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.
Underwater wet welding (UWW) with shielded metal arc welding (SMAW) is employed basically in repairs of offshore structures, including platforms, ships and others. The main problems of this type of welds are related, of course, with water presence in the electric arc that causes higher cooling rates, Oxygen and Hydrogen availability in the arc atmosphere and arc instability. Many of research and test welding programs in laboratory are undertaken in shallow water performed by automatic devices using hyperbaric chambers to simulate depths. Also, welding arc signals are acquired using data acquisition systems and the arc stability is estimated through indexes calculated from values acquired and analyzed. It is very well known the reduced stability of the wet welding process at shallow depths — less than approximately five meters. So this effect would be considerable significant since it can be used to make correlations between the arc stability indexes and the welds quality results. The main objective of this work was to evaluate the efficiency of the most used arc stability indexes reported in the literature in detect the arc instability effect of shallow water wet welding. Bead-on-plate welds had been made using a gravity feeding system device inside a hyperbaric chamber, applying straight polarity (DCEN) in ASTM A36 steel plates, using the same weld parameters in two different depths, 0.5 and 20.0 meters. Rutile, basic and oxidizing commercial electrodes types prepared for UWW with 3.25mm rod diameter were used. Visual analysis, bead morphology and arc stability were the criteria used to evaluate the weld quality. The voltage and current arc signals were acquired at 10 KHz rate. The arc stability indexes measured were average voltage and current and its standard deviation, S (Imax/Imin) parameter, voltage and current square mean, arc “re-ignition” voltage and current, metal transfer time and its deviation, metal transfer frequency and its deviation, short circuit time and its deviation and the voltage versus current graph area. The results shown that none of the stability indexes tested has been shown to indicate, alone, a good relationship to the surface appearance obtained for the three electrodes studied. The rutile type electrode was the only one that clearly produced better weld appearance at 20 meters than in shallow water depth. The rutile and oxidizing electrodes showed better surface appearance with the increased number of short circuits. For the rutile electrode, the globular transfer mode with high voltage were directly related with poor weld bead surface appearance.
The underwater wet welding using SMAW is widely used in maintenance and repairs of submerged structures. In this process, water can dissociate, providing substantial quantities of ions H+ and O2− at the molten pool. Hydrogen and oxygen may constitute gas bubbles in the molten weld metal which may result in formation of pores. The hydrogen can diffuse by the weld metal and heat-affected zone or be trapped in the structure of the weld metal in the form of residual hydrogen. The diffusible hydrogen in the weld metal and heat-affected zone might have a deleterious effect in the mechanical properties of welded joint. The diffusible hydrogen plus susceptible microstructure, such as martensite, presence of tensile residual tension and temperatures lower than 200°C can lead the arising of cracks in the weld metal and heat-affected zone. All these conditions are satisfied in underwater wet welding. The amount of diffusible hydrogen in the weld metal can be influenced by several factors. However, it is not yet known whether the depth of welding (pressure) affects the amount of diffusible hydrogen in weld metal. In this work, several measurements of diffusible hydrogen were made at following depth: 0.30m, 10m, 20m and 30m at wet welding. The electrode used was commercial waterproofed E6013. The diffusible hydrogen measurements were made through the gas chromatography method following the AWS D3.6M procedure. The porosity was measured using the macrographic method and a software called Quantikov. The weld bead reinforcement and width were also measured. The residual hydrogen also was measured. The results showed that diffusible hydrogen reduced substantially as the hydrostatic pressure increased. The porosity, as it was related previously, increased as the hydrostatic pressure increased. Changes in the residual hydrogen of the weld metal were not observed. So, it was possible to conclude that the welding depth affects directly the diffusible hydrogen and porosity levels of underwater wet welds.
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