Experimental Study of Dynamic Interaction Between a Steam Generator Tube and an Anti-Vibration Bar

A first experimental work was previously carried out to study the dynamic behavior of a tube simply supported at both ends in interaction with an anti-vibration bar at mid-span. This paper presents modifications to the previous setup with the aim of improving the accuracy of the results. A comparison of the dynamic behavior of the tube is made between both setups. The objective of this experimental study is to characterize the vibration behavior of U-tubes found in steam generators of nuclear power plants. Indeed, two-phase cross-flow in the U-tubes section of steam generators can cause many problems related to vibration. In fact, flow-induced vibration of the U-tubes can cause impacts or rubbing of the tubes against their flat bar supports. Variation of the clearance between the AVB and the U-tubes may lead to ineffective supports. The resulting in-plane and out-of-plane motions of the tubes are causing fretting-wear and impact abrasion. In this study, the clearance between the tube and the AVB, as well as the amplitude, form and frequency of the excitation force are controlled parameters. The first two modes of the tube are studied. The modifications made to the setup lead to significant improvements in the results. The natural frequencies of both setups are compared to theoretical values. The difference between experimental and theoretical frequencies confirms that the new setup better represents the theoretical model of a simply supported tube. The damping of both setups is also compared to values found in literature. The results show that the new setup is more representative of realistic steam generator situations. Compared to the first setup, the displacements of the new setup clearly indicate that the movement of the tube is mostly parallel to the flat bar and in the same direction as the excitation force. The whirling motion of the tube is prevented in the new setup. The accuracy of the contact force as a function of clearance was also improved. The use of more sensitive force sensors helped to reduce the noise level of the contact force. Finally, the dynamic interaction between the tube and the AVB, defined by the fretting wear work-rate, presents a more consistent behavior. The maximum work-rate occurs when the tube is excited around the second mode for clearance between −0.10 and 0.00 mm. Such clearance between the tube and the AVB should then be avoided to minimize fretting damage.

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Dynamic Interaction Between a Straight Tube and an Anti-Vibration Bar

Volume 4: Fluid-Structure Interaction ◽

10.1115/pvp2009-77804 ◽

2009 ◽

Cited By ~ 2

Author(s):

Isabelle Nowlan ◽

Annie Ross ◽

Michel J. Pettigrew

Keyword(s):

Dynamic Behavior ◽

Dynamic Interaction ◽

Plane Motion ◽

Work Rate ◽

Fretting Wear ◽

Straight Tube ◽

Local Excitation ◽

Out Of Plane ◽

Simple Supports ◽

Excitation Force

Fretting-wear is a known problem in steam generator U-tubes. These tubes are supported by flat bars called anti-vibration bars (AVB) in the plane of the U-bend. Clearances between the tubes and the bars are designed to be minimal, but cumulative tolerances and manufacturing variations may lead to clearances larger than expected. Large clearances may result in ineffective support leading to in-plane and out-of-plane motion causing fretting-wear and impact abrasion. In the present work, the problem is investigated with a single two span tube, an anti-vibration bar at mid-span and a local excitation force. The dynamic behavior of a tube with simple supports at both ends and an anti-vibration bar at mid-span is characterized. The influence of clearance, preload and tilt of the support on the dynamics of the tube are investigated experimentally. The results indicate that the fretting-wear work-rate is very low with preloads, reaches a maximum around a zero clearance and diminish again for larger clearances. The tilt of the anti-vibration bar in our experiments seems to change the dynamic behavior of the tube.

