Designation: G32 – 10

Standard Test Method for

Cavitation Erosion Using Vibratory Apparatus1
This standard is issued under the fixed designation G32; 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. Referenced Documents

1.1 This test method covers the production of cavitation 2.1 ASTM Standards:2
damage on the face of a specimen vibrated at high frequency A276 Specification for Stainless Steel Bars and Shapes
while immersed in a liquid. The vibration induces the forma- B160 Specification for Nickel Rod and Bar
tion and collapse of cavities in the liquid, and the collapsing B211 Specification for Aluminum and Aluminum-Alloy
cavities produce the damage to and erosion (material loss) of Bar, Rod, and Wire
the specimen. D1193 Specification for Reagent Water
1.2 Although the mechanism for generating fluid cavitation E177 Practice for Use of the Terms Precision and Bias in
in this method differs from that occurring in flowing systems ASTM Test Methods
and hydraulic machines (see 5.1), the nature of the material E691 Practice for Conducting an Interlaboratory Study to
damage mechanism is believed to be basically similar. The Determine the Precision of a Test Method
method therefore offers a small-scale, relatively simple and E960 Specification for Laboratory Glass Beakers
controllable test that can be used to compare the cavitation G40 Terminology Relating to Wear and Erosion
erosion resistance of different materials, to study in detail the G73 Test Method for Liquid Impingement Erosion Using
nature and progress of damage in a given material, or—by Rotating Apparatus
varying some of the test conditions—to study the effect of test G117 Guide for Calculating and Reporting Measures of
variables on the damage produced. Precision Using Data from Interlaboratory Wear or Ero-
1.3 This test method specifies standard test conditions sion Tests
covering the diameter, vibratory amplitude and frequency of G119 Guide for Determining Synergism Between Wear and
the specimen, as well as the test liquid and its container. It Corrosion
permits deviations from some of these conditions if properly G134 Test Method for Erosion of Solid Materials by Cavi-
documented, that may be appropriate for some purposes. It tating Liquid Jet
gives guidance on setting up a suitable apparatus and covers
test and reporting procedures and precautions to be taken. It 3. Terminology
also specifies standard reference materials that must be used to 3.1 Definitions:
verify the operation of the facility and to define the normalized 3.1.1 See Terminology G40 for definitions of terms relating
erosion resistance of other test materials. to cavitation erosion. For convenience, important definitions
1.4 A history of this test method is given in Appendix X4, for this standard are listed below; some are slightly modified
followed by a comprehensive bibliography. from Terminology G40 or not contained therein.
1.5 The values stated in SI units are to be regarded as 3.1.2 average erosion rate, n—a less preferred term for
standard. The inch-pound units given in parentheses are for cumulative erosion rate.
information only. 3.1.3 cavitation, n—the formation and subsequent collapse,
1.6 This standard does not purport to address all of the within a liquid, of cavities or bubbles that contain vapor or a
safety concerns, if any, associated with its use. It is the mixture of vapor and gas.
responsibility of the user of this standard to establish appro- 3.1.3.1 Discussion—In general, cavitation originates from a
priate safety and health practices and determine the applica- local decrease in hydrostatic pressure in the liquid, produced
bility of regulatory limitations prior to use. For specific safety by motion of the liquid (see flow cavitation) or of a solid
warning information, see 6.1, 10.3, and 10.6.1. boundary (see vibratory cavitation). It is distinguished in this
way from boiling, which originates from an increase in liquid
temperature.
1
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
2
Solids and Liquids. For referenced ASTM standards, visit the ASTM website, www.astm.org, or
Current edition approved Dec. 1, 2010. Published February 2011. Originally contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
approved in 1972. Last previous edition approved in 2009 as G32–09. DOI: Standards volume information, refer to the standard’s Document Summary page on
10.1520/G0032-10. the ASTM website.

Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.

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 G32 – 10
3.1.3.2 Discussion—The term cavitation, by itself, should 3.1.12 incubation period, n—the initial stage of the erosion
not be used to denote the damage or erosion of a solid surface rate-time pattern during which the erosion rate is zero or
that can be caused by it; this effect of cavitation is termed negligible compared to later stages.
cavitation damage or cavitation erosion. To erode a solid 3.1.12.1 Discussion—The incubation period is usually
surface, bubbles or cavities must collapse on or near that thought to represent the accumulation of plastic deformation
surface. and internal stresses under the surface, that precedes significant
3.1.4 cavitation erosion, n—progressive loss of original material loss. There is no exact measure of the duration of the
material from a solid surface due to continued exposure to incubation period. See related terms, erosion threshold time
cavitation. and nominal incubation period.
3.1.5 cumulative erosion, n—the total amount of material 3.1.13 maximum erosion rate, n—the maximum instanta-
lost from a solid surface during all exposure periods since it neous erosion rate in a test that exhibits such a maximum
was first exposed to cavitation or impingement as a newly followed by decreasing erosion rates. (See also erosion rate-
finished surface. (More specific terms that may be used are time pattern.)
cumulative mass loss, cumulative volume loss, or cumulative
3.1.13.1 Discussion—Occurrence of such a maximum is
mean depth of erosion. See also cumulative erosion-time
typical of many cavitation and liquid impingement tests. In
curve.)
some instances it occurs as an instantaneous maximum, in
3.1.5.1 Discussion—Unless otherwise indicated by the con-
others as a steady-state maximum which persists for some
text, it is implied that the conditions of cavitation or impinge-
time.
ment have remained the same throughout all exposure periods,
with no intermediate refinishing of the surface. 3.1.14 mean depth of erosion (MDE), n—the average thick-
ness of material eroded from a specified surface area, usually
3.1.6 cumulative erosion rate, n—the cumulative erosion at
calculated by dividing the measured mass loss by the density of
a specified point in an erosion test divided by the correspond-
ing cumulative exposure duration; that is, the slope of a line the material to obtain the volume loss and dividing that by the
from the origin to the specified point on the cumulative area of the specified surface. (Also known as mean depth of
erosion-time curve. (Synonym: average erosion rate) penetration or MDP. Since that might be taken to denote the
average value of the depths of individual pits, it is a less
3.1.7 cumulative erosion-time curve—a plot of cumulative
preferred term.)
erosion versus cumulative exposure duration, usually deter-
mined by periodic interruption of the test and weighing of the 3.1.15 nominal incubation time, n—the intercept on the
specimen. This is the primary record of an erosion test. Most time or exposure axis of the straight-line extension of the
other characteristics, such as the incubation period, maximum maximum-slope portion of the cumulative erosion-time curve;
erosion rate, terminal erosion rate, and erosion rate-time curve, while this is not a true measure of the incubation stage, it
are derived from it. serves to locate the maximum erosion rate line on the cumu-
3.1.8 erosion rate-time curve, n—a plot of instantaneous lative erosion versus time coordinates.
erosion rate versus exposure duration, usually obtained by 3.1.16 normalized erosion resistance, Ne, n—a measure of
numerical or graphical differentiation of the cumulative the erosion resistance of a test material relative to that of a
erosion-time curve. (See also erosion rate-time pattern.) specified reference material, calculated by dividing the volume
3.1.9 erosion rate-time pattern, n—any qualitative descrip- loss rate of the reference material by that of the test material,
tion of the shape of the erosion rate-time curve in terms of the when both are similarly tested and similarly analyzed. By
several stages of which it may be composed. “similarly analyzed” is meant that the two erosion rates must
3.1.9.1 Discussion—In cavitation and liquid impingement be determined for corresponding portions of the erosion rate
erosion, a typical pattern may be composed of all or some of time pattern; for instance, the maximum erosion rate or the
the following “periods” or “stages”: incubation period, accel- terminal erosion rate.
eration period, maximum-rate period, deceleration period, 3.1.16.1 Discussion—A recommended complete wording
terminal period, and occasionally catastrophic period. The has the form, “The normalized erosion resistance of (test
generic term “period” is recommended when associated with material) relative to (reference material) based on (criterion of
quantitative measures of its duration, etc.; for purely qualitative data analysis) is (numerical value).”
descriptions the term“ stage” is preferred. 3.1.17 normalized incubation resistance No, n—the nominal
3.1.10 erosion threshold time, n—the exposure time re- incubation time of a test material, divided by the nominal
quired to reach a mean depth of erosion of 1.0 µm. incubation time of a specified reference material similarly
3.1.10.1 Discussion—A mean depth of erosion of 1.0 µm is tested and similarly analyzed. (See also normalized erosion
the least accurately measurable value considering the precision resistance.)
of the scale, specimen diameter, and density of the standard 3.1.18 tangent erosion rate, n—the slope of a straight line
reference material. drawn through the origin and tangent to the knee of the
3.1.11 flow cavitation, n—cavitation caused by a decrease in cumulative erosion-time curve, when that curve has the char-
local pressure induced by changes in velocity of a flowing acteristic S-shaped pattern that permits this. In such cases, the
liquid, such as in flow around an obstacle or through a tangent erosion rate also represents the maximum cumulative
constriction. erosion rate exhibited during the test.

