A pipeline butt welding machine has support means, a first vise assembly and a second vise assembly associated with the support means and adapted to engage respectively a first and a second tubular element to be joined by welding; at least one of the vise assemblies being movable relative to the other between a position of maximum mutual distance and a position of minimum mutual distance; the mobile vise unit being operatively connected to at least one fluid-dynamic cylinder comprising a casing and a piston slidingly housed within the casing and defining in the casing a first and a second mutually variable volume chamber. The welding machine has a fluid-dynamic circuit configured to feed fluid under pressure simultaneously to the first and second chambers and to control the motion of the movable vise assembly as a function of a pressure difference between the first and second chambers.