IEC 62364:2013

IEC 62364 ®
Edition 1.0 2013-06
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
colour
inside
Hydraulic machines – Guide for dealing with hydro-abrasive erosion in Kaplan,
Francis, and Pelton turbines
Machines hydrauliques – Guide relatif au traitement de l'érosion hydro-abrasive
des turbines Kaplan, Francis et Pelton

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IEC 62364 ®
Edition 1.0 2013-06
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
colour
inside
Hydraulic machines – Guide for dealing with hydro-abrasive erosion in Kaplan,

Francis, and Pelton turbines
Machines hydrauliques – Guide relatif au traitement de l'érosion hydro-abrasive

des turbines Kaplan, Francis et Pelton

INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
PRICE CODE
INTERNATIONALE
CODE PRIX XC
ICS 23.100.10; 27.140 ISBN 978-2-83220-829-8

– 2 – 62364 © IEC:2013
CONTENTS
FOREWORD . 5

INTRODUCTION . 7

1 Scope . 8

2 Terms, definitions and symbols . 8

2.1 Units . 8

2.2 Terms, definitions and symbols . 9

3 Abrasion rate . 11

3.1 Theoretical model . 11
3.2 Introduction to the PL variable . 13
3.3 Survey results . 15
3.4 Reference model . 16
4 Design . 17
4.1 General . 17
4.2 Water conveyance system . 17
4.3 Valve . 18
4.3.1 General . 18
4.3.2 Selection of abrasion resistant materials and coating . 18
4.3.3 Stainless steel overlays . 19
4.3.4 Protection (closing) of the gap between housing and trunnion . 19
4.3.5 Stops located outside the valve . 19
4.3.6 Proper capacity of inlet valve operator . 19
4.3.7 Increase bypass size to allow higher guide vane leakage . 19
4.3.8 Bypass system design . 20
4.4 Turbine . 20
4.4.1 General . 20
4.4.2 Hydraulic design . 20
4.4.3 Mechanical design . 22
4.4.4 Operation . 28
4.4.5 Spares and regular inspections . 29
4.4.6 Particle sampling and monitoring . 29
5 Abrasion resistant materials . 30
5.1 Guidelines concerning relative abrasion resistance of materials including

abrasion resistant coatings . 30
5.1.1 General . 30
5.1.2 Discussion and conclusions . 31
5.2 Guidelines concerning maintainability of abrasion resistant coating materials . 32
5.2.1 Definition of terms used in this sublcause . 32
5.2.2 Time between overhaul for protective coatings . 32
5.2.3 Maintenance of protective coatings . 33
6 Guidelines on insertions into specifications . 34
6.1 General . 34
6.2 Properties of particles going through the turbine. 35
6.3 Size distribution of particles . 35
6.4 Mineral composition of particles for each of the above mentioned periods . 36
Annex A (informative) PL calculation example . 37
Annex B (informative) Measuring and recording abrasion damages . 39

62364 © IEC:2013 – 3 –
Annex C (informative) Water sampling procedure . 52

Annex D (informative) Procedures for analysis of particle concentration, size,

hardness and shape . 53

Annex E (informative) Tests of abrasion resistant materials . 56

Annex F (informative) Typical criteria to determine overhaul time due to abrasion

erosion . 67

Annex G (informative) Example to calculate the amount of erosion in the full model . 68

Annex H (informative) Examples to calculate the TBO in the reference model . 70

Bibliography . 73

Figure 1 – Estimation of the characteristic velocities in guide vanes, W , and runner,
gv
W , as a function of turbine specific speed . 13
run
Figure 2 – Example of flow pattern in a Pelton injector at different load . 14
Figure 3 – Example of protection of transition area . 19
Figure 4 – Runner blade overhang in refurbishment project . 21
Figure 5 – Example of “mouse-ear” cavitation on runner band . 22
Figure 6 – Detailed design of guide vane trunnion seals . 23
Figure 7 – Example of fixing of facing plates from the dry side . 25
Figure 8 – Head cover balancing pipes with bends . 26
Figure 9 – Step labyrinth with optimized shape for hard coating . 28
Figure 10 – Development of spiral pressure over time . 33
Figure D.1 – Typical examples of particle geometry . 55
Figure E.1 – Schematic of test rig used for test 1 . 56
Figure E.2 – ASTM test apparatus . 58
Figure E.3 – Test coupon . 59
Figure E.4 – Slurry pot test facility . 60
Figure E.5 – High velocity test rig . 61
Figure E.6 – Samples are located on the rotating disk . 62
Figure E.7 – Comparison of two samples after testing . 62
Figure E.8 – Whole test system of rotating disk . 62
Figure E.9 – Schematic of test rig used for test 8 . 64
Figure E.10 – Testing of samples on hydro abrasive stand . 65