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 G32 – 10
3.1.19 terminal erosion rate, n—the final steady-state ero- and is deemed suitable for compliant coatings, is the “stationary speci-
sion rate that is reached (or appears to be approached asymp- men” method. In that method, the specimen is fixed within the liquid
totically) after the erosion rate has declined from its maximum container, and the vibrating tip of the horn is placed in close proximity to
it. The cavitation “bubbles” induced by the horn (usually fitted with a
value. (See also terminal period and erosion rate-time pattern.) highly resistant replaceable tip) act on the specimen. While several
3.1.20 vibratory cavitation, n—cavitation caused by the investigators have used this approach (see X4.2.3), they have differed with
pressure fluctuations within a liquid, induced by the vibration regard to standoff distances and other arrangements. The stationary
of a solid surface immersed in the liquid. specimen approach can also be used for brittle materials which can not be
formed into a threaded specimen nor into a disc that can be cemented to
4. Summary of Test Method a threaded specimen, as required for this test method (see 7.6).
4.1 This test method generally utilizes a commercially 5.4 This test method should not be directly used to rank
obtained 20-kHz ultrasonic transducer to which is attached a materials for applications where electrochemical corrosion or
suitably designed “horn” or velocity transformer. A specimen solid particle impingement plays a major role. However,
button of proper mass is attached by threading into the tip of adaptations of the basic method and apparatus have been used
the horn. for such purposes (see 9.2.5, 9.2.6, and X4.2). Guide G119
4.2 The specimen is immersed into a container of the test may be followed in order to determine the synergism between
liquid (generally distilled water) that must be maintained at a the mechanical and electrochemical effects.
specified temperature during test operation, while the specimen 5.5 Those who are engaged in basic research, or concerned
is vibrated at a specified amplitude. The amplitude and with very specialized applications, may need to vary some of
frequency of vibration of the test specimen must be accurately the test parameters to suit their purposes. However, adherence
controlled and monitored. to this test method in all other respects will permit a better
4.3 The test specimen is weighed accurately before testing understanding and correlation between the results of different
begins and again during periodic interruptions of the test, in investigators.
order to obtain a history of mass loss versus time (which is not 5.6 Because of the nonlinear nature of the erosion-versus-
linear). Appropriate interpretation of this cumulative erosion- time curve in cavitation and liquid impingement erosion, the
versus-time curve permits comparison of results between shape of that curve must be considered in making comparisons
different materials or between different test fluids or other and drawing conclusions. See Section 11.
conditions. 5.7 The results of this test may be significantly affected by
the specimen’s surface preparation. This must be considered in
5. Significance and Use planning, conducting and reporting a test program. See also 7.4
5.1 This test method may be used to estimate the relative and 12.2.
resistance of materials to cavitation erosion as may be encoun- 5.8 The mechanisms of cavitation erosion and liquid im-
tered, for instance, in pumps, hydraulic turbines, hydraulic pingement erosion are not fully understood and may differ,
dynamometers, valves, bearings, diesel engine cylinder liners, depending on the detailed nature, scale, and intensity of the
ship propellers, hydrofoils, and in internal flow passages with liquid/solid interactions. “Erosion resistance” may, therefore,
obstructions. An alternative method for similar purposes is Test represent a mix of properties rather than a single property, and
Method G134, which employs a cavitating liquid jet to produce has not yet been successfully correlated with other indepen-
erosion on a stationary specimen. The latter may be more dently measurable material properties. For this reason, the
suitable for materials not readily formed into a precisely consistency of results between different test methods or under
shaped specimen. The results of either, or any, cavitation different field conditions is not very good. Small differences
erosion test should be used with caution; see 5.8. between two materials are probably not significant, and their
5.2 Some investigators have also used this test method as a relative ranking could well be reversed in another test.
screening test for materials subjected to liquid impingement 5.9 If a test program must deviate from the standard
erosion as encountered, for instance, in low-pressure steam specifications for apparatus, test specimens, or test conditions,
turbines and in aircraft, missiles or spacecraft flying through the reasons shall be explained, and the results characterized as
rainstorms. Test Method G73 describes another testing ap- obtained by “ASTM Test Method G32 modified.” See also 5.4,
proach specifically intended for that type of environment. 5.5, and 12.1.
5.3 This test method is not recommended for evaluating
elastomeric or compliant coatings, some of which have been 6. Apparatus
successfully used for protection against cavitation or liquid 6.1 The vibratory apparatus used for this test method
impingement of moderate intensity. This is because the com- produces axial oscillations of a test specimen inserted to a
pliance of the coating on the specimen may reduce the severity specified depth in the test liquid. The vibrations are generated
of the liquid cavitation induced by its vibratory motion. The by a magnetostrictive or piezoelectric transducer, driven by a
result would not be representative of a field application, where suitable electronic oscillator and power amplifier. The power of
the hydrodynamic generation of cavitation is independent of the system should be sufficient to permit constant amplitude of
the coating. the specimen in air as well as submerged. An acoustic power
NOTE 1—An alternative approach that uses the same basic apparatus, output of 250 to 1000 W has been found suitable. Such systems

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 G32 – 10

FIG. 2 Schematic of Vibratory Cavitation Erosion Apparatus

FIG. 1 Important Parameters of the Vibratory Cavitation Test

are commercially available, intended for ultrasonic welding,

emulsifying, and so forth.3 (Warning—This apparatus may
generate high sound levels. The use of ear protection may be
necessary. Provision of an acoustical enclosure is recom-
mended.)
6.1.1 The basic parameters involved in this test method are
pictorially shown in Fig. 1. Schematic and photographic views
of representative equipment are shown in Figs. 2 and 3
respectively.
6.2 To obtain a higher vibratory amplitude at the specimen
than at the transducer, a suitably shaped tapered cylindrical
member, generally termed the “horn” or “velocity trans-
former,” is required. Catenoidal, exponential and stepped horn
profiles have been used for this application. The diameter of the
horn at its tip shall conform to that specified for the specimen
(see 7.1).
6.3 The test specimen (see also Section 7 and Fig. 4) is
shaped as a button with the same outer diameter as the horn tip,
and has a smaller diameter threaded shank, which is screwed
into a threaded hole at the end of the horn. The depth of the
hole in the horn shall be the minimum consistent with the
required length of engagement of the specimen shank.
6.4 The transducer and horn assembly shall be supported in
a manner that does not interfere with, and receives no force
input from, the vibratory motion. This can be accomplished,
for example, by attaching the support structure to a stationary
housing of the transducer, or to a flange located at a nodal plane
of the vibrating assembly. It is also necessary to prevent any
misalignment of the horn due to forces caused by the electrical
cable, cooling system, or transducer enclosure. FIG. 3 Photograph of a Typical Apparatus
6.5 Frequency Control:
6.5.1 The frequency of oscillation of the test specimen shall
3
Several manufacturers of ultrasonic processing or plastics welding equipment be 20 6 0.5 kHz.
offer apparatus off-the-shelf, or specially modified, to meet the specifications given 6.5.2 The whole transducer-horn-specimen system shall be
in this standard. A list of those known to the subcommittee having jurisdiction is designed for longitudinal resonance at this frequency.
available from its chairman. Inclusion in this list does not imply such equipment has
been qualified in a test program. NOTE 2—If both light and heavy alloys are to be tested, then two horns

