The invention relates to a device for centring and clamping conduits which are preferably made from alloy steel and which are positioned end to end in order to be welded to form a pipeline. The invention comprises: means for centring and clamping two conduits that are to be welded, optional leak-tight partition means which define an inerting chamber at the mating surface, and inert gas distribution means for creating a protective atmosphere at the mating surface. The inventive device also comprises at least means for regulating the flow of inert gas and/or the supply pressure of said inert gas as a function of the concentration of O2 measured in the protective atmosphere and/or the pressure measured within said atmosphere, such as to maintain the O2 content of the atmosphere below a pre-determined alarm threshold value and/or the pressure of the atmosphere below a pre-determined threshold value.
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