Effect of Local Wall Thinning on the Dynamic Behavior of Piping Systems

2005 ◽  
Author(s):  
Izumi Nakamura ◽  
Akihito Otani ◽  
Masaki Shiratori
Keyword(s):  
Dynamic Behavior ◽  
Failure Behavior ◽  
Piping System ◽  
Test Model ◽  
System Models ◽  
Wall Thinning ◽  
Piping Systems ◽  
Out Of Plane ◽  
Plane Bending ◽  
Local Wall Thinning

In order to investigate the influence of degradation on dynamic behavior and the failure mode of piping systems with local wall thinning, shake table tests using 3-D piping system models were conducted. The degradation considered in this study was wall thinning, which would be caused in piping systems due to the effects of aging. The degradation condition induced in the piping system model was 50% full circumferential wall thinning at an elbow. The test model was designed to cause out-of-plane bending moment to the thinned-wall elbow by excitation tests. The model without wall thinning was also used in the excitation test to compare the behavior of the piping system models. These models were excited under same input acceleration until fatigue cracks penetrated or an excessive deformation occurred to the models. Through these tests, the vibration characteristic and the process to failure of degraded piping models were obtained for the out-of-plane bending model. This paper describes the dynamic response and failure behavior of piping systems with wall thinning based on the test results.

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.

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

2007 ◽  
Author(s):  
Satoshi Tsunoi ◽  
Akira Mikami ◽  
Izumi Nakamura ◽  
Akihito Otani ◽  
Masaki Shiratori
Keyword(s):  
Analytical Model ◽  
Failure Modes ◽  
Experimental Investigations ◽  
Seismic Load ◽  
Piping System ◽  
Wall Thinning ◽  
Piping Systems ◽  
Out Of Plane ◽  
Seismic Loadings ◽  
Local Wall Thinning

The authors have proposed an analytical model by which they can simulate the dynamic and failure behaviors of piping systems with local wall thinning against seismic loadings. In the previous paper [13], the authors have carried out a series of experimental investigations about dynamic and failure behaviors of the piping system with fully circumferential 50% wall thinning at an elbow or two elbows. In this paper these experiments have been simulated by using the above proposed analytical model and investigated to what extent they can catch the experimental behaviors by simulations.

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

2007 ◽  
Author(s):  
Izumi Nakamura ◽  
Akihito Otani ◽  
Masaki Shiratori
Keyword(s):  
Failure Modes ◽  
Seismic Load ◽  
Piping System ◽  
Shake Table ◽  
Shake Table Tests ◽  
Wall Thinning ◽  
Piping Systems ◽  
Out Of Plane ◽  
Plane Bending ◽  
The Difference

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 3-D 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 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 piping models with wall thinning subjected to out-of-plane bending may reduce significantly.

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.

Influence of Local Wall Thinning and Support Stiffness in Piping Systems on Safety Assessments for Dynamic Loading

2014 ◽  
Author(s):  
Klaus Kerkhof ◽  
Fabian Dwenger ◽  
Gereon Hinz ◽  
Siegfried Schmauder
Keyword(s):  
Stress Analysis ◽  
Response Spectrum ◽  
System Response ◽  
Piping System ◽  
Load Bearing ◽  
Wall Thinning ◽  
Safety Margins ◽  
Piping Systems ◽  
Bearing Behavior ◽  
Local Wall Thinning

The load bearing behavior of piping systems depends considerably on support distances and stiffness as well as cross section characteristics. Stiffness of supports can often be defined only with difficulty by applying simplified procedures or guidelines based on assumptions. Load cases can be estimated quite well, but the safety assessment of a piping system can only be as reliable as the system model can realistically describe the present support stiffness or imperfections e.g. local wall thinning. As a consequence, the prediction of the system response may be poor. It is likely that calculated frequencies differ from natural frequencies determined experimentally. These frequency shifts lead to unrealistic predictions of stress analysis. Examples for overestimations and underestimations of stress analysis are given regarding the load case earthquake, depending on whether the frequency shift runs into or out of the plateau of the applied floor response spectrum. The influence of local wall thinning on modal characteristics is investigated. Conservative estimations of the influence on the load bearing behavior regarding severe local wall thinning are given. For fatigue checks the linear response of an experimental piping system is calculated and safety margins are demonstrated by comparing calculated with experimental results.

