Coating for Pelton Turbine

Sandblasting hoses are lined with some kind of synthetic rubber, which might work in turbine impellers also. You might find something by searching on "coated impeller pumps" or similar phrases.

I already lost 1 post that didn't show up. According to what I have read I stand with your rubber proposal too.

Worth a GA of course.

In these turbines the

(1) flow: high flow takes considerable sizes of pebbles with the water stream - and

(2) density ( read this as water + plus air), when the turbine feed is containing non saturated air (and thus oxygen) like a wild river suggests.

Building a basin to slow down the flow depends on where it can be. I suppose a mountain doesn't deliver always accommodation for that.

At 2,000 liter/min, 10 mm pebbles may travel along. The abrasive character is demonstrated in how a river scratches through a canyon.

Form and composition of silt can vary a lot and will determine wear and tear, while the oxygen content in the water flow determines cavitation. The rubber, when almost used up could perhaps pose a clogging problem, when it becomes separated from the base.

Other than that, the bigger rotor, the more speed at the outer circumference.

Perhaps the form of the "scoops" can be optimized too? Working on the place and impact (bombardment) might help a lot. Just as we all like to get, pictures can tell more than words.

What size of generator is powered and what is the head?

3 units, each of 40MW capacity, head is 365m

I second this comment. What is the duty flow, and head pressure? Take careful consideration of the system parameters.

From your comments, the high silt content may be causing erosion (mechanical damage or wearing of the impeller), this may be solved by coating the impeller as others have suggested.

If there is corrosion occuring (possibly through high chloride content - the usual suspect) then the solution may be to change the materials of construction to something better suited (possibly stainless steel, or even one of the duplex SS's high chromium).

If there is any risk of cavitiation around the impeller, no coating will be suitable, no matter how hard or impervious to mechanical damage it is. The cavitation will break it right off. Cavitation is serious, and should be avoided through careful and correct design of the system, taking all of the hydraulic considerations into account.

To accurately diagnose your problem, we'll need alot more information. I would suggest you trust the recommendation of your supplier (as they know the system far better than I do) - but make them put thier money where thier mouth is - make them warranty the system for a few years (see how confident they are).

Hope this helps,

Anthony

You are confronted with same problem as the teeth and buckets of earth moving machines as baggers or chain trench cutting.

Teeth and bucket reams are weld-coated wit high wear resistant alloys and in some cases the material is a special steel which increases its hardness under dynamic loading (as far as I remember it is an alloy with a very high manganese content).

In the case of the turbines the cups can be made of such a steel or coated. The disc can be of another steel corrosion resistant but less resistant to silt impact and sliding wear.

Considering the height you mention and resulting jet velocities I have some doubts about the solution for sand blasting hoses since in those systems air pressure is around 6...10 bar and the specific mass of air is only 1/1000 of water.

What protection is suggested by the manufacturers ? It would be good to ask for details.

For general information do you have by any chance pictures of worn parts ? Simple curiosity.

Hope it helps.

As an alternative to welding a surface layer on, you can thermal spray a suitable coating (Inconel, or a cored carbide wire) onto the corroded / eroded faces of the turbines. It should be cheaper than welding and can provide a solution.

Samuel -- I'll admit I'm out of my league here having no practical experience with pelton wheel impulse turbines in power generating service. So bear with me please while I ask a basic question....... Are the cups, or whatever you call the hydraulic members of the Pelton wheel, separate castings? If so then investment casting them in a high manganese steel alloy may be the answer. Such materials are commonplace in the machinery used in foundry operations for cleaning embedded sand out of iron castings. Media in such operations is usually an abrasive sand or hardened steel shot and causes rapid wear of the blasting equipment nozzles and media handling parts.

