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

SIGNIFICANCE AND USE
5.1 This test method is intended for use in analytical laboratories including onsite in-service oil analysis laboratories.  
5.2 Hard particles in lubricating or fluid power systems have a detrimental effect on the system as they cause operating components to wear and also accelerate the degradation of the oil. Hard particles in the oil originate from a variety of sources including generation from within an operating fluid system or contamination, which may occur during the storage and handling of new oils or via ingress into an operating fluid system.  
5.3 High levels of contaminants can cause filter blockages and hard particles can have a serious impact on the life of pumps, pistons, gears, bearings, and other moving parts by accelerating wear and erosion.  
5.4 Particle count results can be used to aid in assessing the capability of the filtration system responsible for cleaning the fluid, determining if off-line recirculating filtration is needed to clean up the fluid system, or aiding in the decision of whether or not a fluid change is required.  
5.5 To accurately measure hard particle contamination levels, it is necessary to negate the particle counts contributed by the presence of small levels of free water. This method includes a process by which this can be accomplished using a water-masking diluent technique whereby water droplets of a size below the target level are finely distributed.  
5.6 Certain additives or additive by-products that are semi-insoluble or insoluble in oil, namely the polydimethylsiloxane defoamant additive and oxidation by-products, are known to cause light scattering in automatic particle counters, which in turn causes falsely high counts. These and similar materials are commonly termed “soft particles” (see 3.2.4) and are not known to directly increase wear and erosion within an operating system. The contribution of these particles to the particle size cumulative count is negated with this method.  
5.7 The use of dilution i...
SCOPE
1.1 This test method covers the determination of particle concentration and particle size distribution in new and in-service oils used for lubrication and hydraulic purposes.  
1.2 Particles considered are in the range from 4 µm (c) to 200 µm (c) with the upper limit being dependent on the specific automatic particle counter being used.
Note 1: For the purpose of this test method, water droplets not masked by the diluent procedure are detected as particles, and agglomerated particles are detected and reported as a single larger particle.
Note 2: The subscript (c) is used to denote that the apparatus has been calibrated in accordance with ISO 11171. This subscript (c) strictly only applies to particles up to 50 µm.  
1.3 Lubricants that can be analyzed by this test method are categorized as petroleum products or synthetic based products, such as: polyalpha olefin, polyalkylene glycol, or phosphate ester. Applicable viscosity range is up to 1000 mm2/s at 40 °C. This procedure may be appropriate for other petroleum and synthetic based lubricants not included in the precision statement.  
1.4 Samples containing visible particles may not be suitable for analysis using this test method.  
1.5 Samples that are opaque after dilution are not suitable for analysis using this test method.  
1.6 The test method is specific to automatic particle counters that use the light extinction principle and are calibrated according to the latest revision of ISO 11171.  
1.7 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.  
1.8 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.  
1.9 This international standard was d...

General Information

• Status: Published
• Publication Date: 31-Jan-2024
• ICS: 75.100 - Lubricants, industrial oils and related products
• ICS: 75.120 - Hydraulic fluids
• Technical Committee: D02 - Petroleum Products, Liquid Fuels, and Lubricants
• Drafting Committee: D02.96.05 - In-Service Lubricants Particle Counting Practices and Techniques

Relations

• Replaces: ASTM D7647-10(2018) - 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
• Referred By: ASTM D4378-22 - Standard Practice for In-Service Monitoring of Mineral Turbine Oils for Steam, Gas, and Combined Cycle Turbines
• Effective Date: 01-Feb-2024
• Referred By: ASTM D6224-23 - Standard Practice for In-Service Monitoring of Lubricating Oil for Auxiliary Power Plant Equipment
• Effective Date: 01-Feb-2024
• Referred By: ASTM D7684-11(2020) - Standard Guide for Microscopic Characterization of Particles from In-Service Lubricants
• Effective Date: 01-Feb-2024
• Referred By: ASTM D7720-21 - Standard Guide for Statistically Evaluating Measurand Alarm Limits when Using Oil Analysis to Monitor Equipment and Oil for Fitness and Contamination
• Effective Date: 01-Feb-2024
• Referred By: ASTM D6439-23 - Standard Guide for Cleaning, Flushing, and Purification of Steam, Gas, and Hydroelectric Turbine Lubrication Systems
• Effective Date: 01-Feb-2024
• Referred By: ASTM D4174-23 - Standard Practice for Cleaning, Flushing, and Purification of Petroleum Fluid Hydraulic Systems
• Effective Date: 01-Feb-2024
• Referred By: ASTM D4304-22 - Standard Specification for Mineral and Synthetic Lubricating Oil Used in Steam or Gas Turbines
• Effective Date: 01-Feb-2024

Overview

ASTM D7647-24 is the 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. Published by ASTM International, this standard specifies procedures for determining particle concentration and size distribution in both new and in-service lubricating and hydraulic oils. By employing dilution techniques and automatic particle counters calibrated per ISO 11171, this method effectively reduces false readings caused by water and soft, non-damaging particles, ensuring precise contamination monitoring.

Particle contamination control is critical in fluid power and lubrication systems. Hard contaminants can cause accelerated wear, filter blockage, and premature failure of components such as pumps, bearings, and gears. ASTM D7647-24 provides a reliable analytical approach for oil condition monitoring and maintenance decision support.

Key Topics

• Applicability: Suitable for petroleum-based and synthetic lubricants (including polyalpha olefin, polyalkylene glycol, and phosphate ester) with viscosity up to 1000 mm²/s at 40°C.
• Particle Size Range: Detects particles from 4 µm to 200 µm; accuracy assured up to 50 µm for ISO 11171 calibrated instruments.
• Dilution Techniques: Water-masking diluents are used to disperse water and negate particle count errors from soft, non-damaging matter such as defoamant additives and oxidation by-products.
• Instrument Requirements: Automated liquid particle counters utilizing light extinction method and calibrated to ISO 11171 are mandatory.
• Sampling and Handling: Emphasis on correct, contamination-free sampling procedures to maintain data integrity.
• Interferences Addressed: Outlines how air bubbles, excess water, soft particles, soots, and certain dyes can distort results and details how to mitigate these effects.
• Data Reporting: Results are presented as cumulative particle counts per milliliter, often referenced using ISO 4406 cleanliness codes.

