Failure Behavior of Piping Systems With Wall Thinning Under Seismic Loading

2004 ◽  
Vol 126 (1) ◽  
pp. 85-90 ◽  
Author(s):  
Izumi Nakamura ◽  
Akihito Otani ◽  
Masaki Shiratori
Keyword(s):  
Failure Modes ◽  
Low Cycle Fatigue ◽  
Three Dimensional ◽  
Seismic Loading ◽  
Shaking Table ◽  
Failure Behavior ◽  
Shaking Table Tests ◽  
Wall Thinning ◽  
Piping Systems ◽  
Input Acceleration

Shaking table tests of three-dimensional piping models with degradation were conducted in order to investigate the influence of degradation on dynamic behavior and failure modes of piping systems. The degradation condition induced in the piping models was about 50 percent full circumferential wall thinning at elbows. Four types of models were made for the shaking table tests by varying the location of wall thinning in the piping models. These models were excited under the same input acceleration until the models failed and a leak of pressurized internal water occurred. Through these tests, the change of the vibration characteristics and processes to failure of degraded piping models were obtained. The deformation of the piping models tended to concentrate on the degraded elbows, and the damage was concentrated on the weakest elbow in the piping models. The failure mode of the piping models was a low-cycle fatigue failure at the weakest elbow.

Failure Behavior of Piping Systems With Wall Thinning Under Seismic Loading

2002 ◽  
Author(s):  
Izumi Nakamura ◽  
Akihito Otani ◽  
Masaki Shiratori
Keyword(s):  
Failure Modes ◽  
Low Cycle Fatigue ◽  
Seismic Loading ◽  
Shaking Table ◽  
Failure Behavior ◽  
Vibration Characteristic ◽  
Shaking Table Tests ◽  
Wall Thinning ◽  
Piping Systems ◽  
Input Acceleration

In order to investigate the influence of degradation on dynamic behavior and failure modes of piping systems, shaking table tests of 3-D piping models with degradation were conducted. The degradation condition induced in the piping models was about 50% full circumferential wall thinning at an elbow or elbows. By varying the induced parts in the piping model, 4 kinds of models were made for the shaking table tests. These models were excited under the same input acceleration until the models failed and caused leak of pressurized internal water. Through these tests, the change of the vibration characteristic and the process to failure of degraded piping models were obtained. The deformation of the piping models tended to concentrate on the degraded elbows, and therefore the damage concentrated to a weakest elbow in the piping models. The failure mode of the piping models was a low-cycle fatigue failure at the weakest elbow.

Hybrid Seismic Response Evaluation Method for Wall Thinning Piping System

2013 ◽  
Author(s):  
Michiya Sakai ◽  
Shinichi Matsuura ◽  
Fumio Inada
Keyword(s):  
Seismic Response ◽  
Evaluation Method ◽  
Low Cycle Fatigue ◽  
Shaking Table ◽  
Piping System ◽  
Shaking Table Tests ◽  
Seismic Safety ◽  
Pipe Model ◽  
Wall Thinning ◽  
Piping Systems

Pipe wall thinning is a one of the major degradation mechanisms in aged nuclear power plants (NPPs). In Japan, the seismic safety of wall thinning piping system during earthquake must be evaluated in aged NPPs. Seismic safety of piping systems with wall thinning had been investigated by other researchers using shaking table tests of reduced scale and numerical analyses. However, there exist the limitations such as the scale effect of pipe model for shaking table tests and the limit of the evaluation for numerical analysis concerning the criteria of pipe integrity. By the way, elbow can be one of the most important elements to evaluate the seismic safety of piping system. So, in order to evaluate seismic safety of piping systems with wall thinning elbow, hybrid tests have been conducted, in which the seismic response of the whole piping system is treated as a numerical model, and the real piping is used only for the element on which the transformation and damage locally concentrated. The through-wall crack only occurred in the case of a uniform thinning model although cracks didn’t penetrate in the non thinning model and the local thinning model. In the experimental condition, the failure mode of wall thinning elbow under seismic loadings had been low cycle fatigue, and effectiveness of this evaluation method has been demonstrated.

Discussion On Failure Behavior of Piping Systems Under Extremely Large Seismic Loads in BDBE

2021 ◽  
Author(s):  
Izumi Nakamura ◽  
Naoto Kasahara
Keyword(s):  
Static Loading ◽  
Failure Modes ◽  
Shaking Table ◽  
Failure Behavior ◽  
Seismic Loads ◽  
Shaking Table Tests ◽  
Additional Mass ◽  
Pure Lead ◽  
Piping Systems ◽  
Loading Tests

