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: D7684 − 11 (Reapproved 2016)

Standard Guide for

Microscopic Characterization of Particles from In-Service
Lubricants1
This standard is used under the fixed designation D7684; 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 2. ReferencedDocuments
1.1 This guide covers the classification and reporting of 2.1 ASTMStandards:2
results from in-service lubricant particulate debris analysis D4130 Test Method for Sulfate Ion in Brackish Water, Sea
obtained by microscopic inspection of wear and contaminant water, and Brines
particles extracted from in-service lubricant and hydraulic oil D4175 Terminology Relating to Petroleum Products,
samples. This guide suggests standardized terminology to LiquidFuels, and Lubricants
promote consistent reporting, provides a logical framework to D7416 Practice for Analysis of In-Service Lubricants Using
document likely or possible root causes, and supports a Particular Five-Part (Dielectric Permittivity, Time-
inference associated machinery health condition or severity Resolved Dielectric Permittivity with Switching
based on available debris analysis information. MagneticFields, Laser Particle Counter, Microscopic
DebrisAnalysis, and Orbital Viscometer) Integrated
1.2 This guide shall be used in conjunction with an
Tester
appropriate wear debris analysis sample preparation and
D7596 Test Method for Automatic Particle Counting and
inspection technique including, but not limited to, one of the
Particle Shape Classification of Oils Using a
following:
DirectImaging Integrated Tester
1.2.1 Ferrography using linear glass slides, D7647 Test Method for Automatic Particle Counting of
1.2.2 Ferrography using rotary glass slides, Lubricating and Hydraulic Fluids Using Dilution
1.2.3 Patch analysis using patch makers (filtration through Techniques to Eliminate the Contribution of Water and
membrane filters), Interfering Soft Particles by Light Extinction
1.2.4 Filter debris analysis, D7690 Practice for Microscopic Characterization of
1.2.5 Magnetic plug inspection, or Particles from In-Service Lubricants by Analytical
1.2.6 Other means used to extract and inspect particulate Ferrography
debris from in-service lubricants. G40 Terminology Relating to Wear and Erosion
2.2 ISOStandard:3
1.3 This standard is not intended to evaluate or characterize ISO 11171Hydraulic fluid power – Calibration of automatic
the advantage or disadvantage of one or another of this particle counters for liquids
particular particle extraction and inspection methods.
3. Terminology
1.4 The values stated in SI units are to be regarded as
standard. No other units of measurement are included in this 3.1 Definitions:
standard. 3.1.1 abrasive wear, n—wear due to hard particles or hard
protuberances forced against and moving along a solid
1.5 This standard does not purport to address all of the
surface.G40
safety concerns, if any, associated with its use. It is the
responsibility of the user of this standard to establish 3.1.2 abrasion, n—wear by displacement of material
appropriate safety and health practices and determine the caused by hard particles or hard protuberances.D4175
applicability of regulatory limitations prior to use. 3.1.3 break-in,n—see run-in.G40
3.1.4 fatigue wear, n—wear of a solid surface caused by
fracture arising from material fatigue.G40
1
This guide is under the jurisdiction of ASTM Committee D02on Petroleum
Products, Liquid Fuels, and Lubricants and is the direct responsibility of Subcom- 2
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
mitteeD02.96.06 on Practices and Techniques for Prediction and Determination of contact ASTM Customer Service at service@astm.org. For the Annual Book of
Microscopic Wear and Wear-related Properties. ASTM Standards volume information, refer to the standard’s Document Summary
Current edition approved Oct. 1, 2016. Published November 2016. Originally page on the ASTM website.
approved in 2011. Last previous edition approved in 2011 as D7684 – 11. DOI: 3
Available from International Organization for Standardization (ISO), 1, ch. De
10.1520/D7684-11R16. la Voie-Creuse, Case Postale 56, CH-1211, Geneva 20, Switzerland, www.iso.org.

