wolfgang wrote:
On Aug 25, 3:58 pm, "William Wixon" wrote:
"Randy" wrote in message

...



On Tue, 25 Aug 2009 08:29:25 -0500, Ignoramus27816
wrote:
On 2009-08-25, Randy wrote:
On Tue, 18 Aug 2009 12:05:38 -0500, RBnDFW
wrote:
http://www.guardian.co.uk/world/2009...er-plant-death...
The firm that built the destroyed turbine told Reuters that it was too
old to work
safely. "The machine is 30 years old. All guarantees of its functioning
had
passed," said Maria Aliyeva, a spokeswoman for engineering firm Power
Machines
How long did the turbines at Hoover dam go before they were rebuilt?
50 years?
Let us now if you find anything out, I am interested.
i
38 years without a problem
http://www.hmdb.org/marker.asp?marker=1413
Thank You,
Randy
Remove 333 from email address to reply.
jeez, they showed on modern marvels (or some such)(maybe it was dirty jobs?)
them replacing individual turbine blades, i can't remember if it was hoover
dam, but maybe (now i can't even remember if they were only replacing
individual blades or the entire turbine). showed the back sides of the
blades are eroded by cavitation. was FASCINATING to think water (i mean,
not water under 20,000 lb. of pressure like a water jet cutter) can erode
(whatever kind of) metal (it was). i assumed after seeing that (modern
marvels/dirty jobs) they have regular (fastidious) monitoring and
maintenance.
that's what i wondered after seeing the russian video, if like a turbine
blade broke off (or part of a blade) and smashed the others on it's way out
and that ruptured the housing or sumphin'. i mean, they replace the blades
on the hoover dam(?) i assume for a GOOD reason.
i think it's unwise to ridicule the russians, bad karma.

b.w.


Water jet cutting is usually done a pressures of 50,000 to 80,000 psi,
and an abrasive is added to enhance the cutting process.

I am sure the lake water from Lake Meade also contains some abrasives.

Cavitation damage is caused by impingement pressures of 200,000 to
300,000 psi. Hard to believe, I know, but the collapsing bubble wall
forms a spike that impinges onto the surface with such velocity that
these pressures are achieved.

On modern hydraulic turbines several things can be done to decrease
and slow down this damage:

1) in cavitation prone areas use a material with a high work function
ie. a material that requires a lot of energy to remove bits. Examples
are 10% aluminum bronze and 17-4 ph heat treated stainless steel.

2) design the flow passages so that cavitation bubbles separate from
the flow guides/turbine surfaces thus, when the bubbles collapse, they
are removed from any surfaces. This is not an easy task and much
modelling work is required to get a good grip on this; even then some
of the professors get it wrong:-)).

3) add compressed air to the water just upstream of the turbine.

Old hydraulic turbines are often refurbished to increase their
efficiencies. On large machines, say 400 Mw and up, 94% efficiency is
claimed by some manufacturers.

Smaller machines are refurbished to re-establish original output.
Over the years some turbine blades may have been knocked-out or badly
bent because of ingestion of scrap iron such as steel fence posts. In
order to get the machine up-and-running as quickly as possible the
maintenance people would simply remove a diametrically opposite blade
and re-water the unit. Of course power production is seriously
impaired but electricity is produced. The full repair is then
scheduled during low water periods or when finances permit.

Modern turbine runners have odd numbers of blades or buckets and this
type of "repair" cannot be used.

Why an odd number - harmonics?