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Experimental Fretting-Wear Studies of Steam Generator Materials

Journal of Pressure Vessel Technology ◽

10.1115/1.2842129 ◽

1995 ◽

Vol 117 (4) ◽

pp. 312-320 ◽

Cited By ~ 52

Author(s):

N. J. Fisher ◽

A. B. Chow ◽

M. K. Weckwerth

Keyword(s):

Steam Generator ◽

Contact Force ◽

Environmental Conditions ◽

Analytical Techniques ◽

Work Rate ◽

Fretting Wear ◽

Flow Induced Vibration ◽

Dynamic Interactions ◽

Support Materials ◽

Wear Damage

Flow-induced vibration of steam generator tubes results in fretting-wear damage due to impacting and rubbing of the tubes against their supports. This damage can be predicted by computing tube response to flow-induced excitation forces using analytical techniques, and then relating this response to resultant wear damage using experimentally derived wear coefficients. Fretting-wear of steam generator materials has been studied experimentally at Chalk River Laboratories for two decades. Tests are conducted in machines that simulate steam generator environmental conditions and tube-to-support dynamic interactions. Different tube and support materials, tube-to-support clearances, and tube support geometries have been studied. The effect of environmental conditions, such as temperature, oxygen content, pH and chemistry control additive, have been investigated as well. Early studies showed that damage was related to contact force as long as other parameters, such as geometry and motion, were held constant. Later studies have shown that damage is related to a parameter called work-rate, which combines both contact force and sliding distance. Results of short and long-term fretting-wear tests for CANDU steam generator materials at realistic environmental conditions are presented. These results demonstrate that work-rate is an appropriate correlating parameter for impact-sliding interaction.

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Time Domain Simulation of the Vibration of a Steam Generator Tube Subjected to Fluidelastic Forces Induced by Two-Phase Cross-Flow

Journal of Pressure Vessel Technology ◽

10.1115/1.4023426 ◽

2013 ◽

Vol 135 (3) ◽

Cited By ~ 5

Author(s):

Téguewindé Sawadogo ◽

Njuki Mureithi

Keyword(s):

Steam Generator ◽

Two Phase Flow ◽

Work Rate ◽

Fretting Wear ◽

Phase Flow ◽

Reference Case ◽

Two Phase ◽

Steam Generator Tube ◽

Wide Range ◽

Instability Regime

Having previously verified the quasi-steady model under two-phase flow laboratory conditions, the present work investigates the feasibility of practical application of the model to a prototypical steam generator (SG) tube subjected to a nonuniform two-phase flow. The SG tube vibration response and normal work-rate induced by tube-support interaction are computed for a range of flow conditions. Similar computations are performed using the Connors model as a reference case. In the quasi-steady model, the fluid forces are expressed in terms of the quasi-static drag and lift force coefficients and their derivatives. These forces have been measured in two-phase flow over a wide range of void fractions making it possible to model the effect of void fraction variation along the tube span. A full steam generator tube subjected to a nonuniform two-phase flow was considered in the simulations. The nonuniform flow distribution corresponds to that along a prototypical steam-generator tube based on thermal-hydraulic computations. Computation results show significant and important differences between the Connors model and the two-phase flow based quasi-steady model. While both models predict the occurrence of fluidelastic instability, the predicted pre-instability and post instability behavior is very different in the two models. The Connors model underestimates the flow-induced negative damping in the pre-instability regime and vastly overestimates it in the post instability velocity range. As a result the Connors model is found to underestimate the work-rate used in the fretting wear assessment at normal operating velocities, rendering the model potentially nonconservative under these practically important conditions. Above the critical velocity, this model largely overestimates the work-rate. The quasi-steady model on the other hand predicts a more moderately increasing work-rate with the flow velocity. The work-rates predicted by the model are found to be within the range of experimental results, giving further confidence to the predictive ability of the model. Finally, the two-phase flow based quasi-steady model shows that fluidelastic forces may reduce the effective tube damping in the pre-instability regime, leading to higher than expected work-rates at prototypical operating velocities.

