ASTM G73-10(2017)

Standard Test Method for Liquid Impingement Erosion Using Rotating Apparatus

SIGNIFICANCE AND USE
5.1 Erosion Environments—This test method may be used for evaluating the erosion resistance of materials for service environments where solid surfaces are subjected to repeated impacts by liquid drops or jets. Occasionally, liquid impact tests have also been used to evaluate materials exposed to a cavitating liquid environment. The test method is not intended nor applicable for evaluating or predicting the resistance of materials against erosion due to solid particle impingement, due to “impingement corrosion” in bubbly flows, due to liquids or slurries “washing” over a surface, or due to continuous high-velocity liquid jets aimed at a surface. For background on various forms of erosion and erosion tests, see Refs (1) through (2).4 Ref (3)  is an excellent comprehensive treatise.  
5.2 Discussion of Erosion Resistance—Liquid impingement erosion and cavitation erosion are, broadly speaking, similar processes and the relative resistance of materials to them is similar. In both, the damage is associated with repeated, small-scale, high-intensity pressure pulses acting on the solid surface. The precise failure mechanisms in the solid have been shown to differ depending on the material, and on the detailed nature, scale, and intensity of the fluid-solid interactions (Note 1). Thus, “erosion resistance” should not be regarded as one precisely-definable property of a material, but rather as a complex of properties whose relative importance may differ depending on the variables just mentioned. (It has not yet been possible to successfully correlate erosion resistance with any independently measurable material property.) For these reasons, the consistency between relative erosion resistance as measured in different facilities or under different conditions is not very good. Differences between two materials of say 20 % or less are probably not significant: another test might well show them ranked in reverse order. For bulk materials such as metals and structural plastics, th...
SCOPE
1.1 This test method covers tests in which solid specimens are eroded or otherwise damaged by repeated discrete impacts of liquid drops or jets. Among the collateral forms of damage considered are degradation of optical properties of window materials, and penetration, separation, or destruction of coatings. The objective of the tests may be to determine the resistance to erosion or other damage of the materials or coatings under test, or to investigate the damage mechanisms and the effect of test variables. Because of the specialized nature of these tests and the desire in many cases to simulate to some degree the expected service environment, the specification of a standard apparatus is not deemed practicable. This test method gives guidance in setting up a test, and specifies test and analysis procedures and reporting requirements that can be followed even with quite widely differing materials, test facilities, and test conditions. It also provides a standardized scale of erosion resistance numbers applicable to metals and other structural materials. It serves, to some degree, as a tutorial on liquid impingement erosion.  
1.2 The values stated in SI units are to be regarded as standard. The inch-pound units in parentheses are provided for information.  
1.3 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 and health practices and determine the applicability of regulatory limitations prior to use.  
1.4 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: Historical
• Publication Date: 14-Jul-2017
• ICS: 19.060 - Mechanical testing
• ICS: 77.060 - Corrosion of metals
• Technical Committee: G02 - Wear and Erosion
• Drafting Committee: G02.10 - Erosion by Solids and Liquids

Standards Content (Sample)

NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.
