Hamedreza Hajghassem - Master of Civil Engineering, Water and hydraulic structures, Kharazmi University of Tehran
Saeed Baay - Bachelor of Civil Engineering, Islamic Azad University, Gonbad-Kavous branch
Mirvahid Hossini - Director of Research and Development Unit, Pishtaz Beton Company
Amir Ayazi - Assistant professor and faculty member of Shahr-Quds University
Majid Tadayon - Master of Civil Engineering, Geotechnic, Faculty of Civil Engineering, Khajeh Nasir toussi University of Tehran

welds were developed with a rutile electrode in air welding conditions and at the simulated depths of ۵ and ۱۰ m with the use of a hyperbaric chamber and a gravity feeding system. In this way, voltage and current signals were acquired. Data processing involved the welding voltage, determination of the sum of the anodic and cathodic drops, calculation of the short-circuit factor, and determination of the melting rate. Cross-sectional samples were also taken from the weld bead to assess bead geometry. As a result, the collected data show that the generation of energy in the arc–electrode connection in direct polarity (direct current electrode negative-DCEN) is affected by the hydrostatic pressure, causing a loss of fusion efficiency, a drop of operating voltage.The underwater welding robots are replacing humans in several harsh working environments however further strategies are required to achieve better control of robotic motion in order to extend their utility. This paper presents a smooth trajectory control strategy to improve the welding quality and efficiency using an underwater

wet welding; polarity; arc phenomena; weld bead morphology; underwater welding robot