• Journal of Ocean Engineering and Technology
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• v.22 no.5
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• pp.100-105
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• 2008

A106 Carbon Steel has recently been used as the material for pipes, nozzles, and tank shells in nuclear power plants. Its corrosion resistance gives the steel many advantages for use in structures under high temperature and high pressure. This steel is also expected to be used as a structural material in the shipbuilding industry for applications involving severe conditions, such as high temperature and pressure. In this study, the mechanical properties of A106 carbon steel were evaluated in regard to its corrosion times. The tensile and yielding strengths decreased as the corrosion time increased. In particular, the tensile strength was influenced by corrosion. In addition, an acoustic emission (AE) technique was used to clarify the microscopic damage to specimens that had undergone corrosion for a certain period. It was found that AE parameters, such as events, energy, duration time, and amplitude were useful for evaluating the degree of damage and remaining life of the corroded specimen. Various properties of the waveform and frequency range were also seen, based on the degree of damage to the specimen from the corrosion time.

• Nuclear Engineering and Technology
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• v.55 no.6
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• pp.2256-2262
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• 2023

The electrochemical corrosion behaviors of SA106 Grade B (SA106B) carbon steel in H₂SO₄4-N₂H₄ and H₂SO₄-N₂H₄-CuSO₄ solutions at 95 ℃ have been investigated with the addition of commercial corrosion inhibitors (CI#30 and No. 570S), to determine the stability of SA106B in the hydrazine-based reductive metal ion decontamination (HyBRID) process. The potentiodynamic polarization experiment revealed that the corrosion inhibitors were capable of lowering the corrosion rate of SA106B in H₂SO₄-N₂H₄ solution. It was found that the corrosion inhibitors induced formation of fixed surface layer on the carbon steel upon the corrosion. This corrosion inhibition performance was reduced in the presence of CuSO₄ in the solution owing to the chemical reactions between organic compounds in the corrosion inhibitors and CuSO₄. CI#30 showed a better corrosion inhibition effect in the H₂SO₄-N₂H₄-CuSO₄ solution. Although the corrosion inhibitors can provide better stability to SA106B in the HyBRID solution, their application should be carefully considered because it may result in reduced decontamination performance and increased secondary waste generation.

• Journal of the Korean Society for Heat Treatment
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• v.6 no.2
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• pp.98-106
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• 1993

Ultra high carbon steel (Fe-1.4%C) was prepared by means of a high frequency induction furnace. The preferred nucleation site of martensite was observed. The changes of hardness and impact thoughness due to tempering temperatures, and the spheroidization of cementite by controlled -rolling were also studied for the steel. The preferred nucleation site of martensite in the ultra high carbon steel is prior austenite grain boundary. The hardness of the steel is slightly increased up to about $300^{\circ}C$, and then decreased with further tempering temperature. However, the impact energy keeps a almost constant value, independent of the tempering temperature. The spheroidization of cementite is accelerated as the reduction in thickness per rolling pass is increased and the number of the rolling passes becomes greater.

• Korean Journal of Materials Research
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• v.33 no.3
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• pp.106-114
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• 2023

The carbon concentration in the carburized steels was measured by electron probe microanalysis (EPMA) for a range of soluted carbon content in austenite from 0.1 to 1.2 wt%. This study demonstrates the problems in carbon quantitative analysis using the existing calibration curve derived from pure iron (0.008 wt%C) and graphite (99.98 wt%C) as standard specimens. In order to derive an improved calibration curve, carbon homogenization treatment was performed to produce a uniform Kα intensity in selected standard samples (AISI 8620, AISI 4140, AISI 1065, AISI 52100 steel). The trend of detection intensity was identified according to the analysis condition, such as accelerating voltage (10, 15, 30 keV), and beam current (20, 50 nA). The appropriate analysis conditions (15 keV, 20 nA) were derived. When the carbon concentration depth profile of the carburized specimen was measured for a short carburizing time using the improved calibration curve, it proved to be a more reliable and accurate analysis method compared to the conventional analysis method.

• Corrosion Science and Technology
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• v.14 no.2
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• pp.47-53
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• 2015

Recently, the bending process is greatly applied to fabricate the pipe line. Bending process can reduce welding joints and then decrease the number of inspection. Thus, the maintenance cost will be reduced. Induction heat bending process is composed of bending deformation by repeated local heat and cooling. By this thermal process, corrosion properties and microstructure can be affected. This work focused on the effect of induction heating bending process on the properties of ASME SA106 Gr. C low carbon steel pipes. Microstructure analysis, hardness measurements, and immersion corrosion test were performed for base metal and bended area including extrados, intrados, crown up, and down parts. Microstructure was analyzed using an optical microscope and SEM. Hardness was measured using a Rockwell B scale. Induction heat bending process has influenced upon the size and distribution of ferrite and pearlite phases which were transformed into finer structure than those of base metal. Even though the fine microstructure, every bent area showed a little lower hardness than that of base metal. It is considered that softening by the bending process may be arisen. Except of I2, intrados area, the others showed a similar corrosion rate to that of base metal. But even relatively high rate of intrados area was very low and acceptable. Therefore, it is judged that induction heat bending process didn't affect boric acid corrosion behaviour of carbon steel.

