API Mpms Chapter 14.6 (1998)

~ ~

STD.API/PETRO MPMS 14.b-ENGL 19’13 IBI 0732270 ULZ2183 075 m

Date of Issue: August 5,1998 Affected Publication: API MPMS Chapter 14.6, Continuous Density Measurement, Second Edition, April 1991

ERRATA

Several errata have been found in API MPMS Chapter 14.6 “ C O ~ ~ ~ ~ U O U S Density Measure- ment,” dated April 1991, Second Edition. Known erram are listed below:

Page 7, section 14.6.6.6.2. ïñe second equation on this page, which is the jìrst equation for variable C,, is only for evacuated weight pycnometers. The C,equation found on page 45 is only for air- filled weight calculations, as described in section 14.6.6.6.3, on page 9.

Page 25, section 14.6.14.8, steps c, ri, and e. The conversion factors listed here should not be used To obtain appropriate conversion factors with more signifcant digits, refer to the following docwnent (or its successor): “Standad for Use of the International System of Units (SI): The Modem Memk System” (IEWASTM SI-IO; 1997). IEEE SrandantF Coodimthg Committee I4 and ASTM Committee E-43, published by Institute of Electrical and Electronics Engineers, Inc.. 345 h t 47th St., New Yo& NY 10017. This document has replaced ASTM E380 and Ah‘SMEEE Std 268- 1992.

Page 41, equation. Datum pressure, Pdp is genemiiy equal to 14.6Wpsia thmughout the document, and is never equal to local atmospheric pressure. However; in the equation listed on page 41, P d is equal to 0.0 psia.

Page 42. The average water &ta shown on this page is not relevant.

Copyright American Petroleum Institute Provided by IHS under license with API Licensee=Technip Abu Dabhi/5931917101

Not for Resale, 02/22/2006 01:40:01 MSTNo reproduction or networking permitted without license from IHS

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Pages 42,43, and 44. On page 42, C,, was incorrectly calculated using the air-filled weight calculations, as described in section 14.6.6.4.3. I t was not calculated using the 14.6.6.6.2 evacuated weight method. Aditiornliy, the values for shown on pages 42.43, and 44 are not correct. Futhemwre, for the Test A and Test B Data tables, only Weigh N0.s 2, 4, IO, 12, 17 are signijicant. ïñe rest of the Weighs are of little use. See the following two tables for corrected values:

2 4 10 12 17

Test B Data

_. . I

50 77.5 2360.26 994.76 0.9970810 997.67 995.45 200 77.5 2360.89 995.39 0.9975464 997.84 995.62 800 77.5 2363.46 997.96 0.9993975 998.56 996.34 1000 77.5 2364.30 998.80 1.0000108 998.79 996.57 1500 77.4 2366.45 1000.95 1.0015514 999.40 997. i 8

In the above Test A and Test B tables, the following values also apply: Pd = 14.696 psia datum pressure, E, = 2.88E-5 per degree Fahrenheit, pA = 0.001 I75 g /cd for Test A calculated by using the air density equation on page 45 at 79"E pA = 0.001 I79 g/cm'for Test B calculated by using the air density equation on page 45 at 77"E C,, = 0.99985 for both Test A and Test B.

Page 45. ïñe equation for K, is incorrect. The value 58.4772 should read: 58.47727. The h t line of the equation should start with a division sign, not a multiplication sign. The corrected version is as shown here:

K, = isothermal compressibility of water at 14.696 psia and T,, in degrees Celsius

= [50.88496 + (6.163813 x lW)(Tf ) + (1.459187 x lP3)(Tf2)

-

+ (20.08438 x lW)(T3) - (58.47727 x lW)(Tp) + (410.41 1 x 10-lz)(T:)]

i- { [ 1 + (19.67348 x 10-3)(Tf)]( 14.50377 x l W ) }



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STD.API/PETRO MPNS i 4 - b - E N G L 1791 m 0732290 0!,2211AC YLiö E

,.- :..+ .. . .

Page 48. Replace the existing K,equation with the same corrected version, above, for p g e 45.

Replace the Kip equation with the correct version as shown on page 45.

Page 48, Table 7. Several values are incorrect, and have been updated here:

Table 7-Predicted Water Density

Georgc S. Kell Isothamal

Compressibility of Water Watex at 14.6% psia

Pressure Temperature (K,)

wagtom p i a bar "C "F Iob/bar i/pSi R, (i/psi> Pw, (g/cm3)

77 5.31 0.00 32.0 50.8850 35084x I 0 4 3.5061 x 104 0.999840 77 5.31 20.00 68.0 45.8914 3.1641 x I 0 4 3.1620~ 104 0.998202 77 5.31 50.00 122.0 44.1727 3.0456~ I 0 4 3.0436~ 104 0.988058

611 42.13 0.00 32.0 50.8850 3.5084~ I 0 4 3.4860~ 104 0.999840 611 42.13 20.00 68.0 45.8914 3.1641 x I 0 4 3.1439~ I 0 4 0.998202 611 42.13 50.00 122.0 44.1727 3.0456~104 3.û261 x 1 0 1 0.988058

1465 101.01 0.00 32.0 50.8850 3 .5084~ IO+ 3.4547~104 0.999840 1465 101.01 20.00 68.0 45.8914 3.1641 xl04 3.1157~ I 0 4 0.998202 1465 101.01 50.00 122.0 44.1727 3.0456~104 29990x104 0.988058

3050 210.29 0.00 32.0 50.8850 35084x104 3.3996~ 106 0.999840 3050 210.29 20.00 68.0 45.8914 3.1641 x I 0 4 3.0660~ I 0 4 0.998202 3050 210.29 50.00 122.0 44.1727 3.0456~ I 0 4 2.9511 x 104 0.988058

MPMS 14.6 p w , wem', 1 .oooO58 0.9983% 0.988245

I .O01 922 I .oooOn 0.989844

1 .o04874 I .o02733 0.992374

1.010264 I .o07579 0.996988



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~~

A P I MPMS*l4mb 91 W 0732290 0095847 T

Manual of Petroleum Measurement Standards Chapter 14-Natural Gas Fluids

Measurement

Section 6-Continuous Density Measurement

SECOND EDITION, APRIL 1991

American Petroleum Institute 1220 L Street, Northwest Washington, D.C. 20005



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A P I MPMS*14.6 91 0732290 O095848 1

-Manual of Petroleum Measurement Standards Chapter 14-Natural Gas Fluids

Measurement Section 6-Continuous Density Measurement

I Measurement Coordination Department

I SECOND EDITION, APRIL 1991

American Petroleum Institute



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A P I MPMS*I4-b 91 = O732290 0095849 3

SPECIAL NOTES

1. API PUBLICATIONS NECESSARILY ADDRESS PROBLEMS OF A GENERAL NATURE. WITH RESPECT TO PARTICULAR CIRCUMSTANCES, LOCAL, STATE, AND FEDERAL LAWS AND REGULATIONS SHOULD BE REVIEWED.

2. API IS NOT UNDERTAKING TO MEET THE DUTIES OF EMPLOYERS, MANU- FACTURERS, OR SUPPLIERS TO WARN AND PROPERLY TRAIN AND EQUIP THEIR EMPLOYEES, AND OTHERS EXPOSED, CONCERNING HEALTH AND SAFETY RISKS AND PRECAUTIONS, NOR UNDERTAKING THEIR OBLIGATIONS UNDER LOCAL, STATE, OR FEDERAL LAWS.

3. INFORMATION CONCERNING SAFETY AND HEALTH RISKS AND PROPER

TIONS SHOULD BE OBTAINED FROM THE EMPLOYER, THE MANUFACTURER OR SUPPLIER OF THAT MATERIAL, OR THE MATERIAL SAFETY DATA SHEET.

4. NOTHING CONTAINED IN ANY API PUBLICATION IS TO BE CONSTRUED AS

PRECAUTIONS WITH RESPECT TO PARTICULAR MATERIALS AND CONDI-

GRANTING ANY RIGHT, BY IMPLICATION OR OTHERWISE, FOR THE MANU- FACTURE, SALE, OR USE OF ANY METHOD, APPARATUS, OR PRODUCT COV- ERED BY LETTERS PATENT. NEITHER SHOULD ANYTHING CONTAINED IN

ITY FOR INFRINGEMENT OF LEITERS PATENT. THE PUBLICATION BE CONSTRUED AS INSURING ANYONE AGAINST LIABIL-

5. GENERALLY, API STANDARDS ARE REVIEWED AND REVISED, REAF- FIRMED, OR WITHDRAWN AT LEAST EVERY FIVE YEARS. SOMETIMES A ONE- TIME EXTENSION OF UP TO TWO YEARS WILL BE ADDED TO THIS REVIEW

TER ITS PUBLICATION DATE AS AN OPERATIVE API STANDARD OR, WHERE AN EXTENSION HAS BEEN GRANTED, UPON REPUBLICATION. STATUS OF THE

CYCLE. THIS PUBLICATION W L L NO LONGER BE IN EFFECT FIVE YEARS AF-

PUBLICATION CAN BE ASCERTAINED FROM THE API AUTHORING DEPART- MENT [TELEPHONE (202) 682-8000]. A CATALOG OF API PUBLICATIONS AND MATERIALS IS PUBLISHED ANNUALLY AND UPDATED QUARTERLY BY API, 1220 L STREET, N. W., WASHINGTON, D.C. 20005.

Copyright O 1991 American Petroleum Institute



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FOREWORD

This standard provides design and operating procedures for continuous density measurement of hydrocarbons and other petroleum-related fluids. Application of these procedures is limited to homogeneous, single-phase liquids or supercritical fluids. Cryogenic fluids are excluded from this standard.

The flow-through pycnometer was developed for field applications in 1971. The original design consisted of a single-shell carbon steel sphere approximately 6 inches in diameter, with a volume of 1000 cubic centimeters and a tare weight of 1875 grams. The carbon steel was eventually replaced with stainless steel to minimize the weight of the sphere. Today, flow-through pycnometers are available in single-sphere, double-wall vacuum sphere, and single-cylinder stainless steel designs.

During the 1970s, as a result of the wider use of sophisticated chemical feedstocks, the industry focused on more precise measurement techniques and equipment. Mass measurement approaches to many difficult-to-measure fluids were predicated on the use of highly accurate density meters. Durhg the early 1980s, mass measurement was expanded to include supercritical carbon dioxide for tertiary recovery operations.

This edition reflects the experience gained since publication of the first edition in 1979. APT publications may be used by anyone desiring to do so. Every effort has been made

by the Institute to assure the accuracy and reliability of the data contained in them; however, the Institute makes no representation, warranty, or guarantee in connection with this publication and hereby expressly disclaims any liability or responsibility for loss or damage resulting from its use or for the violation of any federal, state, or municipal regulation with which this publication may conflict.

Suggested revisions are invited and should be submitted to the director of the Measure- ment Coordination Department, American Petroleum Institute, 1220 L Street, N.W., Wash- ington, D.C. 20005.

iii



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CONTENTS

SECTION 6-CONTINUOUS DENSITY MEASUREMENT 14.6.1 14.6.2 14.6.3 14.6.4 14.6.5 14.6.6 14.6.7 14.6.8 14.6.9 14.6.10 14.6.11 14.6.12 14.6.13 14.6.14 14.6.15 14.6.16 14.6.17 14.6.18 14.6.19

Scope and Field of Application ................................................................ Safety ........................................................................................................ Referenced Publications ........................................................................... Measurement Applications ....................................................................... Nomenclature ........................................................................................... Mass and Apparent Mass Values .............................................................. General Design Considerations .............................................. .................. Density Meters ......................................................................................... Pycnometers ............................................................................................. Density Sampling Systems ....................................................................... Proving Systems ....................................................................................... Proving of Density Meters ....................................................................... Proving Procedures .................................................................................. Calculation Procedures .................................................................. ........... Field Verification Procedures for Pycnometers Laboratory Calibration Procedures for Pycnometers ............................... Density of Water ....................................................................................... Density of Air ........................................................................................... Bibliography .............................................................................................

........................................

APPENDIX-PRECAUTZONARY INFORMATION ...........................................

Figures 1-Typical Measurement System ........................................................................ 2-Typical Primary Apparent Mass Standards Certificate ..................................

4-Net Forces on Pycnometer ............................................................................ 5-Typical Ethylene Density Envelope ............................................................... 6-Density Changes due to Pressure Deviations ................................................ 7-Density Changes due to Temperature Deviations 8-Temperature and Pressure Points for Inferring Density Deviation ................ 9-Single-Sphere Pycnometer ............................................................................ 10-Double-Wall Vacuum Sphere Pycnometer .................................................. 1 1-Single-Cylinder Pycnometer ........................................................................ 12-Classification of Density Sampling Systems ............................................... 13-Insertion-Type Continuous Density Sampling Systems ..............................

3-Typical Secondary Apparent Mass Standards Certificate ..............................

.........................................

14-Slipstream-Type Continuous Density Sampling Systems: Pump Devices . 15 -Slipstream-Type Continuous Density Sampling Systems:

Restriction Devices ..................................................................................... 16-Slipstream-Type Continuous Density Sampling Systems:

Velocity Head Devices ................................................................................ 17-Typical Proving Report: Example 1 ............................................................. 18-Typical Proving Report: Example 2 19-Vacuum Filling the Water Reservoir (Field Verification) ............................ 20-Deaerating the Water Reservoir (Field Verification) ................................... 21-Evacuating the Air-Filled Pycnometer ........................................................ 22-Vacuum Filling the Pycnometer .................................................................. 23-Vacuum Emptying the Pycnometer .............................................................. 24-Field Verification Form ............................................................................... 25-Vacuum Filling the Water Reservoir (Laboratory Calibration) ...................

............................................................

Page

1 1 1 2 3 3

10 14 15 17 21 22 23 24 26 32 47 48 50

51

2 5 6 8

11 12 13 14 17 18 19 19 20 20

21

22- 27 28 29 30 31 31 32 34 35

V



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API M P M S * 1 4 . b 91 0732290 0095852 3

26-Deaerating the Water Reservoir (Laboratov Calibration) .......................... 27-Vacuum Emptying the Pycnometer ............................................................. 28-Pycnometer Calibration Test Apparatus ...................................................... 29-Reinstallation of Test Tubing ...................................................................... 30-Typical Pycnometer Certificate and Calibration Calculations ..................... 3 1-Optional E, Test Apparatus ..........................................................................