Ed Weldon

The coating on turbines in jet engines something like tungsten, it is blasted with a gun, a very noisy process, but tungsten may not be the cure, another process is proprietary, the products that the special material is applied is called "StoneWare", the application I saw demonstrated was able survive unmarked after viciously attacked by a sharp knife. Next, a better solution maybe is to swirl the water in a settling pond before allowing the water to fall down the penstock. Milton Babb

I am definitely not sure on this but google NICASIL

Just a question, are we talking about chemical corrosion or mechanical corrosion or both? I'm wondering because if the salinity of the water is high, it will corrode the steel, just like seawater will corrode SS316. In such cases super duplex is used. Am I on the right train of thought in this discussion?

Yep, the initial post is a bit vauge on that. It eludes that there is errosion, corrosion, and cavitation. but it doesn't say what type of corrosion it is suffering from.

I'd really need a detailed water analysis, and the unit's material of construction to further comment on the corrosion aspect. But you're right - duplex would be good choice (if the chloride content warrants it).

The OP mentioned silt, I think. Most salty lakes are in basins unsuited for hydropower sources, and most seawater level differentials are low head, not well suited to Pelton wheels. So I'm guessing this is about erosion rather than corrosion.

I haven't yet found anything very promising about resilient impeller coatings (as in my earlier speculation), but there was a silicon carbide process (spray-on?) that forms a hard-facing effect.

Not to detract from the other suggestions, but an alternate (or supplementary) approach may be:

If the problem is due to erosion from silt in the water, would it be possible to modify the intake area to reduce the amount of silt flowing through the turbines?

I was thinking of something like a settling pond prior to the intake - a region of very slow flow to allow the silt to drop out of solution, or alternatively a silt filter.

A pond would require minimal maintenance except periodic dredging to remove the silt accumulation, a silt filter would require more maintenance and cleaning.

Regards
Bill

Dear Friends, Thank you all for your thoughtful and helpful suggestions. The main problem is erosion due to silt content in the river water. Corrosion due to chlorine or saline content is a problem which has been overcome e.g., sea going ship impellers, sea water pumping stations etc. For protection against silt, manufacturers are recommending coating of the runner at pretty exorbitant rates. They have made presentations showing damage to runners with and without coating. They have waxed eloquent over the advantages of providing coating to the runners.But none are not willing to stand guarantee over a period of time against damage due to silt content. In South India, (eastern and western ghats), the water is silt free and units are working for the past 60 to 75 years and the runner has not been damaged at all. Material of the runner is 13:4 Nickel Chromium stainless steel

I tend to like the idea of the settling pond as well. It is obvious the erosion from silt cannot be handled by the pump turbine and that would also apply to the intake plumbing. If a settling pond cannot be built, it may be possible to put in double cassion intakes to allow a slowing thus settling of the silt and whatever else is causing the corrosion. The settling of the silt could be configured like a two stage septic tank (large one) or having collection troughs located on the second wall that is allows water that is free of turbidity (or at least significantly less). I too suspect sand and gravel may also be involved.

Other posters have mentioned high chloride water but if this water is in the Himalayan mountains, I doubt that is the problem. Highly turbid water contains the mechanical agents of erosion. I would ask the OP to clarify the chemical results. Coating of the turbine may give some relief but I doubt if it would last very long. It is far better to follow Wawaus suggestion of a settling pond.

Centrifugal silt separator is proposed to be used for the cooling water pumps, where the quantity of water is less. Same principle cannot be used here because the quantity of water and the operating heads are much higher. Upstream silting basin is proposed which will only reduce and not eliminate the silt content before reaching the turbine

How about mechanical automatic strainers by manufacturers like Amiad or Tekleen? These can filter to 100 micron to remove the silt and can backwash by itself at a preset differential pressure as long as there is sufficient feed pressure (say 2 bar).

We usually use this as pretreatment to membrane systems.

Thank you for your suggestion. However, these filters can be used when the quantity of water is less like in cooling water pumps. These cannot be used where the water quantity is much higher

Rubber resists any sandblasting and cavitation so very likely will work here too.

Any metallic surface will be eroded quickly. There is vast experience with grain transportation by airflow in big pipes. Metallic ones will last one day, internal coating with aluminum oxide will last years.

