Discussion Pape2:2002
Erosion testing for materials used for
construction and repair of hydraulic turbine.
Bhola Thapa
Dr. Ing. Student
Hydropower Laboratory, NTNU
Summary
Operation and maintenance is serious problem in hydropower plants operating in sand-laden water. High
resistance material coating on the surface exposed to sand water somewhat reduces the effect of sand erosion.
Velocity (V) of sand particle is one of the major factors, which decides the erosion. The erosion rate is
proportional to Vn. The exponent, n depends on the material and operating condition. The correct value of n
helps to compute erosion rate and prepare erosion map in turbine blade. The value of n is generally established
by experiment. Erosion/corrosion test setup is used at NTNU/SINTEF to study erosion and corrosion resistance
of materials. The equipment will be further used to investigate erosion resistance of materials used in hydraulic
turbine. It will be investigated, if the result of this equipment can be compared with results from other equipment
operating on similar operating condition and the result can be applied for estimating wear of hydraulic turbine
or not. The feedback to this discussion paper will be used for necessary modification and planning for
experiment.
1. Background
The problem of smooth and efficient operation of hydropower plant due to erosion of the turbine runner and
other turbine parts are problems in many power plants in the Himalayan rivers in Asia. This is not a big problem
for Norwegian power plants but the turbines designed and manufactured by Norwegian companies for those
areas are facing problem of short runner life and inefficient operation.
Excessive sediment in the river with hard mineralogical contents erodes turbines components, which are in
regular contact with river water so fast, that there are records of damage of turbine just after running one
monsoon season. Realizing the problem Government of India has even classified the power plants in three
categories A (repair after each 2 monsoon) to C (repair after 7 monsoon) based on their vulnerability to silt
erosion (Mann, 2001).
The turbine is an expensive part in the hydropower plant. Discarding the eroded turbine is not economical and
good decision. Hence normally turbines are refurbished. But the optimum time period for the refurbishment and
economy of refurbishment is again a complex task because of the technology involved, the high cost of new
turbine, downtime during repair and maintenance cost involved. Welding, machining/grinding and hard surface
1
coating with erosion resistant material are normal repair method of eroded turbine. It is quite labor-intensive
process and labor cost is significant in total maintenance cost. The case study for Jhimruk (3 X 4 MW) power
plant in Nepal, showed that the maintenance cost is approximately 25 % of the total annual cost and maintenance
cost is less than 2% of replacement cost. Hence power companies normally prefers to repair the turbine rather
than replacing very often. The challenge for the repair of the eroded turbine is to select and use proper type of
welding and coating material to get best performance from the turbine.
Similar type of problem can be observed in the pumps operating in abrasive condition. The synergy effect
between sand erosion, cavitation erosion and corrosion can be very worst, and lifetime of the hydraulic machine