Tables 1-List of Symbols .............................................................................................. 2-Classification of Density Meters ................................................................... 3-Classification of Density Provers .................................................................. 4-Test Equipment Required for Field Verification of Pycnometers .................. 5 -Atmospheric Water Density as a Function of Temperature 6-Test Equipment for Laboratory Calibration of Pycnometers ......................... 7-Predicted Water Density ................................................................................ 8-Experimental Versus Predicted Water Density ..............................................

..........................

vi

Page

36 37 37 38 39 47

4 15 15 29 33 35 48 49



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A P I MPMS*lt4-b 41 = 0732290 0095853 5

Chapter 14-Natural Gas Fluids Measurement

SECTION 6-CONTINUOUS DENSITY MEASUREMENT

14.6.1 Scope and Field of Application This standard provides criteria and procedures for design-

ing, installing, and operating continuous density measurement systems for newtonian fluids in the petroleum, chemical, and natural gas industries. The intent of this standard is to provide the user with a density accuracy of 0.10 percent for most applications.

The application of this standard is limited to clean, homogeneous, single-phase liquids or supercritical fluids. The procedures and criteria contained in this standard have been successfully applied to fluids whose flowing density is greater than 0.3 gram per cubic centimeter at operating conditions above 60°F (15.6”C) and saturation pressure.

This standard does not advocate the preferential use of any particular type of equipment, Neither is it the intent of this standard to restrict the future development or improve- ment of density measuring equipment. The contracting parties should mutually agree on equipment selection, design, and operating procedures prior to custody transfer.

14.6.2 Safety Personnel involved in the handling of petroleum products

and related fluids are exposed to hazards that demand constant attention to many precautions peculiar to the type of measurement equipment and commodities handled. Follow- ing are some reminders for both designers and operating personnel for density metering systems. This section does not attempt to take the place of individual company safety instructions.

The following precautions should be considered:

a. All electrical components shall be designed in accordance with the appropriate electrical hazardous area classification. b. All equipment shall be designed to withstand the maximum operating pressure to which it can be exposed. c. All materials used shall be resistant to corrosive attack by the fluids with which they come in contact and shall be com- patible with cryogenic temperatures that may occur as a result of autorefrigeration. d. Adequate facilities shall be provided for isolating, depres- surizing, venting, flaring, and draining. e. When highly volatile fluids are vented, appropriate protective clothing should be worn to prevent cold bums due to autorefrigeration of the fluid. f. After filling, the pycnometer should be weighed as soon as is practical to minimize any rise in temperature of the contents, resulting in increased pressures that could cause the

rupture disk to burst. g. As soon as possible after weighing, the pycnometer should be emptied in a safe location. (Temperature rise may cause excessive pressure in a filled prover, resulting in possible release of product.) h. The pycnometer and associated equipment should be reg- ularly inspected and properly maintained by competent personnel. i. The pycnometer shall be stored and transported empty to prevent damage to the pycnometer, bursting of the rupture disk, and other hazardous conditions. j. Cleaning and drying of the pycnometer should conform to established safety procedures and accepted methods of handling compressed gas. k. Personnel should be familiar with the fluid’s properties and hazards.

14.6.3 Referenced Publications The following publications are cited in this chapter:

Threshold Limit Values for Chemical Substances and ACGI“

Physical Agents in the Work Environment

Publ 2026 Safe Descent Onto Floating Roofs of Tanks irr Petroleirm Service

Publ 2217 Guidelines for Conjìned Space Work in the Petroleum Industiy

Manual of Petroleum Measiiremen f Standards Chapter 9, “Density Determination,” Section 1, “Hydrometer Test Method for Density, Relative Density (Specific Gravity), or API Gravity of Crude Petroleum and Liquid Pe- troleum Products,’’ and Section 2, ‘LPressure Hydrometer Test Method for Density or Rel- ative Density” Chapter 11, “Physical Properties Data,” Sec- tion 2.3, “Water Calibration of Volumetric Provers’’

Table of Physical Constants for the P a r e n Hydrocarbons and Other Components of Natural Gas

API

GPA2 Std 2145

IAmerican Conference of Governmental Industrial Hygienists, 6500 Glen- way Avenue, Building D-5, Cincinnati, Ohio 45211. *Gas Processors Association, 6526 East 60th Street, Tulsa, Oklahoma 74145.

1



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2

A P I MPMS*L4.b 91 = 0732290 0095854 7 = CHAPTER 14-NATURAL GAS FLUIDS MEASUREMENT

OSHA3 Occupational Safety and Health Standards (29 Code of

Federal Regulations Sections 1910.1000 and following)

14.6.4 Measurement Applications 14.6.4.1 GENERAL

The following are the two most common applications for continuous density measurement of hydrocarbons and other related fluids in custody transfer service:

a. Mass flow measurement. b. Volume measurement at standard conditions for fluids of varying composition.

As shown in Figure 1, both applications share the same basic components:

a. Density meter. b. Continuous density sampling system. c. Volume meter.

30ccupational Safety and Health Administration, US. Department of Labor. The Code of Federal Regularions is available from the U.S. Government Printing Office! Washington, D.C. 20001.

14.6.4.2 MASS FLOW MEASUREMENT

Mass flow measurement techniques are used on compressible fluids with varying compositions and poorly defined properties of thermal expansion, compressibility, and admixture shrinkage. The criteria given in this standard have been successfully applied to the following fluids:

a. Polymer-grade ethylene. b. Ethane mixtures or raw make. c. Pure CO2 and CO;, mixtures. d. Liquefied petroleum gas mixtures. e. Natural gas liquids.

Mass flow measurement requires the continuous integra- tion of flowing volume times flowing density over a time period to obtain total mass and mass flow rate.

14.6.4.3 VOLUMETRIC MEASUREMENT

Volumetric measurement at standard conditions is used on fluids with variable compositions and well-defined pressure-volume- temperature relationships, such as the following:

LEGEND

Strainer a 71 Straightening vanes

18 I Turbine meter

@ Therrnowell

Pressure indicator

Density meter

Figure i-Typical Measurement System



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A P I MPMS*I<L'+*b 91 m 0732290 0095855 9 m

SECTION 6-CONTINUOUS DENSITY MEASUREMENT 3

a. Propane mixes. b. Butane mixes.

Volumetric measurement at standard conditions requires the correction of density measured at flowing conditions to the equivalent value at standard conditions of temperature and pressure (or equilibrium pressure). A weighted volume- averaged density or the continuous calculation of net standard volume and an API gravity at 60°F (or density at 60'F) can be used for custody transfer applications.

Corrections for the effect of temperature and pressure on the flowing density, commonly referred to as C,, and C,,, are required to arrive at an API gravity at 60°F and equilibrium pressure. Additional corrections for the effect of pressure and temperature on the density meter may be required to measure the flowing density accurately.

14.6.4.4 REFERENCE AND DATUM CONDITIONS

The reference conditions of pressure and temperature for custody transfer of hydrocarbons and other petroleum-related fluids are as follows:

a. The reference pressure is atmospheric pressure (14.696 pounds per square inch absolute). For fluids whose vapor pressure at the reference temperature is greater than atmospheric, the reference pressure shall be the equilibrium vapor pressure at the reference temperature. b. The reference temperature is 60.0"F (156°C).

The datum conditions for pycnometers calibrated in accordance with 14.6.16 are as follows:

a. For U.S. units, a pressure of 14.696 pounds per square inch absolute and a temperature of O.O°F. b. For SI units, a pressure of 101,325 kilopascals and a temperature of -17.8"C.

14.6.5 Nomenclature The symbols used for mathematical variables in this stan-

dard are listed in Table 1.

14.6.6 Mass and Apparent Mass Values 14.6.6.1 DEFINITIONS

In the field of measurement, considerable ambiguity exists with respect to the definitions of mass, apparent mass, and weight. The following definitions are presented to enable the user of this standard to understand more clearly the relation- ship of these terms.

Weight is defined as the net force exerted on an object's mass, compared with a reference standard, In most situations, the net force is a combination of the earth's gravity and the buoyancy of the A uid surrounding the object. Weighing is defined as measuring the net force acting on an object's mass.

Mass is defined in terms of a standard mass, and therefore the mass of an object is simply a multiple of the mass standard. The mass of an object remains constant regardless of its location. Thus, the mass of an object does not vary as it is moved from one part of the earth to another, although the net forces acting on the mass may change. If the net forces change, the weight of the object will vary from location to location.

Apparent mass is defined as the weight of an object in air, compared with a mass standard. A mass measurement by weighing is performed in air, as are virtually all mass reference standards' calibrations. Thus, when two objects are compared in mass, each object is subjected to two principal opposing forces:

a. A lifting force equal to the mass of air displaced by the object times the force of gravity, b. A downward force equal to the mass of the object times the force of gravity,

Since all mass reference standards' calibrations are made in air and are performed by comparing an unknown standard with a known primary standard, the mass of the unknown standard is frequently reported as the mass the standard would appear to have when compared with a reference standard at 20°C in air with a density of 0.0012 gram per cubic centimeter. Whenever apparent mass is used, it is necessary to specify the density of the (normally hypothetical) reference standard against which the unknown standard is being compared. This statement of the density of the reference standard, called reference density, is necessary because the apparent mass value depends in part on the volume of the reference standard. A reference density of 8.0 grams per cubic centimeter is normally used to report the apparent mass of a standard or object. This is referred to as the apparent mass versus 8.0 grams per cubic centimeter at 20°C in normal air (0.0012 gram per cubic centimeter), In the past, the apparent mass was reported against the density of normal brass at 20OC. This is referred to as the apparent mass versus 8.3909 grams per cubic centimeter at 20°C in normal air.

14.6.6.2 MASS AND APPARENT MASS

.

STANDARDS By international agreement, the international mass stan-

dard is the International Prototype Kilogram, a platinum- iridium standard (90 percent platinum. and 10 percent iridium) that is kept at the International Bureau of Weights and Measures in Sèvres, France. The primary mass standard for the United States, which has been compared with the In- ternational Prototype Kilogram, is the U.S. Prototype Kilo- gram 20, a platinum-iridium standard kept at the National Institute of Standards and Technology (NIST) in Gaithers- burg, Maryland.

Mass standards are precise standards whose volume, density, cubical coefficient of thermal expansion, and mass have



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API MPMS*L4.6 91 M 0732290 0095856 O M

4 CHAPTER 14-NATURAL GAS FLUIDS MEASUREMENT

Table 1-List of Symbols

Units

Symbol Meaning U.S. SI

, Apparent mass of fluid Apparent mass of test weights Correction for air buoyancy on weighing Correction for effect of temperature on steel pycnometer Density meter factor Coefficient of expansion due to pressure on pycnometer Coefficient of cubical expansion due to temperature on pycnometer Buoyancy force on fluid Buoyancy force on steel of pycnometer Buoyancy force on test weights Buoyancy force on evacuated pycnometer volume Gravitational force on fluid Gravitational force on steel of pycnometer Gravitational force on test weights Total forces on steel of pycnometer when fluid filled Total forces on steel of pycnometer when evacuated” Total forces on steel of pycnometer when air-filled Dimensional conversion constant, 32. 17405(lbm-ft)/(lbf-s2) or l.O(kg.m)/(N.s’) Local gravitational constant Elevation of weigh scale above sea level Isothermal compressibility of water at 14.696 psia and a temperature Average isothermal compressibility of water at a pressure and a temperature Mass of any object Mass of fluid Mass of test weights Datum pressure of pycnometer, 14.696 psia or 101.325 E a or O psig Test pressure Pycnometer base volume, pycnometer volume at damm pressure and datum temperature Pycnometer volume at datum temperature and test pressure Pycnometer volume at test temperature and 0.0 psia Pycnometer volume at test temperature and test pressure Datum temperature, O.O°F or -17.8OC Test temperature Volume of any object Volume of test weights Weight of air-filled pycnometer Weight of fluid-filled pycnometer Weight of pycnometer with all air evacuated Density of any object Density of dry air Density of fluid at test temperature and test pressure Density of field test weights Density of reference test weights Density of water at test temperature and 14.696 psia Density of water at test temperature and test pressure

I

t.7 g -

- -

cm3/psi I/OF Ibf Ibf Ibf lbf Ibf Ibf i bf Ibf Ibf Ibf -

ft/s2 ft

I/psi I/psi

g g g

psi

psi cm3

cm3 cm3 cm3

O F

O F

cm3 cm3

g g g

g/cm3 g/cm’ g/cm3 g/cm3 g/cm3 g/cm3 g/cm3

g E -

- -

c m ’ k ~ a ipc N N N N N N N N N N -

m/s2 m

IkPa 1kPa

g g g

Wa

!&‘a cm3

cm3 cm’ cm3 “C

“C cm3 cm3

g g g

g/cm3 g/cm’ g/cm’ g/cmJ g/cm’ g/cmJ g/cm3

‘includes buoyancy force associated with the internal

been determined by NIST. Mass standards are used for highly accurate measurements in scientific research laboratories but are impractical for precise commercial measurements.

Apparent mass standards are precise standards whose density and apparent mass have been determined by a high- precision commercial laboratory, as compared with their primary standards. Apparent mass standards are calibrated by

volume.

primary mass or primary apparent mass standards, which in turn have been certified by NIST. Apparent mass standards are used by all states and by commercial laboratories as their primary standards for precise weighings. A typical commercial laboratory’s certificate for a set of primary standards is shown in Figure 2.

The NIST Classification of Mass and Laboratory Weights (mass and apparent mass standards) is based on tolerances



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A P I MPPlS*i<LLi-b 91 0732290 0095857 12 I

1 SECTION 6-CONTINUOUS DENSITY MEASUREMENT 5 I

I from the true value. Generally, NIST Class P and S weights 14.6.6.3 WEIGHING l are apparent mass standards with accuracies of 0.002 percent

and 0.0002 percent, respectively. A typical certificate for a set of apparent mass standards is shown in Figure 3.

