Failure Behavior of Multiple-Axial Part-Through-Wall Flaws in Alloy 690TT Steam Generator Tubes

2015 ◽  
Vol 138 (2) ◽  
Author(s):  
Ki Hyeon Eom ◽  
Jin Weon Kim ◽  
Yun Jae Kim ◽  
Jong Sung Kim
Keyword(s):  
Experimental Data ◽  
Failure Mode ◽  
Steam Generator ◽  
Interaction Effect ◽  
Room Temperature ◽  
Failure Behavior ◽  
Constant Depth ◽  
Failure Pressure ◽  
Axial Part ◽  
Steam Generator Tubes

This study investigates the interaction effect of multiple-axial part-through-wall (PTW) flaws on the failure behavior of Alloy 690TT steam generator (SG) tubes. Burst tests of tubes with single and multiple flaws were conducted at room temperature (RT). The flaws were made by the electrodischarge machining (EDM) method on the outer surface of the specimens. Six different configurations of multiple flaws were considered to see the interaction effect; two and three collinear, two and three parallel, and two and three nonaligned flaws. In all cases, an axial flaw with a constant depth of 50% wall-thickness was considered, and the following variables were systematically varied; the axial and/or circumferential separating ligament lengths between flaws, the flaw length, and the number of flaws. Effects of these variables on the failure pressure and failure mode were investigated based on experimental data. The effects of separating ligament lengths and flaw lengths on the failure pressure were dependent on the type of flaw configuration. For collinear and nonaligned flaws, the decrease in failure pressure by the interaction of multiple flaws became significant as the number of flaws increased. The failure mode of multiple flaws was strongly dependent on the length of the flaws.

Burst Test on the Steam Generator Tube With Multiple Part-Through-Wall Flaws

2015 ◽  
Author(s):  
Jin Weon Kim ◽  
Ki Hyeon Eom
Keyword(s):  
Steam Generator ◽  
Interaction Effect ◽  
Room Temperature ◽  
Ligament Length ◽  
Outer Diameter ◽  
Constant Depth ◽  
Positive Interaction ◽  
Failure Pressure ◽  
Electro Discharge Machining ◽  
Axial Part

This study carried out burst tests on steam generator (SG) tube specimens containing multiple axial part-through-wall (PTW) flaws at room temperature (RT). The specimens were machined from SG tube of Alloy 690TT with an outer diameter of 19.05mm and a thickness of 1.067mm. The flaws were made by electro-discharge machining (EDM) method on the outer surface of specimen. In the experiment, six types of multiple PTW flaws with a constant depth of 50% of wall thickness and single flaw with four different lengths were considered. The results showed that the interaction effect for collinear axial PTW flaws diminished with increasing ligament length between flaws. The ligament length had less influence on the interaction effect for longer flaws than shorter flaws. For non-aligned axial PTW flaws, however, the interaction effect was increased and remained with increase in circumferential ligament length. For parallel axial PTW flaws, the positive interaction effect appeared when the ligament between flaws was less than 2mm. However, the failure pressure decreased with increasing circumferential ligament length between flaws and reached the minimum when they were separated by about 90-degree in circumferential direction. Interaction effect was enhanced as number of flaws for collinear and non-aligned axial PTW flaws increased. Regardless of flaw configurations and ligament lengths, multiple PTW flaws of shorter length were failed by rupture at bottom of flaws followed by coalescence and unstable tearing. But, the flaws of length longer than 25.4mm were failed by rupture at bottom of one of multiple axial flaws.

Failure Pressure for Steam Generator Tube With Two Different Collinear Axial Through-Wall Cracks

2006 ◽  
Author(s):  
Nam-Su Huh ◽  
Yoon-Suk Chang ◽  
Young-Jin Kim
Keyword(s):  
Steam Generator ◽  
Complex Shape ◽  
Structural Integrity ◽  
Failure Behavior ◽  
Multiple Cracks ◽  
Single Crack ◽  
Steam Generator Tube ◽  
3 Dimensional ◽  
Failure Pressure ◽  
Steam Generator Tubes

To maintain the structural integrity of steam generator tubes, 40% of wall thickness plugging criterion has been developed. The approach is for the steam generator tube with single crack, so that the interaction effect of multiple cracks can not be considered. Although, recently, several approaches has been proposed to assess the integrity of steam generator tube with two identical cracks whilst actual multiple cracks reveal more complex shape. In this paper, the failure pressure of steam generator tube containing multiple cracks of different length is evaluated based on the detailed 3-dimensional elastic-plastic finite element (FE) analyses. In terms of the crack shape, two collinear axial through-wall cracks with different length were considered. Furthermore, the resulting FE failure pressures are compared with FE failure pressures and experimental results for two identical collinear axial through-wall cracks to quantify the effect of crack length ratio on failure behavior of steam generator tube with multiple cracks.