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 D7684 − 11 (2016)
in the form of loops or spirals that are generated due to hard,
3.1.5 fretting, n—in tribology, small amplitude oscillatory abrasive particles present between wearing surfaces of unequal
motion, usually tangential, between two solid surfaces in hardness, sometimes called cutting wear particles or ribbons.
contact.
3.1.5.1 Discussion—Here, the term fretting refers only to 3.2.2 Analytical ferrography, n—a technique whereby
the nature of the motion without reference to the wear, particles from an oil sample deposited by a ferrograph are
corrosion, or other damage that may identified to aid in establishing wear mode inside an oil-wetted
ensue.Thetermfrettingisoftenused to denote fretting corrosion path of a machine.
and other forms of fretting wear. Usage in this sense is 3.2.3 Chunks, n—free metal particles >5 µm with a shape
discouraged due to the ambiguity that may arise. G40 factor(major dimension to thickness ratio)of<5:1.
3.1.6 fretting wear, n—wear arising as a result of fretting 3.2.4 Contaminant particles, n—particles introduced from
(see fretting). G40 an extraneous source into the lubricant of a machine or engine.
3.1.7 lubricant, n—any material interposed between two
3.2.5 Corrosive wear debris, n—usually, extremely fine
surfaces that reduces the friction or wear between them.
partially oxidized particles caused by corrosive attack.
D4175
Particles can be come quite large in case so extreme corrosion.
3.1.8 lubricating oil, n—liquid lubricant, usually
comprising several ingredients, including a major portion of 3.2.6 Debris, n—in tribology, solid or semi-solid particulate
base oil and minor portions of various additives. D4175 matter introduced to lubricant through contamination or
detached from a surface due to wear, corrosion, or erosion
3.1.9 rolling, v—motion in a direction parallel to the plane process.
of a revolute body (ball, cylinder, wheel, and so forth) on a
surface without relative slip between the surfaces in all or part 3.2.7 ferrograph, n—apparatus that magnetically separates
of the contact area. G40 and deposits wear and contaminant particles onto a specially
prepared glass microscope slide.
3.1.10 rolling contact fatigue, n—damage process in a tribo
element subjected to repeated rolling contact loads, involving 3.2.8 Fibers, n—long, thin, nonmetallic particles.
the initiation and propagation of fatigue cracks in or under the 3.2.9 Filter debris analysis, n—in tribology, a process for
contact surface, eventually culminating in surface pits or extracting and inspecting debris accumulated on the filter
spalls. G40 media taken from an in-line circulating lubrication system.
3.1.11 run-in, n—in tribology, an initial transition process
3.2.10 Filter patch analysis, n—in tribology, a process
occurring in newly established wearing contacts, often
using a filter patch maker to extract solid or semi-solid matter
accompanied by transients in coefficient of friction or wear
from a liquid and subsequently analyzing the extracted solid or
rate, or both, that are uncharacteristic of the given tribological
semi-solid matter.
system’s behavior. Syn. break-in and wear-in. G40
3.1.12 rust, n—of ferrous alloys, a corrosion product 3.2.11 Filter patch maker, n—in tribology, apparatus to
consisting primarily of hydrated iron oxides. D4175 extract solid or semi-solid matter from liquid by drawing a
volume of solid-containing-liquid through a filter patch having
3.1.13 sliding wear, n—wear due to the relative motion in pores of a prescribed dimension sufficient to retain the solid or
thetangentialplaneofcontactbetweentwosolidbodies.G40 semi-solid matter while allowing the liquid to pass through.
3.1.14 sludge, n—precipitate or sediment from oxidized
3.2.12 Normal, n—in a five-level severity ranking, a one-of-
mineral oil and water. D4130
five relative severity rating commonly associated with the
3.1.15 spalling, n—in tribology, the separation of undamaged or as-new condition having reasonable wear or
macroscopic particles from a surface in the form of flakes or expected operational condition; see also low alert, high alert,
chips, usually associated with rolling element bearings and low fault, and high fault severity conditions.
gear teeth, but also resulting from impact events. G40
3.2.13 Low alert, n—in a five-level severity ranking, a
3.1.16 three-body abrasive wear, n—form of abrasive wear
two-of-five level relative severity commonly associated with
in which wear is produced by loose particles introduced or
some deterioration from the normal condition; however,
generated between the contacting surfaces.
intervention is not yet recommended; see also normal, high
3.1.16.1 Discussion—In tribology, loose particles are alert, low fault, and high fault severity ranking.
considered to be a “third body.” G40
3.1.17 two-body abrasive wear, n—form of abrasive wear 3.2.14 High alert, n—in a five-level severity ranking, a
in which the hard particles or protuberances that produce the three-of-five level relative severity commonly associated with
wear of one body are fixed on the surface of the opposing significant deterioration from normal condition closely
body.G40 approaching the need for intervention; see also normal,
lowalert, low fault, and high fault severity ranking.
3.1.18 wear,n—damage to a solid surface, usuallyinvolving
progressive loss or displacement of material, due to relative 3.2.15 low fault, n—in a five-level severity ranking, a four-
motion between that surface and a contacting substance or of-five relative severity commonly associated with significant
substances. D4175,G40 deterioration from the alert condition, and intervention is
recommended now; see also normal, low alert, high alert, and
3.2 Definitions of Terms Specific to This Standard: high fault severity ranking.
