ASTM G134-17(2023)

This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the
Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
Designation: G134 − 17 (Reapproved 2023)
Standard Test Method for
Erosion of Solid Materials by Cavitating Liquid Jet
This standard is issued under the fixed designation G134; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope 1.6 This standard does not purport to address all of the
safety concerns, if any, associated with its use. It is the
1.1 This test method covers a test that can be used to
responsibility of the user of this standard to establish appro-
compare the cavitation erosion resistance of solid materials. A
priate safety, health, and environmental practices and deter-
submerged cavitating jet, issuing from a nozzle, impinges on a
mine the applicability of regulatory limitations prior to use.
test specimen placed in its path so that cavities collapse on it,
1.7 This international standard was developed in accor-
thereby causing erosion. The test is carried out under specified
dance with internationally recognized principles on standard-
conditions in a specified liquid, usually water. This test method
ization established in the Decision on Principles for the
can also be used to compare the cavitation erosion capability of
Development of International Standards, Guides and Recom-
various liquids.
mendations issued by the World Trade Organization Technical
1.2 This test method specifies the nozzle and nozzle holder
Barriers to Trade (TBT) Committee.
shape and size, the specimen size and its method of mounting,
and the minimum test chamber size. Procedures are described
2. Referenced Documents
for selecting the standoff distance and one of several standard
2.1 ASTM Standards:
test conditions. Deviation from some of these conditions is
A276/A276M Specification for Stainless Steel Bars and
permitted where appropriate and if properly documented.
Shapes
Guidance is given on setting up a suitable apparatus, test and
B160 Specification for Nickel Rod and Bar
reporting procedures, and the precautions to be taken. Standard
B211 Specification for Aluminum and Aluminum-Alloy
reference materials are specified; these must be used to verify
Rolled or Cold-Finished Bar, Rod, and Wire (Metric)
the operation of the facility and to define the normalized
B0211_B0211M
erosion resistance of other materials.
D1193 Specification for Reagent Water
1.3 Two types of tests are encompassed, one using test
E691 Practice for Conducting an Interlaboratory Study to
liquids which can be run to waste, for example, tap water, and
Determine the Precision of a Test Method
the other using liquids which must be recirculated, for
G32 Test Method for Cavitation Erosion Using Vibratory
example, reagent water or various oils. Slightly different test
Apparatus
circuits are required for each type.
G40 Terminology Relating to Wear and Erosion
G73 Test Method for Liquid Impingement Erosion Using
1.4 This test method provides an alternative to Test Method
Rotating Apparatus
G32. In that method, cavitation is induced by vibrating a
submerged specimen at high frequency (20 kHz) with a 2.2 ASTM Adjuncts:
Manufacturing Drawings of the Apparatus
specified amplitude. In the present method, cavitation is
generated in a flowing system so that both the jet velocity and
3. Terminology
the downstream pressure (which causes the bubble collapse)
can be varied independently.
3.1 See Terminology G40 for definitions of terms relating to
cavitation erosion. For convenience, definitions of some im-
1.5 The values stated in SI units are to be regarded as
portant terms used in this test method are reproduced below.
standard. No other units of measurement are included in this
standard.
3.2 Definitions:
1 2
This test method is under the jurisdiction of ASTM Committee G02 on Wear For referenced ASTM standards, visit the ASTM website, www.astm.org, or
and Erosion and is the direct responsibility of Subcommittee G02.10 on Erosion by contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
Solids and Liquids. Standards volume information, refer to the standard’s Document Summary page on
Current edition approved June 1, 2023. Published June 2023. Originally the ASTM website.
approved in 1995. Last previous edition approved in 2017 as G134 – 17. DOI: Available from ASTM International Headquarters. Order Adjunct No.
10.1520/G0134-17R23. ADJG0134.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
G134 − 17 (2023)
3.2.1 cavitation, n—the formation and subsequent collapse, maximum-slope portion of the cumulative erosion-time curve.)
within a liquid, of cavities or bubbles that contain vapor or a G40
mixture of vapor and gas.
