"The two-week process of adapting, testing and certifying the integrated control system for the twin pipelines requires the valves at both Russian and German landfall to be shut, gas from the Portovaya compressor station to be stopped and the flow of gas through the pipeline to be temporarily halted," the Nord Stream project consortium said in a statement.
Russia aims to diversify European transit options through Nord Stream. The dual pipeline runs from the shores of the Gulf of Finland through the Baltic Sea to Germany.
The consortium said it was entering "an intensive period" as it prepares the control system for the integration of the twin pipelines into a single network. Completion of the second line is expected by June.
Both lines, once fully operational, will transport around 1.9 trillion cubic feet of Russian gas each year to European consumers for at least 50 years.
Celebrity Couples of 2014 [PHOTOS]