The presentation on Sediment Erosion in Hydro-Turbines has been prepared by collecting information available on various research papers and journals. These slides can serve just as an introduction part to the board world of sediment erosion in hydro turbines.

1. 1
Sediment Erosion in
Hydro-Turbines
Anuj Pathak
Date: 6-26-2018

2. 2
Outlines
 Introduction
 Definition and Importance of Study
 Process and Types of Erosion
 Causes and factors affecting erosion
 Discussion
 Sediment Analysis
 Erosion Models in Pelton and Francis Turbines
 Case Studies of Different Hydro Power Plants in Nepal
 Techniques to Reduce Sediment Erosion
 Conclusion
 Reference
Details of Outlines

3. 3
Introduction
 Sediments are the solid particles that are moved and deposited in a new location
by a medium (flowing water)
 Sediments consist of rocks and minerals fragments.
 According to the standard of ASTM 640-88
 Wear is defined as “damage to a solid surface, generally involving
progressive loss of material, due to relative motion between that surface
and a contacting substance or substances.”
 Damage/Progressive loss of Turbine materials due to the sediment content in high
velocity water that strikes the Turbine.
Definition and Importance of Study
Sediment
Erosion/Wear
Sediment Erosion in Hydro-Turbines

4. 4
Introduction
Definition and Importance of Study
 Sediment Erosion reduces efficiency of turbine
 Original design of turbine gets changed
 Rotational Dynamics gets changed
 Vibrations
 Reduce life of the turbine
 Continuous material losses
 Turbine can no longer work to produce energy
 Causes problems in operation and maintenance
 Decrease in availability factor(AF) of machine
 Ultimately leads to economic losses
 Maintenance
 Turbine replacement
‫ܣ‬ ‫ܨ‬ =
ܶ‫݈ܽݐ݋‬ ‫ܿܽܯ‬h݅݊݁ ܴ‫݃݊݅݊݊ݑ‬ h‫ݏݎݑ݋‬ ݂‫ݎ݋‬ ‫݂݀݁݅݅ܿ݁݌ݏ‬ ‫݀݋݅ݎ݁݌‬
ܶ‫݈ܽݐ݋‬ h‫ݏݎݑ݋‬ ‫݂݋‬ ‫ݐ‬h݁ ‫݀݋݅ݎ݁݌‬
𝑥100

5. 5
Introduction
Process and Types of Erosion
(Stachowiak and Batchelor, 1993)
Abrasive/Cutting Erosion Fatigue Erosion
Plastic Deformation Brittle Fracture

6. 6
Introduction
Erosion Rate and Impingement Angle
Schematic representation of erosion rate as a function of impingement angle for brittle
and ductile material (Bardal, 1985)
ErosionRate
Impingement Angle0 ˚ 90 ˚

7. 7
Introduction
Causes of Erosion
 Climatic and Physical conditions are highly responsible for the erosion and
sedimentation problem. The tropical climate (hot and humid), immature geology,
and intense seasonal rainfall, are the main reasons for this problem (Neopane,
2010).
 Less erosion in stable geology and old rocks
 The geological problem seems to be a major obstacle. It has been studied that out
of 20 billion tons of global sediment lux from rivers to the oceans per year, around
6 billion tons is contributed by Asian rivers, particularly from Indian subcontinent
(Naidu, 1996)
(a) (b)
Basic factors affecting wear of hydraulic machines
 properties of the solid particles (sand)
(hardness, size, shape, relative density and concentration)
 properties of the eroded material
(composition, structure and hardness)
 the operating condition
(speed, temperature and impact angle)

8. 8
Introduction
Sedimentation Affected Regions
Andes
Mountain
Range
Himalayas Range
Alps Mountain Range
The problem seems to be more crucial for Himalayan region and Andes Mountain in
South America, it has an application throughout the globe for example Alps in Europe
(Thapa Bhola, 2004).

