ASTM D7690-11(2021)

Standard Practice for Microscopic Characterization of Particles from In-Service Lubricants by Analytical Ferrography

SIGNIFICANCE AND USE
5.1 The objective of ferrography is to diagnose the operational condition of the machine sampled based on the quantity and type of particles observed in the oil. After break-in, normally running machines exhibit consistent particle concentration and particle types from sample to sample. An increase in particle concentration, accompanied by an increase in size and severity of particle types is indicative of initiation of a fault. This practice describes commonly found particles in in-service lubricants, but does not address methodology for quantification of particle concentration.  
5.2 This practice is provided to promote improved and expanded use of ferrographic analysis with in-service lubricant analysis. It helps overcome some perceived complexity and resulting intimidation that effectively limits ferrographic analysis to the hands of a specialized and very limited number of practitioners. Standardized terminology and common reporting formats provide consistent interpretation and general understanding.  
5.3 Without particulate debris analysis, in-service lubricant analysis results often fall short of concluding likely root cause or potential severity from analytical results because of missing information about the possible identification or extent of damaging mechanisms.  
5.4 Ferrographic analysis, as described in this practice, provides additional particle identification capabilities beyond methods described in Guide D7684 for the following reasons:
(1) The ferrographic particle separation method is magnetic thus making it possible to readily distinguish between ferrous and nonferrous wear particles.
(2) Ferrography separates ferrous (magnetic) particles by size.
(3) Deposition is on a glass substrate so that particles may be examined using transmitted light as well as reflected light allowing particle types to be identified that cannot be identified when examination is done using only reflected light.
(4) Ferrograms may be heat treated providing im...
SCOPE
1.1 This practice covers the identification by optical microscopy of wear and contaminant particles commonly found in used lubricant and hydraulic oil samples that have been deposited on ferrograms. This practice relates to the identification of particles, but not to methods of determining particle concentration.  
1.2 This practice interfaces with but generally excludes particles generated in the absence of lubrication, such as may be generated by erosion, impaction, gouging, or polishing.  
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: 30-Sep-2021
• ICS: 75.100 - Lubricants, industrial oils and related products
• Technical Committee: D02 - Petroleum Products, Liquid Fuels, and Lubricants
• Drafting Committee: D02.96.06 - Practices and Techniques for Prediction and Determination of Microscopic Wear and Wear-related Properties

Relations

• Refers: ASTM D4175-23a - Standard Terminology Relating to Petroleum Products, Liquid Fuels, and Lubricants
• Effective Date: 15-Dec-2023
• Refers: ASTM D4175-23e1 - Standard Terminology Relating to Petroleum Products, Liquid Fuels, and Lubricants
• Effective Date: 01-Jul-2023
• Refers: ASTM G40-15 - Standard Terminology Relating to Wear and Erosion
• Effective Date: 01-Nov-2015
• Refers: ASTM G40-13 - Standard Terminology Relating to Wear and Erosion
• Effective Date: 01-Jun-2013
• Refers: ASTM G40-12 - Standard Terminology Relating to Wear and Erosion
• Effective Date: 01-May-2012
• Refers: ASTM D4057-06(2011) - Standard Practice for Manual Sampling of Petroleum and Petroleum Products
• Effective Date: 01-Jun-2011
• Refers: ASTM D7684-11 - Standard Guide for Microscopic Characterization of Particles from In-Service Lubricants
• Effective Date: 01-Jan-2011
• Refers: ASTM G40-10b - Standard Terminology Relating to Wear and Erosion
• Effective Date: 01-Dec-2010
• Refers: ASTM G40-10a - Standard Terminology Relating to Wear and Erosion
• Effective Date: 01-Jul-2010
• Refers: ASTM G40-10 - Standard Terminology Relating to Wear and Erosion
• Effective Date: 01-Jan-2010
• Refers: ASTM G40-09 - Standard Terminology Relating to Wear and Erosion
• Effective Date: 15-Nov-2009
• Refers: ASTM G40-05 - Standard Terminology Relating to Wear and Erosion
• Effective Date: 01-May-2005
• Refers: ASTM G40-04 - Standard Terminology Relating to Wear and Erosion
• Effective Date: 01-Dec-2004
• Refers: ASTM G40-02 - Standard Terminology Relating to Wear and Erosion
• Effective Date: 10-Oct-2002
• Refers: ASTM G40-01 - Standard Terminology Relating to Wear and Erosion
• Effective Date: 10-Jun-2001

Overview

ASTM D7690-11(2021): Standard Practice for Microscopic Characterization of Particles from In-Service Lubricants by Analytical Ferrography provides a systematic approach for identifying wear and contaminant particles in used lubricants using optical microscopy after magnetic separation. Developed by ASTM International, this standard is integral to condition monitoring and maintenance diagnostics for machinery, engines, and hydraulic equipment. By defining consistent methods and terminology, ASTM D7690-11(2021) helps standardize the practice of analytical ferrography and expands its effective use beyond specialist laboratories.

