There have been two cathodic protection methods to inhibit corrosion of the structural steel piles which are being immerged under seawater, or to control corrosion of a hull part of the ship exposed to sea water. One of them is a sacrificial anode cathodic protection method that the steel pile can be protected with galvanic current by potential difference between sacrificial anode and corrosive structural steel. And, the sacrificial anode cathodic protection method have generally merits compared to impressed current method because it can be easily applied to everywhere which is not connected with electricity. However, when the steel piles are being submerged in low conductivity solution mixed with fresh water and sea water, the structural steel piles mentioned above have not been protected occasionally perfectively due to decreasing of galvanic current of zinc anode caused by deposited with oxide film on the surface of anode. In this study, four types of zinc anodes samples which are included with three types of additives such as NaCl, KCl, and ZnCl2were prepared, and galvanic currents, the polarization characteristics of these anodes was investigated using electrochemical methods such as polarization curves, impedance, cyclic voltammogtam and galvanic current in order to evaluate the effect of additive affecting to quality of zinc anode. The sample added with NaCl indicated the highest value of galvanic current density compared to other samples in the case of lower and higher conductivity solutions such as 0.32 and 2.97mS respectively, and the sample added with KCl revealed the smallest galvanic current density in middle value of conductivities such as 1.53 and 2.27 mS. Moreover, Zn sample no added with additive exhibited the smallest value of galvanic current density in the lowest conductivities such as 0.32 and 0.98 mS. Therefore, it is considered that the galvanic current of the sacrificial anode can be increased by adding of additive when the anode is submerged in low conductivity solution mixed with fresh water and sea water.
A heavy oil of low quality has been mainly used in the diesel engine of the merchant ship as the oil price has been significantly jumped for several years. Thus, a combustion chamber of the engine has been often exposed to severely corrosive environment more and more because temperature of the exhaust gas of the combustion chamber has been getting higher and higher with increasing of using the heavy oil of low quality. As a result, wear and corrosion of the engine parts such as exhaust valve, piston crown and cylinder head surrounded with combustion chamber are more serious compared to the other parts of the engine. Therefore, an optimum repair welding for these engine parts is very important to prolong their lifetime in a economical point of view. In this study, 1.25Cr-0.5Mo filler metal was welded with SMAW method in the forged steel which would be generally used with piston crown material. And the corrosion properties of weld metal, heat affected and base metal zones were investigated using electrochemical methods such as measurement of corrosion potential, anodic polarization curves, cyclic voltammogram and impedance etc. in 35% H 2 SO 4 solution. The weld metal and base metal zones exhibited the highest and lowest values of hardness respectively. And, the corrosion resistance of the heat affected and weld metal zones was also increased than that of the base metal zone. Furthermore, it appeared that the corrosive products with red color and local corrosion like as a pitting corrosion were more frequently observed on the surface of the base metal zone compared to the heat affected and weld metal zones. Consequently, it is suggested that the mechanical and corrosion characteristics of the piston crown can be predominantly improved by repair welding method using the 1.25Cr-0.5Mo electrode.
Since the oil price has been significantly jumped for recent some years, the diesel engine of the merchant ship has been mainly used the heavy oil of low quality. Thus, it has been often exposed to severely corrosive environment more and more because temperature of the exhaust gas of a combustion chamber is getting higher and higher with increasing of using the heavy oil of low quality. As a result, wear and corrosion of the enginet parts surrounded with combustion chamber is more serious compared to the other parts of the engine. Therefore, an optimum repair welding for these parts is very important to prolong their lifetime in a economical point of view. In this study, Inconel 718 filler metal were welded with GTAW method in the cast steel which would be generally used with piston crown material. In this case, the mechanical and corrosion properties between weld metal zone (WM) welded to the groove which were artificially made in the base metal and deposited metal zone (DM) only welded on the surface of the base metal by Inconel 718 filler metal were investigated using electrochemical methods, such as measurement of corrosion potential, anodic polarization curves, cyclic voltammogram and impedance etc. in 35% H2SO4 solution. The deposited metal zone exhibited a lower value of hardness compared to the weld metal zone. Moreover, the corrosion current density also indicated significantly a lower value in the deposited metal zone compared to the weld metal zone, showing a nobler corrosion potential than the weld metal zone. The corrosive products was not observed both in the weld and deposited metal zones. The microstructure of the pearlite with black color was hardly observed in the weld metal zone, while, the microstructure of ferrite with white color indicated nearly mostly in the weld metal zone. However, ferrite microstructure considerably appeared in the deposited metal zone with crystal pattern, and pearlite microstructure was more or less observed in the deposited metal zone. In particular, the polarization characteristics such as impedance, polarization curve and cyclic voltammogram associated with corrosion resistance property were well in good agreement with each other.
