• Corrosion Science and Technology
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• 제16권6호
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• pp.278-284
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• 2017

The effects of TIG welding and post-treatment procedures on the microstructure and the pitting corrosion resistance of welded lean duplex stainless steel S82441 were investigated. Autogenous TIG welding was used with different amounts of heat input and shielding gases such as Ar, and mixtures of $Ar-N_2$ and Ar-He. The addition of 5% to 15% of nitrogen to argon practically did not affect the level of the pitting corrosion resistance. However, the application of gas mixtures (50% Ar + 50% He) resulted in a significant decrease in pitting corrosion resistance. We found that increased current (200 A and 250 A) led to lower values of CPT of welds compared with welds obtained with 50 A, 100 A and 150 A. In addition, the removal of the weld surface layer (0.2 ~ 0.3 mm thickness) in most cases not only resulted in a significant increase in resistance to the pitting corrosion but also post-treatment of weld, implying that corrosion resistance depended on factors such as surface roughness or the presence of undesirable oxides.

• 한국방사성폐기물학회:학술대회논문집
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• 한국방사성폐기물학회 2018년도 추계학술논문요약집
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• pp.179-180
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• 2018

Al - MMC, used as a neutron absorber, shows pitting corrosion and/or galvanic corrosion in 3.5wt.% NaCl solution. If pitting corrosion penetrates the core, neutron absorption performance could be affected. Galvanic corrosion was observed between Al 5052 and Al 1070, and pitting corrosion was observed around $B_4C$.

• Journal of the Korean Data and Information Science Society
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• 제11권2호
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• pp.157-172
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• 2000

Metal containers represent a situation where a specific metal is exposed to a wide variety of electrolytes of varying degrees of corrosivity. For example, hundreds, if not thousands of different products are packaged in an aluminum beverage can. These products vary in pH, chloride concentration and other natural or artificial ingredients which can effect the type and severity of potential corrosion. Both localized (perforation) and uniform corrosion (metal dissolution without the onset of pitting) may occur in the can. A quick test or series of tests which could predict the propensity towards both types of corrosion would be useful to the manufacturer. Electrochemical noise data is used to detect the onset and continuation of pitting corrosion. Specific noise parameters such as the noise resistance (the potential noise divided by the current noise) have been used to both detect pitting corrosion and also to estimate the pitting severity. The utility of noise resistance and other electrochemical parameters has been explored through the application of artificial neural networks. The versatility of artificial neural networks is further demonstrated by combing electrochemical data with electrolyte properties such as pH and chloride concentration to predict both the severity of both localized and uniform corrosion.

• Journal of Advanced Marine Engineering and Technology
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• 제40권10호
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• pp.883-887
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• 2016

This study aims to evaluate the corrosion behavior of a newly developed high-strength steel in marine environments. Metals used in seawater are easily deteriorated because of the presence of corrosive species such as chloride ions in it. Seawater causes much higher corrosion than fresh water. Thus, the corrosion of steel in marine environment has been recognized as a crucial problem in designing structures which cannot be cathodically protected. In this study, the corrosion resistance of a newly developed high-strength steel was evaluated. Four different specimens were tested to confirm the corrosion resistance. The exposure corrosion test was carried out by exposing the specimens to different marine environments such as atmospheric, tidal, splash, and submerged zones for two years. The specimens taken out from each location were cleaned ultrasonically and chemically prior to the evaluation of their corrosion resistance by the weight loss method. Finally, the pitting depth of the specimens was also measured to evaluate their pitting corrosion. The conditions used for the corrosion test were similar to the environmental conditions. The corrosion test results revealed that the corrosion rate and pitting corrosion of the newly developed high-strength steel was lower than that of the other carbon steels.

• Corrosion Science and Technology
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• 제16권5호
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• pp.247-256
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• 2017

The feasibility of using hydrazine for inhibiting pitting corrosion in copper sprinkler tubes was investigated by examining microscopical and structural evolution of corrosion by-products with SEM, EDS, and XRD. Hydrazine removed dissolved oxygen and reduced CuO and $Cu_2O$ as well. The stable phase was changed from CuO to $Cu_2O$ or Cu depending on hydrazine concentration. Hydrazine concentration of 500 ppm could convert all CuO corrosion by-products to $Cu_2O$. In a tightly sealed acryl tube filled with aqueous solution of 500 ppm hydrazine, octahedral $Cu_2O$ particles were formed while plate-like structures with high concentration of Cu, O, N and C were formed near a corrosion pit. The inside structure of a corrosion pit was not altered by hydrazine aqueous solution. Uniform corrosion of copper was almost completely stopped in aqueous solution of 500 ppm hydrazine. Corrosion potential of a copper plate was linearly dependent on log (hydrazine concentration). The concept of stopping pitting corrosion reaction by suppressing oxygen reduction reaction could be verified by applying this method to a reasonable number of real sprinkler systems before full-scale application.