Abstract To investigate the failure behavior of piping systems under severe seismic loads considering beyond design basis event (BDBE), an experimental approach to use pipes made of simulation materials was applied. "Simulation material" means the substitute material for steel to realize the structural experiment by the existing testing facilities. The simulation materials adopted in this study were pure lead (Pb) or lead-antimony (Pb-Sb) alloy. Using pipe elbows made of simulation materials, static loading tests on elbows and shaking table tests on simple piping system models composed of one or two elbows and an additional mass were conducted. From the static loading tests, the load-deflection relationship of an elbow under monotonic loading was obtained as well as the fatigue failure modes under cyclic loading depending on the several cyclic displacement levels. From the shaking table tests, several failure modes were obtained, namely, "Collapse by self-weight", "Collapse by a few cycles of input", "Ratchet and subsequent collapse", "Overall deformation", and "No failure". It was considered that the occurrence of these failure modes was affected by the ratio of the input frequency to the specimen's natural frequency, the ratio of additional mass weight to the limit mass weight, the configuration of the specimen, and the input acceleration level. The experimental results indicated that it was crucial to understand the structure's ultimate behavior when treating BDBE, and that the research approach using simulation material is effective to investigate the ultimate behavior of piping systems.

Failure Behavior of Elbows With Local Wall Thinning Under Cyclic Load

2004 ◽  
Author(s):  
Izumi Nakamura ◽  
Akihito Otani ◽  
Masaki Shiratori
Keyword(s):  
Failure Modes ◽  
Seismic Load ◽  
Failure Behavior ◽  
Cyclic Bending ◽  
Wall Thinning ◽  
Bending Load ◽  
Piping Systems ◽  
Out Of Plane ◽  
Effects Of Aging ◽  
Local Wall Thinning

Pressurized piping systems used in nuclear power plants are supposed to be degraded by the effects of aging. Local wall thinning is one of the defects considered to be caused in piping systems due to the effects of aging, but the failure behavior of thinned wall pipes under seismic load is still not clear. Therefore an experimental and analytical study to clarify the failure behavior of thinned wall pipes is being conducted. In this paper, the experimental results of locally thinned wall elbows under cyclic bending load are described. Displacement-controlled cyclic bending tests were conducted on elbows with local wall thinning. The test models were pressurized to 10MPa with room temperature water and were subjected to in-plane or/and out-of-plane cyclic bending load until their failures. From the tests, the failure modes of the thinned wall elbows were found to be fatigue failure at the flank of the elbow, or fatigue and buckling failure accompanied with ratchet deformation. It was also found that the life of the thinned wall elbow subjected to out-of-plane bending were extremely lower than that of the elbow without wall thinning. The failure modes and fatigue lives of elbows seemed to be affected by a ratchet phenomenon.

Investigation on Failure Behavior of Two-Elbow Piping System Models Made of the Simulation Material Under Excessive Seismic Loads

2020 ◽  
Author(s):  
Izumi Nakamura ◽  
Naoto Kasahara
Keyword(s):  
Failure Modes ◽  
Shaking Table ◽  
System Model ◽  
Failure Behavior ◽  
Piping System ◽  
Seismic Loads ◽  
Sinusoidal Wave ◽  
Additional Mass ◽  
System Models ◽  
Piping Systems

Abstract To investigate the failure behavior of piping systems under excessive seismic loads, shaking table tests on piping system models made of a simulation material have been executed. The simulation material adopted in the experiment was lead-antimony (Pb-Sb) alloy. The piping system model was composed of two elbows made of Pb-Sb alloy, one additional mass, and two fixed anchors. Input motions were sinusoidal wave. The failure modes of the piping system were examined by varying the additional mass and frequency of the input sinusoidal wave. Through the excitation tests, the failure mode which was named as “ratchet and subsequent collapse” was obtained successfully. The result which was classified as “no failure after 500 cycles” was also obtained. It was found that the occurrence of the failure depended on the ratio of the input frequency to the specimen’s natural frequency, and the ratio of additional mass weight to the limit mass weight. Though the effect of higher modes on the failure behavior was necessary to be more investigated, it seemed that the tendency of dominant failure behavior was similar to that of the single-elbow specimen investigated in the previous study. Moreover, it was confirmed that the experimental approach to use a simulation material was applicable for piping system model with multiple elbows.

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.

Excitation Tests on Elbow Pipe Specimens to Investigate Failure Behavior Under Excessive Seismic Loads

2015 ◽  
Author(s):  
Izumi Nakamura ◽  
Naoto Kasahara
Keyword(s):  
Nuclear Power ◽  
Power Plants ◽  
Failure Modes ◽  
Safety Management ◽  
Dominant Frequency ◽  
Failure Behavior ◽  
Seismic Loads ◽  
Energy Agency ◽  
Piping Systems ◽  
Input Acceleration

After the accident at Fukushima Dai-ichi Nuclear Power Plant in the 2011 Great East Japan Earthquake, the International Atomic Energy Agency (IAEA) requires to consider the design extension conditions (DEC) for the safety management of nuclear power plants (NPPs). In considering DEC, it is necessary to clarify the possible failure modes of the structures and their mechanism under the extreme loadings. Because piping systems are one of the representative components of NPP, and there is a possibility to failure at seismic events, the authors conducted an experimental investigation on failure modes and their mechanisms of piping systems under excessive seismic loads. The experiments are categorized into the fundamental plate tests and pipe component tests. In this paper, the results of the pipe component tests would be described. In the pipe component tests, the authors used piping specimens constituted with one steel elbow and a weight. Though the input acceleration level was much over the allowable level to prevent collapse failure by the seismic design, the failure mode obtained by the excitation tests were mainly the fatigue failure. The reduction of the dominant frequency and the increase of the hysteresis damping were clearly observed in the high-level input acceleration due to the plastic deformation, and they affected the specimens’ vibration response greatly.

