• Journal of Surface Science and Engineering
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• v.50 no.4
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• pp.259-265
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• 2017

5000 series aluminium alloys and austenitic stainless steels have excellent corrosion resistance and sufficient strength, which are widely used as materials for marine equipment and their parts in the marine environment. The corrosion characteristics of materials are important factors for selecting the appropriate material due to fluid component changes in the estuarine and coastal areas where seawater and fresh water are mixed. Therefore, for 5083 Al alloy, STS304 and STS316L widely used in the marine environment, anodic polarization experiments were performed to compare the corrosion damage characteristics of each material by three kinds of solutions of 100 % tap water, 50 % tap water+50 % natural seawater and 100 % natural seawater. As a result of the anodic polarization experiments, aluminum alloy (5083) caused locally corrosion on the surface in the tap water, and corrosion damage occurred all over the surface when the seawater was included. Stainless steels (STS304 and STS316L) presented almost no corrosion damage in tap water, but they grew pitting corrosion damage with increasing seawater concentration. STS316L showed better corrosion resistance than STS304.

• Corrosion Science and Technology
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• v.8 no.3
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• pp.119-125
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• 2009

Corrosion assessment has a number of uses but the use considered here is as a precursor to Risk-Based Inspection (RBI) planning. Systematic methods consisting of technical modules of RBI program were used to assess the effect of specific corrosion mechanism on the probability of failure in equipments of petrochemical plants. Especially in part of the damage and corrosion assessment, screening step involved evaluating the combinations of process conditions and construction materials for each equipment item in order to determine which damage mechanisms are potentially active. For general internal corrosion, either API 510 or API 570 was applied as the damage rate in the calculation to determine the remaining life and inspection frequency. In some cases, a measured rate of corrosion may not be available. The technical modules of RBI program employ default values for corrosion, typically derived from published data or from experience with similar processes, for use until inspection results are available. This paper describes the case study of corrosion and damage assessment by using RBI methodology in petrochemical plant. Specifically, this paper reports the methodology and the results of its application to the petrochemical units using the $KGS-RBI^{TM}$ program, developed by the Korea Gas Safety Corporation to suit Korean situation in conformity with API 581 Codes.

• Journal of Surface Science and Engineering
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• v.49 no.5
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• pp.423-430
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• 2016

In this study, we investigated the corrosion damage characteristics of steel for offshore wind turbine tower substructure using an accelerated electrochemical test. The galvanostatic corrosion test method was employed with a conventional 3 electrode cell in natural sea water, and the steel specimen was served as a working electrode to induce corrosion in an accelerated manner. Surface and cross-sectional image of the damaged area were obtained by optical microscope and scanning electron microscope. The weight of the specimens was measured to determine the gravimetric change before and after corrosion test. The result revealed that the steel tended to suffer uniform corrosion rather than localized corrosion due to active dissolution reaction under the constant current regime. With increasing galvanostatic current density, the damage depth and surface roughness of surface was increased, showing approximately 25 times difference in damage depth between the lowest current density ($1mA/cm^2$) and the highest current density ($200mA/cm^2$). The gravimetric observation showed that the weight loss was proportionally increased with increment of current density that has 75 times different according by experimental conditions. Consequently, uniform corrosion of the steel specimen was conveniently induced by the electrochemically accelerated corrosion technique, and it was possible to control the extent of the corrosion damage by varying the current density.

• Corrosion Science and Technology
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• v.20 no.5
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• pp.281-288
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• 2021

Due to advancement of the industry, operation of a device in a harsh environment is increasing. Especially, the marine environment contains Cl^- ions which causes localized corrosion such as pitting and crevice corrosion of stainless steel and various metals. In this study, electrochemical corrosion behaviors of austenitic stainless steel (STS 316L) and nickel alloy (Inconel 600) with different seawater concentrations (fresh water, seawater, mixed water) were investigated. The STS 316L and Inconel 600 were etched in 10% oxalic acid and composed of an austenitic phase. Results of Tafel analysis in seawater showed that STS 316L and Inconel 600 presented the highest corrosion current densities of 7.75 × 10^-4 mA/cm² and 1.11 × 10^-4 mA/cm² and the most negative pitting potentials of 0.94 V and 1.06 V, respectively. The maximum damage depths and surface damage ratio by pitting corrosion increased with chloride concentration. The STS 316L had higher PREN than Inconel 600. However, the surface damage and weight loss of Inconel 600 were superior to STS 316L. It was difficult to compare the pitting resistance of STS 316L based on Fe and Inconel 600 based on Ni with PREN simply.