Figure E.11 – Cover of disc . 65
Figure E.12 – Curve of unit abrasion rate with circumference velocity for 3 kinds of
materials . 66

Table 1 – Data analysis of the supplied questionnaire . 16
Table 2 – Overview over the feasibility for repair C . 33
Table 3 – Form for properties of particles going through the turbine . 35
Table 4 – Form for size distribution of particles . 36
Table 5 – Form for mineral composition of particles for each of the above mentioned
periods . 36
Table A.1 – Example of documenting sample tests . 37
Table A.2 – Example of documenting sample results . 38
Table B.1 – Inspection record, runner blade inlet form . 44

– 4 – 62364 © IEC:2013
Table B.2 – Inspection record, runner blade outlet form . 45

Table B.3 – Inspection record, runner band form. 46

Table B.4 – Inspection record, guide vanes form. 47

Table B.5 – Inspection record, facing plates and covers form . 48

Table B.6 – Inspection record, upper stationary seal form . 49

Table B.7 – Inspection record, upper rotating seal form . 49

Table B.8 – Inspection record, lower stationary seal form . 50

Table B.9 – Inspection record, lower rotating seal form . 51

Table E.1 – Relative wear resistance in laboratory test 1 . 57
Table E.2 – Relative wear resistance in laboratory test 2 . 57
Table E.3 – Relative wear resistance in laboratory test 3 . 58
Table E.4 – Relative wear resistance in test 4 . 59
Table E.5 – Results of test . 60
Table E.6 – Results of test . 61
Table E.7 – Results from test . 63
Table E.8 – Relative wear resistance in laboratory test 8 . 64
Table E.9 – Results of relative wear resistance for some materials (U = 40m/s) . 66
Table G.1 – Calculations . 69
Table H.1 – Pelton turbine calculation example . 70
Table H.2 – Francis turbine calculation example . 71

62364 © IEC:2013 – 5 –
INTERNATIONAL ELECTROTECHNICAL COMMISSION

____________
HYDRAULIC MACHINES –
GUIDE FOR DEALING WITH HYDRO-ABRASIVE EROSION

IN KAPLAN, FRANCIS, AND PELTON TURBINES

FOREWORD
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patent rights. IEC shall not be held responsible for identifying any or all such patent rights.
International Standard IEC 62364 has been prepared by IEC technical committee 4: Hydraulic

turbines.
The text of this standard is based on the following documents:
FDIS Report on voting
4/279/FDIS 4/283/RVD
Full information on the voting for the approval of this standard can be found in the report on
voting indicated in the above table.
This publication has been drafted in accordance with the ISO/IEC Directives, Part 2.

– 6 – 62364 © IEC:2013
The committee has decided that the contents of this publication will remain unchanged until

the stability date indicated on the IEC web site under "http://webstore.iec.ch" in the data

related to the specific publication. At this date, the publication will be

• reconfirmed,
• withdrawn,
• replaced by a revised edition, or

• amended.
IMPORTANT – The 'colour inside' logo on the cover page of this publication indicates
that it contains colours which are considered to be useful for the correct
understanding of its contents. Users should therefore print this document using a
colour printer.
62364 © IEC:2013 – 7 –
INTRODUCTION
Many owners of hydroelectric plants contend with the sometimes very aggressive

deterioration of their machines due to particle abrasion. Such owners must find the means to

communicate to potential suppliers of machines for their sites, their desire to have the

particular attention of the designers at the turbine design phase, directed to the minimization

of the severity and effects of particle abrasion.

