Coalescence Pressure Evaluation of Multiple Through-Wall Cracks in Steam Generator Tube Using Elastic-Plastic Finite Element Analyses

2015 ◽  
Author(s):  
Jin-Won Hong ◽  
Jae-Boong Choi ◽  
Nam-Su Huh
Keyword(s):  
Finite Element ◽  
Steam Generator ◽  
Interaction Effect ◽  
Evaluation Model ◽  
Multiple Cracks ◽  
Crack Interaction ◽  
Collinear Cracks ◽  
Elastic Plastic ◽  
Parallel Cracks ◽  
Steam Generator Tubes

During an in-service inspection, if multiple cracks have been found in a nuclear component, the crack interaction effect due to adjacent cracks should be taken into account to characterize the detected multiple cracks into equivalent single combined crack or independent single crack. However, there must be many factors to be considered to quantify crack interaction effect, many experimental and numerical works should be made to propose robust guidelines on crack interaction effect depending on material characteristics of interest. Although many works have been made during the past few years to evaluate crack interaction effect of steam generator tubes with multiple cracks, the robust guidelines are still lacking. In this study, systematic 3-dimensional (3D) elastic-plastic finite element (FE) analyses are performed for steam generator tubes with multiple through-wall cracks. As for geometries of multiple through-wall cracks, four different cases are considered; axial collinear cracks, axial parallel cracks, circumferential collinear cracks, and circumferential parallel cracks. The geometric variables affecting the Pc (coalescence pressure), i.e. crack length and distance between multiple cracks, are systematically varied in the present study. Based on the coalescence pressure evaluation model proposed by authors in the previous study and the present FE results, the Pc of steam generator tubes with multiple cracks are investigated.

Evaluation of Interaction Effects on Part-Through Cracks in Steam Generator Tubes

2013 ◽  
Author(s):  
Yong-Seok Kang ◽  
Hong-Deok Kim ◽  
Kuk-Hee Lee ◽  
Jai-Hak Park
Keyword(s):  
Steam Generator ◽  
Interaction Effect ◽  
Structural Integrity ◽  
Structural Parameters ◽  
Interaction Effects ◽  
Multiple Cracks ◽  
Performance Limit ◽  
Steam Generator Tubing ◽  
Steam Generator Tubes

Degraded steam generator tubing can affect its safety functions. Therefore, its integrity should be maintained for each degradation form and all detected degradation must be assessed to verify that if adequate integrity is retained. Determination of tube integrity limits includes identifying acceptable structural parameters such as flaw length, depth, and amplitude of signals. If we consider just single-cracked tubes, short and deep flaws are not likely to threaten structural integrity of tubes. But if it has multiple-cracks, we have to consider interaction effects of multiple adjacent cracks on its burst pressure. Because adjacent multiple cracks can be merged due to the crack growth then it can challenge against the structural performance limit. There are some studies on the interaction effects of adjacent cracks. However, existing works on the interaction effect consider only through-wall cracks. No study has been carried out on the interaction effects of part-through cracks. Most cracks existing in real steam generator tubing are not through-wall cracks but part-through cracks. Hence, integrity of part-through cracks is more practical issue than that of through-wall cracks. This paper presents experimental burst test results with steam generator tubing for evaluation of interaction effects with axial oriented two collinear and parallel part-through cracks. The interaction effect between two adjacent cracks disappeared when the distance exceeds about 2 mm.

Rules for the Assessment of Interacting Cracks Under Creep Conditions

2009 ◽  
Vol 132 (1) ◽  
Author(s):  
Fu-Zhen Xuan ◽  
Jun Si ◽  
Shan-Tung Tu
Keyword(s):  
Load Ratio ◽  
Limit Load ◽  
Multiple Cracks ◽  
Crack Interaction ◽  
Combination Rule ◽  
Collinear Cracks ◽  
Creep Crack ◽  
Parallel Cracks ◽  
Interaction Factor ◽  
Cracked Structures

Multiple interacting cracks are generally treated as an enveloping single crack if the prescribed criterion is satisfied in the current fitness-for-service codes. To examine the applicability of the existing criteria under creep regime, in this report, creep crack interaction effects of plates containing collinear cracks or parallel cracks are first analyzed under the framework of reference stress method and finite element computations. An equivalent crack growth rate criterion is then proposed to develop a congruous multiple crack treatment rule for different growth mechanisms. The current combination rule for multiple cracks is examined and modified in terms of the proposed new criterion. The results reveal that the creep crack interaction factor is a combined function of creep exponent n of materials, limit load ratio of cracked structures, and interaction of stress intensity factor. More pronounced interaction is observed for both interacting cracks in the same plane and that in different planes. Although a higher intensity of creep crack interaction is observed, a greater value of γcreep is permissible compared with that of linear-elastic crack interaction denoted by SIF. Accordingly, a modified combination rule for collinear cracks of S/a=3.0 is proposed to exclude the nonconservativeness, while the current alignment rule for offset parallel cracks of H/a=2.0 is still practicable in terms of the proposed criterion.

