Natural gas high-pressure pipeline in Lower Austria
Minimal impact on the ecosystem
The Lower Austrian electricity and gas grid operator Netz Niederösterreich GmbH laid a new high-pressure natural gas pipeline to ensure sufficient natural gas supply to Burgenland. For the demanding pipe-laying project in nature and water reserves, Mannesmann Line Pipe delivered HFI-welded steel pipes with fiber cement mortar coating to the customer‘s specifications.
The new high-pressure natural gas pipeline from southeast of Velm to Mannersdorf replaces an undersized DN150 pipeline and will cover the increasing natural gas demand in northern Burgenland.
Nature and water protection
Richard Karlberger, chartered engineer at Netz Engineering Gas of Netz Niederösterreich GmbH, points out: "It was a very demanding route with several river, railway, road and pipeline crossings, and we also had to cross the Mitterndorfer Senke, one of the largest groundwater reservoirs in Europe." Above all, the engineers had to deal with extremely difficult soil conditions: In some cases, the groundwater level was less than 20 cm below ground, with unstable soils and thick layers of peat.
With respect to the extensive nature protection requirements, the horizontal flush drilling technique had to be employed for a large part of the pipeline. Project manager Richard Karlberger: "We can draw on years of experience with this technique. But the special challenge with this project was that we had to use the horizontal directional drilling (HDD) method for an approximately six-kilometer section of the route."
A convincing concept
Thorsten Schmidt was responsible for the project at Mannesmann Line Pipe: "Fortunately, we were able to present our expertise from numerous HDD installations to the responsible manager at Netz Niederösterreich and bring our experience into the challenging project.
In 2017, an about 1,000 m long test section was laid. Economically superior to a glass fiber reinforced (GFR) coating, the FCM-S coating in combination with the user-friendly MAPUR® casting resin field coating proved convincing as a system solution. "We also met the specifications regarding the length to be left uncoated at the pipe ends to the customer‘s full satisfaction," says Thorsten Schmidt.
The system of pipe coating and field coating of the welds has completely convinced us.D.I. (FH) Richard Karlberger, Project Manager Niederösterreich GmbH
Mannesmann Line Pipe then supplied around 14 kilometers of HFI-welded steel pipes with a diameter of 273.0 mm in lengths of 14 m. The pipeline in steel grade L360NE was dimensioned for a maximum permissible operating pressure of 70 bar. The steel pipes for the HDD strings were supplied in wall thicknesses of 5.6 mm, 6.3 mm, and 8.8 mm. For the FCM-S special design, they were given a 10 mm coating of fiber cement mortar.
18 site-specific boreholes
"In order to keep the impact on the nature reserves as low as possible, we have selected the drilling sections in such a way that the entry and exit points were positioned directly on field paths," continues Richard Karlberger. Where this was impossible, the access roads to the drilling sites were covered with steel plates.
The pipes for the HDD strings were field coated with MAPUR® casting resin in the weld area as a preparation for this pipe-laying process. It was not only the ideally matched FZM-S/MAPUR® system that was found convincing, but also the fact that the field coating achieved its maximum strength after only one day - even at temperatures around the freezing point. In all, 18 horizontal boreholes were drilled for pipeline sections between 200 and 500 m in length and pipe-laying depths of up to 10 meters.
Eight-kilometer section laid conventionally
The remaining 8 kilometers of the high-pressure natural gas pipeline were laid using the conventional open-trench method. On the agricultural land, the soil was initially removed over a width of about 23 meters. The steel pipes were aligned along the route, welded, tested and field coated. The welded pipe string was then lowered into the dug-out trench and provided with sand bedding. Subsequently, the pipe trench was backfilled and the topsoil was returned to its original position.
"The conventional open-trench method would have serious disadvantages for the ecologically sensitive natural reserves," explains Karlberger, who looks back with enthusiasm on the complex project. "I am more than satisfied about the way it went, and I would like to thank all those involved for their cooperation and their dedicated commitment."
After a successful pressure test, the integration and commissioning of the new high-pressure natural gas pipeline is planned for July 2019.
The HDD pipe-laying method
In the Horizontal Directional Drilling method – or HDD method for short – a horizontal hole is drilled below the ground surface. Through this hole the actual pipe is pulled in when the drill stem is retracted.
The impact on the landscape is significantly lower than in conventional open-trench pipe-laying. But there are more advantages to the HDD method. For example, there is no need to lower the groundwater level over large areas, or to build seepage reservoirs. Furthermore, no water discharges are involved.