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 G32 – 10
6.7.2 The vessel shall be cylindrical in cross-section, and
the depth of liquid in it shall be 100 6 10 mm, unless otherwise
required.
6.7.3 The vessel’s inside diameter will depend on whether
the cooling method (see 6.8) is an external cooling bath into
which the vessel is immersed, or a cooling coil immersed
within the vessel. In either case, it is recommended that the
unobstructed diameter (that is, the internal diameter of the
vessel or of the cooling coil within it if used) be 100 6 15 mm.
6.7.4 A standard commercially available low-form glass
beaker (for example, Type I or II of Specification E960) may be
suitable. A 600-mL beaker may be suitable when a cooling bath
is used, and a 1000-mL to 1500-mL beaker when a cooling coil
is used.
6.8 Means shall be provided to maintain the temperature of
the test liquid near the specimen at a specified temperature (see
TABLE OF VALUES
9.1.1.5). This is commonly achieved by means of a cooling
mm inch bath around the liquid-containing vessel or a cooling coil
D* 15.9 6 0.05 0.624 6 0.002 immersed within it, with suitable thermostatic control. The
E* 0.15 0.006 temperature sensor should be located as close as practicable to
F (W + 2.2) 6 0.25 (W + 0.09) 6 0.01 the specimen, but at a point where it does not interfere with the
H See 7.2
L 10.0 6 0.5 0.394 6 0.02 cavitation process and is not damaged by it. A suggested
R 0.8 6 0.15 0.0316 0.006 location is approximately 3 mm radially from the specimen
T Thread, see X2.2.1 periphery, and at a depth of immersion approximately 3 mm
U 2.0 6 0.5 0.08 6 0.02
W Thread minor dia, see Table X2.2 below that of the specimen face.
Z 0.8 6 0.15 0.031 6 0.006 6.9 Optionally, a heating system may be provided, for two
r* 0.050 0.002 purposes: (1) to achieve degassing of the liquid, and (2) to
s* 0.025 0.001
bring the liquid temperature to the desired value before the test
NOTE—Asterisk (*) indicates mandatory; others recommended. begins. Such a system may consist of a separate heating coil, or
FIG. 4 Dimensions and Tolerances of the Test Specimen combined with the cooling system, with suitable thermostatic
control. A comprehensive thermal control system that includes
cooling, heating, and magnetic stirring provisions has been
of different length may be needed in order to permit use of similarly sized used by at least one investigator.
specimens. One horn might be used for specimens having densities 6.10 A timer should be provided to measure the test duration
5 g/cm3 or more and tuned for a button mass of about 10 g (0.022 lb), and or to switch off the test automatically after a preset time.
the other for densities less than 5 g/cm3, tuned for a button mass of about
5 g (0.011 lb). See also 7.2 and Table X2.2. 7. Test Specimens
6.5.3 A means for monitoring or checking frequency shall 7.1 The specimen button diameter (see also 6.3) shall be
be provided; this could be a signal from the power supply or a 15.9 6 0.05 mm (0.626 6 0.002 in.). The test surface shall be
transducer, feeding into a frequency counter. plane and square to the transducer axis within an indicator
6.6 Amplitude Control: reading of 0.025 mm (0.001 in.). No rim on or around the
6.6.1 Means shall be provided to measure and control specimen test surface shall be used. The circular edges of the
vibration amplitude of the horn tip within the tolerances specimen button shall be smooth, but any chamfer or radius
specified in 9.1.1.7 or 9.1.2. shall not exceed 0.15 mm (0.006 in.).
6.6.2 If the ultrasonic system has automatic control to 7.2 The button thickness of the specimen (Dimension H in
maintain resonance and constant amplitude, amplitude calibra- Figs. 1 and 4) shall be not less than 4 mm (0.157 in.) and not
tion may be done with the specimen in the air and will still more than 10 mm (0.394 in.). See Table X2.2 for relationships
apply when the specimen is submerged. This may be done with between button thickness and mass.
a filar microscope, dial indicator, eddy-current displacement 7.3 Specimens of different materials to be tested with the
sensor, or other suitable means (see also Appendix X1). same horn should have approximately the same button mass,
6.6.3 If the apparatus does not have automatic amplitude within the dimensional limits of 7.2. See also 6.5.2.
control, it may be necessary to provide a strain gage or 7.4 Specimens should be prepared in a manner consistent
accelerometer on some part of the vibrating assembly for with the purposes of the test. Three options are given in
continuous monitoring. 7.4.1-7.4.3.
6.7 Liquid Vessel: 7.4.1 Unless otherwise required, the test surface shall be
6.7.1 The size of the vessel containing the test liquid is a lightly machined, then ground and polished to a maximum
compromise. It must be small enough to permit satisfactory surface roughness of 0.8 µm (32 µin.), in such a way as to
temperature control, and large enough to avoid possible effects minimize surface damage or alteration. While an extremely
of wave reflections from its boundaries, and of erosion debris. fine finish is not required, there shall be no visible pits or

5
 G32 – 10
scratch marks that would serve as sites for accelerated cavita- TABLE 1 Material Used in Interlaboratory Study
tion damage. Final finishing with 600 grit emery cloth has been Designation: Nickel 200, UNS N02200, ASTM B160
found satisfactory. Composition (limit values): Ni 99 min; max others: 0.25 Cu, 0.40 Fe, 0.35 Mn,
0.15 C, 0.35 Si, 0.01 S
7.4.2 For screening of materials for their erosion resistance Specific gravity (nominal): 8.89
in a particular application, the surface preparation method Form: 0.75-in. (19 mm) rod, cold drawn and annealed
should be as close as possible to that used in the end Properties:
Yield strength (nominal)A: 103 to 207 MPa (15 to 30 ksi)
application. For example, rolled sheet material would be tested (measured)B: 284 MPa (41.2 ksi)
in the as-rolled condition and weld-deposited hard facings Tensile strength (nominal): 379 to 517 MPa (55 to 75 ksi)
would be tested in the as-deposited and final machined or (measured): 586 MPa (85 ksi)
Elongation (nominal): 40 to 55 %
polished condition, or both. (measured): 58 %
7.4.3 In tests where any possible effects of surface prepara- Reduction of area (nominal): N/A
(measured): 76 %
tion (for example, subsurface alterations, or work hardening)
Hardness (nominal): 45 to 70 HRB, 90 to 120 HB
on the results are to be minimized, the following procedure is (measured): 49 HRB
recommended: Prepare machined surfaces for testing by suc- A
“Nominal” properties are from “Huntington Alloys” data sheets. (Strength
cessively finer polishing down to 600 grit, with at least 50 properties were listed in ksi; SI values in this table are conversions.)
B
strokes of each grade of paper. This method provides a surface “Measured” properties reported from tests on sample from same rod as used
for erosion test specimens. (Strength properties were reported in ksi; SI values in
finish on the order of 0.1 to 0.2 µm (4 to 8 µin.) rms, with a this table are conversions.)
depth to the plastic/elastic boundary on the order of 20 µm.
Should the experiment require the complete removal of any
altered layer, an additional 25 µm of material should be
of specimens of same button mass and length. Also calibrate
removed via electropolishing.
the temperature measurement system by an appropriate
NOTE 3—Information on subsurface alterations due to machining and method.
grinding can be found in Refs (1 and 2).4 8.1.2 To qualify the apparatus initially, and to verify its
7.5 The threaded connection between specimen and horn performance from time to time, perform tests with the pre-
must be carefully designed, and sufficiently prestressed on ferred reference material specified in 8.1.3 (annealed Nickel
assembly, to avoid the possibility of excessive vibratory 200) or, if a laboratory cannot obtain Ni 200, one of the
stresses, fatigue failures, and leakage of fluid into the threads. supplementary reference materials specified in 8.1.4. Do this at
There must be no sharp corners in the thread roots or at the standard test conditions (see 9.1) even if the apparatus is
junction between threaded shank and button. A smooth radius normally operated at optional conditions. Detailed guidelines
or undercut shall be provided at that junction. Other recom- and criteria for qualification are given in Appendix X3.
mendations are given in Fig. 4 and Appendix X2. 8.1.3 The preferred reference material is annealed wrought
7.6 For test materials that are very light, or weak, or brittle, Nickel 200 (UNS N02200), conforming to Specification B160.
or that cannot be readily machined into a homogeneous This is a commercially pure (99.5 %) nickel product; see Table
specimen, it may be desirable to use a threaded stud made of 1 for its properties. Test curves from a “provisional” interlabo-
the same material as the horn (or some other suitable material) ratory study are shown in Fig. 5, and statistical results from that
and to attach a flat disk of the test material by means of study are shown in Table 2. The appearance of a test specimen
brazing, adhesives, or other suitable process. Such a disk shall at various stages is shown in Fig. 6.
be at least 3 mm (0.12 in.) in thickness, unless it is the purpose 8.1.4 A supplementary reference material of greater erosion
of the specimen to test an overlay or surface layer system. In resistance is annealed austenitic stainless steel Type 316, of
that case, the test report shall describe the overlay material, its hardness 150 to 175 HV (UNS S31600, Specification A276). A
thickness, the substrate material, and the deposition or attach- supplementary reference material of lesser erosion resistance is
ment process. For such nonhomogeneous specimens, the but- Aluminum Ally 6061-T6 (UNS A96061, Specification B211).
ton weight recommendation given in 7.3 still applies. Their properties are shown in Table 3. A comparative test study
7.7 No flats shall be machined into the cylindrical surface of with these materials was conducted for the original develop-
the specimen or horn tip. Tightening of the specimen should be ment of this Test Method; see Refs (3 and 4). Curves and
accomplished by a tool that depends on frictional clamping but limited statistical results from four laboratories are presented in
does not mar the cylindrical surface, such as a collet or X3.2.
specially designed clamp-on wrench, preferably one that can 8.2 Normalization of Test Results:
be used in conjunction with a torque wrench. (See 10.3 and 8.2.1 In each major program include among the materials
Appendix X2 for tightening requirements and guidelines.) tested one or more reference materials, tested at the same
condition to facilitate calculation of “normalized erosion resis-
8. Calibration tance” of the other materials.
8.1 Calibration and Qualification of Apparatus: 8.2.2 If possible include the preferred reference material,
8.1.1 Perform a frequency and amplitude calibration of the annealed Ni 200, as specified in 8.1.3.
assembled system at least with the first sample of each group 8.2.3 Alternatively, or in addition, include one of the supple-
mentary reference materials (see 8.1.4). The choice may be
4
The boldface numbers in parentheses refer to a list of references at the end of based on the range of expected erosion resistance of the group
this standard. of materials being tested.

