Condition Monitoring, Troubleshooting and Reliability in Rotating Machinery
Description
This third volume in a broad collection of current rotating machinery topics, written by industry experts, is a must-have for rotating equipment engineers, maintenance personnel, students, and anyone else wanting to stay abreast with current rotating machinery concepts and technology.
Rotating Machinery Fundamentals and Advances represents a broad category of equipment, which includes pumps, compressors, fans, gas turbines, electric motors, internal combustion engines, etc., that are critical to the efficient operation of process facilities around the world. These machines must be designed to move gases and liquids safely, reliably, and in an environmentally friendly manner. To fully understand rotating machinery, owners must be familiar with their associated technologies, such as machine design, lubrication, fluid dynamics, thermodynamics, rotordynamics, vibration analysis, condition monitoring, maintenance practices, reliability theory, and others.
The goal of the "Advances in Rotating Machinery" book series is to provide industry practicioners a time-saving means of learning about the most up-to-date rotating machinery ideas and best practices. This three-book series covers industry-relevant topics, such as design assessments, modeling, reliability improvements, maintenance methods and best practices, reliability audits, data collection, data analysis, condition monitoring, and more.
Readers will find a good mix of theory and sage experience throughout this book series. Whether for the veteran engineer, a new hire, technician, or other industry professional, this is a must-have for any library.
This outstanding new vcolume includes:
* Machinery monitoring concepts and best practices
* Optimizing Lubrication and Lubricant Analysis
* Machinery troubleshooting
* Reliability improvement ideas
* Professional development advice
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Person
Robert X. Perez is a mechanical engineer with more than 40 years of rotating equipment experience in the petrochemical industry. He has worked in petroleum refineries, chemical facilities, and gas processing plants. He earned a BSME degree from Texas A&M University at College Station, an MSME degree from the University of Texas at Austin and holds a Texas PE license. Mr. Perez has written numerous technical articles for magazines and conferences proceedings and has authored five books and coauthored four books covering machinery reliability, including several books also available from Wiley-Scrivener.
Content
Preface xix
Acknowledgements xxi
Part 1: Condition Monitoring 1
1 An Introduction to Machinery Monitoring 3
By Robert X. Perez
2 Centrifugal Pump Monitoring, Troubleshooting and Diagnosis Using Vibration Technologies 15
By William D. Marscher
Introduction 15
Vibration Definitions 16
How Vibration vs. Time Relates to a Vibration vs. Frequency "Spectrum" 18
What are Reasons for Excess Vibration? 19
Relationship of Vibration to Centrifugal Pump Acceptability and Reliability 20
Vibration Standards, Informal and Formal: Intent and Basis 21
Vibration Measurement Form 22
Vibration Detection Sensors 25
Accelerometers 26
Proximity Probes 27
Motion Magnified Video (aka Vibration Video Amplification) 28
International Vibration Acceptance Standards 30
Pump Components Playing Key Roles in Vibration Diagnostics 33
Rotor Support by Bearings: Fluid Film Journal Bearings vs. Rolling Element Bearings 33
Rotor Support by Seals: Annular Seal "Lomakin Effect" 35
Couplings 38
Bearing Housings and Attachment Bolts 39
Pump Casing, Feet, and Foot Attachment Bolts 39
Pump Pedestals, Baseplate, and Foundation 40
Piping, Suction, and Discharge 40
Pump Drivers 43
Evaluating Causes of Excess Vibration: Excitation vs. Amplification 43
Process of Resonant Amplification due to Coincidence of Excitation and Natural Frequencies 45
Impact Test Method of Determining Natural Frequencies 46