Key Topics

• Analytical Ferrography: Utilizes a ferrograph to separate wear and contaminant particles from oil samples by magnetic means, depositing them on glass slides (ferrograms) for detailed microscopic examination.
• Particle Identification: Focuses on characterizing particles based on morphology, reflectivity, and response to light-distinguishing between ferrous, nonferrous, and nonmetallic particles.
• Standardized Terminology: Defines particle types such as rubbing wear, severe wear, abrasive wear, chunks, spheres, nonmetallic crystalline, and amorphous particles, supporting consistent reporting and interpretation.
• Diagnostic Value: Emphasizes the correlation between particle characteristics (size, type, quantity) and machine condition, helping to identify trends that signal equipment faults, improper lubrication, or contamination.
• Methodological Scope: Specifically addresses the identification of wear particles but does not cover methods for quantifying particle concentration.
• Sample Handling and Preparation: Outlines best practices for acquiring, diluting, and preparing lubricant samples to ensure accurate, representative results.

Applications

The ASTM D7690-11(2021) standard is widely applicable for:

• Predictive Maintenance Programs: Enables the early detection of wear and potential faults in machinery by identifying abnormal wear patterns before catastrophic failure occurs.
• Root Cause Analysis: Assists maintenance teams in determining whether issues arise from abrasion, corrosion, fatigue, or other wear mechanisms by analyzing the specific types of debris present in lubricants.
• Operational Health Monitoring: Offers ongoing surveillance of engines, turbines, gearboxes, and hydraulic systems, ensuring safe and efficient operation across industries such as energy, transport, manufacturing, and aviation.
• Data-Driven Decision Making: Provides standardized reporting formats for particle analysis results, facilitating comparison over time and across different machine types.
• Training and Quality Control: Reduces barriers to entry for ferrographic analysis, making the method accessible for broader use by setting clear procedures and interpretive criteria.

Related Standards

Practitioners may also reference or use in conjunction:

• ASTM D7684: Guide for Microscopic Characterization of Particles from In-Service Lubricants, covering related methodologies.
• ASTM D4057: Practice for Manual Sampling of Petroleum and Petroleum Products, for correct sample collection techniques.
• ASTM D4175: Terminology Relating to Petroleum Products, Liquid Fuels, and Lubricants.
• ISO Tribology Standards: For broader context in wear and lubrication analysis.

Practical Value

Adopting ASTM D7690-11(2021) enhances the reliability and utility of lubricant particle analysis, transforming raw sample data into actionable insights for asset management. This standard bridges the gap between laboratory findings and real-world equipment health, helping maintenance, reliability, and quality teams prevent costly downtime and extend machine longevity. Its emphasis on accessibility, terminology, and reporting supports both novice and expert practitioners in making informed, consistent maintenance decisions.

By applying ASTM D7690-11(2021), organizations position themselves to proactively protect critical infrastructure through advanced oil analysis and wear debris monitoring, ensuring machinery operates efficiently and safely.

