluids typically used in power plant control systems.
5. General Properties of Lubricating Oils
5.1 In general, lubricating oils are designed to reduce friction and wear, provide cooling, control deposits, and combat the effects
of contamination. A base oil’s lubricating properties are enhanced by selected additives. Different machines have different lubricant
additive requirements, some of which are described in this section. Proper lubrication minimizes or precludes contact between
metal surfaces and reduces component wear.
5.2 Gear Oils—The primary requirement of gear oils is that they prevent wear and minimize other forms of damage such as pitting
and scuffing by maintaining a lubricant film between the moving surfaces.
5.3 Hydraulic Oils—A hydraulic fluid is required to transmit hydraulic pressure and energy, minimize friction and wear in pumps,
valves, and cylinders, and protect metal surfaces against corrosion. To obtain optimum efficiency of machine operation and control,
the viscosity of the oil should be low enough to minimize frictional and pressure losses in piping. However, it also is necessary
Available from American National Standards Institute (ANSI), 25 W. 43rd St., 4th Floor, New York, NY 10036, http://www.ansi.org.
Available from SAE International (SAE), 400 Commonwealth Dr., Warrendale, PA 15096, http://www.sae.org.
D6224 − 23
to have a sufficiently high viscosity to provide satisfactory wear protection and minimize leakage of the fluid. High-viscosity index
fluids help to maintain a satisfactory viscosity over a wide temperature range. The anti-wear properties of high-quality hydraulic
oils usually are improved by suitable additives. Since the clearances in pumps and valves tend to be critical, it is important to
provide adequate filtration equipment (full flow or bypass, or both) to maintain a minimum particle content and thus minimize
wear. The antioxidant additives in the hydraulic oil should give the oil good oxidation stability to avoid the formation of insoluble
gums or sludges; the oil should have good water separation properties, and, because air may be entrained in the system, the oil
should have good air-release properties and resistance to foaming. Similarly, good rust protection properties will assist in keeping
system metals in satisfactory condition.
5.4 Diesel Engine Oils—In addition to the typical role of lubricating oils which is to lubricate, clean, cool and seal, diesel engine
oils are formulated to provide protection from acids and disperse soot particles that are created during the combustion process.
Diesel engine oils are compounded with alkaline additives to neutralize the sulfuric acids that are produced when the diesel fuel
is combusted. They are also compounded with dispersant/detergents to keep the engine clean and the by-products of combustion
(fuel soot) suspended. The combination of wear regimes found in the diesel engine require the lubricants to have high levels of
anti-wear additives to protect the engine from wear during the most severe condition. Multi-grade lubricants (high viscosity index)
are often employed in diesel engine lubricants that are required to operate over a wide temperature range.
5.5 Turbine Oils or Circulating Oils, or Both—These oils provide satisfactory lubrication and cooling of bearings and gears (for
example, in auxiliary turbines, pumps and gearboxes as circulating oils). They also can function as a governor hydraulic fluid. The
oil must have a viscosity high enough to maintain a sufficiently thick film of oil on load-bearing surfaces, but low enough to
minimize energy losses while providing adequate cooling. These oils are recommended where the degree of loading on bearings
and gears is less than in gear oil applications. Turbine or circulating oils, or both, have excellent oxidation resistance and contain
rust inhibitors; they are often referred to as rust and oxidation inhibited (R&O) oils. They can also contain additives to improve
water separability and decrease foaming tendency.
5.6 Compressor Oils—In addition to possessing the correct viscosity for satisfactory bearing and cylinder lubrication, particularly
for air compressors, very good oxidation resistance is required to avoid degradation of the lubricant in the presence of heated air.
This is particularly important for mineral oils where discharge temperatures are high, since carbon and oxidized oil deposits may
autoignite if exposed continuously to temperatures above 148 °C. The fire potential that exists under these conditions make low
volatility and high auto-ignition values equally or more important than high-flash or fire points. In compressor lubrication,
condensed water is present frequently. For this reason, the oil must possess properties that ensure that the oil rather than water wets
the metal surfaces. Also, to avoid the accumulation of water-in-oil emulsions in the after coolers, the water should separate out
rather than form an emulsion.