Contact ASTM International (www.astm.org) for the latest information
Designation: G73 − 10 (Reapproved 2017)
Standard Test Method for
Liquid Impingement Erosion Using Rotating Apparatus
ThisstandardisissuedunderthefixeddesignationG73;thenumberimmediatelyfollowingthedesignationindicatestheyearoforiginal
adoptionor,inthecaseofrevision,theyearoflastrevision.Anumberinparenthesesindicatestheyearoflastreapproval.Asuperscript
epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope 2. Referenced Documents
2.1 ASTM Standards:
1.1 This test method covers tests in which solid specimens
D1003Test Method for Haze and Luminous Transmittance
are eroded or otherwise damaged by repeated discrete impacts
of Transparent Plastics
of liquid drops or jets. Among the collateral forms of damage
E92Test Methods for Vickers Hardness and Knoop Hard-
considered are degradation of optical properties of window
ness of Metallic Materials
materials, and penetration, separation, or destruction of coat-
E140Hardness Conversion Tables for Metals Relationship
ings. The objective of the tests may be to determine the
Among Brinell Hardness, Vickers Hardness, Rockwell
resistance to erosion or other damage of the materials or
Hardness, Superficial Hardness, Knoop Hardness, Sclero-
coatings under test, or to investigate the damage mechanisms
scope Hardness, and Leeb Hardness
and the effect of test variables. Because of the specialized
E177Practice for Use of the Terms Precision and Bias in
natureofthesetestsandthedesireinmanycasestosimulateto
ASTM Test Methods
some degree the expected service environment, the specifica-
E179Guide for Selection of Geometric Conditions for
tionofastandardapparatusisnotdeemedpracticable.Thistest
Measurement of Reflection and Transmission Properties
method gives guidance in setting up a test, and specifies test
of Materials
andanalysisproceduresandreportingrequirementsthatcanbe
G1Practice for Preparing, Cleaning, and Evaluating Corro-
followed even with quite widely differing materials, test
sion Test Specimens
facilities, and test conditions. It also provides a standardized
G32Test Method for Cavitation Erosion Using Vibratory
scale of erosion resistance numbers applicable to metals and
Apparatus
other structural materials. It serves, to some degree, as a
G40Terminology Relating to Wear and Erosion
tutorial on liquid impingement erosion.
G134Test Method for Erosion of Solid Materials by Cavi-
tating Liquid Jet
1.2 The values stated in SI units are to be regarded as
2.2 Military Standards:
standard.The inch-pound units in parentheses are provided for
MIL-C-83231Coatings, Polyurethane, Rain Erosion Resis-
information.
tance for Exterior Aircraft and Missile Plastic Parts
1.3 This standard does not purport to address all of the
MIL-P-8184Plastic Sheet, Acrylic, Modified
safety concerns, if any, associated with its use. It is the
responsibility of the user of this standard to establish appro-
3. Terminology
priate safety and health practices and determine the applica-
3.1 See Terminology G40 for definitions of terms that are
bility of regulatory limitations prior to use.
notdefinedbelowineither3.2or3.3.Definitionsappearin3.2
1.4 This international standard was developed in accor-
that are taken from Terminology G40 for important terms
dance with internationally recognized principles on standard-
related to the title, Scope, or Summary of this test method.
ization established in the Decision on Principles for the
Definitions of Terms Specific to this Test Method are given in
Development of International Standards, Guides and Recom- 3.3 that are not in Terminology G40.
mendations issued by the World Trade Organization Technical
3.2 Definitions:
Barriers to Trade (TBT) Committee.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
This test method is under the jurisdiction of ASTM Committee G02 on Wear contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM
and Erosion and is the direct responsibility of Subcommittee G02.10 on Erosion by Standards volume information, refer to the standard’s Document Summary page on
Solids and Liquids. the ASTM website.
Current edition approved July 15, 2017. Published August 2017. Originally Available from Standardization Documents Order Desk, DODSSP, Bldg. 4,
approved in 1982. Last previous edition approved in 2010 as G73–10. DOI: Section D, 700 Robbins Ave., Philadelphia, PA 19111-5098, http://
10.1520/G0073-10R17. dodssp.daps.dla.mil.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
G73 − 10 (2017)
3.2.1 AlldefinitionslistedbelowarequotedfromTerminol- a specified reference material similarly tested and similarly
ogy G40–05 (some modified). analyzed. (See also normalized erosion resistance.)
3.2.2 cumulative erosion-time curve, n—in cavitation and
3.3 Definitions of Terms Specific to This Standard:
impingement erosion, a plot of cumulative erosion versus
3.3.1 apparatus severity factor, F—an empirical factor that
cumulative exposure duration, usually determined by periodic
accounts for the systematic differences between rationalized
interruption of the test and weighing of the specimen. This is
erosionrates(orrationalizedincubationperiods)asdetermined
the primary record of an erosion test. Most other
forthesamematerialandimpactvelocityindifferentfacilities.
characteristics, such as the incubation period, maximum ero-
It reflects variations in test conditions not accounted for by the
sionrate,terminalerosionrate,anderosionrate-timecurve,are
data reduction procedures of this test method.
derived from it.