Limited consensus and very little quantitative data exists on the steps which the designer

could and should take to extend the useful life before major overhaul of the turbine

components when they are operated under severe particle abrasion service. This has led

some owners to write into their specifications, conditions which cannot be met with known
methods and materials.
– 8 – 62364 © IEC:2013
HYDRAULIC MACHINES –
GUIDE FOR DEALING WITH HYDRO-ABRASIVE EROSION

IN KAPLAN, FRANCIS, AND PELTON TURBINES

1 Scope
This Guide serves to:
a) present data on particle abrasion rates on several combinations of water quality, operating
conditions, component materials, and component properties collected from a variety of
hydro sites;
b) develop guidelines for the methods of minimizing particle abrasion by modifications to
hydraulic design for clean water. These guidelines do not include details such as hydraulic
profile shapes which should be determined by the hydraulic design experts for a given
site;
c) develop guidelines based on “experience data” concerning the relative resistance of
materials faced with particle abrasion problems;
d) develop guidelines concerning the maintainability of abrasion resistant materials and hard
facing coatings;
e) develop guidelines on a recommended approach, which owners could and should take to
ensure that specifications communicate the need for particular attention to this aspect of
hydraulic design at their sites without establishing criteria which cannot be satisfied
because the means are beyond the control of the manufacturers;
f) develop guidelines concerning operation mode of the hydro turbines in water with particle
materials to increase the operation life;
It is assumed in this Guide that the water is not chemically aggressive. Since chemical
aggressiveness is dependent upon so many possible chemical compositions, and the
materials of the machine, it is beyond the scope of this Guide to address these issues.
It is assumed in this Guide that cavitation is not present in the turbine. Cavitation and
abrasion may reinforce each other so that the resulting erosion is larger than the sum of
cavitation erosion plus abrasion erosion. The quantitative relationship of the resulting
abrasion is not known and it is beyond the scope of this guide to assess it, except to
recommend that special efforts be made in the turbine design phase to minimize cavitation.
Large solids (e.g. stones, wood, ice, metal objects, etc.) traveling with the water may impact

turbine components and produce damage. This damage may in turn increase the flow
turbulence thereby accelerating wear by both cavitation and abrasion. Abrasion resistant
coatings can also be damaged locally by impact of large solids. It is beyond the scope of this
Guide to address these issues.
This guide focuses mainly on hydroelectric powerplant equipment. Certain portions may also
be applicable to other hydraulic machines.
2 Terms, definitions and symbols
2.1 Units
The International System of Units (S.I.) is adopted throughout this guide but other systems
are allowed.
62364 © IEC:2013 – 9 –
2.2 Terms, definitions and symbols

For the purposes of this document, the following terms, definitions and symbols apply.

NOTE They are also based, where relevant, on IEC/TR 61364.

Sub- Term Definition Symbol Unit

clause
2.2.1 specific E J/kg
specific energy of water available between the high and

hydraulic
low pressure reference sections 1 and 2 of the machine

energy of a
machine
Note 1 to entry: For full information, see IEC 60193.

2.2.2 acceleration local value of gravitational acceleration at the place of g m/s
due to gravity testing
Note 1 to entry: For full information, see IEC 60193.
H
2.2.3 turbine head available head at hydraulic machine terminal m
H = E/g
pump head
2.2.4 reference reference diameter of the hydraulic machine D m
diameter
Note 1 to entry: For Pelton turbines this is the pitch
diameter, for Kaplan turbines this is the runner chamber
diameter and for Francis and Francis type pump turbines
this is the blade low pressure section diameter at the
band
Note 2 to entry: See IEC 60193 for further information.
2.2.5 abrasion depth depth of metal layer that has been removed from a S mm
component due to particle abrasion
2.2.6 characteristic characteristic velocity defined for each machine W m/s
velocity component and used to quantify particle abrasion
damage
Note 1 to entry: See also 2.2.20 to 2.2.24.

3 3
2.2.7 particle the mass of all solid particles per m of water solution C kg/m
concentration
Note 1 to entry: In case the particle concentration is
expressed in ppm it is recommended to use the mass of
particles per mass of water, so that 1 000 ppm
approximately corresponds to 1 kg/m .
the particle concentration integrated over the time, T, that PL
2.2.8 particle load kg × h/m
is under consideration
T
PL = C(t )× K (t )× K (t )× K (t )dt

size shape hardness
∫
N
 
 
≈ C × K × K × K ×T
n size,n shape,n hardness,n s,n
∑
 
 n=1 
C(t) = 0 if no water is flowing through the turbine.
If the unit is at standstill with pressurized spiral case then
C(t)=0 when calculating PL for runner and labyrinth seals,
but C(t)≠0 when calculating PL for guide vanes and facing
plates.
2.2.9 size factor factor that characterizes how the abrasion relates to the K
size
size of the abrasive particles
2.2.10 shape factor factor that characterizes how the abrasion relates to the K

shape
shape of the abrasive particles
2.2.11 hardness factor factor that characterizes how the abrasion relates to the K
hardness
hardness of the abrasive particles

