Virtual study is performed using deterministic mathematical model of the welding process to assess the effect of arc interruptions on the formation of the weld pool and seam. It is found that interruptions in arc burning lead to the appearance of craters, the depth of which can reach the thickness of the filling layer. It is shown that the effect of the duration of the interruptions in arc burning on the crater depth depends weakly on the welding speed, but noticeably depends on the spatial position of the weld pool. It is necessary to take into account the criteria for the formation of defects from disturbances in the thermal circuit of the arc when analyzing of the welding monitoring data.