3.3.2 erosion resistance number, NER—the normalized ero-
3.2.3 damage, n—in cavitation or impingement, any effect
sion resistance of a test material relative to a standardized
on a solid body resulting from its exposure to these phenom-
scale, calculated from test results with one or more designated
ena.This may include loss of material, surface deformation, or
reference materials as described in this test method. See also
anyotherchangesinmicrostructure,properties,orappearance.
reference erosion resistance (3.3.12).
3.2.3.1 Discussion—This term as here defined should nor-
mally be used with the appropriate modifier, for example,
3.3.3 exposed surface (or area)—that surface (or area) on
“cavitation damage,” “liquid impingement damage,” “single- the specimen nominally subjected to liquid impingement.
impact damage,” and so forth.
(1)For“distributedimpacttests,”itisgenerallytobetaken
astheprojectedareaoftheexposedsurfaceofthespecimenon
3.2.4 incubation period, n—in cavitation and impingement
a plane perpendicular to the direction of impingement.
erosion, the initial stage of the erosion rate-time pattern during
However, if a plane specimen surface is deliberately oriented
which the erosion rate is zero or negligible compared to later
soastoobtainimpingementatanobliqueangle,thentheactual
stages.
plane area is used.
3.2.4.1 Discussion—The incubation period is usually
(2)For “repetitive impact tests,” it is to be taken as the
thought to represent the accumulation of plastic deformation
projected area of the impinging liquid bodies on the specimen,
and internal stresses under the surface that precedes significant
the projection being taken in the direction of relative motion.
material loss. There is no exact measure of the duration of the
3.3.3.1 Discussion—In practice, it is usually found that the
incubationperiod.Seerelatedterm, nominal incubation period
damaged area in repetitive impact tests is greater than the
in 3.3.9.
exposed area as defined above, but the above definition is
3.2.5 liquid impingement erosion, n—progressive loss of
adopted not only for simplicity but also for consistency
original material from a solid surface due to continued expo-
between some of the other calculations for distributed and
sure to impacts by liquid drops or jets.
repetitive tests.
3.2.6 maximum erosion rate, n—in cavitation and liquid
−1
3.3.4 impingement rate, U [LT ]—the volume of liquid
i
impingement,themaximuminstantaneouserosionrateinatest
impinging per unit time on a unit area of exposed surface; for
that exhibits such a maximum followed by decreasing erosion
a plane target surface it is given by ψ V cos θ.
rates. (See also erosion rate–time pattern.)
3.2.6.1 Discussion—Occurrence of such a maximum is 3.3.5 incubation impingement, H [L]—the mean cumula-
typical of many cavitation and liquid impingement tests. In tive impingement corresponding to the nominal incubation
some instances it occurs as an instantaneous maximum, in period; hence, impingement rate times nominal incubation
others as a steady-state maximum which persists for some time.
time.
3.3.6 incubation resistance number, NOR—the normalized
3.2.7 normalizederosionresistance,N,n—ameasureofthe
incubation resistance of a test material relative to a standard-
e
erosion resistance of a test material relative to that of a
ized scale, calculated from test results with one or more
specifiedreferencematerial,calculatedbydividingthevolume
designatedreferencematerialsasdescribedinthistestmethod.
loss rate of the reference material by that of the test material
See also reference incubation resistance (3.3.13).
when both are similarly tested and similarly analyzed. By
3.3.7 incubation specific impacts, N —same as rationalized
“similarlyanalyzed,”itismeantthatthetwoerosionratesmust
incubation period.
be determined for corresponding portions of the erosion
rate-timepattern;forinstance,themaximumerosionrateorthe 3.3.8 mean cumulative impingement, H[L]—thecumulative
terminal erosion rate. volume of liquid impinged per unit area of exposed surface;
impingement rate times exposure time.
