Pulsation and Vibration Control in Positive Displacement Machinery Systems for Petroleum, Petrochemical, and Natural Gas Industry Services

API RECOMMENDED PRACTICE 688 FIRST EDITION, APRIL 2012

REAFFIRMED, JULY 2021

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Copyright © 2012 American Petroleum Institute

Foreword

This document is intended to describe, discuss and clarify the design of pulsation and vibration control for positive displacement machinery systems used for services in the petroleum, petrochemical and natural gas industries. The original focus of this document was to provide insight on the many changes to the pulsation and vibration material in the Clause 7.9 of the 5th Edition of API 618 for reciprocating compressors only. Due to industry interest, the scope of this document has been expanded to include other types of positive displacement equipment (such as pumps and screw compressors). However, due to publication schedules, these other types of positive displacement equipment will be addressed in future editions.

This document is not intended to be an all-inclusive source of information for this complex subject. Rather, it is offered as an introduction to the major aspects of pulsation and vibration control for positive displacement machinery addressed during a typical system design. A significant amount of the material has been extracted from documents previously published by the contributors. The different design philosophies of the various contributors are consolidated in this document to help users understand the choices available and make informed decisions about what is appropriate for their application. While the theory is generally applicable to all types of positive displacement machinery, the text in this edition will frequently refer specifically to reciprocating compressors.

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Suggested revisions are invited and should be submitted to the Standards Department, API, 200 Massachusetts Avenue, NW, Suite 1100, Washington, DC 20001, standards@api.org.

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Part 1: Pulsation and Vibration Control Fundamentals for Positive Displacement Machinery

1. Scope 1

2. Terms and Definitions 1

3. Fundamentals of Pulsation and Mechanical Vibration Theory 3

   1. Overview of Pulsation Concepts 4

   2. Overview of Mechanical Concepts 35

4. Fundamentals of Modeling 66

   1. Overview of Acoustic Modeling 66

   2. Overview of Mechanical Modeling 73

   3. Concurrent Acoustical and Mechanical Design 73

   4. Design Philosophies For Varying Degrees Of Acoustic And Mechanical Control 74

   5. Design Approach and Philosophy Selection Guidelines 76

5. Flow Measurement 78

   1. Introduction 78

   2. Flow Measurement by Measuring Differential Pressure (DP) - Orifice Plate, Nozzle, and Venturi 80

   3. Flow Measurement by Turbine Flowmeters 80

   4. Flow Measurement by Vortex Flowmeters 80

   5. Flow measurement by ultrasonic flowmeters 81

   6. Flow Measurement by Coriolis Flowmeters 82

   7. References 82

6. Results Reporting Guidelines 83

   1. Scope 83

   2. Results 83

7. Field testing 89

   1. Confirmation that Design Requirements Have Been Met 89

   2. Vibration Problems 89

   3. Excessive Pressure Drop 90

   4. Premature Valve Failure 90

   5. Driver Overload 90

   6. Failure to Deliver Expected Flow 90

8. Valve Dynamic Performance Analysis 90

   1. The VDPA Model 90

   2. Valve Reliability and Efficiency 91

   3. Application Of Analysis Results To Valve Selection 91

   4. Valve Dynamics Analysis Report 93

Figures

1. Piston Motion and Velocity for a Slider Crank Mechanism 5

2. Single Acting Compressor Cylinder with Rod Length/Stroke = ∞ and No Valve Losses 5

3. Symmetrical, Double Acting Compressor Cylinder with Rod Length/Stroke = ∞ and

   No Valve Losses 6

   v

   
   