Analytical balances, or weigh scales, are vertical force comparators. In other words, they measure the net force act-

Report of Mass Values One-Piece Metric Mass Standards

NIST Test No. 737/228509- July 1,1982 1 O0 g x 1 mg- Revised June 8,1983

Corrections (mg)

Nominal Brass Stainless Value 8.3909 g/cm3 8.000 g/cm3 Uncertainty (mg)

-25.13 -4.34

8.30 14.15 2.79 4.27

1.62 1.72 0.15

-0.48 1 0.110 O. 103 0.033 0.014

-0.026 -0.0036

0.0208 -0.0381

-0.0201 -0.0171 -0.0193 -0.0232 -0.0006 -0.0115 -0.0252 -0.0135 -0.0042 -0.0034 - 0.00 19

0.0011

114.66 65.56 43.24 35.12 16.77 11.26

5.11 3.82 1.55 0.218 0.459 0.312 O. 173 0.084 0.009 0.0173 0.0348

-0.0311

-0.0166 -0.0150 -0.0179 -0.0226 -0.0002 -0.0112 -0.0251 -0.0135 -0.0041 -0.0033 -0.0019

0.0011

43.89 21.84 10.44 6.83 4.99 0.041

0.027 0.026 0.021 0.034 0.016 0.014 0.012 0.0 14 0.007 0.0049 0.0035 0.0030

0.0016 0.0012 0.0009 0.0009 0.0007 0.0008 0.0007 0.0009 0.0007 0.0008 0.0007 0.0009

Figure 2-Typical Primary Apparent Mass Sfandards Certificate



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6

A P I MPMS*14.b 71 0732270 8875858 4 M

CHAPTER 1 &NATURAL GAS FLUIDS MEASUREMENT

Mass and Laboratory Weight Manufacturer Certificate No. 11 2543-86

Density of stainless steel test weights-7.84 g/cm3 @ 20°C Density of reference test weights-8.0 g/cm3 @ 20°C

NIST Class P Tolerance

Apparent Mass vs. 8.0 g/cm3 Correction (mg) (I mg) (I Yo)

2 kg +27.5 40.0 0.0020 1 kg +13.0 20.0

500 g +3.7 10.0 200 g +2.8 4.0 0.0020 100 g +1.1 2.0 0.0020

0.0020 0.0020

50 g +0.8 1.2 0.0024

These corrections are based on comparisons in normal air, 0.0012 g/cm3, with our primary standard, which was calibrated by the National Institute of Standards and Tech- nology (NIST). The mass of these standards can be calculated from the following equation:

1 1 - (0.0012/8.0) 1 - (0.0012/7.84)

= (Apparent mass)

Figure 3-Typical Secondary Apparent Mass Standards Certificate

ing on an unknown object, compared with the net force acting on a known object (an apparent mass standard). By definition, they are influenced by external vertical forces.

The principal vertical forces that influence the weighing instrument’s performance are local gravity, air buoyancy, air currents, vibration, and attitude. Lesser forces, such as elec- trostatic and magnetic forces, are beyond practical field and laboratory accuracy levels.

The influence of air currents on the analytical balance can be controlled by the use of a draft shield.

The influence of vibration and attitude can be controlled by mounting the analytical balance on a level, stable surface that is free from vibration.

By calibrating in air an analytical balance to a known apparent mass standard, the balance is prepared to read the apparent mass of any object whose density is equal to the apparent mass standard’s reference density. This calibration method also corrects for the effect of local gravitational forces as long as the balance is not moved to a different io- cation.

The influence of air buoyancy forces on an object can be calculated if the object’s density or volume is known. If the

apparent mass standard’s density is greater than the object’s density, the buoyancy correction must be greater than 1. If the apparent mass standard’s density is less than the object’s density, the buoyancy correction must be less than 1. The buoyancy correction equation is given in 14.6.6.5.

14.6.6.4 APPARENT MASS TO MASS VALUES

All hydrocarbon and other petroleum-related fluid densities are based on mass or weight in a vacuum. Air buoyancy corrections are therefore required for all calibrations of density meters, laboratory calibrations of pycnometers, and field verification of pycnometers.

In practical field and laboratory weighings, the mass of an object shall be calculated from its apparent mass by the following equation:

Mass = Apparent mass x Air buoyancy correction

Although it is recognized that a more explicit treatment may be performed, the precision of this equation is sufficient for the limits of practical field and commercial laboratory determinations.



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A P I MPMS*1LI-b 91 W 0732290 0095859 b W


14.6.6.5 CORRECTION FOR AIR BUOYANCY ON

The mass of a test fluid shall be calculated using a pyc-

WEIGHINGS (Cew)

nometer by the following equation:

Mfl = (wf - wo><cBW) The following formula shall be used for laboratory cali-

bration of pycnometers:

Keeping in mind the practicality of field conditions, the formula becomes the following for proving and verification tests:

'BW = - (PA /PTWí)

For field weighings, the value of pA is calculated as a function of elevation only (see 14.6.14.2). To simplify field calculations, the value for C,, can be constant for each balance location using a specified set of weights.

14.6.6.6 DERIVATION OF EQUATION FOR CBw

14.6.6.6.1 General

The derivation of the C,, equation has been written for qualified technical personnel with a background in physics.

To derive the equation to correct for the air buoyancy on all weighings, the use of a perfect electronic balance is as- sumed. The balance has been calibrated with the apparent mass standards shown in Figure 3, in an air densify of 0.001 18 gram per cubic centimeter. When a fluid-filled pycnometer is placed on the balance, it indicates a scale reading of 2000 grams, The evacuated weight of the pycnometer indicates a scale reading of 1000.0 grams. The air-filled weight of the pycnometer indicates a scale reading of 1001.18 grams. The Pvp value for the pycnometer is 1000.00 cubic centimeters.

As shown in Figure 4, the net forces may be calculated as follows: By definition,

= PFtpPVlp

PYP = M/PF,, For both the apparent mass standard and the fluid,

Net force = Force due to gravity - Buoyan€ force of air

Since the electronic balance is perfect, no corrections are needed for the balance:

(Net force), = (Net force),

14.6.6.6.2 Using the Pycnometer's Evacuated Weight (Wo)

The fluid's net force is calculated as follows:

(Net force), = Net force of fluid-filled pycnometer - Net force of evacuated pycnometer

or ,

(Net force), = (4 + epyC) - Fzp,c Where:

FR + Flpsc = total forces exerted on the fluid-filled pyc-

Fzpyc = total forces exerted on an evacuated pycnom-

The forces on the fluid combined with the forces exerted on the steel shell of the pycnometer are expressed as folIows:

nometer.

eter.

F, + epsc = (F, - 4,) + ( E - es) Although the pycnometer is evacuated, the internal volume is displacing air and therefore has a buoyancy force for the evacuated volume. The forces on the steel shell of the pycnometer and the buoyancy force exerted on the evacuated volume are expressed as follows:

FZpyc = 4 - (Fbs + Fbv)

Substituting,

(Netforce), = [(F, - F b n ) + (e - - [ E - (Fbs + Fbv)l

Reducing the equation yields the following:

(Netforce), = (F, - 6,) + Fbv

And,

Fbfl = @ A p Y p )(gr / 8,)

And,

F b v = (pAp~)(gl /gc)

Assuming that the pycnometer volume does not change significantly between an evacuated and a fluid-filled state,

Pl$) = Pv,

And,

&I = Fbv

Reducing the net force equation yields the following:

(Net force), = F,

Remembering that the scale is perfect,

(Net force),, = (Net force),

Since the test weights have both gravitational and buoyancy forces exerted on them,

- 'blw = Ffl

For the mass standard, the gravitational forces are expressed as follows:



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1 Volume of steel

evacuated pycnometer

Volume of steel

Volume of fluid

5" + 5 s

F,

F , + E USING EVACUATED WEIGHT Wo

5 s 4

Volume of steel

1 'I'

F,

Figure

5, + 5 s \ Volume of steel

Volume of fluid

F , + < USING AIR-FILLED WEIGHT W,

4-Net Forces on Pycnometer

6, = (PTWrv,, )(ål/ g,)

For the fluid, the gravitational forces are expressed as follows:

F f l = ( P F t p p v p )(8l 1 gc )

The air buoyancy forces are expressed as follows:

F b i W = @*Yw )(å, 1 å, 1 Substituting into the equation for net force,

(å, / å, )(PnvrYw - P A K ) = (åi 1 åc ) ( ~ , t p P V , p )

By definition,

Again substituting into the equation for net force and then reducing,

Mfl = MI, - (P, IPnvr 11 The mass value of the apparent mass standard can be cal-

culated by the following equation (in accordance with NIST procedures):

Substituting,

From the previous section,




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API M P M S * L Y - b 91 m 0732290 0 0 9 5 8 b L Y m

SECTION C CONTINUOUS DENSITY MEASUREMENT 9

Solving for the mass of the fluid,

- (o’oo12/8’o) [i - (0.00118/7.84)] 1 - (0.0012/7.84) I Mfl = 1000

= 999.85 grams

14.6.6.6.3 Using the Pycnometer’s Air-Filled Weight (W,)

A similar derivation can be performed for open beakers, glass pycnometers, or flow-through pycnometers when W, is used to define the fluid’s net force:

(Net force), = Net force of fluid-filled pycnometer - Net force of air-filled pycnometer

The net force of the fluid-filled pycnometer is expressed as follows:

(Net force), = (Ffl + KpJ - Kpyc The net force of the air-filled pycnometer is expressed as follows:

Ffl + K p y c = (& - &fl) + (Fs - Fbn)

Since the pycnometer is air filled, the internal volume is not displacing air and therefore has no bouyancy force:

K p y c = - Fbs

Substituting,

(Net force), = [(F, - Fb,) + ( F , - &)I - ( F , - Fbs)

Reducing the equation yields the following:

(Net force), = F, - Fb,

And,

Fbfl = (PApyp )(gl / gc Remembering that the scale is perfect,

(Net force),, = (Net force),

&w - ‘biw = Ffl - 6fl For the mass standard, the gravitational forces are expressed as follows:

K v = (P,vfv,w)(gl /gc) And the air buoyancy forces are expressed as follows:

%w = (PAYw)(gl / gc)

For the fluid, the gravitational forces are expressed as follows:

Ffl = (PFtppyp )(gl 1 gc) And the air buoyancy forces are expressed as follows:

Fbfl = (PApyp )(8, /gc)

Substituting into the equation for net force,

Solving for the mass of the fluid, r

The mass value of the apparent mass standard can be calculated as follows:

Substituting,

From the previous section,


Therefore,

And,

PFrp = (K - wa)/pyp Solving for the mass of the fluid,

1 1 - (0.0012/8.0) 1 - (0.0012/7.84)

M , = 998.82

1 - (0.00118/7.84) { 1 - [0.00118/(998.82/1000.0)] = 999.85 grams

14.6.6.6.4 Summary of C,, Equation

For the Wo application, the CBw equation corrects only for the buoyancy of the additional test weights required to determine the difference between the Wf and Wo values.

In both the Wo and W, derivations, the simplified CBw equation was not used to accurately reflect the results. The simplified CBw equations are as follows: When using Wo,



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10

API MPMS*L4.b 91 E 0732290 0075862 b

CHAPTER 1 &NATURAL GAS FLUIDS MEASUREMENT

14.6.6.6.5 Mass and the C,, Equation Since the laboratory-determined pycnometer volume and

evacuated weight are considered more accurate than the field-determined W, values, the Wo method shall be used for all flow-through pycnometers.

The mass density of the fluid contained in a flow-through pycnometer shall be calculated using the following equation:

PFIP = [(Wf - W o ~ / ~ Y p 1 C , ,

The mass of the fluid contained in a flow-through pycnometer shall be calculated using the following equation:

M f l = cWf - wo)cB\V

14.6.7 General Design Considerations 14.6.7.1 GENERAL

Before a density measurement system is designed, a thor- ough understanding of the fluid and the measuring equipment is necessary to achieve a density accuracy of 0.10 percent. A systematic approach to the design should include close attention to the following areas:

a. Fluid properties and behavior. b. Density meter. c. Pycnometer (flow-through design). d. Density sampling system. e. Density proving system. f. Volumetric meter influence.

Accurate continuous density measurement requires thermal insulation of the volume meter, density meter, pycnometer, and all interconnecting piping to minimize density deviations due to temperature differences.

General areas of importance are presented below. De- tailed criteria are presented throughout this publication.

14.6.7.2 FLUID PROPERTIES AND BEHAVIOR 14.6.7.2.1 - General

The properties and behavior of the fluid being measured, as well as their impact on the measuring equipment, must be fully understood. The areas described in 14.6.7.2.2 and 14.6.7.2.3 should be considered.

14.6.7.2.2 Fluid Density Assuming a constant fluid composition, the fluid density

can be inferred by measuring the fluid temperature and pressure. Therefore, temperature and pressure differences be-

tween selected points are indicative of density differences. The sensitivity of the fluid density to temperature and

pressure variations should be analyzed by means of an en- thalpy diagram, a density envelope, or generalized density deviation curves (see Figures 5 ,6 , and 7).

The temperatures and pressures between the density meter, pycnometer, and volume meter should coincide as closely as possible, such that the following criteria are met:

a. During normal operation, the density deviation between the density meter, pycnometer, and volumetric meter shall not exceed 0.05 percent. b. Error resulting from pressure differences shall not exceed 0.01 percent or 1 pound per square inch gauge, whichever is greater. c. Error resulting from temperature differences shall not exceed 0.04 percent or 0.2"F, whichever is greater.

Figure 8 is a piping schematic that shows the temperature and pressure points.

For some fluids, the deviation criteria above are not practical (for example, applications in which operation is close to the critical point). For these applications, the density meter shall be installed so that the following criteria are met:

a. During proving, the density deviation between the sample point, the density meter, and the pycnometer shall not exceed 0.05 percent (see Figure 8, Points 1, 2, and 3). b. To minimize any density deviation due to pressure, the density meter shall be located as close as is practical to the volume meter. c. To minimize any density deviation due to temperature, the main line piping between the volume meter and the sample point shall be fully insulated.

Density variation of the fluid with respect to compositional changes should be evaluated to determine its effect on the density meter and the volume meter.

14.6.7.2.3 Other Properties and Behavior

Other process fluid properties and behavior should be reviewed to assess the possible impact on the safety, accuracy, and reliability of the system. The following areas should be considered:

a. Cleanliness. b. Homogeneity. c. Corrosiveness. d. Polymerization. e. Viscosity. f. Autorefrigeration. g. Solids precipitation.

Fluid separation behavior should be assessed to prevent liquid-liquid separation, hydrate formation, or dry ice formation (for CO2 service).