• Nuclear Engineering and Technology
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• v.37 no.4
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• pp.375-384
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• 2005

To investigate the flow-accelerated corrosion (FAC) dependency of carbon steel (A106 Gr. B) and low-alloy steels (1Cr-1/2Mo, 21/4Cr-1Mo) on pH, orifice distance, and material, experiments were carried out. These experiments were performed using a flow velocity of 4 m/sec (partly 9 m/sec) at pH $8.0\~10.0$ in an oxygen-free aqueous solution re-circulated in an Erosion-Corrosion Test Loop at $130^{\circ}\;{\ldots}$ for 500 hours. The weight loss of the carbon steel specimens appeared to be positively dependent on the flow velocity. That of the carbon and low-alloy steel specimens also showed to be distinguishably dependent on the pH. At pH levels of $8.0\~9.5$ it decreased, but increased from 9.5 to 10.0. Utility water chemistry personnel should carefully consider this kind of pH dependency to control the water system pH to mitigate FAC of the piping system material. The weight loss of the specimens located further from the orifice in the distance range of $6.8\~27.2$ mm was shown to be greater, except for 21/4Cr-1Mo, which showed no orifice distance dependency. Low alloy steel specimens exhibited a factor of two times better resistance to FAC than that of the carbon steel. Based on this kind of FAC dependency of the carbon and low-alloy steels on the orifice distance and material, we conclude that it is necessary to alternate the composition of the secondary piping system material of NPPs, using low-alloy steels, such as 21/4Cr-1Mo, particularly when the system piping has to be replaced.

• Journal of the Korean institute of surface engineering
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• v.43 no.4
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• pp.205-210
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• 2010

The A106 Gr B low carbon steel, which was used in the electric power plants and heavy chemical plants, was welded by multi-pass arc welding. The heat affected zone (HAZ) formed by welding was corroded in acid chloride solution, or in saturated $H_2S$ containing acid chloride solution, or in saturated $H_2S$ containing acid chloride solution under applied current. In this order of corrosion solution, the rate of corrosion increased, because $H_2S$ accelerated the iron dissolution, hydrogen evolution, and the formation of nonprotective FeS, whereas the applied current accelerated the electrochemical reaction. The scales formed in acid chloride solution consisted primarily of $Fe_3O_4$, while those formed in $H_2S$ containing acid chloride solution consisted primarily of $Fe_3O_4$ and FeS.

• Transactions of the Korean Society of Automotive Engineers
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• v.15 no.3
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• pp.106-113
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• 2007

The effect of chemical composition on the microstructural change and tensile property in TRIP-assisted steels with different chemical composition was investigated by using SEM, TEM, XRD and UTM. As a result of microscopic observation, the morphology of retained austenite could be identified as two types : a granular type in a steel containing higher sillicon and a film type in a steel having higher carbon. For the case of higher carbon-containing steel with a tensile strength of 860 MPa and a total elongation of 38%, film-typed retained austenite could be observed between lath bainitic ferrite. Actually, metastable retained austenite was a requisite for the good formability, which means that chemical composition plays a significant role in the microstructure and tensile property of TRIP-assisted steels. With respect to tensile property, the steels containing suitable silicon and manganese, respectively, showed a typical TRIP effect in stress-strain curve, while a steel containing higher manganese content exhibited the assimilar behavior shown in dual phase steel.

• Nuclear Engineering and Technology
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• v.54 no.6
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• pp.2329-2333
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• 2022

Base metal corrosion forms a significant issue during the chemical decontamination of the primary coolant loop in nuclear power plants as it is directly related to the economic and safety viability of decommissioning. In this technical note, potentiodynamic evaluations of several base metals (304 stainless steel, SA106 Grade B carbon steel, and alloy 600) were performed to determine their corrosion behavior during the hydrazine (N₂H₄)-based reductive ion decontamination (HyBRID) process. The results suggested that N₂H₄ protected the surface of the base metals in the HyBRID solution, which is primarily composed of H₂SO₄. The corrosion resistance of the carbon steel was further improved through the addition of CuSO₄ to the solution. The corrosion rate of carbon steel in the H₂SO₄-N₂H₄-CuSO₄ solution was lower than that exhibited in an oxalic acid solution, a commonly used reaction medium during commercial decontamination processes. These results indicate the superiority of the HyBRID process with respect to the base metal stability.

• Corrosion Science and Technology
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• v.11 no.6
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• pp.257-262
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• 2012

Flow accelerated corrosion (FAC) of the carbon steel piping in nuclear power plants (NPPs) has been major issue in nuclear industry. Rotating cylinder FAC test facility was designed and fabricated and then performance of the facility was evaluated. The facility is very simple in design and economic in fabrication and can be used in material and chemistry screening test. The facility is equipped with on line monitoring of pH, conductivity, dissolved oxygen(DO), and temperature. Fluid velocity is controlled with rotating speed of the cylinder with a test specimen. FAC test of SA106 Gr. B carbon steel under 4 m/s flow velocity was performed with the rotating cylinder at DO concentration of less than 1 ppb and of 1.3 ppm. Also a corrosion test of the carbon steel at static condition, that is at zero fluid velocity, of test specimen and solution was performed at pH from 8 to 10 for comparison with the FAC data. For corrosion test in static condition, the amount of non adherent corrosion product was almost constant at pH ranging from 8 to 10. But adherent corrosion product decreased with increasing pH. This trend is consistent with decrease of Fe solubility with an increase in pH. For FAC test with rotating cylinder FAC test facility, the amount of non adherent corrosion product was also almost same for both DO concentrations. The rotating cylinder FAC test facility will be further improved by redesigning rotating cylinder and FAC specimen geometry for future work.