Severed Tubes in Operating Nuclear Steam Generators: Case Analysis — I

2003 ◽  
Author(s):  
M. K. Au-Yang ◽  
Stephen Leshnoff
Keyword(s):  
Linear Theory ◽  
Fatigue Failure ◽  
Cross Flow ◽  
Ductile Failure ◽  
Integral Approach ◽  
Elastic Instability ◽  
Steam Generators ◽  
Flow Induced Vibration ◽  
Fluid Structure ◽  
Eddy Current Inspection

During a routine inspection in October 2001, it was discovered that a plugged tube in one of the steam generators at a nuclear station was completely severed at the upper tubesheet. The severed surface appeared to be fresh, clean, 360-deg. and with no evidence of necking down, ductile failure or visible flaws. Eddy current inspection revealed that the four neighboring tubes downstream of the severed tube each had wedge-shaped wear marks starting from the tubesheet end. However, there was no visible mid-span impact wear marks. Furthermore, the tube was visibly swollen due to over-pressurization. This tube was plugged in 1986 with no indications of flaw or wear marks. It was replugged later. The tube was not stabilized because there was no apparent potential for a circumferential sever to occur anywhere in the tube. Flow-induced vibration based on classic linear theory showed that this tube should have wide margin against fluid-elastic instability, turbulence or vortex-induced fatigue failure. However, it also was found that if for any reason the tube was laterally restrained (clamped) at the support plates, the margin against fluid-elastic instability would be reduced significantly. Still, this tube should have been stable and turbulence or vortex-induced vibration alone, as predicted by the classic linear theory without fluid-structure interaction, should not have caused fatigue failure. This study points out a deficiency in the classic linear turbulence-induced vibration analysis without taking into account the effect of fluid-structure coupling. When the cross-flow gap velocity is near the critical velocity, fluid-structure coupling would greatly increase the vibration amplitude over what is predicted by the classic acceptance integral approach. It is this increase in turbulence-induced vibration that caused this particular tube to fail by fatigue.

An Experimental Investigation of the Dynamics of a Loosely Supported Tube Array

2017 ◽  
Author(s):  
Amro Elhelaly ◽  
Marwan Hassan ◽  
Atef Mohany ◽  
Soha Moussa
Keyword(s):  
Experimental Investigation ◽  
Impact Force ◽  
Cross Flow ◽  
Open Loop ◽  
Diameter Ratio ◽  
Force Level ◽  
Steam Generators ◽  
Flow Induced Vibration ◽  
System Integrity ◽  
Tube Bundles

The integrity of tube bundles is very important especially when dealing with high-risk applications such as nuclear steam generators. A major issue to system integrity is the flow-induced vibration (FIV). FIV is manifested through several mechanisms including the most severe mechanism; fluidelastic instability (FEI). Tube vibration can be constrained by using tube supports. However, clearances between the tube and their support are required to allow for thermal expansion and for other manufacturing considerations. The clearance between tubes may allow frequent impact and friction between tube and support. This in turn may cause fatigue and wear at support and potential for catastrophic tube failure. This study aims to investigate the dynamics of loosely supported tube array subjected to cross-flow. The work is performed experimentally in an open-loop wind tunnel to address this issue. A loosely-supported single flexible tube in both triangle and square arrays subjected to cross-flow with a pitch-to-diameter ratio of 1.5 and 1.733, respectively were considered. The effect of the flow approach angle, as well as the support clearance on the tube response, are investigated. In addition, the parameters that affect tube wear such as impact force level are presented.

An Overview of IAEA Technical Guidelines on Fluid-Structure Interaction

2014 ◽  
Author(s):  
M. Kim ◽  
P. Hughes ◽  
R. A. Ainsworth
Keyword(s):  
Fluid Structure Interaction ◽  
Cross Flow ◽  
External Loading ◽  
Flow Induced Vibration ◽  
Energy Agency ◽  
Fluid Structure ◽  
Safety Standards ◽  
Structure Interaction ◽  
Fluid Sloshing ◽  
Reactor Types

This paper provides an overview of International Atomic Energy Agency (IAEA) draft technical guidelines on Fluid-Structure Interaction (FSI), which is supporting document for IAEA Safety Standards aimed at providing method and practices. The technical guidelines are based on sections in codes and standards, more general documents on FSI and documents describing particular plant issues or problems. The technical guidelines recognise that FSI has led to a range of problems in a range of reactor types including: flow-induced vibration in light water reactor (LWR) steam generators under external loading including seismic loading; fretting of LWR heat exchangers with the fretting loading dependent on cross-flow velocity; seismic effects and fluid sloshing in liquid metal cooled faster breeder reactor (LMFBR); and water hammer. In addition to providing an overview description of the technical guidelines, the paper also describes the process followed to produce and obtain peer review of the document.