3.2.8 maximum erosion rate, n—in cavitation and liquid
3.2.1.1 Discussion—Cavitation originates from a local de-
impingement erosion, the maximum instantaneous erosion rate
crease in hydrostatic pressure in the liquid, usually produced
in a test that exhibits such a maximum followed by decreasing
by motion of the liquid (see flow cavitation) or of a solid
erosion rates. (See also erosion rate-time pattern.)
boundary (see vibratory cavitation). It is distinguished in this
3.2.8.1 Discussion—Occurrence of such a maximum is
way from boiling, which originates from an increase in liquid
typical of many cavitation and liquid impingement tests. In
temperature.
some instances, it occurs as an instantaneous maximum, in
3.2.1.2 Discussion—The term cavitation, by itself, should others as a steady-state maximum which persists for some
not be used to denote the damage or erosion of a solid surface time. G40
that can be caused by it; this effect of cavitation is termed
3.2.9 normalized erosion resistance, N , n—in cavitation
e
cavitation damage or cavitation erosion. To erode a solid
and liquid impingement erosion, a measure of the erosion
surface, bubbles or cavities must collapse on or near that
resistance of a test material relative to that of a specified
surface. G40
reference material, calculated by dividing the volume loss rate
of the reference material by that of the test material, when both
3.2.2 cavitation erosion, n—progressive loss of original
are similarly tested and similarly analyzed. By “similarly
material from a solid surface due to continued exposure to
analyzed,” it is meant that the two erosion rates must be
cavitation. G40
determined for corresponding portions of the erosion rate time
3.2.3 cumulative erosion, n—in cavitation and impingement
pattern; for instance, the maximum erosion rate or the terminal
erosion, the total amount of material lost from a solid surface
erosion rate.
during all exposure periods since it was first exposed to
3.2.9.1 Discussion—A recommended complete wording has
cavitation or impingement as a newly-finished surface. (More
the form, “The normalized erosion resistance of (test material)
specific terms that may be used are cumulative mass loss,
relative to (reference material) based on (criterion of data
cumulative volume loss, or cumulative mean depth of erosion.
analysis) is (numerical value).” G40
See also cumulative erosion-time curve.)
3.2.10 normalized incubation resistance, N , n—the nomi-
o
3.2.3.1 Discussion—Unless otherwise indicated by the
nal incubation period of a test material, divided by the nominal
context, it is implied that the conditions of cavitation or
incubation period of a specified reference material similarly
impingement have remained the same throughout all exposure
tested and similarly analyzed. (See also normalized erosion
periods, with no intermediate refinishing of the surface. G40
resistance.) G40
3.2.4 cumulative erosion rate, n—the cumulative erosion at
3.2.11 terminal erosion rate, n—in cavitation or liquid
a specified point in an erosion test divided by the correspond-
impingement erosion, the final steady-state erosion rate that is
ing cumulative exposure duration; that is, the slope of a line
reached (or appears to be approached asymptotically) after the
from the origin to the specified point on the cumulative
erosion rate has declined from its maximum value. (See also
erosion-time curve. (Synonym: average erosion rate) G40
terminal period and erosion rate-time pattern.) G40
3.2.5 cumulative erosion-time curve, n—in cavitation and
3.3 Definitions of Terms Specific to This Standard:
impingement erosion, a plot of cumulative erosion versus
3.3.1 cavitating jet, n—a continuous liquid jet (usually
cumulative exposure duration, usually determined by periodic
submerged) in which cavitation is induced by the nozzle design
interruption of the test and weighing of the specimen. This is
or sometimes by a center body. See also jet cavitation.
the primary record of an erosion test. Most other
3.3.2 cavitation number, σ—a dimensionless number that
characteristics, such as the incubation period, maximum ero-
measures the tendency for cavitation to occur in a flowing
sion rate, terminal erosion rate, and erosion rate-time curve, are
stream of liquid, and that, for the purpose of this test method,
derived from it. G40
is defined by the following equation. All pressures are absolute.
3.2.6 flow cavitation, n—cavitation caused by a decrease in
p 2 p
~ !
d v
local pressure induced by changes in velocity of a flowing
σ 5 (1)
liquid. Typically, this may be caused by flow around an
ρV
obstacle or through a constriction, or relative to a blade or foil.
A cavitation cloud or “cavitating wake” generally trails from
where:
some point adjacent to the obstacle or constriction to some
p = vapor pressure,
v
distance downstream, the bubbles being formed at one place
p = static pressure in the downstream chamber,
d
and collapsing at another. G40
V = jet velocity, and
ρ = liquid density.