9. 9
Discussion
Sediment Analysis
The river sediments are in the form of clay, silt, sand and gravel with specific gravity
approximately 2.6.
(Lysne et al., 2003)
Classification of river sediment
Steps Involved in Sediment Analysis
 Sample Collection and Processing
 Sieve Analysis
 Mineral Analysis
 Erosion Test
a) Drying of samples
b) Separating debris from samples
c) Proper labeling of samples
d) Safe storing of samples

10. 10
Sediment Analysis
Sieve Analysis
 Procedure used to assess the particle size distribution (PSD)
 Material is passed through a series of sieves of progressively smaller mesh size
 Sieve sizes used for the analysis are: 75, 125, 200, 300, 600 and 1000 μm.
 It is a simple, easy and probably the most common technique for PSD
www.basiccivilengineering.com/2017/06/sieve-analysis-test.html, Accessed: 06-22-2018

11. 11
Sediment Analysis
Sieve Analysis
Sieve analysis graph for Marsyangdi HPP (Bastola,2014)

12. 12
Sediment Analysis
Mineral Analysis
 A site specific task to determine its mineral content and composition
 Methods: Fourier Transform Infrared, X-ray diffraction (XRD) and X-ray fluorescence
spectroscopy method
 Particle Count Method was used for Marsyangdi HPP (Bastola, 2014) as it is cost
efficient and easier to use although it is time consuming
 A magnifying Trinocular Stereo zoom Microscope was used to observe the sample,
identify and count them.
 Quartz was the most common mineral in river sediments with Mohs hardness of 7.
 Other minerals harder than turbine materials includes feldspar, garnet, tourmaline,
etc.

13. 13
Sediment Analysis
Erosion Test (Rotating Disc Apparatus)
 Clean set of test specimen (eg: Francis runner blade) is mounted on the disc
 Weights of the specimens are recorded before they are mounted on the disc.
 The cover is closed, and the nut and bolts are tightened to ensure no leakage of water.
 The casing is then completely filled with water and the sand sample of required size and
concentration and motor is started.
 After being run for specific period, the test specimens are dried and weighed.
(B. Rajkarnikar, 2013)

14. 14
Erosion Models
Pelton Runner
Krause and Grein (1996) proposed the abrasion rate on conventional steel Pelton runner
made of X5CrNi 13/4 (stainless steel) which was expressed by the expression given
below
is the erosive wear rate (mm/h)
P is a constant
Q is the quartz content
C is the mean sand concentration
V is the relative jet velocity
f(D50) is a function defining particle size
Where,
Bajracharya et al. (2008) proposed a relationship between the efficiency reduction and
erosion rate of Pelton Turbine of Chilime Hydro Electric Plant.
Efficiency reduction ∝ a(erosion rate)b
where a = 0.1522, b = 1.6946 and erosive wear rate is in kg/year

15. 15
Erosion Models
Francis Runner
According to IEC 62364, the hydro-abrasive erosion depth in a Francis turbine can be
estimated by using following equation
PL = ∫ C (t) ×K size (t) ×K shape (t) ×K hardness (t) dt
W is the characteristic velocity
Km is the material factor
Kf is the flow coefficient
RS is the turbine reference size (m)
PL (particle load) is the integral of the modified particle concentration over time
C is the concentration of particles (kg/m3)
Ksize is the size factor
Kshape is the shape factor
Khardness is the hardness factor

16. 16
Case Studies
Sediment Erosion in few Hydropower Plants in Nepal
 The history of sediment data collection in Nepal goes back to 1963 in Karnali river
basin in relation to hydropower development.
 Marsyangdi hydropower project started regular monitoring of sediment and its
effects on turbines since 1989.
 Sedimentology has emerged as important task in most of the recent hydropower
projects in Nepal.
 Even though Jhimruk, Khimti and some other power plants are monitoring
sediment and its effect, still there is a lack of information for scientific analysis for
estimation of its effects.
 Except Kulekhani, all others are Run-off-River (ROR) projects and all of them have
effect of sand erosion.
 Francis turbines of Panauti, Trishuli and Sunkoshi are eroded frequently and
mostly refurbished by welding and grinding. (Bhola Thapa, 2014)

17. 17
Case Studies
Sediment erosion at Jhimruk HEP
(a) Guide vanes (b) Turbine runner
The pictures illustrate the extent of sediment erosion in guide vane cover and the runner
blades after operating during a single monsoon. the sediment concentration exceeds
4,000 ppm for about 15 % of the monsoon. The average content of quartz in the sediment
is found to be above 60 % (Basnyat, 1999).

