• Transactions of the Korean Society of Mechanical Engineers A
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• v.39 no.1
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• pp.27-35
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• 2015

The material properties of crack growth models at an elevated temperature were derived from the results of numerous crack growth tests for Mod.9Cr-1Mo (ASME Grade 91) steel specimens under fatigue loading and creep loading at an elevated temperature. These crack growth models were needed for defect assessment under creep-fatigue loading. The mathematical crack growth rate models for fatigue crack growth (FCG) and creep crack growth (CCG) were determined based on the test results, and the models were compared with those of the French design code RCC-MRx to investigate the conservatism of the code. The French design code RCC-MRx provides an FCG model and a CCG model for Grade 91 steel in Section III Tome 6. It was shown that the FCG model of RCC-MRx is conservative, while the CCG model is non-conservative compared with the present test data. Thus, it was shown that further validation of the property was required. Mechanical strength tests and creep tests were also conducted, and the test results were compared with those of RCC-MRx.

• Transactions of the Korean Society of Pressure Vessels and Piping
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• v.20 no.1
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• pp.66-74
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• 2024

This study investigates the effects of temperatures and strain rates on the strength and ductility of Gr.91 (ASME Grade 91) steel which is widely being used as a heat-resistant material in Generation IV nuclear and super critical thermal power plants. The tensile behavior of modified 9Cr-1Mo (Gr.91) steel was studied for the three strain rates of 6.67×10^-5/s, 6.67×10^-4/s and 6.67×10-3/s over the temperature range from room temperature (RT) to 650℃. Experimental results showed that at specific combinations of temperatures (300~400℃) and strain rates, serrations appeared in the stress-strain curves. Concurrently, abnormal behaviors such as a plateau in yield strength and tensile strength, a minimum in ductility and negative strain rate sensitivity were observed. These phenomena were analyzed as significant characteristics of dynamic strain aging (DSA). Since this abnormal behavior in Gr.91 steel affects the material strength, it is judged that a correlation analysis between DSA and material strength should be crucial in the design and integrity evaluation of Gr. 91 steel pressure vessel and piping subjected to high-temperature loading.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.39 no.12
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• pp.1257-1263
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• 2015

A correlation between the transient regime and steady state regime on the creep crack growth (CCG) for Grade 91 steel, which is used as the structural material for the Gen-IV reactor systems, was investigated. A series of CCG tests were performed using 1/2" CT specimens under a constant applied load and at a constant temperature of $600^{\circ}C$. The CCG rates for the transient and steady state regimes were obtained in terms of $C^*$ parameter. The transient CCG rate had a close correlation with the steady-state CCG rate, as the slope of the transient CCG data was very similar to that of the steady state data. The transient rate was slower by 5.6 times as compared to the steady state rate. It can be inferred that the steady state CCG rate, which is required for long-time tests, can be predicted from the transient CCG rate obtained from short-time tests.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.34 no.1
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• pp.103-110
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• 2010

In this study, an assessment method on creep-fatigue crack initiation and crack growth for a Mod.9Cr-1Mo steel (ASME Grade 91) structure has been developed with an extension of the French RCC-MR A16 procedure. The current A16 guide provides defect assessment procedure for a creep-fatigue crack initiation and crack growth for an austenitic stainless steel, but no guideline is available yet for a Mod.9Cr-1Mo steel which is now widely being adopted for structural materials of future nuclear reactor system as well as ultra super critical (USC) thermal plant. In the present study an assessment method on creep-fatigue crack initiation and crack growth is provided for the FMS (Ferritic-Martensitic Steel) and assessment on the creep-fatigue crack behavior for a structure has been carried out. The assessment results were compared with the observed images from a structural test.

• Journal of Power System Engineering
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• v.19 no.5
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• pp.45-51
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• 2015

Grade 91 steel is used for the major structural components of Generation-IV reactor systems such as a very high temperature reactor (VHTR) and sodium-cooled fast reactor (SFR). Since these structures are designed for up to 60 years at elevated temperatures, the prediction of long-term creep life is very important to determine an allowable design stress of elevated temperature structural component. In this study, a large body of creep rupture data was collected through world-wide literature surveys, and using these data, the long-term creep life was predicted in terms of three methods: Larson-Miller (L-M), Manson-Haferd (M-H) and Wilshire methods. The results for each method was compared using the standard deviation of error. The L-M method was overestimated in the longer time of a low stress. The Wilshire method was superior agreement in the long-term life prediction to the L-M and M-H methods.

• Journal of the Korean Recycled Construction Resources Institute
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• v.11 no.1
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• pp.62-69
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• 2023

For the nuclear power concrete plant structures in the UAE, it is necessary to consider the deterioration from high sulfate ions in the atmosphere and high chloride ions from the coast. In this study, two strength grade concrete mixture (40 MPa and 27 MPa) and two curing/diffusion temperatures (20 ℃ and 50 ℃) were considered for evaluating the temperature effects on diffusion and strength due to high average temperature above 38 ℃ a year in UAE. When the initial curing temperature was high, the compressive strength increased in high-temperature curing to 7 days, but the strength slightly increased in the 20 ℃ curing condition at 28 days. Regarding diffusion test, unlike the compressive test results, reduced chloride diffusion coefficients were evaluated both in 40 MPa and 27 MPa grade at 28 days. In the case of 91 days of curing, an increase in diffusivity due to high temperature and a decrease in diffusivity due to age effect occur simultaneously. Compared to the results of the curing and diffusion tests at 20 ℃ and 28 days, when the curing and diffusion tests were conducted at 50 ℃ in 91 days, the diffusion coefficients decreased to 76.2 % in 40 MPa grade and 85.4 % in 37 MPa grade with increasing curing period, respectively.