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: D7690 − 11 (Reapproved 2021)
Standard Practice for
Microscopic Characterization of Particles from In-Service
Lubricants by Analytical Ferrography
This standard is issued under the fixed designation D7690; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision.Anumber in parentheses indicates the year of last reapproval.A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope D7684Guide for Microscopic Characterization of Particles
from In-Service Lubricants
1.1 Thispracticecoverstheidentificationbyopticalmicros-
G40Terminology Relating to Wear and Erosion
copy of wear and contaminant particles commonly found in
used lubricant and hydraulic oil samples that have been
3. Terminology
deposited on ferrograms. This practice relates to the identifi-
3.1 Definitions:
cation of particles, but not to methods of determining particle
3.1.1 abrasion, n—wearbydisplacementofmaterialcaused
concentration.
by hard particles or hard protuberances. D4175
1.2 This practice interfaces with but generally excludes
3.1.2 abrasive wear, n—wear due to hard particles or hard
particles generated in the absence of lubrication, such as may
protuberancesforcedagainstandmovingalongasolidsurface.
be generated by erosion, impaction, gouging, or polishing.
G40
1.3 The values stated in SI units are to be regarded as
3.1.3 adhesive wear, n—wear due to localized bonding
standard. No other units of measurement are included in this
between contacting solid surfaces leading to material transfer
standard.
between the two surfaces or loss from either surface. G40
1.4 This standard does not purport to address all of the
3.1.4 break-in, n—See run-in. D4175, G40
safety concerns, if any, associated with its use. It is the
3.1.5 break in, v—See run in. G40
responsibility of the user of this standard to establish appro-
priate safety, health, and environmental practices and deter- 3.1.6 catastrophic wear, n—rapidly occurring or accelerat-
mine the applicability of regulatory limitations prior to use.
ing surface damage, deterioration, or change of shape caused
1.5 This international standard was developed in accor- by wear to such a degree that the service life of a part is
dance with internationally recognized principles on standard-
appreciably shortened or its function is destroyed. G40
ization established in the Decision on Principles for the
3.1.7 corrosion, n—chemical or electrochemical reaction
Development of International Standards, Guides and Recom-
between a material, usually a metal surface, and its environ-
mendations issued by the World Trade Organization Technical
ment that can produce a deterioration of the material and its
Barriers to Trade (TBT) Committee.
properties. D4175
3.1.8 corrosive wear, n—wear in which chemical or electro-
2. Referenced Documents
chemical reaction with the environment is significant. G40
2.1 ASTM Standards:
3.1.9 debris, n—in tribology, particles that have become
D4057Practice for Manual Sampling of Petroleum and
detached in a wear or erosion process. G40
Petroleum Products
D4175Terminology Relating to Petroleum Products, Liquid 3.1.10 debris, n—in internal combustion engines, solid
contaminant materials unintentionally introduced in to the
Fuels, and Lubricants
engine or resulting from wear. D4175
3.1.11 fatigue wear, n—wear of a solid surface caused by
This practice is under the jurisdiction ofASTM Committee D02 on Petroleum
fracture arising from material fatigue. G40
Products, Liquid Fuels, and Lubricants and is the direct responsibility of Subcom-
mittee D02.96.06 on Practices and Techniques for Prediction and Determination of
3.1.12 fretting, n—in tribology, small amplitude oscillatory
Microscopic Wear and Wear-related Properties.
motion, usually tangential, between two solid surfaces in
Current edition approved Oct. 1, 2021. Published November 2021. Originally
contact.
approved in 2011. Last previous edition approved in 2017 as D7690–11 (2017).
DOI: 10.1520/D7690-11R21.
3.1.12.1 Discussion—Here the term fretting refers only to
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
the nature of the motion without reference to the wear,
contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM
corrosion,orotherdamagethatmayensue.Theterm frettingis
Standards volume information, refer to the standard’s Document Summary page on
the ASTM website. often used to denote fretting corrosion and other forms of
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
D7690 − 11 (2021)
fretting wear. Usage in this sense is discouraged due to the 3.1.28 three-body abrasive wear, n—form of abrasive wear
ambiguity that may arise. G40 in which wear is produced by loose particles introduced or
generated between the contacting surfaces.
3.1.13 fretting wear, n—wear arising as a result of fretting.