Applications

ASTM D7647-24 is widely used in:

• In-service oil analysis laboratories: Enables facilities to monitor machinery health, support predictive maintenance, and extend equipment lifespan by tracking hard particle contamination levels in lubricants and hydraulic fluids.
• Equipment reliability programs: Provides actionable insights into the performance of filtration systems, alerting maintenance personnel when filters require service or fluid changes are necessary.
• Quality control for new oils: Ensures products meet cleanliness specifications before deployment in sensitive systems.
• OEM and aftermarket support: Used by manufacturers and service providers to validate oil cleanliness and diagnose system issues related to wear and contamination.
• Hydraulic and lubrication system optimization: Data supports decisions about off-line filtration, system flushing, and fluid replacement intervals, helping minimize costly downtime.
• Compliance and best practices: Essential for organizations adhering to international best practices for fluid maintenance in sectors such as power generation, manufacturing, transportation, and heavy industry.

Related Standards

For comprehensive oil analysis and particle counting, ASTM D7647-24 references or aligns with several key standards:

• ISO 11171: Calibration of automatic particle counters for liquids.
• ISO 4406: Fluid contamination coding by particle concentration.
• ASTM D4057: Manual sampling of petroleum products.
• ASTM D4177: Automatic sampling of petroleum products.
• ISO 3722: Cleaning methods for hydraulic fluid sample containers.
• ASTM D4175: Terminology for petroleum products, lubricants, and fuels.
• ASTM D6786: Particle count in mineral insulating oils by automatic optical methods.

These standards, when used alongside ASTM D7647-24, establish a robust framework for accurate, repeatable, and reliable oil contamination monitoring and machinery lubrication health management.

By implementing ASTM D7647-24 in oil analysis protocols, organizations can enhance equipment reliability, comply with global quality benchmarks, and support proactive maintenance strategies.