Depending on grain size of the silt and velocity and hardness of incoming particles you may have success with a hard coating by flame spraying metal-oxide mixtures. This can be done on-site so minimises downtime.

Rubber has the big advantage that the elasticity will absorb any kinetic energy from incoming particles.

Temperature rise at sandblasting metallic surfaces is up to above melting level in very tiny regions around any hit. High velocity combined with very short impact duration will eat up any hard material.

RHABE

Ihave worked for a buterfly valves manufacturer, when exposed to abrasion, we used a liner made of nitrile carboxyle (X-NBR) with very good results. The liner was in many cases more resistant than stellite or hard metal coated butterflies.

I think that RHABE is onto a workable solution with the coatings aspect. Rubber coatings live much longer in high abrasive conditions due to their energy absorption qualities. This does hold promise given that you are still dealing with fluid. Ceramic coatings will aid in the overall life of the impeller, but wear is still a factor. You will still have to live with a reduced lifecycle of the impeller, but it may give you longer times between replacement of the impeller.

In the steel mill I worked in we had water pumps in the slag pits and the wear was rapid, several hard coatings were tried but a rubber coating was by far the best. I believe the rubber was almost ten times better than the hard coat. Price was also very reasonable. I am not able to recall the process but some members probably use it and can help more. Hope it helps.

I know this is hard to read.. but basically what it shows is that higher head systems will yield higher outputs (Kw) comparatively using a Pelton turbine. (high number on right is 3000 feet head)

What is the head of your system? (did I miss it?)

Thank you Chris. Head is 365m. Both Pelton and Francis turbines are suitable. But manufacturers are proposing Pelton turbines because it is easier to replace. Personally speaking, I will prefer Francis turbine because there is loss of head in Pelton turbine since it has to be installed about 5m above the max tail race level. But, Pelton turbine is simpler to erect, operate and maintain

Samuel -- Please help me out here. Can you describe for me the general construction of the Pelton wheel rotors that your potential suppliers are offering. I visualize a machined rotor fitted to a rotor shaft with close fitting dimensions, a key to transmit torque and some kind sleeves to rotate within sealing chambers and shaft locknuts to hold the assembly together. This rotor mounts within a cast horizontally split casing with the nozzle positioned in the one half. (the upper half?). All of this somewhat similar to a horizontal split case centrifugal pump.

I would think a small pelton wheel is a single part with individual buckets permanently attached. However, I would think a large wheel for a substantial power station would have individually made buckets that are removable for repair or replacement. As such they would have precision machined mounting surfaces. With respect to the hydraulic surfaces of the buckets I would think a fairly high level of precision to ensure highest efficiency performance. My interest is in how these features are manufactured and which materials the manufacturers are commonly set up to use.

Perhaps those of us well versed in manufacturing methods can give you some useful specific recommendations, especially in the realm of manufacturing technologies with which your suppliers are not familiar.

Ed Weldon

Ed - I'll try to answer all your questions 1. The generating unit is vertical. The Pelton turbine is directly coupled to the synchronous generator. 2. For large generating units, the spiral casing is not the split type but made up of different sized segments which are welded and tested at site 3. The no. of jets proposed is 4/ 5 4. The Pelton turbine is monocast, i.e., it is of one piece. There are some manufacturers who can give Pelton turbines with buckets bolted on to the hub. But even today, the major players recommend monocast Pelton turbine 5. The profile of the buckets are based on model studies which are carried out by the manufacturer at his works. The efficiencies of the model turbine is measured at different loads and heads. The efficiency of the turbine is guaranteed by the manufacturer and has to be proved by him at site. Any shortfall of efficiency is liable for penalty and even rejection if the difference between guaranteed and actual efficiency is beyond the standards stipulated in IEEE 6. The entire water conducting system comprising of penstock, spiral casing and turbine is subjected to erosion due to the silt content in the water, however, the damage to the turbine is more and replacing the turbine every year due to damage is a pretty costly affair and should be avoided (loss in generation thereby revenue) 7. Material of the runner is 13:4 Nickel Chromium stainless steel, which is the normal standards I hope that I have cleared your doubts. Come back to the original question. How to prevent damage to the runner due to silt. Around the world, many generating units have been installed in Africa, Europe etc., where the silt content in the water is just as bad or perhaps, even worse. What steps have been taken to avoid damage to the runner due to silt?