4. Unsymmetrical, Double Acting Compressor Cylinder with Rod Length/Stroke = 5 and

   No Valve Losses 6

5. Traveling Wave in Infinite Length Pipe 7

6. Mode Shapes of Half Wave Responses 7

7. Mode Shapes of Quarter Wave Responses 8

9 Reducer with Dynamic Forces 10

8 Elbow with Dynamic Forces 10

10 Tee with Dynamic Forces 11

12 Pulsation Suppression Device with Dynamic Forces 12

11 Elbow with Dynamic Forces 12

1. Shaking Force for Sample Pulsation Damper 13

2. Shaking Force for Sample Pipe Lateral 14

3. Head End (HE) Pressure-Volume Card 15

4. Ideal (Adiabatic) PV Diagrams 16

5. Valve Losses 21

6. Losses Due to Pulsation 21

7. Losses Due to Pressure Drop 22

8. Effect of Clearance Volume, Condition 1 23

9. Effect of Clearance Volume, Condition 2 24

10. Effect of Clearance Volume, Condition 3 25

11. Effect of Suction Temperature, Condition 4 26

12. Effect of Suction Temperature, Condition 5 27

13. Effect of Suction Pressure, Condition 6 28

14. Effect of Suction Pressure, Condition 7 29

15. Pump Cavitation 31

16. Pump Cavitation Field Data 32

17. Components of Pump Section Head 33

18. Amplification Factor for Various Damping Ratios 38

19. Effect of Separation Margin from Mechanical Natural Frequency on Amplification Factor 39

20. Common Piping Configurations 40

21. Non-dimensional Piping Shaking Force Guideline 42

22. API 618 Design Vibration Guideline 45

23. Non-dimensional Pulsation Suppression Device Shaking Force Guideline 47

24. Example of Internal Cylinder Pressure Force versus Crank Angle and Frequency Spectrum 48

25. Example of Rod Loads Due to Gas Force, Inertial Force and Combined Rod Load 49

26. Conceptual Guidelines for Vent and Drain Piping Valve Supports 49

27. Conceptual Guidelines for Vent and Drain Piping Valve Supports 50

28. Conceptual Guidelines for Vent and Drain Piping Valve Supports 50

29. Frequency Factors for Idealized Pipe Spans and Bends (1st and 2nd Natural Frequencies) 53

30. Frequency Factor (l) versus Ratio (L/h) for Uniform U-Bend 54

31. Concentrated Weight-Correction Factors for Ideal Piping Spans

    (P = Concentrated Load, W = Weight per Unit Length) 55

32. Typical Compressor Flange Deflections 56

33. Plot of a Pipe System 57

47 Typical Branch Connection Finite Element Model 58

46 Lowest Mode Shape 58

1. Example of a Partial Finite Element Model of a Compressor 59

2. Typical Dynamically Fixed Clamps 61

3. Example of a Hold Down Type Support with no Allowance for Thermal Displacement

   in the Vertical Direction 62

4. Example of a Spring Hold Down Type Support which Allows Thermal Motion in the

   Vertical Direction 63

5. Allowable Shaking Forces per API 618, 5th Edition 65

6. Example of Pipe and Support Configurations 67

7. Lumped Acoustic Model 70

8. Analogous Electrical Model 71

9. Electronic Analog for One Pipe Section (Simplified Version without Flow Resistance) 71

10. Measuring Flow Expressed a Change of the Vortex Frequency 81

11. Compressor Configuration 85

12. Cylinder Nozzle Pulsation (Predicted vs. Guideline) 85

13. Pulsation Suppression Device Line-Side Pulsation (Predicted vs. Guideline) 86

14. Pulsation Suppression Device Shaking Force (Predicted vs. Guideline) 86

15. Compressor System Finite Element Model with Test Points 87

16. Typical Display of Valve Motion versus Crank Angle, Cylinder Pressure versus Volume

and Analysis Results Table 92

Tables

1. Frequency Factors for Various Pipe and Support Arrangements 44

2. Example of a Maximum Span Table for 25 Hz 55

3. Effect of Pipe Support Structures on Mechanical Natural Frequencies 57

4. Generic Piping Shaking Force Criterion from Clause 7.9 of the 5th Edition of API 618 64

5. Generic Piping Shaking Force Criterion from Clause 7.9 of the 5th Edition of API —

   Based on Pipe Size 4

6. Overview of Pulsation Impact on Various Flowmeters 79

7. Compressor Geometry 84

8. Operating Conditions 84

9. Gas Composition 85

10. Lowest Mode Shape and Mechanical Natural Frequency. 88

11. Recommended Design Results for Cylinder Stretch Load Case 88

12. Expected Results 88

Part 2: Reciprocating Compressors

1. General 94

2. Comments On API 618, 5th Edition, Clause 7.9 – Pulsation and Vibration Control 94

API 618 Annex M (informative) Design Approach Work Process Flowcharts 113

API 618 Annex N (informative) Guideline for Compressor Gas Piping Design and Preperation

for an Acoustic Simulation Analysis 116

API 618 Annex O (informative) Guidelines for Sizing Low Pass Acoustic Filters 119