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 BEHAVIOR OF ELBOWS WITH LOCAL WALL THINNING

2008 ◽  
Vol 22 (11) ◽  
pp. 845-850 ◽  
Author(s):  
SUNG-HO LEE ◽  
JEONG-KEUN LEE ◽  
JAI-HAK PARK
Keyword(s):  
Test System ◽  
Failure Behavior ◽  
Piping System ◽  
Bending Tests ◽  
Steel Pipes ◽  
Wall Thinning ◽  
Load Carrying ◽  
Set Up ◽  
Aging Phenomena ◽  
Local Wall Thinning

Wall thinning defect due to corrosion is one of major aging phenomena in carbon steel pipes in most plant industries, and it results in reducing load carrying capacity of the piping components. A failure test system was set up for real scale elbows containing various simulated wall thinning defects, and monotonic in-plane bending tests were performed under internal pressure to find out the failure behavior of them. The failure behavior of wall-thinned elbows was characterized by the circumferential angle of thinned region and the loading conditions to the piping system.

Limit and Shakedown Loads Determination for Locally Thinned Wall Pipe Branch Connection Subjected to Pressure and Bending Moments

2012 ◽  
Author(s):  
Youssef A. F. Hafiz ◽  
Maher Y. A. Younan ◽  
Hany F. Abdalla
Keyword(s):  
Numerical Models ◽  
Bending Moment ◽  
Limit Load ◽  
Tension Stress ◽  
Assessment Procedure ◽  
Wall Thinning ◽  
Out Of Plane ◽  
Plane Bending ◽  
Shakedown Limit ◽  
Local Wall Thinning

In this paper the shakedown limit load for unreinforced locally thinned wall pipe branch connection is determined using the Simplified Technique. Loadings were considered to be internal pressure, as a steady load, with in-plane bending or with out-of-plane bending applied on the branch, as alternating loads. Two locations of local wall thinning were taken; one was on the run pipe opposite to the branch and other on the branch at the maximum tension stress side of the bending moment applied whether in in-plane or out-of-plane situation. Two Finite Element (FE) limit load models were used to verify the modeling of the pipe branch connection with its local wall thinning. First model results were compared with experimental data taken from the literature, and the second results were compared with numerical models taken also from the literature and also compared with API 579 “Fitness For Service” (FFS), part-five, level-two assessment procedure. First and second comparisons lead to good agreement but for API 579 comparison it was found that it is slightly changing with the depth of the local wall thinning but does not reflect the expected behavior of the limit load as the FEA models showed. For the results of the shakedown limit load analysis, Bree diagrams were constructed to show elastic, shakedown and plastic collapse regions. Then, comparison was made to show the effect of the local wall thinning depth and location on previous limits. Finally, the shakedown results were verified using the elastic-plastic ratcheting analysis of API 579, level three assessment and it showed successfully the shakedown, ratcheting and reversed plasticity regions. This verifications and results can prove that the Simplified Technique can be used as a level-three ratcheting assessment in API 579.

Investigation of the Seismic Safety Capacity of Aged Piping System: Shake Table Test on Piping Systems With Wall Thinning by E-Defense

2011 ◽  
Author(s):  
Izumi Nakamura ◽  
Akihito Otani ◽  
Yuji Sato ◽  
Hajime Takada ◽  
Koji Takahashi ◽  
...  
Keyword(s):  
System Model ◽  
Seismic Load ◽  
Piping System ◽  
Shake Table ◽  
Shake Table Tests ◽  
Seismic Safety ◽  
System Models ◽  
Primary Stress ◽  
Wall Thinning ◽  
Piping Systems

In order to investigate the seismic safety capacity of the piping system with local wall thinning, shake table tests on 3-D piping system models were conducted using E-Defense. Two piping system models which were the same in appearance and different in degradation condition were arranged on the shake table of E-Defense. One of the models was put into degradation condition of about 50% wall thinning at four elbows and one tee. Modified seismic motions were applied to these models at the same time. As a result, the piping system model with wall thinning did not fail for the primary stress limit level of sound piping system model, though a ratchet deformation was observed on the thinned wall tee. The model with wall thinning finally failed at the thinned wall tee by over five times larger excitation than the limit level. From the experiment, it was found that the life of the piping system with wall thinning would be reduced compared with that of the piping system without wall thinning, but it was also found that the degraded piping system still had a certain seismic margin until the piping system failed by the seismic load.

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