3.2.7.1 Discussion—Arecommended complete wording has
the form, “The normalized erosion resistance of (test material)
3.3.9 nominal incubation period, t —the intercept on the
relative to (reference material) based on (criterion of data
time or exposure axis of the straight-line extension of the
analysis) is (numerical value).”
maximum-slope portion of the cumulative erosion-time curve;
3.2.8 normalized incubation resistance, N , n—in cavitation while this is not a true measure of the incubation stage, it
and liquid impingement erosion,thenominalincubationperiod serves to locate the maximum erosion rate line on the cumu-
of a test material, divided by the nominal incubation period of lative erosion versus exposure coordinates.
G73 − 10 (2017)
3.3.10 rationalized erosion rate, R —volume of material
S = normalizedincubationresistance(relativetoaspeci-
e
lostperunitvolumeofliquidimpinged,bothcalculatedforthe
fied reference material),
same area.
S = reference incubation resistance,
or
t = exposure time, s,
3.3.11 rationalized incubation period, N —the duration of
t = nominal incubation time, s,
the nominal incubation period expressed in dimensionless
U = linear erosion rate (dY/dt), m/s= Q /A,
e e
terms as the number of specific impacts; hence, the specific
U = impingement rate (dH/dt), m/s,
i
impact frequency times nominal incubation time. (Also re-
U = rainfall rate, m/s,
r
ferred to as incubation specific impacts.)
U = terminal velocity of drops in falling rainfield, m/s,
t
3.3.12 reference erosion resistance, S —a normalized ero- V = impact velocity of drop or jet relative to specimen,
er
sion resistance, based on interlaboratory test results, assigned m/s,
V = component of impact velocity normal to specimen
to a specified reference material in this test method so as to
n
surface, m/s,
constitute a benchmark in the “erosion resistance number”
Y = mean depth of erosion, m,
scale. The value of unity is assigned to 316 stainless steel of
θ = angle of incidence—the angle between the direction
hardness 155 to 170 HV.
of impacting drops and the normal to the solid
3.3.13 reference incubation resistance, S —a normalized
or
surface at point of impact,
incubation resistance, based on interlaboratory test results,
ψ = volume concentration of liquid in rainfield or in
assigned to a specific reference material in this test method so
space swept through by specimen, and
as to constitute a benchmark in the “incubation resistance
Ω = rotational speed of specimens, rev/s.
number” scale. The value of unity is assigned to 316 stainless
3.5 Except in equations where different units are expressly
steel of hardness 155 to 170 HV.
specified,theuseofSIunitslistedin3.4,oranyother coherent
3.3.14 specific impacts, N—the number of impact stress
system of units, will make equations correct without the need
cycles of damaging magnitude experienced by a typical point
of additional numerical factors.When referring to quantities in
on the exposed surface, or an approximation thereof as
text, tables, or figures, suitable multiples or submultiples of
estimated on the basis of simplified assumptions as described
these units may, of course, be used.
in this test method. (This concept has sometimes been termed
“impacts per site.”) 4. Summary of Test Method
−1
3.3.15 specific impact frequency, f [T ]—the number of
4.1 Liquid impingement tests are usually, but not always,
i
specific impacts experienced per unit time, given by (a/b) U. conducted by attaching specimens to a rotating disk or arm,
i
suchthatintheircircularpaththeyrepeatedlypassthroughand
3.3.16 volume concentration,ψ—the ratio of the volume of
impactagainstliquidspraysorjets(Sections6and7).Standard
liquid to the total volume in the path traversed or swept out by
reference materials (Section 8) should be used to calibrate the
the exposed area of the specimen.
apparatus and included in all test programs.
3.3.17 volume mean diameter [L]—in a population of drops
4.2 Data analysis begins by establishing a cumulative
of different sizes, the diameter of a sphere whose volume
erosion-time curve from measurements of mass loss (or other
equalsthetotalvolumeofalldropsdividedbythetotalnumber
damage manifestation) periodically during the tests (Section
of drops.
9). These curves are then characterized by specified attributes
3.4 Symbols:
such as the nominal incubation time and the maximum erosion
2 rate (Section 10).
