<p>Fluid flow motion controls energy transfer in the weld pool and drives solidification process. Experimental investigation of fluid flow during welding is made particularly difficult by unsteady movements in the molten pool. Fluid flow measurements in tungsten inert gas (TIG) welding are important to understand and control energy transfers during the process. In this paper, a setup was designed to observe free surfaces during a fully penetrated TIG welding. Edge detection is applied to obtain the weld pool border, and particle tracking velocimetry (PTV) method is applied based on gas bubbles and particles along the free surface opposite to the arc. The method allows to investigate velocities and fluid flow motion. The method is carried on three different welding speeds at a constant current (80 A) leading to three different linear heat inputs. Images on the penetrated side showed oscillations of the fluid flow that goes from one vortex on the side of the weld pool to the other vortex on the other side. Velocity measurements can give insight to the intensity of the fluid flow. Finally, its behavior are discussed in relation with assumption of its 3D component and its physical origin.</p>