Estimation of Low-Cycle Fatigue Life of Elbow Pipes Considering the Multi-Axial Stress Effect

2012 ◽  
Author(s):  
Koji Takahashi ◽  
Kazuya Matsuo ◽  
Kotoji Ando ◽  
Yoshio Urabe
Keyword(s):  
Power Plants ◽  
Low Cycle Fatigue ◽  
Axial Stress ◽  
Stress Factor ◽  
Stress Effect ◽  
Cycle Fatigue ◽  
Element Analysis ◽  
Cyclic Bending ◽  
Slope Method ◽  
Inner Pressure

Elbow pipes are commonly used in the piping systems of power plants and chemical plants. The stress states at the elbow part are complex and quite different from those of the straight pipes. It is well known that the fatigue lives of metals under simple push-pull conditions can be successfully predicted by Manson’s universal slope method. However, the low-cycle fatigue lives of elbow pipes under combined cyclic bending and inner pressure cannot be predicted by this method, though the reasons for this have not been clarified. In this work, the low-cycle fatigue tests and finite element analysis of elbows under cyclic bending and inner pressures were carried out. The results showed that the multi-axial stress factor, which is a ratio of hoop stress and axial stress, at elbows is quite high. Considering the multi-axial stress factor, a revised Manson’s universal slope method is proposed in this paper. Using the proposed method, we were able to predict conservatively the low-cycle fatigue lives of elbows under combined cyclic bending and inner pressure.

Estimation of Low-Cycle Fatigue Life of Elbow Pipes Considering the Multi-Axial Stress Effect

2014 ◽  
Vol 136 (4) ◽  
Author(s):  
Koji Takahashi ◽  
Kotoji Ando ◽  
Kazuya Matsuo ◽  
Yoshio Urabe
Keyword(s):  
Internal Pressure ◽  
Low Cycle Fatigue ◽  
Axial Stress ◽  
Fatigue Tests ◽  
Stress Factor ◽  
Stress Effect ◽  
Cycle Fatigue ◽  
Element Analysis ◽  
Cyclic Bending ◽  
Slope Method

The stress states of elbow pipes are complex and different from those of straight pipes. Manson's universal slope method cannot predict the low-cycle fatigue lives of elbow pipes under combined cyclic bending and internal pressure. In this work, fatigue tests and finite element analysis showed that the multi-axial stress factor (i.e., ratio of axial stress to hoop stress) is quite high at elbows. This paper proposes a revised Manson's universal slope method that considers the multi-axial stress factor to predict the low-cycle fatigue lives of elbows under combined cyclic bending and internal pressure with considerably high accuracy.

Component Low Cycle Fatigue Behavior Based on Standard Calculation Procedure and Non-Linear FEA

2017 ◽  
Author(s):  
Jürgen Rudolph ◽  
Adrian Willuweit ◽  
Steffen Bergholz ◽  
Christian Philippek ◽  
Jevgenij Kobzarev
Keyword(s):  
Power Plants ◽  
Low Cycle Fatigue ◽  
Fatigue Behavior ◽  
Hybrid Approach ◽  
Combined Cycle ◽  
Cycle Fatigue ◽  
Element Analysis ◽  
Constitutive Material Model ◽  
Standard Design ◽  
Creep Fatigue

Components of conventional power plants are subject to potential damage mechanisms such as creep, fatigue and their combination. These mechanisms have to be considered in the mechanical design process. Against this general background — as an example — the paper focusses on the low cycle fatigue behavior of a main steam shut off valve. The first design check based on standard design rules and linear Finite Element Analysis (FEA) identifies fatigue sensitive locations and potentially high fatigue usage. This will often occur in the context of flexible operational modes of combined cycle power plants which are a characteristic of the current demands of energy supply. In such a case a margin analysis constitutes a logical second step. It may comprise the identification of a more realistic description of the real operational loads and load-time histories and a refinement of the (creep-) fatigue assessment methods. This constitutes the basis of an advanced component design and assessment. In this work, nonlinear FEA is applied based on a nonlinear kinematic constitutive material model, in order to simulate the thermo-mechanical behavior of the high-Cr steel component mentioned above. The required material parameters are identified based on data of the accessible reference literature and data from an own test series. The accompanying testing campaign was successfully concluded by a series of uniaxial thermo-mechanical fatigue (TMF) tests simulating the most critical load case of the component. This detailed and hybrid approach proved to be appropriate for ensuring the required lifetime period of the component.

