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.

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.

Prediction of Low-Cycle Fatigue Lives of Elbow and Tee Pipes Using Revised Universal Slope Method

2016 ◽  
Author(s):  
Hiun Nagamori ◽  
Koji Takahashi
Keyword(s):  
Finite Element ◽  
Crack Initiation ◽  
Internal Pressure ◽  
Low Cycle Fatigue ◽  
Growth Direction ◽  
Cycle Fatigue ◽  
Finite Element Analyses ◽  
Slope Method ◽  
Crack Growth Direction ◽  
Stress States

The stress states of elbow and tee pipes are complex and different from those of straight pipes. Several researchers have reported the low-cycle fatigue lives of elbows and tees under cyclic bending with internal pressure conditions. In this work, finite element analyses were carried out to simulate the reported experimental results of elbows and tees. The crack initiation area and the crack growth direction were successfully predicted by the analyses. The analytical results showed that the revised universal slope method can accurately predict the low-cycle fatigue lives of elbow and tee pipes under internal pressure conditions regardless of differences in shape and dimensions.

Influence of Initial and Welding Residual Stresses on Low Cycle Fatigue and Ratcheting Response Simulations of Elbows

2017 ◽  
Author(s):  
Nazrul Islam ◽  
Tasnim Hassan
Keyword(s):  
Residual Stress ◽  
Residual Stresses ◽  
Low Cycle Fatigue ◽  
Simulation Models ◽  
Cycle Fatigue ◽  
Residual Stress Field ◽  
Element Analysis ◽  
Girth Welding ◽  
Stress States ◽  
Welding Processes

Earlier studies [1] showed that the ANSYS software package customized with an advanced rate-independent constitutive model was unable to simulate some of the low-cycle fatigue responses of elbow components. Hence, simulations are performed to investigate the influence of manufacturing and welding residual stresses on elbow low-cycle fatigue responses. The sequentially coupled thermo-mechanical finite element analysis is performed to determine the initial residual stress states in elbows due to the elbow manufacturing processes and welding of elbows to straight pipes. Real-time girth-welding processes are taken into account to simulate the welding induced residual stress field. Incorporating these initial residual stresses in the computations, low-cycle fatigue and strain ratcheting responses are simulated by ANSYS. The simulation responses demonstrate that the influence of manufacturing and welding residual stresses in elbows on its low-cycle fatigue responses is negligible. Hence, the question remains what is missing in the simulation models that some of the elbow low-cycle fatigue responses cannot be simulated.

scholarly journals An Experimental Study on Low-Cycle Fatigue Crack Initiation Life Prediction of Powder Superalloy FGH96 Based on the Manson-Coffin and Damage Mechanics Methods

Metals ◽  
2021 ◽  
Vol 11 (3) ◽  
pp. 489
Author(s):  
Yuanming Xu ◽  
Hao Chen ◽  
Shuming Zhang ◽  
Tianpeng He ◽  
Xuerong Liu ◽  
...  
Keyword(s):  
Experimental Data ◽  
Fatigue Life ◽  
Life Prediction ◽  
Damage Mechanics ◽  
Prediction Models ◽  
Low Cycle Fatigue ◽  
Fatigue Crack Initiation ◽  
Life Cycles ◽  
Cycle Fatigue ◽  
Element Analysis

The applicability of both prediction methods for low-cycle fatigue life of powder superalloy based on the Manson-Coffin equation and damage mechanics were addressed. Both fatigue life prediction models were evaluated by low-cycle fatigue experimental data of powder superalloy FGH96 with non-destructive standard parts and those with inclusions. Due to the characteristics of high strength and low plasticity of powder superalloy FGH96, errors in calculating the plastic strain amplitude deviate severely the prediction outcomes when using Manson-Coffin method. Meanwhile, by introducing the damage variable which characterizes the material damage, the damage evolution equation can be built by fitting the experimental data of standard parts and also applied to powder superalloy specimens containing inclusion. It is indispensable to accurately calculate the damage characterization parameter through finite element analysis in local stress concentration around the inclusion. The applicability of the prediction model was verified by the test life cycles of experimental specimens with different types and sizes of inclusions subsequently. Testing and simulation work showed much better prediction accuracies globally for the damage mechanics approach.