6
 G32 – 10
9.1.1.7 The peak-to-peak displacement amplitude of the test
surface of the specimen shall be 50 µm (0.002 in.) 65 %
throughout the test.
9.1.2 An alternative peak-to-peak displacement amplitude
of 25 µm (0.001 in.) may be used for weak, brittle, or
nonmetallic materials that would be damaged too rapidly or
could not withstand the inertial vibratory stresses with the
standard amplitude of 9.1.1.7. See Appendix X2 for guidance.
This amplitude may also be appropriate for erosion-corrosion
studies. If this amplitude is used, this must be clearly stated in
conjunction with any statement that this test method (Test
Method G32) was followed.
9.2 Optional Test Conditions:
9.2.1 The standard test conditions of 9.1.1 satisfy a large
number of applications in which the relative resistance of
materials under ordinary environmental conditions is to be
determined. However, there can be applications for which
other temperatures, other pressures, and other liquids must be
used. When such is the case, any presentation of results shall
clearly refer to and specify all deviations from the test
conditions of 9.1.1. (See also 12.1.) Deviations from standard
test conditions should not be used unless essential for purposes
of the test.
9.2.2 Investigations of the effect of liquid temperature on
cavitation erosion (see X4.2.2) have shown that the erosion rate
peaks strongly at a temperature about halfway between freez-
ing and boiling point, for example, for water under atmospheric
pressure at about 50°C (122°F). Near the standard temperature
of 25°C, each increase of 1°C probably increases the erosion
NOTE—The curves for Laboratories 1 through 3 represent averages from
rate by 1 to 2 %. Thus, there may be economic incentive to
three replicate tests; that for Laboratory 5 is based on two replicate tests. conduct water tests with especially resistant materials (for
FIG. 5 Cumulative Erosion-Time Curves for Nickel 200 from Four example, tool steels, stellites) at a temperature higher than that
Laboratories (see 13.1.2) specified in 9.1.1.5. This can generally be done simply by
adjusting the temperature control, since without any cooling
9. Test Conditions the liquid temperature may rise even beyond the optimum.
9.1 Standard Test Conditions: 9.2.3 To conduct specialized tests at elevated temperature or
9.1.1 If this test method is cited without additional test pressure, or with difficult or hazardous liquids, the liquid-
parameters, it shall be understood that the following test containing vessel must be appropriately designed. Usually, a
conditions apply: seal must be provided between the vessel and the horn
9.1.1.1 The test liquid shall be distilled or deionized water, assembly. While bellows seals can be used, it is preferable to
meeting specifications for Type III reagent water given by design the supporting features (see 6.4) to incorporate the
Specification D1193. sealing function.
9.1.1.2 The depth of the liquid in its container shall be 100 9.2.4 The procedures specified in Section 10 still apply.
6 10 mm (3.94 6 0.39 in.), with cooling coils (if any) in place. Opening and disassembling the test vessel should be mini-
9.1.1.3 The immersion depth of the specimen test surface mized, as this may distort the erosion results by causing
shall be 12 6 4 mm (0.47 6 0.16 in.). extraneous oxidation, etc., through additional exposure to air.
9.1.1.4 The specimen (horn tip) shall be concentric with the
cylindrical axis of the container, within 65 % of the container 9.2.5 When testing with liquids that may be corrosive (for
diameter. example, seawater) Guide G119 may be followed in order to
9.1.1.5 Maintain the temperature of the test liquid at 25 6 determine the synergism between the mechanical and electro-
2°C (77 6 3.6°F). Caution—Failure to maintain specified chemical effects. See, for example, Ref (5).
temperature can significantly affect the results; see 9.2.2. 9.2.6 For tests intended to simulate cavitation erosion-
9.1.1.6 The gas over the test liquid shall be air, at a pressure corrosion conditions, it may be appropriate to operate the
differing less than 6 % from one standard atmosphere (101.3 equipment in a pulsed or cyclic manner. A 60-s-on/60-s-off
kPa; 760 mm (29.92 in.) Hg). If the pressure is outside this cycle is recommended as a basic duty cycle for such tests. If
range, for example, because of altitude, this must be noted in the nature of the interactions between erosion and corrosion is
the report as a deviation from standard conditions. to be studied, then varying duty cycles may be required.

7
 G32 – 10
TABLE 2 Statistical ResultsA of Provisional Interlaboratory Study using Ni 200
Maximum erosion rate Nominal Incubation Time to 50 µm Time to 100 µm
Test Result:
(µm/h) time (min) MDE (min) MDE (min)
Statistic
Individual Laboratory ResultsB
Laboratory 1 average: 29.6 29.7 131 234
standard deviation: 0.88 6.8 4.7 4.6
coefficient of variation %: 3.0 22.9 3.6 2.0

Laboratory 2 average: 27.6 19.0 128 236

standard deviation: 0.66 2.7 2.9 4.5
coefficient of variation %: 2.4 14.2 2.3 1.9

Laboratory 3 average: 23.5 18.3 147 275

standard deviation: 0.14 2.5 3.1 4.5
coefficient of variation %: 0.6 13.7 2.1 1.6

Laboratory 5 average: 26.0 19.7 133 248

standard deviation: 1.90 3.5 14.9 24.7
coefficient of variation %: 7.3 17.8 11.2 10.0
Average of laboratory averages: 26.6 21.7 135 248
Pooled Variabilities—Absolute Values
“Repeatability” standard deviation: 1.12 4.24 8.07 13.0
“Reproducibility” standard deviation: 2.74 6.40 10.6 21.7
“95 % Repeatability Limit”:C 3.13 11.9 22.6 36.4
“95 % Reproducibility Limit”:C 7.67 17.9 29.8 60.8
Pooled Variabilities—Normalized ValuesD
“Repeatability” coefficient of variation, %: 4.2 19.6 6.0 5.2
“Reproducibility” coefficient of variation, % 10.3 29.5 7.9 8.7
“95 % Repeatability Limit” coefficient, %: 12 55 17 14
“95 % Reproducibility Limit” coefficient, %: 29 83 22 25
A
This table is revised from that in the research report5 in that values for Laboratory 4, and pooled values including Laboratory 4, have been omitted.
B
All laboratory results are based on three replications, except time to 50 µm and 100 µm for Laboratory 5 (two replications).
C
A “95 % limit” represents the difference between two random test results that would not be exceeded in 95 % of such pairs (see Practice E177).
D
Normalized variabilities: coefficients of variation are corresponding standard deviations, and “95 % limit” coefficients are corresponding limits, expressed as percent
of the “average of laboratory averages.”

10. Procedure ensure effective preloading and to prevent galling between

10.1 For each new test specimen, clean the liquid vessel and specimen and horn. However, excessive amounts of liquid or
fill it with fresh liquid. grease lubricants can result in damage to mating surfaces in the
joint, due to cavitation of the lubricant. See also Appendix X2.)
NOTE 4—Early versions of this test method called for stabilizing the gas
(Warning—Heating of the horn and unusual noise are indica-
content of the liquid before beginning a test on a new specimen, by first
running a “dummy specimen” of high erosion resistance for 30 min. tions of either fatigue failure or improper tightening of the
However, there is no convincing evidence that this makes any significant specimen, or presence of dirt or excessive amount of lubricant.)
difference to the results, and it may be supposed that operating with the 10.4 Insert the specimen into the liquid to a depth as
test specimen for the first 30 min produces the same effect. However, this specified in 9.1.1.3, and concentric with the container as
procedure may be suitable when very early stages of the test are to be
investigated.
specified in 9.1.1.4.
10.5 Start the apparatus and the timer, and bring the
10.2 Clean the test specimen carefully and weigh it on an
amplitude as quickly as possible to the specified value. On
accurate and sensitive balance (0.1-mg accuracy and sensitiv-
ity) before the test. apparatus with automatic amplitude control this is usually
10.3 After making sure that the threads and contact surfaces accomplished simply by repeating the control settings or dial
of the horn and the specimen are perfectly free of debris, thread readings determined in a previous calibration (see 6.6 and
the specimen into the horn until finger tight, then tighten to a 8.1.1). Also make sure that the temperature is stabilized at the
suitable torque. The resulting prestressing of the threaded desired value as soon as possible. Monitor these conditions
shank must be sufficient to ensure that contact is not lost from time to time.
between horn and specimen shoulder as a result of vibratory 10.6 At the end of the test interval, stop the apparatus,
inertial loads. See guidelines given in Appendix X2. remove the specimen, and carefully clean, dry and weigh it to
(Warning—Fatigue failure of the threaded portion of the determine its new mass and hence the mass loss. See 10.6.1 for
specimens may become a problem under some circumstances. cleaning and drying recommendations. Repeat the cleaning,
The specimen must be tightly secured to the horn to ensure drying and weighing operations until two successive weighings
good energy transmission and avoid any separation between yield identical (or acceptably similar) readings, unless prior
specimen button and horn tip. A very thin (virtually invisible) qualification of the cleaning procedure has proved such repeti-
layer of liquid or solid boundary lubricant may be used to tion unnecessary.

