ASTM G32-98

NOTICE: This standard has either been superceded and replaced by a new version or discontinued.
Contact ASTM International (www.astm.org) for the latest information.
Designation: G 32 – 98
Standard Test Method for
Cavitation Erosion Using Vibratory Apparatus
This standard is issued under the fixed designation G 32; 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 (e) indicates an editorial change since the last revision or reapproval.
1. Scope 2. Referenced Documents
1.1 This test method produces cavitation damage on the face 2.1 ASTM Standards:
of a specimen vibrated at high frequency while immersed in a A 276 Specification for Stainless Steel Bars and Shapes
liquid. The vibration induces the formation and collapse of B 160 Specification for Nickel Rod and Bar
cavities in the liquid, and the collapsing cavities produce the B 211 Specification for Aluminum and Aluminum-Alloy
damage to and erosion (material loss) of the specimen. Bar, Rod, and Wire
1.2 Although the mechanism for generating fluid cavitation D 1193 Specification for Reagent Water
in this method differs from that occurring in flowing systems E 177 Practice for Use of the Terms Precision and Bias in
and hydraulic machines (see 5.1), the nature of the material ASTM Test Methods
damage mechanism is believed to be basically similar. The E 691 Practice for Conducting an Interlaboratory Study to
method therefore offers a small-scale, relatively simple and Determine the Precision of a Test Method
controllable test that can be used to compare the cavitation E 960 Specification for Laboratory Glass Beakers
erosion resistance of different materials, to study in detail the G 40 Terminology Relating to Wear and Erosion
nature and progress of damage in a given material, or—by G 73 Practice for Liquid Impingement Erosion Testing
varying some of the test conditions—to study the effect of test G 134 Test Method for Erosion of Solid Materials by a
variables on the damage produced. Cavitating Liquid Jet
1.3 This test method specifies standard test conditions
3. Terminology
covering the diameter, vibratory amplitude and frequency of
3.1 Definitions:
the specimen, as well as the test liquid and its container. It
permits deviations from some of these conditions if properly 3.1.1 See Terminology G 40 for definitions of terms relating
to cavitation erosion. For convenience, definitions of some
documented, that may be appropriate for some purposes. It
gives guidance on setting up a suitable apparatus and covers important terms used in this test method are quoted below from
Terminology G 40 – 98.
test and reporting procedures and precautions to be taken. It
also specifies standard reference materials that must be used to 3.1.2 average erosion rate, n—a less preferred term for
cumulative erosion rate.
verify the operation of the facility and to define the normalized
erosion resistance of other test materials. 3.1.3 cavitation, n—the formation and subsequent collapse,
1.4 The values stated in SI units are to be regarded as within a liquid, of cavities or bubbles that contain vapor or gas,
or both.
standard. The inch-pound units given in parentheses are for
information only. 3.1.3.1 Discussion—In general, cavitation originates from a
local decrease in hydrostatic pressure in the liquid, produced
1.5 This standard does not purport to address all of the
safety concerns, if any, associated with its use. It is the by motion of the liquid (see flow cavitation) or of a solid
boundary (see vibratory cavitation). It is distinguished in this
responsibility of the user of this standard to establish appro-
priate safety and health practices and determine the applica- way from boiling, which originates from an increase in liquid
temperature.
bility of regulatory limitations prior to use. For specific safety
precautionary information, see Note 2, Note 4, Note 5, and 3.1.3.2 Discussion—The term cavitation, by itself, should
not be used to denote the damage or erosion of a solid surface
Note 6.
Annual Book of ASTM Standards, Vol 01.03.
1 3
This test method is under the jurisdiction of ASTM Committee G-2 on Wear Annual Book of ASTM Standards, Vol 02.04.
and Erosion and is the direct responsibility of Subcommittee G02.10 on Erosion by Annual Book of ASTM Standards, Vol 02.02.
Liquids and Solids. Annual Book of ASTM Standards, Vol 11.01.
Current edition approved April 10, 1998. Published December 1998. Originally Annual Book of ASTM Standards, Vol 14.02.
e1 7
published as G 32 – 72. Last previous edition G 32 – 92 . Annual Book of ASTM Standards, Vol 03.02.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
NOTICE: This standard has either been superceded and replaced by a new version or discontinued.
