ABSTRACT

A submersible centrifugal pump test rig has been developed for fault detection analysis in the laboratory. A microcontroller designed and programmed in C++ was used alongside sensors for vibration monitoring, flow rates measurement, current and/or load sensors to collect faulty parts data. Five post-test experiments, the designed test-rig was used. Experimental data collected from the bearing of the pump test rig was used to investigate the effects of bearings on the performance of the centrifugal pump. The pump was made up of a motor, shaft, bearings, pump pipes, and a tank. The pump bearing used in the study was a FAG Type 6307 Ball Bearing with the geometric dimensions. Furthermore, the accelerometer and (sensor) measurement system were installed vertically on the bearing pump case to provide a complete vibration data measurement.The effects of the time, current and amplitude on the submersible pump was evaluated. The result depicted continuous decrease in the flow rate as the time increases. Increase in the amplitude increased the flow rate while increase in current decreased the flow rate. The result of the Fast Fourier Transform (FFT) showed that characteristic frequencies and their harmonics are significant, The vibration spectrum frequency result indicated that faults were first detected at frequency of 42Hz, 50Hz and 62Hz for the baseline bearing vibration signal, with the amplitude of the outer race defect frequency around 242Hz appearing on almost the same peaks in the three cases when compared to the baseline case. Furthermore, the results of the envelope analysis showed that the method can be used to detect faults. It can also be used to determine the specific fault type by analyzing the frequency of the fault characteristics.

TABLE OF CONTENTS

Page

Title Page                                                                                                                                i

Declaration                                                                                                                              ii

Dedication                                                                                                                              iii

Certification                                                                                                                            iv

Acknowledgements                                                                                                                v

Table of Contents                                                                                                                   vi

List of Tables                                                                                                                          viii

List of Figures                                                                                                                         ix

Abstract                                                                                                                                  x         

CHAPTER 1

INTRODUCTION

1.1       Background of the Study                                                                                           1

1.2       Statement of Problem                                                                                                             2

1.3       Aim and Objectives of this Study                                                                              3

1.4       Scope of Study                                                                                                           3

1.5       Justification of the Study                                                                                           4

CHAPTER TWO

LITERATURE REVIEW

2.1       Pumps                                                                                                                         5

2.2       Pump Classification                                                                                                    5

2.2.1    Centrifugal Pumps - Basics and Principles of Operation                                            8

2.3       Pump Failures                                                                                                 10

2.3.1    Hydraulic Failures                                                                                                       10

2.3.2    Pressure pulsations                                                                                                      13

2.3.3    Radial thrust                                                                                                               16

2.3.4    Axial thrust                                                                                                                 17

2.3.5    Suction and discharge recirculation                                                                            18

2.3.6    Mechanical Failure                                                                                                      19

2.3.7    Bearing Failure                                                                                                            19

2.3.8    Seal Failure                                                                                                                 21

2.3.9    Lubrication Failure                                                                                                      22

2.3.10  Excessive Vibrations                                                                                                   22

2.3.11  Fatigue                                                                                                                        25

2.3.12  Other Modes of Failure                                                                                              26

2.4       Common Failure Modes in Centrifugal Pumps                                                          32

2.4.1    Cavitation                                                                                                                   32

2.4.2    Very Low or Zero Flow Operation                                                                             34

2.4.3    Dry Running                                                                                                               34

2.4.4    Damage to the Pump Impeller                                                                                    35

2.4.5    Degradation of Mechanical Seals                                                                               35

2.5       Overview of Fault Detection Methods                                                                       36

2.4.1    Reactive Maintenance                                                                                                 36

2.4.2    Preventive Maintenance                                                                                              36

2.4.3    Predictive or Proactive Maintenance                                                                          36

2.5       Classification of Fault Detection Methods                                                                 37

2.5.1    Signal-Based Fault Detection Methods                                                                      37

2.5.2   Model-Based Fault Detection Methods                                                                     38

2.6       The Basic Principle of Detecting Pump Faults Using Motor Electrical Signals         40

2.6.1   Impeller                                                                                                                       41

2.6.2   Motor and Shaft                                                                                                         41

2.6.3   Coupling                                                                                                                     42

2.6.4   Pipeline and Tank                                                                                                       42

2.6.5   Unbalance                                                                                                                   42

2.6.6   Misalignment                                                                                                              42

2.6.7   Hydraulic Fluid Pump                                                                                                43

2.6.8   Hydraulic Vibration Source                                                                                        43

2.6.9   Turbulent Flow and Vortex                                                                                        43

2.6.10  Erosion                                                                                                                        43

2.6.11  Noise                                                                                                                           44

2.6.12  Radial Thrust                                                                                                              44

2.6.13  Axial Thrust                                                                                                                43

2.7       Vibration analysis of rotating machines                                                                      46

2.7.1    Vibration Characteristics of Centrifugal Pumps                                                         47

2.8       Mechanical Vibration Source                                                                          48

2.8.2    Advances in Data Driven Computational Modelling                                                             48

2.9       Empirical Literature Review                                                                                       51

2.10     Gap in Literature                                                                                                         57

CHAPTER THREE

MATERIALS AND METHODS

3.1       Materials                                                                                                                     58

3.2       Methods                                                                                                                      59

3.3       Performance evaluation of the test rig                                                                        62

CHEPTER 4

RESULTS AND DISCUSSION                                                                                          64

4.1       Effect of the detection parameters on the flow rate                                                   64

4.1.1    Effect of time on the flow rate of the centrifugal pump                                            64

4.1.2    Effect of amplitude on the flow rate of the centrifugal pump                                               65

4.1.3    Effect of current on the flow rate of the centrifugal pump                                        65

CHAPTER 5

CONCLUSION AND RECOMMENDATIONS

5.1       Conclusion                                                                                                                  72

5.2       Recommendation                                                                                                        73

5.3       Contribution to knowledge                                                                                         73

5.4       Possible application of research results                                                                       73

REFERENCES                                                                                                                    74

APPENDIX

LIST OF TABLES

Table                                                   Title                                                                 Page

2.1       Maintenance programmes used in various industries                          37

2.2       Modified Impeller Data                                                                                  54

2.3       Results of Kriging, FSI simulation, and experiment                                      56

3.1       Materials for small scale submersible centrifugal pump test bench                58

4.1       Bearing fault characteristic frequency and equation                                      70

LIST OF FIGURES

Figure                                                 Title                                                                      Page

2.1.      Pump classification tree Non-self-priming, open impeller, radial flow pump 7

2.2.      Inside of a centrifugal pump                                                                                       8

2.3       Typical performance curves of a centrifugal pump                                                     9

2.4       Signal-based fault detection method                                                                                     38

2.5       Model-based fault detection framework                                                                    39

2.6       Generalized system for pump fault detection                                                             40

2.7       Single and double volute                                                                                            45

2.8       Axial thrust components                                                                                             46

2.9       Vibration sources of centrifugal pumps                                                                      48

3.1       Flow diagram for the design of the submersible pump testing rig                             61

3.2       Diagrammatic views of the submersible pump testing                                               61

3.3       Bearing components for balling elements and fault location                                      62

4.1       Flow rate – time characteristics                                                                                  64

4.2       Flow rate – amplitude characteristics                                                             65

4.3       Flow rate – current characteristics                                                                              66

4.4       FFT analysis of baseline bearing vibration signal.                                                      67

4.5       Normalized FFT of baseline bearing vibration signal                                                 68

4.6       Vibration signal with faulty outer bearing ring                                                           70

4.7       FFT analysis of faulty outer bearing ring vibration signal.                                         70

4.8       Normalized FFT of outer bearing ring vibration signal                                              71