8
 G32 – 10
exposure time can be established with reasonable accuracy.
The duration of these intervals, therefore, depends upon the test
material and its erosion resistance and cannot be rigorously
specified in advance. Suitable intervals may be approximately
15 min for aluminum alloys, 30 min for pure nickel, 1 to 2 h
for stainless steel, and 4 to 8 h for stellite. Intervals near the
beginning of a test may need to be shorter if the shape of the
erosion-time curve during the “incubation” and “acceleration”
periods, and the erosion threshold time, are to be accurately
established.
10.10 It is recommended that the testing of each specimen
be continued at least until the average rate of erosion (also
termed cumulative erosion rate) has reached a maximum and
begins to diminish, that is, until the “tangent erosion rate” line
(see 3.1) can be drawn.
NOTE 5—This recommendation assumes that either the “maximum
erosion rate” or the “tangent erosion rate” is considered a significant
measure of the resistance of the material, and ensures that both can be
determined. However, there is another school of thought that holds the
maximum rate is a transient phenomenon, and a truer measure is the
eventual “terminal erosion rate” if that can be established. Thus, the
desirable total duration of the test may depend on the test objectives, the
school of thought to which the investigator adheres, and the practical
limitations. For stainless steel, it can take 40 h to get beyond the maximum
rate stage, see Ref (6); for stellite probably more than 100.
10.11 It is recommended that when several materials are to
be compared, all materials be tested until they reach compa-
rable mean depths of erosion.
FIG. 6 Photographs of a Nickel 200 Specimen Taken at Several
Cumulative Exposure Times 11. Calculation or Interpretation of Results
11.1 Interpretation and reporting of cavitation erosion test
TABLE 3 Properties of Supplementary Reference Materials data is made difficult by the fact that the rate of erosion
(from tables in Ref (4))
(material loss) is not constant with time, but goes through
Aluminum Alloy Stainless Steel several stages (see Fig. 7). This makes it impossible to
Property
6061-T6 AISI 316
represent the test result fully by a single number, or to predict
Hardness, HRB 60.1 74.8
Tensile strength, MPA (ksi) 328 (40.7) 560 (81.3)
long-term behavior from a short-term test. The following
Elongation, % 21.5 69.0 paragraphs describe required as well as optional data interpre-
Reduction of area, % 44 76.9 tation steps.
Density, g/cm3 2.71 7.91
11.2 The primary result of an erosion test is the cumulative
erosion-time curve. Although the raw data will be in terms of
mass loss versus time, for analysis and reporting purposes this
10.6.1 Very carefully clean and dry the specimen before should be converted to a “mean depth of erosion” (MDE)
each weighing. Rinsing with ethyl alcohol or other suitable versus time curve, since a volumetric loss is more significant
solvent may be sufficient. An ultrasonic cleaning bath (such as than a mass loss when materials of different densities are
for cleaning dentures), has also been found satisfactory. compared. Calculate the mean depth of erosion, for the purpose
(Warning—This should NOT be used with solvents.) Dry with of this test method, on the basis of the full area of the test
a stream of hot, dry air, as from a hair dryer. For porous (for surface of the specimen, even though generally a narrow
example, cast) materials a vacuum desiccator may be used. Do annular region at the periphery of the test surface remains
not dry with cloth or paper products that may leave lint on the virtually undamaged. For the button diameter specified in 7.1,
specimen.) this area is 1.986 cm2 (0.308 in.2).
10.7 Repeat 10.3-10.6 for the next test interval, and so on 11.3 Because of the shape of the cumulative erosion-time
until the criteria of 10.10 or 10.11 have been met. It is curve, it is not meaningful to compare the mass loss or MDE
recommended that a running plot of cumulative mass loss for different materials after the same cumulative exposure time.
versus cumulative exposure time be maintained. (The reason is that a selected time may still be within the
10.8 After 8 to 12 h of testing with the same liquid, strain incubation or acceleration stage for a very resistant material,
out the debris, or discard and refill with fresh liquid. whereas for a weak material the same time may be within the
10.9 As shown in Fig. 7, the rate of mass loss varies with maximum rate or deceleration stage.) However, one may
exposure time. The intervals between measurements must be compare the cumulative exposure times to reach the same
such that a curve of cumulative mass loss versus cumulative cumulative MDE. For that purpose, the following values shall

9
 G32 – 10

NOTE—A = nominal incubation time; tan B = maximum erosion rate; tan C = terminal erosion rate; and D = terminal line intercept.
FIG. 7 Characteristic Stages of the Erosion Rate-Time Pattern, and Parameters for Representation of the Cumulative Erosion-Time
Curve

be reported: (1) Time to 50 µm, designated t50; (2) time to 100 11.5 The use of other carefully defined test result represen-
µm, designated t100; and (3) optionally, if practicable, time to tations, in addition to those required above, is optional. Some
200 µm, designated t200. that have been used include the “tangent erosion rate” (the
11.4 For a more complete description of the test result, use slope of a straight line drawn through the origin and tangent to
the following parameters (refer to Fig. 7): the knee of the cumulative erosion-time curve), the MDE of
11.4.1 The “maximum rate of erosion,” that is, slope of the that tangency point, and curves of “instantaneous erosion rate”
straight line that best approximates the linear (or nearly linear) versus time or of “average erosion rate” versus time. A recent
steepest portion of the cumulative erosion-time curve, ex- proposal is to plot the results on Weibull Cumulative Distribu-
pressed in micrometres per hour. This is the most commonly tion Function coordinates, and determine several parameters
used single-number result found in the literature, and its use is from the resulting straight line(s); see Ref (7) and others by the
required in this test method. same author.
11.4.2 The “nominal incubation time,” that is, intercept of 11.6 This test method is sufficiently well specified that
the maximum erosion rate line on the time axis. This also is direct comparisons between results obtained in different labo-
required. However, this is not a measure of the incubation ratories are meaningful, provided that the standard test con-
period, whose duration remains undefined. See also 11.4.3 figuration, conditions, and procedures are rigorously adhered
below. to; see 13.1.4 and Table 2. However, to facilitate comparisons
11.4.3 The “erosion threshold time” (ETT) or time required between results from different types of cavitation erosion tests,
to reach a mean depth of erosion (MDE) of 1.0 µm. This is an it is also recommended to present results in normalized form
indication of when measurable mass loss begins. Reporting of relative to one or more standard reference materials included in
this is optional. the test program (see 8.2). Specific parameters used include
11.4.4 The “terminal erosion rate” if exhibited in a test that normalized erosion resistance and normalized incubation re-
is continued for a sufficiently long time. This is optional. sistance (see definitions in Section 3).
11.4.5 If the terminal erosion rate is reported, then the MDE
corresponding to the intersection of the terminal-rate line with 12. Report
the maximum-rate line, or alternatively its intercept on the 12.1 Report clearly any deviations from the standard speci-
MDE axis, must also be reported. fications for the apparatus (Section 6), test specimen (Section