3.2.1 abrasive wear particles, n—long wire-like particles
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 D7684 − 11 (2016)
3.2.16 high fault, n—in a five level severity ranking, a five- a result of sliding and they frequently have straight edges.
of-five relative severity commonly associated withsignifi- cant Their major dimension-to-thickness ratio is approximately
deterioration from alert condition, and intervention isboth 10:1.
recommended and overdue; see also normal, low alert, high 3.2.29 severe wear particles, n—in tribology, free metal
alert, and low fault severityranking. particles >15 µm with major dimension-to-thickness ratios
3.2.17 magnetic plug inspection—process for inspecting between 5:1 and30:1.
and, if necessary, extracting ferrous alloy debris from in- 3.2.30 spheres, n—in tribology, metal spheres may be the
service lubricants using a magnetic object placed in the oil result of incipient rolling contact fatigue or they may be
compartment,typicallyassociatedwithadrainplug. contaminant particles from welding, grinding, coal burning,
3.2.18 nonmetallic particles, n—in tribology, particlescom- and steel manufacturing. Spheres may also be caused by
prised of compounds, organic material, sand, dirt, glasses, and electro-pitting.
so forth, that often demonstrate some element of translucence 3.2.31 wear particles, n—particles generated from a wear-
under microscopicbacklight. ing surface of amachine.
3.2.19 platelets, n—flat metal particles with a length more-
or-less equal to their width, and a major dimension-to- 4. Summary ofGuide
thickness ratio in the range of approximately 5:1 to 10:1 or 4.1 Periodic in-service lubricant samples are collected from
more (see rolling contact fatigueparticles). a machine as part of a routine condition monitoring program.
3.2.20 red oxide particles, n—rust particles present as poly- The sample is prepared to separate particles from the sample
crystalline agglomerates of Fe2O3 appearing orange in re- fluid. The separated particles are subsequently examined using
flected white light. These are usually due to water in the an optical microscope to identify the types of particles present
lubricatingsystem. to aid in identifying the wear mode occurring in the oil-wetted
3.2.21 reworked particles, n—large, very thin, free metal path of themachine.
particles often in the range of 20 to 50 µm in major dimension 4.2 In usual practice of a routine condition monitoring
with the frequent occurrence of holes consistent with the program, particle separation and examination is not done for
explanation that these are formed by the passage of a wear every sample taken, but may be done when routine tests such
particle through a rollingcontact. as spectrometric analysis, particle counting, or ferrous debris
3.2.22 ribbons, n—see abrasive wearparticles. monitoring indicate abnormalresults.
3.2.23 rolling contact fatigue particles, n—flat platelets, 4.3 This guide is to be used with a sample preparation
with a length more-or-less equal to their width, with smooth method that extracts particulate debris from in-service lubri-
surfaces, random, jagged and irregularly shaped cant systems for subsequent microscopicexamination.
circumferences, and a major dimension-to-thickness ratio in 4.4 The user of this guide should employ consistent termi-
therangeofapproximately5:1to10:1ormore. nology to achieve accepted and understandable interpretations
3.2.24 rolling contact fatigue wear, n—in tribology, fatigue when communicating instructions and findings based on par-
wear caused by loaded rolling contact typically between roller ticleanalysis.
and race in bearings or between gear teeth in the vicinity ofthe 4.5 Aprocessissuggestedinstandardizedformattoidentify and
pitch line, typically forming spall-type pitting and releasing further classify multiple distinct groups of particulate debris
rolling contact fatigue particles (see 3.2.23); also calledrolling extracted from an in-service machinery lubricating sample.
fatigue wear or subsurfacespalling.
4.6 A grid format is suggested in which the user of this
3.2.25 rubbing wear particles, n—particles generated as a guide can present findings and report possible root causes
result of sliding wear in a machine, sometimes called mild along with an assessment of associated machinery health
adhesive wear. Rubbing wear particles are free metal platelets condition or severity based on available debris analysis infor-
with smooth surfaces, from approximately 0.5 to 15 µm in mation.
major dimension and with major dimension-to-thickness ratios
from about 10:1 for larger particles to about 3:1 for smaller 4.7 An alternate classification scheme is suggested that is
particles. Any free metal particle <5 µm is classified as a consistent with PracticeD7690.
rubbing wear particle regardless of shape factor unless it is a
sphere. 5. Significance andUse
3.2.26 scoring, n—in tribology, a consequence ofsevere 5.1 The objective of particle examination is to diagnose the
sliding wear characterized by formation of extensive grooves operational condition of the machine sampled based on the
andscratchesinthedirectionofsliding;alsocalledstriation. quantity and type of particles observed in the oil. After break-
in,normallyrunningmachinesexhibitconsistentparticle
3.2.27 severeslidingwear,n—intribology,slidingwearthat concentration and particle types from sample to sample. An
removessubsurfacemetal;alsocalledabnormalslidingwear. increase in particle concentration, accompanied by an increase
3.2.28 severe sliding wear particles, n—in tribology, severe in size and severity of particle types, is indicative of initiation
slidingwearparticlesare>15µmandseveraltimeslongerthan ofafault.Thisguidedescribescommonlyfoundparticlesin
theyarewide.Someoftheseparticleshavesurfacestriationsas