could be reduced considerably.
Dr. ing. study is on progress at Institute of Thermal Energy and Hydropower, NTNU with focus on the effect of
wear of hydraulic machinery due to sand particle in the water with following aim:
1.
To study the flow regimen in the turbine and identify the highest velocity and acceleration regimen where
most serious sand erosion occurs. This work will be concentrated on Francis Turbine, Pelton Turbine and
Simplified Small Hydro Turbine.
2.
Study of erosion rate as a function of head and speed in the location where the highest velocity and
acceleration occurs.
3.
Study the erosion process on different materials. A comparison of lifetime of hard surface coating on
lifetime of turbine and
4.
Finally analyze repair method and interval between repair that gives optimal economy of the power
production in hydropower plants by comparing the loss in efficiency with the cost and downtime of repair.
It is expected to study part of aim 2 and 3 by means of experiments with controlled flow velocity in the
laboratory. The findings of the experiment will be useful to understand the problem of aim 1 and can be used as
input for investigating aim 4.
2. Sand Erosion in Hydraulic Machinery
Almost all the mechanical components subject to wear during lifetime. Depending on the method of material
removal and rate of material removal, wear can be classified in several ways. Erosion, corrosion and cavitation
wears are predominant wear type for hydraulic machinery because of the sediment-laden water. The wear rate is
the rate of the material removal or dimensional change due to wear per unit of exposure parameter. The wear rate
can be considered as one of the indicator to measure effect of wear and can be used for maintenance decision
making along with other operational data of the system. Erosive wear of material takes place in two-phase flow.
When a fluid containing solid particles repeatedly hits against the solid surface, erosion of the material takes
place. The wear of hydraulic turbine caused by sediment is erosive wear. The erosion of material due to sand
originates at weak spots such as soft & weak point in the metallographic structure, rough surfaces and points of
high stress concentration and easily spreads over the entire surface of exposure.
2
The solid particles in the fluid can break the protective oxide layer in the metal surface and may accelerate
corrosion. The synergic effect between corrosion is reported in several literatures, but the synergy between
cavitation and sand erosion is not yet clearly understood. Velocity of the fluid (thus velocity of particle) is one of
the important factors affecting erosive wear. Sand erosion is assumed to be proportional to be velocity with some
positive exponent index. Which signifies, as velocity increases, sand erosion also increases. But on the other
hand, cavitation is a phenomenon, which is observed in the flow regimen where pressure is reduced to less than
vapor pressure. Considering Bernoulli’s equation in a flow passage, if the velocity of fluid rises, it is possible to
drop the pressure. Hence theoretically it is possible to have cavitation in the regimen where velocity is very high,
which is favorable condition for sand erosion. But still synergy effect between these two is not known.
Following are main factors, which affects the erosive wear:
3.

