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.

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.

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.

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.

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.

Fatigue Life Estimation Method Considering Inelastic Behavior of Ni-Based Directionally Solidified Superalloy With Multiple Holes

2012 ◽  
Author(s):  
Takashi Yokoyama ◽  
Masaru Sekihara
Keyword(s):  
Crack Initiation ◽  
Low Cycle Fatigue ◽  
Estimation Method ◽  
Inelastic Strain ◽  
Maximum Tensile Stress ◽  
Fatigue Tests ◽  
Inelastic Behavior ◽  
Cycle Fatigue ◽  
Directionally Solidified ◽  
Element Analysis

Low cycle fatigue tests at high temperature were conducted on test specimens with small holes made of a Ni-based directionally solidified superalloy, which are intended as the cooling structures formed in the components in the fossil fuel power plant. The tests included those cases with and without a strain holding process, i.e., fatigue creep interaction (FCI) tests and low cycle fatigue (LCF) tests, respectively. The number of LCF crack initiation cycles of the one- and seven-hole specimens decreased compared to that of the smooth one. The number of FCI crack initiation cycles of a compressive hold case for the seven-hole specimen decreased compared to that of the LCF test, while that of a tensile hold case decreased further. The test results were evaluated based on the inelastic behavior around the center hole of the specimens, where the most serious inelastic strain occurred, using finite element analysis that takes into account the inelastic anisotropy of material properties. The number of crack initiation cycles of the LCF and the compressive FCI tests correlated with the maximum tensile stress around the hole, while that of all the tests correlated with the frequency-modified strain energy. We propose a method for evaluating cyclic inelastic behavior around a hole using cyclic Neuber’s rule for anisotropic materials to simply evaluate the failure life of actual components.

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 Evaluation of Pipe Bends With Local Wall Thinning Considering Multi-Axial Stress State

2015 ◽  
Vol 137 (4) ◽  
Author(s):  
Yoshio Urabe ◽  
Koji Takahashi ◽  
Hisanori Abe
Keyword(s):  
Fatigue Strength ◽  
Stress State ◽  
Low Cycle Fatigue ◽  
Axial Stress ◽  
Fatigue Tests ◽  
Cycle Fatigue ◽  
Pipe Bend ◽  
Wall Thinning ◽  
Damage Rule ◽  
Local Wall Thinning

Low cycle fatigue tests and finite element (FEM) analysis were conducted using 100A pipe bend specimens made of STPT410 carbon steel with and without local wall thinning local wall thinning was machined on the inside of the elbow and was prepared at extrados, crown, and intrados. The parameters of the wall thinning were same (the wall thinning ratio = 0.5, the wall thinning angle = 180 deg, and the wall thinning length = 100 mm) in the all test cases. The pipe bend specimens were subjected to the prescribed cyclic in-plane bending displacement with constant internal pressure of 0–12 MPa. Also, low cycle fatigue tests using sound pipe bend specimens were carried out for comparison. According to the test results, low cycle fatigue strength of wall thinned pipe bend specimens was not so different, regardless of location of wall thinning. Low cycle fatigue strength of the pipe bend specimens was beneath the best fit fatigue curve and its reason can be explained quantitatively by a proposed cumulated damage rule introducing ductility exhaustion considering multi-axial stress state. The validity of the new proposed cumulative damage rule was also confirmed by the another sample analysis using other reference data obtained by pre-overloaded in-plane cyclic bending tests.

Low Cycle Fatigue Behaviors of Elbow With Local Wall Thinning Under Combined Bending and Internal Pressure

2011 ◽  
Author(s):  
Koji Takahashi ◽  
Kazuya Matsuo ◽  
Kyohei Sato ◽  
Kotoji Ando ◽  
Yoshio Urabe ◽  
...  
Keyword(s):  
Internal Pressure ◽  
Low Cycle Fatigue ◽  
Three Dimensional ◽  
Growth Direction ◽  
Fatigue Tests ◽  
Metal Loss ◽  
Cycle Fatigue ◽  
Crack Penetration ◽  
Wall Thinning ◽  
Local Wall Thinning

Low-cycle fatigue tests were conducted using elbow specimens with local wall thinning in order to investigate the influences of position of local wall thinning on the low-cycle fatigue behaviors of elbows. Local wall thinning was machined on the inside of the elbow in order to simulate metal loss from erosion corrosion. The local wall thinning was located in three different areas. The elbow specimens were subjected to cyclic in-plane bending under displacement control with internal pressure of 9 MPa. In addition, three-dimensional elastic-plastic analyses were also carried out using the finite element method. As a result, the crack penetration area and the crack growth direction were successfully predicted by the analyses.

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.

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.

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