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 D7684 − 11 (2016)
in-service lubricants, but does not address methodology for 7.3 Prepare specimens using one of the following particle
quantification of particle concentration. extractiontechniques:
5.2 This guide is provided to promote improved and ex- 7.3.1 Analytical ferrography using ferrograph to produce
panded use of particulate debris analysis with in-service linearglassslidesinaccordancewithPracticeD7690,
lubricant analysis. It helps overcome some perceivedcomplex- 7.3.2 Analytical ferrography using ferrograph to produced
ity and resulting intimidation that effectively limits particulate rotary glassslides,
debris analysis to the hands of a specialized and very limited 7.3.3 Filterpatchanalysisusingfilterpatchmakers,
number of practitioners. Standardized terminology and com- 7.3.4 Filter debrisanalysis,
mon reporting formats provide consistent interpretation and 7.3.5 Magnetic plug inspection,or
generalunderstanding. 7.3.6 Other means used to extract and inspect particulate
debris from in-service lubricants.
5.3 Without particulate debris analysis, in-service lubricant
analysis results often fall short of concluding likely root cause 7.4 Inspect the specimen using an optical microscope and
or potential severity from analytical results because of missing classify particles using the following procedures. It is common
information about the possible identification or extent of for a single specimen to carry multiple kinds of particles so
damagingmechanisms. classification is normally done for a group of particles by
5.4 Caution shall be exercised when drawing conclusions characterizing individual particles representative of thatgroup.
fromtheparticlesfoundinaparticularsample,especiallyifthe 7.5 Therefore, the first step when inspecting a specimen
sample being examined is the first from that type of machine. normally involves scanning the entire specimen toidentify
Some machines, during normal operation, generate wear par- particle types that are of interest by group. Next, each group is
ticles that would be considered highly abnormal in other characterized in a logical sequence. An atlas of example
machines. For example, many gear boxes generate severewear images is typically used to provide consistency and to assist
particles throughout their expected service life, whereas just a with cross-training between operators. One such atlas is
few severe wear particles from an aircraft gas turbine oil described in the Wear ParticleAtlas.4
sample may be highly abnormal. Sound diagnostics require 7.6 For each group of particles the user should apply
that a baseline, or typical wear particle signature, be estab- consistent characterization criteria. Two example approaches
lished for each machine type under surveillance. are given below in 7.7and 7.8that outline processes and format
for analyzing and recording wear debris analysis
6. Reagents
classificationfindings.
6.1 Use reagents of type and purity following specifications
7.7 For the first example of a particle classification
from the manufacturer of the wear debris analysis sample
approach, see Table 1, which shows a tabular grid a user may
preparation apparatus. Use reagents and solvents that do not
constructtoguideinspectionanddocumentationofweardebris
contribute significant particles to thesample.
analysis findings from a specimen. This kind of tabular grid
7. Procedure may be printed out for note taking or it may be set up as a
computerized form that an operator can click, check, or mark
7.1 Particulate matter extracted from in-service lubricants for ease of recording and database entry. An advantage of
are displayed on a relatively flat surface such as a filter patch, computerized record keeping using this sort of particle char-
glass slide, or other substrate for microscopic inspection. The acterization is that a body of knowledge may be used together
procedure normally involves the following steps. These steps with this standardized terminology to support computerized
maybeperformedinthisorderorinadifferentorder,andsteps may expert system interpretation, review, and checking of data and
be added as needed. This guide applies to interpreting results.Thistabulargrid(seeTable1)istypicallyusedtogether with
microscopic observations (7.1.6) and reporting results (7.1.7) an image atlas including previously analyzed samples,
butdoesnotaddresssteps7.1.1–7.1.5. particularly to assist new users to follow this logical thought
7.1.1 Collecting or concentrating particulatematter, and documentation sequence. Sections 7.7.1 – 7.7.11 describe
7.1.2 Depositing it on a surface to produce a specimen the eleven columns found inTable 1.
suitableforplacementonanopticalmicroscopestage, 7.7.1 Choose a sequence number to represent a particular
7.1.3 Removing residual in-service lubricant fluid from the group of particles observed for this specimen. Chooseone
specimen, identifier from a list such as 1, 2, 3, 4, and 5 as shown in
7.1.4 Transportingthespecimentoamicroscopestage, Column 1 of Table1.
7.1.5 Usingthemicroscopetoinspectthespecimen, 7.7.2 From Column 2, choose the relative concentration
7.1.6 Interpreting observations,and descriptive for particles in this group as seen on this specimen.
7.1.7 Recordingresults. choose one from a list such as: few, moderate, many, dense, as
7.2 Use a desired particulate extraction technique toprepare shown in Column 2 ofTable 1.
a specimen for microscopic wear debris analysis. Specimens
are prepared using an apparatus that effectively extracts solid
particles from liquid samples and deposits the particles on a 4
Anderson, D. P., Wear Particle Atlas (Revised), prepared for the Naval Air
relatively flat supporting surface that can be placed on the Engineering Center, Lakehurst, NJ 08733, 28 June 1982, Report NAEC-92-163.
viewing stage of an opticalmicroscope. (Approved for public release; distribution unlimited.)