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: 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
This standard is issued under the fixed designation D7647; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope* 1.8 This standard does not purport to address all of the
safety concerns, if any, associated with its use. It is the
1.1 This test method covers the determination of particle
responsibility of the user of this standard to establish appro-
concentration and particle size distribution in new and in-
priate safety, health, and environmental practices and deter-
service oils used for lubrication and hydraulic purposes.
mine the applicability of regulatory limitations prior to use.
1.2 Particles considered are in the range from 4 μm to
1.9 This international standard was developed in accor-
(c)
200 μm with the upper limit being dependent on the specific
(c) dance with internationally recognized principles on standard-
automatic particle counter being used.
ization established in the Decision on Principles for the
NOTE 1—For the purpose of this test method, water droplets not masked
Development of International Standards, Guides and Recom-
by the diluent procedure are detected as particles, and agglomerated
mendations issued by the World Trade Organization Technical
particles are detected and reported as a single larger particle.
Barriers to Trade (TBT) Committee.
NOTE 2—The subscript is used to denote that the apparatus has been
(c)
calibrated in accordance with ISO 11171. This subscript strictly only
(c)
applies to particles up to 50 μm. 2. Referenced Documents
1.3 Lubricants that can be analyzed by this test method are 2.1 ASTM Standards:
D4057 Practice for Manual Sampling of Petroleum and
categorized as petroleum products or synthetic based products,
such as: polyalpha olefin, polyalkylene glycol, or phosphate Petroleum Products
D4175 Terminology Relating to Petroleum Products, Liquid
ester. Applicable viscosity range is up to 1000 mm /s at 40 °C.
This procedure may be appropriate for other petroleum and Fuels, and Lubricants
D4177 Practice for Automatic Sampling of Petroleum and
synthetic based lubricants not included in the precision state-
ment. Petroleum Products
D6786 Test Method for Particle Count in Mineral Insulating
1.4 Samples containing visible particles may not be suitable
Oil Using Automatic Optical Particle Counters
for analysis using this test method.
2.2 ISO Standards:
1.5 Samples that are opaque after dilution are not suitable
ISO 3722 Hydraulic fluid power—Fluid sample
for analysis using this test method.
containers—Qualifying and controlling cleaning methods
1.6 The test method is specific to automatic particle coun- ISO 4406 Hydraulic fluid power—Fluids—Method for cod-
ters that use the light extinction principle and are calibrated ing level of contamination by solid particles
according to the latest revision of ISO 11171. ISO 11171 Hydraulic fluid power—Calibration of automatic
particle counters for liquids
1.7 The values stated in SI units are to be regarded as
standard. No other units of measurement are included in this
3. Terminology
standard.
3.1 Definitions:
This test method is under the jurisdiction of ASTM Committee D02 on
Petroleum Products, Liquid Fuels, and Lubricants and is the direct responsibility of For referenced ASTM standards, visit the ASTM website, www.astm.org, or
Subcommittee D02.96.05 on In-Service Lubricants Particle Counting Practices and contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM
Techniques. Standards volume information, refer to the standard’s Document Summary page on
Current edition approved Feb. 1, 2024. Published February 2024. Originally the ASTM website.
approved in 2010. Last previous edition approved in 2018 as D7647 – 10 (2018). Available from American National Standards Institute (ANSI), 25 W. 43rd St.,
DOI: 10.1520/D7647-24. 4th Floor, New York, NY 10036, http://www.ansi.org.
*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
D7647 − 24
3.1.1 For definitions of terms used in this test method, refer 4. Summary of Test Method
to Terminology D4175.
4.1 Inspect sample.
3.1.2 free water, n—water in excess of that soluble in the
4.2 Agitate sample.
sample and appearing in the sample as a haze or cloudiness, as
droplets, or as a separated phase or layer. 4.3 Obtain aliquot from homogeneous sample if not diluting
in original container.
3.1.3 soot-in-oil, n—in internal combustion engines, <1 μm
size particles, primarily carbon, created in the combustion 4.4 Dilute with appropriate diluent for the sample type.
chamber as products of incomplete combustion.
4.5 Agitate diluted sample.
3.2 Definitions of Terms Specific to This Standard:
4.6 Degas sample.
3.2.1 coincidence, n—the presence of more than one particle
4.7 Begin testing within 90 s (or repeat agitation and degas-
in the sensing zone of a particle analyzer at the same time,
sing).
causing incorrect sizing and incorrect counting of the particle
present. The coincidence limit of the counter is determined by 4.8 Obtain particle counts in triplicate (for sample and
method blank).
the maximum acceptable concentration of particles in the
sensing zone and is supplied by the instrument manufacturer.
4.9 Analyze data and conduct validity checks.
Refer to Section 3.4 in ISO 11171.
4.10 Report results.
3.2.2 diluent, n—a solvent listed in Annex A1, Table A1.1,
having viscosity less than 10 mm /s at 40 °C that is physically
5. Significance and Use
and chemically compatible with the apparatus used and easily
5.1 This test method is intended for use in analytical
soluble at room temperature with the sample lubricant or
laboratories including onsite in-service oil analysis laborato-
hydraulic fluid.
ries.
3.2.3 emulsified water, n—water that exists in oil between
5.2 Hard particles in lubricating or fluid power systems have
the states of fully dissolved and phase-separated. An emulsi-
a detrimental effect on the system as they cause operating
fying agent in the oil causes the two immiscible liquids to
components to wear and also accelerate the degradation of the
coexist in a heterogeneous mixture.
oil. Hard particles in the oil originate from a variety of sources
3.2.4 interfering soft particles, n—an undissolved, dispersed
including generation from within an operating fluid system or
material (such as an additive) within an oil blend or substance
contamination, which may occur during the storage and han-
that is formed during the service life of an oil blend.
dling of new oils or via ingress into an operating fluid system.
3.2.4.1 Discussion—When these substances are present in a
5.3 High levels of contaminants can cause filter blockages
sample and not completely solubilized, they are likely to be
and hard particles can have a serious impact on the life of
counted by an optical particle counter in a similar manner to
pumps, pistons, gears, bearings, and other moving parts by
dirt and wear metal particles, air bubbles, and free water
accelerating wear and erosion.
droplets.
5.4 Particle count results can be used to aid in assessing the
3.2.5 ISO Codes, n—a standard classification for coding the
capability of the filtration system responsible for cleaning the
level of contamination by solid particles.
fluid, determining if off-line recirculating filtration is needed to