Evaluation of the Creep Rupture Behavior of Alloy 690 Steam Generator Tubes Considering the Pressure Ramp Rate

2021 ◽  
Author(s):  
Jongmin Kim ◽  
Min-Chul Kim ◽  
Joonyeop Kwon
Keyword(s):  
Steam Generator ◽  
Creep Rupture ◽  
Parameter Method ◽  
Alloy 600 ◽  
Steam Generator Tube ◽  
Failure Pressure ◽  
Alloy 690 ◽  
Rupture Model ◽  
Temperature And Pressure ◽  
Steam Generator Tubes

Abstract The materials used previously for steam generator tubes around the world have been replaced and will be replaced by Alloy 690 given its improved corrosion resistance relative to that of Alloy 600. However, studies of the high- temperature creep and creep-rupture characteristics of steam generator tubes made of Alloy 690 are insufficient compared to those focusing on Alloy 600. In this study, several creep tests were conducted using half tube shape specimens of the Alloy 690 material at temperatures ranging from 650 to 850C and stresses in the range of 30 to 350 MPa, with failure times to creep rupture ranging from 3 to 870 hours. Based on the creep test results, creep life predictions were then made using the well-known Larson Miller Parameter method. Steam generator tube rupture tests were also conducted under the conditions of a constant temperature and pressure ramp using steam generator tube specimens. The rupture test equipment was designed and manufactured to simulate the transient state (rapid temperature and pressure changes) in the event of a severe accident condition. After the rupture test, the damage to the steam generator tubes was predicted using a creep rupture model and a flow stress model. A modified creep rupture model for Alloy 690 steam generator tube material is proposed based on the experimental results. A correction factor of 1.7 in the modified creep rupture model was derived for the Alloy 690 material. The predicted failure pressure was in good agreement with the experimental failure pressure.

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.

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.

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.

Failure Pressure Estimates of Steam Generator Tubes Containing Wear-Type Defects

2006 ◽  
Author(s):  
Yoon-Suk Chang ◽  
Jong-Min Kim ◽  
Nam-Su Huh ◽  
Young-Jin Kim ◽  
Seong-Sik Hwang ◽  
...  
Keyword(s):  
Steam Generator ◽  
Equivalent Stress ◽  
Three Dimensional ◽  
Plastic Instability ◽  
Failure Behavior ◽  
Dimensional Finite Element ◽  
Estimation Scheme ◽  
Wrap Angle ◽  
Three Dimensional Finite Element ◽  
Steam Generator Tubes

It is commonly requested that steam generator tubes with defects exceeding 40% of wall thickness in depth should be plugged to sustain all postulated loads with appropriate margin. The critical defect dimensions have been determined based on the concept of plastic instability. This criterion, however, is known to be too conservative for some locations and types of defects. In this context, the accurate failure estimation for steam generator tubes with a defect draws increasing attention. Although several guidelines have been developed and are used for assessing the integrity of defected tubes, most of these guidelines are related to stress corrosion cracking or wall-thinning phenomena. As some of steam generator tubes are also failed due to fretting and so on, alternative failure estimation schemes for relevant defects are required. In this paper, three-dimensional finite element (FE) analyses are carried out under internal pressure condition to simulate the failure behavior of steam generator tubes with different defect configurations; elliptical wastage type, wear scar type and rectangular wastage type defects. Maximum pressures based on material strengths are obtained from more than a hundred FE results to predict the failure of the steam generator tube. After investigating the effect of key parameters such as wastage depth, wastage length and wrap angle, simplified failure estimation equations are proposed in relation to the equivalent stress at the deepest point in wastage region. Comparison of failure pressures predicted according to the proposed estimation scheme with some corresponding burst test data shows good agreement, which provides a confidence in the use of the proposed equations to assess the integrity of steam generator tubes with wear-type defects.

Failure Pressure and Leak Rate of Steam Generator Tubes With Stress Corrosion Cracks

2002 ◽  
Author(s):  
S. Majumdar ◽  
K. Kasza ◽  
J. Y. Park ◽  
S. Bakhtiari
Keyword(s):  
Stress Corrosion ◽  
Steam Generator ◽  
Eddy Current ◽  
Leak Rate ◽  
Rectangular Crack ◽  
Failure Pressure ◽  
Post Test ◽  
Steam Generator Tubes ◽  
Test Failure ◽  
Made In

This paper illustrates the use of an “equivalent rectangular crack” approach to predict leak rates through laboratory generated stress corrosion cracks. A comparison between predicted and observed test data on rupture and leak rate from laboratory generated stress corrosion cracks are provided. Specimen flaws were sized by post-test fractography in addition to pre-test advanced eddy current technique. The test failure pressures and leak rates are shown to be closer to those predicted on the basis of fractography than on NDE. However, the predictions based on NDE results are encouraging, particularly because they have the potential to determine a more detailed geometry of ligamented cracks from which more accurate predictions of failure pressure and leak rate can be made in the future.

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