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).

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

2008 ◽  
Vol 130 (1) ◽  
Author(s):  
Kunio Hasegawa ◽  
Katsumasa Miyazaki ◽  
Izumi Nakamura
Keyword(s):  
Cyclic Loading ◽  
Crack Initiation ◽  
Failure Mode ◽  
Seismic Event ◽  
Low Cycle Fatigue ◽  
Seismic Loading ◽  
Fatigue Curve ◽  
Wall Thinning ◽  
Piping Systems ◽  
Asme Code

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 4in. diameter straight pipes and 8in. diameter elbow pipes at ambient temperature. The experiments were low cycle fatigue under displacement controlled conditions. It is shown that a 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 deep, the failure mode is burst and crack growth with ratchet swelling. In addition, failure strengths were compared with the design fatigue curve of the ASME Code Sec. III. It is shown that pipes with wall thinning less than 50% of wall thickness have sufficient margins against a seismic event of the safety shutdown earthquake.

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.

Detection of the Crack Initiation by Means of AE Method Under Low Cycle Fatigue of Elbow Pipe Having Local Wall Thinning

2010 ◽  
Author(s):  
Naoya Kasai ◽  
Kotoji Ando ◽  
Maki Nishio ◽  
Yoshio Urabe ◽  
Koji Takahashi
Keyword(s):  
Crack Initiation ◽  
Low Cycle Fatigue ◽  
Axial Strain ◽  
Wide Band ◽  
Fatigue Tests ◽  
Crack Growth Behavior ◽  
Cycle Fatigue ◽  
Accelerated Corrosion ◽  
Wall Thinning ◽  
Local Wall Thinning

This paper describes the detectability of the crack initiation by means of the AE method under low cycle fatigue of the elbow pipe having local wall thinning to clarify the crack growth behavior for the pipes. Elbow specimens having local wall thinning were prepared, and local wall thinning due to flow accelerated corrosion was simulated by machined pipe wall thinning. Low cycle fatigue tests for the specimens were then carried out. AE method during low cycle fatigue tests was conducted to evaluate the crack initiation and location. In AE measurement, wide band AE sensors of 5mm in diameter were used to attach to the convex surfaces of the specimens. The circumference and axial strain of the specimens and the cross head displacement were also stored to the digital AE system signal. As a result, it is clear that the AE signals indicated the crack initiation in small circumference strain.

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.

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.

Experimental Study on Low Cycle Fatigue Behaviours of Wrinkled Pipes

2010 ◽  
Author(s):  
Jianmin Zhang ◽  
J. J. Roger Cheng ◽  
Joe Zhou
Keyword(s):  
Cyclic Loading ◽  
Internal Pressure ◽  
Failure Modes ◽  
Low Cycle Fatigue ◽  
Bending Moment ◽  
Monotonic Loading ◽  
Cycle Fatigue ◽  
Axial Deformation ◽  
Deformation Localization ◽  
Loading Procedure

Buried pipelines can be locally buckled (wrinkled) by a load combination of axial deformations and rotations. Previous test results show that those wrinkled pipes do not lose their safety and integrity if they possess sufficient ductility. However, if those wrinkled pipes are going to continue operating under the condition of cyclic loading, their low cycle fatigue (LCF) behaviours have to be thoroughly investigated. This paper presents LCF tests for two full-scale pipes and the relevant results. Those two pipes were tested under a complicated loading procedure. The entire loading consisted of two stages: the monotonic loading stage and the cyclic loading stage. The monotonic loading was designed to form an enclosed wrinkle around the pipe under a locked curvature, and the cyclic loading was planned to fracture the wrinkled pipe. Firstly, the loading procedure was demonstrated by viewing the spectra of MTS load, MTS stroke, jack load, internal pressure, as well as pipe end average rotation. Secondly, the global behaviour was investigated by examining the relation between bending moment and global curvature, the relation between pivot axial load and relative axial deformation (RAD) between pivots, and the relation between internal pressure and RAD between pivots. Thirdly, the phenomenon of ‘deformation localization’ was studied by investigating the relation between the global RAD and the local RAD, and it was found that the global deformation was totally localized into the wrinkle area. Fourthly, the failure modes were discussed and it was found that the seam weld was more liable to be fractured under the condition of cyclic axial deformation. At last, the failure mechanism was investigated by macroscopically examining fracture surfaces. It found out that the cracks initiated from multi-locations on surfaces, then those cracks propagated from surfaces into the interior and finally fractured the pipe wall. Moreover, it found out that more damage was generated from the inside surface than from the outside surface.

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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