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.

Experimental and Numerical Investigation of Pressurized Pipe Elbows Under Strong Cyclic Loading

2013 ◽  
Author(s):  
George E. Varelis ◽  
Jan Ferino ◽  
Spyros A. Karamanos ◽  
Antonio Lucci ◽  
Giuseppe Demofonti
Keyword(s):  
Internal Pressure ◽  
Low Cycle Fatigue ◽  
Numerical Models ◽  
Local Strain ◽  
Material Model ◽  
Testing Procedure ◽  
Cyclic Plasticity ◽  
Cycle Fatigue ◽  
Element Analysis ◽  
Dimensional Measurements

The present work examines the behavior of pipe elbows subjected to strong cyclic in-plane bending loading in the presence of internal pressure. In the first part of this work the experimental procedure is presented in detail. The tests are conducted in a constant amplitude displacement-controlled mode resulting to failures in the low-cycle fatigue range. The overall behavior of each tested specimen, as well as the evolution and concentration of local strains are monitored throughout the testing procedure. Different internal pressure levels are used in order to examine their effect on the fatigue life of the specimens. The above experimental investigation is supported by rigorous finite element analysis. Using detailed dimensional measurements and material testing obtained prior to specimen testing, detailed numerical models are developed to simulate the conducted experiments. An advanced cyclic plasticity material model is employed for the simulation of the tests. Emphasis is given on the local strain development at the critical part of the elbow where cracking occurs. Finally, the results of the present investigation are compared with available design provisions in terms of both ultimate capacity and low-cycle fatigue.

Effect of Local Wall Thinning on Low-Cycle Fatigue Behaviors of Elbow With Internal Pressure: Estimation of Fatigue Life Based on Revised Universal Slope Method

2013 ◽  
Author(s):  
Koji Takahashi ◽  
Kyohei Sato ◽  
Kazuya Matsuo ◽  
Kotoji Ando ◽  
Yoshio Urabe ◽  
...  
Keyword(s):  
Fatigue Crack ◽  
Crack Initiation ◽  
Internal Pressure ◽  
Low Cycle Fatigue ◽  
Fatigue Crack Initiation ◽  
Local Buckling ◽  
Cycle Fatigue ◽  
Slope Method ◽  
Wall Thinning ◽  
Local Wall Thinning

Low-cycle fatigue tests and finite element analysis were conducted using 100A elbow specimens made of STPT410 with local wall thinning in order to investigate the influences of local wall thinning on the low-cycle fatigue behaviors of elbows with internal pressure. Local wall thinning was machined on the inside of the elbow in order to simulate metal loss by flow-accelerated corrosion. The local wall thinning located in three different areas, called extrados, crown and intrados. Eroded ratio (eroded depth/wall thickness) was 0.5 and 0.8. The elbow specimens were subjected to cyclic in-plane bending under displacement control with internal pressure of 0 or 9 MPa. Fatigue failure was classified into two types. The one is the type of fatigue crack initiation and another is the type of crack initiation after local buckling. In the type of fatigue crack initiation, fatigue crack initiated at crown and propagates to the axial direction. In the type of crack initiation after local buckling, at first local buckling occurs and secondary, crack initiates at the same place and propagates to the circumferential direction. The low-cycle fatigue lives of elbows were predicted conservatively by the revised universal slope method.