• Corrosion Science and Technology
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• v.20 no.6
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• pp.435-450
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• 2021

The interest in eco-friendly energy is increasing, and polymer electrolyte membrane fuel cell (PEMFC) is attracting attention as alternative power sources. Research on metallic bipolar plates, a fuel cell component, is being actively conducted. However, since the operating conditions of PEMFC, in which sulfuric acid (H₂SO₄) and hydrofluoric acid (HF) are mixed, are strong acidity, the durability of the metallic bipolar plate is very important. In this research, the electrochemical characteristics and corrosion damage behavior of 316L stainless steel, a material for metallic bipolar plates, were analyzed through potentiostatic corrosion tests with test times and chloride concentrations. As the test times and chloride concentrations increased, the current density and corrosion damage increased. As a result of observation with scanning electron microscope(SEM) and 3D microscope, both the depth and width of pitting corrosion increased with increases in test times and chloride concentrations. In particular, the pitting corrosion damage depth at test conditions of 6 hours and 1000 ppm chloride increased the most. The growth of the pitting corrosion damage was not directly proportional to time and increased significantly after a certain period.

• 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 ℃.

• KIEAE Journal
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• v.7 no.4
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• pp.141-146
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• 2007

It is necessary to guarantee the safety, serviceability and durability of reinforced concrete structures over their service life. However, concrete structures represent a decrease in their durability due to the effects of external environments according to the passage of time, and such degradation in durability can cause structural degradation in materials. In concrete structures, some degradations in durability increase the corrosion of embedded rebars and also decrease the structural performance of materials. Thus, the structural condition assessment of RC materials damaged by corrosion of rebars becomes an important factor that judges needs to apply restoration. In order to detect the damage of reinforced concrete structures, a visual inspection, a nondestructive evaluation method(NDE) and a specific loading test have been employed. However, obscurities for visual inspection and inaccessible members raise difficulty in evaluating structure condition. For these reasons, detection of location and quantification of the damage in structures via structural response have been one of the very important topics in system identification research. The main objective of this project is to develope a methodologies for the damage identification via static responses of the members damaged by durability. Six reinforced concrete beams with variables of corrosion position and corrosion width were fabricated and the damage detections of corroded RC beams were performed by the optimization and the conjugate beam methods using static deflection. In results it is proved that the conjugate beam method could predict the damage of RC members practically.

• Journal of Surface Science and Engineering
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• v.50 no.5
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• pp.332-338
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• 2017

In this study, we evaluated tendency and degree of corrosion damages of Inconel 600 after chemical decontamination treatments under three different conditions. In the decontamination processes, the oxidation and reduction were performed as one cycle. Each process was continued up to 5 cycles. Characteristics of corrosion under decontamination processes were evaluated by Tafel analysis and weight loss. Characteristics of surface damage were observed by scanning electron microscope(SEM) and three-dimensional(3D) microscope. As the cycle proceeded, weight loss and corrosion current density increased. Intergranular corrosion damage occurred on the surface of the materials. The result revealed that the surface of Inconel 600 was attacked by the strong acid solution under all chemical decontamination processes, but the degree of the corrosion damage was different depending on the processes.

• Journal of Surface Science and Engineering
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• v.51 no.5
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• pp.291-296
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• 2018

In this study, we carried out an ultrasonic-chemical decontamination process with immersion type, reproduced in the laboratory. The corrosion damage characteristics, depending on kind of materials and ultrasonic process time, were investigated. Inconel 600, which showed lower corrosion potential and higher corrosion current density than that of STS 316, revealed severer corrosion damage and higher weight-loss rate than STS 316. Weight-loss rate of Inconel 600 increased with increasing ultrasonic process time. On the other hands, STS 316 presented a negligibly small corrosion damage, which was almost indistinguishable from visual observation. There was no effect of ultrasonic process time on the weight-loss rate of STS 316.

• Corrosion Science and Technology
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• v.19 no.4
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• pp.231-231
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• 2020