10
 G32 – 10
7), and test conditions (9.1) as well as the reasons for these bar. The material properties are given in Table 1. A research
deviations. This includes specification of the test liquid, tem- report has been filed with ASTM.5
perature and pressure of the liquid, vibration amplitude and 13.1.2 A summary of the test result statistics is given in
frequency, etc. When results from such tests are reported in Table 2, and averaged erosion-time curves for each lab are
abbreviated form, state that “ASTM Test Method G32 modi- shown in Fig. 5.
fied” was used and specify deviations from 9.1. NOTE 6—Although five laboratories participated, the results of Labo-
12.2 Erosion test results, especially during the incubation ratory No. 4 have been excluded here for the reason that this laboratory
period, can be significantly affected by the preparation of the reported overheating problems that led to unscheduled interruptions of the
specimen and the resulting alteration of its surface layers (see test and resulted in anomalous test curves with greater variability than
7.4.3 and Note 3). The test report should state if the objective those from the other laboratories. The full results may be found in the
was to study the material response with minimal effect of research report.5
surface preparation, or with surface preparation corresponding 13.1.3 Within-Laboratory Variability:
to an intended field application. 13.1.3.1 For maximum erosion rates, the pooled coefficient
12.3 Report the following information, if applicable, for of variation (COV) for repeatability was 4.2 %, but Laboratory
each material tested: 1, 2, and 3 each achieved individual within-lab coefficients of
12.3.1 Identification, specification, composition, heat treat- variation of 3 % or less.
ment, and mechanical properties including hardness, as mea- 13.1.3.2 For the other measures, Laboratories 1 through 3
sured on the specimen or the stock from which it came, again generally had the lowest coefficients of variation: For the
12.3.2 Method of preparing test specimens and test surface time to 100 µm MDE, while the pooled value was 5.2 %,
(preferably including initial surface roughness measurement), Laboratories 1 through 3 each achieved 2 % or lower. For the
12.3.3 Number of specimens tested, time to 50 µm MDE, the pooled value was 6 %, but Labora-
12.3.4 A tabulation giving the following information on tories 1 through 3 each achieved lower than 4 %. The greatest
each specimen tested: within-lab variability is found for the nominal incubation time;
12.3.4.1 Total cumulative length of exposure, hours (h), the pooled value was about 20 % and the lowest individual lab
12.3.4.2 Total cumulative mass loss, milligrams (mg), result was about 14 %.
12.3.4.3 Total cumulative mean depth of erosion, microme- 13.1.3.3 These results suggest that a laboratory that obtains
tres (µm), calculated from mass loss, specimen area (see 11.2), a repeatability coefficient of variation of 5 % or more, for any
and specimen density, parameter other than nominal incubation time, should carefully
12.3.4.4 Maximum rate of erosion (see 11.4.1), review its specimen preparation and testing procedures. The
12.3.4.5 Nominal incubation time (see 11.4.2), and results also underscore the importance of consistent surface
12.3.4.6 The cumulative exposure times to reach a mean preparation of the specimens, since surface preparation can
depths of 50, 100, and possibly 200 µm; designated t50, t100 and strongly affect the whole erosion-time curve, especially during
t200 respectively (see 11.3). the early stages.
12.3.5 A tabulation giving the normalized erosion resistance 13.1.4 Between-Laboratory Variability—The reproducibil-
and normalized incubation resistance for each material tested, ity coefficients of variation for all variables except the nominal
relative to one of the reference materials (see 8.2) included in incubation time ranged from 8 to 10 %; for the nominal
the test. Calculate these values from averaged data of replicate incubation time it was about 30 %.
tests of the same material. 13.2 Bias—No statement can be made regarding the bias of
12.3.6 A full report should also include the following on this test method, because there are no “accepted reference
each specimen tested: values” (as defined in Practice E177, Section 16) for the
12.3.6.1 Tabulation of cumulative mass losses and corre- properties measure in this (or any other) erosion test, nor is
sponding cumulative exposure time for each specimen, and there an “accepted reference method.” Erosion test results from
12.3.6.2 Plot of cumulative mean depth of erosion versus different methods are not directly comparable, and even
cumulative exposure time for each specimen. relative (for example, “normalized”) results for the same group
12.4 Report any special or unusual occurrences or observa- of materials may differ according to the test method or test
tions. conditions employed. However, a laboratory may determine its
own “provisional laboratory bias” by comparing its results for
13. Precision and Bias Nickel 200 with the provisional average results obtained in the
13.1 Precision: limited interlaboratory study shown in Table 2. See also 8.1.
13.1.1 The limited interlaboratory study on which the fol-
lowing information is based did not meet all the requirements 14. Keywords
of Practice E691; however, it does meet the requirements of a 14.1 cavitation; cavitation erosion; erosion by liquids;
provisional study as defined in Guide G117. The variabilities erosion-corrosion; erosion of solids; erosion resistance; erosion
are calculated as prescribed by Practice E691 and Guide G117. test; vibratory cavitation
The statistics are based on the tests of one material, Nickel 200,
by four laboratories, using this test method with only minor 5
Supporting data have been filed at ASTM International Headquarters and may
deviations. All laboratories used specimens cut from the same be obtained by requesting Research Report RR:G02-1007.

11
 G32 – 10

APPENDIXES

(Nonmandatory Information)

X1. AMPLITUDE MEASUREMENT AND CALIBRATION

X1.1 Commercially-obtained ultrasonic equipment is gen- ary and with it turned on. Since the indicator cannot follow the
erally provided with a meter or power adjustment that can be horn tip vibrations, it then takes on a position corresponding to
used to set and monitor vibration amplitude once it has been the peak displacement. Thus the difference in the readings is
calibrated against a direct measurement of tip amplitude. The the rest-to-peak amplitude.
following subsections briefly describe some calibration tech-
niques that have been found satisfactory, as well as alternative X1.4 Noncontacting Probes—Various noncontacting prox-
monitoring methods. imity probes and vibration probes are commercially available.
Any such vibration probe may be suitable. The suitability of a
X1.2 Filar Microscope—This technique requires a micro- proximity probe would depend on whether it would respond to
scope having a filar scale with divisions of 5 µm (0.0002 in.) or the closest position of a vibrating surface.
smaller, and a very bright light source. A light scratch mark, X1.5 Strain Gages—Theoretically, if the exact shape of the
perpendicular to the horn axis, may be scribed on the side of horn is known and its vibratory strain measured by a strain
the horn tip or specimen, if necessary. The width of an gage at one location, the corresponding tip amplitude can be
appropriate mark or edge perpendicular to the horn axis is calculated. It can also be calibrated with one of the other
observed with the apparatus turned off, and its “apparent methods listed above. This technique would permit constant
width” observed with the apparatus turned on. The difference is monitoring of the amplitude during a test with the tip im-
the peak-to-peak amplitude of vibration. mersed.
X1.3 Dial Indicator—This technique requires a precision X1.6 Accelerometers—An accelerometer sensing axial mo-
dial indicator with scale divisions of 2.5 µm (0.0001 in.) or tion can be attached at some suitable location that is not a node
smaller. The indicator is mounted on the platform or base of the (for instance on top of the transducer stack), and its signal
apparatus, with the indicator tip contacting the face of the horn calibrated by one of the other methods or by theoretical
tip or specimen. Readings are taken with the apparatus station- calculation.

X2. RECOMMENDATIONS FOR SPECIMEN THREADS AND PRESTRESSING TORQUE

X2.1 Basic Considerations its threaded hole, must resist the full inertial alternating force
X2.1.1 The prestressing force in the threaded shank, pro- due to the whole specimen and horn tip region below that
duced by adequate torquing on assembly, must exceed the peak section.
vibratory inertial force on the specimen button, so that a
positive contact pressure is always maintained between the X2.2 Thread Selection
specimen shoulder and the horn tip during each cycle of X2.2.1 While this test method does not mandate the use of
vibration. This is essential for two reasons: firstly, to reduce the a particular thread for the specimen shank, the following thread
alternating force imposed on the threaded shank, by spreading and shank dimensions are recommended:
it over the horn tip area as well, and secondly, to prevent any X2.2.2 The preferred recommended threads, to be desig-
leakage of the test liquid into the threads, where it could cause nated “Group A,” are either 3⁄8 UNF-24, M10-1.0, or M10-
damage and heating. 1.25. Alternative recommended threads, to be designated
X2.1.2 The prestress in the threaded shank, on the other “Group B,” are either 5⁄16-UNF-24 or M8-1.0. Some investi-
hand, must not be so great that it, in combination with the gators have used 7⁄16-UNF-20. The inch-based unified threads
reduced but still existing alternating stress, could cause failure should be Class 2 or, if desired, Class 3. The metric threads
in the threads or in the junction between threads and button. It should be of the “medium” class of fit (6g and 6H) or, if
should be noted that while in some bolting applications a desired, of the “close” class of fit (4h and 5H). The thread roots
proper preload can virtually eliminate all alternating stresses of the external thread must be rounded; the specification of the
from the threaded member, that cannot be assumed true in this British standards, calling for a root radius of 0.1443 times
case. The reason is that the horn tip area and rigidity is not pitch, may be followed. Some properties of these threads are
vastly greater than that of the shank, so that in essence the given in Table X2.1.
alternating load will be shared by the horn and the shank in X2.2.3 The length of the threaded shank should be 10 6 0.5
proportion to their areas and their moduli of elasticity. mm (0.394 6 0.02 in.).
X2.1.3 A final requirement, usually met without difficulty, is X2.2.4 At the junction between the threaded shank and the
that the horn annulus cross-section area, just below the top of shoulder of the specimen, there should be a smooth radius of at

12
 G32 – 10
TABLE X2.1 Properties of Specimen Threads
NOTE—Dimensions are given in mm or mm . (Dimensions in parentheses are given in in. or in.2.)
2