API 618 Annex P (informative) Piping and Pulsation Supression Device Shaking Force Guidelines 122

Figures

618-4Piping Design Vibration at Discrete Frequencies108

1. Design Approach 1 113

2. Design Approach 2 114

3. Design Approach 3 115

O-1 Nonsymetrical Filter 119

1. Non-dimensional Piping Shaking Force Guidelines 123

2. Non-dimensional Pulsation Supression Device Shaking Force Guidelines 123

3. Shaking Forces along the Piping Axis 124

4. Shaking Forces along the Pulsation Supression Device Axis 124

5. Examples of Shaking Force Restraints 126

Tables

618-6Design Approach Selection97

N-1 Compressor Data Required for Acoustic Simulation 118

P-1 Cylinder Assembly Weights Possibly Requiring Strengthening 127

Pulsation and Vibration Control in Positive Displacement Machinery Systems for Petroleum, Petrochemical, and Natural Gas Industry Services

Part 1: Pulsation and Vibration Control Fundamentals for Positive Displacement Machinery

1. Scope

   
   

   The purpose of this document is to provide guidance on the application of pulsation and vibration control requirements found in the API purchasing specifications for positive displacement machinery. The fundamentals of pulsation and piping system analysis are presented in this Part.

   
   

   The text begins with an overview of the fundamentals of pulsation and mechanical theory in Section 3. The intent of Section 3 is to introduce terminology and define the elements of the analysis process. Section 4 begins with a discussion of the acoustic and mechanical modeling techniques associated with the different design philosophies, which emphasize either pulsation or mechanical control, and concludes with a discussion on the appropriate selection of a Design Approach and Philosophy. Section 5 discusses the effects of pulsation on the accuracy of various types of flow measurement devices. Section 6 summarizes the requirements for documenting study results. Section 7 offers guidance on the performance of field testing to validate the results of the design process and to troubleshoot pulsation or vibration problems. Finally, methodologies for conducting a dynamic analysis of the compressor or pump valve performance are described in Section 8. The material in this Part is generally applicable to all types of positive displacement machinery.

   
   

   Part 2 deals specifically with reciprocating compressors and provides commentary regarding each paragraph of Clause 7.9 of API 618, 5th Edition. It is the intent of the API Subcommittee on Mechanical Equipment that similar material be provided on reciprocating pumps and screw compressors in future editions.

   
   

2. Terms and Definitions

For the purposes of this document, the following definitions apply.

2.1

acoustic simulation

Process whereby the one-dimensional acoustic characteristics of fluids, and the reciprocating compressor dynamic flow influence on these characteristics, are modeled taking into account the fluid properties, the compressor model and the connected vessels and piping, and other equipment. The model is based upon the governing mathematical equations (motion, continuity, etc.). The simulation should allow for determination of pressure/flow modulations at any point in the piping model resulting from any generalized compressor excitation. (Refer also to 2.2, 2.4, 2.9, 2.13, 2.16, and 2.18.)

2.2

active analysis

Portion of the acoustic simulation in which the pressure pulsation amplitudes due to imposed compressor(s) operation for the anticipated loading, speed range and state conditions are predicted. (Refer to 2.1.)

2.3

amplification factor

Measure of acoustic or vibration sensitivity to excitation when the frequency of the excitation source is coincident with or near an acoustic or mechanical natural frequency. A high amplification factor (AF > 10) indicates that vibration during operation near a natural frequency could be excessive. A low amplification factor (e.g. AF < 5) indicates that the system is not as sensitive to excitation when operating in the vicinity of the associated acoustic or mechanical

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