• Transactions of the Korean Society of Mechanical Engineers A
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• v.23 no.7 s.166
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• pp.1182-1195
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• 1999

The purpose of this study is to investigate experimentally the effects of both seismic loading and crack length on the fracture behavior of piping system with a circumferential crack in nuclear power plants. The experiments were performed using both large scale piping system facility and 4 points bending test machine under PWR operating conditions. The difference in the load carrying capacities between cracked piping and non-cracked piping was also investigated using the results from experiments and numerical calculations. The results obtained from the experiments and estimation are as follows : (1) The safety margin under seismic loading is larger than those under quasi static loading or simple cyclic loading. (2) There was no significant effect of crack length on tincture behavior of piping system with both a surface crack and a through-wall crack. (3) The load carrying capacity in cracked piping was reduced by factors of 7 to 46 compared to non-cracked piping.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.38 no.10
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• pp.1157-1162
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• 2014

Two acceleration methods, an effective force method (or inertia method) and a large mass method, have been applied for performing time history seismic analysis. The acceleration methods for uncracked structures have been verified via previous studies. However, no study has identified the validity of these acceleration methods for cracked piping. In this study, the validity of the acceleration methods for through-wall cracked piping is assessed via time history implicit dynamic elastic seismic analysis from the viewpoint of linear elastic fracture mechanics. As a result, it is identified that both acceleration methods show the same results for cracked piping if a large mass magnitude and maximum time increment are adequately selected.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.25 no.7
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• pp.1031-1038
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• 2001

In order to verify the analytical methods predicting failure behavior of cracked piping, full-scale pipe tests are crucial in nuclear power plant piping. For this reason, series of international test programs have been conducted. However, full-scale pipe tests require expensive testing equipment and long period of testing time. The objective of this paper is to develop a test system which can economically simulate the full-scale pipe test regarding the integrity evaluation. This system provides the failure behavior of cracked pipe by testing a wide-plate specimen. The system provides the failure behavior of cracked pipe by testing a wide-plate specimen. The system was developed for the integrity evaluation of nuclear piping based on the methodology of hardware-in-the-loop (HiL) simulation. Using this simulator, the piping integrity can be evaluated based on the elastic-plastic behavior of full-scale pipe, and the high cost full-scale pipe test may be replaced with this economical system.

• Transactions of the Korean Society of Pressure Vessels and Piping
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• v.12 no.2
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• pp.1-24
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• 2016

The original fracture criteria developed by Maxey/Kiefner for axial through-wall and surface-cracked pipes have worked well for many industries for a large variety of relatively low strength and toughness materials. However, newer line pipe steels have some unusual characteristics that differ from these older materials. One example is a test data that has demonstrated that X80 line-pipe with an axial through-wall-crack can fail at pressures about 30 percent lower than predicted with commonly used analysis methods for older steels. Thus, it is essential to review the currently available models and investigate the applicability of these models to newer high-strength line pipe materials. In this paper, the available models for predicting the failure behavior of axial-cracked pipes (through-wall-cracked and external surface-cracked pipes) were reviewed. Furthermore, the applicability of these models to high-strength steel pipes was investigated by analyzing limited full-scale pipe fracture initiation test results. Based on the analyzed results, the shortcomings of the available models were identified. For both through-wall and surface cracks, the major shortcomings were related to the characterization of the material toughness, which generally leads to non-conservative predictions in the J-T analyses. The findings in this paper may be limited to the test data that were consider for this study. The requisite characteristics of a potential model were also identified in the present paper.

• Transactions of the Korean Society of Pressure Vessels and Piping
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• v.15 no.2
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• pp.31-39
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• 2019

Cracked component analysis is needed for structural integrity analysis under seismic loading. Under large amplitude cyclic loading conditions, the change in material properties can be complex, depending on the magnitude of plastic strain. Therefore the cracked component analysis under cyclic loading should consider appropriate cyclic hardening model. This study introduces a procedure for determining an appropriate cyclic hardening model for cracked component analysis. The test material was nuclear-grade TP316 stainless steel. The material cyclic hardening was simulated using the Chaboche combined hardening model. The kinematic hardening model was determined from standard tensile test to cover the high and wide strain range. The isotropic hardening model was determined by simulating C(T) test under cyclic loading using ABAQUS debonding analysis. The suitability of the material hardening model was verified by comparing load-displacement curves of cyclic C(T) tests under different load ratios.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.27 no.1
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• pp.26-33
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• 2003

Based on detailed FE limit analyses, the present paper provides tractable approximations fer plastic limit pressure solutions fur axially through-wall-cracked pipe; axially (inner) surface-cracked pipe; circumferentially through-wall-cracked pipe; and circumferentially (inner) surface-cracked pipe. In particular, for surface crack problems, the effect of the crack shape, the semi-elliptical shape or the rectangular shape, on the limit pressure is quantified. Comparisons with existing analytical and empirical solutions show a large discrepancy in circumferential short through-wall cracks and in surface cracks (both axial and circumferential). Being based on detailed 3-D FE limit analysis, the present solutions are believed to be the most accurate, and thus to be valuable information not only for plastic collapse analysis of pressurised piping but also for estimating non-linear fracture mechanics parameters based on the reference stress approach.

• Nuclear Engineering and Technology
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• v.53 no.3
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• pp.974-987
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• 2021

This paper presents ductile fracture simulation of full-scale cracked pipe for nuclear piping materials using the cohesive zone model (CZM). The main objective of this study is to investigate the applicability of CZM to predict ductile fracture of cracked pipes with various crack shapes and under quasi-static/dynamic loadings. The transferability of the traction-separation (T-S) curve from a small-scale specimen to a full-scale pipe is demonstrated by simulating small- and full-scale tests. T-S curves are calibrated by comparing experimental data of compact tension specimens with finite element analysis results. The calibrated T-S curves are utilized to predict the fracture behavior of cracked pipes. Three types of full-scale pipe tests are considered: pipe with circumferential through-wall crack under quasistatic/dynamic loadings, and with 360° internal surface crack under quasi-static loading. Computational results using the calibrated T-S curves show a good agreement with experimental data, demonstrating the transferability of the T-S curves from small-scale specimen.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.25 no.9
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• pp.1350-1358
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• 2001

During the last decade, a number of experiments and numerical analyses had been performed in conjunction with the development of simplified analytical methods to estimate the fracture behavior of cracked piping in nuclear power plant. However, the necessity of further investigation for the analytical methods was issued because of the discrepancies with the experimental data. The objective of this paper is to find out the optimum methods to evaluate the load-carrying capacities for cracked pipes. To do this, numerous analytical and finite element analyses were carried out for various pipe and crack geometries and materials. These results were synthesized for crack shapes and can be used as basic data for leak before analyses and risk informed inspections.

• Transactions of the Korean Society of Pressure Vessels and Piping
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• v.9 no.1
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• pp.56-61
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• 2013

This paper presents the results of integrity assessment for the cracks happened in reactor vessel upper head penetration nozzles. The crack morphology for a boat sample from crack area was analyzed through microscope. The stress condition including weld residual stress around crack was analyzed using finite element analysis. From the results of crack morphology and stress condition, the crack was concluded as primary water stress corrosion cracking. The integrity of the cracked nozzle was assessed by the methodology provided in ASME Section XI. According to the assessment results, the remaining life of the cracked nozzle was 1.43 yrs. and the plant decided to repair it.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.39 no.5
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• pp.453-460
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• 2015

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.