CRANFIELD UNIVERSITY Mohamed Ali Elforjani Condition Monitoring of Slow Speed Rotating Machinery Using Acoustic Emission Technology SCHOOL OF ENGINEERING PhD THESIS Academic Year: 2009 - 2010 Supervisor: Dr. David Mba June 2010 CRANFIELD UNIVERSITY SCHOOL OF ENGINEERING PhD THESIS Academic Year: 2009 - 2010 Mohamed Ali Elforjani Condition Monitoring of Slow Speed Rotating Machinery Using Acoustic Emission Technology Supervisor: Dr. David Mba June 2010 © Cranfield University 2010. All rights reserved. No part of this publication may be reproduced without the written permission of the copyright owner ConditionMonitoringofSlowSpeedRotatingMachineryUsingAcousticEmissionTechnology M.A.Elforjani ABSTRACT Slow speed rotating machines are the mainstay of several industrial applications worldwide. They can be found in paper and steel mills, rotating biological contractors, wind turbines etc. Operational experience of such machinery has not only revealed the early design problems but has also presented opportunities for further significant improvements in the technology and economics of the machines. Slow speed rotating machinery maintenance, mostly related to bearings, shafts and gearbox problems, represents the cause of extended outages. Rotating machinery components such as gearboxes, shafts and bearings degrade slowly with operating time. Such a slow degradation process can be identified if a robust on-line monitoring and predictive maintenance technology is used to detect impending problems and allow repairs to be scheduled. To keep machines functioning at optimal levels, failure detection of such vital components is important as any mechanical degradation or wear, if is not impeded in time, will often progress to more serious damage affecting the operational performance of the machine. This requires far more costly repairs than simply replacing a part. Over the last few years there have been many developments in the use of Acoustic Emission (AE) technology and its analysis for monitoring the condition of rotating machinery whilst in operation, particularly on slow speed rotating machinery. Unlike conventional technologies such as thermography, oil analysis, strain measurements and vibration, AE has been introduced due to its increased sensitivity in detecting the earliest stages of loss of mechanical integrity. This programme of research involves laboratory tests for monitoring slow speed rotating machinery components (shafts and bearings) using AE technology. To implement this objective, two test rigs have been designed to assess the capability of AE as an effective tool for detection of incipient defects within low speed machine components (e.g. shafts and bearings). The focus of the experimental work will be on the initiation and growth of natural defects. Further, i ConditionMonitoringofSlowSpeedRotatingMachineryUsingAcousticEmissionTechnology M.A.Elforjani this research work investigates the source characterizations of AE signals associated with such bearings whilst in operation. It is also hoped that at the end of this research program, a reliable on-line monitoring scheme used for slow speed rotating machinery components can be developed. Keywords: Acoustic Emission, Condition Monitoring, Natural Cracks, Source Characterizations, Slow Speed Rotating Machinery. ii ConditionMonitoringofSlowSpeedRotatingMachineryUsingAcousticEmissionTechnology M.A.Elforjani DEDICATION T here are not enough words in the world to tell people how much I love my mother Kheria Daw and my father Ali Elforjani, how much I appreciate them, or how much I want to thank them. Without their knowledge, wisdom, and guidance I would not have the goals I have to strive and be the best to reach my dreams. For all the times they have taught me the true meaning of education and for all the sacrifices, my work is dedicated to them. iii ConditionMonitoringofSlowSpeedRotatingMachineryUsingAcousticEmissionTechnology M.A.Elforjani ACKNOWLEDGEMENTS My ultimate thanks are to ALLAH almighty that created me and gave me strength and knowledge. I would deeply like to express my appreciation and gratitude to my supervisor Dr. David Mba for his superb guidelines and the fruitful discussion with him on which this thesis is based. I also wish a warm thank to my brother Fathi Forjani for his support and assistance in doing this work. A very special appreciation is due to my wife Eman Elmodham not only for her constant encouragement but also for her patience and understanding throughout my study period. May ALLAH bless her in all her endeavours because without her unreserved support, completion of this study would not have been possible. I am deeply indebted to all the members of my family; Amna, Ahmed, Rabyah, Ezdeen, Fatma and Salma for their support, prayer, love and encouragement. Special thanks should be given to the Libyan Government. Without its support and dedication this work would not have been possible. I would also like to express my gratitude to the many people for their help. Particular mention goes to those individuals and bodies listed below: Mr. Josh Redmond (Cranfield University, UK) Mrs Kay Roly (Housing Manager, Cranfield University, UK) Mr. Aymen El-Namy Mr. Makalowf Al-Twer Mr. Abo-Jareeda Salme (Elfornaj Communications, Tripoli-Libya) Dr. Ghaith Beshish (Faculty of Engineering, Tripoli-Libya) Dr. Ahmed Al-Gady (Faculty of Engineering, Tripoli-Libya) Mr. Scott Booden (Cranfield University, UK) Mrs. Deborah Hiscock (Cranfield University, UK) Many individuals and institutions have contributed information that was used to do this work. Their contributions are