On Categorization of Seismic Load As Primary or Secondary for Multi-Modal Piping Systems

2020 ◽  
Author(s):  
Pierre Labbé
Keyword(s):  
Linear Time ◽  
Seismic Load ◽  
Piping System ◽  
Ductility Demand ◽  
Plastic Yield ◽  
Wide Range ◽  
Piping Systems ◽  
Practical Engineering ◽  
Input Motion ◽  
Input Level

Abstract Categorizing the seismic load requires calculating the input level associated with the ultimate capacity and comparing it to the level associated with the plastic yield. Therefore, an analysis of the seismically induced ductility demand in oscillators of variable frequencies was carried out by running non-linear time response analyses, the seismic input motion being simulated as samples of a stochastic process of central frequency fc. The response of oscillators with frequencies, f0, varying from 0.1 fc to 10 fc, was systematically analyzed. For every oscillator, 10000 time-responses were performed, corresponding to 1000 input samples multiplied by 10 input levels, covering a wide range of ductility demand up to 20. Output is that seismic loads should be regarded as secondary for flexible oscillators (f0 < fc) while it should be regarded as primary for very stiff oscillators (f0 > cut-off frequency of the input motion, fcut), with intermediate situations for fc < f0 < fcut. A practical engineering rule is presented to incorporate this result when calculating the primary part of seismically induced streeses in a multimodal piping system. This rule is currently tested in the framework of the OECD-NEA international benchmark MECOS.

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.

On Categorization of Seismic Load As Primary or Secondary for Piping Systems With Hardening Capacity

2018 ◽  
Author(s):  
Pierre B. Labbé
Keyword(s):  
Natural Frequency ◽  
Response Spectrum ◽  
A Priori ◽  
Effective Stiffness ◽  
Linear Oscillator ◽  
Seismic Load ◽  
Wide Range ◽  
Non Linear ◽  
Piping Systems ◽  
Non Linear Oscillator

The concept of primary/secondary categorization is first reviewed and generalized for its application to a non-linear oscillator subjected to a seismic load. Categorizing the seismic load requires calculating the input level associated with the oscillator ultimate capacity and comparing it to the level associated with the plastic yield. To resolve this problem, it is assumed that the non-linear oscillator behaves like a linear equivalent oscillator, with an effective stiffness (or frequency) and an effective damping. However, as it is not a priori possible to predict the equivalent stiffness and damping, a wide range of possibilities is systematically considered. The input motion is represented by its conventional response spectrum. It turns out that key parameters for categorization are i) the “effective stiffness factor” (varying from 0 for perfect damage behaviour to 1 for elastic-perfectly plastic) and the slope of the response spectrum in the vicinity of the natural frequency of the oscillator. Effective damping and spectrum sensitivity to damping play a second order role. A formula is presented that enables the calculation of the primary part of a seismically induced stress as a function of both the oscillator and input spectrum features. The formula is also presented in the form of a diagram. This paper follows-up on a similar paper presented by the author at the PVP 2017 Conference [1]. The new development introduced here is that the oscillator exhibits hardening capacity, while no hardening was assumed in [1]. It appears that the conclusions are slightly modified but the trend is very similar to the non-hardening case. Regarding piping systems, it appears that even when experiencing large plastic strains under beyond design input motions, their observed effective frequency is very close to their natural frequency, decreasing only by a few percents (experimental data from USA, Japan and India are processed). These observations lead to the conclusion that the seismic load, or the seismically induced inertial seismic strains, should basically be regarded as secondary.

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.

Finite Element Simulation of Dynamic Behavior of Pressurized Piping System Under Large Seismic Load

2006 ◽  
Author(s):  
A. Ravi Kiran ◽  
M. K. Agrawal ◽  
G. R. Reddy ◽  
A. K. Ghosh ◽  
H. S. Kushwaha
Keyword(s):  
Nuclear Power ◽  
Analytical Study ◽  
Kinematic Hardening ◽  
Seismic Load ◽  
Piping System ◽  
Test Results ◽  
Unexpected Events ◽  
Element Simulation ◽  
Piping Systems ◽  
Cause Of Failure

The nuclear power plant piping systems are often subjected to the cyclic loading conditions due to transients, seismic or other unexpected events. During these events, the probable mode of failure for piping component is fatigue-ratcheting. Earlier the design of piping subjected to seismic excitation was based on the principle of static collapse. Later on, it was postulated that the cause of failure of piping components is fatigue ratcheting and not plastic collapse. The 1995 ASME Boiler & Pressure Vessel code, Section-III, has incorporated the reverse dynamic loading and ratcheting into the code. An Analytical study is carried out to investigate the behavior of the pressurized piping system under large seismic loading. The analysis is performed using equivalent inertial forces. Chaboche nonlinear kinematic hardening model is used for ratcheting simulation. The capability of the model to simulate the ratcheting response of the piping system is of particular interest. Comparison of analysis results against test results are presented in the paper.