3.2.7 incubation period, n—in cavitation and impingement
erosion, the initial stage of the erosion rate-time pattern during
3.3.2.1 For liquid flow through any orifice:
which the erosion rate is zero or negligible compared to later
stages. Also, the exposure duration associated with this stage.
ρ V 5 p 2 p (2)
u d
(Quantitatively it is sometimes defined as the intercept on the
time or exposure axis, of a straight line extension of the where:
G134 − 17 (2023)
accurately before testing begins and again during periodic
p = upstream pressure.
u
interruptions of the test, in order to obtain a history of mass
3.3.2.2 For erosion testing by this test method, the cavitat-
loss versus time (which is not linear). Appropriate interpreta-
ing flow in the nozzle is choked, so that the downstream
tion of the cumulative erosion-time curve derived from these
pressure, as seen by the flow, is equal to the vapor pressure.
measurements permits comparisons to be drawn between
The cavitation number thus reduces to:
different materials, different test conditions, or between differ-
p 2 p
ent liquids. A typical test rig can be built using a 2.5 kW pump
d v
σ 5 (3)
p 2 p
u d capable of producing 21 MPa pressure. The standard nozzle
bore diameter is 0.4 mm, but this may be changed if required
which for many liquids and at many temperatures can be
for specialized tests.
approximated by:
p
5. Significance and Use
d
σ 5 (4)
p
u
5.1 This test method may be used to estimate the relative
resistances of materials to cavitation erosion, as may be
since
encountered for instance in pumps, hydraulic turbines, valves,
p .p .p (5)
u d v
hydraulic dynamometers and couplings, bearings, diesel engine
3.3.3 jet cavitation, n—the cavitation generated in the vor-
cylinder liners, ship propellers, hydrofoils, internal flow
tices which travel in sequence singly or in clouds in the shear
passages, and various components of fluid power systems or
layer around a submerged jet. It can be amplified by the nozzle
fuel systems of diesel engines. It can also be used to compare
design so that vortices form in the vena contracta region inside
erosion produced by different liquids under the conditions
the nozzle.
simulated by the test. Its general applications are similar to
G32.
those of Test Method
3.3.4 stand-off distance, n—in this test method, the distance
between the inlet edge of the nozzle and the target face of the
5.2 In this test method cavitation is generated in a flowing
specimen. It is thus defined because the location and shape of
system. Both the velocity of flow which causes the formation
the inlet edge determine the location of the vena contracta and
of cavities and the chamber pressure in which they collapse can
the initiation of cavitation.
be changed easily and independently, so it is possible to study
the effects of various parameters separately. Cavitation condi-
3.3.5 tangent erosion rate, n—the slope of a straight line
tions can be controlled easily and precisely. Furthermore, if
drawn through the origin and tangent to the knee of the
cumulative erosion-time curve, when the shape of that curve tests are performed at constant cavitation number (σ), it is
possible, by suitably altering the pressures, to accelerate or
has the characteristic S-shape pattern that permits this. In such
cases, the tangent erosion rate also represents the maximum slow down the testing process (see 11.2 and Fig. A2.2).
cumulative erosion rate exhibited during the test.
5.3 This test method with standard conditions should not be
3.3.6 vena contracta, n—the smallest locally occurring di-
used to rank materials for applications where electrochemical
ameter of the main flow of a fluid after it enters into a nozzle corrosion or solid particle impingement plays a major role.
or orifice from a larger conduit or a reservoir. At this point the
However, it could be adapted to evaluate erosion-corrosion
main or primary flow is detached from the solid boundaries, effects if the appropriate liquid and cavitation number, for the
and vortices or recirculating secondary flow patterns are
service conditions of interest, are used (see 11.1).
formed in the intervening space.
5.4 For metallic materials, this test method could also be
used as a screening test for applications subjected to high-
4. Summary of Test Method
speed liquid drop impingement, if the use of Practice G73 is
4.1 This test method produces a submerged cavitating jet
not feasible. However, this is not recommended for elastomeric
which impinges upon a stationary specimen, also submerged,
coatings, composites, or other nonmetallic aerospace materials.