Specific Forces in Centrifugal Pumps 48
Mechanical Excitation Forces 48
Balance 48
Misalignment 50
Mechanical Forces Due to Dry Running Pump, Dry Running Seal, Overtightened Seal 52
Hydraulic Forces and Blade Passing Frequency 52
Hydraulic Vibration Forces Below Running Speed, Including Subsynchronous Whirl 54
Detection of Effects of Cavitation 57
Torsional Excitations 59
Vibrations Particular to Various Centrifugal Pump Types 62
Vertical Turbine Pump Evaluation 62
Vertical Dry Pit Pump Vibration Issues 65
Submersible Pump Vibration Issues 65
End Suction Overhung Single Stage Pump Vibration Issues 66
Between Bearing Double Suction Single Stage Pump Vibration Issues 66
Horizontal Multistage Pump Vibration Issues 67
Steps in Pump Evaluation through Vibration Monitoring 68
Use of the Bode and Nyquist Plots to Confirm Natural Frequencies 70
Operating Deflection Shapes (ODS) 71
Conclusions 73
Nomenclature 73
References & Bibliography 74
Acknowledgements 75
3 Proximity Probes are a Good Choice for Monitoring Critical Machinery with Fluid Film Bearings 77
By Robert X. Perez
Proximity Probe Benefits 77
Theory of Operation 78
Runout Concerns 80
Grounding and Noise 80
Shaft Orbits 81
General Machinery Monitoring Recommendations 82
Final Thoughts 85
References 86
4 Optimizing Lubrication and Lubricant Analysis 87
By Jim Fitch and Bennett Fitch
Introduction 87
Optimum Reference State 88
Lubrication Excellence and the Ascend Chart 91
Bringing Awareness to Lubrication, Contamination, and Oil Analysis 94
What You Might Not Know About Lubrication 94
Machine Surface Interaction 94
The Lubricant Film 95
Film Strength 96
Unlubricated Surface Interactions 96
Friction and Wear Generation 96
Mitigating Surface Interactions 97
Physics and Chemistry 97
Contamination: The Antagonist to Lubrication 98
Contamination Control and Condition Monitoring is More Often about Training than Advanced Technology 98
Contamination Control 99
Don't Leave It to Instinct 99
Creating a Balance Between Exclusion and Removal 100
Why Perform Oil Analysis 102
Fluid Properties Analysis 102
Contamination Analysis 103
Wear Debris Analysis 103
Achieving Oil Analysis Success by Looking Holistically 103
Obtaining a Representative Oil Sample 105
Select the Right Machines for Oil Analysis 105
Clean and Correct Sampling Containers and Extraction Tools 105
Correctly Located Sampling Ports 106
Proper Sampling Frequency 107
Proper and Consistent Sampling Procedures 107
Forward Samples Immediately to the Laboratory 108
Ensuring Reliable Testing 108
Certified Training of Laboratory Technicians 108
Optimized Selection of Tests 109
Onsite Oil Analysis 109
Determining the Optimum Course of Action 110
Effective Organization of Analysis with Proper Trending 110
Accurate Data Interpretation by the Laboratory 110
Enhanced Data Interpretation by the End-User 111
Take Corrective Action and Determine the Root Cause 112
Continuous Improvement and Key Performance Indicator (KPI) 112
Oil Analysis Tests 112
Viscosity 113
Acid Number and Base Number 113
Ftir 114
Elemental Analysis 114
Particle Counting 114
Moisture Analysis 115
Interpreting Oil Analysis Reports 116
Following the Data Trends 118
Looking Back at the Past 123
Inspection 2.0: Advances in Early Fault Detection Strategy 124
Low-Hanging Fruit 124
Inspection Frequency Trumps High Science 125
Beware of Short P-F and Sudden-Death Failures 127
Inspection Windows and Zones 128
Inspection 2.0 is a Nurturing Strategy 129
Final Tips to Help Error-Proof Your Lubrication Program 130
References 134
5 Troubleshooting Temperature Problems 135
By Robert X. Perez
Temperature Assessments 135
How do Infrared Thermometers Work? 136
Bearing Temperature Trending 137
Rolling Element and Sleeve Bearing Temperature Guidelines 139
Rule of Thumb for Rolling Element Bearings: 142
Bearing Temperature Guidelines for Instrumented Hydrodynamic Bearings 142
Recommended Guidelines for Babbitt Bearings 142
Bearing Temperature Sensor Placement 143
Sleeve Bearings 143
