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Welding & Preservation

Welding & Preservation

Wendefurth Dam - overhauling the hydraulic steel structural components

Commissioned by: Talsperrenmeisterei (TSM) of the State of Saxony-Anhalt

Work performed: September 1993 to July 1995

Introduction by Dipl.-Ing. Helmut Pape, Talsperrenmeisterei Manager in the State of Saxony-Anhalt

"The Wendefurth Dam in the Eastern Harz region is 43 metres high and seals the Bodetal dam system. It is the only plant in this system which is not used for the provision of drinking water. Its main task lies in controlling floods in the Wendefurth Dam with a total capacity of 8.5 million m³.

Towards evening, it serves to discharge water into the Bode river. The minimum specifications are 1 m³/second. The Wendefurth Dam reservoir also serves as a sub-basin for operation of the Wendefurth pump-fed hydraulic power station with a capacity of 80 MW when completed. The shut-off plant was built as a curved gravity dam with a radius of 420 metres.

Two DN 2000 tapping systems serve as bottom outlet pipes with intake construction and upstream collecting basin. The bottom outlets are sealed by three independent sealing systems. The screen is located in the intake area and can be substituted by two emergency shutters. This is followed by arrangement of the main protection which serves as a quick-action stop line. Two DN 2000 cylindrical piston valves are arranged in the downstream side slide chamber to regulate output volumes. A DN 800 junction leads from the bottom outlet pipe B to the slide chamber followed by another reduced to DN 600 to a cylindrical piston valve of the same size. This automatic controller is used for raising low water levels to an output volume of 3.5 m³/second.

The Wendefurth Dam was commissioned in 1967. After 18 years of operation, the hydraulic steel structural components were overhauled."

Repair and overhaul work

Repair and overhal work was planned by Hydroprojekt Ingenieurgesellschaft mbH Büro in Dresden.

Maschinen- und Stahlbau Dresden GmbH was contracted to overhaul the hydraulic steel structural components.

Initial overhaul measures commenced in September 1993 and were necessitated by renewal of the DN 600 cylindrical piston valve.

The main protection, a wedge roller gate and the corresponding hydraulic drive were overhauled. On the upstream side, the volume of leaking water on the wedge roller gate was reduced from approx. 200 l/s to less than 10 litres/second by means of structural alterations to the seals.

All of the steel components encased in concrete, the main protection and hydraulic drive were given a new anti-corrosion coating.

This required the emergency protection device of bottom outlet pipe "B" to be sealed off first. It soon became apparent that the corrosion damage extended along the junction inlets as far as the beginning of the bottom outlet pipe. The pipes were therefore sand-blasted to a particle cleanliness of SA 2 1/2. One particular feature of the anti-corrosion measures which proved to be difficult was the fact that the pipes could not be kept dry and there was a constant risk of a drop below dew point.

For this reason, the owner and engineer decided to use LECO artificial underwater resins which are easily applied, even under such difficult conditions. The LECO-UWB-S-2 coating containing zinc was chosen as the filling material and the non-abrasive LECO-UWB-M-3 coating as a protective coating. Both coatings were applied using a modler - a hard, short-haired brush specially developed for epoxy resin coatings - in thicknesses of 300 µm, giving a total coating thickness of 600 µm.

This anti-corrosion work was performed by a local company.

After the renovation work, the emergency protection device was reopened and the dam put back into temporary operation. This was followed by the more difficult part of the protection work: upstream conservation of the junction inlets and guide rails for the emergency protection devices. For this work, which would be taking place at depths of up to 21 metres, it was necessary to bring in commercial divers.

In addition to our underwater work, Nordseetaucher is also a specialist in underwater conservation.

Underwater work on bottom outlet "A" commenced in October/November 1994 and work started on bottom outlet "B" in June/July 1995.

First of all, the components under water were carefully sand-blasted to a particle cleanliness of SA 2 1/2. Using a modler, the divers applied the LECO-UWB-S-2 filling material to the sand-blasted surfaces on the same day. The UWB-M-3 top coat was then applied the next day. Both coats were reapplied at a thickness of 300 µm. The coats were measured under water using a film thickness metre for underwater applications. As the LECO underwater artificial resins are free of solvents, the wet film thickness corresponds to the final thickness of the dry film.

During the coating work on bottom outlet "A", the drawn intake screen was also sand-blasted and coated in the same manner.

During conservation work on bottom outlet "B" in June/July 1995, the initial work performed on bottom outlet "A" was also inspected, photographed and recorded on video. The inspection showed that the LECO underwater resin coating provided full, faultless coverage.

Manufactured by the Lestin & Co. diving company in Vienna and used by specialist firms, the LECO underwater artificial resins applied in this job impressively displayed their excellent universal properties underwater and in wet problem zones. These underwater artificial resins, which have enjoyed success for the past 10 years, were developed specially for the applications described above. However, to ensure that the application is successful, the diving company contracted to apply the coating must have experience in the use of such products and also be prepared to invest time in examining new potential uses and new techniques.

Nordseetaucher is committed to providing ongoing training for our divers, and this enables us to carry out even difficult tasks with the very latest technologies at a very competitive price.

Companies involved in the project:

Hydroprojekt Ingenieurgesellschaft mbH,
Dresden office

Corrosion protection:
KSE Korrosionsschutz GmbH
Lutherstadt Eisleben

Nordseetaucher GmbH, Ammersbek/Hamburg

LECO-Unterwasser-Kunstharze, Vienna
LECO distribution in Germany: Jens Th. Umstaetter, Vaterstett