Speed of erosive particle/Velocity of fluid

Impingement angle of the jet or particle

Particle characteristic such as particle size, shape, hardness etc

Particle flux rate or concentration

Temperature

Effect of media

Metallurgy of material

Substrate material hardness and surface morphology
Wear of Water Turbines/Pumps
High head Pelton and Francis turbines are most affected by sand erosion. Kaplan turbines operating on high
sediment content water may also have effect of sand erosion. Small turbines except Pelton turbines are not very
much affected by sand erosion because of low head. But poor disilting system in small hydropower projects and
inferior material quality used to manufacture simple indigenous small turbine may cause the sand erosion even
on low head turbine.
The impulse turbine parts can be classified in four categories in order to study the effect of influence of sand
water. These are inlet system (including inlet valve), nozzles, runner and wheel pit. Because of the high-pressure,
any leakage due to sand erosion causes cavitation damage of closed seals. The needle and nozzles can be eroded
especially with fine grain sand because of extremely high velocity at the outlet of nozzle. Nozzle is a part, which
is prone to cavitation, and in the presence of solid, the synergy effect between erosion and cavitation can be
experienced. The buckets of the Pelton wheel will be eroded due to high acceleration of sand particle. The
maximum absolute acceleration normal to the bucket surface will be 50000 to 100000 m/sec. The most severe
damage occurs at the bottom towards the outlet. Other places of erosion due to direct contact of sand are splitter
and entrance lip and erosion is also observed in the backside of the bucket inlet due to rebound particle. The
deflector and turbine pit linear also erodes due to sand but these are not serious, because it does not affect much
on the performance of the turbine.
3
The wear of valve and inlet system in Francis turbines is similar to Pelton turbines. High turbulence in the spiral
casing causes removal of the paint and material can be removed by turbulence erosion followed by corrosion.
There is slight possibility of sand erosion on the draft tube close to the turbine outlet due to high velocity. But
other part of draft tube is not susceptible to sand erosion. The erosion of the guide vane system, turbine runner,
labyrinth seal and shaft seal are most serious in the Francis turbines.
Guide vane system faces highest acceleration and absolute velocity in the Francis turbine. The erosion of guide
vane due to sand water can be classified in following four categories.
1.
Turbulence erosion at the outlet region and facing plate due to high velocity of fine grain sand.
2.
Secondary flow erosion in the corner between guide vane and facing plates.
3.
Leakage Erosion at the clearance between guide vane and facing plate due to local separation and
turbulence.
4.
Erosion due to acceleration of main flow creating the rotation of water in front of the runner. This effect is
severe by particles of large size.
High relative velocity at the outlet and high acceleration at the inlet region of Francis turbine causes turbulence
and acceleration erosion due to fine and coarse grains at outlet and inlet respectively. The turbulence erosion is
always susceptible in the labyrinth seal. Mechanical shaft seal will be damaged if the sand-laden water come in
contact with it.
The wear of pump is similar to the reaction turbine. The wear of side linear of the centrifugal pump effects the
performance of pump.
Pelton turbine has large drop in efficiency in full load compared to part load but reverse phenomenon is observed
in Francis turbine. In a Francis turbine, the largest drop in efficiency is at part load. The repair time of the
Francis turbine is more as compared to Pelton turbine. Hence Pelton turbine should be preferred for operation in
the sand-laden water for operation at part load.
4.
Operation Of Hydropower Plant
The head and flow of water decides the power produced by the turbine. The general philosophy of the design for
Francis turbine is that, at guide vane 50% energy is converted in to kinetic energy and 50% of energy is retained
as pressure energy (Brekke, 2001). At the outlet of the turbine runner the water velocity is maintained
approximately 40 m/s. For a pump maximum outlet velocity can be up to 55 m/s. Normally concrete can
withstand only about 10 m/s, hence spiral casing is designed for less than 20 m/s water velocity. Considering a
turbine with 400m net head, about 63 m/s velocity is expected (considering conversion of 50% of energy in
kinetic energy) at guide vane outlet. Depending on the profile of shape of turbine (profile of runner) and guide
vane, the velocity profile can be different. But the velocity of water will continuously increase from stay vane to