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A P I MPMS*lJLl-b 91 W 0732290 00958b3 8 W


14.6.7.3 DENSITY METER 14.6.7.4 PYCNOMETER

The selected density meter should be evaluated for sensitivity to the sample system’s flow rate, attitude, velocity of sound in a flowing fluid, temperature and pressure variations, dirt and pipe rouge, accumulation of liquids (for example, glycols, oils) or particulates, mechanical vibration, and fluid pulsations and pressure surges.

Only pycnometers with a flow-through design shall be used, The selected pycnometer should be evaluated for sensitivity to the sample system’s flow rate, attitude, liquid and particulate accumulation, and atmospheric water condensation.

2200

2000

1800

1600

Q> c 5 1400 2 m c o C .-

1200 5 m v>

Q ln

3 O a

8

1000

gj 2 800 2 a

600

400

200

O

1 pound per cubic foot -

I I I I I I I I I I 35 40 60 80 1 O0 120 140 160 180 200 220

Temperature, degrees Fahrenheit

Figure 5-Typical Ethylene Density Envelope



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A P I M P M S U / 4 . 6 91 0732270 0075864 T


Ethane

0.40 0.50 0.60

Liquid density (p), g/cm3

Notes: I . The curve is intended only to illustrate general relationships and the need for closer pressure tolerances on light hydrocarbons. Compressibility varies with actual composition and increases significantly as bubble-point or critical temperatures are approached. 2. The curve is based on a Rackett equation with pure components ri-hexane, n-butane, propane, and ethane.

Figure 6- Density Changes due to Pressure Deviations

DENSITY SAMPLING SYSTEM

The density meter and pycnometer can only measure the fluid passing through them. As a result, the density sampling system shall meet the following criteria:

a. Be installed in a location where the fluid is homogeneous. b. Not induce separation of the process fluid. c. Provide the necessary test points for determining temperature and pressure at each device. d. Provide sufficient flow to minimize response delays between the density meter and the pycnometer.

e. Be installed to minimize fluid pulsation and pressure surges. f. Be installed so that associated pipeline facilities can be cleaned without an impact on density measurement. g. Provide connections for one or more pycnometers.

Since the density sampling system requires a continuous slipstream sample, it is time dependent and may not precisely correspond to rapid variations in density. This is commonly referred to as densify lagging.

Density determination errors normally result from the following:



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A P I MPMS*14*b 91 = 0732290 00958b5 1

SECTION CONTINUOUS DENSITY MEASUREMENT -

a. Process temperature and/or pressure changes. b. Ambient temperature differences. c. Fluid compositional changes.

To minimize the effect of temperature differences, thermal bonding of the density sampling system is necessary for all installations, The sampling system must be installed in close thermal contact with the main pipeline, and the entire system (density meter and sampling system) must be thermally insulated against ambient conditions.

If the density varies by more than 0.05 percent over the period of time needed to fully stabilize the pycnometer, it is not likely that a prover repeatability of 0.05 percent will be obtained for two consecutive proving runs. For this situation, the parties may agree to take one or both of the following approaches:

!+ 2 e 8

O

3 O

$ 8 ô Y-

C O m > a> U

3

.- c .-

!? c

$ c E 9.

z '8 H

I 0.30

0.06 (0.033"C)

0.075 (0.042"C)

0.1 (0.056"C)

0.15 (0.083"C)

0.2 (0.1 1°C)

0.5 (0.28"C)

13 ~

a. Average the results of several provings. b. Increase the repeatability tolerance. The accuracy of the measurement may suffer as a result of this practical approach.

14.6.7.6 DENSITY PROVING SYSTEM

correction factor and consists of the following equipment:

a. Pycnometer. b. Weigh scale and test weights. c. Temperature instrument. d. Pressure instrument.

The density proving system determines the density meter

To assure that the density deviation meets the criteria called for in 14.6.7.2, temperature and pressure measure-

I I I

0.40 0.50 0.60

Liquid density (p) at 60°F, g/crn3

Notes: 1. The curve is intended only to illustrate general relationships and the need for closer pressure tolerances on light hydrocxbons. Thermal expansion rates vary with actual composition and increase significantly as bubble-point or critical temperatures are approached. The use of actual physical data is recommended. 2. The curve is based on a Rackett equation with pure components n-hexane, n-butane, propane, and ethane.

Figure 7-Density Changes due to Temperature Deviations



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14

- d

A P I MPMSUL4.b 91 0732290 00958bb 3

CHAPTER 1 ‘&NATURAL GAS FLUIDS MEASUREMENT

Point 1 n TW 111 PI 1 I

Flow

W Density meter location

(see Detail A)

Point 3 n- SVent

DETAIL A

Notes: I . The maximum density deviation between Points 1,2, and 3 shall not exceed 0.05 percent as a result of changes in pressure and temperature. 2. The maximum density deviation due to pressure shall not exceed 0.01 percent. 3. The maximum density deviation due to temperature shall not exceed 0.04 percent.

Figure 8-Temperature and Pressure Points for Inferring Density Deviation

ments are required immediately prior to or at the time of proving.

14.6.7.7 INFLUENCE OF VOLUMETRIC METER Density meters may be installed upstream or downstream

from the flowmeter, as near as is practical to the primary measuring device to minimize density errors.

Care shall be taken not to disturb the velocity profile for turbine, vortex, and orifice meters. Flow shall not be by- passed around the flowmeter.

Restriction devices installed between the flowmeter and the prover (if applicable) may create flowmeter proving errors if they create a density difference between the prover and the flowmeter.

14.6.8 Density Meters 14.6.8.1 GENERAL

two groups: Insh-uments used to measure fluid density are divided into

a. Discrete, or noncontinuous, density meters. b. Continuous density meters.

Table 2 illustrates the classification of density meters.

14.6.8.2 DISCRETE DENSITY METERS Discrete density meters, which rely on a discrete represen-

tative sample, consist of the following instruments:

a. A hydrometer or thermohydrometer. b. A Westphal balance. c. A pycnometer, which may be of the glass or the flow- through type.

The Westphal balance, glass pycnometer, and atmospheric hydrometer are limited to density determination for atmo- spherically stable, well-defined fluids. The method for determining density using an atmospheric hydrometer is described in Chapter 9, Section 1.

The pressure hydrometer is limited to density determination for well-defined fluids that are stable at operating pres-



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A P I MPMS*i<14.6 71 0732270 0075867 5

SECTION C CONTINUOUS DENSITY MEASUREMENT 15

Table 2- Classification of Density Meters

Discrete Continuous

Atmospheric hydromefer Vibrating element Pressure hydrometer Buoyancy Westphai balance Continuous weighing Pycnometer [glass or flow through) Consfant head

Acoustic Nuclear Capacitance

sures below 203 pounds per square inch absolute (14 bar). The method for determining density using a pressure hydrometer is described in Chapter 9, Section 2.

14.6.8.3 CONTINUOUS DENSITY METERS

14.6.8.3.1 General

Continuous density meters, which require a continuous representative sample from a homogeneous process stream, use a variety of measurement principles to hfer density. The most common instruments currently used in custody transfer applications use the vibrating-element (natural-resonance), buoyancy, or continuous weighing technique. The descrip- tions given in 14.6.8.3.2 through 14.6.8.3.4 are not meant to advocate the preferential use of any particular technique.

14.6.8.3.2 Vibrating- Element Technique

The vibrating-element, or natural-resonance, method is based on the principle that frequency is inversely proportional to density. A continuous sample of the fluid is passed through or around a body vibrating at its natural frequency. The vibrating body can be a tube, cylinder, or flat plate.

Meters that use the vibrating-element technique are sensitive to velocity-of-sound effects and dirty fluids. Protection from rouge buildup, oil films, and particulates that might scratch the element is necessary.

14.6.8.3.3 Buoyancy Technique

The buoyancy technique is based on Archimedes’ principle, which states that an immersed body is buoyed up by a force equal to the weight of the fluid it displaces. A contín- uous sample is passed through a chamber that maintains a float in a balanced position. The electric force needed to maintain the balanced position is directly proportional to density.

Meters that use the buoyancy technique are sensitive to vibration, horizontal position, and dirt buildup. Application is limited to fluids of low or moderate viscosity.

14.6.8.3.4 Continuous Weighing Technique

The continuous weighing technique is carried out by continuously passing the fluid through a vessel (a bulb or U

tube) of known volume. The vessel is continuously weighed, and the result is divided by the volume to determine density. Depending on the required accuracy, corrections for the fluid temperature and pressure are applied to the results.

Meters that use the continuous weighing technique are sensitive to vibration and horizontal position, Application is limited to ñuids of low or moderate viscosity.

14.6.8.4 ACCURACY

The selected density meter shall have a minimum overall accuracy of 0.001 gram per cubic centimeter and a repeatability of 0.0005 gram per cubic centimeter over the range of design operating conditions. Depending on the density meter, compensation may be required for the effects of operating temperature and pressure on the meter’s performance.

To ensure accuracy, the meter shall be installed in accordance with the criteria given in 14.6.7 and 14.6.10, as well as the manufacturer’s recommendations.

Proving of the density meter (or determination of its operating accuracy) shall be performed in accordance with the criteria and procedures given in 14.6.11 and 14.6.12.

14.6.9 Pycnometers 14.6.9.1 GENERAL

A flow-through pycnometer is the most accurate device for calibrating a density meter under flowing conditions. Dis- crete density meters, which require a grab sample, can also be used as density proving devices. Table 3 illustrates the classiücation of density provers.

14.6.9.2 DEFINITION

The term pycnometer refers to both glass and flow- through pycnometers. This standard only covers the use of flow-through pycnometers. In the remaining sections of this standard, pycnometer refers to a flow-through pycnometer.

a. They are vessels with a flow-through design that traps a representative sample of the test fluid at operating conditions. b. They permit safe handling of high-pressure fluids during sampling and transport. c. Their volume and evacuated weight are known to a precision of 0.02 percent over the operating pressure and temperature range.

Pycnometers are defined by the following criteria:

Table 3-Classification of Density Provers

Flow-Through Pycnometers Discrete Density Meters

Single sphere Atmospheric hydrometer Doubie-wall vacuum sphere Pressure hydrometer Single cylinder Westphal balance

Glass pycnometer



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16

A P I MPMS*14.b 71 H 0732270 0095868 7 H

CHAPTER NATURAL GAS FLUIDS MEASUREMENT

The pycnometer’s volume and evacuated weight shall be based on its unique values, as determined by the procedures described in 14.6.16. Those values are as follows:

a. Pycnometer base volume (PBV) . b. Coefficient of expansion due to internal pressure (EJ . c. Coefficient of expansion due to test fluid temperature (E,). d. Evacuated weight of the pycnometer (Wo>.

14.6.9.3 DESIGN CRITERIA

The following criteria should be considered when the size, design, and construction of pycnometers are determined:

a. To minimize weighing errors, the ratio of the pycnometer’s evacuated weight to the weight of the fluid should be kept low. b. Because of current scale limitations, the mass of a water- filled pycnometer shall not exceed 5000 grams. c. Considering balance capabilities, the pycnometer’s volume shall not be less than 500 cubic centimeters. For most applications a volume of approximately 1 O00 cubic centimeters is recommended. d. The pycnometer’s shape and materials of construction shall provide a safe, precise, easy-to-clean device. All sur- faces shall be smooth and polished to facilitate cleaning. The pycnometer’s flow pattern shall be designed to eliminate deposition and gas entrapment, ensure proper purging, and allow temperature stabilization. e. Precision shutoff valves shall be fitted at each end of the pycnometer. The valves shall either be welded or form an integral part of the pycnometer. The valves shall provide a fast, positive, zero-leakage shutoff and shall be resistant to abra- sive material. f. A full-flow rupture disk shall be installed to prevent over- pressure due to thermal expansion of the test fluid. g. A serial number shall be permanently affixed to the vessel.

14.6.9.4 CLASSIFICATION

14.6.9.4.1 General

There are three types of flow-through pycnometers-single sphere, double-wall vacuum sphere, and single cylinder.

14.6.9.4.2 Single Sphere

A single-sphere pycnometer consists of a stainless steel sphere with a capacity of approximately 1000 cubic centimeters that is designed and constructed for a maximum allowable working pressure specified by the user.

Figure 9 shows the single-sphere design. The fluid flows through the inlet valve into the sphere and then up through the siphon tube. The gas vent and siphon tube minimize the possibility of gases being trapped and assist in removing deposition.

The volume temperature and pressure corrections have been determined to be linear.

14.6.9.4.3 Double-Wall Vacuum Sphere

A double-wall vacuum sphere pycnometer consists of two stainless steel spheres (one inside the other, with a vacuum pulled on the annulus) with an internal capacity of approximately 1000 cubic centimeters. It is designed and constructed for a maximum allowable working pressure specified by the user.

The vacuum minimizes thermal exchange between the test fluid and the ambient air. For test fluids that operate at temperatures below ambient, this eliminates the possibility of water condensing on the outside of the pycnometer.

Figure 10 shows the double-wall vacuum sphere design. The fluid flows through the inlet valve into the sphere and then up through the siphon tube. The gas vent and siphon tube minimize the possibility of gases being trapped and assist in removing deposition.


14.6.9.4.4 Single Cylinder

A single-cylinder pycnometer consists of a stainless steel cylinder with a capacity of approximately 500 cubic centimeters, fitted with integral valves at each end, that is designed and constructed for a maximum allowable working pressure specified by the user.

Figure 11 shows the single-cylinder design. The fluid flows from bottom to top, minimizing the possibility of gases being trapped.


14.6.9.5 CERTIFICATION

Certification of flow-through pycnometers shall be in accordance with 14.6.16. Certification shall be performed when any of the following occurs:

a. Original construction is completed. b. Two years have elapsed since the last certification. c. The vessel has been damaged. d. The vessel has been disassembled. e. The valve parts have been replaced. f. The rupture disk has been replaced.

If the valve manufacturer can substantiate claims that replacement of the welded valve parts will not change the pycnometer volume or its evacuated weight by more than 0.02 percent, then recertification is not required. A similar verification is required for replacement of the rupture disk. An evaluation should be performed to assure that the E,, value is not altered when these parts are replaced.



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A P I MPMS*14-b 91 = 0732290 0095869 9


14.6.9.6 VERIFICATION

Verification of the pycnometer’s base volume (PBV) and its evacuated weight (Wo) may be performed in accordance with the procedures described in 14.6.15. It is important to note that the prover’s Ep and E, values can only be confirmed by performing the tests called for in 14.6.16.