18. 18
Case Studies
Sediment erosion at Kaligandaki HEP
The Francis turbine of Kaligandaki “A” severely damaged within one year after the
commissioning of the machine. Furthermore, after repairs and replacement of the eroded
components, the turbine components continue to get damaged after 3000- 4000 hours of
operation (NEA, 2013).
(a) Damages of runner blades (b) Damages in spindle of guide vanes

19. 19
Case Studies
Sediment erosion at Modi Khola HEP
(a) damage of seal ring (b) eroded facing plate of bottom cover
Observation Allowable Design Value
side clearance between
guide vanes and facing plates
Max: 2.0 mm
Min: 0.75 mm
0.5mm
value of shutter gap between
guide vanes
Max: 1.0 mm 0.0mm Chhettry B et al. (2014)

20. 20
Case Studies
Sediment erosion at Khimti I Hydropower Plant
The damage in the turbine components were inspected in July 2003. After 1 year of
operation (about 6000 hours), significant amount of erosion had appeared in turbine
bucket and needles. The sharp edge of the splitter has blunted and the width became
approximately 4 mm. With this 1% loss of relative efficiency can be expected in these
runners, which is significant loss of revenue for this power plant (S. Chitrakar et al.).
(a) Needle (b) Bucket

21. 21
Reduce Sediment Erosion
Techniques to Reduce Sediment Erosion
 Stop sediments from entering into Turbine
 Settling basins/reservoirs
 Eliminate direct contact between sediment and turbine material
 Coating Techniques in Turbine Materials exposed to erosion
 ceramic‐metallic coatings are generally used
 Design Modifications of Turbine
 Maintenance
 Welding/Grinding

22. 22
Conclusion
 Erosion depends on several factors, including materials of the turbine, as well as shape,
size and mineral contents of sand.
 Sediment Erosion not only reduces efficiency and life of the turbine but also causes
problems in operation and maintenance, and ultimately leads to economic losses.
 Sediment transport from the rivers is a natural phenomenon, it neither can be
completely controlled, it nor can be completely avoided; it should however be managed.
 The future turbines operating in sediment affected power plants should consider the
particles and their erosion potential during the design phase.
 In order to have reliable investments for hydropower development in a country, the
challenges of sediment erosion in turbines need to be addressed with a sustainable
solution.

23. 23
Reference
[1] H. Brekke, Design of hydraulic machinery working in sand laden water, in Abrasive
erosion and corrosion of hydraulic machinery, Imperial College Press, London, pp. 155-
81, 2002
[2] IEC, Hydraulic machines. Guide for dealing with hydro-abrasive erosion in Kaplan,
Francis, and Pelton turbines, BS EN 62364:2013
[3] ASTM G40-88 (1988) Standard terminology related to wear and erosion, American
society for testing and materials (ASTM)
[4] Stachowiak G.W. and Batchelor A. W. (1993) Engineering Tribology, Elesevior,
Amesterdam
[5] Bardal E. (1985) Korrosjon og korrosjonsvern, Tapir, Trondheim (In Norwegian)
[6] Hari Prasad Neopane, “Sediment Erosion in Hydro Turbine,” Ph. D thesis, Department
of Engineering Science and Technology, Norwegian University of Science and Technology
(NTNU), Trondheim, Norway, 2010.
[7] Naidu B.K.S. (1996) Silt erosion problems in hydropower stations and their possible
solutions, Proc. Silt damages to equipment in hydro power stations and remedial
measures, New Delhi, pp 1-53.

24. 24
[8] Thapa, Bhola, ʺSand erosion in hydraulic machinery, PhD thesisʺ, Trondheim:
NorwegianUniversity of Science and Technology, Faculty of Engineering Science and
Technology, Department of energy and process engineering, 2004.
[9] Lysne D.K., Glover B., Støle H. and Tesaker E. (2003) Hydropower development book
series number 8 - Hydraulic design, NTNU
[10] Anil K. Bastola, Hari P. Neopane, “Mineral Analysis and Erosion Potential of
Sediment Samples from Nepalese Hydro Power Plant”, Journal of Machinery
Manufacturing and Automation, Sept. 2014, Vol. 3 Iss. 3, PP. 50-55
[11] Rajkarnikar B., Neopane H. P. and Thapa B. S., 2013, “Development of rotating disc
apparatus for test of sediment-induced erosion”
[12] Krause, M., and H. Grein. 1996. “Abrasion Research and Prevention.” International
Journal of Hydropower and Dams 4: 17–20.
[13] Bajracharya TR, Acharya B, Joshi CB, Saini RP, Dahlhaug OG. Sand erosion of
Pelton turbine nozzles and buckets: a case study of Chilime hydropower plant. Wear
2008; 264: 177-84.

25. 25
[14] Basnyat S. (1999) Monitoring sediment load and its abrasive effects in Jhimruk
hydropower plant Nepal, Proc. Optimum use of run-off-river conf., Trondheim.
[15] S.Chitrakar et al., A Review on Sediment Erosion Challenges in Hydraulic
Turbines, 2018.

26. 26
Thank You