Be aware also that the erosion problem will affect not only the Pelton wheel but also all the feed piping.

This also needs to be considered because as the wall thickness decreases the feed pipes will become dangerously thin.

I believe that this situation has resulted in the close down of some otherwise servicable hydo power stations because the piping is embedded in the concrete structure of the dam and is not economically replaceable!

If you get a zyclone, maybe need a special build, to remove the first 90% or more and coat with rubber as I suggested you will get near 50 year lifetime.

Zyclone was suggested above as centrifugal separator. Zyclone is a special type of this optimise for efficiency.

Smallest one I have used was 6mm diameter for removing oxide particles above 2 µm diameter from a watery suspension.

Biggest one I have seen was 12m diameter to remove dust from power-plant exhausts.

So depending on your flow rate and if full pressure inside and no pressure outside is necessary you may get an off the shelf unit or have to encircle this with a pressure housing.

RHABE

I am quite sure many have not understood the terrain. Samuel is talking of free flowing water on Himalayan ranges. Water here, when it moves has potential to wipe out every thing in its way. In normal course, this moving water carries with it all kinds of rubble/metal and all such things.

In the recent past, a lot of companies have ventured in to generating Electricity through these water channels expecting to make a fast buck. They underestimated the power of nature. Trying to control the flow of this 'untamed' water in runners and allowing it to pass over the blades of turbine to rotate and generate - it all sounds good - well! till they attempt it. I am talking all this because a close friends company too ventured in to this and then the guy was looking for the solutions for the problems that are raised today by Samuel.

First of all Samuel (are you one of those Plant incharge?), please understand the turbines that have been sold in that area are not meant to face this kind of harsh inputs and have to be redesigned with consideration to all kinds of possibilities.

Being specific to your question, try coating blades with Aluminium Oxide with the process known as detonation Gun coating (The Guest referred to this) and hope for the best. But anyway, try to accept the fact that you (or your Boss), have already reclaimed more than the investment - So be happy.

Good luck.

Hello everybody:

At last, somebody calls bread to the bread and wine to the wine. I absolutely agree with capri.

In a rough calculation, the flow rate for each turbine is around 13 m­³/s, this is at least, 39 m³/s in total. I would like to know if a zyclone can make this task of removing silt from such a quantity of water by second.

It is not compulsory to have only one cyclone (zyclone is as far as I know a gaz) it is possible to use several in parallel. The separation capacity ( I used as RHABE small special cyclones to clean oil for transmissions) depend on the value pf r*ω², the finer the particles the higher it should be so that in fact to clean the water two steps should be used: a first one with a velocity reduction to take off big parts and a second one (in one or several steps in series) to take off the silt. It is most probably not feasible to do it in only one step. From an other point of view stones have a high impact energy and generate what was mentioned (local high temperature rise), silt has more an abrasive wear effect which can be better countered by different coatings. One should also take into consideration the very high velocity of the jet and thus the high sliding velocity of particles on the cup surfaces. If stones are not any more present I presume that the wear will decrease in a considerable way. Now the problem is to know how big or how small could be a "stone" and where particles have to be considered as "silt".

Exactly. These methods can be used only when quantity of water required is small. Centrifugal separators are included in scope of supply for cooling water pumps. These methods cannot be used in penstocks, where the velocity is around 22 feet per sec and pressure is around 35 bar

What I was actually suggesting was to build your own centrifugal separator, with only a few degrees of turn (I said 1 rotation), and able to handle the high volume and pressure. A cyclone device uses ax 5 rotations to acheive its very high stratification. I suggest that the less rotation, the less loss of head to friction. (the reason you can't use centrifugation to purify.) What you need to do is experiment to figure out how much rotation can be accomodated vs how much silt can be removed. This doesn't have any more rotation than a francis turbine... but it might help. You have control over the radius of rotation, which would be the critical factor driven by water flow speed vs stratification of particulate.