3.2.5.1 Discussion—This code simplifies the reporting of
clean up the fluid system, or aiding in the decision of whether
particle count data by converting the number of particles per
or not a fluid change is required.
mL into three classes covering ≥4 μm , ≥6 μm and
(c) (c)
5.5 To accurately measure hard particle contamination
≥14 μm . ISO 4406 classifications are used as an option to
(c)
levels, it is necessary to negate the particle counts contributed
report results for this test method.
by the presence of small levels of free water. This method
3.2.6 particle size, μm , n—diameter of a circle with an
(c)
includes a process by which this can be accomplished using a
area equivalent to the projected area of a particle passing
water-masking diluent technique whereby water droplets of a
through the detecting cell in accordance with ISO 11171.
size below the target level are finely distributed.
3.2.7 particle size cumulative count, n—total number of
5.6 Certain additives or additive by-products that are semi-
particles with sizes greater than a specified particle size (for
insoluble or insoluble in oil, namely the polydimethylsiloxane
example, ≥4 μm , ≥6 μm , ≥10 μm , ≥14 μm ,
(c) (c) (c) (c)
defoamant additive and oxidation by-products, are known to
≥21 μm , ≥38 μm , etc.).
(c) (c)
cause light scattering in automatic particle counters, which in
NOTE 3—All particle counts are expressed on per 1 mL basis. turn causes falsely high counts. These and similar materials are
commonly termed “soft particles” (see 3.2.4) and are not
3.2.8 water-masking diluent, n—a particular kind of diluent
known to directly increase wear and erosion within an operat-
capable of dissolving otherwise immiscible substances such as
ing system. The contribution of these particles to the particle
water or soft particles in the sample lubricant or hydraulic
size cumulative count is negated with this method.
fluid.
3.2.8.1 Discussion—In Annex A1, Table A1.1, 25 % isopro- 5.7 The use of dilution in this test method counteracts
panol / 75 % toluene and dipropylene glycol n-propyl ether are viscosity effects for highly viscous oils that impact the accu-
the only water-masking diluents in Table A1.1. racy of automatic optical particle counting results.
D7647 − 24
6. Interferences instrument shall be capable of recording the size and number of
NOTE 4—This section is consistent with the interferences described in
particles as they pass across the detector. The particle counter
Test Method D6786.
shall include a sampling apparatus that automatically delivers
6.1 Dirty environmental conditions and poor handling tech- a predetermined volume of specimen at a controlled flow rate
niques can easily contaminate the sample or test specimen, or to the sensing zone of the analyzer.
both. Care shall be taken to ensure test results are not biased by
7.2 Analytical Balance, for mass dilution, calibrated, with a
introduced particles.
resolution of 100 mg.
6.2 Air bubbles in the oil may be counted as particles giving
7.3 Mechanical Shaker, paint shaker, table shaker, or other
false positive readings. Mixing or agitating the sample intro-
mechanical device to vigorously agitate sample containers.
duces bubbles into the oil, but these readily dissipate with
2 2
7.4 Ultrasonic Bath, rated at 3000 W ⁄m to 10 000 W ⁄m .
sonication or vacuum degassing.
This bath aids in the removal of air bubbles generated in the
6.3 Suspended or free water in the oil will generally be
sample during the agitation process while also working to
counted as particles.
suspend particles in the sample and slow the settling process.
NOTE 5—Free or emulsified water interference presented can be
7.5 Liquid Dispensers, fitted with 0.8 μm or finer filter.
negated by using the water-masking diluent as described in this test
method.
7.6 Volumetric Pipette and Bulb, if volumetric dilution or
6.4 Excessive concentrations of particles in the oil will
fluid transfer with a pipette is desired. Pipettes made of
cause coincidence or electronic saturation errors, or both.
graduated glass or disposable polyethylene. Any glassware
Limits are determined by ISO 11171 and are generally supplied
used shall be cleaned and verified in accordance with ISO
by the instrument manufacturer. These errors may be avoided
3722.
by increasing the dilution ratio with the diluent used in this test
7.7 Density Meter, with an accuracy of 0.01 g ⁄cm , if the
method.
mass dilution method is used.
6.5 Odd-shaped particles and fibers may be classified with
7.8 Filter Apparatus, for filtering the diluent. There is no
incorrect calculated particle size, depending on their orienta-
requirement for the apparatus itself but it shall be capable of
tion as they pass through the sensing zone of the instrument.
producing acceptably clean diluent as necessary. Take appro-
6.6 Dye-in-oil is used by some lubricant manufacturers to
priate safety precautions in handling low flash materials.
distinguish certain lubricant types or brands. It is unusual for
7.9 Vacuum Degassing Apparatus, capable of pulling full
that dye to have a discernible impact on particle count data.
vacuum on the sample container in a vacuum chamber (per
Nonetheless, it is worthwhile to evaluate possible interferences
12.4.1) or syringe degassing port (per 12.4.3) within time limit
for dye-in-oil by testing a sample of filtered, dyed, lubricant. If
specified.
the automatic particle counter yields unusual results or if it
7.10 Glassware, any glassware used shall be cleaned and
reports an optical warning message, then this may be an
verified in accordance with ISO 3722.
indication of this type of interference.
7.11 Sample Container, a container used for collecting the
6.7 Excessive soot-in-oil is an interference that makes it
neat sample per 9.1 and 9.2, or for diluting sample specimens.
impractical to test in-service diesel engine lubricants, espe-
7.11.1 Sample containers shall not be reused.
cially when soot level exceeds 1 %. This is not normally a
7.11.2 Recommended containers are cylindrical specimen
problem for natural gas and gasoline engine oils. However
bottles (or jars) typically made of polypropylene, polystyrene,
heavy duty diesel engine oils typically produce excessive soot
PET, or glass with nominally flat bottoms, fitted with a suitable
for most automatic particle counters. The coincident, opaque,
non-shedding threaded cap.
soot particles reduce light transmission and produce very high
7.11.3 The dimensions and capacity of sample containers
false particle counts.
depends on specimen requirements and APC design. Sample
6.8 Solid lubricants, such as molybdenum disulfide or
containers often have an approximate capacity of 125 mL.
graphite are used in some lubricating oils, especially for
However individual specimen requirements and APC design
extreme pressure applications. These materials are typically
may call for substantially smaller or much larger sample
used at levels high enough to render the fluid opaque or to
containers.
cause coincidence errors due to high particle concentrations in
7.11.4 After performing any cleaning procedures, the
the detector. Even if these factors can be overcome with
sample containers shall meet the cleanliness criteria of contrib-
sufficient dilution, increases in particle counts are difficult to
uting less than 1 % of the total particles expected in the
