"Witznitz" Reservoir

Overhauling the water pipes

In order to safeguard the supply of untreated water for the Thierbach hydraulic power station (which will soon be replaced by the new Lippendorf hydraulic power station), 2 suction lines (NW1200) with a strainer run into the Witznitz Reservoir. The strainer is 207 metres distance from the pump plant.

Under normal operating conditions, the lines are submerged all year round. For the first 50 metres after the building (on the banks) the lines are also fully underground.

Renovation work essentially comprised cleaning, sand-blasting and coating the pipe, the weld seams on the inside and outside, the damaged areas on the inside and outside as well as overhauling the two pipe feedthroughs.

To facilitate access, hatchways were welded onto the pipes and the protective screen above the pipe was replaced. The lake area was demarcated with large buoys in order to secure the pipelines.

Defective areas on the pipe interior and exterior

The renovation work was performed from 12th June to 14th August 1995.

The old grid over the pipe was detached, removed and disposed of. The opening of the pipe was measured and four new screens manufactured as covers.

The area around the 42 pipe weld seams and the defective points on the pipe interior and exterior were suctioned free under water and dug out from above, thus providing access to all parts of the pipe.

The old anti-corrosion protection (bitumen sheets) was removed, allowing cleaning, sand-blasting/standard particle cleanliness of 2 1/2 and preservation work on the weld seams to be carried out.

LECO artificial resins were used as anti-corrosion protection coatings.

1st coat: UWB-S-2 dark grey (approx. RAL 7005) 1.5 kg/m² = 300 µm
Top coat: UWB-M-3 brown (approx. RAL 8000) 1.5 kg/m² = 300 µm

Access hatchways below and above the water

The suction pipes were opened below and above the water at the specified points. The openings were arranged in parallel on both lines.

• First opening: 30 metres from the pipe
• Second opening: 80 metres from the pipe
• Third opening: 130 metres from the pipe
• Forth opening: 180 metres from the pipe

The access hatchways measured 800 x 800 mm and projected 120 mm above the pipe. The hatches were manufactured using 37-2 steel. The divers welded the hatches into the openings in the pipe, both below and above the water.

When work was complete, the hatches were closed using lids and seals. In order to protect them from unauthorised access, the hatches above water were welded all round and preserved in the same manner using the same coating colours.

Official inspection and approval of the building site

After the renovation work had been completed, the riders were repositioned on the lines and the ground evened out in the vicinity of the pipes. Nine small blocking vats were spaced out to protect the line.

On 12th August 1995, the building site was inspected by representatives of the VEAG and officially approved. All remaining paints and blasting product were collected and disposed of in a suitable manner.

Work process and performance was documented and submitted to VEAG Vereinigte Energiewerke AG Kraftwerk Lippendorf / Thierbach, Thierbach Hydraulic Power Station.