3.1.28.1 Discussion—In tribology, loose particles are con-
(See fretting.) G40
sidered to be a “third body.” G40
3.1.14 friction, n—resistance to sliding exhibited by two
3.1.29 triboelement, n—oneoftwoormoresolidbodiesthat
surfaces in contact with each other. Basically there are two
comprise a sliding, rolling, or abrasive contact, or a body
frictional properties exhibited by any surface; static friction
subjected to impingement or cavitation. (Each triboelement
and kinetic friction. D4175
contains one or more tribosurfaces.)
3.1.15 impact wear, n—wear due to collisions between two
3.1.29.1 Discussion—Contacting triboelements may be in
solid bodies where some component of the motion is perpen-
direct contact or may be separated by an intervening lubricant,
dicular to the tangential plane of contact. G40
oxide, or other film that affects tribological interactions be-
tween them. G40
3.1.16 lubricant, n—any material interposed between two
3.1.30 two-body abrasive wear, n—formofabrasivewearin
surfacesthatreducesthefrictionorwearbetweenthem. D4175
which the hard particles or protuberances which produce the
3.1.17 lubricating oil, n—liquid lubricant, usually compris-
wearofonebodyarefixedonthesurfaceoftheopposingbody.
ing several ingredients, including a major portion of base oil
G40
and minor portions of various additives. D4175
3.1.31 viscosity, n—ratio between the applied shear stress
3.1.18 pitting, n—in tribology, form of wear characterized
and rate of shear. It is sometimes called the coefficient of
by the presence of surface cavities the formation of which is
dynamic viscosity. This value is thus a measure of the
attributed to processes such as fatigue, local adhesion, or
resistance to flow of the liquid. The SI unit of viscosity is the
cavitation. G40
pascal second (Pa·s). The centipoise (cP) is one millipascal
3.1.19 rolling, v—in tribology,motioninadirectionparallel second (mPa·s) and is often used. D4175
to the plane of a revolute body (ball, cylinder, wheel, and so
3.1.32 wear, n—damagetoasolidsurface,usuallyinvolving
forth)onasurfacewithoutrelativeslipbetweenthesurfacesin
progressive loss or displacement of material, due to relative
all or part of the contact area. G40
motion between that surface and a contacting substance or
substances. G40, D4175
3.1.20 rolling contact fatigue, n—damage process in a
triboelement subjected to repeated rolling contact loads, in-
3.2 Definitions of Terms Specific to This Standard:
volving the initiation and propagation of fatigue cracks in or
3.2.1 abrasive wear particles, n—long wire-like particles in
under the contact surface, eventually culminating in surface
the form of loops or spirals generated due to hard, abrasive
pits or spalls. G40
particles present between wearing surfaces of unequal hard-
ness.
3.1.21 run-in, n—in tribology, initial transition process
3.2.1.1 Discussion—Sometimes called cutting wear par-
occurring in newly established wearing contacts, often accom-
ticles.
panied by transients in coefficient of friction, or wear rate, or
both, which are uncharacteristic of the given tribological 3.2.2 analytical ferrography, n—technique whereby par-
system’s long term behavior. (Synonym: break-in, wear-in.) ticles from an oil sample deposited by a ferrograph are
D4175, G40 identified to aid in establishing wear mode inside an oil-wetted
path of a machine.
3.1.22 run in, v—in tribology, to apply a specified set of
3.2.3 bichromatic microscope, n—optical microscope
initial operating conditions to a tribological system to improve
equipped with illumination sources both above and below the
its long term frictional or wear behavior, or both. (Synonym:
microscope stage such that objects may be viewed either with
break in,v,and wear in, v.) See also run-in,n) G40
reflected light, or with transmitted light, or with both simulta-
3.1.23 rust, n—of ferrous alloys, a corrosion product con-
neously.
sisting primarily of hydrated iron oxides. D4175
3.2.4 black oxides of iron, n—generallysmall,blackclusters
3.1.24 scoring, n—in tribology, severe form of wear char-
with pebbled surfaces showing small dots of blue and orange
acterized by the formation of extensive grooves and scratches
color. These are nonstoichiometric compounds containing a
in the direction of sliding. D4175, G40
mixture of Fe O,Fe O and FeO.
3 4 2 3
3.1.25 sliding wear, n—wear due to the relative motion in
3.2.5 contaminant particles, n—particles introduced from
the tangential plane of contact between two solid bodies. G40
an extraneous source into the lubricant of a machine or engine.
3.2.6 chunks, n—free metal particles >5µm with a shape
3.1.26 soot, n—in internal combustion, engines, sub-micron
size particles, primarily carbon, created in the combustion factor (major dimension to thickness ratio) of <5:1.
chamber as products of incomplete combustion. D4175