determine with adequate precision due to the inherently high
cleanest sample.
particle counts in these fluids.
7.11.5 Sample containers shall be compatible with fluid and
6.9 Specimen bottles shall not be reused. This is a source of
able to withstand the temperature of the fluid when collecting
cross-contamination interference.
the sample. Sample containers with certified cleanliness levels
(for example, “ultra clean”) may be used to collect samples for
7. Apparatus particle counting.
7.1 Liquid Automatic Particle Counter (APC), liquid optical 7.12 Specimen Bottle, or sample specimen bottle, a sample
particle counter based on the light extinction principle. The container used for diluting at least a portion of a sample. A
D7647 − 24
specimen bottle shall meet the same criteria as the sample 9.5 Determine whether water-masking diluent (see 6.3) or
container (7.11.1 – 7.11.5). diluent (non water-masking) is to be used for dilution based on
indication or not of emulsified water-in-oil.
7.13 Filters, to be used with filter apparatus (see 7.8).
Recommended filters are cellulose or polycarbonate with a 9.6 Determine the desired dilution ratio. The dilution ratio
0.8 μm or smaller pore size. may vary depending on the viscosities of the sample and the
diluent and the range of viscosities that can be accommodated
7.14 Disposable, Single-Use Syringes, uncontaminated and
by the APC.
directly taken from individually sealed pouches are sometimes
9.6.1 A dilution ratio of ~50 % sample to ~50 % diluent is
used instead of a sample inlet tube to deliver samples to
acceptable for most applications although a smaller sample-to-
automatic particle counters.
diluent ratio is often used.
9.6.2 If the sample is very dark or high particulate contami-
8. Reagents and Materials
nation is suspected, a lower sample to diluent dilution ratio is
8.1 Calibration Fluid, a suspension of ISO Medium Test
suggested. This sort of excessively high contamination deserv-
Dust in oil or hydraulic fluid, using either a primary sample
ing lower dilution ratio is often evidenced when ISO ≥4 μm
(c)
obtained directly from NIST (SRM 2806) or a secondary
is equivalent to ISO ≥6 μm indicating unusually small
(c)
sample prepared in accordance to ISO 11171 and at least
difference in particle counts between these size ranges.
secondary traceable to NIST.
9.6.3 For the temporary precision statement of reproducibil-
8.2 Diluent, from list in Annex A1, Table A1.1, shall be
ity reported in Section 14, a mass dilution ratio of 25 % 6 2 %
filtered to ensure it contributes less than 12.5 % of the total
sample to 75 % 6 2 % diluent was consistently used and the
particles counted in the diluted sample tested according to this
diluent was a blend of 33 % 6 2 % lamp oil with 67 % 6 2 %
method.
dipropylene glycol n-propyl ether (DPnB) for water-masking.
8.3 Water-Masking Diluent, from Annex A1, Table A1.1,
9.7 Take appropriate safety precautions when collecting
is either a volumetric mixture of toluene and 2-propanol (also
samples.
called isopropanol or isopropyl alcohol), typically in 75:25
10. Calibration and Verification
proportions, or dipropylene glycol n-propyl ether. The water-
masking diluent shall be filtered to ensure it contributes less
10.1 Calibration:
than 12.5 % of the total particles counted in the diluted sample
10.1.1 Calibration of the APC shall be done with an
tested according to this method.
undiluted NIST-traceable calibration fluid in accordance with
ISO 11171.
9. Sample Collection and Handling
10.1.2 Calibration of the APC shall be done within the
9.1 Unless otherwise specified, take a representative sample
timeframe indicated by the particle counter manufacturer, or at
in accordance with Practices D4057, D4177, or other compa-
least annually if no frequency is specified. Refer to reference in
rable sampling practices using a clean and appropriate sample
10.2.1 to establish calibration frequency.
container. Containers previously holding a sample or any other
10.2 Verification:
type of fluid are not considered appropriate containers.
10.2.1 Verify that the APC is holding its calibration by
9.2 Ensure that enough sample is collected to perform all
analyzing a primary or secondary calibration fluid allowing for
analysis methods of interest. The container shall not be filled
sample-to-sample variation outlined in Annex A2, Table A2.1
beyond 80 % of its total capacity to allow volume for sufficient
and allowing for calibration fluid batch-to-batch variation.
agitation.
10.2.2 Verify that the APC is providing internally consistent
results by analyzing diluent looking for expected results and
9.3 Label the sample according to the expectations of the
allowing for sample-to-sample variation outlined in Annex A2,
analyzing laboratory, including oil type at a minimum.
Table A2.1.
9.4 Upon receipt at the analyzing laboratory, the sample
10.2.3 Verification checks are recommended on a quarterly
shall be inspected and any non-standard conditions noted. This
basis for instruments analyzing multiple samples regularly
includes inappropriate container, overfilled container, visible
(such as weekly). Checks shall also be performed if an
particulates, and free water. Recommend a re-sample if inap-
instrument has not been used for over three months or if the
propriate container or overfilled container is noted.
particle counter has been altered in such a way that could
impact its calibration.
A water-masking method for counting light obstructing particles in a test oil
11. Preparation of Apparatus
sample containing a substantially immiscible fluid, and where the test oil sample is
mixed with a masking fluid that is soluble with the oil and with the substantially
11.1 The APC shall be set up according to the instrument
immiscible fluid, is covered by US Patent 6,064,680 issued May 16, 2000.
5 manufacturer’s operating manual.
The sole source of manufacturer of the diluent known to the committee at this
time is DOWANOL DPnB, a registered trademark of Dow Chemical Company,
11.2 Ensure that the ISO 4406 mode of operation is selected
Abbott Rd., Midland, MI 48640. Dow Chemical Company supplies 1–L bottles of
and displayed. If the APC has printing or electronic data output
DOWANOL DPnB through Sigma-Aldrich Corp., St. Louis, MO, www.sigma-
aldrich.com. If you are aware of alternative suppliers, please provide this informa- capabilities, ensure those are also set to ISO 4406.
tion to ASTM International Headquarters. Your comments will receive careful
11.3 Set the flow-rate to the setting at which the APC was
consideration at a meeting of the responsible technical committee, which you may
attend. calibrated.
D7647 − 24
11.4 If the APC is capable of running a pre-set program, set 12.1.2 Shake the sample container and its contents in the
the APC to flush 10 mL to 25 mL of sample prior to analysis, mechanical shaker. For samples 200 mL or less, shake for one
then run three analyses consecutively of at least 5 mL per run. min. For samples 200 mL or larger, shake for 3 min. (Samples
If the APC cannot run a preset flush, set it to run four analyses that are provided in containers larger than the capacity of the
consecutively of at least 10 mL per run. When setting the mechanical shaker may be shaken using a lateral shaker or
amount of fluid to be analyzed per run, ensure
...