Coalescence Criterion of Part-Through Wall Cracks in Steam Generator Tubes of Nuclear Power Plants

2004 ◽  
Author(s):  
Jeries Abou-Hanna ◽  
Timothy McGreevy ◽  
Saurin Majumdar ◽  
Amit J. Trivedi ◽  
Ashraf Al-Hayek
Keyword(s):  
Finite Element ◽  
Steam Generator ◽  
Nuclear Power ◽  
Power Plants ◽  
Nuclear Power Plants ◽  
Local Instability ◽  
Element Analysis ◽  
Failure Pressure ◽  
Ligament Failure ◽  
Steam Generator Tubes

In scheduling inspection and repair of nuclear power plants, it is important to predict failure pressure of cracked steam generator tubes. Nondestructive evaluation (NDE) of cracks often reveals two neighboring cracks. If two neighboring part-through cracks interact, the tube pressure, under which the ligament between the two cracks fails, could be much different than the critical burst pressure of an individual equivalent part-through crack. The ability to accurately predict the ligament failure pressure, called “coalescence pressure,” is important. The coalescence criterion, established earlier for 100% through cracks using nonlinear finite element analyses [1–3], was extended to two part-through-wall axial collinear and offset cracks cases. The ligament failure is caused by local instability of the radial and axial ligaments. As a result of this local instability, the thickness of both radial and axial ligaments decreases abruptly at a certain tube pressure. Good correlation of finite element analysis with experiments (at Argonne National Laboratory’s Energy Technology Division) was obtained. Correlation revealed that nonlinear FEM analyses are capable of predicting the coalescence pressure accurately for part-through-wall cracks. This failure criterion and FEA work have been extended to axial cracks of varying ligament width, crack length, and cases where cracks are offset by axial or circumferential ligaments. The study revealed that rupture of the radial ligament occurs at a pressure equal to the coalescence pressure in the case of axial ligament with collinear cracks. However, rupture pressure of the radial ligament is different from coalescence pressure in the case of circumferential ligament, and it depends on the length of the ligament relative to crack dimension.

Structural Integrity Assessment of Steam Generator Tube by the Use of Heterogeneous Finite Element Method

2008 ◽  
Vol 130 (4) ◽  
Author(s):  
Xinjian Duan ◽  
Michael J. Kozluk ◽  
Sandra Pagan ◽  
Brian Mills
Keyword(s):  
Finite Element ◽  
Steam Generator ◽  
Failure Modes ◽  
Structural Integrity ◽  
Fretting Wear ◽  
Defect Depth ◽  
Steam Generator Tube ◽  
Integrity Assessment ◽  
Failure Pressure ◽  
Steam Generator Tubes

Aging steam generator tubes have been experiencing a variety of degradations such as pitting, fretting wear, erosion-corrosion, thinning, cracking, and denting. To assist with steam generator life cycle management, some defect-specific flaw models have been developed from burst pressure testing results. In this work, an alternative approach; heterogeneous finite element model (HFEM), is explored. The HFEM is first validated by comparing the predicted failure modes and failure pressure with experimental measurements of several tubes. Several issues related to the finite element analyses such as temporal convergence, mesh size effect, and the determination of critical failure parameters are detailed. The HFEM is then applied to predict the failure pressure for use in a fitness-for-service condition monitoring assessment of one removed steam generator tube. HFEM not only calculates the correct failure pressure for a variety of defects, but also predicts the correct change of failure mode. The Taguchi experimental design method is also applied to prioritize the flaw dimensions that affect the integrity of degraded steam generator tubes such as the defect length, depth, and width. It has been shown that the defect depth is the dominant parameter controlling the failure pressure. The failure pressure varies almost linearly with defect depth when the defect length is greater than two times the tube diameter. An axial slot specific flaw model is finally developed.

