While working on a bid, we faced a common task: "Running a natural gas high-pressure pipe DN 150, PN 70, from Dießen at the lake Ammersee to Aidenried". We examined the bidding documents and determined that the pipe could not be run along the shore or around the southern end of the lake. This was due to government regulations and the soil conditions at the lake. Hence, we decided to run the pipe right through the lake.
In the days and nights that followed, we developed, discussed, calculated and rejected numerous laying techniques. Ultimately, we came up with a solution that promised to be safe as well as an economic and technical success.
We wanted to rule out as many hazards as possible from the very beginning. We had the Supply Engineering department of the Munich College of Applied Sciences examine our solution.
Running the pipe through the lake
After a number of calculations and optimization suggestions, we were able to offer the following laying technique.
The pipe was preassembled on land. Using a system of reels and a stabilization pontoon, it was placed in the lake.
Support pulley, mounting ramp, castors, partial filling with water, pipe bundle, guide pontoon
The entire pipe was able to float, due to three extra flotation lines (PE).
A government regulation mandated that the laying work not restrict ship traffic on the lake.
For this reason, the flotation lines were designed such that filling the middle pipe with water would create just enough weight to lower the entire pipe bundle to a depth of 5.00 m below the water's surface.
This allowed ships to run on the lake without any danger, while construction work was being done.
Placing the pipe bundle in the lake
For safety reasons, buoys marked the course of the pipeline or that part of the pipe under water.
Pontoons were attached along the planned and approved course of the pipeline. They were temporarily connected with the pipe bundle.
Finally, GPS navigation equipment was used to determine and adjust the desired course of the pipeline. With cable winches, the pipe was put into the required position.
After the pipeline was successfully lowered to the bottom of the lake, its course was checked by sonar. This verified the precise work which had been done.