gratefully acknowledged. iv ConditionMonitoringofSlowSpeedRotatingMachineryUsingAcousticEmissionTechnology M.A.Elforjani Last, but not least, I would like to express my thanks to the staff members of the Department of Power and Propulsion and my colleagues for their help. v ConditionMonitoringofSlowSpeedRotatingMachineryUsingAcousticEmissionTechnology M.A.Elforjani TABLE OF CONTENTS ABSTRACT......................................................................................................... i DEDICATION.....................................................................................................iii ACKNOWLEDGEMENTS...................................................................................iv LIST OF FIGURES...........................................................................................viii LIST OF TABLES............................................................................................... x NOTATIONS......................................................................................................xi LIST OF EQUATIONS.......................................................................................xii 1 Introduction.................................................................................................1 1.1 Background and Motivation...................................................................1 1.2 Project Scope........................................................................................2 1.3 Thesis Outline.......................................................................................3 1.4 Scientific Contribution............................................................................3 1.5 Publications...........................................................................................4 1.5.1 Journal Publications........................................................................4 1.5.2 Conference Publications.................................................................5 2 Literature Review........................................................................................6 2.1 Failure Modes and Their Causes in Rotating Machinery.......................6 2.1.1 Shafts.............................................................................................6 2.1.2 Bearings .........................................................................................8 2.2 Condition Monitoring...........................................................................10 2.2.1 Condition Monitoring Technologies...............................................11 2.2.2 Viabilities and Drawbacks of Technologies...................................15 2.3 Signal Processing Techniques and Fault Index Extraction..................18 2.4 Previous Work.....................................................................................26 2.4.1 Vibration Analysis.........................................................................26 2.4.2 Acoustic Emission Technology.....................................................29 3 Acoustic Emission Technology..................................................................34 3.1 Introduction.........................................................................................34 3.2 Definition of Acoustic Emission (AE)...................................................35 3.3 Applications of Acoustic Emission Technology ...................................38 3.4 Acoustic Emission Sensors.................................................................39 3.5 Calibration and Attenuation Test.........................................................40 3.6 Acoustic Emission Measurements ......................................................43 3.6.1 Hit Driven Data Measurements.....................................................44 3.6.2 Time Driven Data Measurements.................................................45 3.6.3 Acoustic Emission Source Location..............................................47 3.7 Advantages and Disadvantages of AE Technology ............................49 4 Bearing Condition Monitoring....................................................................51 4.1 Test-Rig Design and Layout................................................................52 4.2 Instrumentation and Acquisition System Calibration...........................55 4.3 Bearing Tests......................................................................................60 4.3.1 Case I...........................................................................................63 4.3.2 Case II..........................................................................................70 4.3.3 Case III.........................................................................................75 4.3.4 Formation of Grooved Pathway on the flat Bearing Race.............81 vi ConditionMonitoringofSlowSpeedRotatingMachineryUsingAcousticEmissionTechnology M.A.Elforjani 4.3.5 Defect Size...................................................................................84 4.3.6 Case IV.........................................................................................85 5 AE Source Location Analysis....................................................................89 5.1 Bearing Tests......................................................................................89 5.1.1 Case I...........................................................................................91 5.1.2 Case II..........................................................................................93 5.1.3 Case III.........................................................................................96 