Tilting Pad Journal (TPJ) Bearings-Load on Pad 144
Tilting Pad Journal Bearings-Load between Pads 144
Thrust Bearings-Tilting Pad 144
General Temperature Probe Installation Guidelines 145
Compressor Discharge Temperature Assessments 146
Heat of Compression 146
Types of Compression Processes 147
Adiabatic Compression 148
Polytropic Compression 152
Polytropic Example 1: 154
Polytropic Example 2: 154
Why Compression Ratio Matters 155
What Role It Plays in Compressor Design and Selection 155
Compression Ratio versus Discharge Temperature 155
Design Temperature Margin 158
Design Tradeoffs 159
Reciprocating Compressor Temperature Monitoring 160
Valve Temperature Monitoring 162
Temperature Monitoring Example 164
Summary 165
References 165
6 Assessing Reciprocating Compressors and Engines 167
By Robert X. Perez
Overview of Reciprocating Compressors 169
General Monitoring Guidelines for Reciprocating Compressors 174
Impact Monitoring 177
Rod Drop Monitoring 178
Using Ultrasonics to Assess Reciprocating Machinery 178
Mystery Reciprocating Compressor Knock 179
Natural Gas Engines 181
How Accurate are Rotating Equipment and Reciprocating Equipment Analyst Findings? 190
References 193
7 Managing Critical Machinery Vibration Data 195
By Robert X. Perez
Beware of False Positives and False Negatives 195
Vibration Analysis Strategies 197
Part 2: Troubleshooting 201
8 Addressing Reciprocating Compressor Piping Vibration Problems: Design Ideas, Field Audit Tips, and Assessment Methods 203
By Robert X. Perez
Piping Restraints 205
Pipe Clamping Systems 207
Guidelines 207
Preloading Clamp Bolts 209
Piping Assessment Steps 210
Small-Bore Piping 211
Attaching Pipe Clamps to Structural Members 212
The Ideal Pipe Clamp Installation 213
Installation Examples 214
Collecting and Assessing Piping Vibration 217
Piping Analysis Steps 220
Piping Vibration Examples 221
Bolt Torque Tables 223
Chapter Glossary 224
9 Remember to Check the Rotational Speed When Encountering Process Machinery Flow Problems 227
By Robert X. Perez
10 Troubleshooters Need to be Well Versed in the Equipment They are Evaluating 233
By Robert X. Perez
What is the Difference Between Troubleshooting and Conducting a Failure Analysis? 236
Equipment Details 237
Performance Characteristics 238
Centrifugal Compressors 238
Reciprocating Compressors 239
Basic Fluid Film Bearing Troubleshooting Tips 240
Design Basis: Speed, Pressures, Flows 241
System Design Details 243
OEM Recommendations 244
History 244
Putting it All Together 245
11 Precise Coupling Properties are Required to Accurately Predict Torsional Natural Frequencies 247
By Robert X. Perez
Introduction 247
Case Study 247
Start-Up Issues 249
Field Vibration Study 249
Lesson Learned 252
Final Thoughts 253
12 Is Vibration Beating on Machinery a Problem? 255
By Robert X. Perez and Andrew P. Conkey
What is Vibration Beating? 255
Zoom FFT (Fast Fourier Transform) Analysis 257
Electric Motor Zoom Analysis 258
Field Case Study: "Beating" Effect Caused by Two Closely Spaced Mechanical Frequencies Observed on Two-Shaft, Gas Turbine Drive 259
Background Information 260
Vibration Response Analysis 261
Investigation of System and Analysis 261
Frequency Analysis 262
Case Study Solution 263
Case Study Conclusions and Lessons Learned 263
Final Comments 263
References 264
Part 3: Reliability 265
13 Using Standby Machinery to Improve Process Reliability 267
By Robert X. Perez
Introduction 267
Basic Reliability Theory 267
Exercising Spared Machinery 273
Alternating Twin, Non-Critical, Process Pumps 273
Recommended Swapping Procedures for Critical Motors, Pumps, Blowers, Compressors, Generators, and Steam Turbines 274
Recommended Swapping Procedures for Reciprocating Process Plant Machinery above 200 HP 275
Raptor Modeling Software 276
Modeling Examples 277
Example 1: Unspared Compressor 278
Example 2: Main and Spare Compressor Installation 279
Example 3: Two out of Three (2oo3) Compressor Configuration 280
The Cost of Redundancy 282
