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1、Recommendations for Controlling Cavitation, Flashing, Liquid Droplet Impingement, and Solid Particle Erosion in Nuclear Power Plant Piping Systems Technical Report L I C E N S E D M A T E R I A L Effective December 6, 2006, this report has been made publicly available in accordance with Section 734.
2、3(b)(3) and published in accordance with Section 734.7 of the U.S. Export Administration Regulations. As a result of this publication, this report is subject to only copyright protection and does not require any license agreement from EPRI. This notice supersedes the export control restrictions and
3、any proprietary licensed material notices embedded in the document prior to publication. EPRI Project Managers A. Machiels D. Munson EPRI 3412 Hillview Avenue, Palo Alto, California 94304 PO Box 10412, Palo Alto, California 94303 USA 800.313.3774 650.855.2121 Recommendations for Controlling Cavita
4、tion, Flashing, Liquid Droplet Impingement, and Solid Particle Erosion in Nuclear Power Plant Piping Systems 1011231 Final Report, November 2004 DISCLAIMER OF WARRANTIES AND LIMITATION OF LIABILITIES THIS DOCUMENT WAS PREPARED BY THE ORGANIZATION(S) NAMED BELOW AS AN ACCOUNT OF WORK SPONSORED OR COS
5、PONSORED BY THE ELECTRIC POWER RESEARCH INSTITUTE, INC. (EPRI). NEITHER EPRI, ANY MEMBER OF EPRI, ANY COSPONSOR, THE ORGANIZATION(S) BELOW, NOR ANY PERSON ACTING ON BEHALF OF ANY OF THEM: (A) MAKES ANY WARRANTY OR REPRESENTATION WHATSOEVER, EXPRESS OR IMPLIED, (I) WITH RESPECT TO THE USE OF ANY INFO
6、RMATION, APPARATUS, METHOD, PROCESS, OR SIMILAR ITEM DISCLOSED IN THIS DOCUMENT, INCLUDING MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE, OR (II) THAT SUCH USE DOES NOT INFRINGE ON OR INTERFERE WITH PRIVATELY OWNED RIGHTS, INCLUDING ANY PARTYS INTELLECTUAL PROPERTY, OR (III) THAT THIS DOCUMEN
7、T IS SUITABLE TO ANY PARTICULAR USERS CIRCUMSTANCE; OR (B) ASSUMES RESPONSIBILITY FOR ANY DAMAGES OR OTHER LIABILITY WHATSOEVER (INCLUDING ANY CONSEQUENTIAL DAMAGES, EVEN IF EPRI OR ANY EPRI REPRESENTATIVE HAS BEEN ADVISED OF THE POSSIBILITY OF SUCH DAMAGES) RESULTING FROM YOUR SELECTION OR USE OF T
8、HIS DOCUMENT OR ANY INFORMATION, APPARATUS, METHOD, PROCESS, OR SIMILAR ITEM DISCLOSED IN THIS DOCUMENT. ORGANIZATION(S) THAT PREPARED THIS DOCUMENT dba Jeffrey Horowitz ORDERING INFORMATION Requests for copies of this report should be directed to EPRI Orders and Conferences, 1355 Willow Way, Suite
9、278, Concord, CA 94520. Toll-free number: 800.313.3774, press 2, or internally x5379; voice: 925.609.9169; fax: 925.609.1310. Electric Power Research Institute and EPRI are registered service marks of the Electric Power Research Institute, Inc. EPRI. ELECTRIFY THE WORLD is a service mark of the Elec
10、tric Power Research Institute, Inc. Copyright 2004 Electric Power Research Institute, Inc. All rights reserved. CITATIONS This report was prepared by dba Jeffrey Horowitz 3331 Avenida Sierra Escondido, CA 92029 Principal Investigator J. Horowitz This report describes research sponsored by EPRI. The
11、report is a corporate document that should be cited in the literature in the following manner: Recommendations for Controlling Cavitation, Flashing, Liquid Droplet Impingement, and Solid Particle Erosion in Nuclear Power Plant Piping Systems: EPRI, Palo Alto, CA: 2004. 1011231. iii REPORT SUMMARY Th
12、is report describes the most common forms of erosion encountered in nuclear power plant piping systemscavitation, flashing, liquid droplet impingement, and solid particle erosion and provides utility engineers with information on how to deal with these forms of damage. Background Although all nuclea
