Helical Steam Generator Tubes Containing Crack Under External Pressure: A Review of Applicability for Existing Integrity Evaluation Method

2011 ◽  
Author(s):  
Tae-Young Ryu ◽  
Han-Beom Seo ◽  
Jong-Min Kim ◽  
Jae-Boong Choi ◽  
Young-Jin Kim ◽  
...  
Keyword(s):  
Fracture Mechanics ◽  
Steam Generator ◽  
Evaluation Method ◽  
Crack Opening ◽  
Three Dimensional ◽  
External Pressure ◽  
Steam Generator Tube ◽  
Integrity Assessment ◽  
Dimensional Finite Element ◽  
Three Dimensional Finite Element

For integrity assessment of structure containing crack, evaluation method based on fracture mechanics such as linear-elastic and elastic-plastic fracture mechanics has been relatively common method and becoming more widespread. However, it can be used only if the crack opening or tearing is occurred. If the crack exists on the piping components subjected to internal pressure, net-section stress is occurred in the direction on crack opening no matter where crack locate. On the contrary to this, if the external pressure is applied to piping components, net-section stress is occurred opposite direction and it is expected crack opening not to be occur. The subject of this study is SMART steam generator tube which is designed as helical geometrical feature and to be pressurized outside. Three dimensional finite element analyses are carried out to investigate crack behavior under external pressure considered various crack geometries and locations. Furthermore, the possibility of failure of SMART steam generator tube under design pressure is investigated.

A Simplified Thermal Load Evaluation Method for Localized Lug Stresses Beyond Sec. III Appendix-Y

2019 ◽  
Author(s):  
Tsubasa Matsumiya ◽  
Daniel Garcia-Rodriguez ◽  
Akira Nebu ◽  
Noriyuki Takamura
Keyword(s):  
Thermal Stresses ◽  
Evaluation Method ◽  
Three Dimensional ◽  
Parameter Study ◽  
Element Analysis ◽  
Class 1 ◽  
Dimensional Finite Element ◽  
3D Fea ◽  
Three Dimensional Finite Element ◽  
Load Evaluation

Abstract In this work an evaluation method for local thermal stresses on class 1 piping due to U-shaped lugs is presented. First, a three-dimensional finite element analysis (3D-FEA) is used to perform a thermal transient evaluation, obtaining the time-dependent temperature distribution of a realistic range of pipe-lug systems. These results are then used as an input for both a structural 3D-FEA and the corresponding thermal stress term in Non-Mandatory Appendix Y [1]. It was seen that the formula in Appendix-Y cannot account for the thermal stresses obtained through the detailed FEA evaluation. A parameter study using a simplified two-dimensional (2D) FEA approach, shows that the localized thermal stresses due to lugs are significantly affected by: (1) pipe-to-lug thickness ratio, (2) distance between adjacent lugs, and (3) lug height. A set of correction coefficients depending on these parameters is therefore proposed. When applying the proposed correction coefficients to the Appendix Y method, adequately conservative (when compared with 3D FEA results) stresses can be obtained. Since these correction coefficients can be obtained from simple geometric considerations, the proposed method successfully accounts for the complex lug-to-lug interaction while retaining the simplicity of the original Appendix Y approach.

Propagation of Buckles in Sandwich Pipes Under External Pressure

2005 ◽  
Author(s):  
I. P. Pasqualino ◽  
M. I. Lourenc¸o ◽  
T. A. Netto
Keyword(s):  
Three Dimensional ◽  
Nonlinear Behavior ◽  
Element Model ◽  
External Pressure ◽  
Core Material ◽  
Small Scale ◽  
Ongoing Research ◽  
Scale Models ◽  
Dimensional Finite Element ◽  
Three Dimensional Finite Element

Sandwich pipes have been considered feasible conceptions for ultra deepwater pipelines, since they are capable to work at low temperatures and withstand high hydrostatic pressures. Sandwich pipelines are composed by inner and outer metallic pipes and a suitable core material which must provide high compression strength and good thermal insulation. The aim of this ongoing research is to study the quasi-static propagation of buckles in sandwich pipes. In this paper, a three-dimensional finite element model considering material and geometric nonlinear behavior is presented. The mesh discretization is determined through a detailed mesh sensitivity analysis. Some experiments with small scale models combining aluminum pipes and polypropylene as core material were carried out to calibrate the numerical model. The propagation pressure is evaluated under different bonding conditions between pipe layers.

