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VA TECH HYDRO

www.vatech-hydro.com

HIWELD™Optimized Fabrication of Pelton Turbine Runners

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HIWELD™ – Optimized Fabrication ofPelton Turbine Runners

A project team formed by engineers andtechnicians coming from various competencefields from HYDRO VEVEY SA andVOEST-ALPINE MCE has developed a newprocess to manufacture Pelton runners.

The rigorous studies performed to validateeach stage of the fabrication have led to anoperational technique, whose benefits willconvince the power plant owners.

Pelton runners are traditionally casted in one piece,

more often with stainless steel G-X5 CrNi 13.4.

This process leads to long delivery times, especially

due to the mould preparation and runner finishing

tasks.

It is also known that the risk of hidden residual

defects in the casted material, also in high stressed

areas of the runner, cannot be totally eliminated.

In order to assure a perfect control of the severe

quality criteria imposed for Pelton turbine runners,

the method is characterized by an appropriate choice

of materials and processes.

An optimized process

Following economical and technical studies of many

solutions, the idea of separating the runner into

a central disk containing the bucket roots and

bucket pieces fixed

by welding, was

retained as

reaching very

good objectives of

delivery time

reduction, quality

increase and costs

mastery. The

central disk is

machined into a

forged stainless steel CrNi 13.4 block. The choice of

the bucket separation planes allows to fabricate a

narrow disk.

It indeed ensures that high stress areas remain inside

the disk, therefore taking profit of the higher

mechanical properties (ultimate tensile strength) of

forged steel.

The central pieces of the buckets are casted in

CrNi 13.4 steel with an overthickness. Those pieces

are welded on the bucket roots following a sequence

to correct continuously the distortion.

We take profit of the good lateral access to mill the

inner profile of the bucket before welding the lateral

parts of buckets.

The lateral pieces are also casted in CrNi 13.4 steel

with a small overthickness and milled to the final

profile before being fixed on the runner.

Even if it is also possible to manufacture the bucket

pieces in forged steel, the casting of such small

and simple pieces is easy to perform by a great

number of foundries with a quality higher than for a

full casted runner.

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The runner is submitted to a post-weld heat

treatment. All the welding areas are

controlled by non-destructive surface and

volumic testing methods before and after

the heat treatment. After the final machining

of coupling and cut outs, only a final

polishing is necessary.

Demonstrated Quality

Mastering the welding process is a key

point of the technique. A welding test using

an old runner has been performed in order

to check the accessibility for welding and

non-destructive controls, and also to define

the best suited welding sequence

minimizing the distortions. Buckets were

separated in accordance with our studies and the

runner was rebuilt choosing for this test the most

difficult case of the last bucket to weld.

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Beside those tests, in accordance with the

current European standards in use for this kind of

operating mode, the welding procedure was

qualified with a test piece having a similar geometry

to this of a bucket. By those tests, a welding

sequence was defined, allowing to reduce the

distortion to the minimum. 100 % of the welding

volume is controllable and controlled by ultrasonic

method.

The results of non-destructive and destructive

controls performed from this qualification test have

demonstrated that the welding rocedure developed

for this application reached atisfactorily the very

demanding quality criteria imposed for the welding

areas. The exact location of the bucket separation

planes is defined through a Finite Element Method

(FEM) calculation of the stresses, completed in all the

bucket volume. The welding is placed out of the high

stress areas.

Benefits for the power plantowners

With this Pelton runner fabrication process,

mechanical properties of material are increased

in all the runner areas: in the disk and bucket roots

through the forged steel, in the middle and

lateral parts through high quality of casting or

through forged steel pieces, in the welding areas

through an adapted qualified procedure reaching

higher mechanical properties than integral cast

steel, and through a 100 % controllable welding

volume.

Very demanding quality criteria have been defined

for the welding procedure, the testing methods

and the acceptability of welding and constitutive

parts of runner, all this in collaboration with the TVFA

(Technische Versuchs- und Forschungsanstalt,

Technical University of Vienna, Austria), a

neutral institute accredited and renowned in the

material and construction domains.

The bucket profile, completely milled on a

CNC machine, guarantees the exact hydraulic

shape and therefore the high level of runner

performances.

Manufacture time is reduced by 30 % in comparison

with integral casted runners.

Apart from the material supply, all the fabrication

(milling, machining, welding, grinding and testing) is

performed in our own workshop, under our own

responsibility, leading to a perfect mastery of quality

and delivery time.

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Outlook

The process allows to meet quickly the

clients demand, while assuring an optimal

quality through very demanding criteria.

Presented lately on the market, the method

has immediately won a very promising

success as 15 prototype runners are already

ordered from our clients.

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8www.vatech-hydro.com

VA TECH HYDRO worldwide

Set ups in Austria, Australia, Bolivia, Canada, Chile, China, Columbia, France, Germany, Hungary, India, Indonesia, Iran, Italy, Malaysia,Mexico, Peru, Philippines, Sweden, Switzerland, South-Africa, Spain, Taiwan, Thailand, Turkey, United Arab Emirates,

United Kingdom, USA, Venezuela and Vietnam

VA TECH HYDROe-mail: contact@vatech-hydro.com

Penzinger Strasse 76 Lunzerstrasse 78 Obernauerstrasse 4A-1141 Vienna, Austria A-4031 Linz, Austria CH-6010 Kriens

Phone (+43/1) 89 100-2659 Phone (+43/732) 6987-3451 Phone (+41) 41 329 51 11Fax (+43/1) 89 46 370 Fax (+43/732) 6980-2554 Fax (+41) 41 329 51 52

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