13、r utilities have programs in place to protect against flow-accelerated corrosion (FAC), there has not been a similar effort to protect nuclear piping from erosion damage. The most common forms of erosion encounteredcavitation, flashing, liquid droplet impingement, and solid particle erosionhave caus
14、ed wall loss, leaks, and ruptures and resulted in unplanned shutdowns in nuclear power plants. Repair and replacement of damaged piping and equipment have been a continuing expense. Additionally, noise and vibration caused by cavitation or flashing have led to control and maintenance problems. Objec
15、tive To summarize the various erosion damage mechanisms in nuclear power plant piping and discuss means to control them. Approach The research team reviewed and summarized the information available in the literature on erosion damage relevant to nuclear power plant piping. In addition, members of th
16、e CHECWORKS Users Group (CHUG) contributed photographs of nuclear plant components damaged by erosion. Results The report summarizes the technical details of cavitation, flashing, liquid droplet impingement, and solid particle erosion, the four most common erosive mechanisms that damage nuclear powe
17、r plant piping. The report presents the typical morphology exhibited by these modes of attack and discusses where they are most likely to occur. Guidance is provided as to where inspections should be performed to locate damage and which inspection techniques should be used. The report discusses mate
18、rials and design options available to reduce or eliminate these forms of attack. Care has been taken to compare and contrast the four mechanisms; for despite their similarities, there also differ in substantial ways. The report includes several appendices that describe some of the erosion processes
19、in greater detail. Also included is a large photo gallery of erosion experience from nuclear plants in Belgium, Canada, and the United States. v EPRI Perspective As FAC programs have been successful in reducing leaks, ruptures, and unplanned maintenance, attention has increasingly focused on the rol
20、e of erosion in causing maintenance problems. This report should provide the utility engineers with the information needed to deal with erosion damage. It should be stressed that while there are materials such as stainless steel that are virtually immune to attack by FAC, erosive mechanisms will eve
21、ntually damage almost any material. Keywords Erosion Cavitation Droplet Impingement Flashing Erosion Solid Particle Erosion vi EPRI Proprietary Licensed Material ACKNOWLEDGEMENTS The author would like to acknowledge the following people and organizations who provided the photographs used in this rep
22、ort: Ricky Allen, Southern Nuclear, Joseph M. Farley Nuclear Plant. Ian Breedlove, Dominion Virginia Power, Surry Power Station David Crawley, Southern Nuclear, Edwin I. Hatch Nuclear Plant Whit Galman, Duke Power, McGuire Nuclear Station Tim Giles, Constellation Nuclear, Calvert Cliffs Nuclear Powe
23、r Plant. David Grabski, FirstEnergy, Beaver Valley Power Station Emile Groteclaes, Tractebel/Electrabel, Tihange Nuclear Power Plant Chris Hooper, Dominion Virginia Power, North Anna Power Station Aaron Kelley, Exelon, LaSalle County Generating Station Patrick Mannens, Electrabel, Doel Nuclear Power
24、 Plant Bob Montgomery and Matt Murray, Public Service Electric Steve Ewens, AmerenUE; Lee Goyette, Pacific Gas Bill Klein, Florida Power Sherm Shaw, Southern California Edison; and, Steve Slosnerick of FirstEnergy in assisting in the preparation of this report are also acknowledged. vii EPRI Proprie
25、tary Licensed Material CONTENTS 1 INTRODUCTION 1-1 2 MECHANISMS .2-1 2.1 Cavitation.2-1 2.1.1 Cavitation in Valves.2-2 2.1.2 Cavitation in Orifices2-4 2.2 Flashing .2-4 2.3 Droplet Impingement or Liquid Impingement Erosion2-7 2.4 Solid Particle Erosion.2-10 3 LOCATING POTENTIAL DAMAGE.3-1 3.1 Cavita