– 10 – 62364 © IEC:2013
Sub- Term Definition Symbol Unit

clause
2.2.12 material factor factor that characterizes how the abrasion relates to the K
m
material properties of the base material

3,4
2.2.13 flow coefficient coefficient that characterizes how the abrasion relates to K mm × s
f
α
the water flow around each component
kg × h × m
2.2.14 sampling the time interval between two water samples taken to T h
s
interval determine the concentration of abrasive particles in the

water
the total PL for 1 year of operation, i.e. PL for T = 8 760 h PL
2.2.15 yearly particle kg × h/m
year
load calculated in accordance with 2.2.8

2.2.16 maximum the maximum concentration of abrasive particles over a C kg/m
max
concentration specified time interval
2.2.17 particle median the median diameter of abrasive particles in a sample, dP mm
diameter i.e. such diameter that the particles with size smaller than
the value under consideration represent 50 % of the total
mass of particles in the sample
2.2.18 wear abrasion depth or volume of a reference material WRI -
resistance (generally some version stainless steel) divided by the
index abrasion depth or volume of the material in question,
tested under the same conditions
o
2.2.19 impingement the angle between the particle trajectory and the surface
angle of the substrate
2.2.20 characteristic flow through unit divided by the minimum flow area at the
velocity in guide vane apparatus estimated at best efficiency point
W m/s
gv
Francis guide
Q
vanes
W =
gv
a × Z × B
characteristic
0 0
velocity in
Kaplan guide
vanes
2.2.21 characteristic speed of the water flow at guide vane location
velocity in
W m/s
guide vanes of gv
W = 0,5 × 2× E
gv
Kaplan,
Francis or
tubular
turbines
2.2.22 characteristic speed of the water flow at injector location
velocity in
W m/s
Pelton injector inj
W = 2× E
inj
2.2.23 characteristic the relative velocity between the water and the runner W m/s
run
velocity in blade estimated with below formulas at best efficiency
Kaplan or point
Francis tubular
turbine runner 2 2
W = u + c
run 2 2
u = n ×π × D
Q × 4
c =
π × D
Note 1 to entry: In calculation of c for Kaplan turbines,
the hub diameter has been neglected in the interest of
simplicity.
2.2.24 characteristic speed of the water flow at a Pelton runner
velocity in
W m/s
Pelton runner run
W = 0,5 × 2 × E
run
2.2.25 discharge volume of water per unit time passing through any section Q m /s
(volume flow in the system
rate)
2.2.26 guide vane average shortest distance between adjacent guide vanes A m
opening (at a specified section if necessary)

62364 © IEC:2013 – 11 –
Sub- Term Definition Symbol Unit

clause
Note 1 to entry: For further information, see IEC 60193.

z
2.2.27 number of total number of guide vanes in a turbine
guide vanes
2.2.28 distributor height of the distributor in a turbine B m
height
2.2.29 rotational number of revolutions per unit time n 1/s
speed
2.2.30 specific speed commonly used specific speed to of an hydraulic machine n
s
60 × n × P
n =
s
5 / 4
H
P and H are taken in the rated operating point and given
in kW and m respectively
2.2.31 output output of the turbine in the rated operating point P kW
S
2.2.32 actual abrasion the estimated depth of metal that will be removed from a target, mm