Simulation of Ductile Fracture for Multiple Flaws

2010 ◽  
Author(s):  
Masanori Kikuchi ◽  
Kazuhiro Suga ◽  
Shota Kawasaki
Keyword(s):  
Constitutive Equation ◽  
Ductile Fracture ◽  
Interaction Effect ◽  
Evaluation Method ◽  
Crack Problem ◽  
Fracture Pattern ◽  
Crack Coalescence ◽  
Multiple Cracks ◽  
Parallel Cracks ◽  
Fracture Processes

Interaction effect of multiple flaws on ductile fracture is studied numerically by using Gurson’s constitutive equation. Based on experiments, 2 parallel cracks problems and 3 parallel cracks problems are simulated. In some problems, crack coalescence does not occur, and it occurs in other cases. In all cases, ductile fracture processes are obtained, and results are compared with experimental ones. Fracture pattern and load-displacement curves agree well with experiments. It is shown that void growth term is dominant for the coalescence of cracks. Slanted crack problem and non-uniform length crack problem are simulated and evaluation method of multiple cracks problem is discussed.

Numerical Investigation on 3-D Two Collinear Cracks in Offshore Pipelines Under Bending

2015 ◽  
Author(s):  
Yanmei Zhang ◽  
Zhongmin Xiao ◽  
Mohammad Zaidi Bin Ariffin ◽  
Wengang Zhang
Keyword(s):  
Research Work ◽  
Multiple Cracks ◽  
Collinear Cracks ◽  
Offshore Pipelines ◽  
Ductile Materials ◽  
Elastic Plastic ◽  
Lack Of Information ◽  
Fracture Behaviors ◽  
Nonlinear Elastic ◽  
Embedded Crack

Under complicated loading conditions, small yet closely located cracks can grow and coalesce into a large crack which may pose a significant threat to the reliability of marine structures. A lot of research work has been carried out for the investigation of multiple cracks’ stress intensity factors and estimation of fatigue growth of multiple cracks. However, there is a lack of information on nonlinear elastic plastic analysis on fracture behavior of ductile materials. In this study, 3-D finite element analyses are conducted on offshore pipelines with two collinear cracks (a semi-elliptical surface crack and an elliptical embedded crack). The nonlinear elastic-plastic investigations are performed on fracture behaviors of these two interacting cracks subjected to large plastic strains. A comparison of fracture response (in terms of CTOD value) has been made between the current numerical results and the computational outcomes derived from BS7910: 2005. Last but not least, strain-based CTOD estimation formulas are proposed for assessing the fracture response of flawed pipelines with two collinear cracks under large plastic strain conditions.

Elastic-plastic fracture mechanics assessment for steam generator tubes with through-wall cracks

2007 ◽  
Vol 30 (2) ◽  
pp. 131-142 ◽  
Author(s):  
NAM-SU HUH ◽  
JONG-MIN KIM ◽  
YOON-SUK CHANG ◽  
YOUNG-JIN KIM ◽  
SEONG-SIK HWANG ◽  
...  
Keyword(s):  
Fracture Mechanics ◽  
Steam Generator ◽  
Elastic Plastic ◽  
Steam Generator Tubes

Finite Element Simulations of the Remote Field Eddy Current Signal in Steam Generator Tubes of Monju Fast Breeder Reactor

2004 ◽  
Author(s):  
Ovidiu Mihalache ◽  
Yoshiyuki Imai ◽  
Masashi Ueda ◽  
Takuya Yamashita
Keyword(s):  
Finite Element ◽  
Steam Generator ◽  
Eddy Current ◽  
Computational Cost ◽  
Fast Breeder Reactor ◽  
3D Simulations ◽  
Convergence Error ◽  
Boundary Limit ◽  
Eddy Current Effect ◽  
Steam Generator Tubes

The present paper describes and clarifies the main difficulties arising in the 3D numerical simulations using finite element method of the remote field eddy current effect in magnetic steam generator tubes. The 2D axisymmetric and full 3D simulations are compared with experimental results from outer discontinuities in Monju fast breeder reactor steam generator tubes. Very good agreements were obtained between measurements and 2D simulations. The influences of several parameters are evaluated by 3D simulations: convergence error of the iterative matrix solutions, pattern of the mesh discretization, the boundary limit and finite element interpolation order. The computational cost of the remote field 3D model in Monju steam generator tubes and the numerical aspects of the 3D simulations are discussed in detail in the paper.

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