Contact ASTM International (www.astm.org) for the latest information.
G32–98
that can be caused by it; this effect of cavitation is termed some instances it occurs as an instantaneous maximum, in
cavitation damage or cavitation erosion. To erode a solid others as a steady-state maximum which persists for some
surface, bubbles or cavities must collapse on or near that time.
surface. 3.1.12 mean depth of erosion (MDE), n—the average thick-
ness of material eroded from a specified surface area, usually
3.1.4 cavitation erosion, n—progressive loss of original
calculated by dividing the measured mass loss by the density of
material from a solid surface due to continued exposure to
the material to obtain the volume loss and dividing that by the
cavitation.
area of the specified surface. (Also known as mean depth of
3.1.5 cumulative erosion, n—the total amount of material
penetration or MDP. Since that might be taken to denote the
lost from a solid surface during all exposure periods since it
average value of the depths of individual pits, it is a less
was first exposed to cavitation or impingement as a newly
preferred term.)
finished surface. (More specific terms that may be used are
3.1.13 normalized erosion resistance, N , n—the volume
cumulative mass loss, cumulative volume loss,or cumulative
e
loss rate of a test material, divided into the volume loss rate of
mean depth of erosion. See also cumulative erosion-time
a specified reference material similarly tested and similarly
curve.)
analyzed. By “similarly analyzed” is meant that the two
3.1.5.1 Discussion—Unless otherwise indicated by the con-
erosion rates must be determined for corresponding portions of
text, it is implied that the conditions of cavitation or impinge-
the erosion rate time pattern; for instance, the maximum
ment have remained the same throughout all exposure periods,
erosion rate or the terminal erosion rate.
with no intermediate refinishing of the surface.
3.1.13.1 Discussion—A recommended complete wording
3.1.6 cumulative erosion rate, n—the cumulative erosion at
has the form, “The normalized erosion resistance of (test
a specified point in an erosion test divided by the correspond-
material) relative to (reference material) based on (criterion of
ing cumulative exposure duration; that is, the slope of a line
data analysis) is (numerical value).”
from the origin to the specified point on the cumulative
3.1.14 normalized incubation resistance N , n—the incuba-
o
erosion-time curve. (Synonym: average erosion rate)
tion period of a test material, divided by the incubation period
3.1.7 cumulative erosion-time curve—a plot of cumulative
of a specified reference material similarly tested and similarly
erosion versus cumulative exposure duration, usually deter-
analyzed. (See also normalized erosion resistance.)
mined by periodic interruption of the test and weighing of the
3.1.15 tangent erosion rate—the slope of a straight line
specimen. This is the primary record of an erosion test. Most
drawn through the origin and tangent to the knee of the
other characteristics, such as the incubation period, maximum
cumulative erosion-time curve, when that curve has the char-
erosion rate, terminal erosion rate, and erosion rate-time curve,
acteristic S-shaped pattern that permits this. In such cases, the
are derived from it.
tangent erosion rate also represents the maximum cumulative
3.1.8 erosion rate-time curve, n—a plot of instantaneous
erosion rate exhibited during the test.
erosion rate versus exposure duration, usually obtained by
3.1.16 terminal erosion rate, n—the final steady-state ero-
numerical or graphical differentiation of the cumulative
sion rate that is reached (or appears to be approached asymp-
erosion-time curve. (See also erosion rate-time pattern.)
totically) after the erosion rate has declined from its maximum
3.1.9 erosion rate-time pattern, n—any qualitative descrip-
value. (See also terminal period and erosion rate-time pattern.)
tion of the shape of the erosion rate-time curve in terms of the
3.1.17 vibratory cavitation, n—cavitation caused by the
several stages of which it may be composed.
pressure fluctuations within a liquid, induced by the vibration
3.1.9.1 Discussion—In cavitation and liquid impingement
of a solid surface immersed in the liquid.
erosion, a typical pattern may be composed of all or some of
the following “periods” or “stages”: incubation period, accel- 4. Summary of Test Method
eration period, maximum-rate period, deceleration period,
4.1 This test method generally utilizes a commercially
terminal period, and occasionally catastrophic period. The
obtained 20-kHz ultrasonic transducer to which is attached a
generic term “period” is recommended when associated with
suitably designed “horn” or velocity transformer. A specimen
quantitative measures of its duration, etc.; for purely qualitative
button of proper mass is attached by threading into the tip of
descriptions the term“ stage” is preferred.
the horn.