• Transactions of the KSME C: Technology and Education
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• v.4 no.2
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• pp.101-109
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• 2016

The material properties of heat resistant materials at power plants are affected by thermal aging as operating time is accumulated. In this study, the influence of thermal aging on yield strength, tensile strength and fracture behavior for Mod.9Cr-1Mo (ASME Grade 91) steel which is a material widely adopted for Generation IV nuclear energy system has been investigated and analyzed. Service exposed Gr.91 steel materials sampled from a piping system of an ultra-supercritical (USC) plant in Korea with accumulated operation time of 73,716 hours were used for material testing. The test results of the service exposed material specimens were compared with those of the virgin Gr.91 steel specimens. Those test data were compared with the material properties of ASME code and RCC-MRx code. Conservatisms of the material properties in the design codes have been quantified based on the comparisons of those from virgin and service exposed material specimens.

• Transactions of the Korean Society of Pressure Vessels and Piping
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• v.16 no.1
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• pp.74-83
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• 2020

A number of so-called 'Type IV' cracking was reported to occur at the welded joints of the P91 steel or P92 steel reheat steam piping systems in Korean supercritical thermal power plants. The reheat steam piping systems are subjected to severe thermal and pressure loading conditions of coolant higher than 570℃ and 4MPa, respectively. In this study, piping analyses and design evaluations were conducted for the piping system of a specific thermal plant in Korea and suggestions were made how structural integrity could be improved so that type IV cracks at the welded joints could be prevented. Integrity evaluations were conducted as per ASME B31.1 code with implicit consideration of creep effects which was used in original design of the piping system and as per nuclear-grade RCC-MRx code with explicit consideration of creep effects. Comparisons were made between the evaluation results from the two design rules. Another approach with modification or reduction of the redundant supports in the piping systems was investigated as a tool to mitigate thermal stresses which should essentially contribute to prevention of Type IV cracking without major modification of the existing piping systems. In addition, a post weld heat treatment method and repair weld method which could improve integrity of the welded joint of P91 steel were investigated.

• Journal of Korean Society of Forest Science
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• v.110 no.1
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• pp.91-105
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• 2021

We conducted a study to identify the relationships between the investigated factors and provide a methodology and generate data by applying deterioration classes to the Seonjaryeong Forest Trail (4.3 km) in the Baekdudaegan Ridge. The average trail width (1.7 m) and bare width (1.4 m) were wider than those obtained in the previous studies. The frequency of trail deterioration was also high. Specific data on deterioration classes were obtained and evaluated using qualitative criteria. Specific data for heavy class stands at 20.1% in trail grade, 13.3 cm on average, and 16.1 cm in the center of erosion depth, 16.2 cm of CSA, 12.3 kg/cm (20.1 mm) on average and maximum 39.3 kg/cm (29.6 mm) of soil hardness. We observed a positive correlation between the deterioration class and trail grade, and the average and maximum soil erosion depths of the hill side were deeper than those of the ridge. The soil hardness data showed a statistically significant difference in terms of the transect site and calculation method (㎏/㎠, mm). Therefore, trail deterioration was observed at the sites having ≥20% trail grade; thus, continuous monitoring at fixed sites over time will be required for sustainability. Furthermore, the trail grade should be of the utmost priority in trail design and management.

• Journal of Acupuncture Research
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• v.19 no.5
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• pp.149-160
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• 2002

Objetive : To evaluate the effect of treatment for Heel Pain by using Bee-venom Acupuncture that is well known for anti-inflamatory effect and function of activating immunine system. Methods : We investigated 32 cases of patient with Heel Pain. From 1th November 2001 to 30th June 2002, 32 cases of patient with Heel Pain treated at the Department of Acupuncture & Moxibustion of Kyung-won University Oriental Hospital were selected for two group. One group was treated by Bee-venom Acupuncture therapy (Bee-venom Acupuncture Group : BAG), the other group was treated by Common Acupuncture therapy (None Bee-venom Acupuncture Group : NBAG). Both group were composed of 16 patients. After treatment, we evaluated the effects per each group. Results : 1. In the distribution by sex & age : 5 cases were male, 11 cases were female in BAG. 10 cases were male, 6 cases were female in NBGA. Forty aged cases were the most in BAG. Thirty aged cases were the most in NBAG. 2. Assessment of treatment by therapeutic frequency : 14 cases(87.5%) were above "Fair" within 6 times in BAG, 7 cases(43.8%) were above "Fair" beyond 10 times. 3. Assessment of treatment : Excellent were 9 cases, Good 5 cases, Fair 2 cases in BAG, Excellent were 2 cases, Good 7 cases, Fair 2 cases, Poor 5 cases in NBAG. Therapeutic effect above "Fair" were 16 cases(100%) in BAG, 11 cases(68.8%) in NBAG. 4. Comparing BAG with NBAG by therapeutic frequency and assessment in Grade II state : 11 cases(91.7%) were above "Good" within 6 times in BGA, 3 cases (57.1%) above "Fair" beyond 10 times. 5. About average frequency of treatment in the distribution of Grade : Grade III was 5.3 times, Grade II 4.0 times in BGA, whereas Grade III 16.0 times, Grade II 8.4 times in NBGA. Conclusions : In the treatment of Heel Pain, the Bee-venom Acupuncture can be regarded as more useful method in the clinical practice, because it has comparatively shorter duration of treatment and is more effective.