Woo-Seog Ryu

Oxidation behaviors of wrought nickel-based superalloys in various high temperature environments

Abstract Oxidation characteristics of Alloy 617 and Haynes 230 at 900 °C in simulated helium environment, hot steam environment containing H 2 as well as in air and pure helium conditions were investigated. Compared to air condition, the oxidation rate of Alloy 617 was not significantly affected in helium and hot steam environments, while Haynes 230 showed lower oxidation rate in helium environment. On the other hand, the oxide morphology and structure of Alloy 617 were strongly affected by the environments, but those of Haynes 230 were less dependent on the environments. For Haynes 230, a Cr 2 O 3 inner layer and a protective MnCr 2 O 4 outer layer were formed in all environments, which contributed to the better oxidation resistance. As the mechanical properties, such as creep and tensile properties, were significantly affected by the oxidation behaviors, surface treatment methods to enhance oxidation resistance of these alloys should be developed.

Probabilistic Analysis of the Creep Crack Growth Rate of Type 316LN Stainless Steel by the Monte Carlo Simulation

This paper presents a probabilistic analysis for evaluating the creep crack growth rate (CCGR) of type 316LN stainless steel. The CCGR data was obtained from the creep crack growth tests, which are conducted under various applied loads at 600°C. The crack growth rate was characterized as a function of the C* fracture parameter. In order to logically obtain the B and q values in the CCGR equation of a=B(C*)q, three methods of the least square fitting method (LSFM), a mean value method (MVM), and a probabilistic distribution method (PDM) were adopted. Also, using the Monte Carlo simulation, a number of random variables was generated, and the CCGR lines were predicted probabilistically. The three methods did not show a large difference in the CCGR lines, but the PDM was most useful because the CCGR line can be evaluated with a probabilistic reliability. Both the B and q coefficients followed a lognormal distribution, even though the B ones were a little scattered for the points of the data. In the case of a standard deviation of 1 σ for the probability variables, P (B,q), the results of the MCS and the PDM for the distribution ranges of the CCGR lines were compared and discussed.

Creep-Life Prediction and Its Error Analysis by the Time Temperature Parameters and the Minimum Commitment Method

To predict long-term creep life from short-term creep life data, various parametric methods such as Larson-Mille. (L-M), Orr-Sherby-Dorn (O-S-D), Manson-Haferd (M-H) parameters, and a Minimum Commitment Method (MCM) were suggested. A number of the creep data were collected through literature surveys and experimental data produced in KAERI. The polynomial equations for type 316LN SS were obtained by the time-temperature parameters (TTP) and the MCM. Standard error (SE) and standard error of mean (SEM) values were obtained and compared with the each method for various temperatures. The TTP methods showed good creep-life prediction, but the MCM was much superior to the TTP ones at and . It was found that the MCM were lower in the SE values when compared to the TTP methods.

Regulatory Clearance of Spent Steel Drums

At KAERI (Korea Atomic Energy Institute), radioactive soil and concrete wastes with extremely low level of activity were regulatory cleared in 2008 and large amount of spent drums remained. After generation, drums having good physical integrity reused for packaging radioactive wastes and about 50 tons of drums unsuitable for reuse were stored as radioactive wastes. Having once been used for packaging regulatory cleared radioactive wastes, these spent drums were determined to be regulatory cleared. Before regulatory clearance, steel drums were radiation monitored, washed with pressurized water two times, compacted and stored at a designated area. Based on radiological dose assessment results using a recycling scenario derived from actual situation, the regulatory clearance of steel drums was permitted by the regulatory body. Treatment of the regulatory cleared drums was then committed to a scrap-metal dealer for recycling. In this study, a process of regulatory clearance for spent steel drums and a modified radiological dose assessment model for staff members of a scrap-metal dealer will be discussed.Copyright

Feasibility Study on the Nuclide Analysis of the Radwaste Drum Using the Spectrum to Dose Conversion Factor

Estimating the radioisotope inventory of a drum based on the measured dose rate information, which is called as the dose to curie (DTC) conversion [1–3], has been known that there could be extremely high uncertainty associated with establishing the radioactivity of gamma emitters in a drum. However, the DTC method is still an effective assay method to calculate the radioisotope inventory because of their simple and easy procedures to be applied. To make the DTC method practical, numerous assumptions have to be made and limitations placed on its use. These assumptions and limitations were related to the dose rate measurement and the relative abundance of gamma emitters in a drum. These two variables were generally obtained from the different detection mechanism. Unfortunately, that expanded the limitation of using the DTC method. The spectrum to dose (STD) conversion factor [4,5] that was calculated from the measure pulse height spectrum of the gamma ray detector could be made obtaining two variables from the drum to be assayed at once. This method could be made estimating the radioisotope inventory of a drum more practical.Copyright

Usefulness of Creep Work-Time ]Relation for Determining Stress Intensity Limit of High-Temperature Components

In order to determine creep stress intensity limit of high-temperature components, the usefulness of the creep work and time equation, defined as Wc/tp/ = B(where Wc/ = is the total creep work done during creep, and p and B are constants), was investigated using the experimental data. For this Purpose, the creep tests for generating 1.0% strain for commercial type i16 stainless steel were conducted with different stresses; 160 MPa, 150 MPa, 145 MPa, 140 MPa and 135 MPa at 593. The plots of log Wc/ - log t showed a good linear relation up to 105/ hr, and the results of the creep work-time relation for p, B and stress intensity values showed good agreement to those of isochronous stress-strain curves (ISSC) presented in ASME BPV NH. The relation can be simply obtained with only several short-term 1% strain data without ISSC which can be obtained by long-term creep data. Particularly, this relation is useful in estimating stress intensity limit for new and emerging class of high-temperature creeping materials.

Creep Analysis of Type 316LN Stainless Steel Using Reference Stress

Creep damage using a reference stress(RS) was analyzed for type 316LN stainless steel. The generalized K-R equation was reconstructed into the RS equation using a critical stress value . The RS equation was derived from the critical stress in failure time instead of material damage parameter , which indicates the critical condition of collapse or approach to gross instability of materials during creep. For obtaining the reference stress, a series of creep tests and tensile tests were conducted with at 55 and . The stress-time data obtained from creep tests were applied to the RS equations to characterize the creep damage of type 316LN stainless steel. The value of creep constant r with stress levels was about 18 at 55 and 21 at . This value was almost similar with r