Design, Modeling and Reliability in Rotating Machinery

This 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 represents a broad category of equipment, which includes pumps, compressors, fans, gas turbines, electric motors, internal combustion engines, and other equipment, 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 other topics.

The goal of the “Advances in Rotating Machinery” book series is to provide industry practitioners a time-savings means of learning about the most up-to-date rotating machinery ideas and best practices. This three-book series will cover 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.

This first volume begins the series by focusing on rotating machinery design assessments, modeling and analysis, and reliability improvement ideas. This 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.

Design, Modeling, and Reliability in Rotating Machinery covers, among many other topics:

• Rotordynamics and torsional vibration modeling
• Hydrodynamic bearing design theory and current practices
• Centrifugal and reciprocating compressor design and analysis
• Centrifugal pump design, selection, and monitoring
• General purpose steam turbine sizing

Robert 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. 

Preface xiii

Acknowledgements xv

Part 1: Design and Analysis 1

1 Rotordynamic Analysis 3
By William D. Marscher

Introduction 3

Rotor Vibration – General Physical Concepts 4

Rotor Vibration – Mathematical Description 6

Natural Frequencies and Resonance 6

Critical Speed Analysis 10

Phase Angle, and Its Relationship to Natural Frequency 15

Gyroscopic Effects 16

Accounting for Bearings 18

Cross-Coupling Versus Damping and “Log Dec” 20

Annular Seal “Lomakin Effect” 21

Fluid “Added Mass” 23

Casing and Foundation Effects 24

Lateral Vibration Analysis Methods for Turbomachinery and Pump Rotor Systems 25

Manual Methods Single Stage 25

Computer Methods 26

Forced Response Analysis 30

Mechanical Excitation Forces 32

Balance 32

Fluid Excitation Forces 37

Impeller Reaction Forces 37

Impeller Active Forces 38

Rotordynamic Stability 43

Subsynchronous Whirl & Whip 43

Stabilizing Component Modifications 47

Vertical Turbine Pump Rotor Evaluation 48

Conclusions 51

Nomenclature 52

Acknowledgements 53

References 53

2 Torsional Analysis 57
By William D. Marscher

Introduction 58

General Concerns in the Torsional Vibration Analysis of Pump and Turbomachinery Rotor Assemblies 58