Example 4: Cost of Unreliability 283
Economics 284
Justifying of a Spare Compressor 285
Closing Thoughts 287
References 287
14 Gas Turbine Drivers: What Users Need to Know 289
By Robert X. Perez
Overview 289
Theory of Operation 292
How Does a Gas Turbine Work? 292
Air Compressor 294
Combustors 296
Transition Pieces 297
Expansion Turbine 298
Turbine Section Challenges and Solutions 299
Two Shaft Gas Turbine Construction Details 301
Gas Producer 301
Lower Pressure Power Turbine (LP) 301
Typical Conditions Inside an Industrial Gas Turbine 303
Effect of Atmospheric Conditions 304
Gas Turbine Controls 305
Protection 305
Fuel and Fuel Treatment 306
Gas Fuels 306
Degradation and Water Washing 306
Advanced Materials for Land Based Gas Turbines 307
Blade Degradation 308
Condition Monitoring Approaches 309
Aerothermal Performance Analysis 309
Vibration Analysis 310
Transient Analysis 311
Mechanical Transient Analysis 311
Dynamic Pressure Analysis 312
Lube Oil Debris Analysis 312
Borescope Inspection 312
Condition Monitoring as a System 313
Gas Turbine Maintenance Inspections 313
Standby Inspections 314
Running Inspections 314
Combustion Inspections 316
Hot Gas Path Inspections 316
Major Inspections 316
Life Cycle Management 318
Non-Destructive Testing (NDT) 320
Spare Parts 321
Final Words of Advice 322
References 323
15 Reliability Improvement Ideas for Integrally Geared Plant Air Compressors 325
By Abdulrahman Alkhowaiter
Integrally Geared Plant Air Compression Packages 325
Reliability Concerns 327
Developing Enhancements for Air Compressor Reliability and Performance 330
Reliability Improvement Program to Achieve Reliability and Eliminate Frequent Failures 330
Reliability Improvements (based on 2008 Report) Made to Five (5) 850 HP Air Compressor Failures by Engineering and Maintenance: 331
16 Failure Analysis & Design Evaluation of a 500 KW Regeneration Gas Blower 341
By Abdulrahman Alkhowaiter
Introduction 341
Detail Design Analysis 343
Conclusion 349
Needed Action by Repair Shop 350
Action Required by Refinery 350
17 Operating Centrifugal Pumps with Variable Frequency Drives in Static Head Applications 353
By Robert X. Perez
VFD Advantages 354
Static Head Systems 356
Recommended Startup Sequence 359
Final Thoughts 362
References 362
18 Estimating Reciprocating Compressor Gas Flows 363
By Robert X. Perez
Swept Volume 364
Clearance Volume 365
Volumetric Efficiency 365
Flow Calculation Example 370
Factors Affecting Compressor Flow 371
Final Words 371
19 Use Your Historical Records to Better Manage Time Dependent Machinery Failure Modes 373
By Robert X. Perez
Part 4: Professional Development 379
20 Soft Skills and Habits that All Machinery Professionals Need to Develop 381
By Robert X. Perez
Asking Probing Questions 383
Listening More Carefully 384
Observing 385
Continuously Learning 386
Praising 387
Teaching 388
Closing Remarks 390
21 Developing Rotating Machinery Competency 391
By Robert X. Perez
Part I: Preparing Students to Work with Rotating Machinery 391
Rotating Machinery Related Job Functions 391
Part II: Steps to Improving Rotating Machinery Competency: Study-Practice-Share 396
About the Editor 403
About the Contributors 405
Index 409
1
An Introduction to Machinery Monitoring
By Robert X. Perez
The aim of employing predictive maintenance technologies in process facilities is to assess the condition of equipment by performing periodic inspections such as vibration analysis, temperature monitoring, oil analysis, ultrasonic analysis, etc. or by using permanently installed equipment, such as vibration or temperature sensors. The primary tenant of the predictive maintenance philosophy is that it is more cost-effective to perform maintenance when degradation or distress is detected than to risk running equipment until it loses performance capability and adversely affects the process (Figure 1.1). Operating personnel hope to identify and address machinery issues in the primary state before costly secondary damage is experienced.