3.2.7 corrosive wear debris, n—extremely fine partially
oxidized particles caused by corrosive attack.
3.1.27 spalling, n—in tribology, the separation of macro-
scopic particles from a surface in the form of flakes or chips, 3.2.8 dark metallo-oxide particles, n—partially oxidized
usuallyassociatedwithrollingelementbearingsandgearteeth, ferrous wear particles indicating high heat during generation
but also resulting from impact events. G40 most likely due to lubricant starvation.
D7690 − 11 (2021)
3.2.9 entry, n—entryareaoftheferrogram,regionwherethe 3.2.24 severe sliding wear particles, n—severe wear par-
sample first touches down onto the glass surface of the ticles displaying surface striations and straight edges.
ferrogramandwherethelargestferrousparticlesaredeposited.
3.2.25 severe wear particles, n—free metal particles
>15µm,andwithmajordimension-to-thicknessratiosbetween
3.2.10 ferrograph, n—apparatus to magnetically separate
and deposit wear and contaminant particles onto a specially 5:1 and 30:1.
prepared glass microscope slide.
3.2.26 spheres, n—metal spheres may be the result of
3.2.11 ferrogram, n—specially prepared glass microscope incipient rolling contact fatigue or they may be contaminant
particles from welding, grinding, coal burning and steel manu-
slide that has ferrographically deposited particles on its sur-
face. facturing. Spheres may also be caused by electro-pitting.
3.2.27 wear particles, n—particles generated from a wear-
3.2.12 fibers, n—long, thin, nonmetallic particles.
ing surface of a machine.
3.2.13 friction polymers, n—these are characterized by
small metal particles embedded in an amorphous matrix.
4. Summary of Practice
3.2.14 nonferrous metal particles, n—free metal particles
4.1 Periodic in-service lubricant samples are collected from
composed of any metal except iron. All common nonferrous
a machine or engine as part of a routine condition monitoring
metals behave nonmagnetically except nickel.
program.Aferrogram is prepared from the sample to separate
particles from sample fluid. The ferrogram is subsequently
3.2.15 nonmetallic particles, n—particles comprised of
examined using an optical microscope to identify the types of
compounds, organic material, glasses, etc., that have bound
particles present to aid in identifying the wear mode occurring
electrons in their atomic structure.
in the oil-wetted path of the machine.
3.2.16 nonmetallic amorphous particles, n—particles with-
4.2 In usual practice of a routine condition monitoring
outlongrangeatomicorderthataretransparentandthatdonot
program, a ferrogram is not prepared for every sample taken,
appear bright in polarized light.
but may be prepared when routine tests such as spectrochemi-
3.2.17 nonmetallic crystalline particles, n—particles with
cal analysis, particle counting or ferrous debris monitoring
long range atomic structure that appear bright in polarized
indicate abnormal results.
light. These may be single crystals but are most likely
4.3 Theuserofthispracticeemploysconsistentterminology
polycrystalline or polycrystalline agglomerates.
to achieve accepted and understandable interpretations when
3.2.18 platelets, n—flat, free metal wear particles that are
communicatinginstructionsandfindingsbasedonferrographic
longer and wider than they are thick. They have a major
analysis.
dimension-to-thickness ratio in the range of approximately 5:1
to 10:1 or more.
5. Significance and Use
3.2.19 red oxide particles, n—rust particles present as poly-
5.1 The objective of ferrography is to diagnose the opera-
crystalline agglomerates of Fe O appearing orange in re-
2 3
tional condition of the machine sampled based on the quantity
flected white light. These are usually due to water in the
and type of particles observed in the oil. After break-in,
lubricating system.
normally running machines exhibit consistent particle concen-
tration and particle types from sample to sample. An increase
3.2.20 red oxide sliding particles, n—sliding wear particles
in particle concentration, accompanied by an increase in size
that appear gray in reflected white light, but are dull reddish-
brown in white transmitted light. and severity of particle types is indicative of initiation of a
fault. This practice describes commonly found particles in
3.2.21 reworked particles, n—large, very thin, free metal
in-service lubricants, but does not address methodology for
particles often in the range of 20µm to 50µm in major
quantification of particle concentration.
dimension with the frequent occurrence of holes consistent
5.2 This practice is provided to promote improved and
with the explanation these are formed by the passage of a wear
particle through a rolling contact. expandeduseofferrographicanalysiswithin-servicelubricant
analysis. It helps overcome some perceived complexity and