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TABLE 1 Suggested Grid for Analysis and Classification of Particles

NOTE 1—Choose one item from each column for each particle group.
1 2 3 4 5 6 7 8 9 10 11
Group Concentration Size, average Size, max Aspect Shape Color Texture Composition Classification Severity
1 Few Fine, <6 µm Fine, <6 µm 1:1 Platelets Red Bright orReflective Ferrous Metal Abrasive Wear Normal
2 Moderate Small, 6 to 14 µm Small, 6 to 14 µm 1:2 Ribbons Black Dull or Oxidized Cupric Metal Mild Sliding Wear Low Alert
Severe Sliding

D7684 − 11 (2016)
Medium, 14 to 40 Medium, 14 to 40
3 Many 1:3 Chunks Tempered Pitted Other Metal Wear High Alert
µm µm
(Metal Removal)
Rolling
5

Large, 40 to 100 Large, 40 to 100 FatigueWear

4 Dense 1:10 Spheres Metallic Striated Dust Low Fault
µm µm (Subsurface
Spall)
5 Huge, >100 µm Huge, >100 µm 1:100 Spiral Straw Smeared Organic Corrosive Wear High Fault
Thermal Copper Amorphous Sludge Other Wear
Needles Brass Other texture Paint Chips Lube Degradation
Dust Contamina-
Fibrous Other Color Other Material
tion
Other Contamina-
Powder
tion
Other Shape
 D7684 − 11 (2016)
7.7.3 From Column 3, choose the average size range that is 7.7.7 Choose the particle color that is generally descriptive
generally descriptive for particles in this group. Use a mea- for this group of particles. Choose from a list such as the
surement technique with microscopic imaging to approximate following: red, black, tempered (showing high temperature
relative size range. Choose from a list of estimated size ranges effects), metallic (showing reflection or other indication of a
corresponding to the following: fine (<6 µm), small (6 µm to metal surface), straw, copper, or other color as shown in
14 µm), medium (14 µm to 40 µm), large (40 µm to 100 µm), Column 7 of Table1.
andhuge(>100µm)asshowninColumn3ofTable1. 7.7.8 Choose the particle texture that is generally descrip-
7.7.3.1 It is best practice, for oil samples not heavilysooted, tive for this group of particles. Choose from a list such as the
to correlate this microscopic average wear particle size ap- following: bright or reflective, dull or oxidized, pitted,striated,
proximationwithcorrespondingparticlecountandparticlesize smeared, amorphous, or other texture as shown in Column
distribution information using an automatic particle counter 8ofTable1.
calibrated in accordance with ISO 11171 and tested in accor- 7.7.9 Choose the term that is generally descriptive, basedon
dance with Test Method D7647. For example, see paragraph visual appearance, for the suspected composition of particles
15.2.3, under Reports, in Practice D7416. Following this best from this group. Choose from a list such as the following:
practice, the analyst seeks to confirm the average size of ferrous metal, cupric metal, other metal, dust, organic (such as
particles from this group by looking for a peak or shoulder in plastic or biological), sludge, paint chips, or other material as
that portion of and Fig. 5 in Practice D7416, as a type ofreport shown in Column 9 ofTable 1.
showingparticlecountinparts-per-millionbyvolumeplot. 7.7.9.1 To distinguish ferrous from nonferrous matter, use
relevant supplemental information including spectrometric
7.7.3.2 Another best practice, especially for oil samples
analysis, a ferrous density measurement, or observing particle
blackened by soot, is to confirm these average size particles
response to a magneticfield.
from this group by comparison to results from a directimaging
7.7.10 Choose the term that is generally descriptive for
integrated tester in accordance with Test MethodD7596.
classification of a mechanism or root cause suspected to
7.7.4 Choose the maximum size range that is generally produce particles found in this group of particles. Choose from
descriptive for particles in this group of particles. Use a alistsuchasthefollowing:abrasivewear,mildslidingwearor
measurement technique with microscopic imaging to approxi- rubbing wear removing mostly metal oxides, severe sliding
mate relative size range. Choose from a list of estimated size wear removing some base metal beneath the metal oxides,
ranges corresponding to the following: fine (<6 µm), small rolling fatigue wear likely to produce subsurface spall, corro-
(6 µm to 14 µm), medium (14 µm to 40 µm), large (40 µm to sive wear, other wear mechanisms, lube degradation by-
100 µm), and huge (>100 µm) as shown in Column 4 of products, dust contamination, or other contamination as shown
Table1. in Column 10 of Table1.
7.7.4.1 It is best practice to correlate this microscopic wear 7.7.11 Choose the level of severity the operator assigns to
debris analysis information regarding particle size with corre- this specimen based on observations regarding this particular
sponding particle count and particle size distribution informa- group of particles. Choose from a list such as the following:
tion using an automatic particle counter calibrated in accor- normal, low alert, high alert, low fault, or high fault as shown
dance with ISO 11171 and tested in accordance with Test in Column 11 of Table1.
Method D7647. For example, see paragraph 15.2.3, under 7.7.11.1 An example of alternate choices for levels of
Reports, in Practice D7416. Following this best practice, the severity in place of the ones listed in Column 11 of Table 1 is
analyst seeks to confirm these maximum size particles from normal, alert (first warning of a developing problem), report-
this group by looking for an inflection in that portion of and able (fault has progressed to a serious stage), moderate trend
Figure5inPracticeD7416,asatypeofreportshowingparticle count (fault is progressing and action may be required), and rapid
in parts-per-million by volumeplot. trend(faultisprogressingrapidlyandactionisrequired).
7.7.4.2 Another best practice is to confirm these maximum 7.8 Second Particle Classification Approach—For a second
size range particles from this group by comparison withresults particle classification approach, the decision grid in Table 2 is
from a direct imaging integrated tester in accordance with Test
MethodD7596.
TABLE 2 Decision Table for Classification by Size and Shape of
7.7.5 Choose the approximate particle dimensional aspect Particles
ratio,alsocalled“aspect,”thatbestdescribesthisgroupof ParticleType Shape Factor
particles.Choosefromalistsuchasthefollowing:1:1,1:2, Size, (Major/Minor Dimension)
MajorDime
nsion
1:3, 1:10, or 1:100, or other dimensional aspect ratio as shown RubbingWearParticles <15µm Thin,>5:1,
in Column 5 of Table 1. Dimensional aspect ratio is the ratioof usually about 10:1
RubbingWearParticles <5µm Any shapeexcept
orthogonal minimum to maximum dimensions for the two- curved or curled
dimensional image of aparticle. AbrasiveWearParticles AnySize Long, thin,curled
or curved,
7.7.6 Choose the particle shape that is generally descriptive ribbon-like
for this group of particles as seen on the specimen. Choose SevereWearParticles >15µm >5:1 to<30:1
from a list such as the following: platelets, ribbons, chunks, Chunks >5µm <5:1
Reworked (Laminar)
spheres, fibers, or other shape as shown in Column 6 of Table1. Particles

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>15µm >30:1
D7684 − 11 (2016)