The results of the verification test shall not be used to redefine the PBV and W, values,

The results of the verification test can be used to confirm that a replacement valve or rupture disk has not changed the PBV and Wo values by more than 0.02 percent.

14.6.1 O Density Sampling Systems 14.6.10.1 DESIGN CRITERIA

The density meter measures only the fluid passing through the density sampling system. The density sampling system shall meet the following criteria:

a. The system shall be installed in a location where the fluid is homogeneous and within the density deviation criteria of 14.6.7.2.2.

b. The system shall include a sample probe in the center third of the pipe for slipstream flow. c. The system shall not induce separation of the process fluid. d. The system shall provide sufficient flow to minimize density lags between the density meter and the pycnometer. e. The system shall not cause cavitation or flashing of the fluid. f. The installation shall permit the escape of any air or gas bubbles. g. The installation shall minimize fluid pulsation and pressure surges. h. The installation shall permit cleaning of associated pipeline facilities without an impact on density measurement. i. The entire sampling system, including the density metes and pycnometer, shall be thermally bonded in accordance with the requirements in 14.6.7.5. j. The system shall include vertically mounted thermowells for temperature instruments, to relate density deviation to temperature differences. k. The system shall include taps for pressure instruments, to relate density deviation to pressure differences.



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A P I MPMSUL4.b 91 0732290 0095870 5


1. The system shall provide adequate filtration and condi- tioning to prevent particulates from damaging the density meter or pycnometer. m. The system shall include connections to permit conve- nient installation and removal of the pycnometer. n. The system shall include a means of venting or flaring fluid when the pycnometer is installed. o. The system shall not affect the velocity profile for turbine, vortex, or orifice meters. p. The system shall not bypass flow around the volume meter. q. The pycnometer installation shall take into account flow rate, mounting attitude, and thermal bonding. r. The density meter installation shall take into account flow rate, mounting attitude, thermal bonding, and maintenance. s. Any pumps associated with the sample system shall be installed downstream from the pycnometer and density me-

As an option, the system may include a flow indicator to assure adequate flow through the sampling system at all times.

14.6.1 0.2 TYPES

14.6.1 0.2.1 General Density sampling systems are divided into two major

groups: grab-sample and continuous-sample systems. Figure 12 summarizes the classification system.

14.6.10.2.2 Grab-Sample Systems

Grab-sample systems take a spot sample of the fluid at the sampling point. Discrete density meters normally use these systems. The user assumes that a representative sample of the fluid has been provided. Grab-sample systems are not covered by this standard.

ter to preclude errors caused by pump-induced pressure or temperature increases. 14.6.1 0.2.3 Continuous-Sample Systems

t. The installation of restriction devices between the flowmeter, the density meter, the pycnometer, and the prover, which could result in density differences, shall be avoided.

Continuous-sample systems constantly pass a representative sample of the fluid through or around the density instruments. Continuous-sample systems are classified in two

Figure 1 O-Double-Wall Vacuum Sphere Pycnometer



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A P I MPMS*L4-b 91 m 0732290 009547L 7 m

SECTION &CONTINUOUS DENSITY MEASUREMENT 19

Plug valve

Vessel

\

Rupture disk

I

I ü

I

Plug valve

Note: The vaive body is an integral part of the vessel.

Figure 1 I-Single-Cylinder Pycnometer

groups, based on the mounting of the density meter: insertion and slipstream.

14.6.10.3 INSERTION SYSTEMS Figure 13 shows a typical insertion continuous-sample

system. Even though the density meter is installed in the

Density sampling systems

I I Grab

Insertion - Slipstream

Direct Pump devices In line Restriction devices

Orifice plates S bends Control valves Reduced pipe Velocity head devices Scoop tubes Pitot tubes

Figure 12-Classification of Density Sampling Systems

pipe, the pycnometer and its associated sampling system still constitute a slipstream design.

14.6.10.4 SLIPSTREAM SYSTEMS

Slipstream continuous-sample systems are the most commonly used. As shown in Figure 12, there are three types of slipstream systems, based on flow inducement:

a. Pumps. b. Restriction devices. c. Velocity head devices.

Pumps can provide the energy needed to maintain flow through the slipstream sample system. However, the success of this type of installation is contingent on the operation of the pump. Figure 14 shows two typical installations.

Restriction devices provide the energy needed to maintain flow through the system by inducing a differential pressure in the main line pipe. Differential pressure can be induced through the use of orifice plates, S bends, control valves, and reduced pipe diameters. Figure 15 shows two typical installations.

Velocity head devices provide the energy needed to maintain flow through the slipstream sample system by using the impact energy associated with scoop tubes or cross-sectional velocity profiles. Figure 16 shows two typical installations.

When restriction or velocity head devices are used, it may be necessary to temporarily install a pump when the density meter is proved. The increased pressure drop caused by installing the pycnometer in series may stop flow through the density sampling system. An alternative method is to install the pycnometer sampling system in parallel with the density meter sampling system.

14.6.10.5 THERMAL BONDING

Thermal bonding is required on all installations to minimize density errors due to temperature differences. Various levels of thermal bonding, based on the fluid’s sensitivity to



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Pycnometer FI

Pycnometer

I v DIRECT INSERTION

- Flow

o Flow

6- I I II

I

IN-LINE INSERTION

Note: With both insertion types, the pump is downstream of both the density meter and the pycnometer.

Figure 13-Insertion-Type Continuous Density Sampling Systems

temperature changes, should be considered by the designer. Two types of thermal bonding systems have been successful:

a. The sampling system is installed in close thermal contact with the main pipeline, and the entire system (density meter and sampling system) is insulated against ambient con-

ditions. Insulation is installed between the volume meter and the sampling system. b. The sampling system is installed externally to the main pipeline, and the entire system is insulated against ambient conditions by being installed in an insulated housing. In some cases a density meter building is installed to provide

b PYCNOMETER IN SERIES WITH DENSITY METER

Pvcnometer n

4 DT - I -

PYCNOMETER IN PARALLEL WITH DENSITY METER

Figure 14-Slipstream-Type Continuous Density Sampling Systems: Pump Devices



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API MPtlS* l14-6 91 0732290 0095873 O i


protection from the elements when the density meter is proved. Insulation is installed between the volume meter and the sampling system.

14.6.11 Proving Systems 14.6.11.1 GENERAL

The accuracy of the proving system is vitally important in obtaining a successful pycnometer proving. One of the most important pieces of equipment is the weigh scale or analytical balance,

14.6.11.2 APPARATUS 14.6.11.2.1 General

Five pieces of equipment are needed to perform an accurate pycnometer calibration of a density meter. This equipment is described in 14.6.11.2.2 through 14.6.11.2.6.

14.6.11.2.2 Pycnometer A pycnometer is a vessel whose volume (PQ and evac-

uated weight (Wo) are known within 0.02 percent. Thepyc- nometer shall be calibrated in accordance with the criteria and procedures described in 14.6.16.

14.6.11.2.3 Weigh Scale

A weigh scale, or analytical balance, of sufficient precision to obtain measurement accuracy of 0.02 percent of the test fluid’s weight or the air-filled pycnometer’s weight, whichever is less, shall be used. Weigh scales are classified in two groups:

a. Electronic scales. b. Mechanical scales (triple beam and hanging basket).

Both types of scales have been successfully used, but a higher degree of success has been achieved with electronic scales.

Scales shall be calibrated at the time of proving with certified apparent mass standards (test weights) to assure accuracy and to avoid weighing errors due to local gravitional forces.

Selection of the type of weigh scale should take into account the fluid- or air-filled mass of the pycnometer, the precision of the scale, and environmental conditions.

The scale shall be mounted on a level, stable, vibration- free surface. If the scale is not equipped with an internal level, an appropriate level shall be used to verify that the scale pan is horizontal.

I+ 30 maximum +I ORIFICE

Pycnometer,, O( - I I I

CONTROL VALVE

Figure 15-Slipstream-Type Continuous Density Sampling Systems: Restriction Devices



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A P I MPMS*L4.b 9L W 0732290 0095874 2 = 22 CHAPTER I '&NATURAL GAS FLUIDS MEASUREMENT

Flow __*

PYCNOMETER IN SERIES WITH DENSITY METER

I Flow -

PYCNOMETER IN PARALLEL WITH DENSITY METER Note: When the pycnometer is connected in series with the density meter, the pressure drop caused by the pycnometer may be too high, resulting in inadequate flow through the density sampling system.

Figure 16-Slipstream-Type Continuous Density Sampling Systems: Velocity Head Devices

Air shields shall be provided to minimize the effect of air

A pycnometer holding tray is recommended for centering currents on the scale's measurements.

and stabilizing the pycnometer during weighing.

14.6.11.2.4 Certified Test Weights

Certified apparent mass standards (test weights) that conform to NIST Class S or P shall be used to calibrate the weigh scale. Figure 3 shows a certificate for typical secondary apparent mass standards traceable to NIST.

The test weights shall be recertified if they have been damaged or are suspected of being in error.

14.6.11.2.5 Temperature Instrument

Temperatures shall be measured with a portable device accurate to 0.2"F (O. 1 OC) and traceable to NIST. Electronic devices are preferred because of their readability.

To eliminate possible errors, the same device shall be used at all three points (the thermowells shown in Figure 8).

14.6.11.2.6 Pressure Instrument Pressures shall be measured with a device accurate to 1

pound per square inch (6.90 kilopascals) and traceable to NIST. Electronic devices are preferred because of their readability.

In some situations, a differential pressure device may be required to assure that the density deviation due to pressure is within the design criteria given in 14.6.7.2.2 and depicted in Figure 8.

14.6.12 Proving of Density Meters 14.6.12.1 METHOD

Proving a density meter at actual operating conditions (at elevated pressures) and with a precision of 0.05 percent shall be accomplished by using a flow-through pycnometer. The pycnometer method consists of four discrete steps:

a. Entrapping a homogeneous, representative sample of fluid at the density meter's operating conditions in a pycnometer of precisely known volume and evacuated weight.



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A P I MPMS*L4*b 9L m 0732290 0095875 4 m I

SECTION &CONTINUOUS DENSITY MEASUREMENT 23 I

b. Accurately determining the fluid-filled weight of the pycnometer. c. Correcting the pycnometer volume for the effects of fluid temperature and pressure. d. Correcting for the effect of air buoyancy.

Successful proving criteria require that the density meter factors (DMFs) for two consecutive proving runs have a repeatability tolerance not greater than 0.05 percent.

For most applications, the pycnometer is installed in series with the density meter. For some applications, the pycnometer is installed in parallel with the density meter. Caution must be observed to assure that the density meter and pycnometer are experiencing the same homogeneous fluid at the same density conditions.

14.6.12.2 DENSITY STABILITY

Unless otherwise agreed upon by the two parties, provings should be conducted when fluid conditions approach steady state. If the density varies more than 0.05 percent over ape- riod of time required to fully stabilize the pycnometer, the required repeatability of 0.05 percent is likely to be unobtainable.

14.6.12.3 FLUID BEHAVIOR

Fluid behavior, along with its impact on the performance of the pycnometer, should be evaluated. Errors may be in- troduced as a result of the following factors:

a. Polymerization-Will polymerization occur during filling, operation, or emptying of the pycnometer? b. Liquid-liquid separation-Will liquid-liquid separation occur during filling, operation, or emptying of the pycnometer? Will lubricating oil or glycol adhere to the inside of the pycnometer? c. Autorefrigeration-Will autorefrigeration occur? If so, will hydrates form? For CO,, will dry ice form? What impact will autorefrigeration have on the time required to reach temperature stability?

To eliminate autorefrigeration, the pycnometer and its piping may be preloaded with an inert gas at a pressure sufficient to prevent the phenomenon.

14.6.1 3 Proving Procedures 14.6.13.1 GENERAL

Before a proving run can be performed, all test equipment shall be calibrated or checked. Refer to Figure 8 in following the proving procedures.

14.6.13.2 CLEANING THE PYCNOMETER

The following procedure shall be performed to clean the pycnometer:

a. Wash the inside of the pycnometer with solvent and then with acetone to remove any residual solvent. b. Dry the inside of the pycnometer thoroughly by purging with clean, dry air or clean, dry nitrogen for several minutes to evaporate the remaining acetone. c. Wash the outside of the pycnometer with distilled water. Rinse with acetone. Blow dry the outside of the pycnometer.

14.6.13.3 CALIBRATING AND CHECKING THE TEST EQUIPMENT

The following procedure shall be performed to calibrate and check the test equipment:

a. Calibrate the weigh scale using the certified test weights. b. Verify the operation of the temperature and pressure devices.

14.6.13.4 VERIFYING THE PYCNOMETER’S EVACUATED WEIGHT

The following procedure shall be performed to verify the pycnometer’s evacuated weight (Wo):

a. Place the air-filled pycnometer on the weigh scale and record the scale’s reading. b. Calculate the field Wo and verify that it does not differ from the certificate value by more than 0.02 percent. If the pycnometer has been weighed with the field fittings attached, add the fittings’ weight to the certificate Wo before comparing the Wo values. c. If the field Wo differs from the certificate value by more than 0.02 percent, verify the calculations, recheck the scale calibration, or both. d. If the field Wo has increased more than 0.02 percent from the certificate Wo, either the pycnometer has been insuf- ficiently cleaned and driedor the fittings’ weight is incorrect. Continue to clean the pycnometer or remove the fittings until the Wo variance is less than or equal to 0.02 percent. e. If the field Wo has decreased by more than 0.02 percent from the certificate Wo, either the pycnometer has been damaged or the fittings’ weight is incorrect. Remove the fittings to verify possible damage. If the pycnometer is damaged, it shall not be used.

14.6.13.5 INSTALLING THE PYCNOMETER

The following procedure shall be performed to install the pycnometer or pycnometers:

a. Install the pycnometer in series with the density mefer or in a parallel slipstream. Allow product to enter the upstream pycnometer valves first. Then vent or flare any gases or vapors from the pycnometer and its piping through the vent valve. b. When the pycnometer is filled with fluid, fully or partially close the bypass valve to initiate flow.



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24

A P I MPMS*14-b 91 E 0732270 0075876 b

CHAPTER NATURAL GAS FLUIDS MEASUREMENT

c. Install an insulation blanket on the pycnometer. Except when a double-wall vacuum sphere pycnometer is used, the pycnometer shall be insulated to speed temperature stabilization and prevent water condensation.