3.1.10 incubation period, n—the initial stage of the erosion
4.2 The specimen is immersed into a container of the test
rate-time pattern during which the erosion rate is zero or
liquid (generally distilled water) that must be maintained at a
negligible compared to later stages. Also, the exposure duration
specified temperature during test operation, while the specimen
associated with this stage. (Quantitatively it is sometimes
is vibrated at a specified amplitude. The amplitude and
defined as the intercept on the time or exposure axis, of a
frequency of vibration of the test specimen must be accurately
straight line extension of the maximum-slope portion of the
controlled and monitored.
cumulative erosion-time curve.)
4.3 The test specimen is weighed accurately before testing
3.1.11 maximum erosion rate, n—the maximum instanta-
begins and again during periodic interruptions of the test, in
neous erosion rate in a test that exhibits such a maximum
order to obtain a history of mass loss versus time (which is not
followed by decreasing erosion rates. (See also erosion rate-
linear). Appropriate interpretation of this cumulative erosion-
time pattern.)
versus-time curve permits comparison of results between
3.1.11.1 Discussion—Occurrence of such a maximum is different materials or between different test fluids or other
typical of many cavitation and liquid impingement tests. In conditions.
NOTICE: This standard has either been superceded and replaced by a new version or discontinued.
Contact ASTM International (www.astm.org) for the latest information.
G32–98
5. Significance and Use dently measurable material properties. For this reason, the
consistency of results between different test methods or under
5.1 This test method may be used to estimate the relative
different field conditions is not very good. Small differences
resistance of materials to cavitation erosion as may be encoun-
between two materials are probably not significant, and their
tered, for instance, in pumps, hydraulic turbines, hydraulic
relative ranking could well be reversed in another test.
dynamometers, valves, bearings, diesel engine cylinder liners,
ship propellers, hydrofoils, and in internal flow passages with
6. Apparatus
obstructions. An alternative method for similar purposes is Test
6.1 The vibratory apparatus used for this test method
Method G 134, which employs a cavitating liquit jet to produce
produces axial oscillations of a test specimen inserted to a
erosion on a stationary specimen. The latter may be more
specified depth in the test liquid. The vibrations are generated
suitable for materials not readily formed into a precisely
by a magnetostrictive or piezoelectric transducer, driven by a
shaped specimen. The results of either, or any, cavitation
suitable electronic oscillator and power amplifier. The power of
erosion test should be used with caution; see 5.7.
the system should be sufficient to permit constant amplitude of
5.2 Some investigators have also used this test method as a
the specimen in air as well as submerged. An acoustic power
screening test for materials subjected to liquid impingement
output of 250 to 1000 W has been found suitable. Such systems
erosion as encountered, for instance, in low-pressure steam
are commercially available, intended for ultrasonic welding,
turbines and in aircraft, missiles or spacecraft flying through
emulsifying, and so forth.
rainstorms. Practice G 73 describes another testing approach
specifically intended for that type of environment.
NOTE 2—Warning: This apparatus may generate high sound levels.
5.3 This test method is not recommended for evaluating
The use of ear protection may be necessary. Provision of an acoustical
elastomeric or compliant coatings, some of which have been enclosure is recommended.
successfully used for protection against cavitation or liquid
6.1.1 The basic parameters involved in this test method are
impingement of moderate intensity. This is because the com-
pictorially shown in Fig. 1. Schematic and photographic views
pliance of the coating on the specimen may reduce the severity
of representative equipment are shown in Figs. 2 and 3
of the liquid cavitation induced by its vibratory motion. The
respectively.
result would not be representative of a field application, where
6.2 To obtain a higher vibratory amplitude at the specimen
the hydrodynamic generation of cavitation is independent of
than at the transducer, a suitably shaped tapered cylindrical
the coating.
member, generally termed the “horn” or “velocity trans-
former”, is required. Catenoidal, exponential and stepped horn
NOTE 1—An alternative approach that uses the same basic apparatus,
and is deemed suitable for compliant coatings, is the “stationary speci- profiles have been used for this application. The diameter of the
men” method. In that method, the specimen is fixed within the liquid
horn at its tip shall conform to that sp
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