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.

Low-Cycle Fatigue of Pressurized Steel Elbows Under In-Plane Bending

2014 ◽  
Vol 137 (1) ◽  
Author(s):  
George E. Varelis ◽  
Spyros A. Karamanos
Keyword(s):  
Low Cycle Fatigue ◽  
Strain Curve ◽  
Local Strain ◽  
Material Model ◽  
Fatigue Curve ◽  
Cyclic Stress ◽  
Cyclic Plasticity ◽  
Cycle Fatigue ◽  
Element Analysis ◽  
Analysis And Design

The present study examines the mechanical behavior of steel process piping elbows, subjected to strong cyclic loading conditions. The work is numerical, supported by experimental data on elbow specimens subjected to in-plane cyclic bending, with or without internal pressure, resulting in failure in the low-cycle-fatigue range. The investigation of elbow behavior is conducted using rigorous finite element analysis accounting for measured elbow geometry and the actual material properties. An advanced cyclic plasticity material model is employed for the simulation of the tests. Emphasis is given on the value of local strain and its accumulation at the critical elbow location where cracking occurs. Based on the cyclic stress–strain curve of the material and the strain-based fatigue curve from the test data, the use of Neuber's formula leads to a fatigue analysis and design methodology, offering a simple and efficient tool for predicting elbow fatigue life.

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.

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.

Low Cycle Fatigue of Corroded Pipes Under Cyclic Bending and Internal Pressure

2010 ◽  
Author(s):  
Marcelo Igor Lourenc¸o ◽  
Theodoro A. Netto
Keyword(s):  
Internal Pressure ◽  
Cyclic Load ◽  
Low Cycle Fatigue ◽  
Numerical Models ◽  
Experimental Tests ◽  
Small Scale ◽  
Cycle Fatigue ◽  
Operational Conditions ◽  
Oil Transportation ◽  
Operational Load

Corroded pipes for oil transportation can eventually experience low cycle fatigue failure after some years of operation. The evaluation of the defects caused by corrosion in these pipes is important when deciding for the repair of the line or continuity in operation. Under normal operational conditions, these pipes are subject to constant internal pressure and cyclic load due to bending and/or tension. Under such loading conditions, the region in the pipes with thickness reduction due to corrosion could experience the phenomenon known as ratcheting. The objective of this paper is to present a revision of the available numerical models to treat the ratcheting phenomenon. Experimental tests were developed allowing the evaluation of occurrence of ratcheting in corroded pipes under typical operational load conditions as well as small-scale cyclic tests to obtain the material parameters. Numerical and experimental tests results are compared.

High Temperature, Multi-Material, Cyclic Plasticity of a P91 Welded Branch-Header Connection Under Cyclic Pressure

2015 ◽  
Author(s):  
S. B. Leen ◽  
M. Li ◽  
R. A. Barrett ◽  
S. Scully ◽  
D. Joyce ◽  
...  
Keyword(s):  
High Temperature ◽  
Weld Metal ◽  
Heat Affected Zone ◽  
Low Cycle Fatigue ◽  
Material Model ◽  
Cyclic Plasticity ◽  
Cycle Fatigue ◽  
Parent Metal ◽  
Premature Failure ◽  
Metal Weld

This paper presents a study on high temperature cyclic plasticity of a welded P91 T-joint under cyclic internal pressure, in the context of high temperature low cycle fatigue (HTLCF) performance of such connections. In the present work, attention is focused on the development of a multi-material model for high temperature cyclic plasticity, including the effects of the different weld-related material zones, namely, parent metal, weld metal and heat-affected zone. The cyclic plasticity behaviour of the three zones is identified from previously-published high temperature, low cycle fatigue test results on uniaxial test specimens, including parent metal, weld metal and cross-weld specimens, obtained from a specially fabricated pipe girth weld, using ex-service P91 material. The cyclic plasticity material model includes the effects of kinematic hardening and cyclic softening. A three-dimensional finite element model of the welded T-joint is developed, incorporating the three sets of identified cyclic plasticity constants. The study is limited to isothermal conditions of 500°C, with a view to understanding the complex effects of multiple material zones with inhomogeneous cyclic plasticity behaviour. The heat affected zone is shown to play a key role in the development of plastic strains and localised stresses. The particular T-joint geometry is the subject of an investigation due to premature failure in a combined cycle gas turbine plant.

scholarly journals CFRP Reinforcement and Repair of Steel Pipe Elbows Subjected to Severe Cyclic Loading

2017 ◽  
Vol 139 (5) ◽  
Author(s):  
Ioannis Skarakis ◽  
Giannoula Chatzopoulou ◽  
Spyros A. Karamanos ◽  
Nicholas G. Tsouvalis ◽  
Aglaia E. Pournara
Keyword(s):  
Cyclic Loading ◽  
Structural Integrity ◽  
Mechanical Response ◽  
Low Cycle Fatigue ◽  
Numerical Models ◽  
Strain Curve ◽  
Steel Pipe ◽  
Cyclic Plasticity ◽  
Loading Conditions ◽  
Element Analysis

In order to ensure safe operation and structural integrity of pipelines and piping systems subjected to extreme loading conditions, it is often necessary to strengthen critical pipe components. One method to strengthen pipe components is the use of composite materials. The present study is aimed at investigating the mechanical response of pipe elbows, wrapped with carbon fiber-reinforced plastic (CFRP) material, and subjected to severe cyclic loading that leads to low-cycle fatigue (LCF). In the first part of the paper, a set of LCF experiments on reinforced and nonreinforced pipe bend specimens are described focusing on the effects of CFRP reinforcement on the number of cycles to failure. The experimental work is supported by finite element analysis presented in the second part of the paper, in an attempt to elucidate the failure mechanism. For describing the material nonlinearities of the steel pipe, an efficient cyclic-plasticity material model is employed, capable of describing both the initial yield plateau of the stress–strain curve and the Bauschinger effect characterizing reverse plastic loading conditions. The results from the numerical models are compared with the experimental data, showing an overall good comparison. Furthermore, a parametric numerical analysis is conducted to examine the effect of internal pressure on the structural behavior of nonreinforced and reinforced elbows, subjected to severe cyclic loading.

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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