5.7 Electrohydraulic Control (EHC) Fluids—Triaryl phosphate ester EHC fluids are inherently fire-resistant and maintain this
property throughout their service life. The very low vapor pressure and chemical nature of these fluids result in high flash point,
fire point, and autoignition temperature. EHC fluids should be continuously purified using bypass systems to maintain acid number,
moisture, and particulates at low levels. Moisture can cause hydrolysis of EHC fluids which results in elevated acid number.
Components constructed of copper and lead alloys should be avoided. These fluids are chemically different from mineral oils;
consequently, the interpretation of test results will be significantly different. The fluid supplier should be consulted if there is a
question about interpretation of analytical results.
6. Operational Factors Affecting the Service Life of Oils
6.1 New Oil Quality and Suitability for Intended Use—Use of high-quality oils that meet recognized standards (such as
manufacturer military specifications and OEM specifications) is the best assurance of potentially long service life. Careful oil
storage is important to prevent the degradation of the lubricant while in storage or being dispensed. Accurate labeling of lubricant
containers is vital to ensure proper identification.
6.1.1 Viscosity is the most important characteristic of an oil. Oil load bearing and lubricating properties are related to its viscosity.
The use of oil with incorrect viscosity can increase wear rates, heat build-up, and lube degradation. In extreme cases, the use of
oils with incorrect viscosities can result in rapid catastrophic failures.
6.1.2 Oils that meet the equipment manufacturers’ requirements should be used. For situations where the manufacturer simply
offers a generic viscosity classification without specific performance criteria, the user should consult the equipment manufacturer,
lubricant suppliers, and experts in the field of lubrication.
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6.1.3 When fresh, unused lubricants are received, it is advisable to obtain typical test data from the oil supplier. Upon receipt of
the first oil charge, take a sample of oil to confirm the typical test data.
6.1.3.1 Because systems usually contain some residual oil, (whether from a previous charge or a flush) the baseline sample to be
used for condition monitoring comparisons should be taken after the new oil is charged and circulated for up to 24 h (depending
on the size of the reservoir and turnover time).
6.1.3.2 This baseline should be the reference sample for the physical and chemical properties of the fluid, and for future
comparisons with in-service oil information. This is most important! Recommended tests for new oil are given in the schedules
of this practice. (Warning—Physical and chemical properties of lubricants after installation may not match results obtained for
new oil as received from the supplier.) (Warning—Storage conditions affect the shelf life of lubricants. Manufacturing shelf life
recommendations should be followed. If no shelf life guidance information is available and the lubricants is greater than two years
old, the lubricant manufacturer should be consulted to confirm suitability for use.)
6.1.4 Manufacturer shelf life recommendations should be observed. Oils should be stored to preserve their original quality and
prevent contamination. Stored oils may be tested to ensure and document their quality, cleanliness, and continued suitability for
their intended use. It is suggested that oil manufacturers’ recommendations be followed when storing lubricants to ensure
maximum product life.
6.1.5 Make-up oils should normally be of the same type, quality, and manufacturer. Available formulations may change over a
period of time. Lubricant incompatibility can arise from mixing differing base stocks and additive packages and should be avoided.
When oils must be mixed, testing should be performed in an attempt to determine compatibility in accordance with Practice D7155.
Consideration should be given to consulting the lubricant supplier(s) and equipment manufacturer prior to mixing oils.
6.2 Deterioration of Oils in Service—Air (oxygen), elevated temperatures, metals, and water (moisture) are present to some extent
in lubricating systems. Record these factors that promote lubricant degradation. Lubricant deterioration occurs by one or more of
the following processes:
6.2.1 Oxidative Degradation—This process occurs as the result of chemical changes brought about by oxygen in the atmosphere
and proceeds by a chain reaction that is with the presence of water, heat, and certain metals. The results of oxidation can consist
of AN increase, viscosity (KV) increase), or sludge and varnish deposits, or a combination thereof as end-products within the
lubricating system.