exit of guide vane. The exit of the guide vane experiences the highest velocity. Between guide vane and runner
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inlet the velocity drops suddenly to approximate velocity of stay vane (say 15 m/s) and increases up to the runner
outlet velocity. The schematic variation of velocity at different section of turbine is shown in figure (1).
The wear rate of sand erosion is dependent on positive exponent index of the velocity. From above figure, it can
be easily seen that guide vane and runner outlet are area which has high velocity. Hence it can be presumed that
these are the areas, which will be highly affected by sand erosion. This logic is in accordance with the experience
in the sand-eroded turbine. Velocity distribution at different turbine location can be mapped with the help of
design parameter. Magnitude of sand erosion can also be mapped with the help of models for erosion and
velocity map for different turbine section. If the value of index is known, sand erosion can be mapped correctly,
keeping other parameters constant. Wear mapping will depend upon the value of exponent and determining the
correct value of this exponent is a challenge.
 20 m/s
60 m/s
Velocity
40 m/s
15 m/s
Turbine section
Fig 1: Velocity distribution in the Francis turbine sections
5
5. Wear Estimate And Effect Of Velocity
Several researchers have developed mathematical model for erosive wear. Since actual mechanism of the wear is
not yet clearly understood; simple, reliable and generalized quantitative model for erosion is not yet developed
which can be used for engineering purpose.
Most common expression for the erosive wear found in literature is based on experimental experience and they
are generally expressed as a function of velocity, material hardness, particle size, concentration etc.
The most often quoted expression is:
Wear Rate  (velocity)n,
(1)
Where, index n may vary depending on the material and other factor.
The index suggested by researcher lies close to 3, which is in accord with energy of striking particle.
There is a general agreement on wear rate in terms of weight loss (mg) per unit mass of erodent (mg) on the
following empirical expression (Bjordal, 1995 and references there on):
WE = k` upn f()
(2)
Where k` is a parameter depending on materials and properties, u p is velocity of particle and f() is function of
impingement angle.
If WE is given as a weight loss per unit area and the time of exposure, the expression will be
WE = k` (mp/At) upn f()
(3)
Substituting (mp/At) = Cpup gives, where Cp, is concentration of particle.
WE = k` Cpupn+1 f()
(4)
If we consider the wear of a material due to striking particle is dependent in kinetic energy of the particle, then
the value of n in equation (2) will be 2 and overall value of exponent of velocity will be 3. Hence equation (4)
can be written as:
WE = k` Cpup3 f()
(5)
The value of index, n suggested by different researcher is presented in Table 1. Wellinger (1958) suggested the
value of index, n between 1.4 to 2.9 for different metals, but since then up to now, there is not general agreement
on this index. Brekke et al (1994) reported value of n between 1.44 and 2.78. Bjordal (1995) found spectrum of n
(-2.4 to 9.6) for total particle impact velocity and the normal component using data from numerical modeling.
Such a wide variation of exponent index makes it difficult to estimate erosion rate.
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Table 1: Index suggested by different researchers
Table 2: Index for materials suggested by Wellinger
Researcher
Index, n
(1957)
Truscott (1972)
3
Material
Index, n
Woster (1955)
greater than 3
Steel (St 37)
1.4
Koztrev (1970)
2.2
C60H
1.6
Goodwin (1970)
2.3
Cast basalt
2.9
Rubber
4.6
Source: Survey from literatures.
6.
Previous work
Very little literature is available on the study of water turbine with solid content in water. Truscott (1972) has
done literature survey on abrasive wear on hydraulic machinery and presented findings of different researcher in
his paper. Several mathematical models for estimation of wear and findings of experimental studies are reported
in research papers.
Bovet (1958) states that wear is proportional to “abrasive power” of a particle impingement on the surface and
this abrasive power is dependent on co-efficient of friction between particle and surface, volume of particle,
density of particle and liquid, velocity of particle and radius of curvature of particle. Bergeron (1950)(1952)
develops a complicated expression based on parameters similar to those on Bovet’s model. Bergeron also
presents the expression to predict wear of pump handling solids with varying properties. Bitter (1963) presents
two models for erosive wear. The wear caused by repeated deformation during collisions is deformation wear
and cutting action of free moving particle is cutting wear. In practice these two types of wear occurs