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: D7647 − 10 (Reapproved 2018) 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
This standard is issued under the fixed designation D7647; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope Scope*
1.1 This test method covers the determination of particle concentration and particle size distribution in new and in-service oils
used for lubrication and hydraulic purposes.
1.2 Particles considered are in the range from 4 μm to 200 μm with the upper limit being dependent on the specific automatic
(c) (c)
particle counter being used.
NOTE 1—For the purpose of this test method, water droplets not masked by the diluent procedure are detected as particles, and agglomerated particles
are detected and reported as a single larger particle.
NOTE 2—The subscript is used to denote that the apparatus has been calibrated in accordance with ISO 11171. This subscript strictly only applies
(c) (c)
to particles up to 50 μm.
1.3 Lubricants that can be analyzed by this test method are categorized as petroleum products or synthetic based products, such
as: polyalpha olefin, polyalkylene glycol, or phosphate ester. Applicable viscosity range is up to 1000 mm /s at 40 °C. This
procedure may be appropriate for other petroleum and synthetic based lubricants not included in the precision statement.
1.4 Samples containing visible particles may not be suitable for analysis using this test method.
1.5 Samples that are opaque after dilution are not suitable for analysis using this test method.
1.6 The test method is specific to automatic particle counters that use the light extinction principle and are calibrated according
to the latest revision of ISO 11171.
1.7 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.
1.8 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.
This test method is under the jurisdiction of ASTM Committee D02 on Petroleum Products, Liquid Fuels, and Lubricants and is the direct responsibility of Subcommittee
D02.96.05 on In-Service Lubricants Particle Counting Practices and Techniques.
Current edition approved April 1, 2018Feb. 1, 2024. Published May 2018February 2024. Originally approved in 2010. Last previous edition approved in 20102018 as
D7647 – 10.D7647 – 10 (2018). DOI: 10.1520/D7647-10R18. 10.1520/D7647-24.
*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
D7647 − 24
1.9 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.
2. Referenced Documents
2.1 ASTM Standards:
D4057 Practice for Manual Sampling of Petroleum and Petroleum Products
D4175 Terminology Relating to Petroleum Products, Liquid Fuels, and Lubricants
D4177 Practice for Automatic Sampling of Petroleum and Petroleum Products
D6786 Test Method for Particle Count in Mineral Insulating Oil Using Automatic Optical Particle Counters
2.2 ISO Standards:
ISO 3722 Hydraulic fluid power—Fluid sample containers—Qualifying and controlling cleaning methods
ISO 4406 Hydraulic fluid power—Fluids—Method for coding level of contamination by solid particles
ISO 11171 Hydraulic fluid power—Calibration of automatic particle counters for liquids
3. Terminology
3.1 Definitions:
3.1.1 For definitions of terms used in this test method, refer to Terminology D4175.
3.1.2 free water, n—water in excess of that soluble in the sample and appearing in the sample as a haze or cloudiness, as droplets,
or as a separated phase or layer.
3.1.3 soot-in-oil, n—in internal combustion engines, <1 μm size particles, primarily carbon, created in the combustion chamber
as products of incomplete combustion.
3.2 Definitions:Definitions of Terms Specific to This Standard:
3.1.1 For the purposes of this test method, the following definitions apply:
3.2.1 coincidence, n—the presence of more than one particle in the sensing zone of a particle analyzer at the same time, causing
incorrect sizing and incorrect counting of the particle present. The coincidence limit of the counter is determined by the maximum
acceptable concentration of particles in the sensing zone and is supplied by the instrument manufacturer. Refer to Section 3.4 in
ISO 11171.
3.2.2 diluent, n—a solvent listed in Annex A1, Table A1.1, having viscosity less than 10 mm /s at 40 °C that is physically and
chemically compatible with the apparatus used and easily soluble at room temperature with the sample lubricant or hydraulic fluid.
3.2.3 emulsified water, n—water that exists in oil between the states of fully dissolved and phase-separated. An emulsifying agent
in the oil causes the two immiscible liquids to coexist in a heterogeneous mixture.
3.1.5 free water, n—water that exists in a separate phase in an oil sample. This occurs when the water content of the oil exceeds
the water holding capacity of the oil.
3.2.4 interfering soft particles, n—an undissolved, dispersed material (such as an additive) within an oil blend or substance that
is formed during the service life of an oil blend.
3.2.4.1 Discussion—
When these substances are present in a sample and not completely solubilized, they are likely to be counted by an optical particle
counter in a similar manner to dirt and wear metal particles, air bubbles, and free water droplets.
3.2.5 ISO Codes, n—a standard classification for coding the level of contamination by solid particles.
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.
Available from American National Standards Institute (ANSI), 25 W. 43rd St., 4th Floor, New York, NY 10036, http://www.ansi.org.
D7647 − 24
3.2.5.1 Discussion—
This code simplifies the reporting of particle count data by converting the number of particles per mL into three classes covering
≥4 μm , ≥6 μm and ≥14 μm . ISO 4406 classifications are used as an option to report results for this test method.
(c) (c) (c)
3.2.6 particle size, μm , n—diameter of a circle with an area equivalent to the projected area of a particle passing through the
(c)
detecting cell in accordance with ISO 11171.
3.2.7 particle size cumulative count, n—total number of particles with sizes greater than a specified particle size (for example,
≥4 μm , ≥6 μm , ≥10 μm , ≥14 μm , ≥21 μm , ≥38 μm , etc.).
(c) (c) (c) (c) (c) (c)
NOTE 3—All particle counts are expressed on per 1 mL basis.
3.1.10 soot-in-oil, n—a sub-micron particulate product of incomplete combustion commonly found in in-service diesel engine
crankcase oil.
3.2.8 water-masking diluent, n—a particular kind of diluent capable of dissolving otherwise immiscible substances such as water
or soft particles in the sample lubricant or hydraulic fluid. See Annex A1, Table A1.1.
3.2.8.1 Discussion—
In Annex A1, Table A1.1, 25 % isopropanol / 75 % toluene and dipropylene glycol n-propyl ether are the only water-masking
diluents in Table A1.1.
4. Summary of Test Method
4.1 Inspect sample.
4.2 Agitate sample.
4.3 Obtain aliquot from homogeneous sample if not diluting in original container.
4.4 Dilute with appropriate diluent for the sample type.
4.5 Agitate diluted sample.
4.6 Degas sample.
4.7 Begin testing within 90 s (or repeat agitation and degassing).
4.8 Obtain particle counts in triplicate (for sample and method blank).
4.9 Analyze data and conduct validity checks.
4.10 Report results.
5. Significance and Use
