# Effect of Welding Parameter on the Corrosion Rate of Underwater Wet Welded SS400 Low Carbon Steel
## 3 Results and Discussion  
Potentiodynamic polarization testing was carried out using a 3.5% NaCl solution and produced a Tafel diagram to show the corrosion rate of SS400 steel underwater welded specimens. This test is used to see the resistance of samples to oxidation when given potential from the outside so that corrosion occurs. Potential corrosion (\(E_{corr}\)) was determined by the amount of negative charge that occurs when the metal is in a NaCl solution and produces chloride ions. These ions will damage the protective layer (passive film) on the metal surface due to chloride ions that infiltrate into small cavities. Damage to this protective layer is utilized by the oxygen element around it so that corrosion occurs [11]. The results of potentiodynamic corrosion testing are shown in Figure 2. Corrosion test graphs show polarization curves are close together. The difference lies in the value of \(E_{corr}\) and \(I_{corr}\) and the passivity line. The passivation line whose shape approaches the anodic and cathodic tangents tends to be more corrosion resistant. The corrosion process occurs due to an electrochemical reaction on the surface of  
Figure 1: Cutting and dimensions of corrosion test specimens. the specimen with an electrolyte solution. Chloride ions in NaCl electrolyte solution that damage the surface of the protective layer of steel by infiltrating the small cavities of the underwater weld can cause pitting corrosion to occur [12]. Potentiodynamic corrosion testing will produce a curve on the Tafel graph, and then resulting data values \(E_{corr}\) and \(I_{corr}\). Those data values are determined by the number of negative charges formed. The size of the value indicates the tendency of the material to experience oxidation. The highest \(E_{corr}\) value is obtained by welding with an RB26 electrode. A low \(E_{corr}\) value will have a tendency to be more easily corroded, and vice versa. The corrosion current density was used to calculate the corrosion rate sought using the Tafel extrapolation method based on [PERSON]'s law [10; 13; 14]. Corrosion current value (\(I_{corr}\)) in the Tafel diagram is susceptible to the shape of the curve because the value of \(I_{corr}\) is taken from the tangent intersection of the curve that changes from the cathode to the anode or vice versa. Hence, even though the shape is almost the same, but when the trajectory changes at a different point it will produce a different \(I_{corr}\). A different \(I_{corr}\) will produce a different corrosion rate. Comparison of corrosion rates on ground welding and underwater wel  
Figure 2: Tafel diagram of weld joint with electrode parameters and 100-A electric current. Figure 3 shows that the lowest corrosion rate occurred in welding with a variation of RB26 electrode and a welding water depth of 2.5 m with a welding current of 100 A which is equal to 0.093126 mm/year. The highest corrosion rate was spotted in welding with variations of RD26 electrodes and 0 m welding depth with a welding current of 110 A, which was equal to 0.23720 mm/year. The reason for the welding corrosion rate on land is higher than underwater welding because, at the time of welding on land, individual underwater welding electrodes that are already in the oven are used, so they are dehydrated. Amount of hydrogen, which can increase weld penetration, decreases on the electrode for underwater welding. Electrodes that are too dry are expected to cause the penetration of the weld experienced deterioration [15]. The research of [PERSON] et al. [16] describes the microstructure that occurs in welding underwater SS400 steel. Grain Boundary Ferrite transformed into a nucleation site for the second phase ferrite during the process of cooling weld metal from high temperatures. The high cooling rate of underwater welding stimulates nucleation. Then columnar grains form along the direction of the cooling temperature.