Abstract: The method comprises a first-run weld performed from the outside without pads for backing the weld pool, which is obtained by: preparing a welding bevel (C) having a closed bottom by arranging, so that they are mutually adjacent, two pipe segments (T-T′) having symmetrical welding bevel half-profiles (p-p′) with respective annular abutment surfaces (sp-sp′) which are meant to form, by arranging them mutually adjacent so as to obtain front contact, the closed bottom of the welding bevel (C), the closed bottom being further delimited by a groove (SV) which has a maximum chord of preset width (H); performing the first welding run with one or more welding torches which are supplied with a welding wire whose diameter “d” is dependent on the maximum chord (H) of the bottom groove (SV) of the welding bevel (C); maintaining, during the first welding run, the welding arc at a controlled length, by relating the distance (h) between the end of the welding wire and the vertex of the bottom g

Abstract: The system comprises: a distance sensing device for sequentially acquiring, during the welding process or before it, individual transverse profiles of the welding gap by gauging its various depths; electronic units for parametrically reconstructing, by combined numeric and vector calculation, the parametric and topological features of the welding gap starting from the various depths acquired by gauging points; electronic circuits that are adapted to compare the features of the acquired welding gap profile and the stored features of the profile of a corresponding nominal ideal welding gap and to infer corresponding data for varying the parameters of the welding process; and control subsystems using, selectively or in combination, one or more of the variation data to adapt corresponding welding parameters.