5.1 This test method is intended for use in analytical laboratories including onsite in-service oil analysis laboratories.
5.2 Hard particles in lubricating or fluid power systems have a detrimental effect on the system as they cause operating
components to wear and also accelerate the degradation of the oil. Hard particles in the oil originate from a variety of sources
including generation from within an operating fluid system or contamination, which may occur during the storage and handling
of new oils or via ingress into an operating fluid system.
5.3 High levels of contaminants can cause filter blockages and hard particles can have a serious impact on the life of pumps,
pistons, gears, bearings, and other moving parts by accelerating wear and erosion.
D7647 − 24
5.4 Particle count results can be used to aid in assessing the capability of the filtration system responsible for cleaning the fluid,
determining if off-line recirculating filtration is needed to clean up the fluid system, or aiding in the decision of whether or not a
fluid change is required.
5.5 To accurately measure hard particle contamination levels, it is necessary to negate the particle counts contributed by the
presence of small levels of free water. This method includes a process by which this can be accomplished using a water-masking
diluent technique whereby water droplets of a size below the target level are finely distributed.
5.6 Certain additives or additive by-products that are semi-insoluble or insoluble in oil, namely the polydimethylsiloxane
defoamant additive and oxidation by-products, are known to cause light scattering in automatic particle counters, which in turn
causes falsely high counts. These and similar materials are commonly termed “soft particles” (see 3.1.63.2.4) and are not known
to directly increase wear and erosion within an operating system. The contribution of these particles to the particle size cumulative
count is negated with this method.
5.7 The use of dilution in this test method counteracts viscosity effects for highly viscous oils that impact the accuracy of
automatic optical particle counting results.
6. Interferences
NOTE 4—This section is consistent with the interferences described in Test Method D6786.
6.1 Dirty environmental conditions and poor handling techniques can easily contaminate the sample or test specimen, or both.
Care shall be taken to ensure test results are not biased by introduced particles.
6.2 Air bubbles in the oil may be counted as particles giving false positive readings. Mixing or agitating the sample introduces
bubbles into the oil, but these readily dissipate with sonication or vacuum degassing.
6.3 Suspended or free water in the oil will generally be counted as particles.
NOTE 5—Free or emulsified water interference presented can be negated by using the water-masking diluent as described in this test method.
6.4 Excessive concentrations of particles in the oil will cause coincidence or electronic saturation errors, or both. Limits are
determined by ISO 11171 and are generally supplied by the instrument manufacturer. These errors may be avoided by increasing
the dilution ratio with the diluent used in this test method.
6.5 Odd-shaped particles and fibers may be classified with incorrect calculated particle size, depending on their orientation as they
pass through the sensing zone of the instrument.
6.6 Dye-in-oil is used by some lubricant manufacturers to distinguish certain lubricant types or brands. It is unusual for that dye
to have a discernible impact on particle count data. Nonetheless, it is worthwhile to evaluate possible interferences for dye-in-oil
by testing a sample of filtered, dyed, lubricant. If the automatic particle counter yields unusual results or if it reports an optical
warning message, then this may be an indication of this type of interference.
6.7 Excessive soot-in-oil is an interference that makes it impractical to test in-service diesel engine lubricants, especially when
soot level exceeds 1 %. This is not normally a problem for natural gas and gasoline engine oils. However heavy duty diesel engine
oils typically produce excessive soot for most automatic particle counters. The coincident, opaque, soot particles reduce light
transmission and produce very high false particle counts.
6.8 Solid lubricants, such as molybdenum disulfide or graphite are used in some lubricating oils, especially for extreme pressure
applications. These materials are typically used at levels high enough to render the fluid opaque or to cause coincidence errors due
to high particle concentrations in the detector. Even if these factors can be overcome with sufficient dilution, increases in particle
counts are difficult to determine with adequate precision due to the inherently high particle counts in these fluids.
6.9 Specimen bottles shall not be reused. This is a source of cross-contamination interference.
D7647 − 24
7. Apparatus
7.1 Liquid Automatic Particle Counter (APC), liquid optical particle counter based on the light extinction principle. The
instrument shall be capable of recording the size and number of particles as they pass across the detector. The particle counter shall
include a sampling apparatus that automatically delivers a predetermined volume of specimen at a controlled flow rate to the
sensing zone of the analyzer.
7.2 Analytical Balance, for mass dilution, calibrated, with a resolution of 100 mg.
7.3 Mechanical Shaker, paint shaker, table shaker, or other mechanical device to vigorously agitate sample containers.
2 2
7.4 Ultrasonic Bath, rated at 3000 W ⁄m to 10 000 W ⁄m . This bath aids in the removal of air bubbles generated in the sample
during the agitation process while also working to suspend particles in the sample and slow the settling process.
7.5 Liquid Dispensers, fitted with 0.8 μm or finer filter.
7.6 Volumetric Pipette and Bulb, if volumetric dilution or fluid transfer with a pipette is desired. Pipettes made of graduated glass
or disposable polyethylene. Any glassware used shall be cleaned and verified in accordance with ISO 3722.
7.7 Density Meter, with an accuracy of 0.01 g ⁄cm , if the mass dilution method is used.
7.8 Filter Apparatus, for filtering the diluent. There is no requirement for the apparatus itself but it shall be capable of producing
acceptably clean diluent as necessary. Take appropriate safety precautions in handling low flash materials.
7.9 Vacuum Degassing Apparatus, capable of pulling full vacuum on the sample container in a vacuum chamber (per 12.4.1) or
syringe degassing port (per 12.4.3) within time limit specified.
7.10 Glassware, any glassware used shall be cleaned and verified in accordance with ISO 3722.
7.11 Sample Container, a container used for collecting the neat sample per 9.1 and 9.2, or for diluting sample specimens.
7.11.1 Sample containers shall not be reused.
7.11.2 Recommended containers are cylindrical specimen bottles (or jars) typically made of polypropylene, polystyrene, PET, or
glass with nominally flat bottoms, fitted with a suitable non-shedding threaded cap.
7.11.3 The dimensions and capacity of sample containers depends on specimen requirements and APC design. Sample containers