14.6.1 3.6 VERIFYING DENSITY DEVIATION AND STABILITY

The following procedure shall be performed to verify density deviation and stability:

a. Observe the output of the density meter for several minutes to verify steady-state density conditions. b. When temperature and pressure differences between the density meter and the pycnometer or pycnometers have stayed within the criteria given in 14.6.7 for a sufficient period of time, record the following field data:

1. Observed density (density meter output). 2. Density meter temperature. 3. Pycnometer temperature. 4. Density meter pressure. 5. Pycnometer pressure.

c. Partially open the pycnometer bypass valve and then immediately close the pycnometer’s inlet and outlet valves. Be sure to close the outlet valve first. d. Remove the pycnometer from the sample system piping and check for leakage. Any leakage from a pycnometer shall void the test.

14.6.13.7 DETERMINING THE FLUID-FILLED WEIGHT

The following procedure shall be performed to determine the pycnometer’s fluid-filled weight (W,): Note: To prevent operation of the rupture disk, the time required to remove the pycnometer, weigh it, and empty it in a safe location shall kept to a minimum.

a. Remove the insulation blanket from the pycnometer or pycnometers. b. If necessary, wash both valve openings and the outside of the pycnometer. Blow dry with dry air or nitrogen. Repeat if necessary. c. Place the pycnometer on the weigh scale and record the weight.

14.6.13.8 CALCULATING THE DENSITY METER CORRECTION FACTOR

The following procedure shall be performed to calculate the density meter correction factor:

a. Calculate the density meter correction factor ( D M F ) in accordance with the instructions given in 14.6.14. b. Repeat the steps described in 14.6.13.5 through 14.6.13.7 and Item a above to obtain the second consecutive DMF. (When using two pycnometers in series, two consecutive DMF values have already been obtained from Item a above.)

c. Calculate the repeatability. A successful proving requires that the DMFs for two consecutive proving runs not differ by more than 0.05 percent. d. When two successful consecutive provings have been performed, calculate the average DMF. e. For applications in which the density meter’s output is adjusted, an additional proving run shall be performed to confirm that the adjusted density meter’s output does not differ from the new test’s result by more than 0.05 percent.

14.6.13.9 EMPTYING THE PYCNOMETER

The following procedure shall be performed to empty the pycnometer or pycnometers: Note: For some applications, the steps described in Items b and c below may be waived if agreed upon by the two parties.

a. Empty the pycnometer in a safe location by either venting or flaring the contents. b. Clean the pycnometer in accordance with 14.6.13.2. c. Verify the pycnometer’s evacuated weight (Wo) using the procedures described in 14.6.13.4. If the pycnometer’s evacuated weight differs from the certificate value by more than 0.02 percent, the test results are voided.

14.6.1 4 Calculation Procedures 14.6.14.1 GENERAL

The steps described in this subsection outline the appropriate calculation procedures for proving density meters by the use of pycnometers.

From the pycnometer’s certificate, obtain the following data:

a. The pycnometer’s air-filled weight (W,). b. The pycnometer’s evacuated weight (Wo). c. The pycnometer’s base volume (PBV). d. The coefficient of cubical expansion due to temperature on the pycnometer (Et) . e. The coefficient of cubical expansion due to pressure on the pycnometer ( E J . f. The datum pressure of the pycnometer (P,) . g. The datum temperature (&).

If the pycnometer’s fluid-filled weight (W,) was determined with the fittings attached, add the weight of the field fittings to the certificate W, and W, values before proceeding.

a. The elevation of the facility above sea level (h). b. The density of the reference test weights (pnv,). c. The density of the field test weights (pnvf). d. The existing density meter factor (DMF).

for each of a minimum of two consecutive proving runs:

In addition, obtain the following data:

From the proving procedures, obtain the following data



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A P I MPMSxL4-6 91 m 0732290 0095877 8 m


a. The meter reading. b. The pycnometer’s air-filled weight OY,). c. The pycnometer’s fluid-filled weight (Wf). d. The test pressure (PJ. e. The test temperature (Tf).

14.6.14.2 CALCULATE THE AIR DENSITY

For calibration of density meters by pycnometers, the dry air density shall be calculated using the following equation (ü.S. Units):

pA = 0.0012[1 - (0.032h 1 lOOO)]

Where:

ti = elevation above sea level, in feet.

For a given proving location, the air density is constant. As a result, the air density need only be calculated once.

14.6.14.3 VERIFY THE PYCNOMETER’S EVACUATED WEIGHT (Wo)

The field Wo shall be calculated using the following equation:

Field Wo = Field W, - pAPBV

Compare the field Wo with the certificate Wo. If the difference exceeds 0.02 percent, the pycnometer shall not be used.

14.6.14.4 CALCULATE THE PYCNOMETER’S FLOWING VOLUME (PV;,)

The PK, shall be calculated using one the following equations: When Pf is in pounds per square inch absolute,

Pyp = [PBV + Ep(P, - Pd)][l + Et(Tf - Td)]

When Pf is in pounds per square inch gauge,

Pyp = [PBV + EpP,][l + Et(T, - T,)]

14.6.14.5 CALCULATE THE APPARENT MASS OF THE FLUID

The apparent mass of the fluid (AM,) shall be calculated using the following equation:

AMfl = W, - r-V,

14.6.14.6 CORRECT FOR AIR BUOYANCY ON TEST WEIGHTS (&)

The CBw for field provings shall be cakulated using the following equation:

‘BW = - (pA/pT!Vf) A constant value for CBw may be used for a specific site and test equipment.

14.6.14.7 DETERMINE THE MASS OF THE FLUID (M‘J

The mass of the fluid (M,) shall be calculated using the following equation:

Mfl = (w, - Wo>C,,v

14.6.14.8 DETERMINE THE DENSITY AT TEST CONDITIONS (pFip)

The value for pFlp shall be calculated using the following equation:

PFip = lpvv If necessary, convert the density to the appropriate units. The conversion factors are as follows:

a. To convert from grams per cubic centimeter to kilograms per cubic meter, multiply by 1000. b. To convert from grams per cubic centimeter to specific gravity, divide by 0.999012. c. To convert from grams per cubic centimeter to pounds per cubic foot, multiply by 62.428. d. To convert from grams per cubic centimeter to pounds per gallon, multiply by 8.3454. e. To convert from grams per cubic centimeter to pounds per barrel, multiply by 350.51.

14.6.14.9 DETERMINE THE DENSITY METER FACTOR (DMF)

The DMF shall be calculated using the following equation, with pFtp in the same units as the density meter’s read-

DMF = pFiP /(Density meter reading)

ing:

14.6.14.10 DETERMINE THE RESULTS OF THE SECOND PROVING RUN

Repeat the calculations described in 14.6.14.2 through 14.6.14.9 for the second proving run.

14.6.1 4.11 DETERMINE THE REPEATABILITY OF THE RESULTS

The repeatability of the results can be calculated using the following equation:

x 100 Maximum DMF - Minimum DMF Minimum DMF

For a successful test, the DMFs for two successive proving runs shall not differ by more than 0.05 percent.

% =

14.6.14.12 CALCULATE THE NEW DMF

lowing equation: The average DMF value shall be calculated using the fol-



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26

A P I M P M S * 1 4 - 6 91 0732290 0095878 T

CHAPTER 14-NATURAL GAS FLUIDS MEASUREMENT

Average DMF = ( D M F for Run 1 + D M F for Run 2) 1 2

The method of applying the average D M F to the custody transfer quantities depends on the secondary equipment that converts the density meter’s raw output to engineering units, the mass flow integrating equipment, and the accounting policies of the operator. The equipment manufacturers should be consulted to assure the correct application of the proving results.

Both parties should agree on the method by which the average DMF is to be applied to the custody transfer quantities prior to commencement of movements.

Figures 17 and 18 show examples of density meter proving reports that use the data for the pycnometer.

14.6.1 5 Field Verification Procedures for Pycnometers

14.6.15.1 OBJECTIVE OF TEST

The objective of the field verification test is to determine whether the pycnometer’s base volume (PBV) and evacuated weight (Wo) have changed since the last calibration. An acceptable verification is determined by the repeatability of the test results for two consecutive runs.

A repeatability of at least 0.02 percent for each of the following values for two consecutive runs is needed to provide an acceptable test:

a. The pycnometer’s evacuated weight (Wo). b. The pycnometer’s air-filled weight (W,). c. The pycnometer’s base volume (PBV) at 14.696 pounds per square inch absolute.

If the field-determined PBV and Wo do not differ from the certificate values by more than 0.02 percent, then the pycnometer does not require recertification. The field verification test does not confirm the Ep and E, values.

14.6.15.2 TEST EQUIPMENT

The test equipment required for field verification of pycnometers is listed in Table 4.

14.6.15.3 CLEAN THE PYCNOMETER AND CHECK THE TEST EQUIPMENT

Before a pycnometer can be verified, it must be thoroughly cleaned, and all test equipment must be calibrated or checked, in accordance with the following procedure:

a. Wash the inside of the pycnometer with a petroleum- based solvent, such as kerosene, and then with acetone to remove any residual solvent. b. Rinse the pycnometer with distilled water, and then wash with acetone to remove any residual water. c. Dry the inside of the pycnometer thoroughly by purging with dry nitrogen, and then evacuate it with a vacuum pump

for 10 minutes. Close the inlet valve. (The pycnometer is probably not yet fully evacuated.) d. Wash the outside of the pycnometer with distilled water, and then rinse with acetone. Blow dry the outside of the pycnometer. e. Conduct all weigh tests without field or laboratory fittings. Conduct weigh tests on pycnometers equipped only with valves. The removal of all fittings accomplishes two goals:

1. The pycnometer’s base volume is verified as it was de- teimined in the calibration (without any fittings). 2. Entrapment of air and water by the fittings is elimi- nated.

f. Calibrate the weigh scale with the apparent mass standards.

14.6.15.4 VACUUM FILL AND DEAERATE THE WATER RESERVOIR

The water reservoir shall be vacuum filled and deaerated in accordance with the following procedure:

a. Set up the test apparatus as shown in Figure 19. b. Close Valve A and pull a vacuum on the system. The water will be displaced from the 1-gallon container to the water reservoir. c. When enough water has been displaced, turn off the vacuum pump. d. Set up the test apparatus as shown in Figure 20. e. Close Valve A. Deaerate the distilled water by pulling a vacuum on the water reservoir, as shown in Figure 20, until all air bubbles have ceased. Close Valve F, and disconnect the Tygon tubing from Valve E

14.6.15.5 DETERMINE THE EVACUATED AND AIR-FILLED WEIGHT

The pycnometer’s evacuated weight (Wo) and air-filled weight (W,) shall be determined in accordance with the following procedure:

a. Connect the pycnometer to the Tygon tubing, as shown in Figure 2 1. b. Evacuate the pycnometer with the vacuum pump to at least 29.0 inches of mercury for 2 minutes. Shut the outlet valve. c. Disconnect the pycnometer from the Tygon tubing, place the evacuated pycnometer on the weigh scale, and record the evacuated weight (Wo) to the nearest O. 1 gram. d. Repeat the steps described in Items a-c above until two successive weighings for Wo do not differ by more than 0.02 percent. Record the last Wo reading. e. Open the inlet valve. After 30 seconds, weigh the pycnometer and record the air-filled weight (W,) to the nearest 0.1 gram.

(text ronrinued on page 29)



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A P I MPMS*I ' I .b 9% 0732290 0095879 I


DENSITY METER PROVING REPORT Pipeline: CO^ Pipeline Date: 6/18/87 Location: Meter station Report: 8

I

Meter No.: DT-i01 1 NewDMF: 1.0032 Meter Data Pycnometer Data

Serial No.: 000178 Serial No.: 501 Serial No.: Manufacturer: API PBV(cm3): 992.39 P B V ( cm3) : Model: Vibrat ìncr W,: 1355.57 W,: CBW: O. 99985 Ep: O. O0132 Ep:

E,: 2.88 x lod5 E,: Run 1 Run 2 Run 3

Flowing Conditions 1 Observed density I b/W 45.620 45.622 2 Meter temperature OF 86.8 86.8

3 1 Meter pressure 1 psig I 1200 1 1200 1 4 I Pycnometer 7; I O F 86.8 } 86.8 5 Pycnometer pt I psig 1200 1200

Pycnometer Volume 6 I Serial no. 501 501 7 I PBV I cm3 1 992.39 I 992.39 1 8 € , X E cm3 1.58 1.58 9 PV, = line 7 + line 8 cm3 993.97 993.97

10 c,,, 1.0025 1.0025 11 I P V;, = line 9 x line 10 I cm3 996.45 996.45 Mass of Fluid 12 w, 9 2086.36 2086.06 13 wo g 1355.57 1355.57 14 M = (line 12 - line 13) x C,, 9 730.68 730.38 Density of Fluid 15 pFlp = line 14 + line 11 g/cm3 O . 7333 O . 7330 16 line 15 x 62.428 I b/f t3 45.778 45.760 17 DMF = line 16 i line í 1.0035 1.0030

~

Resu Its I I I 18 Repeatability % 0.05 19 Average DMF 1.0033 20 Previous DMF 1.0002 Remarks, Repairs, Adjustmenfs, etc.:

Figure 17-Typical Proving Report: Example 1



--`,,,,,``,`,,,`,,,`,```,-`-`,,`,,`,`,,`---

A P I MPMS*14.b 91 W 0732290 0095880 8 = 28 CHAPTER 14-NATURAL GAS FLUIDS MEASUREMENT

DENSITY METER PROVING REPORT

PiDeline: CO-, P i D e l i n e I Date: 6/18/86 ~ ~ ~

Location: Meter s t a t i o n I Report: 8 Meter No.: DT-101 I NewDMF: 1.0033

Meter Data Prover Data Serial No.: 000178 Serial No.: 501 Serial No.: Manufacturer: AP I PBV(cm3): 992.39 PBV(cm3): Model: V i b r a t i n s W" : 1355.57 i w,: Existing DMF i. 0002 I En: O. 00132 I €0:

CBW: O . 99985 1 E,: 2.88 x 10-5 I E ~ : Run 1 Run 2 Run 3

Flowing Conditions I I Observed densitv I Ib/fS 45.62 45.622 2 I Meter temperature I "F I 86.8 I 86.8 I 3 1 Pycnometer temperature 1 "F 1 86.8 I 86.8 1 4 I Pressure I psig I 1200 1200

/ Ambient temperature I "F 62 62 Volume i

I Prover serial no. I I 501 i 501 l I

5 I Prover base volume I cm3 I 992.39 I 992.39 6 Pressure correction = Ep x line 4 1.58 1.58 7 Temperature correction (C,,) = 1 + (Et x 7;) 1.0025 I 1.0025 8 PK, = (line 5 + line 6) x line 7 cm3 996.45 996.45

Weight I I I 9 Gross weight (W,) g 2086.36 2086.06

10 Tare weight in vacuo (Wo) g 1355.57 1355.57 11 Mass (M) = (line 9 - line 10) x Csw(see note) g 730.68 730.38 i

Densitv I

12 1 Test density = line 11 t line 8 I g/cm3 1 0.7333 I 0.7330 I Ib/ft3 45.759 I 45.778 13

14 Density factor = line 13 t line 1 1.0035 1.0030 15 Average density factor 1.0032

Test density = line 12 x 62.428

Note: C,, = 1 - í ~ d o ~ ~ ~ ) . Comments:

Company: Witness :

Figure 18-Typical Proving Report: Example 2



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API MPMS*14mb 91 œ 0732290 0095881 T œ

SECTION 6 ~ O N T i N U O U S DENSITY MEASUREMENT 29

Table 4-Test Equipment Required for Field Verification of Pycnometers

Specifications

instrument Range Accuracy Volume Size

Analytical balance with air shield 0-5000 g Test weights Glass thermometer As needed

Distilled water in glass container Glass-beaker water trap Vacuum pump 0-30 in Hg Stainless steel tubing Clear vacuum tubing

Vacuum manometer 0-120 tiìm Hg

0.1 g

0.2”F 1%

NíST Class P or S

7000 cm’ 250 cm’

O. 1 pm Hg” 20.250 in 20.250 in

“Ultimate vacuum.