causing cavitation bubbles to collapse on that specimen and
5.5 The mechanisms of cavitation erosion and liquid im-
thereby to erode it. This test method generally utilizes a
pingement erosion are not fully understood and may vary,
commercially available positive displacement pump fitted with
depending on the detailed nature, scale, and intensity of the
a hydraulic accumulator to damp out pulsations. The pump
liquid/solid interactions. Erosion resistance may, therefore,
delivers test liquid through a small sharp-entry cylindrical-bore
arise from a mix of properties rather than a single property, and
nozzle, which discharges a jet of liquid into a chamber at a
has not yet been successfully correlated with other indepen-
controlled pressure. Cavitation starts in the vena contracta
dently measurable material properties. For this reason, the
region of the jet within the length of the nozzle; it is stabilized
consistency of results between different test methods (for
by the cylindrical bore and it emerges, appearing to the eye as
example, vibratory, rotating disk, or cavitating jet) or under
a cloud which is visible around the submerged liquid jet. A
different experimental conditions is not very good. Small
button type specimen is placed in the path of the jet at a
differences between two materials are probably not significant,
specified stand-off distance from the entry edge of the nozzle.
and their relative ranking could well be reversed in another
Cavitation bubbles collapse on the specimen, thus causing
test.
erosion. Both the upstream and the downstream chamber
pressures and the temperature of the discharging liquid must be 5.6 Because of the nonlinear nature of the erosion-time
controlled and monitored. The test specimen is weighed curve in cavitation erosion, the shape of that curve must be
G134 − 17 (2023)
considered in making comparisons and drawing conclusions. specimen is fitted always in the same angular position. Similar
Simply comparing the cumulative mass loss at the same provision shall be made so that the holder fits only one way
cumulative test time for all materials will not give a reliable into the chamber block.
comparison.
6.4 The complete test circuit is shown in Fig. 4, and further
described in Annex A1. The test chamber (12) can be used with
6. Apparatus
either open or recirculating systems. The open system uses a
6.1 General Arrangement:
tap water supply with the discharge running to waste, while in
6.1.1 Fig. 1 shows an arrangement of the test chamber. A
the closed system the test liquid is recirculated. (Warning—If
cavitating jet supplied from a constant pressure source (p )
u tests with corrosive liquids are contemplated, all system
discharges, through a long-orifice nozzle (Fig. 2), into a
components including the pump should be of stainless steel or
chamber held at specified constant pressure (p ). A flat-ended
d other materials capable of handling such liquids.)
cylindrical specimen (Fig. 3) is mounted coaxially with the
6.5 A pump capable of producing a pressure of 21 MPa and
nozzle so that the stand-off distance between the nozzle inlet
a flow of 4.5 L/min is required.
edge and the specimen face can be set at any required value. A
6.6 For measurement of upstream and chamber pressures,
movable jet deflector (Fig. 1, Item 11) may be provided to
either standard test gages (0.25 % accuracy) or pressure
protect the specimen while test conditions are being set up.
transducers of at least equal precision and stability, having
Windows may be provided at both sides of the chamber so that
appropriate pressure ranges, shall be provided. It is strongly
the erosion process can be observed. Unless the complete test
recommended that the low-pressure gage used for the down-
chamber assembly can withstand maximum operating pres-
stream pressure measurement be protected by an appropriate
sures that could occur under any conceivable circumstances, a
pressure relief valve.
pressure relief valve must be fitted.
6.1.2 Manufacturing drawings of the apparatus are available
6.7 For measurement of the liquid temperature, a thermom-
at Tohoku University as an adjunct. For special applications;
eter or thermocouple shall be provided in the outlet pipe just
for example, where the nature of the test specimen material is
downstream of the test chamber.
granular with granules comparable to the nozzle size, a larger
6.8 A suitable heater shall be provided in the system so that
apparatus is required. All linear dimensions must then be
the desired test temperature can be maintained.
increased proportionately; for example, by a factor of two to
five for rock or concrete specimens. 6.9 It is useful and makes testing easier if pressure regula-
tors are fitted to control upstream and downstream pressures.
6.2 The long-orifice nozzle (Fig. 2) is simply a cylindrical
bore hole of length equal to 3.0 6 0.1 bore diameters. It is 6.10 As the nozzle and regulating valve openings are small
important that the inlet edge is sharp and free from manufac- and solid particles must not reach the specimen, filters (40 μm
turing defects and burrs. The nozzle must be made from a or finer) shall be fitted in both upstream and downstream lines.
highly erosion- and corrosion-resistant alloy. The shape of the Alternatively a settling tank can be fitted on the downstream
nozzle holder affects the nozzle performance so it is also side.
specified in Fig. 2.