A = exposed area of specimen, m ,
a = projected area of impinging drop or jet, m , 4.3 For comparative materials evaluations, the results are
b = volume of impinging drop or jet, m ,
normalized (Section 10) with respect to the standard reference
d = diameter of impinging drop or jet, m,
materials included in the test program.Astandardized scale of
F = apparatus severity factor for incubation,
“erosion resistance numbers” is provided for structural bulk
F = apparatus severity factor for erosion rate,
e
materials and coatings (10.4.3). For more in-depth analysis of
−1
f = specific impact frequency, s ,
i
the results, the
...

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: G73 − 10 G73 − 10 (Reapproved 2017)
Standard Test Method for
Liquid Impingement Erosion Using Rotating Apparatus
This standard is issued under the fixed designation G73; 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
1.1 This test method covers tests in which solid specimens are eroded or otherwise damaged by repeated discrete impacts of
liquid drops or jets. Among the collateral forms of damage considered are degradation of optical properties of window materials,
and penetration, separation, or destruction of coatings. The objective of the tests may be to determine the resistance to erosion or
other damage of the materials or coatings under test, or to investigate the damage mechanisms and the effect of test variables.
Because of the specialized nature of these tests and the desire in many cases to simulate to some degree the expected service
environment, the specification of a standard apparatus is not deemed practicable. This test method gives guidance in setting up a
test, and specifies test and analysis procedures and reporting requirements that can be followed even with quite widely differing
materials, test facilities, and test conditions. It also provides a standardized scale of erosion resistance numbers applicable to metals
and other structural materials. It serves, to some degree, as a tutorial on liquid impingement erosion.
1.2 The values stated in SI units are to be regarded as standard. The inch-pound units in parentheses are provided for
information.
1.3 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 and health practices and determine the applicability of regulatory
limitations prior to use.
1.4 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:
D1003 Test Method for Haze and Luminous Transmittance of Transparent Plastics
E92 Test Methods for Vickers Hardness and Knoop Hardness of Metallic Materials
E140 Hardness Conversion Tables for Metals Relationship Among Brinell Hardness, Vickers Hardness, Rockwell Hardness,
Superficial Hardness, Knoop Hardness, Scleroscope Hardness, and Leeb Hardness
E177 Practice for Use of the Terms Precision and Bias in ASTM Test Methods
E179 Guide for Selection of Geometric Conditions for Measurement of Reflection and Transmission Properties of Materials
G1 Practice for Preparing, Cleaning, and Evaluating Corrosion Test Specimens
G32 Test Method for Cavitation Erosion Using Vibratory Apparatus
G40 Terminology Relating to Wear and Erosion
G134 Test Method for Erosion of Solid Materials by Cavitating Liquid Jet
2.2 Military Standards:
MIL-C-83231 Coatings, Polyurethane, Rain Erosion Resistance for Exterior Aircraft and Missile Plastic Parts
MIL-P-8184 Plastic Sheet, Acrylic, Modified
This test method is under the jurisdiction of ASTM Committee G02 on Wear and Erosion and is the direct responsibility of Subcommittee G02.10 on Erosion by Solids
and Liquids.
Current edition approved April 1, 2010July 15, 2017. Published May 2010August 2017. Originally approved in 1982. Last previous edition approved in 20042010 as
G73G73 – 10.–04. DOI: 10.1520/G0073-10.10.1520/G0073-10R17.
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 Standardization Documents Order Desk, DODSSP, Bldg. 4, Section D, 700 Robbins Ave., Philadelphia, PA 19111-5098, http://dodssp.daps.dla.mil.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
G73 − 10 (2017)
3. Terminology
3.1 See Terminology G40 for definitions of terms that are not defined below in either 3.2 or 3.3. Definitions appear in 3.2 that
are taken from Terminology G40 for important terms related to the title, Scope, or Summary of this test method. Definitions of
Terms Specific to this Test Method are given in 3.3 that are not in Terminology G40.
3.2 Definitions:
3.2.1 All definitions listed below are quoted from Terminology G40–05 (some modified).
3.2.2 cumulative erosion-time curve, n—in cavitation and impingement erosion, a plot of cumulative erosion versus cumulative
exposure duration, usually determined by periodic interruption of the test and weighing of the specimen. This is the primary record
of an erosion test. Most other characteristics, such as the incubation period, maximum erosion rate, terminal erosion rate, and
erosion rate-time curve, are derived from it.