actual
depth of target component of the target turbine due to particle abrasion
unit
Note 1 to entry: For use with the Reference model.
S
2.2.33 actual abrasion the actual depth of metal that has been removed from a ref, actual mm
depth of component of the reference turbine due to particle
reference unit abrasion
Note 1 to entry: For use with the Reference model.
z
2.2.34 number of number of nozzles in a Pelton turbine
nozzles
B
2.2.35 bucket width bucket width in a Pelton runner 2 mm
z
2.2.36 number of number of buckets in a Pelton runner 2
buckets
TBO
2.2.37 time between time between overhaul for target unit target h
overhaul for
Note 1 to entry: For use with the reference model.
target unit
TBO
2.2.38 time between time between overhaul for reference unit ref h
overhaul for
Note 1 to entry: For use with the reference model.
reference unit
RS
2.2.39 turbine the reference size for calculation curvature dependent m
reference size effects of erosion
Note 1 to entry: For Francis turbines, it is the reference
diameter, D (see 2.2.4).
Note 2 to entry: For Pelton turbines it is the inner bucket
width, B.
Note 3 to entry: For further information in the inner
bucket width, B, see IEC 60609-2.
p
2.2.40 size exponent exponent that describes the size dependant effects of
erosion in evaluating RS
α
2.2.41 exponent numerical value of 0,4-p that balances units for K
f
3 Abrasion rate
3.1 Theoretical model
In order to demonstrate how different critical aspects impact the particle abrasion rate in the
turbine, the following formula is considered:

– 12 – 62364 © IEC:2013
dS/dt = f(particle velocity, particle concentration, particle physical properties, flow pattern,

turbine material properties, other factors)

However, this formula being of little practical use, several simplifications are introduced. The

first simplification is to consider the several variables as independent as follows:

dS/dt = f(particle velocity) × f(particle concentration) × f(particle physical properties, turbine

material properties) × f(particle physical properties) × f(flow pattern) × f(turbine material

properties) × f(other factors)

This simplification is not proven. In fact, many examples can be found where this

simplification was not strictly valid. Nevertheless, based on literature studies and experience,
this simplification is considered to be justified for hydraulic machines.
The next simplification consists in assigning values to the functions. In the following equations
the numerical values for the parameters, without units, have to be used. The units in which
the values should be based are given below:
n
• f(particle velocity) = (particle velocity) . In the literature abrasion is often considered
proportional to the velocity raised to an exponent, n. Most references give values of n
between 2 and 4. In this guide we suggest to use n = 3,4. Particle velocity in m/s,
• f(particle concentration) = particle concentration in kg/m ,
= function of how
• f(particle physical properties, turbine material properties) = K
hardness
hard the particles are in relation to the material at the surface. At the present stage we
suggest to use K = fraction of particles harder than the material at the surface,
hardness
p
• f(flow pattern) = K /RS (K = constant for each turbine component, RS = turbine
f f
reference size in m, p = exponent for each turbine component). K considers
f
p
impingement angle and flow turbulence. RS considers part curvature radius,
• f(particle physical properties) = f(particle size, particle shape, particle hardness) =
f(particle size) × f(particle shape) = K × K . Note that in this simplification it as
size shape
assumed that there is no influence from the particle hardness for this function. The
particle hardness is considered in the K factor,
hardness
• K = median diameter of particles in mm,
size
• K = f(particle angularity). It is believed that K will increase with the degree of
shape shape
irregularity of the particles. Specific data is not available at present but several
literature references indicate that K varies from 1 to 2 from round to sharp,
shape
• f(turbine material properties) = K . In this guide we consider K = 1 for martensitic
m m
stainless steel with 13 % Cr and 4 % Ni and K = 2 for carbon steel. For coated
m
components K should be smaller than 1,
m
• f(other factors) = 1.
Again, these functions are engineering approximations in order to obtain useful results for
hydraulic machines. We then have the following formula
3,4 p
dS/dt = (particle velocity) × C × K × K × K × K /RS × K
hardness size shape f m
The final step is to integrate this formula with respect to time. When we do this we find three
distinct different types of variables with respect to their variations in time:
1) particle velocity and K: these variables vary with the water flow relative to the
f
individual component, which in turn may vary with the head and flow;
2) C, K , K and K : these variables vary with the particle properties.
hardness size shape
Integrated over time these variables become particle load, PL (see 2.2.8 for definition
of PL and Annex A for a sample calculation);
3) RS, p and K : these variables are constant in time.
m
62364 © IEC:2013 – 13 –
To find a simple and reasonably accurate estimate of the time integral, the PL variable (see

2.2.8) is introduced. PL integrates C, K , K and K over time. When using PL,
hardness size shape
the particle velocity and K can be considered approximately constant over a limited variation
f
of head and flow (see 3.2). Since these variables are considered constant, K and p were used
f
as calibration factors to obtain good agreement between actual test data and the formula. The

particle velocity can be replaced with the characteristic velocity, W, defined in 2.2.20 to