6.2.2 Thermal Degradation—This process occurs in the absence of oxygen and at much higher temperatures. Typically,
temperatures of more than 300 °C may cause the hydrocarbon molecule to crack and produce various degradation species. Some
of these species are low molecular weight by-products that evaporate or burn (producing a noticeable “burnt” smell in the oil) and
other degradation species are high molecular weight by-products that form sludge and varnish.
6.2.3 Lubricant Deposits and Sludge (Lacquering/Varnishing)—As lubricants degrade either through thermal and mechanical
forces, they may produce submicron, high molecular weight, polar insoluble particles. These particles may agglomerate, become
insoluble in the oil, as it is non-polar in nature, and adsorb onto the metal parts of a lubricating system. Some highly refined base
oils used in the manufacturing of lubricants (API Group II and above) may be less tolerant to the presence of these degradation
by-products due to their high purity and lower solvency. Base oils with proper formulation can result in low deposit tendency oils.
Deposits (such as varnish) could be very costly to an equipment operator, as they may deposit on bearing and turning gear surfaces
increasing wear, settle in servo-valves causing valves to stick and seize, coat heat exchangers lowering their performance and form
in reservoirs acting as a catalyst to further degradation. If deposits are found in the system, analysis can be performed on the deposit
to identify possible root causes. The insoluble polar compounds (soft contaminants) may be removed by the use of varnish
separation technologies and through carefully performed high velocity flushes.
6.2.3.1 When these conditions of lubricants deposits and sludge occur, dramatic reductions in the viscosity of the oil are possible
and the flash point of the resulting fluid can also change.
6.2.4 Hydrolysis—Hydrolysis is a mode of degradation in the presence of moisture. This is very important for phosphates (and
other esters) and may also have an effect on additive systems in oil-based products. The major characteristic of hydrolysis is the
generation of corrosive acids in the fluids.
D6224 − 23
6.2.5 Loss of Additives—Additives are used to protect the oil and enhance its performance abilities. When these additives are
depleted as a result of service, the performance of the oil will be reduced as a consequence of oil oxidation, foaming, excessive
wear, or premature rusting.
6.2.6 New Oil Make-up Rate—Addition of new oil is required in nearly every system to make up for losses due to leakage, filter
changes, or other maintenance. Monitor the amount and frequency of added make-up oil, since they play a very significant part
in determining the life of a system oil charge.
6.3 Contamination—Contamination of lubricating oils occurs both from outside and from within the system. Common types of
contamination are: debris introduced at initial startup or after an overhaul, lubricant degradation byproducts, component wear
debris, airborne particulates, and water (moisture). Contamination is often the most significant factor affecting oil service life.
Contamination of oil is a valid reason to change oil and flush to restore system cleanliness.
6.3.1 Condition of Equipment on Start-up—Oil system contamination prior to start-up usually consists of preservatives, paint,
moisture, rust particles, and construction debris such as dust, dirt, or welding spatter. Whenever practical, flushing the system
before starting operation is recommended. Fluid cleanliness should be brought to a level of one to two ISO FDIS 4406.2 classes
below warning levels before beginning operation. If flushing is not performed, oils should be tested soon after startup or repair
to verify their cleanliness.
6.3.2 External Contamination-Solids—Solid contamination consists of any material small enough to pass through bearing seals
and vents or which can be introduced with make-up oil. From whatever source, contamination must be dealt with by monitoring
oil condition and using purification devices such as filters and centrifuges on a regular basis.
6.3.3 External Contamination-Liquid—Coolant leaks, moisture or steam condensation, or introduction of improper lubricating oils
can compromise the oil. Accumulated water promotes oil degradation as well as interfering with lubrication. Contamination with
an improper lubricant is not easily corrected without a complete oil change. An oil monitoring program may be used to monitor
and identify contaminants likely to be encountered in service.
6.3.4 Internal Contamination—Contaminants include wear debris, oil degradation products, and microbial growth. The types of
internal contaminants will vary by equipment type and oil type; the rate of generation will be highly dependent on the equipment
operating conditions. The analysis methods employed must be able to identify expected wear debris and degradation products.