• Corrosion Science and Technology
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• 제13권3호
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• pp.95-101
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• 2014

The pitting corrosion behaviors between the constituent phases in F53 super duplex stainless steel (SDSS) in acidified chloride environments were investigated using a critical pitting corrosion temperature test, a potentiodynamic anodic polarization test, and the microstructure analyses through a SEM-EDS and a SAM. As the solution annealing temperature decreased from $1150^{\circ}C$ to $1050^{\circ}C$, the ${\gamma}$-phase fraction increased whereas the ${\alpha}$-phase fraction decreased. The pitting potential and the critical pitting temperature increased with a decrease of solution annealing temperature, thereby increasing the resistance to pitting corrosion. The pitting corrosion of the SDSS was selectively initiated at the ${\alpha}$-phases because the PREN (pitting resistance equivalent number, PREN = %Cr+3.3%Mo+30%N) value of the ${\gamma}$-phase is much larger than that of the ${\alpha}$-phase, irrespective of the solution annealing temperature. The pitting corrosion was finally propagated from the ${\alpha}$-phase to the ${\gamma}$-phase. The decrease of solution annealing temperature enhanced the resistance to pitting corrosion greatly in acidified chloride environments due to a decrease of PREN difference between the ${\gamma}$-phase and the ${\alpha}$-phase, that is, a decrease of $PREN{\gamma}$ by dilution of N in ${\gamma}$-phase with an increase in the ${\gamma}$-phase volume fraction and an increase of $PREN{\alpha}$ by enrichment of Cr and Mo in the ${\alpha}$-phase with a decrease in the ${\alpha}$-phase volume fraction.

• 한국표면공학회지
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• 제39권1호
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• pp.18-24
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• 2006

Although stainless steels have the excellent corrosion resistance by passive film, they are susceptible to pitting corrosion in the environment containing halogen elements such as chloride ions. The resistance to pitting corrosion can be evaluated by measuring the critical pitting temperature (CPT). CPT values can be obtained using immersion, potentiodynamic and potentiostatic polarization test methods. Results on duplex 2205 stainless steels showed that CPT values were measured as $50^{\circ}C,\;55^{\circ}C\;and\;61^{\circ}C$, respectively for immersion, potentiodynamic and potentiostatic polarization test methods, depending upon the different test methods, even though the difference between CPT values are not much.

• 한국환경보건학회지
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• 제33권1호
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• pp.43-48
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• 2007

This study investigated the effects of pH, alkalinity, and chlorine ion which are important water quality impact factors to the corrosion in the simulated distribution system where the copper pipe is affixed. The result shows that pitting index was increased as the alkalinity and chloride ion increase in the distilled water, but there was no relation to pH. Actually the uniform corrosion rate was decreased as the pH increase with the laboratory tap water. In conclusion, it is necessary to control the pH which stands above minimum 7.5 to prevent pitting corrosion in the copper pipe. Consequently, comprehensive research about the effect of lime soda($Ca(OH)_2$) which was used as a coagulation additive in the water treatment plant to pipe corrosion must be accomplished additionally.

• Corrosion Science and Technology
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• 제6권6호
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• pp.316-321
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• 2007

The effect of annealing on the pitting corrosion resistance of anodized Al-Mg alloy (AA5052) processed by equal-channel angular pressing (ECAP) was investigated by electrochemical techniques in a solution containing 0.2 mol/L of $AlCl_3$ and also by surface analysis. The Al-Mg alloy was annealed at a fixed temperature between 473 and 573 K for 120 min in air after ECAP. Anodizing was conducted for 40 min at $100-400A/m^2$ at 293 K in a solution containing 1.53 mol/L of $H_2SO_4$ and 0.0185 mol/L of $Al_2(SO_4)_3$. The internal stress generated in anodic oxide films during anodization was measured with a strain gauge to clarify the effect of ECAP on the pitting corrosion resistance of anodized Al-Mg alloy. The time required to initiate the pitting corrosion of anodized Al-Mg alloy was shorter in samples subjected to ECAP, indicating that ECAP decreased the pitting corrosion resistance. However, the pitting corrosion resistance was greatly improved by annealing after ECAP. The time required to initiate pitting corrosion increased with increasing annealing temperature. The strain gauge attached to Al-Mg alloy revealed that the internal stress present in the anodic oxide films was compressive stress, and that the stress was larger with ECAP than without. The compressive internal stress gradually decreased with increasing annealing temperature. Scanning electron microscopy showed that cracks occurred in the anodic oxide film on Al-Mg alloy during initial corrosion and that the cracks were larger with ECAP than without. The ECAP process of severe plastic deformation produces large internal stresses in the Al-Mg alloy; the stresses remain in the anodic oxide films, increasingthe likelihood of cracks. It is assumed that the pitting corrosion is promoted by these cracks as a result of the higher internal stress resulting from ECAP. The improvement in the pitting corrosion resistance of anodized AlMg alloy as a result of annealing appears to be attributable to a decrease in the internal stresses in anodic oxide films

• Corrosion Science and Technology
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• 제14권4호
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• pp.184-189
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• 2015

In this study, the combined effect of chloride and thiosulfate ions and the effect of the ratio of the two ions on passivation in 304L, 316L, and the duplex stainless steels 2101 and 2205 are investigated using potentiostatic scratch tests. Cyclic polarization and the scratch tests were used to understand the role of anions on localized corrosion in these systems. It was found that the thiosulfate pitting began at a lower potential for 2101 than 304L in 0.6 M NaCl + 0.03 M $Na_2S_2O_3$ solution. The pit morphologies for 304L, 316L, and 2101 in an 0.6 M NaCl + 0.03 M $Na_2S_2O_3$ solution were very different from each other. The results indicate that the pitting switches from predominately thiosulfate pitting to chloride pitting at approximately 0.1 V.