2.2.24.
W may be calculated for a specific turbine based on main data and dimensions. Since the

effect of velocity on abrasion is proportional to the velocity raised to a power of 3,4 it is very
important to estimate it accurately. For new turbines during design and bid stage, W for
different components should be provided by the turbine manufacturer. When this is not

possible, W can be estimated approximately from the diagram in Figure 1.
2.5
0,5
W = (0,25 + 0,003 × n ) × (2 × g × H)
run s
2.0
1.5
1.0
0,5
W = 0,55 × (2 × g × H)
gv
0.5
0.0
0 100 200 300 400 500 600 700 800
Turbine specific speed (using m, kW)

NOTE Values of ns and H in this figure refer to the rated operating point while the characteristic velocities are
given for the points noted in 2.2.
Figure 1 – Estimation of the characteristic velocities in guide vanes, W , and runner,
gv
W , as a function of turbine specific speed
run
So the final, time integrated formula becomes:
3,4 p
S = W × PL × K × K / RS
m f
S is the numerical value of the abrasion depth in mm.
3.2 Introduction to the PL variable
In this code the PL variable has been introduced, which has not been widely used before. One
common way to integrate abrasion over time has been to consider the total weight of particles
Characteristic velocity coefficient W , W
gv run
– 14 – 62364 © IEC:2013
that pass the turbine. However, this approach has usually not considered the effects from

variation in flow or head in the turbine and could therefore lead to erroneous conclusions.

To illustrate this consider the following example. A Pelton injector (see Figure 2) operates for

one day. Assume the head is 800 m and the abrasive particle concentration is 0,1 kg/m .

Case 1: At full opening (top half of Figure 2) the water with particles flows over the seat

0,5
ring with a velocity of (2×g×H) = 125 m/s. In one day the amount of particles that pass

3 3
the injector is 2 m /s × 3 600 s/h × 24 h/day × 0,1 kg/m × 1 day = 17 tons.

Case 2: At 10 % opening (bottom half of Figure 2) the water with particles flows over

the seat ring with the same velocity as in case 1 (125 m/s). In one day the amount of
particles that pass the injector is 0,2 × 3 600 × 24 × 0,1 × 1 = 1,7 tons.
In both cases the seat ring has been subject to abrasion with the same particle concentration,
the same water velocity and the same amount of time. Therefore, the expected abrasion
damage is the same. The PL variable also gives the same value in both cases. However, the
total weight of particles that has passed the unit is 10 times higher in case 1 compared to
case 2. So, PL is expected to correlate better with abrasion damage than the total weight of
particles that has passed the seat ring.
Full opening Q = 2 m /s
10 % opening Q = 0,2 m /s
Figure 2 – Example of flow pattern in a Pelton injector at different load

The same type of reasoning can also be applied to other components subject to abrasion. In
the following is a condensed summary of such analysis.
• Pelton needle tip
Very good correlation between PL and abrasion damage with minor influence of turbine
discharge or head is expected. Some influence from the turbine flow since the water velocity
is lower further inside the injector, where the needle is located at high flows. Some influence
from turbine head since the water velocity is proportional to the square root of the head. With
head and flow variations that are normal in Pelton projects this influence is disregarded in the
interest of simplicity.
• Pelton runner
Good correlation between PL and abrasion damage with minor influence of turbine discharge
or head is expected. Some influence from the turbine flow since the water film is thicker at
higher flows and therefore more particles may be pressed towards the outside surface due to
centrifugal forces. Some influence from turbine head since the relative water velocity in the

62364 © IEC:2013 – 15 –
runner depends on the head. With head and flow variations that are normal in Pelton projects,

this influence is disregarded in the interest of simplicity.

• Francis and Kaplan guide vanes and covers / facing plates

Good correlation between PL and abrasion damage with minor influence of turbine discharge
or head is expected. Some influence from the turbine flow since the water velocity is higher at

low discharge and the pressure difference between the two sides of the guide vane varies

with flow. In particular, if the unit is at standstill with pressurized spiral case the leakage flow

through the guide vanes has high velocity. Some influence from the turbine head since the

relative water velocity in the guide vanes depends on the head. With head and flow variations

that are normal in Francis and Kaplan projects, this influence is disregarded in the interest of

simplicity.
• Francis runner seals / labyrinths
Very good correlation between PL and abrasion damage with minor influence of turbine
discharge or head is expected. Some influence is expected from the turbine flow and head
since they influence the pressure befo
...