Testing frequencies should be sufficient to account for operating conditions.
7. Sampling
7.1 General—When taking lubricant samples from storage tanks or equipment in service, it is important that the extracted sample
is representative and is taken from a specified location(s) to monitor the properties of the lubricant. The following are some
suggested guidelines for proper sampling technique and sample handling techniques. (See also Practice D4057.) The user should
have written procedures to insure that samples are taken consistently according to good maintenance practices.
7.1.1 Microbiological Testing—When sampling in order to perform microbiological testing, refer to Practice D7464 and Guide
D8506 for guidance on sample collection and handling.
7.2 Representative Sampling—A representative sampling location is a sampling location that supports repeatable and represen-
tative lubricant sampling to monitor the health of the equipment and the properties of the lubricant. Collect oil samples when
machines or equipment are running at normal operating temperatures, loads, pressures and speeds. To ensure that insoluble material
is suspended evenly throughout the system. A fluid sample is probably not representative if: (1) the system fluid is hot while the
sample is cold, (2) the fluid in the system is one color or clarity in an in-line sight glass while the sample is a different color or
clarity, and (3) the fluid viscosity of the reservoir fluid is different from that of the sample when both are at the same temperature.
Samples should be taken in the same manner each time to allow reliable trending of oil properties.
7.2.1 It should be noted that on occasion a sample may be requested which will not be representative. At that time, sampling
instructions, as specified by the requestor, must be followed. For example, a sample might be taken off the top or the bottom of
a tank to check for contamination. In all cases, the sample point should be marked on the sample container.
D6224 − 23
7.3 Sampling Location—Assign sample location upstream of filters and downstream of machine components such as bearings and
gears to obtain the best data. The sampling downstream of the filters is only advised to determine the efficiency (beta-ratio) of filters
or filtration systems.
7.4 Flushing Procedures—Always flush a sample line before a sample is taken and flushing will be achieved by flushing properly
the sampling valves, devices, and hardware thoroughly prior to taking oil samples.
7.4.1 The flushing is usually accomplished using a spare container/bottle to catch the purged fluid. It is important to flush 5 to 10
times the dead space volume before obtaining the sample.
7.4.2 All hardware that the oil comes into contact with is considered dead space and must be flushed, including, system dead-legs,
sampling ports, valves and adapters, probe on sampling devices, adapters for using vacuum sample extraction pumps, as well
plastic tubing used for vacuum pumps (this tubing should not be reused to avoid cross-contamination between oils).
7.4.3 After opening the sample port and flushing, fill the sample container/bottle to approximately 50 % of its capacity with the
oil—leave enough void to allow shaking of the sample prior to testing. In case of flash point testing, for most accurate testing,
reduce the head space volume.
7.5 Documenting Sampling Procedures—To ensure that each sample is taken in the same manner and from the same point, the
operator defines and documents oil sampling procedures for each system such as: (1) tools needed, (2) line flushing requirements,
(3) sampling locations, (4) sampling methods, (5) safety requirements, and (6) sample bottle labeling.
7.5.1 It should be noted that on occasion a sample may be requested which will not be representative. At that time, sampling
procedures, as specified by the requestor, must be followed. For example, a sample might be taken off the top or the bottom of
a tank to check for contamination. In all cases, the sample point should be marked on the sample container/bottle.
7.6 Oil Sampling Frequency—Take oil samples at a specified frequency; this will ensure that any problems are identified early.
Sampling frequencies will be set specifically for each machine or piece of equipment, since each is unique in its intended
performance, condition, locality, operating environment, and maintenance schedule.
7.7 Oil Sample Container/Bottles—Take oil samples in oil sample containers or bottles which should be:
7.7.1 Clean—If in doubt about its cleanliness, use another sample container/bottle. If this is not possible, flush it out with the fluid
to be sampled. Take special care to ensure that sample containers/bottles for water separability, particle count, and wear debris
testing are clean.
7.7.2 Resistance to the Material Being Sampled—For example, fire-resistant phosphate ester fluids will dissolve certain plastics.
