Manual of Petroleum Measurement Standards

Chapter 9.4—Continuous Density

Measurement Under Dynamic (Flowing) Conditions

FIRST EDITION, JANUARY 2018

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Foreword

This standard, API MPMS Chapter 9.4, Continuous Density Measurement Under Dynamic (Flowing) Conditions, First Edition, supersedes API MPMS Chapter 14.6, Continuous Density Measurement, Second Edition, which is withdrawn.

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iii

1. Scope 1

2. Field of Application 1

3. Normative References 1

   1. API Manual of Petroleum Measurement Standards (MPMS) 1

   2. ASTM 2

   3. GPA 3

   4. OIML 3

4. Terms, Definitions, and Symbols 3

   1. Terms and Definitions 3

   2. Symbols, Acronyms, and Abbreviations 8

5. Safety Precautions 12

   1. Overview 12

   2. Equipment Design 12

   3. Operation 13

6. Density Determination Methods 13

7. Equipment 14

   1. General 14

   2. Vibrating Element (Natural Resonance) 15

   3. Vibrating Element (Fixed Frequency) 16

   4. Acoustic 16

   5. Nuclear 16

   6. Continuous Weighing 17

   7. Buoyancy 17

   8. Hydrostatic Pressure 17

   9. Gas Chromatograph (GC) 18

8. Applications of Continuous Density Measurement 18

   1. Overview 18

   2. Quantity Applications 18

   3. Quality Determination 20

   4. Interface Detection 20

   5. Inventory Control/Process Control 20

9. Performance Requirements- System and Density Meter 20

   1. General 20

   2. Inferred Mass Flow Measurement 21

   3. Volumetric Measurement 21

   4. Volume from Direct Mass 22

   5. Other Density Measurement Applications 22

10. Design of Density Measurement System 23

    1. General 23

    2. Application Considerations 23

    3. Fluid Properties 24

    4. Process Conditions 25

    5. Density Meter and Method Selection 27

    6. Sample System 29

       v

       
       

    7. Sample Conditioning 31

    8. Density Meter Signals 31

    9. Mechanical Considerations 32

    10. Installation Configurations 34

    11. Verification and Proving Design Considerations 42

11. Proving, Verification, or Calibration of Liquid Density Meters 42

    1. General 42

    2. Representativeness 43

    3. In-situ Proving 44

    4. Methods for Proving, Verification, and Calibration (In-situ) 46

12. Calculations 48

    1. Overview 48

    2. Volume Correction Factor (VCF) Determination and Density 49

    3. Density Conditions 50

    4. Fluid Compressibility 51

    5. Fluid Expansion/Contraction Due to Temperature 51

    6. Density Computation Methods 51

    7. Flow-weighting 52

    8. Density Unit of Measure Conversions 52

Annex A (informative) Density Sensitivity—Light Hydrocarbon Liquids 53

Annex B (normative) Test Equipment—Pycnometer Calibration and Proving 68

Annex C (normative) Pycnometer Calibration—Laboratory Method 72

Annex D (normative) Density Meter Proving—Pycnometer Method 84

Annex E (informative) Derivation of Air Buoyancy Equation 99

Annex F (informative) Reference Fluids (Air and Water) 107

Annex G (informative) Conversion Factors 110

Annex H (normative) Offline Density Meter Factor Determination for Crude Oils and Viscous Fluids 118

Annex I (normative) Density Used in Volume Calculation 122

Annex J (informative) Concepts of Mass and Weight 123

Bibliography 127

Figures

1. Density Determination Methods 14

2. Vibrating-element Density Meters 15

3. Vibrating-element (Insertion) Density Meters 16

4. Nuclear Density Meters 17

5. Volume Measurement 34

6. Inferred Mass Flow Measurement 35

7. Multiple Meter Runs with Individual Density Meters 36

8. Typical Multiple Meter Run with Common Density Meter on Inlet 37

9. Slipstream-type Sampling System: Velocity Head Devices 38

10. Slipstream-type Sampling System: Valve Restriction Devices 38

    
    