Introduction of a Research Activity on the Seismic Safety Evaluation of Nuclear Piping Systems Taking the Effect of Elastic-Plastic Behavior Into Account

2015 ◽  
Author(s):  
Izumi Nakamura ◽  
Masaki Shiratori ◽  
Akihito Otani ◽  
Masaki Morishita ◽  
Tadahiro Shibutani ◽  
...  
Keyword(s):  
Seismic Load ◽  
Failure Behavior ◽  
Plastic Behavior ◽  
Piping System ◽  
Seismic Loads ◽  
Research Activity ◽  
Standard Analysis ◽  
Seismic Safety ◽  
Elastic Plastic ◽  
Piping Systems

According to investigations of several nuclear power plants (NPPs) hit by actual seismic events and a number of experimental researches on the failure behavior of piping systems under seismic loads, it is recognized that piping systems used in NPPs include a large seismic safety margin until boundary failure and the current code design allowable stresses are very conservative. Since the stress assessment based on the elastic analysis does not reflect actual response of piping systems including plastic region, rational procedures to estimate the elastic-plastic behavior of piping systems under a large seismic load are expected to be developed for piping seismic design applications. With the aim of establishing a procedure that takes into account the elastic-plastic behavior effect in the seismic safety estimation of nuclear piping systems, a research activity has been planned. Through the activity, the authors intend to establish two kinds of guidelines; 1) a guideline of a standard analysis procedure to evaluate elastic-plastic behavior of piping systems under extreme seismic loads with rational and conservative margins, and 2) a guideline that provide criteria for the seismic safety assessment of piping systems by the standard analysis to evaluate elastic-plastic behavior established by the above guideline. As the first step of making out the analysis guideline, benchmark analyses are conducted for a pipe element test and a piping system test. In this paper, the outline of the research activity and the preliminary results of benchmark analyses for a pipe element test are described.

Experiences in Developing a Practical Algorithm of Identification and Attenuation of Pressure Pulsation and Piping Vibration in Gas Reciprocating Compressor Plants and Other Systems

2018 ◽  
Author(s):  
Maciej Rydlewicz ◽  
Wojciech Rydlewicz
Keyword(s):  
Pressure Pulsation ◽  
Industrial Applications ◽  
Piping System ◽  
Reciprocating Compressor ◽  
Mechanical Vibrations ◽  
Dynamic Forces ◽  
Piping Systems ◽  
Practical Engineering ◽  
Gaseous Media ◽  
Practical Algorithm

This paper presents results of research on practical engineering solutions to suppress pressure pulsation and mechanical vibrations in piping systems. It concerns both new build and retrofitted plants. Analyses were performed according to ASME B31, EN-13480 and API 618 codes. Solutions were considered for natural gas reciprocating compressor stations (gaseous media) and liquid hydrocarbons plant with various pumps. Pressure pulsation in a piping system is a source of dynamic forces. Unbalanced pressure layout in the piping system results in the presence of dynamic forces that may excite mechanical vibrations [1,7, 22, 23, 24]. In industrial applications, mechanical vibrations are present mostly in resonant conditions. Since hundreds of eigenvalues can characterise the piping system, it is crucial to identify the key ones, which are likely to be excited to vibrate. Therefore, it is necessary to allow adequate modelling and subsequent analysis of the fluid-structure interaction with available engineering tools.

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.

Risk-Based Seismic Performance Assessment of Pressurized Piping Systems Considering Ratcheting

2019 ◽  
Vol 142 (2) ◽  
Author(s):  
A. Ravi Kiran ◽  
G. R. Reddy ◽  
M. K. Agrawal
Keyword(s):  
Performance Assessment ◽  
Seismic Performance ◽  
Fragility Curves ◽  
Limit State ◽  
Frequency Variation ◽  
Seismic Load ◽  
Piping System ◽  
Seismic Performance Assessment ◽  
Limit States ◽  
Piping Systems

Abstract A procedure is described for risk-based seismic performance assessment of pressurized piping systems considering ratcheting. The procedure is demonstrated on a carbon steel piping system considered for OECD-NEA benchmark exercise on quantification of seismic margins. Initially, fragility analysis of the piping system is carried out by considering variability in damping and frequency. Variation in damping is obtained from the statistical analysis of the damping values observed in earlier experiments on piping systems and components. The variation in ground motion is considered by using 20 strong motion records of the intraplate region. Floor motion of a typical reactor building of a nuclear power plant under these actual earthquake records is evaluated and applied to the piping system. The performance evaluation of the piping system in terms of ratcheting is carried out using a numerical approach, which was earlier validated with shake table ratcheting tests on piping components and systems. Three limit states representing performance levels of the piping system under seismic load are considered for fragility evaluation. For each limit state, probability of exceedance at different levels of floor motion is evaluated to generate a fragility curve. Subsequently, the fragility curves of the piping systems are convoluted with hazardous curves for a typical site to obtain the risk in terms of annual probability of occurrence of the performance limits.

Experimental and Numerical Studies of Ratcheting in a Pressurized Piping System Under Seismic Load

2015 ◽  
Vol 137 (3) ◽  
Author(s):  
A. Ravikiran ◽  
P. N. Dubey ◽  
M. K. Agrawal ◽  
G. R. Reddy ◽  
R. K. Singh ◽  
...  
Keyword(s):  
Comprehensive Evaluation ◽  
Response Spectrum ◽  
Three Dimensional ◽  
Seismic Loading ◽  
Seismic Load ◽  
Piping System ◽  
Inelastic Response ◽  
Design Procedures ◽  
Numerical Studies ◽  
Piping Systems

Rational seismic design procedures necessitate comprehensive evaluation of nuclear piping systems under large amplitude seismic loads. This comprehensive assessment requires accurate prediction of inelastic response of piping system till failure to ensure adequate margins for unexpected beyond design basis events. The present paper describes the details of experimental and numerical studies of inelastic response of pressurized piping system under seismic loading. Shake table test has been carried out on a three-dimensional stainless steel piping system under internal pressure and seismic load. The amplitude of base excitation has been increased till failure of the piping system. The tested piping system has been analyzed using iterative response spectrum (IRS) method for various levels of excitation. The comparison of numerical and experimental results is given in the paper.

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