26、tion.3-1 3.2 Flashing .3-2 3.3 Liquid Impingement Erosion 3-2 3.4 Solid Particle Erosion.3-4 3.5 Combined Mechanisms .3-5 3.6 General Recommendations.3-6 4 INSPECTION METHODS.4-1 5 MATERIAL CONSIDERATIONS5-1 5.1 Erosion Is Not FAC5-1 5.2 Characteristics of Cavitation, Flashing and Liquid Impact Eros
27、ion5-1 5.2.1 Materials Consideration for Cavitation and Droplet Impingement Wear.5-3 5.2.2 Anecdotal Experience.5-5 5.2.3 Recommendations5-5 5.3 Materials Considerations for Solid Particle Erosion.5-6 ix EPRI Proprietary Licensed Material 6 DESIGN OPTIONS TO REDUCE EROSION .6-1 6.1 Design Options to
28、 Reduce Cavitation6-1 6.1.1 Valves .6-1 6.1.2 Orifices6-6 6.2 Design Options to Reduce Flashing Erosion.6-7 6.3 Design Options to Reduce Droplet Impingement.6-8 6.4 Design Options to Reduce Solid Particle Erosion6-9 7 REFERENCES .7-1 A THE CAVITATION PROCESSA-1 A.1 Valve Flow Resistance A-1 A.2 Vena
29、 Contracta. A-3 A.3 Cavitation Coefficients A-4 A.4 Examples A-5 A.5 Cavitation and Valve Types A-5 A.6 Flow Curvature or Re-circulation Cavitation . A-7 A.7 Cavitation and Noise. A-9 A.8 References . A-10 B CAVITATION DEFINITIONS AND CALCULATION METHOD B-1 B.1 Basic Definitions . B-1 B.2 Assessing
30、Cavitation in Valves. B-2 B.3 Discussion B-2 B.4 References . B-3 C THE ESTIMATION OF DOWNSTREAM VELOCITYC-1 C.1 Simplified Model.C-1 C.2 Sample Calculation C-3 C.3 More Exact Methods C-4 C.4 References.C-4 D ESTIMATION OF A TWO-PHASE VELOCITY.D-1 D.1 Sample Problem 1D-1 D.2 Sample Problem 2D-2 x EP
31、RI Proprietary Licensed Material D.3 Sample Problem 3D-3 D.4 References.D-4 E SAMPLES OF COMPONENTS DAMAGED BY EROSION . E-1 E.1 Beaver Valley E-1 E.2 Solid Particle Erosion Damage at Bruce. E-3 E.3 Degradation at Calvert Cliffs. E-4 E.4 Thinning in Expanders at Doel E-7 E.5 Impingement and Cavitati
32、on Damage at Farley E-8 E.6 Flashing Damage at Hatch . E-10 E.7 Combined Mechanisms at Hope Creek E-11 E.8 Erosion Damage at LaSalle E-13 E.9 Impingement at McGuire. E-16 E.10 Cavitation and Impingement at North Anna . E-18 E.11 Solid Particle Erosion Damage at Surry. E-21 E.12 Impingement at Tihang
33、e. E-22 E.13 Reference. E-24 F EROSION RESISTANCE OF DUPLEX STAINLESS STEELF-1 F.1 Introduction F-1 F.2 Erosion ResistanceF-2 F.3 References.F-3 xi EPRI Proprietary Licensed Material LIST OF FIGURES Figure 2-1 Schematic Illustration of the Cavitation Process 2-2 Figure 2-2 Cavitation Damage in the B
34、ody of a Plug Valve (Reference 13)2-4 Figure 2-3 Flashing Schematic 2-5 Figure 2-4 Acoustic Velocity of a Steam Water Mixture as a Function of Bubble Percentage (Reference 11)2-5 Figure 2-5 Typical Morphology of Flashing Damage .2-7 Figure 2-6 Liquid Impact Erosion of a Copper Alloy Condenser Tube (
35、Reference 1)2-8 Figure 2-7 Cross-Section of Figure 2-6 (Reference 1).2-8 Figure 2-8 Comparison of an Eroded Turbine Blade with a Test Sample (Reference 20).2-9 Figure 2-9 Two Views of Valve Internals Damaged by Solid Particle Erosion (Photographs courtesy of Dominion Virginia Power)2-11 Figure 2-10
36、Solid Particle Erosion Behavior of a Brittle and a Ductile Material (Reference 25) .2-12 Figure 3-1 Perforated Elbow from Hope Creek (Photograph courtesy of Public Services Electric namely, cavitation, flashing, liquid droplet impingement, and solid particle erosion. It is organized as follows: Sect
37、ion 2 presents a description of these four damage mechanisms Section 3 presents recommendations for locating potential damaged areas Section 4 presents inspection considerations Section 5 presents materials considerations Section 6 presents design considerations for reducing or eliminating the erosi