I'm no expert.. it is just an idea.

Here is another version of this... with replaceable lining plates. pm me for larger image with your email. the diameter of this would have to be determined by testing.. 20 feet, 30 feet.. I don't know. There is lots you can do with this.. (gate style valve on silt outlet, etc.)

Chris

This is a picture from a hopper modification at a rock crusher plant, that I participated in last year. (where the big trucks dump) The hopper is lined with 'armor' plating. (sorry I don't know the material spec) but each plate is about 2" thick.. (x 8" x 12") and of course bolted on.. extremely hard stuff, and this hopper has been running for 2 years already, and the plates are basically unscathed...

so that is the kind of plate I'm referring to.

Gentlemen,

What about a combination of my settling pond idea and Chris' centrifugal separator, designed something along the lines of a very large version of the air pre-cleaner used on trucks.
With the water entering tangentially into a large cylindrical pond, forming a whirlpool from which the turbine feed is taken from near the top in the centre and a self flushing flow is maintained at the bottom outside edge to remove the silt and debris.

This pond would then be lined with very strong replaceable panels like Chris' armour plate suggestion, and have an inlet gate which could be closed for maintenance and a very coarse strong inlet screen, say 50mm high tensile rods at 50cm centres to catch large debris - large rocks, branches, trees, etc, placed between the gate and pond.

Regards
Bill

Hi Bill,

I appreciate your creative thoughts. There is no difference between centrifugal force and gravity for moving the silt out of the water. Both are force fields that stratifiy matter by weight.

I only suggest centrifugation as it allows as much of the head to be maintained at the bottom of the penstock. If your settling pond idea is near the top of the penstock then I can see some version working. Obviously at this site, silt is a a problem. There are real costs associated with liner plate replacement in any technology implemented, and while there are also real costs associated with centrifugation or settling ponds in terms of lost head pressure and subsequent lost power production, the settling pond idea has less cost for maintenance/plates, and therefore is a reasonable idea in my book. If that can be coupled with a simple centrifugation method, that can also work as a trade-off to keep flow at maximum.

The inlet screen is an essential idea, and works well with the settling pond too I think. I'd love to see some sketches, concept photos, and more description too.

Chris

Sorry Chris.

I'll even mention my dyslexic attributes before I say any thing but would not the silt use the least way of resistance and accumulate towards the centre of the rotation. Like, if I have sand in a bucket with water and stir the sand will always travel to the centre of the bucket.

Not sure mate, just asking.

Nice CAD work Chris. Talk soon, Ky.

Hi Ky,

F = ma

so there is a greater radial force for heavier particles.

but I understand the problem... if one is dyslexic, the equation is m = fa and its dinner time.

chris

Dyslexic and down under. What a mix. Things seem to be working the other way around here. I have difficulty explaining why it is but it seems to make sense to me that it is this way.

Some ancients and new wavers clean the water like this. Cascading spirals of water flow decontamination. I think I should google it. They always know more than I do.

Still like your Cad's, Ky.

very interesting... hmmm.

I have a friend who has pointed out that centrifugal separation uses high speed rotation to accomplish the goal.. maybe that is it.

the cad stuff is fun, but if it doesn't work, not much value. This is why I say it must be experimented with.

cheers,

Chris

Yeah, I'm not sure what would happen at higher speeds and in an enclosed spiral pipe my self. If I were to clean a large body of water though, I would collect the more dense stuff at the centre.

It only took me 10 minutes to set up for the pics so that's as far as I needed to go. The heavier the particles the more in the centre they will be found.

Nice side track though, and maybe even helpful to the OP, Ky.

Good point Ky, one further thought.

If I remember, the gathering of suspended material there is towards the bottom centre. The centre top of the water column is clear - that is where I would place the pickup for the turbine.

Your experiment is similar to tea leaves in a tea cup, and I believe that that phenomena is related to the fluid velocity gradient applying a centripetal force to the suspended particles.