(This includes the liner in bottle caps.) To verify the sample container/bottle’s resistance, if time permits, allow the sample to stand
in the sample container/bottle and observe its effects. Aluminum foil or polytetrafluoroethylene (PTFE) make good, resistant cap
liners.
7.7.3 Appropriate for Required Handling—Sample containers/bottles with leaking tops and glass sample containers/bottles
improperly protected are not suitable for shipment. Stringent packaging requirements must be followed if shipment is to be made
by air.
7.7.4 Appropriate for the Analyses Required—As an example, some plastic sample containers/bottles may not be acceptable for
flash point testing (per Test Method D92) because volatile materials may leak through the container/bottle walls. Use sample
containers/bottles of either glass or polyethylene for wear debris analysis samples (to avoid material leaching).
NOTE 2—Some lubricant suppliers and commercial testing laboratories provide sample containers/bottles that meet all these requirements. Use these
whenever possible. If frequent samples are taken, an adequate supply of containers/bottles should be kept.
NOTE 3—For samples intended for microbiological testing, see Practice D7464. Although the guidance provided in Practice D7464 is nominally for fuel
sample collection, the procedures provided are equally applicable to turbine oils.
D6224 − 23
7.8 Sample Labeling—Properly label a sample container/bottle in order to track the history of a particular piece of equipment. The
equipment must be identified uniquely. Labels should include the following information as appropriate:
7.8.1 Customer name,
7.8.2 Site (or plant name),
7.8.3 Location (unit number, tank number, compartment number, and so forth),
7.8.4 Equipment serial number (or other ID),
7.8.5 Oil and machine service hours,
7.8.6 Date sample taken,
7.8.7 Type of fluid sampled,
7.8.8 Sampling point,
7.8.9 System operating temperature and temperature of oil at sampling point,
7.8.10 Type of purification system (filters, centrifuge, and so forth),
7.8.11 Make-up (volume) since last sample was taken, and
7.8.12 Coolant additives.
7.9 Sampling of New Oil Deliveries—Thoroughly clean all sampling devices before use to avoid cross-contamination.
7.9.1 Take samples representative of the fluid being examined but obtained from the point(s) most indicative of gross
contamination by debris and water, that is, just above the bottom of the drum or tanker compartment bottom.
7.9.2 When consignments of oil are in drums, sample them in accordance with Practice D4057.
7.9.3 In cases where the product is suspected of being non-uniform, sample a larger number of drums. Where contamination is
suspected, there may be no alternative to sampling every drum.
7.9.4 For bulk consignments, sample each tanker compartment. If these are clear of debris and water, then the samples can be
combined for subsequent laboratory analysis of the consignment. The user may decide to perform a limited number of tests on
individual compartment samples; a composite sample may be tested for other properties.
7.9.5 From tanker deliveries, sample individual tanker compartments. The sample should be taken preferably from the outlet of
the flexible pipework or at least from the tanker bottom valve manifold. This is important because the tanker contents can become
contaminated by residual material left in the bottom valve manifold. This can occur particularly when different products are being
carried in separate compartments or previous deliveries of a different product have been made to other locations without
subsequent adequate cleaning and flushing. Dead leg piping should always be drained and flushed prior to sampling.
7.9.6 Bottom samples (if desired) must be collected by either a tube or thief sampler (for example, Bacon bomb). These samplers
permit collection of settlings on the bottom of the containers without introducing false contamination by scraping the container
lining or wall.
7.10 Preservation of Sample and Analysis of Oil Samples—It is generally advised to ship the oil samples immediately to the oil
analysis laboratory, as ideally, oil should be analyzed within as soon as reasonably achievable after being sampled. If oil samples
are stored for an extended period of time, this may result in a non-representative sample.
7.10.1 If the samples are to be retained for extended periods of time, special arrangements should be made in agreement with the
D6224 − 23
oil analysis laboratory to ensure that the integrity of the sample is not compromised. The special arrangement may include storing
in dark amber glass bottles in an ambient temperature area as the longer an oil sample is stored in the container/bottle, the more
oxidation products will be generated.
