Corrosion resistance of underwater wet welds produced with a new oxyrutile electrode: influence of polarity, welding current, and depth

Abstract

In this work, the influence of underwater wet welding process parameters on the corrosion resistance of welds produced with oxyrutile electrode was investigated. Although in the standard for underwater wet welds (AWS D3.6 M: 2017), only mechanical strength specifications are required, corrosion is a critical factor since its occurrence is a major cause of mechanical failure in offshore metallic structures. Underwater wet welding experiments were performed in a hyperbaric chamber using a gravity mechanized welding device in direct (DCEN) and reverse (DCEP) welding polarities at currents of 150 A and 180 A and depths of 0.3 and 30 m. Corrosion resistance of the welded zones was evaluated by electrochemical techniques of electrochemical impedance spectroscopy and potentiodynamic polarization in NaCl solution 3.5 wt.%, to reproduce the seawater salinity. The electrochemical results showed different behaviors among the direct and inverse polarities. In DCEN, the corrosion potential values (E_Corr) were close, and the corrosion current densities (i_Corr) varied, while in DCEP, an inverse behavior was observed. Although the lowest corrosion rates were obtained in direct polarity, in both polarities at the lowest welding current the welds showed a higher corrosion resistance.