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Probabilistic Assessment of Fretting Wear in Steam Generator Tubes Under Flow Induced Vibrations

Flow-Induced Vibration ◽

10.1115/pvp2003-2081 ◽

2003 ◽

Cited By ~ 5

Author(s):

Greg D. Morandin ◽

Richard G. Sauve´

Keyword(s):

Steam Generator ◽

Degradation Mechanism ◽

Probabilistic Methods ◽

Fretting Wear ◽

Nonlinear Flow ◽

Impact Wear ◽

Steam Generators ◽

Flow Induced Vibration ◽

Wear Damage ◽

The Impact

Successful life management of steam generators requires an ongoing operational assessment plan to monitor and address all potential degradation mechanisms. A degradation mechanism of concern is tube fretting as a result of flow-induced vibration. Flow induced vibration predictive methods routinely used for design purposes are based on deterministic nonlinear structural analysis techniques. In previous work, the authors have proposed the application of probabilistic techniques to better understand and assess the risk associated with operating power generating stations that have aging re-circulating steam generators. Probabilistic methods are better suited to address the variability of the parameters in operating steam generators, e.g., flow regime, support clearances, manufacturing tolerances, tube to support interactions, and material properties. In this work, an application of a Monte Carlo simulation to predict the propensity for fretting wear in an operating re-circulation steam generator is described. Tube wear damage is evaluated under steady-state conditions using two wear damage correlation models based on the tube-to-support impact force time histories and work rates obtained from nonlinear flow induced vibration analyses. Review of the tube motion in the supports and the impact/sliding criterion shows that significant tube damage at the U-bend supports is a result of impact wear. The results of this work provide the upper bound predictions of wear damage in the steam generators. The EPRI wear correlations for sliding wear and impact wear indicate good agreement with the observed damage and, given the preponderance of wear sites subject to impact, should form the basis of future predictions.

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Vibration and Work-Rate Measurements of Steam-Generator U-Tubes in Air-Water Cross-Flow

5th International Symposium on Fluid Structure International, Aeroeslasticity, and Flow Induced Vibration and Noise ◽

10.1115/imece2002-32842 ◽

2002 ◽

Cited By ~ 2

Author(s):

Victor P. Janzen ◽

Erik G. Hagberg ◽

James N. F. Patrick ◽

Michel J. Pettigrew ◽

Colette E. Taylor ◽

...

Keyword(s):

Cross Flow ◽

Work Rate ◽

Vibration Response ◽

Fretting Wear ◽

Steam Generators ◽

Two Phase ◽

Void Fractions ◽

Vibration Properties ◽

Wide Range ◽

Fluidelastic Instability

In nuclear power plant steam generators, the vibration response of tubes in two-phase cross-flow is a general concern that in some cases has become a very real long-term wear problem. This paper summarizes the results of the most recent U-bend vibration-response tests in a program designed to address this issue. The tests involved a simplified U-tube bundle with a set of flat-bar supports at the apex, subjected to two-phase air-water cross-flow over the mid-span region of the U-bend. Tube vibration properties and tube-to-support interaction in the form of work-rates were measured over a wide range of flow velocities for homogeneous void fractions from zero to 90%, with three different tube-to-support clearances. The measured vibration properties and work-rates could be characterized by the relative influence of the two most important flow-induced excitation mechanisms at work, fluidelastic instability and random-turbulence excitation. As in previous similar tests, strong effects of fluidelastic instability were observed at zero and 25% void fraction for pitch velocities greater than approximately 0.5 m/s, whereas random turbulence dominated the tube vibration and work-rate response at higher void fractions. In both cases, a link between vibration properties and the effect of the flat-bar supports could be established by comparing the vibration crossing frequency, extracted from time-domain vibration signals, to the participation of the lowest few vibration modes and to the measured work-rate. This approach may be useful when fluidelastic instability, random turbulence and loose supports all combine to result in high work-rates. Such a combination of factors is thought to be responsible for excessive U-tube fretting-wear in certain types of operating steam generators.

