HVOF Coatings To Combat Hydro Abrasive Erosion

International Conference on Hydropower for Sustainable Development
Feb 05-07, 2015, Dehradun
HVOF COATINGS TO COMBAT HYDRO ABRASIVE EROSION
Dr.D.A.Karandikar
Head-coating plant, ndritz Hydro Pvt Ltd, Village –Prithla, Dist-Palwal
Haryana 121102, India
ABSTRACT
Hydro abrasive erosion is a common damaging mechanism in Hydropower plants situated on
the rivers carrying excessive hard particles such as quartz along with other minerals. These
hard particles with high velocity, damage the most common stainless steel being used for
manufacturing the underwater components of hydropower plant. Hydro abrasive erosion is a
complex phenomenon and is the result of abrasion and cavitation damage mechanism and
hence the solution to avoid such damage has to be a unique and addressing to both of them.
Abrasion is normally caused by movement of hard particles at high speeds whereas cavitation
is because of disturbances in the water flow .Abrasion can be minimized with choosing a
material harder than the particles hardness, and cavitation could be minimized by selecting
appropriate design parameters to ensure smooth water flow. From both these damaging
mechanisms mostly abrasion starts at the early stage resulting in damaging the profile and then
cavitation takes over. Hence the efforts have been made to avoid or delay the abrasion with
either using hard material or material with modified surface to match the hardness to that of
quartz particles. HVOF is high velocity oxy fuel spray technique which provides such harder
surfaces on stainless steel components. This paper discusses the damaging mechanism,
solutions to avoid or delay them alonwith ANDRTZ long experience in this field. Also some
typical coating applications of underwater components pertaining to hydropower plants of
Indian origin are also discussed with their performance.
INTRODUCTION
Hydro abrasive erosion is common damaging mechanism in hydropower plants situated on the
rivers with water containing hard particles such as quartz and mica along with other minerals
such feldspar, muscovite etc. These particles in appreciable amount travelling at high speeds
strike the surfaces of underwater parts causing abrasion –removal of material. These damages
then cause the disturbance in water flow resulting in cavitation. Abrasion can be minimized by
selecting appropriate stainless steel material for manufacturing the underwater parts, removing
the particles from turbined water through desilting chamber and modifying their surfaces to
resist the attack of such hard particles like quartz.ANDRITZ, since last four decades are
providing solutions for hydro abrasive erosion worldwide with their expertise in modeling,
cavitation free designing and modifying the surfaces with appropriate coatings through various
techniques. The computational fluid dynamics technique is being used to predict the damages
at the design stage itself and modify the water path accordingly to minimize the velocity and
also abrasion. Even coating can be designed to suit the areas with more abrasion as detected in
this study. The channels and gap between the channels are chosen in such a manner to
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facilitate the movement of coating tool. Various coating materials and techniques were tried in
the past to conclude that the HVOF (high velocity oxy fuel spraying) Fig 1, with tungsten
carbide as material providing the optimum hydro abrasive erosion resistance. Recently under
the umbrella of HVOF, many of its variants are also available, such as gas /liquid fuel
equipment’s with the aim of getting optimum particle velocity and temperature to result in
best properties Fig 2. Under tungsten carbide material also various combinations are available
depending on manufacturing techniques such as agglomerated, sintered and crushed with
carbide particle size of submicron level(Nano powders) Fig 3.Theses coatings have some
roughness and can be ground by diamond wheel as per the required surface finish (Mainly on
injector components in pelton and guide vanes in Francis turbines ).Recently some more
coating techniques have been surfaced to provide still better properties such as WARM
SPRAYING,HIGH VELOCITY AIR FUEL SPRAYING but its actual use in hydropower
industry in INDIA is yet to be ascertained.
TECHNIQUE SELECTION
Fig. 1 Thermal spray technology family
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International Conference on Hydropower for Sustainable Development
Feb 05-07, 2015, Dehradun
HVOF Spray
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Material selection
Fig 3: Material selection
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SXH70/7X/80/8X: a brief description
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A unique coating proprietary to ANDRITZ VA TECH
Type: Tungusten-carbide
Density: 13500 kg/m3 (as sprayed)
Chemical composition: Proprietary composition for highest silt abrasion resistance.
Micro hardness: 900 - 1200 HV0.3 (Vickers Diamond Pyramid Hardness, DPH 0.3 kg
load).
Adhesive bond strength:
70 – 100 MPa (tensile test in normal direction to
surface).
Corrosion resistant in turbine waters, even if waste water or sea water
Not resistant to cavitation:
• avoid use on bad hydraulic designs
• avoid bad flow conditions (Pelton: general beam quality, obstacles in injector,
displacement between injector-housing and seat-ring)
HYDRO ABRASIVE EROSION
Hydro abrasive erosion is a complex damaging mechanism involving abrasive wear alone or
in combination with cavitation phenomenon. Abrasive wear is caused due to rubbing of hard
particles present in water and moving with high speeds. The extent of wear shall depend on
amount of hard particles in water, particle size of the particles and shape of particles.Himalyan
rives mainly contains the particles hard particles such as Quartz, feldspar, muscovite and mica.