Experimental and Numerical Characterization of Flow-Induced Vibration of Multi-Span U-Tubes

2010 ◽  
Author(s):  
Atef Mohany ◽  
Victor P. Janzen ◽  
Paul Feenstra ◽  
Shari King
Keyword(s):  
Tube Bundle ◽  
Measurement Techniques ◽  
Cross Flow ◽  
Process Conditions ◽  
Steam Generators ◽  
Test Program ◽  
Flow Induced Vibration ◽  
Two Phase ◽  
Support Design ◽  
Set Up

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 geometry is similar to the geometry used in preliminary designs for future CANDU® steam generators. This test program is one of the initiatives that Atomic Energy of Canada Limited (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. In particular, the tests will address issues related to in- and out-of-plane fluidelastic instability and random turbulent excitation of a U-tube bundle with Anti-Vibration Bar (AVB) supports. Therefore, the measurements include tube vibration amplitudes and frequencies, work-rate due to impacting and sliding motion of the tubes against their supports, bulk process conditions and local two-phase flow properties. Details of the test rig set-up and the measurement techniques are described in the paper. Moreover, a numerical prediction of the U-tube vibration response to flow was performed with AECL’s PIPO-FE code. A summary of the numerical results is presented.

Experimental and Numerical Characterization of Flow-Induced Vibration of Multispan U-tubes

2011 ◽  
Vol 134 (1) ◽  
Author(s):  
Atef Mohany ◽  
Victor P. Janzen ◽  
Paul Feenstra ◽  
Shari King
Keyword(s):  
Tube Bundle ◽  
Measurement Techniques ◽  
Cross Flow ◽  
Process Conditions ◽  
Steam Generators ◽  
Test Program ◽  
Flow Induced Vibration ◽  
Two Phase ◽  
Support Design ◽  
Numerical Characterization

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 geometry is similar to the geometry used in preliminary designs for future CANDU steam generators. This test program is one of the initiatives that Atomic Energy of Canada Limited (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. In particular, the tests will address issues related to in- and out-of-plane fluidelastic instability and random turbulent excitation of a U-tube bundle with AVB supports. Therefore, the measurements include tube vibration amplitudes and frequencies, work-rate due to impacting and sliding motion of the tubes against their supports, bulk process conditions and local two-phase flow properties. Details of the test rig setup and the measurement techniques are described in the paper. Moreover, a numerical prediction of the U-tube vibration response to flow was performed with AECL’s pipo-fe code. A summary of the numerical results is presented.

Severed Tubes in Operating Nuclear Steam Generators: Case Analysis — II

2003 ◽  
Author(s):  
M. K. Au-Yang
Keyword(s):  
Failure Mechanisms ◽  
Case Analysis ◽  
Root Cause Analysis ◽  
Steam Generators ◽  
Shell Side ◽  
Flow Induced Vibration ◽  
Cause Analysis ◽  
Root Cause ◽  
Eddy Current Inspection ◽  
Cast Doubt

During an eddy current inspection in April 2002, it was found that three tubes downstream of an out-of-service tube in a once-through nuclear steam generator (OTSG) had significant wear indications. Wear indications of these tubes has been recorded as early as 1995 and apparently has been progressing with time. A shell-side video inspection revealed that this tube was completely severed at the bottom tubesheet. This severed tube was discovered immediately after a tube in another OTSG of similar design was found to have severed at the top tubesheet. In the root-cause analysis of the other severed tube, the possibility of a similar tube failure due to flow-induced vibration at the bottom tubesheet was explicitly ruled out and corrective action was implemented based on this conclusion. This discovery cast doubt on the earlier analysis and raised concern on both steam generators. The purpose of this study is to carry out a root cause analysis of the failure of the second severed tube and show that even though the two failures appeared to be similar, the causes and failure mechanisms were different. The study also showed that what appeared to be an obvious fix turned out to be invalid upon more in-depth flow-induced vibration analysis.

Vibration of Tube Bundles Subjected to Two-Phase Cross-Flow

1985 ◽  
Vol 107 (4) ◽  
pp. 335-343 ◽  
Author(s):  
M. J. Pettigrew ◽  
J. H. Tromp ◽  
J. Mastorakos
Keyword(s):  
Heat Exchangers ◽  
Tube Bundle ◽  
Cross Flow ◽  
Elastic Instability ◽  
Steam Generators ◽  
Two Phase ◽  
Vibration Excitation ◽  
Mass Fluxes ◽  
Excitation Mechanisms ◽  
Shell And Tube

Two-phase cross-flow exists in many shell-and-tube heat exchangers such as condensers, reboilers and nuclear steam generators. Thus we are conducting a comprehensive program to study tube bundle vibrations subjected to two-phase cross-flow. This paper presents the results of experiments on a normal-triangular and a normal-square tube bundle, both of p/d = 1.47. The bundles were subjected to air-water mixtures to simulate realistic vapor qualities and mass fluxes. Vibration excitation mechanisms were deduced from vibration response measurements. Results on damping, hydrodynamic mass, fluid-elastic instability and random turbulence excitation in two-phase cross-flow are presented.