14.6.15.6 DETERMINE THE WATER-FILLED WEIGHT

The pycnometer’s evacuated weight and air-filled weight shall be verified using the water-weigh method in accordance with the following procedure:

a. Assure that the water reservoir and the pycnometer are stabilized at room temperature before proceeding with the verification. b. Install the pycnometer on the test apparatus, as shown in Figure 22. Verify that Valve F is closed and Valve A is open. c. Evacuate air from the pycnometer and all vacuum tubing through Valve A and the inlet and outlet valves for 10 minutes. d. Open Valve F. Fill the pycnometer with distilled water from the water reservoir. When a full flow of water is ob-

Bennert-type vacuum mercury manometer

served entering the water trap, close the pycnometer’s outlet valve and then its inlet valve, followed by Valve A. e. Remove the pycnometer, and using a syringe, wash both valve openings with acetone to remove excess water. Blow dry the pycnometer with dry nitrogen. Repeat if necessary. f. Place the water-filled pycnometer on the weigh scale and record the fluid-filled weight (W,) to the nearest O. 1 gram. g. Place the pycnometer on the vacuum-emptying apparatus and empty the water from the pycnometer using the vacuum- emptying method shown in Figure 23, h. Remove the clear vacuum tubing and flush it with acetone to remove excess water. Blow dry the tubing with dry nitrogen. Repeat if necessary. i. Repeat the steps described in 14.6.15.3, Items a-d; 14.6.15.5; and 14.6.15.6, Items a-g. j. Repeat the steps described in 14.6.15.3, Items a-d.

7fL Clear Tygon tubing 1 ’/-inch stainless steel tubing



--`,,,,,``,`,,,`,,,`,```,-`-`,,`,,`,`,,`---

A P I MPMSxL4.b 9 1 0732290 0095882 1


7fL Clear Tygon tubing 1 - %-inch stainless steel tubing


Water reservoir (7000-cm3 glass container of i distilled water)

Vacuum pump

Figure 20-Deaerating the Water Reservoir (Field Verification)

14.6.15.7 VERIFY THE PYCNOMETER’S BASE VOLUME

14.6.1 5.7.1 General

pA = 0.0012[1 - (0.032h/1000)]

c,,v = 1 - (P, /Pnvr)

14.6.15.7.3 Determine the Mass of the Water

The mass of the water (M,) shall be determined using the This subsection describes the calculation method that shall be used to verify the pycnometer’s base volume (PBV). From the procedures described in 14.6.15.1 through

water-weigh verification runs:

following equation:

14.6.15.6, the following data were obtained for each of two Mfl cwf - wo)cB\V

14.6.15.7.4 Determine the Volume of the Pvcnometer at the Test Conditions a. The pycnometer’s evacuated weight (Wo).

b. The pycnometer’s air-filled weight (W,). c. The pycnometer’s fluid-filled weight (W,). d. The test temperature (Tf).

The following data must also be known:

The volume of the prover at the test conditions (PV,,) shall be determined using the following equation:

P Y p = Mfl 1 PWtp

Where: a. The elevation of the facility above sea level (h), in feet. b. The density of the test weights from the test weights’ certificate (pTWf), in grams per cubic centimeter. c. The coefficient of cubical expansion due to temperature (El) , as shown on the certificate. d. The coefficient of expansion due to pressure on the pycnometer (Ep) , as shown on the certificate. e. The datum temperature (&), in degrees Fahrenheit, as shown on the certificate.

pwlp = density of distilled, deaerated water at T, and atmospheric pressure, in grams per cubic centimeter. (pwtp can be obtained from Table 5.)

14.6.15.7.5 Determine the Pycnometer’s Base Volume

The pycnometer’s base volume (PBV) shall be determined as follows: Since P, = Pd = 14.696 pounds per square inch absolute, the equation simplifies to

14.6.15.7.2 Correct for Air Buoyancy on the Test Weights -

Where: The correction for air buoyancy on the test weights (C,,)

shall be calculated using the following equations: Td = 0.O”F.



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A P I MPMS*14.b 91 = 0732290 0095883 3 W


Water trap / Bennert-type vacuum mercury manometer

I f

Vacuum pump

Figure 21 -Evacuating the Air-Filled Pycnometer

Water beaker with


Water reservoir

I Vacuum pump

Figure 22-Vacuum Filling the Pycnometer



--`,,,,,``,`,,,`,,,`,```,-`-`,,`,,`,`,,`---

A P I MPMS*<L4.b 91 W 0732290 0095884 5 W


Outlet - I lo Bennert-type vacuum mercury manometer

/ I \ ir

?r trap Vacuum pump

Figure 23-Vacuum Emptying the Pycnometer

14.6.15.7.6 Determine the Repeatability of the Verification Test

A repeatability of at least 0.02 percent for the following values for two consecutive runs is needed to provide an acceptable verification test:

a. The pycnometer’s evacuated weight (Wo). b. The pycnometer’s air-filled weight (W,). c. The pycnometer’s base volume (PBV).

14.6.15.7.7 Compare Test Results With Certificate Values

If any of the values specified in 14.6.15.7.6 differ from the certificate values by more than 0.02 percent, the pycnometer shall be calibrated in accordance with 14.6.16. Figure 24 shows a sample calculation worksheet for field verification of a pycnometer.

14.6.16 Laboratory Calibration Procedures for Pycnometers

14.6.16.1 OBJECTIVE OF TESTS

The objective of the pycnometer calibration is to determine the following unique values:

a. The pycnometer’s air-filled weight (W,). b. The pycnometer’s evacuated weight (Wo). c. The pycnometer’s base volume (PBV). d. The coefficient of cubical expansion due to temperature on the pycnometer (E,). e. The coefficient of cubical expansion due to internal pressure on the pycnometer (Ep).

An acceptable test is determined by the repeatability of the test results for two consecutive runs.

A run consists of one evacuated weigh (Wo), one air-filled weigh (Wa), and at least three determinations of the pycnom-

eter’s volume at a datum temperature and separate test pressures (PV,).

One test pressure shall be 100 pounds per square inch absolute or less to assure adequate deaeration. A second test pressure shall be above the pycnometer’s normal operating pressure so that the prover will not be operated outside of its calibration data base. The third pressure shall be approximately halfway between the other two pressures.

A repeatability of at least 0.02 percent for the following values for two consecutive runs is needed to provide an acceptable test:

a. The pycnometer’s evacuated weight (Wo). b. The pycnometer’s air-filled weight (W,). c. The pycnometer’s volume (PV,) at the datum temperature and a pressure of 100 pounds per square inch absolute or less. d. The pycnometer’s volume (PV,) at the datum temperature and the maximum operating pressure. e. The pycnometer’s volume ( P h ) at the datum temperature and a pressure midway beteen the two pressures specified in Items c and d.

Based on the empirical data, the pycnometer’s volume at the test temperature and pressure (PV,,) shall be calculated using the following equation:

Pyp = [PBV + Ep(P, - p,)][1 + E,(T, - T,)]

The nominal E, values may be used for calibrations, provided that the manufacturer has confirmed a linear relation- ship for thermal expansion of the pycnometer. If the parties wish to confirm the nominal E, value, the test method dis- cussed in 14.6.16.9 is recommended.

14.6.16.2 TEST EQUIPMENT

The test equipment required for laboratory calibration of pycnometers is listed in Table 6.



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A P I MPMS*14.b 91 m 0732290 O095885 7 = SECTION CONTINUOUS DENSITY MEASUREMENT 33

14.6.16.3 CLEAN THE PYCNOMETER AND a. Wash the inside of the pycnometer with solvent and then with acetone to remove any residual solvent. b. Rinse the pycnometer with distilled water, and then wash with acetone to remove any residual water. c. Dry the inside of the pycnometer thoroughly by purging with dry nitrogen, and then evacuate it with a vacuum pump

CHECK THE TEST EQUIPMENT

Before a pycnometer can be certified, it must be thoroughly cleaned, and all test equipment must be calibrated or checked, in accordance with the following procedure:

Table 5-Atmospheric Water Density as a Function of Temperature

Water Water Water Temperature Temperature Temperature

Density Density Density O F "C ídem') "F OC ídcm3) O F "C ídcm3)

70.00 70.10 70.20 70.30 70.40 70.50 70.60 70.70 70.80 70.90

71.00 71.10 7 1.20 71.30 71.40 71.50 71.60 71.70 71.80 71.90

72.00 72.10 72.20 72.30 72.40 72.50 72.60 72.70 72.80 72.90

73.00 73.10 73.20 73.30 73.40 73.50 73.60 73.70 73.80 73.90

74.00 74.10 74.20 74.30 74.40 74.50 74.60 74.70 74.80 74.90

75.00

21.11 21.17 21.22 21.28 21.33 21.39 21.44 21.50 21.56 21.61

21.67 2 1.72 21.78 21.83 21.89 21.94 22.00 22.06 22.11 22.17

22.22 22.28 22.33 22.39 22.44 22.50 22.56 22.61 22.67 22.72

22.78 22.83 22.89 22.94 23.00 23.06 23.11 23.17 23.22 23.28

23.33 23.39 23.44 23.50 23.56 23.61 23.67 23.72 23.78 23.83

23.89

0.9979661 0.9979539 0.9979418 0.9979296 0.9979174 0.997905 1 0.9978929 0.9978805 0.9978682 0.9978558

0.9978434 0.9978310 0.9978185 0.9978060 0.9977935 0.9977809 0.9977683 0.9977557 0.9977430 0.9977303

0.9977 176 0.9977049 0.9976921 0.9976793 0.9976664 0.9976536 0.9976407 0.9976277 0.9976148 0.9976018

0.9975887 0.9975757 0.9975626 0.9975495 0.9975363 0.9975232 0.9975099 0.9974967 0.9974834 0.9974701

0.9974568 0.9974434 0.9974300 0.9974166 0.9974032 0.9973897 0.9973762 0.9973626 0.9973491 0.9973355

0.9973218

75.00 75.10 75.20 75.30 75.40 75.50 75.60 75.70 75.80 75.90

76.0iJ 76.10 76.20 76.30 76.40 76.50 76.60 76.70 76.80 76.90

77.00 77.10 77.20 77.30 77.40 77.50 77.60 77.70 77.80 77.90

78.00 78.10 78.20 78.30 78.40 78.50 78.60 78.70 78.80 78.90

79.00 79.10 79.20 79.30 79.40 79.50 79.60 79.70 79.80 79.90

80.00

23.89 23.94 24.00 24.06 24.11 24.17 24.22 24.28 24.33 24.39

24.44 24.50 24.56 24.61 24.67 24.72 24.78 24.83 24.89 24.94

25.00 25.06 25.11 25.17 25.22 25.28 25.33 25.39 25.44 25.50

25.56 25.61 25.67 25.72 25.78 25.83 25.89 25.94 26.00 26.06

26.11 26.17 26.22 26.28 26-33 26.39 26.44 26.50 26.56 26.61

26.67

0.9973218 0.9973082 0.9972945 0.9972807 0.9972670 0.9972532 0.9972394 0.9972256 0.99721 17 0.9971978

0.9971838 0.9971699 0.9971559 0.9971419 0.9971278 0.9971í37 0.9970996 0.9970855 0.9970713 0.9970571

0.9970429 0.9970286 0.9970144 0.9970000 0.9969857 0.9969713 0.9969569 0.9969425 0.9969280 0.9969135

0.9968990 0.9968845 0.9968699 0.9968553 0.9968406 0.9968260 0.9968113 0.9967966 0.9967818 0.9967670

0.9967522 0.9967374 0.9967225 0.9967076 0.9966927 0.9966777 0.9966628 0.9966477 0.9966327 0.9966176

0.9966025

80.00 80.10 80.20 80.30 80.40 80.50 80.60 80.70 80.80 80.90

81.00 81.10 8 1.20 8 1.30 8 1.40 81.50 81.60 81.70 81.80 81.90

82.00 82.10 82.20 82.30 82.40 82.50 82.60 82.70 82.80 82.90

83.00 83.10 83.20 83.30 83.40 83.50 83.60 83.70 83.80 83.90

84.00 84.10 84.20 84.30 84.40 84.50 84.60 84.70 84.80 84.90

85.00

26.67 26.72 26.78 26.83 26.89 26.94 27.00 27.06 27.11 27.17

27.22 27.28 27.33 27.39 27.44 27.50 27.56 27.61 27.67 27.72

27.76 27.83 27.89 27.94 28.00 28.06 28.11 28.17 28.22 28.28

28.33 28.39 28.44 28.58 28.56 28.61 28.67 28.72 28.78 28.83

28.89 28.94 29.00 29.06 29.11 29.17 29.22 29.28 29.33 29.39

29.44

0.9966025 0.9965874 0.9965723 0.9965571 0.9965419 0.9965266 0.9965 114 0.9964961 0.9964808 0.9964654

0.9964500 0.9964346 0.9964192 0.9964037 0.9963882 0.9963727 0.9963571 0.9963416 0.9963260 0.9963103

0.9962947 0.9962790 0.9962633 0.9962475 0.99623 17 0.9962159 0.9962001 0.9961843 0.9961684 0.9961525

0.9961365 0.9961206 0.9961046 0.9960885 0.9960725 0.9960564 0.9960403 0.9960242 0.9960080 0.9959918

0.9959756 0.9959594 0.9959431 0.9959268 0.9959105 0.9958941 0.9958777 0.9958613 0.9958449 0.9958284

0.9958119



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API MPMS*LY*b 71 0732270 0075886 7


CALCULATION WORKSHEET

13 Test vs. Certificate No. 702C

W O 1350.85 1350.83 o. 001% w, 1352.05 1351.97 O. 006%

o. 001% PBV 995.43 , 995.44 I

Figure 24-Field Verification Form

for 10 minutes. Close the inlet valve. (The pycnometer is probably not yet fully evacuated.) d. Wash the outside of the pycnometer with distilled water, and then rinse with acetone. Blow dry the outside of the pycnometer. e. Verify the calibration of the pressure transmitters with a deadweight tester. f. Verify the calibration of the digital thermometer with a certified thermometer by placing both in a beaker of water to assure agreement within 0.2"F. g. Conduct all weigh tests without field or laboratory fittings. Conduct weigh tests on pycnometers equipped only with valves. The removal of all fittings accomplishes two goals:

1. The pycnometer's base volume is established without any fittings.

2. Entrapment of air and water by the fittings is elimi- nated.

f. Calibrate the weigh scale with the NIST Class P or S apparent mass standards.