38、ve wear. Several appendices furnish additional information. 1-1 EPRI Proprietary Licensed Material 2 MECHANISMS Three of the four damage mechanisms considered in this report cavitation, flashing, and droplet impingement - are similar in that they involve high velocity liquid drops or liquid streams
39、impacting a metallic surface. They are also similar in that the damage is primarily mechanical in nature (i.e., erosion). However, there are important differences between them; these are discussed in the following sections. Solid particle erosion, on the other hand, requires the presence of hard par
40、ticles moving with the flow stream. It should be stressed that while there are materials immune to attack by FAC (e.g., stainless steel), these erosive mechanisms will, with time, damage virtually any material. Most of the discussion in this section concentrates on carbon steel components normally f
41、ound in the steam and feedwater systems. 2.1 Cavitation Cavitation damage may occur when there is a flowing liquid stream that experiences a drop in pressure followed by a pressure recovery. Such a pressure drop (i.e., the difference between the upstream pressure and the downstream pressure) can occ
42、ur in valve internals where the flow has to accelerate through a small area. As the fluid moves through the restricted area, the fluid velocity increases and the pressure decreases as shown by the momentum equation (i.e., Bernoullis theorem). If the local pressure passes below the vapor pressure at
43、the liquid temperature, then small bubbles are formed. When the downstream pressure rises above the vapor pressure, these bubbles collapse 1. The collapse of the bubbles causes high local pressures and very high local water jet velocities. If the collapsing bubbles are close enough to a solid surfac
44、e, damage to that surface will result. Figure 2-1 schematically illustrates cavitation at a restriction. The collapse of the numerous bubbles generates noise and vibration. Most often, cavitation causes most of its damage with vibration (e.g., cracked welds, broken instrument lines, loosened flanges
45、). The erosion caused by cavitation also generates particles that will contaminate the process fluid. A more detailed description of the cavitation process is presented in Appendix A. Cavitation has caused leaks and thinning in power piping and damage to valve internals. It has also been linked to s
46、purious reactor trips and to increased valve maintenance (references 3, 4). Finally, the use of an unsuitable valve (i.e., one that is cavitating) may result in vibration of the 1 These small bubbles have been called “cavities” which prompted the name “cavitation.” 2-1 EPRI Proprietary Licensed Mate
47、rial Mechanisms valve internals. These vibrations contribute to the noise generated and also cause loosening of parts and mechanical fatigue of valve components or attached piping (reference 5). In addition to noise, vibration and physical damage, cavitation will also alter the hydraulic characteris
48、tics of the pipeline by increasing the resistance in the cavitating region (e.g., see reference 3). 40 50 60 70 80 90 100 00.511.52 Position Pressure Vapor Pressure Figure 2-1 Schematic Illustration of the Cavitation Process Cavitation occurs in such diverse situations as hydroelectric turbines, shi
49、p propellers, and pump internals. However, only cavitation in valves and piping components is discussed in this report. Also note that cavitation has been extensively studied for many years and there is a very large body of literature dealing with various aspects of the issue (see, for examples, references 6 and 7). Although there is still disagreement about the precise nature of the damage mechanism, cavitation is well enough understood that it can be dealt with by competent design practices. For power plan
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