Low Cycle Fatigue Behavior and Seismic Assessment for Pipe Bend Having Local Wall Thinning-Influence of Internal Pressure

2013 ◽  
Vol 135 (4) ◽  
Author(s):  
Yoshio Urabe ◽  
Koji Takahashi ◽  
Kyohei Sato ◽  
Kotoji Ando
Keyword(s):  
Internal Pressure ◽  
Fatigue Failure ◽  
Low Cycle Fatigue ◽  
Fatigue Behavior ◽  
Safety Margin ◽  
Cycle Fatigue ◽  
Element Analysis ◽  
Pipe Bend ◽  
Wall Thinning ◽  
Local Wall Thinning

One of the concerned technical issues in the nuclear piping under operation is pipe wall thinning caused by flow accelerated corrosion. This paper focuses on influence of internal pressure on low cycle fatigue life of pipe bends with local wall thinning and evaluation of safety margin against seismic loading in order to apply the obtained knowledge to the nuclear piping. In-plane bending fatigue tests under several constant internal pressure magnitudes were carried out using carbon steel pipe bends with local wall thinning at the extrados. Also finite element analysis, code-based seismic evaluation and fatigue analysis based on calculated strain range were carried out. Obtained main conclusions are as follows: (1) the tested pipe bends with local wall thinning at the extrados have a strong resistance against fatigue failure based on nuclear seismic piping design in Japan at least up to 12 MPa. That is, the tested pipe bends with severe local wall thinning (eroded ratio = 0.5 and eroded angle = 180 deg) at the extrados have margins against fatigue failure, even though the wall thickness is less than the code-required minimum value based on the nuclear piping seismic design in Japan. (2) Combination of the conventional B2 index and the Ke factor provided in the JSME Design and Construction Code, which is referred by JEAC 4601-2008 overestimates fictitious stress amplitude, when sum of the primary and secondary stress is much greater than 3 Sm.

Features of the kinetics of cyclic elastoplastic deformation diagrams at dwells in cycles and superimposition of variable stresses on them

2020 ◽  
Vol 86 (12) ◽  
pp. 46-53
Author(s):  
M. M. Gadenin
Keyword(s):  
Experimental Data ◽  
Elastoplastic Deformation ◽  
Low Cycle Fatigue ◽  
Cycle Fatigue ◽  
Loading Cycle ◽  
Additional Variable ◽  
Dynamic Creep ◽  
Variable Stresses ◽  
Kinetics Of ◽  
Deformation Diagrams

The goal of the study is determination of the regularities of changes in cyclic strains and related deformation diagrams attributed to the existence of time dwells in the loading modes and imposition of additional variable stresses on them. Analysis of the obtained experimental data on the kinetics of cyclic elastoplastic deformation diagrams and their parameters revealed that in contrast to regular cyclic loading (equal in stresses), additional deformations of static and dynamic creep are developed. The results of the studys are especially relevant for assessing the cyclic strength of unique extremely loaded objects of technology, including nuclear power equipment, units of aviation and space systems, etc. The experiments were carried out on the samples of austenitic stainless steel under low-cycle loading and high temperatures of testing. Static and dynamic creep deformations arising under those loading conditions promote an increase in the range of cyclic plastic strain in each loading cycle and also stimulate an increase in the range of elastoplastic strain due to active cyclic deformation. At the same time the existence of dwells on extrema of stresses in cycles without imposition of additional variable stresses on them most strongly affects the growth of plastic strain ranges in cycles. Imposition of additional variable stresses on dwells also results in the development of creep strains, but their growth turns out to be somewhat less than in the presence of dwells without stresses imposed. The diagrams of cyclic deformation obtained in the experiments are approximated by power dependences, their kinetics being described in terms of the number of loading cycles using corresponding temperature-time functions. At the same time, it is shown that increase in the cyclic plastic deformation for cycles with dwells and imposition of additional variable stresses on them decreases low cycle fatigue life compared to regular loading without dwells at the same stress amplitudes, moreover, the higher the values of static and dynamic creep, the greater decrease in low-cycle fatigue life. This conclusion results from experimental data and analysis of conditions of damage accumulation for the considered forms of the loading cycle using the deformation criterion of reaching the limit state leading to fracture.

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.

Sign in / Sign up

Export Citation Format

Share Document