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
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
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 703
4.7 FFT analysis of faulty outer bearing ring vibration signal. 70
4.8 Normalized FFT of outer bearing ring vibration signal 71
CHAPTER 1
INTRODUCTION
1.1 BACKGROUND OF THE STUDY
Pumps are a versatile type of machinery with varied applications. As pumps consume nearly 22% of the worldwide energy supplied by electric motors, pumps contribute enormous energy consumption, with a tremendous energy saving potential (Arun et al. 2016). With a large flow rate and high pump head, centrifugal pumps are widely used in the various fields and industries (Wang et al. 2017).
As the key element of hydraulic systems, a pump is responsible for the mechanical to hydraulic energy conversion process. Submersible pumps are widely applied in modern industry owing to its advantages such as small and compact design, high efficiency and low manufacturing cost (Ali et al., 2020). The working status of a submersible pump greatly affects the performance of the whole hydraulic system, thus it is necessary to develop its fault diagnosis technique. The condition of mechanical equipment is closely associated with vibration signals, which come about during rotating process for rotating machinery (Ajith and Jeoju, 2015).
Generally, centrifugal pumps operate under stable working conditions for a long time; i.e., the operating rotational speed, load, and other parameters remain at a relatively stable level, or the change fluctuations are very slow or small (Cheng et al. 2022). However, during some transient operating occurrences, the centrifugal pumps begin from a stationary state and rapidly reach a stable operating state, or they abruptly shut down from a stable working state, wherein each of the performance parameters drastically changes in a short period of time. For example, severe pressure fluctuation may occur during the fast start up period, which could be very damaging to the equipment and even lead to accidents (Zhang et al. 2016).
Fault prediction based is used to determine the operating and mechanical condition of equipment. A major advantage is that fault prediction analysis can identify developing problems before they become too serious and cause unscheduled downtime. This can be achieved by conducting regular monitoring of machine vibrations either on continuous basis or at scheduled intervals (Lu et al., 2018).
Regular vibration monitoring can detect deteriorating or defective bearings, mechanical looseness and worn or broken gears. Vibration analysis can also detect misalignment and unbalance before these conditions result in bearing or shaft deterioration. Trending vibration levels can identify poor maintenance practices, such as improper bearing installation and replacement, inaccurate shaft alignment or imprecise rotor balancing.
Therefore, fault prediction of centrifugal submersible pumps can be performed with the characteristic information extracted by the signal processing techniques such as short time Fourier transform, wavelet transform, blind source separation, sparse decomposition method and empirical mode decomposition (EMD).
1.2 STATEMENT OF PROBLEM
Submersible pumps are universally used in today’s homes, manufacturing and process industries. They have been applied from the household appliances, such as well pumps and sophisticated systems using lift pump etc. Due to greater expectations in higher operating speeds, larger applied load, and lighter weight, premature failures due to excessive wear increase substantially, and sometimes, even result in catastrophic injuries, and substantial financial losses. Presently, fault/wear detection becomes an important problem associated with this high speed rotating machinery. If a crack or fault is detected in its early stages, corrective action can be taken promptly.
Also preventive maintenance can be made in advance to replace the damaged part of the machinery. Thus, the detection of excessive wear in machine components could be available diagnostics and prognostics tool for today’s machinery.
Presently, the advancements in research were aimed at finding a reliable monitoring strategy for centrifugal submersible pump systems. For the last two decades, a variety of fault detection procedures have been developed. Visual inspections of the components have been found to be mostly impractical as micro-faults cannot be easily visualized unless specialized equipment’s are used. In addition it is quite impossible to examine fault diagnostic and possible prediction on-line during operation. Currently, visual inspection products are used mainly after machine failure has already been experienced.
On the other hand, current on-line condition monitoring systems for rotor bearing systems often fail to provide sufficient time between warning and failure such that safety procedures can be implemented. At times, a small fault in the pumps or bearing system can quickly develop into a dangerous failure mode without any notable signs. In addition, inaccurate interpretation of operational conditions may often result in false alarms and unnecessary repairs and downtime. All these needs call for the development of an accurate early fault detection system that permits on-line inspections without costly shutdowns during machine operations.
One of the most promising procedures for detecting incipient faults in pumps and bearings is the fault prediction analysis. Faults prediction analysis does not require shutdown of the rotating machinery, and can be carried out on-line by a computer-based machine health monitoring system. The acquired fault signals are processed by a variety of methods to identify the faults of centrifugal submersible pumps. However, the interpretation of the vibration signals, in some cases, may require extensive experiences and knowledge in vibration signal interpretations for an accurate identification of the faults and their corresponding locations.
1.3 AIM AND OBJECTIVES OF THIS STUDY
The aim of this study was to carry out a fault prediction analysis of submersible centrifugal pumps. Specific objectives include to:
i. design and fabricate a submersible centrifugal pump test rig using locally sourced materials
ii. carry out a performance analysis on the fabricated machine using vibration data analysis methods
iii. determine the effectiveness of bearings on the performance of the centrifugal pump
1.4 SCOPE OF STUDY
i. Design and fabricate a submersible centrifugal pump test rig using locally sourced materials
The study carried out asuitable condition monitoring and fault diagnostics using induced faulty parts that pave way for full evaluation of the vibration based condition monitoring techniques developed. In addition, right sensors and measurement systems will be specified for adequately measuring vibrations, suction and discharge pressures, flow rate and overall system energy input.
1.5 JUSTIFICATION OF THE STUDY
Traditional sensors such as accelerometers, gyroscopes, strain gauges, inclinometers, and global positioning systems (GPS) have been widely used in vibration measurement. However, many conventional vibration measurement methods are both labour intensive and expensive owing to complex wiring for power supply and signal transmission, as well as installation and deployment of sensors. In addition, since these types of sensors are physically attached to the target object, the physical properties of the object, such as stiffness, mass, or damping, may be altered, especially when the target object is relatively small compared to the sensor.
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