6 Shaft Condition Monitoring........................................................................99 6.1 Test-Rig Design and Layout..............................................................100 6.2 Instrumentation and Acquisition System Calibration.........................101 6.3 Shaft Tests........................................................................................102 6.3.1 Case I.........................................................................................103 6.3.2 Case II........................................................................................109 7 Discussion...............................................................................................115 7.1 On Existing Knowledge.....................................................................115 7.2 On Results of This Research ............................................................118 8 Conclusion..............................................................................................124 9 Recommendations..................................................................................128 REFERENCES...............................................................................................129 APPENDICES................................................................................................141 Appendix A Bearing Test Rig Design......................................................141 Appendix B Shaft Test Rig Design..........................................................145 vii ConditionMonitoringofSlowSpeedRotatingMachineryUsingAcousticEmissionTechnology M.A.Elforjani LIST OF FIGURES Figure 3—1 Example of Kaiser Effect..............................................................37 Figure 3—2 Basic setup of an AE sensor.........................................................40 Figure 3—3 Example of AE sensor calibration certificate.................................41 Figure 3—4 Hsu-Nielsen source......................................................................43 Figure 3—5 Common measured parameters of AE signals.............................44 Figure 3—6 Example of Acoustic Emission waveforms...................................46 Figure 3—7 Principle of AE localization and the arrival time differences..........48 Figure 3—8 Cluster analysis for spherical storage tank for natural gas...........49 Figure 4—1 Steps of bearing test from basic design to the results interpretation ..................................................................................................................51 Figure 4—2 Test bearing arrangement for accelerated failure on the flat race 53 Figure 4—3 Test bearing run under starvation of grease.................................53 Figure 4—4 Test-Rig layout..............................................................................54 Figure 4—5 Schematic of the data acquisition systems...................................56 Figure 4—6 Breaking lead pencil at four different positions (Program I)..........57 Figure 4—7 Relative attenuation at four different positions (Program I)...........57 Figure 4—8 Breaking lead pencil at three different positions (Program II).......59 Figure 4—9 Relative attenuation at four different positions (Program II)..........59 Figure 4—10 General trend of AE energy throughout the bearing tests (Approach I & Approach II)........................................................................62 Figure 4—11 Test conditions run until visually observable surface damage....64 Figure 4—12 Classical AE parameters ............................................................65 Figure 4—13 Typical AE waveforms associated with case-I............................65 Figure 4—14 Crack zones on flat ring..............................................................66 Figure 4—15 IE, KU, EI and KS-test results.....................................................67 Figure 4—16 AE waveform, enveloping and FFT after 4-hrs...........................68 Figure 4—17 AE waveform, enveloping and FFT after 10-hrs.........................69 Figure 4—18 AE waveform, enveloping and FFT after 16-hrs.........................69 Figure 4—19 Test conditions run until visually observable surface damage....70 Figure 4—20 Classical AE parameters ............................................................71 Figure 4—21 Typical AE waveforms associated with case-II...........................71 Figure 4—22 Crack zones on flat ring..............................................................72 Figure 4—23 IE, KU, EI and KS-test results.....................................................73 Figure 4—24 AE waveform, enveloping and FFT after 6-hrs...........................74 Figure 4—25 AE waveform, enveloping and FFT after 14-hrs.........................74 Figure 4—26 AE waveform, enveloping and FFT after 20-hrs.........................75 Figure 4—27 Test conditions run until visually observable surface damage....76 Figure 4—28 Classical AE parameters ............................................................77 Figure 4—29 Typical AE waveforms associated with case-III..........................77 Figure 4—30 Crack zone on flat ring................................................................78 Figure 4—31 IE, KU, EI and KS-test results.....................................................79 Figure 4—32 AE waveform, enveloping and FFT after 15-hrs.........................80 Figure 4—33 AE waveform, enveloping and FFT after 45-hrs.........................80 Figure 4—34 AE waveform, enveloping and FFT after 50-hrs.........................81 viii