Reference Stresses for Cold-Tube-Bends Including Thickness Variation and Ovality Using Three-Dimensional Finite Element Method

2009 ◽  
Author(s):  
Khosrow Zarrabi ◽  
Felix Kumiadi Kwok
Keyword(s):  
Finite Element ◽  
Cross Section ◽  
Power Plants ◽  
Three Dimensional ◽  
Thickness Variation ◽  
Straight Tube ◽  
Boiler Tube ◽  
Integrity Assessment ◽  
Dimensional Finite Element ◽  
Three Dimensional Finite Element

Tube-bends are extensively used in the boilers of power plants. Tube-bends are manufactured by bending a straight tube section. During this process, the tube cross-section becomes oval and its thickness varies around the circumference of its cross-section. This study uses three-dimensional finite element analysis to establish practical and simple equations for predicting the plastic collapse pressures and the reference stresses of the oval and variable thickness boiler-tube-bends. Such equations are pertinent to the design and integrity assessment of the boiler tube-bends.

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

2015 ◽  
Author(s):  
Min-Kyu Kim ◽  
Han-Bum Surh ◽  
Min-Gu Won ◽  
Nam-Su Huh ◽  
Moon-Ki Kim ◽  
...  
Keyword(s):  
Crack Opening Displacement ◽  
Nuclear Power ◽  
Crack Opening ◽  
Three Dimensional ◽  
Opening Displacement ◽  
Dimensional Finite Element ◽  
Elastic Crack ◽  
Thin Walled ◽  
Three Dimensional Finite Element ◽  
Leak Before Break

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.

scholarly journals A New Technique for Intergranular Crack Formation in Alloy 600 Steam Generator Tubing

2008 ◽  
Vol 130 (1) ◽  
Author(s):  
Tae Hyun Lee ◽  
Il Soon Hwang ◽  
Han Sub Chung ◽  
Jang Yul Park
Keyword(s):  
Steam Generator ◽  
Three Dimensional ◽  
Potential Drop ◽  
Crack Size ◽  
Element Analysis ◽  
Current Test ◽  
Dimensional Finite Element ◽  
Integrity Management ◽  
A New Technique ◽  
Three Dimensional Finite Element

For the integrity management of steam generator (SG) tubes, nondestructive evaluation performed using eddy current test (ECT) is necessary in the assessment. The reliability of ECT evaluation is dependent on the accuracy of ECT for various kinds of defects. For basic calibration and qualification of these techniques, cracked SG tube specimens having mechanical and microstructural characteristics of intergranular cracks in the field are needed. To produce libraries of laboratory-degraded SG tubes with intergranular cracks, a radial denting method was explored for generating inside diameter and outside diameter axial cracks by three-dimensional finite element analysis and experimental demonstration. The technique is proven to be applicable for generating axial cracks with long and shallow geometries as opposed to the semicircular cracks typically obtained by the internal-pressurization method. In addition, a direct current potential drop method with array probes was developed for accurate monitoring and controlling of crack size and shape. By these methods, long and shallow intergranular axial cracks more typical of actual degraded SG tubes were successfully produced.

Assessment of Limit Loads for Circumferential Cracks in Steam Generator Tube Considering Constraining Effect of Tube Support

2005 ◽  
Author(s):  
Hyun Su Kim ◽  
Jong Sung Kim ◽  
Tae Eun Jin ◽  
Hong Deok Kim ◽  
Han Sub Chung
Keyword(s):  
Power Plant ◽  
Nuclear Power Plant ◽  
Steam Generator ◽  
Nuclear Power ◽  
Three Dimensional ◽  
Fission Products ◽  
Limit Load ◽  
Steam Generator Tube ◽  
Integrity Assessment ◽  
Steam Generator Tubes

The steam generator in a nuclear power plant is a large heat exchanger that uses heat from reactor to generate steam to drive the turbine generators. Rupture of a steam generator tube can result in release of fission products to environment. Therefore, an accurate integrity assessment of the steam generator tubes with cracks is of great importance for maintaining safety of a nuclear power plant. The steam generator tubes are supported at periodic intervals by support plates and rotations of the tubes are constrained. Although it was reported that the limit load for a circumferential crack was significantly affected by boundary condition of the tube, existing limit load solutions do not include the constraining effect of tube supports. This paper provides detailed limit load solutions for circumferential cracks in steam generator tubes considering the actual boundary conditions to simulate the constraining effect of the tube supports. Such solutions are developed based on three dimensional (3D) finite element analyses. The resulting limit load solutions are given in a polynomial form, and thus can be simply used in practical integrity assessment of the steam generator tubes.

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.

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