6.11 If a recirculating system is used, a sump large enough
6.3 The specimen is held in place in a two-jaw collet. A line to ensure adequate cooling shall be provided. A sump capacity
shall be scribed on the top of the holder so that it can be aligned of not less than 100 L is recommended; cooling is essential in
with a corresponding line on the specimen to ensure that the such a system.
NOTE 1—Reprinted by permission of the Tohoku University.
FIG. 1 Test Chamber Assembly
G134 − 17 (2023)
NOTE 1—Material is Nitronic 60.
NOTE 2—It is important that the inlet corner is sharp. It must not reflect light.
NOTE 3—Roundness of hole is less than 0.002 mm.
NOTE 4—All dimensions are in mm.
FIG. 2 Nozzle and Nozzle Holder
NOTE 1—See Section 8 for additional information.
NOTE 1—Key:
FIG. 3 Test Specimen
1. Pulsation damper 8.Heater
2. Pump 9.Upstream pressure gage 0 to 25
6.12 A very useful addition to the facility is an automatic
MPa
timer which switches the pump off after a preset test time has 3. Hydraulic accumulator 10.Downstream pressure gage with
pulsation damper protector 0 to 0.6 MPa
elapsed.
4. Pressure-relief valve 11. Thermometer
5. On-Off valve 12.Test chamber
7. Precautions
6. Pressure-regulating valve or 13.Downstream filter
by-pass throttle valve 14.Pressure regulator
7.1 Caution—When testing relatively weak or brittle
7. H.P. filter 15.Drain valve
materials, ensure that they will not be damaged by merely the
stagnation pressure developed by the jet and that, therefore, the
NOTE 2—If closed system with header tank is used, cooling is essential.
erosion is attributable solely to cavitation. This can be done
FIG. 4 Test Circuit
most easily by a preliminary test during which cavitation is
suppressed while the jet velocity is kept constant; this is
7.2 Caution—This apparatus can generate high sound
achieved by increasing both the downstream pressure and the levels, so the use of ear protection may be necessary.
upstream pressure by the same amount. Sometimes it may be
8. Test Specimen
advisable to check on the margin of safety by increasing the
upstream pressure (but not exceeding the safe pressure limits 8.1 The test specimen is shown in Fig. 3. The test surface
for the apparatus) in this preliminary test until damage to the shall be plane, and normal to the specimen axis within an
specimen does occur. indicator reading of 0.02 mm.
G134 − 17 (2023)
8.2 Unless otherwise required, the test surface shall be the apparatus. Conduct this calibration at standard test condi-
lightly machined, then optionally ground or polished to a tions even if the apparatus is usually operated at optional test
maximum surface roughness of 0.4 μm (16 μin.), in such a way conditions.
as to minimize surface damage or alteration. (For some
9.3 As a brief check, a sample of previously tested material
materials, machining at one third the speed and one third the
can be inserted for an interval of time appropriate to the
feed normally recommended has been found satisfactory.)
material, say half an hour for steel. The result can then be
While extremely fine finish is not required, there shall be no
compared with the previously obtained data.
visible pits or scratch marks that would serve as sites for
accelerated cavitation damage. For final finishing, 600 grit
10. Standard Test Conditions
emery cloth may be used.
10.1 If this test method is cited without additional test
8.3 Some materials may require heat treatment to remove
parameters, it shall be understood that the test conditions
effects caused by machining and to ensure uniform hardness.
selected conform to the following:
The treatment must not alter the desired state of the material.
10.1.1 The test liquid shall be tap water or reagent water
8.4 For materials available in sheet form, it is permissible to
conforming to Type IV of Specification D1193.
fix a disk of material by an appropriate adhesive to a suitably
10.1.2 The water temperature at nozzle inlet shall be 35 °C
modified carrier. Ensure that the test material thickness is
6 1 °C.
sufficient to accommodate erosion without weakening the
10.1.3 Preliminary tests shall be carried out at two cavita-
specimen. A thickness of 3 mm would generally be sufficient.
tion numbers on two different specimens, to enable assessment
8.5 A number of additional specimens may be required for
at various cavitation conditions and to determine appropriate
setting up test conditions; for example, pressures, tempera-
testing times. These two values and the corresponding pres-
tures.
sures are prescribed in Table 1.