Excitation Tests on Elbow Pipe Specimens to Investigate Failure Behavior Under Excessive Seismic Loads

2017 ◽  
Vol 139 (6) ◽  
Author(s):  
Izumi Nakamura ◽  
Naoto Kasahara
Keyword(s):  
Nuclear Power ◽  
Failure Modes ◽  
Dominant Frequency ◽  
Failure Behavior ◽  
Seismic Loads ◽  
Experimental Stress ◽  
Safe Management ◽  
Piping Systems ◽  
Input Acceleration ◽  
High Level

The accident at the Fukushima Dai-ichi Nuclear Power Plant (NPP) resulting from the 2011 Great East Japan Earthquake raised awareness as to the importance of considering Beyond Design Basis Events (BDBE) when planning for safe management of NPPs. In considering BDBE, it is necessary to clarify the possible failure modes of structures under extreme loading. Because piping systems are one of the representative components of NPPs, an experimental investigation was conducted on the failure of a pipe assembly under simulated excessive seismic loads. The failure mode obtained by excitation tests was mainly fatigue failure. The reduction of the dominant frequency and the increase of hysteresis damping were clearly observed in high-level input acceleration due to plastic deformation, and they greatly affected the specimens’ vibration response. Based on the experimental results, a procedure is proposed for calculating experimental stress intensities based on excitation test so that they can be compared with design limitations.

Comparison of Failure Modes of Piping Systems With Wall Thinning Subjected to In-Plane, Out-of-Plane, and Mixed Mode Bending Under Seismic Load: An Experimental Approach

2010 ◽  
Vol 132 (3) ◽  
Author(s):  
Izumi Nakamura ◽  
Akihito Otani ◽  
Masaki Shiratori
Keyword(s):  
Dynamic Behavior ◽  
Failure Modes ◽  
Seismic Load ◽  
Piping System ◽  
Shake Table ◽  
Shake Table Tests ◽  
Wall Thinning ◽  
Piping Systems ◽  
Out Of Plane ◽  
Plane Bending

Pressurized piping systems used for an extended period may develop degradations such as wall thinning or cracks due to aging. It is important to estimate the effects of degradation on the dynamic behavior and to ascertain the failure modes and remaining strength of the piping systems with degradation through experiments and analyses to ensure the seismic safety of degraded piping systems under destructive seismic events. In order to investigate the influence of degradation on the dynamic behavior and failure modes of piping systems with local wall thinning, shake table tests using 3D piping system models were conducted. About 50% full circumferential wall thinning at elbows was considered in the test. Three types of models were used in the shake table tests. The difference of the models was the applied bending direction to the thinned-wall elbow. The bending direction considered in the tests was either of the in-plane bending, out-of-plane bending, or mixed bending of the in-plane and out-of-plane. These models were excited under the same input acceleration until failure occurred. Through these tests, the vibration characteristic and failure modes of the piping models with wall thinning under seismic load were obtained. The test results showed that the out-of-plane bending is not significant for a sound elbow, but should be considered for a thinned-wall elbow, because the life of the piping models with wall thinning subjected to out-of-plane bending may reduce significantly.

Development of Ultimate Strength Evaluation Method for Piping Subjected to Seismic Loads

2013 ◽  
Author(s):  
Hideo Machida ◽  
Hiromasa Chitose ◽  
Tatsuhiro Yamazaki
Keyword(s):  
Power Plants ◽  
Evaluation Method ◽  
Failure Modes ◽  
Limit State ◽  
Seismic Loading ◽  
Earthquake Resistance ◽  
State Function ◽  
Limit State Function ◽  
Input Acceleration ◽  
Resistance Tests

This paper reports the results of the study on the failure modes and limit loads of piping in nuclear power plants subjected to cyclic seismic loading. By investigating the past fracture tests and earthquake resistance tests, it became clear that dominant failure mode of piping was fatigue, and the effect of ratchet strain was negligible. Until now, the stress generated with the acceleration of an earthquake was classified into the primary stress. However, the relationship between the input acceleration and the seismic response displacement of the pipe observed from earthquake resistance tests is non-linear, and increasing rate of displacement is lower than that of input acceleration in elastic-plastic stress condition. Therefore, the seismic loading can be treated as displacement controlled loading. To evaluate the reliability-based critical acceleration, a limit state function was defined taking the variations in the fatigue strength or some parameters into consideration. By using the limit state function, the reliability was evaluated for the typical piping of boiling water reactor (BWR) plants subjected to cyclic seismic loading, and a partial safety factors were calculated. Based on these results, a fatigue curve corresponding to the target reliability was proposed.

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