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 D7684 − 11 (2016)
used in conjunction with Fig. 1. Table 2gives guidance for are generated by exfoliation of parts of this layer. As long as
classifying particles based only on their shape. Table 2 allows only rubbing wear particles are observed, the surfaces from
for the distinction among the first five particle types listed in which they came may be assumed to be in a smooth stable
Fig. 1, namely rubbing wear, severe wear, abrasive wear, condition. Disassembly of reciprocating engines that were
chunks, and reworked particles. producingonlyrubbingwearparticlesshowextremelysmooth,
7.8.1 During break-in of a wear surface, a unique layer is mirror likesurfaces.
formed at the surface. Break-in is the transition from the “as 7.8.2 Rubbing wear particles are sometimes called “normal
finished” condition to a smooth low wearing surface.Mechani- rubbing wear” particles. Objections have been raised that wear
cal work at the surface under the influence of load in the of any type should not be considered “normal”. However, in
presence of lubricant causes the formation of a thin layer the context of the design of a specific machine, the presence of
(approximately 1 µm thick for steel) of short range crystalline rubbing wear particles may be the most benign wear condition
order.Thislayerexhibitsgreatductilityandmayflowalongthe that can be expected. Some mechanical designs, such as the
surface hundreds of times its thickness. Rubbing wearparticles shaft of a steam turbine rotating on a journal bearing,generate

FIG. 1 Particle Analysis Report Sheet

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 D7684 − 11 (2016)
a full-film wedge of lubrication that effectively separates the scoring. Severe wear particles from rolling contact fatigue
two wearing surfaces such that virtually no wear particles are wear are smooth flat platelets, more-or-less as long as wide
generated.Suchmechanicalsystemsareknowntorunforyears with jagged irregular edges. Rolling contact fatigue particles,
without appreciable wear. However, incorporating full-film sometimes called spall particles, are thicker than sliding wear
lubrication between all wearing surfaces in machines of particles and can sometimes be in the chunk category, where
practical design is not a reality, so some level of wear must be thickness is less than five times length. Particles from com-
tolerated.Therefore,whenrubbingwearparticlesareobserved, the bined rolling and sliding, such as are generated from meshing
surfaces that generated them will eventually wear out. The gear teeth, may show combinations of these characteristics.
salient question is whether the machine under observation will Gear wear particles from the pitch line where the contact is
continue to operate for its intended lifetime. In this context, rolling look like rolling contact fatigue particles and particles
rubbingwearparticlesmaybeconsiderednormal. from the tips or roots of the gear teeth look like sliding wear
7.8.3 Any free metal particle >15 µm is considered a severe particles. This may aid in determining the site of wear when
wear particle so long as it isn’t too thick or very thin. If the examining gear oil samples.
particle is thick, it is classified as a chunk. If a particle is very 7.8.6 Abrasive wear particles, sometimes called cutting
thin, sometimes with holes, implying it has been flattened by a wear particles, are readily distinguished by their long, thin,
rollingcontact,itisclassifiedasareworkedparticle. curved, curled and ribbon-like appearance. In most cases,these
7.8.4 Severe sliding wear begins when wear surfacestresses are generated by three-body wear in which hard abrasive
increase due to load, speed, or increase in friction, or a particles become embedded in the softer of the twotribological
combination of these factors. Surface stresses cause cracks to componentsandabrasivewearparticlesarecutfromtheharder of
form in the subsurface and to be propagated in the direction of the two sliding surfaces. More rarely, a misaligned or
sliding. Repeated cycles over the same surface cause cracks to fractured machine part can penetrate its wearing pair, generat-