Predicting Torsional Natural Frequencies 59

Torsional Excitations 63

Torsional Forced Response 68

Case History 72

Conclusions 73

Nomenclature 79

Acknowledgements 79

References 80

3 Hydrodynamic Bearings 83
By John K. Whalen

API Mechanical Equipment Standards for Refinery Service 83

Bearings 84

Hydrodynamic Lubrication 85

Tower’s Experiments 86

Reynolds Equation 88

Stribeck Curve 93

Journal Bearings 94

Dynamic Coefficients 101

Tilting Pad Journal Bearings 103

Pivot Types 107

Lubrication Methods 117

Thrust Bearings 120

A Note on Thrust Bearing Diameters 122

Fixed Geometry Thrust Bearings 122

Pivot Types 127

Lubrication 127

Increasing Load Capacity 130

Babbitt 131

Polymer-Lined Bearings 132

Current and Future Work 134

References 135

4 Understanding Rotating Machinery Data Trends and Correlations 139
By Robert X. Perez

Pattern Recognition 139

Static Versus Dynamic Data 141

Trends 142

Flat Trends 142

Trends with Step Changes 144

Upward and Downward Trends 146

Cyclic Trends 148

Is It the Machine or the Process? 148

Correlations 149

“Correlation Does Not Imply Causation” 151

Combination Trends 154

Exponential Growth Trends 155

Erratic Trends 160

Induced Draft Fan Experiences Unpredictable Vibration 160

Erratic Vibration Related to Rotor Instability 161

Some Rules of Thumb 162

5 An Introduction to Sizing General Purpose Steam Turbines 165
By Robert X. Perez and David W. Lawhon

Why Do We Use Steam Turbines? 165

How Steam Turbines Work 165

Steam Generation 167

Waste Heat Utilization 168

The Rankine Cycle 169

General Purpose Steam Turbine Sizing 170

General Purpose, Back Pressure, Steam Turbines 170

Single Stage Back Pressure Steam Turbine 170

Sizing Procedure 171

Closing Comments 185

6 Making the Business Case for Machinery Upgrades 187
By Robert X. Perez

Payback Time Examples 190

Closing Thoughts 193

Part 2: Compressors 195

7 Selecting the Best Type of Compressor for Your Application 197
By Robert X. Perez

Example of How to Convert from SCFM to ACFM 200

Compressibility Factor (Z) 200

Compressor Selection Example 201

Summary 205

Addendum 207

Demystifying Compressor Flow Terms 207

Ideal Gas Law 208

Examples of How to Convert from SCFM to ACFM 210

Visualizing Gas Flow 211

Compressibility Factor (Z) 212

8 Compressor Design: Range versus Efficiency 215
By James M. Sorokes

Introduction 215

Critical Parameters/Nomenclature 216

Operating Requirements 223

Critical Components 225

Impellers 225

Inlet Guides 232

Diffusers 235

Return Channels 238

Other Components 240

Aerodynamic Matching 243

Stage Components 243

Stage to Stage 245

Operating Conditions 246

Movable Geometry – Optimizing Range and Efficiency 248

Concluding Remarks 251

Disclaimer 251

Acknowledgements 251

References 252

9 Understanding Reciprocating Compressor Rod Load Ratings 255
By Robert X. Perez

Introduction 255

Basic Theory 256

Gas Loads 256

Piston Rod Loads 260

Crosshead Pin Loads 261

Crankpin Loads 262

History of “Rod Loads” 262

Glossary of Terms 265

User’s Perspective 266

Performance Study to Evaluate Compressor Re-Rate 268

Combined Load Exceeds Gas Load 269

Distorted Pressure Measurements = Distorted Rod Loads 269

Conclusions 271

Reference 271

10 How Internal Gas Forces Affect the Reliability of Reciprocating Compressors 273
By Robert Perez, Robert Akins and Bruce McCain

Gas Loads 274

Non-Reversing Gas Loads 277

Non-Reversing Rod Conditions Matrix 279

Non-Reversing Gas Load Examples 281

“One Failure from Disaster” 283

Ways to Protect Your Compressor 285

Closing Remarks 285

Robert Akins 286

Acknowledgements 286

Part 3: Pumps 287

11 Should You Use a Centrifugal Pump? 289
By Robert X. Perez

Net Positive Suction Head - NPSH 296

Ways to Increase the Margin Between the NPSHa and the NPSHr 302

Summary 306

12 Practical Ways to Monitor Centrifugal Pump Performance 307
By Robert X. Perez

Why Use Centrifugal Pumps? 307

Head Versus Pressure 309

Centrifugal Pump Performance 311

Assessing Centrifugal Pump Performance 313

Summary 317

Addendum 319

Determining the Best Two-Parameter Analysis Method for a Centrifugal Pump 319

13 Using Electric Motor Horsepower to Protect Centrifugal Pumps Operating in Parallel Flow Applications: A Case Study 325
By Robert X. Perez and Glenn Everett

The Problem 325

Solution 327

Results 331

Conclusions 332

Addendum 332

A Simplified Method of Determining the Efficiency of a Motor-Driven Centrifugal Pump 332

The Traditional Analysis Method 333

A Simplified Alternative Assessment Method 334

Example 335

14 Mechanical Seals and Flush Plans 337
By Robert X. Perez

Recommendations for Optimizing the Service Lives of Mechanical Seals 337

Liquid Properties 339

Expected Seal Cavity Pressure 340

Sealing Temperature 340

Liquid Characteristics 340

Reliability and Emission Concerns 340

Single or Double Seal? 341

Seal Flush Plans 342

Parting Advice 350

About the Editor 351

About the Contributors 353

Index 357

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