Abstract: A process for the acquisition of data in the form of measurements and calculations, for diagnosis and decision assistance for an electric direct spark butt welder and for the resulting weld seams comprises the respective steps of measurement of the instantaneous alternating voltage at the terminals of the primary (19, 33) and of the secondary (16, 35, 36) of the welder transformer, and between the jaws (18, 39) of the welder dies; measurement of the instantaneous current in the primary (24, 34) and the secondary (17, 37, 38) of the transformer; measurement of the instantaneous displacement (41, 42) of the mobile die (4); storage in memory of said voltages, said currents and said displacement during the welding process; calculations of the energy supplied by the primary and the secondary, preferably to the jaws (5, 6), as a function of time; calculation of the energy supplied by the secondary to the jaws and of the heat energy dissipated during sparking as a function of the displacement of the mobile die; calc