coalesce such that particles break free. Sliding wear particles ing long, curved particles. This is referred to as two-body
exhibit surface striations, have straight, often parallel edges, abrasive wear. These tend to be larger than those produced by
andtypicallyhavealengthtothicknessratioof10:1orgreater. As ingression of hard abrasive contaminant particles such assand.
conditions become more severe in sliding wear, particles 7.8.7 Chunks are >5 µm in major dimension and are more-
becomelarger,theratiooflargetosmallparticlesincreasesand the or-less equiaxed with a major dimension to minor dimension
striations and straight edges on particles becomemore ratio <5:1. Particles are classified as chunks regardless of
prominent. surface texture and may be smooth or craggy. The presence of
7.8.4.1 Forslidingsurfacesofapproximatelyequalhardness chunks indicates surface damage is occurring in the machine
the presence of fine abrasive contaminants, such as sand in the beingsampled.
lubrication system, causes a significant increase in the genera-
7.8.8 Reworked particles are large and thin and are most
tionofrubbingwearparticles.Microscopicinspectionwillalso
likely due to thicker wear particles having been squeezed
reveal the contaminant particles. Close examination of the
through a rolling contact. Not only are reworked particles an
rubbing wear particles often indicate that they are somewhat
indication that large particles are present in the machine being
crescent shaped in this situation. If the oil is cleaned and the
sampled, but their passage through a rolling contact is likely to
ingression of contaminants prevented, the concentration of
initiate subsurface cracking that eventually results in rolling
rubbing wear particles will decrease to levels typical for that
contactfatigue.
type of machine indicating the internal wearing surfaces are
again in a smooth, stablecondition. 7.8.9 Spherical particles may be ferrous, nonferrous, or
nonmetallic depending upon how they were generated.Ferrous
7.8.4.2 For rolling contacts of approximately equalhardness
spheres have been reported as a precursor to rolling contact
the presence of fine abrasive contaminants, such as sand in the
fatigue and will be present with a rather tight size distribution
lubrication system, also causes a significant increase in the
typically <5 µm. Ferrous spheres are readily generated by
generation of rubbing wear particles, as is the case for sliding
extraneous sources, such as welding, grinding, and machining.
contacts. However, even though surface damage may heal to
Ferrous spheres are plentiful as aerosols in steel mills. Ferrous
some extent upon removal of contaminants from the lubricant,
spheres are also present in fly ash from coal burning. Fly ash
the passage of contaminants through the rolling contact in-
also contains numerous glass spheres. Spheres from welding,
creases tensile stress at some depth below the surface likely
grinding, machining, steel mills, and coal burning all have a
initiatingcracksthatultimatelyleadtofatiguespalling.
wide size distribution, from submicron to tens ofmicrometers.
7.8.5 Severe wear particles are defined as being >15 µm in
major dimension and having a length to thickness ratio 7.8.10 Red oxide particles are usually present in the formof
between 5:1 and 30:1. If they are thicker, then they are crystalline agglomerates and are often hydrated. Red oxide
classified as chunks. If they are thinner, they are classified as particles are caused by water in the lubricating oil system. Red
reworked particles. Having determined that severe wear par- oxideparticlesarealsogeneratedbyfrettingwear.
ticles are present, it is possible to distinguish if these were 7.8.11 Copper alloy metal wear particles may be identified
generated by a sliding or rolling contact. Severe sliding wear by their characteristic yellow color. The only other common
particles are longer than wide, tend to have straight edges and metal with yellow color is gold and few machine parts aregold
often show lengthwise surface striations. Surfaces from which or gold coated, except for certain exotic applications. It is also
severeslidingwearparticlesaregeneratedshowevidenceof possibleforferrouswearparticlestoappearyellow,gold,or