3.2.22 rolling contact fatigue particles, n—flat platelets,
resultingintimidationthateffectivelylimitsferrographicanaly-
withtheirlengthmoreorlessequaltotheirwidth,withsmooth
sis to the hands of a specialized and very limited number of
surfaces, random, jagged and irregularly shaped circumfer-
practitioners.Standardizedterminologyandcommonreporting
ences and a major dimension-to-thickness ratio in the range of
formats provide consistent interpretation and general under-
approximately 5:1 to 10:1 or more.
standing.
3.2.23 rubbing wear particles, n—particles generated as a
5.3 Without particulate debris analysis, in-service lubricant
result of sliding wear in a machine, sometimes called mild
analysis results often fall short of concluding likely root cause
adhesive wear. Rubbing wear particles are free metal platelets
or potential severity from analytical results because of missing
with smooth surfaces, from approximately 0.5µm to 15µm in
information about the possible identification or extent of
major dimension and with major dimension-to-thickness ratios
damaging mechanisms.
fromabout10:1forlargerparticlesandtoabout3:1forsmaller
particles. Any free metal particle <5µm is classified as a 5.4 Ferrographic analysis, as described in this practice,
rubbing wear particle regardless of shape factor unless it is a provides additional particle identification capabilities beyond
sphere. methods described in Guide D7684 for the following reasons:
D7690 − 11 (2021)
(1)The ferrographic particle separation method is mag- 6.1.3 Blank Ferrogram Glass Substrates—Asupply of spe-
netic thus making it possible to readily distinguish between cially prepared microscope slides with nonwetting barriers to
ferrous and nonferrous wear particles. contain sample flow in the central portion of the substrate are
(2)Ferrography separates ferrous (magnetic) particles by required.
size. 6.1.4 Precision Pipettor—Apipettor capable of delivering a
(3)Deposition is on a glass substrate so that particles may precise volume of 1mL of viscous fluid is required.
be examined using transmitted light as well as reflected light 6.1.5 Mixing Vials—Cleanvials,usually12mLcapacity,are
allowingparticletypestobeidentifiedthatcannotbeidentified needed to mix sample with solvent prior to processing by the
when examination is done using only reflected light. ferrograph.
(4)Ferrograms may be heat treated providing important
6.2 Optional Components:
distinctionsbetweenferrousalloytypes(steelversuscastiron),
6.2.1 Hot Plate—A hot plate capable of achieving surface
further distinctions among various nonferrous alloys and dis-
temperatures of 540°C is required if it is desired to heat treat
tinctions between inorganic and organic particles.
ferrogramstofurtheridentifythemetallurgyofmetalparticles.
6.2.2 Surface Thermometer—A surface thermometer ca-
5.5 Caution must be exercised when drawing conclusions
fromtheparticlesfoundinaparticularsample,especiallyifthe pable of measuring to 540°C is needed for heat treating
ferrograms.
sample being examined is the first from that type of machine.
Some machines, during normal operation, generate wear par- 6.2.3 Tongs—Tongs are needed to remove the heated ferro-
gram from the hot plate.
ticles that would be considered highly abnormal in other
machines.Forexample,manygearboxesgenerateseverewear 6.2.4 Camera—The microscope may be equipped with a
suitable camera for taking photomicrographs for reporting and
particles throughout their expected service life, whereas just a
few severe wear particles from an aircraft gas turbine oil documenting purposes.
sample may be highly abnormal. Sound diagnostics require
7. Reagents
that a baseline, or typical wear particle signature, be estab-
lished for each machine type under surveillance.
7.1 Heptane—The recommended solvent is heptane, but
other solvents may be used if they meet the following criteria:
6. Apparatus
7.1.1 The solvent must be a good oil solvent.
7.1.2 The solvent cannot be too volatile. If the solvent
6.1 Required Components:
evaporates too quickly the strings of particles on the ferrogram
6.1.1 Ferrograph or Ferrogram Maker—Apparatus for
surface will be pulled out of place by the movement of the
magnetically separating particles from fluids.
quickly drying solvent.
6.1.2 Bichromatic Microscope—An optical microscope is
7.1.3 If the solvent evaporates too slowly, excessive time
required with dry metallurgical objective lenses and equipped
will be spent waiting for the ferrogram to dry.
with a reflected light source and a transmitted light source so
7.1.4 The solvent needs to be residue and particle-free.
that objects may be viewed from both above and below the
Prepare a ferrogram using only solvent and examine it under
microscopestage.Thispermitsobjectstobeviewedeitherwith
the microscope to make sure the ferrogram surface is clean.