simultaneously. Bitter presents the formulae for the erosion as a function of mass and velocity of eroding
particles, impingement angle and mechanical and physical properties of both erosive particles and substrates.
Finnie (1960) presents formula for cutting wear of ductile material by free moving particle. He considers the
eroding particle as sharp edged & rigid and substrate to be plastic. His model has limitation of underestimating
wear at angles above 450. Head and Harr (1970) present statistical models for predicting the erosion of both
ductile and brittle materials based on laboratory erosion tests. Sundararajan (1991) presents comprehensive
model for erosion, valid for all impact angles, combining the concept of localization of plastic deformation and
generalized energy absorption relations valid for all impact angles and any shape of eroding particles.
These models compute erosion of material due to strike of solid particle present on moving fluid. For this,
several information of material property and operating condition are required. In practice it is difficult to find out
accurate material property data, especially after the change in material property after coating by welding or
spraying and hence computation of erosion rate becomes difficult. Hence generally Erosion Rate (ratio of loss of
mass of eroding material to the total mass of impinging particles) is used as convenient measure to compare
erosion for all practical purpose.
7
Fixing the specimen in the rotating disk inside the liquid environment with solid particle, fixing the specimen in
the solid-liquid flow field and striking the specimen with solid-liquid mixture are three most commonly used
method for estimating and comparing erosion of material. The test of model turbine and pump in short period of
time is virtually impossible because of heavy weight of model and accuracy in the measurement system for
heavy item. Hence small specimen can be tested in the environment similar to the working environment turbine
or pump and correlated with the turbine or pump wears.
Mann (2000) used Rotating Disc Apparatus (RDA) for high-energy particle impact wear test (sand erosion) for
hard coating materials. Rayan et al (1989) have worked to study the relation between erosive wear in centrifugal
pump impeller and solid particles concentration by using a simple setup. Head et al.(1970) used a erosion device
consisting of a steel blast tube which served to direct shop air-dust mixture to the target. Tabakoff et al (1992)
used the Erosion Wind Tunnel setup to test the high temperature erosion of gas and steam turbines and compared
erosion resistance of different alloy and coating materials. Pool et al (1986) used the erosive wear tester with air
flowing through nozzle to study the erosive wear resistance of composite materials. The same erosion tester was
used by Levy (1986) for the study of solid particle erosion behaviors of steel as function of microstructure.
Preece et al (1980) used wheel and jet apparatus for erosion testing and ultrasonic cavitation device for cavitation
studies.
Rotating Disc Apparatus (RDA) at Hydropower Laboratory at NTNU is used for series of diploma thesis and
two doctor thesis (Kjelsden, 1996)(Marcus, 2001). RDA is used to investigate the cavitation effect in different
material to study the cavitation erosion in hydraulic machinery and presently is at pre-planning stage for the use
for sand erosion-cavitation erosion synergy testing.
Several erosion/corrosion tests are carried out in specially designed test equipment at NTNU/SINTEF (Brekke,
1994) followed by two dr. ing. thesis (Bjordal, 1995)(Berget, 1998). The test specimen fixed in a rotating disc
and rotating cylinder can be tested in different operating condition of velocity, sand concentration and corrosion
potential. This discussion paper is prepared for the use of Erosion/Corrosion test facility at SINTEF to study
erosion of materials for hydraulic machinery.
7. Experiments
Actual erosion of the water turbine is slow process. It takes at least one monsoon season to observe the effect of
sand erosion. As erosion is measured in terms of weight loss, it is quite impossible to measure actual erosion of
turbine component. In some of the cases volume of material removed is measured randomly using general
calipers and wear quantity is estimated. Plaster of Paris can be used to fill eroded groove and estimate equivalent
wear of material. But this method is also not accurate and not a widely acceptable practice. No standard methods
are available to monitor the magnitude of erosion of turbine when it is installed. In such case the accelerated
method to investigate the effect of sand erosion on different material at different operating condition is very
essential. Hence in this study, experiments will be performed with the following general aim:

Perform erosive wear test and establish wear rate for different material

To compare the erosion resistance of :
8
#
different base materials used to fabricate turbine runner,
#
materials (i.e. welding electrodes and hard coating materials) used for repair of turbine runner
#
methods used to improve erosion resistance (surface hardening and heat treatment) and coating done by
different equipment.

To study the effect of factors influencing the erosive wear
7.1 SINTEF Corrosion lab experimental setup
Two experimental set up (i) Rotating Disc Apparatus and (ii) Co-axial Rotating Cylinder Apparatus (explained
in Bjordal, 1995) will be used to compare the erosion resistance of different material (Figure in Appendix 1).
Bjordal (1995) and Berget (1998) have compared erosion resistance of different materials (base material and
ceramic coating) for pure corrosion, pure sand erosion and synergy between sand erosion and corrosion. These
studies were done in different operating condition of velocity, particle concentration, size, corrosion potential
etc.
Mann (2000) used a cylindrical specimen in a Rotating Disc Apparatus with the argument that cylindrical
specimen gives spectrum of 0-900 impingement angle and this spectrum generally occurs around hydro-turbine
blades and vanes. Though he argues the flow pattern around the specimen shows no sign of cavitation erosion, in
practice there could also be a effect of cavitation when specimen is tested at varying condition and with different
aspect ratio.
The steady flow between two concentric rotating cylinders is a Couette flow and the driving force for fluid
flowing in the gap is the wall friction. When the inner cylinder is rotating and outer cylinder is at rest, the flow is
unstable and this instability does not imply turbulence. But occurrence of rows of circumferential torodial Taylor
vortices in laminar flow causes water to flow upward and sand in the water strike the wall several time before it
leaves the cylinder. This situation can be assumed to be very similar to be flow of sand particle in the labyrinth
seal and also represents the movement of particles in turbine blade or Pelton bucket or nozzle. This test may give
better realistic result than test equipment with direct impact jet.
In this work, these setups will be used to test the erosion resistance of hard coating material and base material
actually being used in hydraulic machinery. The results will be compared with actual experience from power
plants. The relation between wear rate and velocity will be verified at different operating condition and the value
of exponent n will be established which will be most appropriate for hydraulic machinery.
The effect of fresh sharp sand and rounded sand on the erosion rate will be investigated. This result will give
indication of the validity of use of this equipment for hydraulic machinery. Berget (1998) suspects, ceramiccoating material with same composition shows different behavior when applied with equipment of different
design with same process parameter. This aspect will be investigated, because this could have direct practical
significance.
7.2 Test Procedure
9
Bjordal (1995) carried out test to study for different velocity, particle concentration, exposure time and particles
size. Same sand and water mixture was used for the test for period of time, Though she has reported that there is
not much significant change in particle shape before and after the test (by comparing shape), actual effect of the
shape of sand is not investigated (except one accidental case). Generally it is assumed that, after striking, the
sand particle will be rounded and its aggressiveness will be less than the fresh sharp sand. Present design of the
equipment does not allow the use of fresh sand continuously. But fresh batch of sand can be changed during each
observation and making observation period short (which depends upon the least count of weighing scale and
erosion rate).
Velocity and sediment concentration is main parameter, which changes in particular power plant. Other
parameters like material properties (both turbine material and solid particle), angle of impact remains constant. It
may vary in the guide vane and Pelton nozzle at different opening position. There will be seasonal variation of
concentration and design of the sediment basin affects the concentration. It is already discussed the effect of
velocity in erosive wear. The operating condition and design of the turbine profile varies velocity and hence the
erosion rates.
It is not convenient to measure the effective concentration in both the setups. Hence nominal sand concentration
(ratio of amount of sand mixed in the water in the container) is used to compare the effect of concentration. The
amount of concentration changes the amount of striking particle and hence changes the wear rate. But in this
setup, wear rate is planned to measure only by varying the velocity.
7.3 Measurement
Series of measurements will be done in the different operating condition. The weighing balance of sufficient
accuracy (normally 1/1000 g) will be used to measure the weight loss due to erosion. Since the magnitude of
wear is less in short period of time, the moisture absorbed and any impurities adhered on specimen affects the
accuracy of result. Hence proper cleaning and drying before weighing is very important. The loss of weight of
specimen will be measured after every 1 hour of exposure to eroding particle. The chart for the measurement,
tentative test duration and number of test specimen required are presented Appendix 2.
10
7.4 Results
The recorded data will be analyzed and results will be compared for following effects. The sample charts and
tentative presentation charts are presented in Appendix 3.
1.
Accumulated wear loss versus exposure time will be plotted for each specimen and for both equipment. The
nature of the curve will be studied and wear rate for different combination will be computed.
2.
The variation of wears rate for different velocity will be plotted for each specimen and equipment. The wear
rate will be used from 1.The value of exponent, n will be estimated from appropriate curve fitting.
3.
Comparison of wears resistance of materials for coating made by two equipment
4.
Effect of fresh sand: This effect can be studied by running some specimens continuously 6 hours without
changing the fresh sand. The result can use to explain weather this equipment with same sand can be used
for comparing material for hydraulic machinery or not.
8. Some unanswered questions??

How results from different machine working on similar operating condition can be co related or compared?

Can aggressiveness of sediment-laden water for different river compared? Can simple equipment like
velocity measurement (propeller type) used for measuring aggressiveness of river water.

What should be the basis for selecting hard facing coating material for test?

Is there any standard method to measure wear of turbine without dismantling it?