The Revised Universal Slope Method to Predict the Low-Cycle Fatigue Lives of Elbow and Tee Pipes

2017 ◽  
Vol 139 (5) ◽  
Author(s):  
Hiun Nagamori ◽  
Koji Takahashi
Keyword(s):  
Experimental Data ◽  
Internal Pressure ◽  
Low Cycle Fatigue ◽  
Experimental Studies ◽  
High Accuracy ◽  
Universal Method ◽  
Cycle Fatigue ◽  
Element Analysis ◽  
Slope Method ◽  
Stress States

The stress states of elbow and tee pipes are complex and different from those of straight pipes. The low-cycle fatigue lives of elbows and tees cannot be predicted by Manson's universal slope method; however, a revised universal method proposed by Takahashi et al. was able to predict with high accuracy the low-cycle fatigue lives of elbows under combined cyclic bending and internal pressure. The objective of this study was to confirm the validity of the revised universal slope method for the prediction of low-cycle fatigue behaviors of elbows and tees of various shapes and dimensions under conditions of in-plane bending and internal pressure. Finite element analysis (FEA) was carried out to simulate the low-cycle fatigue behaviors observed in previous experimental studies of elbows and tees. The low-cycle fatigue behaviors, such as the area of crack initiation, the direction of crack growth, and the fatigue lives, obtained by the analysis were compared with previously obtained experimental data. Based on this comparison, the revised universal slope method was found to accurately predict the low-cycle fatigue behaviors of elbows and tees under internal pressure conditions regardless of differences in shape and dimensions.

scholarly journals Numerical modeling of the low cycle fatigue: effect of manufacturing imperfections caused by machining process

2021 ◽  
Vol 349 ◽  
pp. 02011
Author(s):  
Ikram Abarkan ◽  
Abdellatif Khamlichi ◽  
Rabee Shamass
Keyword(s):  
Surface Roughness ◽  
Fatigue Life ◽  
Power Plants ◽  
Low Cycle Fatigue ◽  
Machining Process ◽  
Loading Conditions ◽  
Cycle Fatigue ◽  
Maximum Shear Strain ◽  
Element Analysis ◽  
The Impact

The majority of mechanical components in nuclear power plants must be designed to withstand extreme cyclic loading conditions. In fact, when these components are subjected to low cycle fatigue, machining imperfections are considered one of the most significant factors limiting their service life. In the present work, using finite element analysis, a methodology has been suggested to predict the fatigue life of cylindrical parts made of 316 SS, at ambient temperature, under nominal strain amplitude ranging from ± 0.5 to ±1.2% with various surface roughness conditions. Two different multiaxial strain-life criteria have been considered to estimate the fatigue life, namely Brown-Miller and maximum shear strain. The comparison between the predicted and the experimental fatigue lifetimes has revealed that the adopted multiaxial strain life criteria can successfully estimate the fatigue life of 316 SS grade under uniaxial loading conditions. Furthermore, it has been found that the fatigue life decreases as the surface roughness average value increases, which indicates that surface regularities have a significant impact on low cycle fatigue life. Therefore, the proposed methodology is found to be capable of assessing the impact of surface roughness on the fatigue life of this specific steel in the low cycle fatigue regime.

A Study on the Temperature Calibration for a Small Electrical Resistance Furnace

2010 ◽  
Author(s):  
Un Bong Baek ◽  
Hae Moo Lee ◽  
Yun-Hee Lee ◽  
Seung Hoon Nahm
Keyword(s):  
Electrical Resistance ◽  
Power Plants ◽  
Low Cycle Fatigue ◽  
Small Scale ◽  
Temperature Calibration ◽  
Cycle Fatigue ◽  
Resistance Furnace ◽  
Small Space ◽  
Start Up ◽  
Electrical Resistance Furnace

A severe thermal stress occurs during start up/shutdown transients in thick walled components of high temperature power plants. Thus, a precise consideration of this issue is very important. Many researchers have studied low-cycle fatigue at high temperatures and small box-type electrical resistance furnaces have been developed for small-sized fatigue specimens. However, these small-scale electrical resistance furnaces need precise temperature calibrations because temperature control is difficult in a small space. Thus, a method for the temperature calibration of a box-type electrical resistance furnace is investigated and calibration procedures are proposed in this study.

scholarly journals Multiaxial fatigue life estimation in low-cycle fatigue regime including the mean stress effect

2018 ◽  
Vol 165 ◽  
pp. 16002
Author(s):  
Daniela Scorza ◽  
Andrea Carpinteri ◽  
Giovanni Fortese ◽  
Camilla Ronchei ◽  
Sabrina Vantadori ◽  
...  
Keyword(s):  
Fatigue Life ◽  
Low Cycle Fatigue ◽  
Equivalent Strain ◽  
Mean Value ◽  
Multiaxial Fatigue ◽  
Stress Effect ◽  
Mean Stress ◽  
Cycle Fatigue ◽  
Structural Components ◽  
Mean Stress Effect

The goal of the present paper is to discuss the reliability of a strain-based multiaxial Low-Cycle Fatigue (LCF) criterion in estimating the fatigue lifetime of metallic structural components subjected to multiaxial sinusoidal loading with zero and non-zero mean value. Since it is well-known that a tensile mean normal stress reduces the fatigue life of structural components, three different models available in the literature are implemented in the present criterion in order to take into account the above mean stress effect. In particular, such a criterion is formulated in terms of strains by employing the displacement components acting on the critical plane and, then, by defining an equivalent strain related to such a plane. The Morrow model, the Smith-Watson-Topper model and the Manson-Halford model are applied to define such an equivalent strain. The effectiveness of the new formulations is evaluated through comparison with some experimental data reported in the literature, related to biaxial fatigue tests performed on metallic specimens under in-and out-of-phase loadings characterised by non-zero mean stress values.