Among all these Quartz is more detrimental and causes severe damages on underwater parts of
hydroturbine.Its hardness on Mohs scale range from 7 to 8 and hence when it moves with a
velocity of 15-25 meters/sec causes heavy wear on 13/4 steel components .A typical particles
analysis is shown below Fig 4 .some of the photos of damaged components are shown in Fig
5.
Fig. 4: Particle analysis
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Fig 5: Damaged components
POSSIBLE SOLUTIONS TO AVOID THE DAMAGES
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ANDRITZ EXPERIENCE
ANDRITZ is providing solution to combat the hydro abrasive erosion since last four decades
.In 1980’s then SULZER HYDRO started an extensive research programme to investigate the
hydro abrasive erosion and the solutions.First they build the test rig to simulate the water flow
conditions such as particle concentration and velocity. The pure quartz is used as particles and
the extreme velocities as experienced in actual power plants were simulated in the test rig.
Different materials were tested for its abrasion resistance factor to get to know the best
suitable material in comparison with reference material of 13/4 stainless steel. Various
parameters such as velocity, particle concentration impingement angle, coatings of different
material were used in this study. It was noted that the coating from tungsten carbide material
composition designated as SXH 70 have been found with optimum abrasion resistance factor
and became the then SULZER HYDRO (ANDRITZ) proprietary coating. Since 1995 with the
development of gas fuelled HVOF spraying technique is employed to provide the coating on
hydro turbine components. Since then ANDRITZ successfully provided the best solution to
combat hydro abrasive erosion globally in areas where the river water has high and hard
particle content. In the meantime ANDRITZ also developed expertise in predicting a wear
index (pattern) in some hydropower plant based on some typical information such as
concentration of particles, mineralogical composition of particles, size and shape of particles,
concentration of particles with respect to time. This model empirically compares the extent of
wear with respect to reference power plant in Switzerland and helps in framing the guarantees
and warrantees for the ANDRITZ coatings. In 2008 ANDRITZ started their coating activities
in India to cater to the needs of Indian power plants. In 2011 ANDRITZ developed a
technique to stabilize the splitter of pelton runners by introducing SXH 7X coating. In 2013
ANDRITZ introduced a premium quality coating SXH 80/8X to replace SXH70/7X have been
introduced with still further better wear resistance than SXH 70/7X. ANDRITZFirst provided
the SXH 70 coatings in India for under water parts in Baglihar STAGE I and Nathpa Jhakri
project Subsequently other projects such as, KARCHAM WANGTOO, MALANA,
CHAMERA, TALA, TEESTA, KALIGANDAKI, ALLAN DUHAGAN, BHILANGANA,
CHINANI, BARAGAON etc. have been provided coatings from Indian operation. The
performance of ANDRITZ coatings has been found to be satisfactory as per the feedback from
our esteem customers.
Baglihar power plant stage 1:-This power plant is in two stage ,1st stage is 3 x 150 MW.The
Francis runners 3 no’s of diameter 3500 mm is fully coated along with guide vanes which are
also fully coated. This was the first fully coated Francis runner in India. Last year we
(ANDRITZ INDIA) coated the guide vanes and labyrinth rings for 2nd stage of Baglihar which
is under commissioning.
Karcham wangtoo:--Runners, guide vanes, labyrinths, wearing rings were all coated.
Teesta urja- This is 6 x 200 MW power plant and needles, runners, seat rings and seal rings
have been coated.
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Nathpa Jhakri power plant: - ANDRITZ supplied 2 sets of guide vanes and four modified
design runners to NJ. The Computational fluid dynamic studies along with wear analysis were
done to frame the guarantee statements.
Malana power plant: -- Malana power plant is a pelton machine and ANDRITZ supplied
Micro guessrunners duly coated 2 no’s.
Chinani and Baragaon projects:—Both projects were under CH segment and these were the
minimum diameter pelton runners coated fully by robot.
Some of the photographs of components coated are shown below.
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2014
SXH80/8X
HVOF
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CONCLUSIONS
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HVOF coatings have been found to protect the underwater parts of hydro turbine to a
sufficient extent.
ANDRITZ coatings have been proved to combat hydro abrasive erosion in hydro
power plants.
More studies are still needed to find newer coatings and techniques to apply them for
extending the life of such components further.
REFERENCES
1)
2)
3)
Andritz internal literature
Andritz sales kit
Dr.winkler, Dr.D.A.Karandikar- “Innovative solutions for turbine erosion “presented
at workshop on regional cooperation on sediment management in hydropower
projects.2009.
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