Figure 1.1 As a machine begins to fail, it begins showing signs of distress. First, vibration levels increase and then noise is detected. In the final stages of failure, heat and smoke are experienced before a catastrophic failure occurs. It makes economic sense to invest in condition monitoring technology that can detect early signs of failure before secondary damage can occur.
There are two types of data collected by condition monitoring systems: a) Dynamic data which is composed of electrical signals that rapidly change versus time, as seen in Figure 1.2. Dynamic data requires some type of signal processing to convert it into a user-friendly format. b) Static data which are signals that do not change rapidly versus time, therefore signal processing is not required. The most common condition indicators used for monitoring machines and piping in critical processes are:
- Vibration-This is dynamic data is collected by measuring the motion of a vibrating surface, such as a bearing housing or shaft. Analysis of this type of data requires complex signal processing and pattern recognition. More on vibration analysis later. (RTD's) are often inserted into a fluid stream or on or below bearing metal surfaces to measure temperature. Portable infrared temperature guns and contact thermometers can also be used to monitor machine surface temperatures. In some applications, thermography is employed to visualize temperature distributions across a machine in order to identify component issues such as failing bearings, etc. Thermography can also be used to spot electrical problems in the field on motors and control panels.
- Pressure-This can be either in the form of static or dynamic data collected by inserting a pressure traducer into a fluid stream. Trending static field pressure data can be used to spot changes in rotating machinery performance or to ensure operating conditions are normal.
- Temperature-This is usually in the form of static data. Thermocouples (TC) or resistance temperature devices
Figure 1.2 Mechanical vibration levels are commonly used to assess the condition of vital process machinery. Complex vibration waveforms measured in the field are a combination of multiple machinery phenomena such as unbalance, looseness, etc.
- Oil Analysis-Oil analysis requires that oil samples be collected in the field and then sent off-site for lab testing. Although most oil properties are usually determined by lab testing, some oil properties can be monitored in real time.
- Piping, Duct Work, and Structural Vibration-The vibration of piping, vents, duct work, and supporting structures connected to machinery can signal problems, such as critical speeds issues, resonances, and unwanted flow conditions. On new installations, excessive piping vibration may be indications of poor installation and/or design practice.
Vibration Analysis
In the simplest terms, mechanical vibration in rotating machinery is simply the back and forth movement or oscillation of machines and components, such as drive motors, driven devices (pumps, compressors, and so on), and the bearings, shafts, gears, belts, and other elements that make up mechanical systems. Vibration in industrial equipment can be both a sign and a source of trouble. With a basic understanding of vibration and its causes, the maintenance professional can quickly and reliably determine the cause and severity of most machine vibration and provide recommendations for repair.