One difference between my suggestion and your experiment was that I was suggesting tangential peripheral silt drains at the bottom, perhaps with a conical base (high in the centre).

Shaping the base and adding drains may change the dynamics

I would have the turbine feed running vertically down the centre.

Alternatively, also with the turbine feed running vertically down the centre, the floor could be conical, low in the centre, with the silt drain concentric in the centre around the turbine feed.

Either approach may work, but undoubtedly one would be better, some modeling would be in order, however I do not have the resources to do any, either simulated or physical.

Chris,

Yes there would be a small loss of head, but I would place the pond as high as possible, so that the pond surface is the minimum drop from the un-impeded water level.

I have discovered that the hydro industry calls the coarse input filter a 'trash rack', one example can be seen here <http://www.hydrocomponentsystems.com/trash_rakers/applications/> with equipment to clean it without shutting down the turbine. There is one like this at the Yarrawonga weir power station in Victoria, but unfortunately I could not find any photos of it.

I do believe there are good ideas presented. I just had another(?), if the mountain stream is picking up and carrying the erosive material why not pipe it down to the turbine ( If it isn't already). The pipe would shield the water from picking up excessive debris. If a pool of water could be located at some height above the turbine, an intake pipe could then be located within the pool and be situated such than only water from the top of the pool would enter the pipe. Screening could be applied. All excess water would be discharged down the stream as normal. Perhaps Chris' idea could be used in the piping.

Kevinm's idea sounds good, maybe as a floating weir a few inches below the water surface, with hopefully most of the silt settling out below. Maybe blow it off through a spillway?

thoughtful and practical. ga.

"Knowledge sharing is WIN-WIN situation."

I would love to hear more of your thoughts on this. Perhaps you could start a thread?

Chris

This is getting off the current path of this thread. Probably should have mentioned it earlier ..........

Hard coatings are really a bandaid over the problem if more elegant solutions, especially hydraulic ones, are possible. But if not; take a look at thermal spraying hardfacing materials.

Most current development in thermal spraying is in the area of plasma spray. The requisite hardware and wide variety of powder compositions are readily available in the USA and EU. But there is much art to the process, especially given the incredible variety of material combinations possible. A lot of that matured in the aircraft engine world some years ago.

But for a pump company in the outer reaches of the G20 it may not be so easy to employ. Also the learning curve on it's application must also be climbed by mechanical engineers whose experience is usually focused in other areas of materials science. Just because there is a local shop that flame sprays worn crankshaft journals everyday does not mean that they are ready to take on an exotic thermal srpay application.

Someone earlier on mentioned detonation gun coating. It indeed creates a denser coating than plasma spray due to the greater possible levels of kinetic energy in the molten material application stream. But it requires more specialized and expensive equipment, costs more to operate, and has orders of magnitude less backup of general industrial experience than plasma spraying. Also it is much more difficult to automate for complex 3d surfaces such as would be encountered in a Pelton wheel or a Francis runner.