reflected light, or with transmitted light, or with both simulta-
From a practical viewpoint, it will be almost impossible to
neously. Bichromatic microscopes for ferrogram examination
prepare a blank ferrogram, that is, one that is totally free of
are required to be equipped with three objective lenses to give
particles. Therefore, some judgment should be exercised re-
varying degrees of magnification. The low magnification
garding an acceptable cleanliness level. A few small nonme-
objective lens is typically 10×, the medium magnification
tallic particles are tolerable in that they would not interfere
objective lens may be 40× or 50× and the high magnification
withevaluationofmachinecondition.Ontheotherhand,ifthe
objective lens may be 80× or 100×. Ten power (10×) ocular
blank ferrogram has metallic particles deposited on it, then
(eyepiece) lenses are used such that total magnification
stepsneedtobetakentoeliminatethesourceofcontamination.
achieved is 100× at low magnification, 400× or 500× at
It may be necessary to filter the solvent through a submicron
medium magnification and 800× or 1000× at high magnifica-
membrane filter to remove particulate contaminants or to let
tion.Thenumericalaperturesoftheobjectivelensesneedtobe
the solvent remain undisturbed for overnight or longer so that
high to maximize illumination of particle surfaces when
particles settle to the bottom of the bottle or container.
viewed in reflected light. It is required to be able to polarize
Withdrawing solvent from near the top of the undisturbed
either light path to facilitate particle identification. Polarized
container will likely yield particle free solvent.
light aids in the identification of nonmetallic particles. A red
filter is required to be optionally placed in the reflected light
8. Sampling and Sample Handling
path and a green filter is required to be optionally placed in the
8.1 Sample Acquisition—The objective of sampling is to
transmitted light path. The simultaneous use of red reflected
obtain a test specimen that is representative of the entire
and green transmitted light aids in the distinction between
quantity. Thus, laboratory samples should be taken in accor-
metallic and nonmetallic particles. One of the ocular lenses
dance with instructions in Practice D4057.
should be fitted with a calibrated scale so that length of objects
maybemeasured.Thestagedriveofthemicroscopeshouldbe
9. Procedure
fitted with calibrated divisions so that thickness of objects may
be measured as the stage is raised or lowered. 9.1 Ferrogram Preparation:
D7690 − 11 (2021)
9.1.1 Sample Preparation—Laboratory samples should be 9.1.4.1 This causes the glass substrate to be elevated at the
shaken or agitated to ensure a representative sample is taken entry end relative to the exit end. The purpose is to reduce the
from the sample bottle. magnetic field strength at the entry end so that small particles
are not deposited as quickly as they might otherwise be. This
9.1.2 In-servicelubricatingoilsamplesmustbedilutedwith
gives better separation between large and small magnetic
solvent to lower their viscosity before the sample is allowed to
particles as they are deposited on the substrate.
flowontothesubstrate.Ifthesolventisparticlefree,itdoesnot
9.1.5 Gently release the positioning pin so that the glass
matter how much solvent is used to dilute the oil sample. The
substrate is held firmly in place against the right edge of the
purpose of the dilution is to make the solvent/sample mixture
magnet channel.
have a viscosity such that it flows onto the ferrogram at an
approximate rate of 0.4mL⁄min. Experience indicates that an 9.1.6 Complete ferrogram preparation following specific
ISO 68 oil (an oil having a viscosity of 68 centistokes (cSt) at manufacturer’s instructions.
40°C), when diluted in the ratio of 3 parts oil sample to one
9.1.6.1 This will entail allowing the prepared solvent/
part heptane, will flow at approximately 0.4mL⁄min. sample mixture to flow slowly across the glass surface of the
ferrogram slide during which time ferromagnetic particles will
9.1.2.1 If the viscosity of the solvent/sample mixture is too
be deposited on the glass surface in an orderly fashion
high, the particles will be retarded in their migration through
according to size. Weakly magnetic and nonmagnetic particles
the fluid toward the magnet pole pieces. This will have the
will be deposited randomly along the length of the ferrogram.
effect of allowing large ferrous particles to penetrate further
Soot particles, as found in diesel engine lubricating oil
along the length of the ferrogram than would normally be the
samples, are repelled by the magnetic field of the ferrograph
case. Worse, however, from an operational viewpoint, is that
and flow off the ferrogram to waste.After the prepared sample