7.10.2 Store the sample(s) away from strong light and as close to room temperature as possible.
8. Examination of New Oil on Delivery
8.1 Experience has shown the need for standardizing procedures and acceptance criteria for the sampling, examination, and
acceptance of incoming supplies of lubricating oil. It is essential that personnel responsible for sampling and testing have the
necessary experience and skills, and that scrupulous attention to detail be applied at all times to avoid erroneous results.
8.2 It is equally essential that all incoming supplies of oil be adequately monitored to guard against incorrect or contaminated
material being delivered. This information can be used from quality control of in-coming fluid as well as future fluid reference data.
The cleanliness of the delivery container should be noted; if the container is dirty on the outside, there may be particulate
contamination of the oil inside. Particulate contamination can also be a problem when the lubricant comes in contact with dirty
or poorly maintained equipment. Final filtration while filling equipment may be used in lieu of or in addition to particle counting.
The final filter should be as fine or finer than the lubrication system filter of the equipment being filled.
8.3 Sampling of incoming supplies should be in accordance with proper sampling procedures (see Section 7).
8.4 All samples should be immediately examined for appearance.
8.5 Testing schedule guidelines for various types of new oils are provided in Table 1. With drums, tests should be completed on
a composite (or bulked) sample before the oil is used in service. Individual samples should be retained until the bulk sample is
passed as satisfactory.
8.6 With tanker deliveries, the additional tests to be completed before the tanker is discharged can only be judged from the risk
involved by the acceptance of non-specification product. That is, can the charge be readily recovered and corrected before passing
into service if the subsequent tests indicate this is necessary.
8.7 Handling and dispensing methods contribute to the required health and cleanliness specifications of the lubricant. All sources
and opportunities of contamination must be avoided.
8.8 The product specifications for new oils should be clearly communicated between the user and supplier. If a sample of oil fails
to meet the product specifications agreed upon by user and supplier, the sample should be retested to verify the initial test result.
A resample should be taken and tested if needed to verify that the sample is representative of the shipment. If the retest or resample
still fails to meet product specification, an investigation should be made to determine whether the problem is due to transportation,
handling, or product formulation. The user must recognize that typical values are not the same as purchase specifications.
9. Significance of Tests
9.1 In determining the condition of the oil and equipment for continued service, important properties of in-service oils include:
9.2 Viscosity—Most commercial turbine oils are sold under ISO (International Standards Organization) viscosity classification
system. Typical turbine fluids fall into ISO VG-32, VG-46, VG-68 and higher viscosity grades corresponding to 32 mm /s, 46
2 2
mm /s, 68 mm /s at 40 °C (Classification D2422). The viscosity of gear oils is classified using either ISO 3448 or D2422 viscosity
classification for industrial gear oils or SAE J306 for automotive gear oils. The viscosity of diesel engine oils is classified according
to SAE J300. The viscosity (for example, for multi-grade oils) can be measured at 40 °C and 100 °C in order to calculate the
viscosity index and determine that the correct oil has been used. The main purpose for checking the viscosity of in-service oil is
to determine if the correct oil is being used and to detect contamination. In extreme cases, in-service oils will experience a
significant increase in viscosity due to thermal or oxidative degradation. Contamination can cause the viscosity to either increase
or decrease, depending on the contaminant. Emulsified water and diesel fuel soot will increase the viscosity, while diesel fuel,
Freon, or solvents will decrease the viscosity. Dissolved water in phosphate ester fluids can reduce the fluid viscosity slightly.
Contamination from a different lubricant can change the viscosity of the oil in either direction. The method normally used for
viscosity determinations is Test Method D445.
D6224 − 23
A
TABLE 1 Guidelines for Sampling and Testing New Oils
NOTE 1—Legend–R = Recommended; O = Optional.
NOTE 2—An infrared spectrum may be obtained for new oil to ensure that the oil is not contaminated and to provide a baseline for comparison to spectra
of in-service oil.