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Experimental Study on Excitation of Heat Exchanger Tubes Based on Turbulence Power Spectrum

Volume 4: Fluid-Structure Interaction ◽

10.1115/pvp2020-21302 ◽

2020 ◽

Author(s):

Yuqi Wang ◽

Ce Tian ◽

Kai Guo ◽

Guorui Zhu ◽

Wei Tan

Keyword(s):

Contact Angle ◽

Heat Exchanger ◽

Heat Exchange ◽

Power Spectrum ◽

Friction Force ◽

Contact Force ◽

Work Rate ◽

Angle Distribution ◽

Heat Exchange Tube ◽

Excitation Force

Abstract In the steam generator, anti-vibration bars are often provided to support the tube bundle. Due to the non-linearity of the support, the fluid-solid coupling simulation of large-scale tube bundles supported by the anti-vibration bars will bring great trouble. In order to solve this problem, this paper conducts experiments on the heat exchange tube based on the turbulent power spectrum to generate the excitation force. By changing the support form, the force of the lift and the direction of the drag and the ratio of the force, the excitation of the heat exchanger tube is researched. The results of the displacement response, the contact force and friction force distribution, and the contact angle distribution provide reference for the subsequent model simplification. Experiments show that the contact rate increases with the increase of the excitation force, and the contact force and the friction force increase with the increase of the excitation force. When the heat exchange tube contacts with the anti-vibration bars, the contact angle is mostly less than 45°, more than 50% of the contact angle is less than 45°. The work rate of the tube at the edge is greater than the work rate of the tube in the center.

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Flow-Induced Vibration and Fretting-Wear Performance of CANDU™ Steam Generator U-Tubes: Instrumentation

Volume 4: Fluid-Structure Interaction ◽

10.1115/pvp2009-78076 ◽

2009 ◽

Cited By ~ 2

Author(s):

Atef Mohany ◽

Victor Janzen

Keyword(s):

Steam Generator ◽

Tube Bundle ◽

Measurement Techniques ◽

Fretting Wear ◽

Process Conditions ◽

Steam Quality ◽

Steam Generators ◽

Test Program ◽

Two Phase ◽

Support Design

This paper describes a test program that was developed to measure the dynamic response of a bundle of steam generator U-tubes with Anti-Vibration Bar (AVB) supports, subjected to Freon two-phase cross-flow. The tube bundle has similar geometrical conditions to those expected for future CANDU™ steam generators. Future steam generators will be larger than previous CANDU steam generators, nearly twice the heat transfer area, with significant changes in process conditions in the U-bend region, such as increased steam quality and a broader range of flow velocities. This test program is one of the initiatives that AECL is undertaking to demonstrate that the tube support design for future CANDU steam generators meets the stringent requirements associated with a 60 year lifetime. The main objective of the tests is to address the issue of in- and out-of-plane fluidelastic instability and random turbulent excitation of a U-tube bundle with AVB supports. Details of the test rig, measurement techniques and preliminary instrumentation results are described in the paper.

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Improved Flow-Induced Vibration and Work-Rate Measurements of Steam-Generator Tubes

Flow-Induced Vibration ◽

10.1115/pvp2003-2074 ◽

2003 ◽

Author(s):

V. P. Janzen ◽

B. A. W. Smith ◽

L. Brunet ◽

S. Fernando ◽

D. Fingas

Keyword(s):

Dynamic Properties ◽

Flow Characteristics ◽

Cross Flow ◽

Work Rate ◽

Fretting Wear ◽

Steam Generators ◽

Flow Induced Vibration ◽

Two Phase ◽

Software Analysis ◽

Wide Range

In the past, the excessive fretting-wear of U-bend tubes observed in some nuclear steam generators has led to increased tube inspections, unexpectedly high numbers of plugged tubes and the prospect of degraded performance if left unchecked. In this paper, recent vibration and work-rate experiments that have attempted to address this problem are summarized, including tests of two-span U-tubes in air-water and straight tubes in two-phase Freon. Tube bundles were subjected to two-phase cross-flow over a wide range of flow conditions, measuring tube vibration, flow characteristics in the bundle, and the dynamic interaction (work-rate) between tubes and supports that gives rise to fretting-wear. Developments in vibration and work-rate instrumentation and software analysis tools are also presented. The result is an improved ability to measure dynamic properties and, thus, to better predict the vibration response and fretting-wear performance of steam generators.

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