the fluid will be so viscous that it will form a large crown and
has flowed completely across the ferrogram surface, the
spill over the non-wetting barrier stripe on the ferrogram
surface necessitating the ferrogram preparation process to be remaining sample on the ferrogram surface is rinsed using an
appropriate solvent, per specific manufacturer’s instructions.
repeated. If the solvent/sample viscosity is too low, the ferrous
(magnetic) particles will migrate too quickly toward the pole After rinsing, remaining solvent is allowed to dry and the
separated wear and contaminant particles become firmly ad-
pieces and many small particles will be deposited at the entry
region of the ferrogram (where the fluid first touches down on hered to the glass surface of the ferrogram.
the ferrogram) along with the large ferrous particles. 9.1.7 After the surface is completely dry, withdraw the
Furthermore,thefastflowratemaycausethefluidtospillover spring-loaded positioning pin and lift the ferrogram off the
attheexitendoftheferrograminsteadofflowingintothedrain magnet assembly. The ferrogram is now ready for microscopi-
tube.Therefore,somejudgmentisrequiredtodilutethesample cal examination.
properly.
9.1.7.1 Use caution—the ferrogram must be lifted straight
up off the magnet assembly. If the ferrogram is slid along the
9.1.2.2 In general, oils with ISO grades up to 68 will flow
magnet assembly, the magnetic field will twist and distort the
properly if diluted in the ratio of 3 parts sample to one part
strings of ferrous particles on the ferrogram surface.To lift the
solvent.Moreviscousoilsrequiremoresolvent,3partssample
ferrogram off smoothly, it is recommended that the exit end be
to 2 parts solvent is recommended.
lifted up first while the front end still rests on the small step at
9.1.2.3 To a large extent, the effect of viscosity on the
the back of the top plate slot. Once the back end has been
deposition pattern is self-compensating. The higher the
raised approximately 2cm, the entire ferrogram can be lifted
viscosity, the longer it takes for the solvent/sample mixture to
away from the magnet assembly.
flow,andthelongerittakesfortheparticlestoflowthroughthe
fluid due to the viscous resistance the particles experience.
9.2 Ferrogram Analysis Procedure:
Likewise,whentheviscosityislow,thesampleflowsdownthe
9.2.1 Place the ferrogram onto the stage of the microscope
substrate more quickly, and the particles move more quickly
and begin inspection of the particles thereon. Table 1 summa-
toward the magnet assembly because the viscous resistance
rizes the suggested procedure for analysis of a ferrogram. Step
they experience is correspondingly less. Therefore, the result-
1 suggests viewing of the ferrogram at low magnification with
ingdepositionpatternontheferrogramismoreorlessthesame
redreflectedandgreentransmittedlight.Atthistime,itmaybe
even though the solvent/sample viscosity varies to some
determined whether the deposit on the ferrogram is too heavy
degree.
forproperparticleidentification.Ifthedepositattheferrogram
9.1.3 Remove the blank ferrogram glass substrate from its
entry is so heavy that particles are piled on top of one another
plasticcoverandpositionitsothatthemarkingdotontheglass
it will be very difficult to determine the types and relative
surface is in the lower left-hand corner of the ferrograph
amounts of particles present. Some piling up is tolerable, but
magnet channel. The purpose of the marking dot is to identify
strings of ferrous particles should be separated and ideally
the side of the glass having the non-wetting barrier stripe.
particles should be deposited in a single layer. If too many
9.1.4 Withdraw the spring-loaded position pin on the left particles are present, it is recommended that the sample be
side of the magnet assembly. Place the glass substrate on the diluted 9:1 with particle free oil and a new ferrogram be
magnet assembly. Position the upper end of the glass substrate prepared with 3 mLof the diluted sample. This will result in a
so that it rests on the small step at the back of the magnet ferrogram prepared from 0.3 mL of sample, rather than the
assembly slot.Allow the exit end of the glass substrate to rest standard 3mL sample volume. It may happen that the ferro-
on the magnet assembly surface. gram prepared from 0.3mL of sample again has too many
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TABLE 1 Suggested Procedure for Analysis of a Ferrogram
Step Magnification Reflected Transmitted Comments
1 100× (low) Red Green View the entry region to determine if too many particles are deposited on the ferrogram. If so, a
new ferrogram needs to be prepared from diluted sample. Otherwise, proceed to Step 2.
2 100× (low) Red Green Look for severe wear particles at entry by presence of bright red particles. Rubbing wear particles
...