• Corrosion Science and Technology
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• v.20 no.5
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• pp.266-280
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• 2021

Since 2020, the International Maritime Organization (IMO) has updated regulations on the sulfur content to be less than 0.5% in exhaust gas emitted from ships. Accordingly, the exhaust gas post-treatment device for ships, which is SOx/NOx reduction technology, was introduced. However, the exhaust gas post-treatment device is suffering corrosion because of the harsh corrosive environment formed by sulfate and chlorine oxide through the desulfurization process. In this investigation, cyclic potentiodynamic polarization (CPDP) experiment for UNS S31603 and UNS N08367 was performed in a green death solution that simulates the environment of a desulfurization device. The corrosion rate of UNS S31603 at the highest temperature was about 3 times higher than that of UNS N83067. Also, electron microscope scan revealed corrosion type UNS N83067 presents intergranular corrosion tendency. On the other hand, UNS S31603 was observed as general corrosion. The α values of UNS N08367 at 30 ℃ and 60 ℃ were higher than those of UNS S31603, thus UNS N08367 is considered to have a higher local damage tendency. Whereas, since the α value of UNS S31603 at 90 ℃ is larger than that of UNS N08367, UNS S31603 is considered to have a higher local damage trend.

• Corrosion Science and Technology
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• v.20 no.6
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• pp.391-402
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• 2021

In this investigation, the electrochemical characteristics of superaustenitic and general austenitic stainless steels were compared by conducting potentiodynamic polarization experiment with varying temperatures in natural seawater solution. From the result of the potentiodynamic polarization experiment, the corrosion rate of UNS S31603 was found to be 17 times faster than that of UNS N08367 under the most severe corrosion conditions. The relationship between the corrosion rate by maximum damage depth and the corrosion rate by the corrosion current density was expressed as α value for each stainless steel. The α value of UNS S31603 under all temperature conditions was higher than that of UNS N08367 under similar conditions. This means that UNS S31603 is more prone to localized corrosion than UNS N08367. UNS S31603 expressed pitting type damages under all temperature conditions as shown by SEM analysis results. The pitting damage rapidly grew at the relatively poor grain boundaries. Damage on UNS N08367 was not clearly represented at 30 ℃ and 60 ℃, and slight intergranular corrosion damage was observed on the entire surface at 90 ℃.

• Corrosion Science and Technology
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• v.21 no.2
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• pp.138-146
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• 2022

The cavitation and potentiodynamic polarization experiments were conducted simultaneously to investigate the effect of cavitation amplitude on the super austenitic stainless steel (UNS N08367) electrochemical behavior in seawater. The results of the potentiodynamic polarization experiment under cavitation condition showed that the corrosion current density increased with cavitation amplitude increase. Above oxygen evolution potential, the current density in a static condition was the largest because the anodic dissolution reaction by intergranular corrosion was promoted. In the static condition, intergranular corrosion was mainly observed. However, damage caused by erosion was observed in the cavitation environment. The micro-jet generated by cavity collapse destroyed the corrosion product and promoted the repassivation. So, weight loss occurred the most in static conditions. After the experiment, wave patterns were formed on the surface due to the compressive residual stress caused by the impact pressure of the cavity. Surface hardness was improved by the water cavitation peening effect, and the hardness value was the highest at 30 ㎛ amplitude. UNS N08367 with excellent mechanical performance due to its high hardness showed that cavitation inhibited corrosion damage.

• Corrosion Science and Technology
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• v.20 no.6
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• pp.412-425
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• 2021

Because austenitic stainless steel causes localized corrosion such as pitting and crevice corrosion in environments containing chlorine, corrosion resistance is improved by surface treatment or changes of the alloy element content. Accordingly, research using cyclic potentiodynamic polarization experiment to evaluate the properties of the passivation film of super austenitic stainless steel that improved corrosion resistance is being actively conducted. In this investigation, the electrochemical properties of austenitic stainless steel and super austenitic stainless steel were compared and analyzed through cyclic potentiodynamic polarization experiment with varying temperatures. Repassivation properties were not observed in austenitic stainless steels at all temperature conditions, but super austenitic stainless steels exhibited repassivation behaviors at all temperatures. This is expressed as α values using a relational formula comparing the localized corrosion rate and general corrosion rate. As the α values of UNS S31603 decreased with temperature, the tendency of general corrosion was expected to be higher, and the α value of UNS N08367 increased with increasing temperatures, so it is considered that the tendency of localized corrosion was dominant.

• Corrosion Science and Technology
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• v.23 no.2
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• pp.154-165
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• 2024

Acetic acid and acetonitrile produced in the chemical process of petrochemical plants are used at high temperatures and pressures. They are exposed to harsh corrosive environments. The present investigation aimed to evaluate corrosion characteristics of metals with excellent corrosion resistance by performing immersion and electrochemical experiments with different composition ratios of acetic acid and acetonitrile in a high-temperature and high-pressure environment. Results of immersion experiment revealed that as acetic acid concentration increased, surface damage and corrosion also increased. In immersion experiments under all conditions, super austenitic stainless steel (UNS N08367) had the best corrosion resistance among various metals. The maximum damage depth under the most severe immersion conditions was observed to be 4.19 ㎛, which was approximately 25.25 ㎛ smaller than that of highly damaged stainless steel (UNS S31804). As a result of electrochemical experiments, electrochemical characteristics of various metals presented some differences with different composition ratios of acetic acid and acetonitrile. However, super austenitic stainless steel (UNS N08367) had the best corrosion resistance at a high pressure condition with a high concentration of acetic acid.

• Corrosion Science and Technology
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• v.22 no.3
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• pp.164-174
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• 2023

Electropolishing technology uses an electrochemical reaction and improves surface roughness, glossiness, and corrosion resistance. In this investigation, electropolishing was performed to improve the corrosion resistance of super austenitic stainless steel. As a result of electropolishing, surface roughness (0.16 ㎛) was improved by about 76.5% compared to mechanical polishing (0.68 ㎛). In addition, the electropolished surface was smooth because the average and variance values of the depth histogram were small. Tafel analysis was performed after a potentiodynamic polarization experiment with seawater temperature, and the microstructure was compared and analyzed. The corrosion current density at 30 ℃, 60 ℃, and 90 ℃ was reduced by 0.083 ㎂/cm², 0.296 ㎂/cm², and 0.341 ㎂/cm², respectively. Pitting occurred in the mechanical polished specimen at 30 ℃, but partial intergranular corrosion was observed in the electropolished specimen, and pitting occurred predominantly at both 60 ℃ and 90 ℃. In addition, the damage depths of the electropolished specimen were shallower than those of mechanical polishing at 30 ℃ and 60 ℃, but the opposite result was seen at 90 ℃.