Ho Wan Ryu

Evaluation of limit loads for circumferentially cracked pipes under combined loadings

Since the Fukushima nuclear accident, several researchers are extensively studying the effect of torsion on the piping systems In nuclear power plants. Piping installations in power plants with a circumferential crack can be operated under combined loading conditions such as bending and torsion. ASME Code provides flaw evaluations for fully plastic fractures using limit load criteria for the structural integrity of the cracked pipes. According to the recent version of Code, combined loadings are provided only for the membrane and bending. Even though actual operating conditions have torsion loading, the methodology for evaluating torsion load is not established. This paper provides the results of limit load analyses by using finite element models for circumferentially cracked pipes under pure bending, pure torsion, and combined bending and torsion with tension. Theoretical limit load solutions based on net-section fully plastic criteria are suggested and verified with the results of finite element analyses.

Determination Method of Ramberg-Osgood Constants for Leak Before Break Evaluation

In this study, a method for determining Ramberg–Osgood constants for leak-before-break evaluation was investigated. The Ramberg–Osgood constants were calculated for SA312, TP316, and SA-508 Gr.1a in an operating temperature of 316 oC. Incremental plasticity, using stress–strain data obtained from experiment, and deformation plasticity, using the Ramberg-Osgood constants, were considered in a finite element analysis. Using incremental plasticity and deformation plasticity, J-integrals and crack opening displacement values were calculated and compared. By comparing the results of incremental plasticity and deformation plasticity, a suitable method for determining Ramberg–Osgood constants for leak-before-break evaluation was confirmed. † Corresponding Author, kimy0308@korea.ac.kr C 2015 The Korean Society of Mechanical Engineers 배경동 · 류호완 · 김윤재 · 김진원 · 김종성 · 오영진 646

Development of a Short-term Failure Assessment of High Density Polyethylene Pipe Welds - Application of the Limit Load Analysis -

In the US, the number of cases of subterranean water contamination from tritium leaking through a damaged buried nuclear power plant pipe continues to increase, and the degradation of the buried metal piping is emerging as a major issue. A pipe blocked from corrosion and/or degradation can lead to loss of cooling capacity in safety-related piping resulting in critical issues related to the safety and integrity of nuclear power plant operation. The ASME Boiler and Pressure Vessel Codes Committee (BPVC) has recently approved Code Case N-755 that describes the requirements for the use of polyethylene (PE) pipe for the construction of Section III, Division 1 Class 3 buried piping systems for service water applications in nuclear power plants. This paper contains tensile and slow crack growth (SCG) test results for high-density polyethylene (HDPE) pipe welds under the environmental conditions of a nuclear power plant. Based on these tests, the fracture surface of the PENT specimen was analyzed, and the fracture mechanisms of each fracture area were determined. Finally, by using 3D finite element analysis, limit loads of HDPE related to premature failure were verified. † Corresponding Author, kimy0308@korea.ac.kr C 2015 The Korean Society of Mechanical Engineers 류호완 · 한재준 · 김윤재 · 김종성 · 김정현 · 장창희 406

Ductile fracture simulation for toughness specimens from low alloy and stainless steel pipes

This paper describes ductile fracture simulation for Battelle fracture toughness and full-scale pipe tests (1). Materials in this research are low carbon steel and TP304 stainless steel. Tensile and Compact tension (CT) specimens are simulated to determine the fracture criteria with finite element (FE) method. Then, pipes containing through wall crack and surface crack are predicted by proposed damage method. The results from simulations are compared with test data for verification of proposed method and to check the applicability on industrial field. It is shown that predicted simulation results are compared with experimentally measured values, showing overall good agreements.

Numerical study on fracture behavior of complex cracked pipes

This study provides the application of damage model to complex cracked pipes which can be found especially in weld overlay region. From the perspective of structural integrity, enough basic and large-scale tests are required to accurately evaluate the components containing a crack-like defect. In this case, damage model using finite element (FE) method can be effectively used for the assessment of full-scale cracked pipes with minimum basic experiments data. The proposed method in this research is based on the stress-modified fracture strain damage model with stress reduction technique.In this paper, Battelle full-scale complex cracked pipe tests are simulated by the proposed damage model with reasonable procedure. FE simulation is conducted for basic experiments to determine failure criteria with calibrations. Then, crack initiation and maximum loads are predicted to characterize the fracture behavior of full-scale complex cracked pipes. Damage model is applied to both of carbon and stainless steel materials and verification with comparing to test data is conducted.Copyright

Effects of Side Groove on Fracture Toughness

This paper describes ductile tearing simulation for compact tension (C(T)) specimens using FE damage analysis based on the stress-modified fracture strain model. The side groove effect on J-resistance curve was estimated by experimental and analytical ways. In this paper, SA508 Grade 1A low alloy steel pipe material was considered. Tensile and C(T) specimens are simulated to determine the failure criteria with finite element method. Then, different shapes of C(T) specimens are analysed and the results from simulations are compared with test data for verification of proposed method. Overall, the predicted simulation results show good agreement with test data.Copyright

Limit Loads for Circumferentially Cracked Pipes Under Combined Bending and Torsion With Tension

In power plants, piping installations with a circumferential crack can be operated under combined bending and torsion. ASME Boiler and Pressure Vessel code Section XI non-mandatory Appendix C provides the flaw evaluations for fully-plastic fracture using limit load criteria for the structural integrity of the cracked pipes. According to the recent version of Code, combined loading is provided only for membrane and bending. Even though actual operating conditions have torsion loading, the methodology for evaluating torsion load is not established, and assumed torsion is relatively small compared to membrane and bending and can be ignored in the evaluation.This paper provides the results of limit load analyses by using finite element models for circumferentially cracked pipes under pure bending, pure torsion and combined bending and torsion with tension. Theoretical limit load solutions based on net-section fully-plastic criteria are compared with the results of finite element analyses. The validation of theoretical limit loads for combined bending and torsion with tension is discussed.Copyright