Modeling and Simulation of Cross-Flow Induced Vibrations in Tube Bundles Using Bondgraph Approach

2006 ◽  
Author(s):  
M. Afzaal Malik ◽  
Badar Rashid ◽  
M. Anwar Khan ◽  
Khawaja Sajid Bashir ◽  
Shahab Khushnood
Keyword(s):  
Research Work ◽  
Cross Flow ◽  
Acoustic Resonance ◽  
Elastic Instability ◽  
Steam Generators ◽  
Two Phase ◽  
Considerable Research ◽  
Tube Bundles ◽  
Flow Induced Vibrations ◽  
Excitation Mechanisms

A considerable research has been carried out in the field of Cross-Flow Induced Vibrations (CFIV) in tube bundles of process exchangers and nuclear steam generators. Various excitation mechanisms such as vortex shedding, turbulent buffeting, fluid-elastic instability and acoustic resonance and other parameters like natural frequencies, damping, wear work rates at the loose tube supports and various geometric tube arrangements have been the focus in single and two-phase cross-flow. In the current research work, CFIV has been studied by using Bondgraph approach. The Bondgraph models have been subjected to simulation using the software (20-SIM). Results obtained have shown a strong usefulness of Bondgraph approach to complex CFIV systems.

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

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.

scholarly journals Cross-Flow Tidal Turbines with Highly Flexible Blades—Experimental Flow Field Investigations at Strong Fluid–Structure Interactions

Energies ◽  
2021 ◽  
Vol 14 (4) ◽  
pp. 797
Author(s):  
Stefan Hoerner ◽  
Iring Kösters ◽  
Laure Vignal ◽  
Olivier Cleynen ◽  
Shokoofeh Abbaszadeh ◽  
...  
Keyword(s):  
Flow Field ◽  
High Speed ◽  
Cross Flow ◽  
Speed Ratio ◽  
Fluid Structure Interactions ◽  
Dimensional Parameter ◽  
Fluid Structure ◽  
Passive Flow Control ◽  
Tidal Turbines ◽  
Tidal Turbine

Oscillating hydrofoils were installed in a water tunnel as a surrogate model for a hydrokinetic cross-flow tidal turbine, enabling the study of the effect of flexible blades on the performance of those devices with high ecological potential. The study focuses on a single tip-speed ratio (equal to 2), the key non-dimensional parameter describing the operating point, and solidity (equal to 1.5), quantifying the robustness of the turbine shape. Both parameters are standard values for cross-flow tidal turbines. Those lead to highly dynamic characteristics in the flow field dominated by dynamic stall. The flow field is investigated at the blade level using high-speed particle image velocimetry measurements. Strong fluid–structure interactions lead to significant structural deformations and highly modified flow fields. The flexibility of the blades is shown to significantly reduce the duration of the periodic stall regime; this observation is achieved through systematic comparison of the flow field, with a quantitative evaluation of the degree of chaotic changes in the wake. In this manner, the study provides insights into the mechanisms of the passive flow control achieved through blade flexibility in cross-flow turbines.

scholarly journals Fluid-Structure Energy Transfer of a Tensioned Beam Subject to Vortex-Induced Vibrations in Shear Flow

2011 ◽  
Author(s):  
Remi Bourguet ◽  
Michael S. Triantafyllou ◽  
Michael Tognarelli ◽  
Pierre Beynet
Keyword(s):  
Energy Transfer ◽  
Shear Flow ◽  
Cross Flow ◽  
Reynolds Numbers ◽  
Structural Vibrations ◽  
Fluid Structure ◽  
Vortex Induced Vibrations ◽  
Linear Shear ◽  
Structural Responses ◽  
Lock In

The fluid-structure energy transfer of a tensioned beam of length to diameter ratio 200, subject to vortex-induced vibrations in linear shear flow, is investigated by means of direct numerical simulation at three Reynolds numbers, from 110 to 1,100. In both the in-line and cross-flow directions, the high-wavenumber structural responses are characterized by mixed standing-traveling wave patterns. The spanwise zones where the flow provides energy to excite the structural vibrations are located mainly within the region of high current where the lock-in condition is established, i.e. where vortex shedding and cross-flow vibration frequencies coincide. However, the energy input is not uniform across the entire lock-in region. This can be related to observed changes from counterclockwise to clockwise structural orbits. The energy transfer is also impacted by the possible occurrence of multi-frequency vibrations.

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