The construction of a gas pipeline South-East of Finland, near the city of Kouvola, consisting of 27 km DN 900 (36") gas pipeline from Pajari to Valkeala natural gas centre and 2.5 km DN700 (28") gas pipeline from Valkeala gas centre to Kymijoki. The contract includes the construction of pig receipt facilities, block valve stations, branch connections, cathodic protection, crossings, civil and mechanical works, including the installation of 1.1 km piping DN700 (28") in a new tunnel, execution of hot-tie-in's to the existing parallel pipeline.
 
Additional capacity is needed because use of the natural gas is estimated to increase remarkably in the future, due to increasing need for heating and energy in the Helsinki Metropolitan Area and the extension of the Porvoo oil refining plant.
The project is executed in Joint Venture with Finnish contractor Skanska-Tekra Oy, who is mostly responsible for the civil works. Nacap focuses on the mechanical works.
The project is characterized by a great versatility of soil conditions (rock, peat, clay, silt, sand, gravel, hilly terrain, groundwater areas) and the following construction methods are used to cope with these different circumstances:
- Rock grading and blasting (approximately 5,000 m3);
- Trench blasting (approximately 5,000 lm);
- Sheet piling (approximately 30,000 m2);
- Trench dewatering (approximately 15,000 lm);
- Drilling, blasting and crushing of approximately 250,000 tons of rock material from designated borrow pit areas in close proximity to the Right of Way;
- Construction of a temporary work road (approximately 28,500 lm), constructed of borrow pit material;
- Buoyancy control and the construction of pipe foundations over a length of approximately 5,000 lm;
- Installation of bottom bedding and protective padding (approximately 8,000 lm);
- Execution of three directional drillings;
- Construction of approximately 1,100 lm of pipeline in an existing tunnel.
All these different construction methods make this project a very interesting opportunity to work with a lot of different methods at a relative short stretch.
All transports of imported materials need to go over the installation road, with a width of only 5 m, and with a welded pipestreng laying on the side, it is complicated for trucks to pass each other. However, weather conditions have proven the necessity of such a road, since the frost only came at the start of January. Access of the site would have been impossible without this installation road, due to very wet and partly soft soil conditions.
The Finnish winter formed an important aspect of this project. During a period of three weeks, work had to done with minimum temperatures of -25 °C and day temperatures of -17 °C. Solutions had to be found for several demands of our client concerning the condition of the trench bottom. Steam-spraying installations were used to defrost pipe trenches and insulation mattresses to prevent the trench bottom from freezing overnight.
The client has prescribed the specified construction methods. The buoyancy control of the pipeline in peat areas (which are currently still in commercial use) is done as follows: first the trench bottom and sides are filled with geotextile and crushed rock material, followed by sand bedding and padding to protect the pipe and then again a cover with crushed material.
To minimize the amount of peat that had to be excavated, the pipe-cover is about 1 m above normal soil level.
The pipeline crosses the river Kymijoki through a tunnel. It is the first time in Finnish history that a pipeline is laid under a river. During feasibility studies other options were explored but the tunnel proved to be the best option for the environment. This tunnel has a depth of 50 m below the water surface, a length of 1.1 km and a diameter of approximately 5 meters.
The presence of a hot bend in the middle of the tunnel, and a bended entrance point on the east side, formed another interesting challenge. It was decided that the pipes were welded one-by-one inside the tunnel because constructing the pipe outside and then pulling it in was too complex and therefore too risky. The natural ventilation was more then sufficient to remove exhaust fumes from the welding equipment.
A special pipe-carrier has been used to transport the pipes in the tunnel and hold the pipes during welding operations.
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