The property of ceramic coating is based on spray parameter. If spray parameter in t different make spray
parameter is kept constant, then what could be the factors which affect the property of coating as suspected
by Berget (1998)?
9. References
1.
Bergeron, P., “Consideration of factors influencing wear due to hydraulic transport of solid material”, in
Proc. 2nd Conf. Hyd Transport and Seperation of Solid Materials,1952
2.
Bergeron, P., “similarity conditions for erosion caused by liquids carrying solid in suspension, Application
to centrifufal pump impeller”, La Houille Blanche, Vol 5, 1950, pp 716-729, BHAR Translation T 408,
1950
3.
Berget, J., Influence Of Power And Spray Parameters On Erosion And Corrosion Properties Of HVOF
Sprayed Wc-Co-Cr Coatings, Dr Ing Thesis, Norwegian University Of Science And Technology, NTNU,
1998:32
4.
Berkke, H., Bardal, E. and Rogne, T., Norwegian Research Work On Erosion Resistive Coating For Water
Turbines, XVII IAHR Symposium, Beijing, 1994, pp 1337-1346.
5.
Bitter, J.G.A.,”A study of erosion phenomenon, Part 1 and 2”, Wear, Vol 6, 1963, pp 5-21 and 169-190.
6.
Bjordal, M., Erosion and Corrosion Of Ceramic-Metallic Coatings And Stainless Steel, Dr. Ing. Thesis,
Universitetet I Trondheim,NTH,1995:33
11
7.
Bovet, T., Contribution to the Study of the Phenomenon of Abrasive Erosion in the Realm of Hydraulic
Turbines, Bull. Tech. Suisse Romende, Vol 84(3), 1958, pp 37 - 49.
8.
Brekke, H, Private Communication, 2001
9.
Finnie, I., “Erosion of surfaces by solid particle”, wear, Vol 3, 1960, pp87-103
10. Goodwin, J.E. et al, “Study of Erosion by solid particles”, ”, Proc. Inst. Mech. Engrs. Vol 184, 1970, pp 15
11. Head, W.J. and Harr, M. E., The Development of Model to Predict the Erosion of Materials by Natural
Contaminants, Wear, Vol. 15, 1970, pp 1 - 46.
12. Kjelsden, M., Cavitation In Hydraulic Machinery, Dr. Ing. Thesis, NTNU 1996:63
13. Kozirev, S.P., “ Hydroabrasive wear of metals under cavitation”, Translation by University of Michigan,
Report No 01357-10-1, 1970
14. Levy, A.V., Man F.Y., “Surface Degradation Of Ductile Materials In Elevated Temperature Gas Particle
Streams”, Wear, Vol 111, 1986, pp 173-186
15. Mann, B. S, “High-Energy Particle Impact Wear Resistance Of Hard Coating And Their Application In
Hydroturbines”, Wear, 2000, pp 140-146
16. Mann, B.S., et al, Hydro Project Equipment: Solutions for Common Challenges, HWR, July 2001, pp 8-12
17. Oledal, M., Cavitation In Complex Separated Flow, Dr. Ing. Thesis, NTNU 2001:03
18. Pool, K. V., Dharana, C. K. H., And Finni, I., “Erosive Wear Of Composite Materials”, Wear, Vol. 107,
1986, pp 1 - 12.
19. Preece, C.M., “A Comparison Of Liquid Impact Erosion And Cavitation Erosion”, Wear, Vol. 60, 1980, pp
269-284
20. Rayan, M.A., Shawky, M., Evaluation Of Wear In A Centrifugal Slurry Pump, Proc. Inst. Mech. Eng., Vol.
203, 1989, pp 19-23
21. Sundararajan, G., A Comprensive Model for The Solid Particle Erosion of Ductile Material, in The
International Conference on Wear of Materials, Orlando, USA, Wear of Material, ASME, 1991, pp 503 511.
22. Tabakoff, W, Hamed, A., et. Al., High - Temperature Erosion Resistance Of Coatings For Gas Turbine,
Trans. ASME, Jr. Of Eng. For Gas Turbines And Power, 1992.
23. Truscott, G. F., “Literature Survey of Abrasive Wear in Hydraulic machinery”, Wear, Vol 20, 1972, pp 2950
24. Willenger, K. And Utez, H., “Sliding Scouring And Blasting Wear Under The Influence Of Granular Of
