In this manuscript is presented a methodology to realize the pipe union by the welding process with the deposition of the root pass. In the butt welding execution external without open root, the height of the root face is a key factor for getting full penetration. Sometimes, copper-joints are used to prevent leaks. Though, copper can cause inclusions and corrosion, producing many troubles during the installation and generating large costs in the work area.Therefore, it was performed a penetration effect analysis using the slanted nose phase, method in root pass welding without the use of copper-joint or root opening, for the following critical welding positions: flat, vertical and overhead. The analysis was performed using the welding process MIG/MAG by derivative short circuit, GMAW-CMT (Gas Metal Arc Welding -Cold Metal Transfer), with AWS ER 70S-6 wires (1.2 mm) a with Ar+25%CO 2 , as shielding gas.The Central Composite Design (CCD) was used as a tool for a better organization of the tests, whereas to analyze the results it was made an optimization based on the Desirability theory for multiple responses, employing flat sheets of 1020 steel with a narrow-gap in U-shape. Then, this full penetration methodology in orbital welding turned down was validated in a ASTM 106 pipe through the conventional short-circuit welding process, with the joint established in the previous stages. The tests were performed with wires of 0.9 and 1.2 mm in order to evaluate the welding power. Macrography tests showed root pass with an acceptable visual appearance and without internal defects, thereby suggesting the possibility of welding execution with full penetration.