Design, Modeling and Reliability in Rotating Machinery

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

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.