Solids”, Vdi-Forschungscheft, 21b, 1955 pp 449 Also Short Version In Wear Vol. 1 1957.
25. Woster, R.C. and Denny, D.F., “Hydraulic Transport of Solid in pipes”, Proc. Inst. Mech. Engrs. Vol 169,
1955, pp 563
12
Appendix 1
SINTEF Erosion/Corrosion Test Equipment (Bjardal, 1995)
Coaxial Rotating Cylinder
Rotating Disc Apparatus
13
Appendix 2
(a)
Observation 1: Effect of change in velocity
Equipment: Rotating disc
Variation: Velocity
Constant: Sand concentration, particle composition and size,
Velocity
Measuring Time
V1
1hr
2hr
3hr
4hr
V2
5hr
6hr
1hr
2hr
3hr
4hr
V3
5hr
6hr
1hr
2hr
3hr
4hr
V4
5hr
6hr
1hr
2hr
3hr
4hr
5hr
6hr
Specimen
Base Material 16/5
Base Material 13/4
Coating company A
Coating 1
Coating 2
Coating 3
Coating 4
Coating company B
Coating 1
Coating 2
Coating 3
Coating 4
Estimated measurement time: 240 observation / 3 different specimens at a time = 80 hours
(Averaging 2 samples of each specimen)
No of specimen required: 10 specimens * 4 sets of velocity measurement = 40
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(b)
Observation 2: Effect of change in velocity
Equipment: Rotating cylinder
Variation: Velocity
Constant: Sand concentration, particle composition and size,
Velocity
Measuring Time
V1
1hr
2hr
3hr
4hr
V2
5hr
6hr
1hr
2hr
3hr
4hr
V3
5hr
6hr
1hr
2hr
3hr
4hr
V4
5hr
6hr
1hr
2hr
3hr
4hr
5hr
6hr
Specimen
Base Material 16/5
Base Material 13/4
Coating company A
Coating 1
Coating 2
Coating 3
Coating 4
Coating company B
Coating 1
Coating 2
Coating 3
Coating 4
The wear rate of rotating cylinder toward top is high compared to entrance in the same test (Bjordal, 1995). Hence multiple specimens can not be used in this equipment.
Estimated measurement time: 240 observation / 1 specimens (5 sets) at a time = 240 hours
No of specimen required: 10 specimens * 4 sets of velocity measurement * 5 rings at each reading = 200
Note: 200 specimens are too large in number and costlier also. The number could be reduced either by using same set of specimens in all velocity range or using only 2 or 3
rings in each test.
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Appendix 3
Results Presentation format samples
1.
Accumulated wear loss versus exposure time – for each specimen and for both equipment
Sample chart 1 (for test equipment, specimen, velocity)
Accumulated
weight loss (mg)
Weight loss
1000
800
600
400
200
0
1
2
3
4
5
6
Exposure tim e (hr)
The nature of the curve will be studied and wear rate for different combination will be computed.
2.
The variation of wears rate for different velocity - for each specimen and equipment. The wear
rate will be used from chart 1.
Sample chart 2 (for test equipment, specimen)
wear rate vs velocity
wear rate (mg/h)
12
10
8
6
4
2
0
14,3
22,9
29,3
velocity m/s
36,7
The value of exponent, n will be estimated from appropriate curve fitting. (Only four different
velocities are possible in the setup with different combination of pulley, which may affect the accuracy
of estimate, exponent, n in curve fitting.)
3.
Comparison of wears resistance of materials: for both equipment
Sample chart 3
Comparision of wear rate (mg/hr)
16/5 SS
4.
13/4 SS
Coating 1 Coating 2 Coating 3 Coating 4
Effect of fresh sand
This effect can be studied by running some specimens continuously 6 hours without changing the fresh
sand. The result can use to explain weather this equipment with same sand can be used for comparing
material for hydraulic machinery or not.
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