Elements of Vibration
Machinery vibration as a repetitive movement around a point of equilibrium characterized by its variation in amplitude and frequency. Vibration can be the dynamic motion of a bearing housing or piping system or the dynamic motion of a rotor relative to a bearing or stator. Both the amplitude and the frequency are used to assess and analyze vibration issues. Amplitude is the maximum extension of the oscillation and it is measured from the lowest point to the highest point of the waveform. We can say the amplitude is the total movement of a surface or object during a cycle which is used to quantify the intensity of the vibration. Frequency measures the rate at which movements in vibration occur per second (Hz) or cycles per minute (CPM). For example, every piano note is tuned to a unique frequency. If you examined the vibration waveform of each note, they would each have a unique frequency corresponding to a defined note. The piano frequencies and amplitudes of each note are combined to create a complex signal. Similarly, vibration can be a composition of multiple frequencies that are the result of different machinery phenomena (Figure 1.2). Every machine will have its own vibration signature related to many factors such as its construction, installation, and condition. It is the job of the monitoring system to faithfully detect and display the vibration that is occurring. The vibration analyst must have complete trust in the vibration monitoring system before they can begin the vibration analysis process.
When Vibration is a Problem
Most industrial devices are engineered to operate smoothly and avoid vibration, not produce it. In these machines, vibration can indicate problems or deterioration in the equipment. If the underlying causes are not corrected, the unwanted vibration itself can cause additional damage. In critical process machinery, smoother operation is generally better and a machine running with vibration levels close to zero is ideal.
Effects of Vibration
The effects of excessive vibration can be severe. If unchecked, machine vibration will accelerate wear rates in mechanical seals, internal seals, and bearings and potentially lead to catastrophic equipment failures. High machine vibration levels usually lead to a shortened machine life and a higher probability of catastrophic failure.
Vibrating machinery will also:
- Create more background noise
- Create safety issues due to flammable product leaks to the atmosphere
- Lead to degradation in plant working conditions due to external product and oil seal leaks
- Lead to excessive power consumption due to the wear of internal seal clearances
- Affect product quality by damaging seals and allowing oil, water, and other contaminates to enter the process
In the worst cases, vibration can damage equipment so severely that it will fail rapidly and potentially halt plant production. Yet, there is a positive aspect to machine vibration. Measured and analyzed correctly, vibration can be used in a preventive maintenance program as an indicator of machine condition and help guide the plant maintenance professional to take remedial action before disaster strikes.
Monitoring Systems
Predictive maintenance programs rely on either portable or permanently installed monitoring systems that can accurately sense and report one or more key equipment condition and performance indicators. For example, vibration monitoring systems, which are commonly used to assess the mechanical condition of process machinery, have several distinct components (Figure 1.3) that work together to deliver a useful output. Other examples of monitoring systems are those that measure bearing temperature by using embedded resistance temperature detectors (RTDs) or thermocouples (TC) with outputs that are connected to temperature monitors. The role of a temperature monitor is to convert the input from a temperature sensor into an output voltage proportional to the temperature that can then be displayed, monitored, or stored for later use. Pressure monitoring systems employ pressure transmitters to measure vital pressures, such as suction and discharge pressures, oil and seal system pressures, and process pressures. The intent of every monitoring system is to sense physical measurements occurring in the field and display them in real time so that it can be analyzed and acted upon as required.
Vibration monitors all have some type of motion sensitive sensor that detects and transmits a motion signal, usually a current or voltage, to the signal processor. To select the proper sensor, the user must ask: What am I trying to measure? To answer this question, you need to know the expected amplitude and frequency range of the vibration phenomena. For example, Figure 1.4 shows spectral analysis bands from a machine with rolling element bearings. Notice there are various potential vibration issues identified based on experience, such as imbalance, alignment, etc. By inspection, we can see that to adequately monitor the vibration phenomena shown in Figure 1.4, we would need a sensor capable of detecting vibration in the range from 0 to 20,0000...