Improved Low Cycle Fatigue Analysis for Ni-Based Turbine Nozzles

2018 ◽  
Author(s):  
Gianluca Maggiani ◽  
Matthew J. Roy ◽  
Simone Colantoni ◽  
Philip J. Withers
Keyword(s):  
Gas Turbines ◽  
Mechanical Test ◽  
Low Cycle Fatigue ◽  
Computation Time ◽  
Cyclic Hardening ◽  
Life Assessment ◽  
Type Model ◽  
Cycle Fatigue ◽  
Element Analysis ◽  
Material Models

The requirements for cleaner energy have driven industrial gas turbines manufacturers to increase firing temperatures and improve cooling of nozzles. The application of high temperature alloys having adequate thermo-mechanical requirements is critical, as assessed by low cycle fatigue performance. The effect of higher firing temperatures combined with higher cooling efficiencies has lead to operating cycles where the level of plastic strain imparted define component life. The capability of material models to account for non-linear effects such as ratchetting or shakedown, cyclic hardening or softening as well as Bauschinger or relaxation effects have been highlighted in this context. Neglecting these effects can lead to over and under-conservative life assessment analysis, while accounting for them using standard multilinear material models lead to convergence issues in finite element analysis. In this paper, Chaboche viscoplastic model has been applied to a transient structural of a first stage gas turbine nozzle. Fitting of the model based on experimental mechanical test data on MAR-M-247 alloy will be described, followed by an overview of how the model may be implemented to a benchmark nozzle thermo-mechanical transient analysis. Finally the details how the Chaboche-type model has provided up to 50% decrease in computation time when compared to using a standard multi-linear material modelling approach.

Low Cycle Fatigue of Nuclear Pipe Components

1974 ◽  
Vol 96 (3) ◽  
pp. 171-176 ◽  
Author(s):  
J. D. Heald ◽  
E. Kiss
Keyword(s):  
Stainless Steel ◽  
Fatigue Life ◽  
Room Temperature ◽  
Fatigue Testing ◽  
Low Cycle Fatigue ◽  
304 Stainless Steel ◽  
Code Design ◽  
Hydraulic Pressure ◽  
Cycle Fatigue ◽  
Cyclic Bending

This paper presents the results of low-cycle fatigue testing and analysis of 26 piping components and butt-welded sections. The test specimens were fabricated from Type-304 stainless steel and carbon steel, materials which are typically used in the primary piping of light water nuclear reactors. Components included 6-in. elbows, tees, and girth butt-welded straight sections. Fatigue testing consisted of subjecting the specimens to deflection-controlled cyclic bending with the objective of simulating system thermal expansion type loading. Tests were conducted at room temperature and 550 deg F, with specimens at room temperature subjected to 1050 psi constant internal hydraulic pressure in addition to cyclic bending. In two tests at room temperature, however, stainless steel elbows were subjected to combined simultaneous cyclic internal pressure and cyclic bending. Predictions of the fatigue life of each of the specimens tested have been made according to the procedures specified in NB-3650 of Section III[1] in order to assess the code design margin. For the purpose of the assessment, predicted fatigue life is compared to actual fatigue life which is defined as the number of fatigue cycles producing complete through-wall crack growth (leakage). Results of this assessment show that the present code fatigue rules are adequately conservative.

Low Cycle Fatigue Tests and Simulations on Steel Elbows

2013 ◽  
Author(s):  
Patricia Pappa ◽  
George E. Varelis ◽  
Spyros A. Karamanos ◽  
Arnold M. Gresnigt
Keyword(s):  
Finite Element ◽  
Low Cycle Fatigue ◽  
Local Strain ◽  
Fatigue Behaviour ◽  
Fatigue Tests ◽  
Cycle Fatigue ◽  
Element Analysis ◽  
Out Of Plane ◽  
Strain Gauge Measurements ◽  
Number Of Cycles

In this paper the low cycle fatigue behaviour of steel elbows under strong cyclic loading conditions (in-plane and out-of-plane) is examined. The investigation is conducted through advanced finite element analysis tools, supported by real-scale test data for in-plane bending. The numerical results are successfully compared with the experimental measurements. In addition, a parametric study is conducted, which is aimed at investigating the effects of the diameter-to-thickness ratio on the low-cycle fatigue of elbows, focusing on the stress and strain variations. Strain gauge measurements are compared with finite element models. Upon calculation of local strain variation at the critical location, the number of cycles to fracture can be estimated.

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