Optional Recommended Group A Group B

⁄
7 16 UNF-20 ⁄ UNF-24
38 M10-1.0 M10-1.25 ⁄
5 16 UNF-24 M8-1.0
Nominal diameter D 11.11 9.5 10.00 10.00 7.94 8.00
(0.4375) (0.375) (0.3937) (0.3937) (0.3125) (0.3150)
Pitch p 1.270 1.059 1.000 1.250 1.059 1.000
(0.0500) (0.0417) (0.0394) (0.0492) (0.0417) (0.0394)
Depth of Ext’l thread h 0.779 0.649 0.613 0.767 0.649 0.613
(0.03067) (0.02556) (0.02415) (0.03019) (0.02556) (0.02415)
Pitch Line diameter Dp 10.29 8.84 9.35 9.19 7.25 7.35
(0.4050) (0.3479) (0.3681) (0.3617) (0.2854) (0.2894)
Minor diameter DR 9.56 8.23 8.77 8.47 6.64 6.77
(0.3762) (0.3239) (0.3454) (0.3333) (0.2614) (0.2667)
Area of minor diameter AR 71.68 53.16 60.45 56.26 34.65 36.06
(0.1111) (0.0824) (0.0937) (0.0872) (0.0537) (0.0559)
“Tensile stress areaA” AS 76.58 56.65 37.42
(0.1187) (0.0878) N/A N/A (0.0580) N/A
B
Width of horn shoulder b 2.38 3.18 2.95 2.95 3.96 3.94
(0.0938) (0.125) (0.116) (0.116) (0.156) (0.155)
Stress area of hornB AH 100.6 126.5 119.4 119.4 148.4 147.7
(0.156) (0.196) (0.185) (0.185) (0.230) (0.229)
AH /AR ... 1.40 2.38 1.97 2.12 4.38 4.10
A
Use AR in place of AS if the latter is not available.
B
b = (0.625 − D)/2 in.; AH = (p/4) (0.6252 − D2) in.2.

least 0.65 mm (0.025 in.), and preferably a smooth undercut of Fb, N 5 400 M (X2.3)
length 2 mm (0.08 in.), as shown in Fig. 4. The horn should or:
have a corresponding countersink chamfer as also shown in Fb, lbf 5 90 M
this figure. The countersink should be no greater than neces- For the alternative displacement amplitude of 25 µm, the
sary, and not unduly reduce the contact surface between horn values are half of the above. The minimum prestress force to be
tip and specimen shoulder. considered should be at least 1.5 Fb. The maximum safe
prestress force is determined by the following steps.
X2.3 Relation Between Tightening Torque and Preload
X2.4.3 Calculate the alternating force amplitude on the
X2.3.1 For the recommended threads, the following equa- specimen threads, Fa, that applies when the preload exceeds
tions may be used to determine the required torque, T, to obtain F b:
a desired prestress force, Fs. Guidelines for selecting Fs are
Fb
given in X2.4. Fa 5 (X2.4)
1 1 ~AH/AR!~EH/ES!
X2.3.2 For thread group “A”:
T/Fs 5 [0.472µ 1 0.0076] ~lb2in./lb! (X2.1) where:
5 [0.012µ 1 0.00019] ~N2m/N!
AH = stress area of horn outside of threads,
AR = stress area of specimen shank,
X2.3.3 For thread group “B”: EH = modulus of elasticity of horn material, and
T/Fs 5 [0.415µ 1 0.0062] ~lb2in./lb! (X2.2) ES = modulus of elasticity of specimen material.
24 Values of (AH/AR) for the recommended threads are given in
5 [0.0105µ 1 1.57 3 10 # ~N2m/N!
Table X2.1.
X2.3.4 In the above equations, µ is the coefficient of X2.4.4 Calculate a conservative upper limit to the prestress
friction, which may be assumed as 0.2 for dry engagement and force FS using the following approximation:
0.1 for lubricated engagement. Fsmax 5 SyAs 2 8 Fa (X2.5)
X2.4 Prestressing Guidelines where:
X2.4.1 Experience has shown that prestressing the speci- Sy = yield strength of specimen material, and
men shank to about one half of its yield strength is satisfactory As = tensile stress area of the thread, given in Table X2.1.
in many cases. However, to evaluate the prestressing limits
more closely and identify potential problems, the following X2.4.5 If Fsmax from (Eq X2.5) exceeds 2 Fb from (Eq X2.3),
calculation steps may be performed. select an intermediate value of Fs, preferably at least 2 Fb and
X2.4.2 Calculate the peak inertial force (Fb) on the speci- calculate the required set-up torque as described in X2.3.
men button as follows. Determine the button mass, M, in X2.4.6 If Fsmax from (Eq X2.5) is less than 2 Fb, recalculate
grams. (See Table X2.2 for guidance.) Then for the standard Fsmax using the following slightly more detailed approxima-
peak-to-peak displacement amplitude of 50 µm at 20 kHz: tion, adapted from (Eq 33) of Ref (8):

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TABLE X2.2 Button Mass and Length Relationships
Material Specific Gravity Aluminum 2.7 Titanium 4.5 Steel 7.9 Nickel, Brass, Stellite 8.8
Button Length mm (in.) Corresponding Mass, g/(weight, lb)
2.14 3.57 6.27 6.99
4.0 (0.157) (0.00472) (0.00787) (0.0138) (0.0154)
3.22 5.36 9.41 10.48
6.0 (0.236) (0.00709) (0.0118) (0.0207) (0.0231)
4.29 7.15 12.55 13.98
8.0 (0.315) (0.00945) (0.0157) (0.0276) (0.0308)
5.36 8.94 15.69 17.47
10.0 (0.394) (0.0118) (0.0197) (0.0346) (0.0385)
Button Mass, g (weight, lb) Corresponding Length,mm/(in.)
7.46 4.47 2.55 2.29
4 (0.0088) (0.294) (0.176) (0.100) (0.090)
9.33 5.59 3.19 2.86
5 (0.0110) (0.367) (0.220) (0.125) (0.113)
14.93 8.95 5.10 4.58
8 (0.0176) (0.588) (0.352) (0.201) (0.180)
18.66 11.19 6.37 5.72
10 (0.0220) (0.735) (0.440) (0.251) (0.225)
Inertial Accelerations of Button
At 20 kHz, 50 µm peak-to-peak: 3.95 3 105 m/s2(40.3 3 103“G”)
At 20 kHz, 25 µm peak-to-peak: 1.97 3 105 m/s2(20.1 3 103“G”)

Fs 5 SuAs/Ns 2 KfFa ~Su/Se! (X2.6) Fsmax 5 SyAs (X2.7)

max

where: X2.4.8 If Fsmax from (Eq X2.6) or (Eq X2.7), whichever is the
Ns = factor of safety, preferably at least 1.5, lower value, exceeds 1.5 Fb from (Eq X2.3), select an interme-
Su = ultimate strength of specimen material, diate value of Fs, preferably at least 2 Fb, and calculate the
Se = unnotched endurance limit of specimen material for required set-up torque as described in X2.3.
fully reversed alternating loading, X2.4.9 If Fsmax from (Eq X2.6) or (Eq X2.7), whichever
Kf = fatigue notch factor
= q (Kt − 1) + 1, is the lower value, is less than 1.5 Fbfrom (Eq X2.3), then the
Kt = stress concentration factor, about 6.7 for threads, and possibility of fatigue failure might be expected. Remedies to be
q = notch sensitivity factor, dependent on notch radius. considered are to use a specimen button with minimum
For threads root radius of about 0.15 mm (0.006 in.), thickness (4 mm), to use the alternative displacement ampli-
q ; 0.5 for annealed or normalized steel; more for tude of 25 µm peak-to-peak, or to try one specimen to see
hardened steel, and less for aluminum. whether it works. In any case, a preload force Fs of less than
X2.4.7 If Fsmax from (Eq X2.6) exceeds SyAs, use: 1.5 Fbshould never be used.

X3. GUIDE FOR APPARATUS QUALIFICATION

X3.1 Introduction participated in this study, but since no standard existed then,
X3.1.1 Subsection 8.1 lists three reference materials that the apparatus and operating parameters varied widely.
may be used to qualify an apparatus. Subsection 8.1 and X3.2.2 Limited statistics, and curves of average results from
Section 13 also refer to precision statistics (Table 2) and four laboratories that operated at or close to the subsequent
“typical” test curves (Fig. 5) for the preferred material, Nickel specifications of this test method, are presented below. They
200, obtained from a provisional interlaboratory study (ILS).5 are designated as Labs A through D. All of these operated at
However, no corresponding statistics are available for the two frequency 20 kHz, amplitude 51 µm, temperature 24°C, and
supplementary reference materials, 316 stainless steel and had specimen diameters ranging from 12.7 to 15.9 mm.
6061-T6 aluminum alloy. This appendix presents some data on Because of this, only mean depth of erosion, but not mass loss,
these materials and guidelines for judging whether an appara- can be compared. Furthermore, while three labs used flat-ended
tus is qualified for this test method. specimens, one used “rimmed” specimens” for the 316 stain-
less steel tests; however, their results seemed to fit in well with
X3.2 Data on Supplementary Reference Materials those from flat specimens. Refs (3 and 4) did not present
X3.2.1 Stainless steel 316 and Aluminum 6061-T6 were individual test curves, only “average” curves from the several
included (along with Nickel 270) in a “round-robin” test labs. This test program was not a rigorous ILS as now
program conducted prior to the original drafting of this test understood, and the data below must be taken with caution, and
method; this is reported in Refs (3 and 4). Eleven labs as approximate.