11. Slipstream-type Sampling System: Orifice Restriction Devices 39

12. Slipstream-type Continuous Density Sampling Systems: Pump Devices

    (for Light Hydrocarbons and Refined Products) 39

13. Insertion-type Sampling System—Pumped Density Prover Loop 40

14. In-line-type Sampling System with Pumped Density Prover Loop 40

15. Parallel Density Prover Loop 41

16. Parallel Pumped Density Prover Loop 41

17. Double-wall Vacuum Sphere Pycnometer 45

18. Density Meter Calculation Sequence 49

1. Vacuum Filling the Water Reservoir (Laboratory Calibration) (optional procedure) 76

2. Deaerating the Water Reservoir (Laboratory Calibration) 76

3. Vacuum Emptying the Pycnometer 77

4. Pycnometer Calibration Test Apparatus 78

5. Reinstallation of Test Tubing 80

6. Optional Et Test Apparatus 83

E.1 Net Forces on Pycnometer 99

F.1 Buoyancy Illustration 107

J.1 Report of Mass Values 125

Tables

1 Typical Density Meter Performance Expectations

at 0.25 % Total Measurement System Uncertainty 21

1. Density Sensitivity for 0.2 °F Difference for Fluid Temperatures

   Between 40 °F and 100 °F and Pressures Between 400 psig and 1200 psig 53

2. Density Sensitivity for 1 psi Difference For Fluid Pressures

   Between 400 psig and 1200 psig and Temperatures Between 40 °F and 100 °F 60

3. Composition Matrix 67

1. Test Equipment for Laboratory Calibration of a Pycnometer 74

2. Pycnometer Certificate Heading 81

3. Pycnometer Weights and Volume 82

4. Pycnometer Report Calibration Devices 82

5. Pycnometer Report Test Run Data 83

1. Proving Report Heading 96

2. Proving Report Density Meter Data 96

3. Proving Report Field Calibration Data 96

4. Proving Report Pycnometer Identification Data 97

5. Proving Report Proving Data and Calculations 98

1. Density Conversion Factors (SI units to SI units) 111

2. Density Conversion Factors (SI units to USC units) 112

3. Density Conversion Factors (USC units to SI Units) 112

4. Density Conversion Factors (USC Units to USC Units—lb/gal and RD) 112

5. Density Conversion Factors (USC Units to USC Units – lb/gal, RD and °API) 113

6. Temperature Conversion Units (SI and USC) 114

7. Pressure Conversion Units (SI and USC) 115

8. Dynamic (Absolute) Viscosity Conversion Units (SI and USC) 117

9. Kinematic Viscosity Conversion Units (SI and USC) 117

Continuous Density Measurement Under Dynamic (Flowing) Conditions

1. Scope

   
   

   This standard covers the continuous on-line determination and application of flowing liquid densities for custody transfer. This standard covers liquid and dense phase fluids, including: natural gas liquids, refined products, chemicals, crude oil, and other liquid products commonly encountered in the petroleum industry. This document does not apply to the density measurement of natural gas, LNG, multiphase mixtures, semi-solid liquids such as asphalt, and solids such as coke and slurries.

   
   

   This standard also provides criteria and procedures for designing, installing, operating, and proving continuous on-line density measurement systems for custody transfer. This standard also discusses the different levels and requirements of accuracy for various applications.

   
   

2. Field of Application

   
   

   The application of this standard provides a minimum set of requirements for density measurement applications, including custody transfer. In all cases, the measured density has to accurately represent the density of the flowing stream. Accurate density measurements are essential for custody transfer and for many quantitative purposes. For allocation measurement and process control applications, this standard can be used as a guide.

   
   

   Common technologies utilized in continuous density measurement include vibrating element, buoyancy, and nuclear devices. The most widely utilized device in custody transfer applications is the vibrating element.

   
   

   This standard also includes analytical systems that work in conjunction with equations of state or empirically derived calculations to determine the flowing density.

   
   

3. Normative References

The following referenced documents are indispensable for the application of this document. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies.

3.1 API Manual of Petroleum Measurement Standards (MPMS)

API MPMS Chapter 8.1, Standard Practice for Manual Sampling Petroleum and Petroleum Products

API MPMS Chapter 8.2, Standard Practice for Automatic Sampling of Petroleum and Petroleum Products

API MPMS Chapter 8.5, Standard Practice for Manual Piston Cylinder Sampling for Volatile Crude Oils, Condensates, and Liquid Petroleum Products

API MPMS Chapter 9.1, Standard Test Method for Density, Relative Density or API Gravity of Crude Petroleum and Liquid Petroleum Products by Hydrometer Method

API MPMS Chapter 9.2, Standard Test Method for Density or Relative Density of Light Hydrocarbons by Pressure Hydrometer

API MPMS Chapter 9.3, Standard Test Method for Density, Relative Density, and API Gravity of Crude Petroleum and Liquid Petroleum Products by Thermohydrometer Method