The Effect of Polarity and Hydrostatic Pressure on Operational Characteristics of Rutile Electrode in Underwater Welding.

Alexandre Q Bracarense,Ezequiel C P Pessoa,Andrés M Moreno-Uribe

doi:10.3390/ma13215001

Alexandre Q Bracarense, Ezequiel C P Pessoa + Show 1 more

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https://doi.org/10.3390/ma13215001

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Abstract

In order to provide a better understanding of the phenomena that define the weld bead penetration and melting rate of consumables in underwater welding, welds were developed with a rutile electrode in air welding conditions and at the simulated depths of 5 and 10 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, decreased arc length, and increased number of short-circuit events. The combination of these characteristics kept the weld bead geometry unchanged, compared to dry weld conditions. With the positive electrode (direct current electrode positive-DCEP), radial losses were derived from greater arc lengths resulting from increasing hydrostatic pressure, which led to a decrease in weld penetration.

Highlights

Introduction and Theoretical ApproachThe stick shielded metal arc welding (SMAW) process applied to aquatic environments is used as a low-cost practical repair and maintenance solution
Experimental results obtained by Lesnewich (1958) [25] in GMAW have indicated that the α coefficient for positive electrode welding is, in a first approximation, independent of the welding current, composition of the shielding gas, arc length, welding voltage (Nunes, 1982) [26], the surface conditions of the wire, and the pressure
In GMAW welding with the negative electrode, Lancaster (1984) [27] mentioned that the α coefficient tends to be higher than when welding with the positive electrode, where this difference can be up to 75%

Summary

Introduction

The stick shielded metal arc welding (SMAW) process applied to aquatic environments is used as a low-cost practical repair and maintenance solution. The characteristics of underwater environments generate defects that affect the quality of the resulting weld joints and, the mechanical properties of the structures. Some inherent aspects of the process that need to be considered include the instability of the electric arc resulting from increased hydrostatic pressure and other environmental factors [2]; further, Ando and Asahina (1983) [3] mentioned that water dissociation promotes the absorption of hydrogen and oxygen by the weld metal, Pope et al (1996) [4] noted the exposure of the weld metal and heat affected zone (HAZ) to rapid cooling due to the aqueous medium, and Suga and Hasui (1990) [5] referred to the decrease in the electrode fusion rate with increasing pressure.

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