Recently, wear and corrosion of the engine parts surrounded with combustion chamber is more serious compared to the other parts of the engine due to using of heavy oil of low quality. Therefore, an optimum repair welding for these parts is very important to prolong their lifetime in a economical point of view. In this study, Inconel 625 filler metal was welded with GTAW method in the forged steel which would be generally used with piston crown material. In this case, the mechanical and corrosion properties between weld metal zone (WM) welded to the groove which were artificially made in the base metal and deposited metal zone (DM) only welded by Inconel 625 filler metal on the surface of the base metal were investigated using electrochemical methods, such as measurement of corrosion potential, anodic polarization curves, cyclic voltammogram and impedance etc. in 35% H2SO4 solution. The deposited metal zone exhibited a better corrosion resistance compared to the weld metal zone, furthermore, its corrosion potential was a nobler value rather than that of the weld metal zone. However, the hardness indicated more or less higher value in the weld metal zone. The corrosive products after measurement of anodic polarization curves was hardly observed both in the weld and deposited zones, while, the morphologies of the corroded surfaces exhibited general and pitting corrosion in the weld and deposited metal zones respectively. The fine pearlite microstructure was a little observed in the weld metal zone, moreover, the microstructure of ferrite with elliptical pattern was significantly increased in the deposited metal zone. As a result, it is considered that the amount of Cr, Mo and Ni having a high corrosion resistance diffuse and migrate from the weld metal zone to the base metal zone, thus, the deposited metal zone indicated a better corrosion resistance than the weld metal zone because the amount of Cr, Mo and Ni were much involved in deposited metal zone compared to the weld metal zone.
A sacrificial anode cathodic protection method has been widely used in the steel pile by galvanic current by potential difference between sacrificial anode and corrosive structural steel. And, the sacrificial anode cathodic protection method have generally merits compared to impressed current method because it can be applied to everywhere which is not connected with electricity. However, when the steel piles of the pier are submerged in low conductivity solution mixed with fresh water and sea water, the structural steel piles mentioned above have not been protected occasionally perfectively due to decreasing of galvanic current caused by deposited with oxide film on the surface of anode. In this study, five types of samples which are added with NaCl(g) to Zn anode were prepared with ratio of NaCl(g)/Zn(g)x100(%). And galvanic currents, surface morphologies characteristics of these samples was investigated using electrochemical methods such as polarization curves, galvanic current and analysis of surface morphologies before and after reduction weight ratio test in order to evaluate the effect of addition of NaCl(g) affecting to quality of zinc anode. The 2.6 % sample added with NaCl(5g) showed the highest value of galvanic current density in 0.8% NaCl solution, however, the highest reduction weight ratio was also observed at the 2.6% sample. Therefore, it is considered that the higher galvanic current density, the higher reduction weight ratio, that is, the life of sacrificial anode is shorted with increasing of galvanic current. Moreover, all samples added with NaCl(g) to Zn sacrificial anode indicated higher galvanic current density compared to the sample with no addition of NaCl(g) in low conductivity solution. Eventually, it is supposed that the galvanic current can be increased with addition of NaCl(g) to Zn sacrificial anode in low conductivity solution.
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