10.1.4 The major tests shall be carried out at one constant
8.6 Ensure that a sufficient number of test specimens are
cavitation number (selected on the basis of 10.1.3) so that
prepared from the same stock.
cavitation conditions remain constant. One of the pressures
9. Calibration
must be specified and the other can be calculated from
definition of cavitation number, σ (see 3.3.2). The value will
9.1 A pressure/flow test as described in A2.1, to determine
depend on the materials tested and should be chosen so that the
its discharge coefficient, shall be carried out on a new nozzle
test durations are acceptable.
and thereafter at regular intervals, initially after 40 h of use, to
10.1.5 The tests shall be carried out at the stand-off distance
check that the nozzle has not deteriorated. If there develops any
at which maximum cumulative erosion rate occurs. This value
change in discharge coefficient greater than 1 %, take correc-
of stand-off distance depends on cavitation number σ. As a
tive action. An increase in the discharge coefficient indicates
guide for establishing this optimum stand-off distance, Fig. 5
wear of the inlet edge; a decrease indicates blockage. Also
may be used. The exact value for the apparatus used shall be
examine the nozzle holder exit for erosion.
determined experimentally; see A2.3. If the value of the
9.2 Perform a complete test on a standard reference material
cavitation number is to be changed, a new optimum stand-off
(see 12.9 and Table 1) at standard test conditions (see 10.1)
distance must be established.
from time to time to verify the consistency of performance of
TABLE 1 Standard Test Conditions and Reference Materials
NOTE 1—Test liquid: Water (tap or deionized)
Test temperature: T = 35 (±1) °C
Corresponding vapor pressure: p = 0.00563 MPa
v
NOTE 2—Upstream pressure (p ) and downstream pressure (p ) given in
u d
MPa absolute, for different cavitation numbers (σ) and reference materi-
als.
NOTE 3—If two materials are to be used as references, nickel is to be
tested at the lower pressure if the other material is aluminum, or at the
higher pressure if the other material is steel.
σ = 0.014 σ = 0.025
Material
p p p p
u d u d
Soft aluminum 1100, UNS A91100, 12.5 0.18 12.5 0.32
Specification B211. (Heat for 2 h at
400 °C, air cool.)
Annealed wrought Nickel 200, UNS 12.5 0.18 12.5 0.32
N02200, Specification B160. (See Note 17.5 0.25 17.4 0.44
3.)
Austenitic stainless steel Type 316, UNS 17.5 0.25 17.4 0.44
S31600, Specification A276/A276M,
Hardness 150 HV to 175 HV.
FIG. 5 Variation of Stand-off Distance with Cavitation Number
G134 − 17 (2023)
11. Optional Test Conditions 12.6 It is well known that the rate of mass loss varies with
exposure time. The intervals between measurements must be
11.1 The standard test conditions conforming to Section 10
such that a curve of cumulative mass loss versus cumulative
satisfy a large number of cases in which the relative resistance
exposure time can be established with reasonable accuracy.
of materials under ordinary environmental conditions is to be
The duration of these intervals, therefore, depends upon the test
determined. However, there are cases in which other
material and its erosion resistance, and cannot be rigorously
temperatures, other pressures, and other liquids must be used.
specified in advance. Time intervals for stainless steel can be
In these cases reference to or citation of this test method shall
inferred from the sample results given in Fig. 6.
clearly refer to and specify all deviations from the provisions of
12.7 Continue the test of each specimen at least until the
Section 10.
cumulative erosion rate has reached a maximum and has
11.2 Testing at higher or lower upstream pressures but still
started to diminish, that is, until a tangent can be drawn from
at the same value of cavitation number must sometimes be
the origin to the knee of the cumulative erosion-time curve. If
done. Testing at high pressure increases erosion rate since
long-term behavior is important, some specimens should be
n
maximum erosion rate is proportional to (p ) where n ≈ 4.
u
tested, if possible, until the terminal erosion rate (if any) is
(The actual value of n will be influenced by the details of the
reached. If several materials are to be compared, all materials
apparatus used and by the cavitation number.) Thus highly
should be tested until they reach about the same volumetric
resistant materials can be tested at higher pressure to speed up
amount of erosion, if feasible within time constraints.
testing. Conversely, less resistant materials can be tested at
12.8 Plot the mass loss against time as the test proceeds; this
lower pressures. Also tests can be made at other values of
may help to identify any errors.
cavitation number. In such cases a new optimum stand-off
di
...