Min-Gu Won

Estimation of Stress Intensity Factor for Circumferential Through-Wall Cracked Elbows Subjected to In-Plane Bending

The stress intensity factor (SIF) is the major fracture mechanics parameter in LEFM concept. Since the SIF can be used for not only calculation of J-integral based on the GE/EPRI and reference stress method but also evaluation of fatigue crack growth, an accurate estimation of the SIF is an important issue for the piping in nuclear power plant. Recently, there is a need to develop the SIF solution which can cover wide geometric variables since there are on-going efforts that are developing next generation reactors in Korea, which is designed to thin-walled structures. For the through-wall cracked straight pipes, many researchers have proposed the SIF solutions which can cover wide range of wall thickness. However, since only limited solutions have been proposed yet for the through-wall cracked elbows, a research related to the SIF estimation for the elbows with wide geometric variables should be performed. In this study, the extended SIF solution for circumferential through-wall cracked elbows subjected to in-plane bending is proposed as the tabulated form through the finite element (FE) analyses. Wide elbow geometries are selected to range between 5 and 50 of Rm/t and range between 2∼20 of Rb/Rm. The existing solutions are then reviewed by comparing with the FE results. Furthermore, effects of geometric variables on the SIF are addressed through systematic investigation of FE based SIF results. These investigated results are expected to contribute to the development of closed form solution for the circumferential through-wall cracked elbows subjected to in-plane bending.Copyright

Estimation of Elastic Crack Opening Displacement for Thin Elbows With Circumferential Through-Wall Cracks

Leak-before-break (LBB) is an important concept that could confirm design and integrity evaluation of nuclear power plant piping. For the LBB analysis, the detective leakage rate should be calculated for a through-wall cracked pipes. For this calculation, the crack opening displacement (COD) calculation is essential.Recently, sodium faster reactor (SFR) which has thin-walled pipes with Rm/t ranged 30–40 was introduced and then the investigation of these thin walled pipes and elbows has received great attention in the LBB evaluation. In this context, the three-dimensional finite element (FE) analyses for thin elbows with circumferential crack under in-plane bending are carried out to investigate the elastic COD values.Finally, the solution for elastic COD which can cover sufficiently thin elbow is successfully addressed.Copyright

Estimations of C* and COD for Non-Idealized Axial Through-Wall Cracks in Cylinders Under Creep Conditions

The present paper provides C*-integral and COD for non-idealized through-wall cracks in cylinders under creep conditions. These solutions are based on detailed 3-dimensional Finite Element (FE) analyses which can be used for structural integrity assessment of nuclear piping. To cover a practical interest range, two types of creep conditions and two types of estimation methods were considered. Furthermore, axial through-wall crack model with internal pressure was considered. As for creep conditions, secondary creep (Norton creep), primary-secondary creep (RCC-MR creep) were considered. To estimate C*-integral and COD for non-idealized axial through-wall crack, GE/EPRI and ERS method were used and the results were compared with numerical solutions. Finally, an appropriate estimating methods for each creep condition were suggested.Copyright