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FIG. X3.1 Cumulative Erosion-Time Curves for Stainless Steel 316 from Data in Ref (4)

X3.2.3 Fig. X3.1, for stainless steel 316, shows the average X3.3.2 First conduct tests on at least two, or preferably
curves of MDE versus time from each lab, copied from Fig. 2 more, specimens of the selected reference material, following
of Ref (3) or Fig 10 of Ref (4). the standard test conditions specified in this test method, and
X3.2.4 Fig. X3.2, for aluminum 6061-T6, shows average determine mean values of the parameters listed above. Also
curves of MDE versus time from each lab, recalculated from verify that the properties of the stock used for the specimens
Fig 9 (weight and volume loss) of Ref (4). The reason is that are within the ranges specified in Table 1 or Table 3. If not, so
in Fig. 4 in Ref (3) and the corresponding Fig. 12 of Ref (4), state in the qualification report.
the individual curves cannot reliably be distinguished.
X3.3.3 The apparatus is “qualified” if these values lie within
X3.2.5 Tables X3.1 and X3.2 present the following data,
two standard deviations from the corresponding mean values
measured from Fig. X3.1 and Fig. X3.2, respectively, and their
from the tables listed above. These limit values are listed in
mean and standard deviation with (n-1) weighting. The column
headings are consistent with those of Table 2 in Section 13, but Table X3.3. (So that all three materials are treated equally, the
no formal repeatability or reproducibility statistics can be standard deviation for Ni 200 is based on lab averages in Table
inferred. 2, not the formal reproducibility standard deviation in that
(1) maximum erosion rate (MER), µm/h. (It must be table.)
pointed out that these values differ from those tabulated in Refs X3.3.4 If all three parameters are within these limits, the
(3 and 4). apparatus is qualified.
(2) nominal incubation time (t0), min. X3.3.5 If that is not the case, then do either or both of the
(3) time to mean depth of erosion of 50 µm (t50), min. following:
(4) time to mean depth of erosion of 100 µm (t100), min. (1) Carefully check the apparatus and operation for com-
X3.3 Guidelines for Determining Qualification of pliance with specified operating conditions and test procedures,
Apparatus and make any adjustments necessary.
X3.3.1 In brief, these guidelines are based on comparing (2) If only two specimens were tested, test a third and
mean results for MER, t50, and if possible t100, from several recompute the results.
samples of the selected reference material, with the statistical X3.3.6 If neither of these steps results in satisfactory quali-
range of results for that material derived from Table 2, Table fication, the discrepancy should be reported in reports or papers
X3.1, or Table X3.2, respectively. based on any test results.

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 G32 – 10

FIG. X3.2 Cumulative Erosion-Time Curves for Aluminum Alloy 6061-T6 from Data in Ref (4)

TABLE X3.1 Results for Stainless Steel 316

Laboratory No. of Specimens MER µm/h t0 min t50 min t100 min
A 2 9.3 57. 380. 700.
B* 3 9.9 41. 344. 648.
C* 3 9.9 41. 344. 648.
D 1 7.6 41. 437. n/a
Mean 9.2 45. 376. 665.
Standard deviation, s 1.1 8. 44. 30.
Coefficient of Variation 0.12 0.18 0.12 0.05

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 G32 – 10
TABLE X3.2 Results for Aluminum 6061–T6
Laboratory No. of Specimens MER µm/h t0 min t50 min t100 min
A 2 188. 10. 24. 42.
B* 3 166. 13. 30. 48.
C* 2 204. 16. 30. 45.
D 1 209. 19. 31. 47.
Mean 192. 14.5 29. 45.5
Standard deviation, s 19. 3.9 3.2 2.8
Coefficient of Variation 0.10 0.27 0.11 0.06

TABLE X3.3 Acceptability Limits for Qualification

Reference Parameter Mean (x) of Lab Results Std Deviation, s Upper Limit x + 2 s Lower Limit x – 2 s
Material
Nickel 200 MER 26.7 2.6 31.9 21.5
t50 135 8.4 152 118
t100 248 19 286 210
316 stainless steel MER 9.1 1.0 11.1 7.1
t50 378 34 445 310
t100 667 26 719 615
6061-T6 aluminum MER 213 15 243 183
t50 30 3 36 24
t100 46 3 52 40

X4. RATIONALE

X4.1 Background and History example, Refs (6), (16), and (17), the dynamics of the
X4.1.1 Ever since Gaines (9) discovered that cavitation “cavitation cloud” of bubbles and cavities (for example, Ref
erosion occurred at the face of a vibrating piston, this phenom- (18), cavitation in slurries (for example, Refs (19 and 20), and
enon has been used for basic research as well as for screening cavitation erosion-corrosion (for example, Refs (5), (21), (22)).
materials. In 1955 the American Society of Mechanical Engi- X4.2.2 Numerous tests have been made with fluids other
neers Committee on Cavitation recommended a standard test than water (such as glycerin, petroleum derivatives, sodium,
procedure based on the state-of-the-art then existent (10). etc.), and with water at various temperatures (for example,
Subsequently much advancement in test apparatus and tech- Refs (16), (17), (23), (24), (25), (26)).
niques took place. Realizing this, ASTM Committee G02 X4.2.3 Tests using a stationary specimen in close proximity
initiated a round-robin test (3 and 4) in 1966, which was to the horn tip have been described by several authors (for
completed in 1969. The test specifications and recommenda- example, Refs (19), (27), (28), (29), (30)), but inconsistent
tions contained in the first publication of this test method were findings concerning optimum separation distance have discour-
the direct outcome of that ASTM round-robin test, although aged standardization to date.
many of the participants in that test used existing apparatus
with specimen diameters, amplitudes and frequencies that X4.3 Revisions to This Test Method—Subsequent to the first
differed from the eventual standard. Similar test specifications issue of this test method, revisions were minor or editorial in
had been proposed earlier by an independent group in the nature until after a “Workshop on Cavitation Erosion Testing”
United Kingdom (6). was held in 1987. This resulted in the establishment of a task
X4.1.2 The reasons for selecting the vibratory method for group to review all facets of this test method, and to revise it
standardization were that it was widely used, relatively simple thoroughly based on the latest experience with its use. In a
and inexpensive to set up, and readily controllable as to its 1992 revision, the text was almost completely revised and
important parameters. Other methods used for cavitation test- reorganized; however, except for the addition of an optional
ing include the “cavitation tunnel” wherein cavitation is lower vibratory amplitude of 25 µm (0.001 in.), and a slight
produced by flow through a venturi or past an obstruction, the increase in standard temperature from 22 to 25°C they will not
“cavitating disc” method wherein a submerged rotating disc change the results to be expected in a well-conducted test. The
with holes or protrusions produces the cavitation, and, more major change to the apparatus was that a larger liquid container
recently, cavitating jet methods. Comprehensive references was specified, and the immersion depth was increased. The
covering cavitation, cavitation damage and cavitation testing other revisions were intended to reduce variability by tighten-
include Refs (11-15). ing the specifications of the test apparatus, setup, and proce-
dures; to provide added guidance in use of this test method; and
X4.2 Applications of Vibratory Apparatus to further standardize the presentation of results. Also, the
X4.2.1 The vibratory method has been used, among other “standard reference material” was changed from Nickel 270 to
purposes, for studying the development of material damage Nickel 200, because the former is no longer commercially
(for example, Ref (14), the influence of test parameters (for available. A new interlaboratory study, using Nickel 200 and

17
 G32 – 10
following the revised standard, was conducted in 1990–1991 It also again revised specifications for the liquid container,
and its results were the basis for a revised precision and bias tightened some procedures and operation, added more guid-
statement. In 2004, another task group was convened to ance, and added some parameters to be reported. The last
consider extensive revision proposals submitted by a commit- revision by this task group, in 2010, relaxed some require-
tee member. The resulting revision of 2006 deleted one ments, added an appendix with test data for the supplementary
laboratory’s results from the precision statistics, because its reference materials from Refs (3 and 4), and specified an
anomalous results were deemed due to apparatus malfunctions. apparatus qualification procedure.

REFERENCES

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