3.2.3 damage, n—in cavitation or impingement, any effect on a solid body resulting from its exposure to these phenomena. This
may include loss of material, surface deformation, or any other changes in microstructure, properties, or appearance.
3.2.3.1 Discussion—
This term as here defined should normally be used with the appropriate modifier, for example, “cavitation damage,” “liquid
impingement damage,” “single-impact damage,” and so forth.
3.2.4 incubation period, n—in cavitation and impingement erosion, the initial stage of the erosion rate-time pattern during which
the erosion rate is zero or negligible compared to later stages.
3.2.4.1 Discussion—
The incubation period is usually thought to represent the accumulation of plastic deformation and internal stresses under the
surface that precedes significant material loss. There is no exact measure of the duration of the incubation period. See related term,
nominal incubation period in 3.3.9.
3.2.5 liquid impingement erosion, n—progressive loss of original material from a solid surface due to continued exposure to
impacts by liquid drops or jets.
3.2.6 maximum erosion rate, n—in cavitation and liquid impingement, the maximum instantaneous erosion rate in a test that
exhibits such a maximum followed by decreasing erosion rates. (See also erosion rate–time pattern.)
3.2.6.1 Discussion—
Occurrence of such a maximum is typical of many cavitation and liquid impingement tests. In some instances it occurs as an
instantaneous maximum, in others as a steady-state maximum which persists for some time.
3.2.7 normalized erosion resistance, N , n—a measure of the erosion resistance of a test material relative to that of a specified
e
reference material, calculated by dividing the volume loss rate of the reference material by that of the test material when both are
similarly tested and similarly analyzed. By “similarly analyzed,” it is meant that the two erosion rates must be determined for
corresponding portions of the erosion rate-time pattern; for instance, the maximum erosion rate or the terminal erosion rate.
3.2.7.1 Discussion—
A recommended complete wording has the form, “The normalized erosion resistance of (test material) relative to (reference
material) based on (criterion of data analysis) is (numerical value).”
3.2.8 normalized incubation resistance, N , n—in cavitation and liquid impingement erosion, the nominal incubation period of
a test material, divided by the nominal incubation period of a specified reference material similarly tested and similarly analyzed.
(See also normalized erosion resistance.)
3.3 Definitions of Terms Specific to This Standard:
3.3.1 apparatus severity factor, F—an empirical factor that accounts for the systematic differences between rationalized erosion
rates (or rationalized incubation periods) as determined for the same material and impact velocity in different facilities. It reflects
variations in test conditions not accounted for by the data reduction procedures of this test method.
3.3.2 erosion resistance number, NER—the normalized erosion resistance of a test material relative to a standardized scale,
calculated from test results with one or more designated reference materials as described in this test method. See also reference
erosion resistance (3.3.12).
3.3.3 exposed surface (or area)—that surface (or area) on the specimen nominally subjected to liquid impingement.
G73 − 10 (2017)
(1) For “distributed impact tests,” it is generally to be taken as the projected area of the exposed surface of the specimen on
a plane perpendicular to the direction of impingement. However, if a plane specimen surface is deliberately oriented so as to obtain
impingement at an oblique angle, then the actual plane area is used.
(2) For “repetitive impact tests,” it is to be taken as the projected area of the impinging liquid bodies on the specimen, the
projection being taken in the direction of relative motion.
3.3.3.1 Discussion—
In practice, it is usually found that the damaged area in repetitive impact tests is greater than the exposed area as defined above,
but the above definition is adopted not only for simplicity but also for consistency between some of the other calculations for
distributed and repetitive tests.
−1
3.3.4 impingement rate, U [LT ]—the volume of liquid impinging per unit time on a unit area of exposed surface; for a plane
i
target surface it is given by ψ V cos θ.
3.3.5 incubation impingement, H [L]—the mean cumulative impingement corresponding to the nominal incubation period;
hence, impingement rate times nominal incubation time.