Ed Weldon

Mount K2 - I'll try to answer to the best of my ability 1 Damage to Pelton turbine after a year of operation - This Pelton turbine was for a unit owned by a different company. I saw the turbine at the manufacturer's works where it had come for repairs/ replacement. I discussed the damage with the owner and the manufacturer. Both blamed each other. The manufacturer said that the owner did not clean the penstock thoroughly of the sand and grit before starting the unit and thereby the damage. The owner said that the penstock was cleaned thoroughly and in spite of the cleaning the damage took place though the manufacturer had guaranteed against damage. Who is correct? 2 Down time to replace the Pelton turbine against Francis turbine - The down time required for a Pelton turbine is about 7 days against 30 days for a Francis runner. Further, the procedure to replace the Francis runner is cumbersome where the tailrace has to be dewatered. Further, periodical inspection of a Pelton runner takes only a day against 10 days for a Francis runner. This is important because in this case the runner may have to be replaced more often and not once in say 15/ 20/ 25 or 30 years 3 Pelton turbines have been installed in the Himalayan region because the operating head is high/ very high (> 200m). As far as my knowledge goes, there are no stations operating with heads in the 50m region 4 Generating units being installed in this region is quite new. There are no standards to deal with the silt problem. So owners have depended on the experience of manufacturers to overcome this problem, and have not been successful 5 Centrifugal silt separators are required for the cooling water pumps which supply cooling water to the generator bearings, generator coolers and transformer coolers. This has nothing to do with either Pelton or Francis turbine. Meaning, whether Pelton or Francis turbine is installed, silt free water has to be provided for cooling purposes 6 You are exactly correct. Replacing runner is lucrative from manufacturer's point of view 7 Yes feasibility studies/ project report have been prepared and approval has to be accorded by the "Central Electricity Authority" before any project can be taken up. CEA is now studying this problem to advise the owners suitably 8. The point under consideration is, how to prevent damage to the turbine due to the silt content in the rivers in the Himalayan region. How have manufacturers overcome this silt problem in the African, Europe and Asian rivers If you require any additional information, please let me know

Samuel Chilliah: My comments are as under:

Item 1: What were the monthly, 3 months 6 months inspection and maintenance schedules and were those followed by the Owner (any observations, non-conformities?). Failure occured after 1 year but prior to that there ought to be reports for excessive vibration or noise level or partial loss of output etc., manufacturer should have been informed about abnormalities for the guarantee to be valid.

Item 2: For A Francis: Gates at intake are closed,Wicket gates at the spiral casing are closed, Gates at tail race are lowered, it takes a few hour to make the turbine ready for inspection, tail race does not require to be de-watered and is not practical since PS comprises many units. My experience with Francis (100 MW) is that inspection can be conveniently completed in 3 days time.

Life of Frances is >30 years, check statistics with the manufacturers.

Item 3: Francis is suitable for 30 - 300 meter head (200 meters is wrong assessment) however at >300 m head the efficiency is comparatively low and you have to take into account specific speed, otherwise your 365 m head is certainly not a limiting factor.

I am not from your country, but please note that Himalaya range extends from India-Nepal-Pakistan and please check Wikipedia and the like to confirm various PS with Heads falling in the range 30 - 300 meters (Frances).

Item 4: In the pondage dead storage is essentially provided as a standard practice world wide to deal with silt problem, no body goes to the manufacturer.

Item 5: There is no compulsion to draw cooling water from intake, alternates such as boring in soil or tail race water could have been used if silt is such an issue.

Item 6: No further comments.

Item 7: Authenticity of that report is in question.

Item 8: Refer to my response item 3,4, etc.

Dear Samuel,

This brings me back to the question: Is the damage mostly due to:[1] 1. Erosion

2. Cavitation

A picture can show this, because visually these 2 effects show clearly different patterns: cavitation on your material shows grey matte- sometimes blackisch spots (like some one tried to weld on it) and wear by erosion is somewhat polished.

Refering to the following diagram, the Reservoir portion below the intake tunnel opening (penstock) is meant for silt accumulation (Dead Storage).

Mountk2 - Evey hydro project has to have a dead storage where the silt settles down. But in the Himalayan rivers, the silt is of a very fine quality and tends to flow along with the water. As I mentioned earlier, de-silting basin is proposed to be provided where the silt will be drained away. However, de-silting basin will only reduce the silt problem and not eliminate it altogether. Solutions that have been proposed in this forum thread like abrasions to earth moving equipments etc., cannot be applied here

And what you have to say to dvmdsc in response to his post # 63 ?

Hello everybody:

Just searching in my small library, I have found (paradoxical) this document related with the sediment problem at the intake of some Himalayan run-of-river power plants.

Even when I know that this document was not elaborated the last week, I am pretty sure that it can be of some help to understand the possible solution to the problem stated by the OP.

Sediment problems at intakes for hydropower plants H. D, Sharma ...
http://iahs.info/redbooks/a122/iahs_122_0330.pdf

Greetings