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 D7684 − 11 (2016)
straw colored due to temper coloring. This is caused by the particulate debris found in in-service lubricants. The example
formation of a thin, uniform oxide layer due to exposure to particleclassificationgridsin7.7–7.9,associatedTables1and2,
high temperature. and Fig. 1 may be adapted and reconstructed in forms and
7.8.12 Nonmetallic crystalline particles are typically due to stylesthatarepracticalandusefulinparticularsituations.
the ingression of dust or dirt into the lubricating oil system.
Abrasive wear particles are often associated with the presence 8. Report
of nonmetallic crystalline particles. Silica (SiO2) particles are
commonly found in sand, dust, and dirt and appear as nonme- 8.1 Report of wear debris analysis findings is a representa-
tallic crystallineparticles. tionofinformationcollectedusingtheproceduresoutlinedin
7.8.13 Fibers are long, thin nonmetallic particles and may 7.7 – 7.9, in addition to photomicrographs showing selected
be from filters that are tearing or shredding. Various types of example particles.
paper are often used in oil filters. Cellulose fibers, the main NOTE1—Itisnottheintentofthisguidetoestablishnormal,cautionary, or
constituent of the cell walls of plants (such as wood, paper, critical alert limits for any machinery or fluids. Such limits should be
cotton, and hemp), have a ribbon-like structure. Other fiber established in conjunction with advice and guidance from the machine
types may also be present. Fiberglass fibers are recognized by manufacturer or maintenancegroup.
their very regular, round cross-section. Asbestos is a generic
name for several mineral fibers. These are distinguished from 9. Keywords
other fibers by their fine size and their seeming ability to split 9.1 analytical ferrography; condition monitoring; contami-
into ever finerfibers. nant particles; filter patch; in-service lubricants; membrane
7.9 It is the intent of this guide to encourage broad and filtration; particle analysis; wear; wear debris analysis; wear
effective use of wear particle analysis for classification of particle analysis; wearparticles

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