often have an approximate capacity of 125 mL. However individual specimen requirements and APC design may call for
substantially smaller or much larger sample containers.
7.11.4 After performing any cleaning procedures, the sample containers shall meet the cleanliness criteria of contributing less than
1 % of the total particles expected in the cleanest sample.
7.11.5 Sample containers shall be compatible with fluid and able to withstand the temperature of the fluid when collecting the
sample. Sample containers with certified cleanliness levels (for example, “ultra clean”) may be used to collect samples for particle
counting.
7.12 Specimen Bottle, or sample specimen bottle, a sample container used for diluting at least a portion of a sample. A specimen
bottle shall meet the same criteria as the sample container (7.11.1 – 7.11.5).
7.13 Filters, to be used with filter apparatus (see 7.8). Recommended filters are cellulose or polycarbonate with a 0.8 μm or smaller
pore size.
D7647 − 24
7.14 Disposable, Single-Use Syringes, uncontaminated and directly taken from individually sealed pouches are sometimes used
instead of a sample inlet tube to deliver samples to automatic particle counters.
8. Reagents and Materials
8.1 Calibration Fluid, a suspension of ISO Medium Test Dust in oil or hydraulic fluid, using either a primary sample obtained
directly from NIST (SRM 2806) or a secondary sample prepared in accordance to ISO 11171 and at least secondary traceable to
NIST.
8.2 Diluent, from list in Annex A1, Table A1.1, shall be filtered to ensure it contributes less than 12.5 % of the total particles
counted in the diluted sample tested according to this method.
8.3 Water-Masking Diluent, from from Annex A1, Table A1.1, is either a volumetric mixture of toluene and 2-propanol (also
called isopropanol or isopropyl alcohol), typically in 75:25 proportions, or dipropylene glycol n-propyl ether. The water-masking
diluent shall be filtered to ensure it contributes less than 12.5 % of the total particles counted in the diluted sample tested according
to this method.
9. Sample Collection and Handling
9.1 Unless otherwise specified, take a representative sample in accordance with Practices D4057, D4177, or other comparable
sampling practices using a clean and appropriate sample container. Containers previously holding a sample or any other type of
fluid are not considered appropriate containers.
9.2 Ensure that enough sample is collected to perform all analysis methods of interest. The container shall not be filled beyond
80 % of its total capacity to allow volume for sufficient agitation.
9.3 Label the sample according to the expectations of the analyzing laboratory, including oil type at a minimum.
9.4 Upon receipt at the analyzing laboratory, the sample shall be inspected and any non-standard conditions noted. This includes
inappropriate container, overfilled container, visible particulates, and free water. Recommend a re-sample if inappropriate container
or overfilled container is noted.
9.5 Determine whether water-masking diluent (see 6.3) or diluent (non water-masking) is to be used for dilution based on
indication or not of emulsified water-in-oil.
9.6 Determine the desired dilution ratio. The dilution ratio may vary depending on the viscosities of the sample and the diluent
and the range of viscosities that can be accommodated by the APC.
9.6.1 A dilution ratio of ~50 % sample to ~50 % diluent is acceptable for most applications although a smaller sample-to-diluent
ratio is often used.
9.6.2 If the sample is very dark or high particulate contamination is suspected, a lower sample to diluent dilution ratio is suggested.
This sort of excessively high contamination deserving lower dilution ratio is often evidenced when ISO ≥4 μm is equivalent to
(c)
ISO ≥6 μm indicating unusually small difference in particle counts between these size ranges.
(c)
9.6.3 For the temporary precision statement of reproducibility reported in Section 14, a mass dilution ratio of 25 % 6 2 % sample
to 75 % 6 2 % diluent was consistently used and the diluent was a blend of 33 % 6 2 % lamp oil with 67 % 6 2 % dipropylene
glycol n-propyl ether (DPnB) for water-masking.
A water-masking method for counting light obstructing particles in a test oil sample containing a substantially immiscible fluid, and where the test oil sample is mixed
with a masking fluid that is soluble with the oil and with the substantially immiscible fluid, is covered by US Patent 6,064,680 issued May 16, 2000.
The sole source of manufacturer of the diluent known to the committee at this time is DOWANOL DPnB, a registered trademark of Dow Chemical Company, Abbott
Rd., Midland, MI 48640. Dow Chemical Company supplies 1–L bottles of DOWANOL DPnB through Sigma-Aldrich Corp., St. Louis, MO, www.sigma-aldrich.com. If you
are aware of alternative suppliers, please provide this information to ASTM International Headquarters. Your comments will receive careful consideration at a meeting of
the responsible technical committee, which you may attend.
D7647 − 24
9.7 Take appropriate safety precautions when collecting samples.
10. Calibration and Verification
10.1 Calibration:
10.1.1 Calibration of the APC shall be done with an undiluted NIST-traceable calibration fluid in accordance with ISO 11171.
10.1.2 Calibration of the APC shall be done within the timeframe indicated by the particle counter manufacturer, or at least
annually if no frequency is specified. Refer to reference in 10.2.1 to establish calibration frequency.
10.2 Verification:
10.2.1 Verify that the APC is holding its calibration by analyzing a primary or secondary calibration fluid allowing for
sample-to-sample variation outlined in Annex A2, Table A2.1 and allowing for calibration fluid batch-to-batch variation.
10.2.2 Verify that the APC is providing internally consistent results by analyzing diluent looking for expected results and allowing
for sample-to-sample variation outlined in Annex A2, Table A2.1.
10.2.3 Verification checks are recommended on a quarterly basis for instruments analyzing multiple samples regularly (such as
weekly). Checks shall also be performed if an instrument has not been used for over three months or if the particle counter has
been altered in such a way that could impact its calibration.
11. Preparation of Apparatus
11.1 The APC shall be set up according to the instrument manufacturer’s operating manual.
11.2 Ensure that the ISO 4406 mode of operation is selected and displayed. If the APC has printing or electronic data output
capabilities, ensure those are also set to ISO 4406.
11.3 Set the flow-rate to the setting at which the APC was calibrated.
11.4 If the APC is capable of running a pre-set program, set the APC to flush 10 mL to 25 mL of sample prior to analysis, then
run three analyses consecutively of at least 5 mL per run. If the APC cannot run a preset flush, set it to run four analyses
consecutively of at least 10 mL per run. When setting the amount of fluid to be analyzed per run, ensure that the total volume
consumed by the APC does not exceed the volume of sample held in the sample specimen bottle.
11.5 If the APC has an inlet tube (also called pickup tube) use a clean, low-lint towe
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