Root Pass

The root pass is the make-or-break layer in groove welds; if it lacks complete fusion or contains defects, no amount of subsequent fill passes will correct the problem. Achieving sound root penetration requires precise control of current, voltage, and travel speed so that the arc melts the sidewalls and root face while remaining shallow enough that the molten pool doesn't sag through to the backing, forming an exposed void.

Root pass technique demands high welder skill, especially when welding open-root joints (without backing bar) on thick material in confined positions. The root bead geometry, width, height, and fusion profile, is visually inspected and, if necessary, confirmed by weld inspection methods like magnetic particle examination before subsequent passes are applied, ensuring that any root defects are detected and repaired immediately rather than trapped inside the final weldment.