Diesel Air EHC EHC
Common Hydraulic Turbine/
Test Gear Oils Engine Compressor (PO (Mineral
Methods Oils Circulating Oils
B
Oils Oils Esters) Oils)
C
Appearance Visual R R R R R R
D
Viscosity, (40 °C) D445 R R O R R R R
Viscosity (100 °C) D445 R
Acid number D664 R R R R R R
D974
E F F F F F F
Water D6304 O O R O O R O
D95/D7546
Antioxidants/Oxidation inhibitor D2668 O O
G G G
D6971 O O
Oxidation stability (RPVOT) D2272 O O
API gravity or density D1298 O
D4052
Flash point (COC) D92 O
Water separability D1401 O O
Particle counts Equipment R O O
Manufacturer’s
Method
Base number D974 R
D2896
D4739
Electrical resistivity D257/D1169 R
H
Elemental Analysis D5185 O O O O O O O
A
Tests which are performed on in-service oils for trending purposes should also be performed on new oils for baseline information.
B
Does not include refrigeration (chiller) oils.
C
Appearance includes observations such as color, clarity, odor, and sediment.
D
A diesel engine oil must be tested at 40 °C and 100 °C if it is necessary to determine whether it is the proper multi-grade oil.
E
Test Method D6304 Procedure C is recommended for lube oils.
F
Recommended if oil is not clear and bright.
G
Test Method D6971 is not recommended for zinc-based lubricating oils.
H
Another spectrochemical method such as rotating disk electrode (RDE), atomic absorption (AA), or x-ray fluorescence (XRF) may be substituted for the ICP method.
9.3 Acid Number—The test most used to indicate the extent of oxidation is the acid number (Test Method D664 or D974). With
phosphate esters, acidity is most frequently an indication of hydrolysis. Many rust inhibitors used in lubricating oils are acidic and
contribute to the acid number of the new oil. An increase in acid number above the value for new oil indicates the presence of acidic
oxidation products or, less likely, contamination with acidic substances. The acid numbers determined by these two test methods
are not identical and only loosely correlate; a single method should be used consistently. The use of Test Method D974 on aged
phosphate ester fluids which have significantly darkened in color, and especially those which have been dyed prior to use, is not
recommended.
9.4 Water Content—If a mineral oil is clear and bright, the amount of dissolved water present is of little significance. Most mineral
oils will remain clear with up to 75 μg ⁄g water at room temperature. Phosphate ester fluids can hold more than 1000 μg ⁄g water
at ambient temperature and still be clear and bright. The presence of water determined by screening methods (such as the hot plate
splatter test for mineral oils) may be confirmed using a standard test method. Adequate lubrication cannot be maintained by an oil
which contains a significant quantity of water. The analytical range for Test Method D95 is 0.05 % to 25 % and the range for Test
Method D6304 is 50 μg ⁄g to 1000 μg ⁄g. Other methods (such as Test Methods D1533 and E1064) are available for measuring the
water content in oils.
D6224 − 23
9.5 Antioxidants Level—The measurement of antioxidant concentration is important for monitoring the oxidation of industrial
lubricants and their remaining useful life. Existing practices for measuring the concentration of phenolic (or amine) antioxidants
include infrared spectrometry Test Method D2668 and linear sweep voltammetry Test Method D6971 or D6810.
9.5.1 FTIR—The Fourier Transform Infrared (FTIR) by Test Method D7414 is a refined infrared spectroscopy method, which can
be used to monitor the remaining antioxidants blended into the oil. It can also be used to monitor the increase in oxidation products
as the oil degrades. Each antioxidant is a specific chemical substance and will absorb infrared light at particular wavelengths and
absorptivities; some antioxidants may not be detectable by infrared spectroscopy. (Test Method D2668 may be used for
antioxidants if the wavelengths and absorptivities are known.)
9.5.2 Linear Sweep Voltammetry—Voltammetry is an electrochemical test technique, which can be used for measuring many
antioxidant additives. The technique applies a voltage ramp through a 3 electrode sensing system and measures the current flow
that occurs when the applied voltage equals the oxidation potential of the antioxidant. The potential at peak current is diagnostic
for the antioxidant, and the amplitude of the peak is proportional to the
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