3.3.6 incubation resistance number, NOR—the normalized incubation resistance of a test material relative to a standardized
scale, calculated from test results with one or more designated reference materials as described in this test method. See also
reference incubation resistance (3.3.13).
3.3.7 incubation specific impacts, N —same as rationalized incubation period.
3.3.8 mean cumulative impingement, H [L]—the cumulative volume of liquid impinged per unit area of exposed surface;
impingement rate times exposure time.
3.3.9 nominal incubation period, t —the intercept on the time or exposure axis of the straight-line extension of the
maximum-slope portion of the cumulative erosion-time curve; while this is not a true measure of the incubation stage, it serves
to locate the maximum erosion rate line on the cumulative erosion versus exposure coordinates.
3.3.10 rationalized erosion rate, R —volume of material lost per unit volume of liquid impinged, both calculated for the same
e
area.
3.3.11 rationalized incubation period, N —the duration of the nominal incubation period expressed in dimensionless terms as
the number of specific impacts; hence, the specific impact frequency times nominal incubation time. (Also referred to as incubation
specific impacts.)
3.3.12 reference erosion resistance, S —a normalized erosion resistance, based on interlaboratory test results, assigned to a
er
specified reference material in this test method so as to constitute a benchmark in the “erosion resistance number” scale. The value
of unity is assigned to 316 stainless steel of hardness 155 to 170 HV.
3.3.13 reference incubation resistance, S —a normalized incubation resistance, based on interlaboratory test results, assigned
or
to a specific reference material in this test method so as to constitute a benchmark in the “incubation resistance number” scale. The
value of unity is assigned to 316 stainless steel of hardness 155 to 170 HV.
3.3.14 specific impacts, N—the number of impact stress cycles of damaging magnitude experienced by a typical point on the
exposed surface, or an approximation thereof as estimated on the basis of simplified assumptions as described in this test method.
(This concept has sometimes been termed “impacts per site.”)
−1
3.3.15 specific impact frequency, f [T ]—the number of specific impacts experienced per unit time, given by (a/b) U .
i i
3.3.16 volume concentration, ψ—the ratio of the volume of liquid to the total volume in the path traversed or swept out by the
exposed area of the specimen.
3.3.17 volume mean diameter [L]—in a population of drops of different sizes, the diameter of a sphere whose volume equals
the total volume of all drops divided by the total number of drops.
3.4 Symbols:
A = exposed area of specimen, m ,
a = projected area of impinging drop or jet, m ,
b = volume of impinging drop or jet, m ,
d = diameter of impinging drop or jet, m,
F = apparatus severity factor for incubation,
F = apparatus severity factor for erosion rate,
e
−1
f = specific impact frequency, s ,
i
H = mean cumulative impingement, m,
H = incubation impingement, m,
N = number of specific impacts for incubation, or “rationalized incubation period,” dimensionless,
G73 − 10 (2017)
NER = erosion resistance number,
NOR = incubation resistance number,
n = number of jets or drops impacting on exposed surface of specimen in one revolution,
Q = volumetric erosion rate, m /s,
e
R = “rationalized erosion rate,” (dY/dH), dimensionless,
e
S = normalized erosion resistance (relative to a specified reference material),
e
S = reference erosion resistance,
er
S = normalized incubation resistance (relative to a specified reference material),
S = reference incubation resistance,
or
t = exposure time, s,
t = nominal incubation time, s,
U = linear erosion rate (dY/dt), m/s = Q /A,
e e
U = impingement rate (dH/dt), m/s,
i
U = rainfall rate, m/s,
r
U = terminal velocity of drops in falling rainfield, m/s,
t
V = impact velocity of drop or jet relative to specimen, m/s,
V = component of impact velocity normal to specimen surface, m/s,
n
Y = mean depth of erosion, m,
θ = angle of incidence—the angle between the direction of impacting drops and the normal to the solid surface at point of
impact,
ψ = volume concentration of liquid in rainfield or in space swept through by specimen, and
Ω = rotational speed of specimens, rev/s.
3.5 Except in equations where different units are expressly specified, the use of SI units listed in 3.4, or any other coherent
system of units, will make equations correct witho
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