Study of the low-cycle fatigue of lens compensators, allowing for internal pressure

1974 ◽  
Vol 6 (3) ◽  
pp. 386-390
Author(s):  
B. M. Ankirskii
Keyword(s):  
Internal Pressure ◽  
Low Cycle Fatigue ◽  
Cycle Fatigue

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.

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.

scholarly journals Limit, Shakedown and Ratchet Analyses of Defective Pipeline Under Internal Pressure and Cyclic Thermal Loading

2011 ◽  
Author(s):  
Weihang Chen ◽  
Haofeng Chen ◽  
Tianbai Li ◽  
James Ure
Keyword(s):  
Plastic Strain ◽  
Internal Pressure ◽  
Low Cycle Fatigue ◽  
Strain Range ◽  
Collapse Mechanism ◽  
Cycle Fatigue ◽  
Matching Method ◽  
Plastic Strain Range ◽  
Fatigue Assessment ◽  
Linear Matching Method

In this study, the limit load, shakedown and ratchet limit of a defective pipeline subjected to constant internal pressure and a cyclic thermal gradient are analyzed. Ratchet limit and maximum plastic strain range are solved by employing the new Linear Matching Method (LMM) for the direct evaluation of the ratchet limit. Shakedown and ratchet limit interaction diagrams of the defective pipeline identifying the regions of shakedown, reverse plasticity, ratcheting and plastic collapse mechanism are presented and parametric studies involving different types and dimensions of part-through slot in the defective pipeline are investigated. The maximum plastic strain range over the steady cycle with different cyclic loading combinations is evaluated for a low cycle fatigue assessment. The location of the initiation of a fatigue crack for the defective pipeline with different slot type is determined. The proposed linear matching method provides a general-purpose technique for the evaluation of these key design limits and the plastic strain range for the low cycle fatigue assessment. The results for the defective pipeline shown in the paper confirm the applicability of this procedure to complex 3-D structures.

Low-Cycle Fatigue and Ratcheting Responses of Elbow Piping Components

2015 ◽  
Vol 137 (3) ◽  
Author(s):  
T. Hassan ◽  
M. Rahman ◽  
S. Bari
Keyword(s):  
Constitutive Model ◽  
Internal Pressure ◽  
Damage Accumulation ◽  
Low Cycle Fatigue ◽  
Fatigue Cracks ◽  
Constitutive Models ◽  
Code Design ◽  
Cycle Fatigue ◽  
Fatigue Damage Accumulation ◽  
Piping Systems

The objective of this study was to investigate low-cycle fatigue and ratcheting responses of elbows through experimental and analytical studies. Low-cycle fatigue and ratcheting damage accumulation in piping components may occur under repeated reversals of loading induced by earthquake and/or thermomechanical operation. Ratcheting and fatigue damage accumulation can cause failure of piping systems through fatigue cracks or plastic buckling. However, the ratcheting damage induced failures are yet to be understood clearly; consequently, ASME Code design provisions against ratcheting failure continue to be a controversial issue over the last two decades. A systematic set of piping component experimental responses involving ratcheting and a computational tool to simulate these responses will be essential to rationally address the issue. Development of a constitutive model for simulating component ratcheting responses remains to be a challenging problem. In order to develop an experimentally validated constitutive model, a set of elbow experiments was conducted. The loading prescribed in the experiments involved displacement-controlled or force-controlled in-plane cyclic bending with or without internal pressure. Force, displacement, internal pressure, elbow diameter change, and strains at four locations of the elbow specimens were recorded. This article presents and discusses the results from the experimental study. A sister article evaluates seven different constitutive models against simulating these elbow ratcheting and fatigue responses.

Failure Mode and Failure Strengths for Wall Thinning Straight Pipes and Elbows Subjected to Cyclic Loading

2005 ◽  
Author(s):  
Kunio Hasegawa ◽  
Katsumasa Miyazaki ◽  
Izumi Nakamura
Keyword(s):  
Cyclic Loading ◽  
Crack Initiation ◽  
Internal Pressure ◽  
Failure Mode ◽  
Seismic Event ◽  
Low Cycle Fatigue ◽  
Cycle Fatigue ◽  
Wall Thinning ◽  
Piping Systems ◽  
Large Burst

It is important to assess the failure strengths for pipes with wall thinning to maintain the integrity of the piping systems and to make codification of allowable wall thinning. Full-scale fracture experiments on cyclic loading under constant internal pressure were performed for 4-inch diameter straight pipes and 8-inch diameter elbow pipes at ambient temperature. The experiments were low cycle fatigue under displacement controlled condition. It is shown that dominant failure mode under cyclic loading for straight pipes and elbows is crack initiation/growth accompanying swelling by ratchet or buckling with crack initiation. When the thinning depth is large, burst occurs after swelling. In addition, it is shown that pipes with wall thinning less than 50% of wall thickness have sufficient margins against seismic event of the safety shut down earthquake (SSE).

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 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.

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.

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