14.6.16.4 VACUUM FILL AND DEAERATE THE WATER RESERVOIR

The water reservoir shall be vacuum filled and deaerated in accordance with the following procedure:

a. Set up the test apparatus as shown in Figure 25. b. Close Valve A and pull a vacuum on the system. The water will be displaced from the 1-gallon container to the water reservoir.



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l SECTION 6-CONTINUOUS DENSITY MEASUREMENT 35

Table 6-Test Equipment for Laboratory Calibration of Pycnometers

Specifications

Instrument Range Accuracy Volume Size

Analytical balance with air shield Stainless steel fest weights Digital thermometer Glass thermometer Bennert-type vacuum manometer Pressure transmitter 1 Pressure transmitter 2 LED display 1 LED display 2 Deadweight tester Distilled water reservoir

(clear glass container) Water trap (clear glass beaker) Water cushion cylindefl Vacuum pump Stainless steel tubing Clear vacuum tubing

Required Equipment

0-5000 g fO.O1 g 50-5000 g As needed fO.l°F As needed M.I°F 0-120 mm 1 % 0-500 psig 0.25%" 0-3000 psig 0.25C/o3 15-515 psia 15-3015 psia

NIST Class P or S

0-3000 psig 0.101 5 gal

7000 cm3 250 cm3

O. 1 p n HgC 90 Ilmin 20.250 in 20.250 in

Optional Equipment (for Determinations of E,) Temperature bathd f 5 8 T Gear pump 0-6 gpm Rotameter 0-6 gpm

aWith LED display. bMaximum allowable working pressure of 3000 pounds per square inch gauge. cultirnate vacuum. dThe bath shall have a stability of 3Al.l°F. eFrom ambient temperature.

Bennett-type vacuum mercury manometer Digital Clear Tygon tubing 9 thermometer 7

%-inch stainless steel tubing

5-gallon container of

Water reservoir

Figure 25-Vacuum Filling the Water Reservoir (Laboratory Calibration)



--`,,,,,``,`,,,`,,,`,```,-`-`,,`,,`,`,,`---

A P I M P M S * l 4 - b 91 œ 0732290 0095888 2 œ


c. When enough water has been displaced, turn off the vacuum pump. d. Set up the test apparatus as shown in Figure 26. e. Close Valve A. Deaerate the distilled water by pulling a vacuum on the water reservoir, as shown in Figure 26, until all air bubbles have ceased. Close Valve E f. Before proceeding with the calibration, assure that the temperature of the water reservoir and the pycnometer has stabilized. The water reservoir need not be stabilized at room temperature, but the water temperature should approximate room temperature.

14.6.16.5 DETERMINE THE EVACUATED AND AIR-FILLED WEIGHT

The pycnometer’s evacuated weight (Wo) and air-filled weight (W,) shall be determined in accordance with the following procedure:

a. Evacuate the pycnometer with the vacuum pump to at least 29.0 inches of mercury for 2 minutes, as shown in Fig- ure 27. b. Place the evacuated pycnometer on the weigh scale and record the evacuated weight (Wo) to the nearest 0.01 gram. c. Repeat the steps described in Items a and b above until two successive weighings for Wo agree within 0.02 percent. Record the last Wo reading. d. Open the inlet valve and allow air to enter. After 30 seconds, weigh the pycnometer and record the air-filled weight (W,) to the nearest 0.01 gram.

14.6.16.6 VACUUM FILL THE PYCNOMETER The pycnometer shall be vacuum filled in accordance with

the following procedure: a. Install the pycnometer on the test apparatus, as shown in Figure 28. b. Evacuate air from the pycnometer and all stainless steel and vacuum tubing through Valves A and D for 10 minutes. Make sure that Valve B is closed. c. Open Valve F and fill the pycnometer with distilled water from the water reservoir. When a full flow of water is observed entering the water trap, close the pycnometer’s outlet valve and Valve A. Open Valve B. d. Pressure the system to 100 pounds per square inch absolute below the set point of the rupture disk. Check for leakage.

14.6.16.7 CALIBRATE USING THE WATER- WEIGH METHOD

The pycnometer’s water-filled weight shall be verified using the water-weigh method in accordance with the following procedure:

a. Adjust the pressure to the desired setting. Close the pycnometer’s inlet valve and ensure that the pressure has not risen. If it has risen, open the pycnometer’s inlet valve, adjust the pressure accordingly, and then close the valve. b. When the pressure is correct, close Valve D. c. Record the water reservoir’s temperature, as indicated by the digital thermometer, to the nearest O. 1°F.


n

(glass container of distilled water)

7fL Clear Tygon tubing

%-inch stainless steel tubing

Figure 26-Deaerating the Water Reservoir (Laboratory Calibration)



--`,,,,,``,`,,,`,,,`,```,-`-`,,`,,`,`,,`---

Point 1

manometer

Valve D

Valve A

U

Valve 0

Valve C

thermometer 9 Valve F *

O

A P I MPMS*i(/4.b 91 9 0732290 0095889 4 9


'/-inch stainless steel tubing

i Figure 27-Vacuum Emptying the Pycnometer

U 7- Water trap (4000 cm3)

Weigh scale with air shield

Water reservoir íalass container of

Vacuum pump

7fL Clear Tygon tubing

'/-inch stainless steel tubing

Figure 28-Pycnometer Calibration Test Apparatus



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A P I MPMS*14-b 9 1 0732290 0095890 O W

38 CHAPTER 14-NATURAL GAS FLUIDS MEASUREMENT -

d. Remove the pycnometer, and using a syringe, wash both the inlet and outlet valve openings with acetone to remove excess water. Blow dry the openings with nitrogen. e. Place the water-filled pycnometer on the weigh scale and record the fluid-filled weight (W,) to the nearest 0.01 gram. f. Remove the section of test tubing and flush it with acetone to remove excess water. Blow dry the tubing with nitrogen. Wash the exposed portion of Valve D with acetone. Blow dry the valve with nitrogen. Repeat if necessary. g. Reinstall the test tubing and the pycnometer on the test apparatus as shown in Figure 29. Open Valve G. h. Evacuate air between Valve D and the pycnometer’s inlet valve through Valve G for 5 minutes. Close Valve B. Open Valves A and D. After a full flow of water enters the water trap, close Valves G and A. Open Valve B. i. Open the pycnometer’s inlet valve. j. Repeat the steps described in 14.6.16.6 and 14.6.16.7, Items a-i, until at least three test weights have been recorded at three different pressures. Record the room air temperature to the nearest O. 1°F. (This completes the first run.)

Point I

Valve E

Valve C

Note: A successful calibration run requires that the temperature of the water reservoir not vary by more than 1 .O”F during the run.

k. Place the pycnometer on the vacuum-emptying apparatus, and empty the water from the pycnometer using the vacuum empyting method, as shown in Figure 27. 1. Repeat the steps described in 14.6.16.3, Items b and c; 14.6.16.5; 14.6.16.6; and 14.6.16.7, Items a-j. (This completes the second run.)

14.6.16.8 CALCULATE THE TEST RESULTS

The test results shall be calculated in accordance with the tolerances given in the example shown in Figure 30. Because of the complexity of the equations, all calculations should be performed with the aid of a personal computer.

14.6.16.9 DETERMINE THE PYCNOMETER’S Et The pycnometer’s thermal expansion factor (E,) should be

supplied by the manufacturer. However, if the pycnometer’s

(text continued on page 47)

Vacuum manometer

h I

Valve A

7 Water trap (4000 cm3 )

7 r l Weigh scale with

air shield

Water reservoir (glass container of distilled, deaerated \ water)

Vacuum pump

7fL Clear Tygon tubing l- %-inch stainless steel tubing

d Figure 29-Reinstallation of Test Tubing



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API MPMS*14.6 71 m 0732290 0075891 2 m


PYCNOMETER CERTIFICATE Page 1 of 8

Date: F e b r u a r y 24, 1 9 8 6 Certificate No.: wErGH1

Ownership: MPMS C h a p t e r 1 4 . 6

Pvcnometer Data

Serial no.: 2 O 6

Manufacturer:

Steel type: S t a i n l e s s , Type 304 Rupture disk pressure: 1800 psig

Thermal coefficient (€J: 2 .88 x

Prover type: S i n g l e s p h e r e

Maximum allowable working pressure: 1900 ps ig

Calibration System Data

Thermometer Scale

Type: D i g i t a l Type: E l e c t r o n i c

Manufacturer: Manufacturer:

Model: Model:

Range: O" F-150" F

Accuracy: O . lo F

Range: 0-5500 g

Accuracy: o . o1 g

Transmitters Certified Test Weights

Type: C a p a c i t a n c e Steel type: S t a i n l e s s

Manufacturer: pWr: 8 . 0 0 g / c m 3

Model: pTW( 7 . 8 4 g/cm3

Range 1 : 0-500 p s i g

Range 2: 0-3000 ps ig

Accuracy: O . 2 5 %

Elevation: 50 ft

NIST Class: P

Deadweight Tester

Manufacturer:

Model:

Range: 0-3500 ps ig

Accuracy: o . 10%

Comments:

Figure 30-Typical Pycnometer Certificate and Calibration Calculations



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A P I MPMS*14.b 71 0732290 0075892 4 = 40 CHAPTER 14-NATURAL GAS FLUIDS MEASUREMENT


Date: February 24, 1986 I Certificate NO.: WEIGH1

Serial No.: 206

Pycnometer Calibration Summary

I Average W,: 1365.32 g (o. 004%) I Average K: 1366.46 g (0.003%)

I PV, (cm3)

-1 Test A vs. Test B Test B Repeatability (%)

Pressure (Psi4 PV, (cm3) Test A

25 25 I NA NA NA

996.63 O. 003

NA

996.60 50 I 996.62 50

100 NA NA I NA 100 I NA

200 996.74 996.77 + 996.80 0.006

NA NA 1 5 300 NA

400 NA 400 I NA

5 0 0 500 I NA NA NA

NA NA

NA

NA 600 1 NA 600 p 13

NA 700 I NA 700

800 997.50 + 997.47 997.53 0.006

NA NA 900 NA

1000 997.75 997.76 I o. 001 1000 1 997.76

1100 NA NA NA

NA NA

19

1200 NA

1300 I NA 1300

1400

NA

NA + 998.38

NA NA

998.39 O. 003 1500 998.36

1600 I NA 1600

1700

NA

NA

NA

NA

NA

NA

NA

NA

1800

1900 1900 I NA NA NA

NA NA 2000

2100 NA I NA I 2200 I NA 2200

2300 NA I 2300 1 NA

~~

Figure 30-Continued



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A P I MPMS* l i4 -b 91 0732290 0095893 b W



Date: February 24, 1986 I Seriai NO.: 206 _ _ _ _ _ _ ~

Pycnometer Calibration Summary (Continued)

PV, (cm3)

Weigh Pressure Test A vs. Test B No. (Psial Test A Test B Repeatability (%)

26 2400 NA NA NA

27 I 2500 I NA I NA I NA

28 2600 NA NA NA

29 2700 NA NA NA

30 I 2800 I NA I NA I NA ~~ ~

3 1 2900 NA NA NA

Pressure ( P W 2400

2500

2600

2700

2800

2900

PV, (cm3)

NA

NA

NA

NA

NA

NA

Using the least-squares method, the prover volume can be calculated as follows:

pv, = [pBv + Ep(F - pd)][1 + E,(T - Td)]

= [996.54 + O.O0122(P, - Pd)][l -i O.O00028S(T, - Td)]

Comments:

Name I Name

Company Company

~

Figure 30- Continued



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.. - -

A P I MPMS*14.6 9 1 W 0732290 0 0 9 5 8 9 4 8

42 CHAPTER 1 4-NATURAL GAS FLUIDS MEASUREMENT

PYCNOMETER CERTIFICATE Page 4 of 8 I ~ ~~ ~ ~ ~~ ~~

Date: February 24, 1986 Serial No.: 206

Water-Weigh Calibration Method-Test A Data

wo:1365.29 g wa:1366.44 g

Water Data Dry Air Data

I Average 7;: 76.4OF (24.64OC) I 7;: 79.0°F (26.11OC)

pw,: O. 9971334 g/cm3 P A : O . 00118 g/cm3

K,,: 3.12 X cRw: 1.001037

2 I 50 I 76.1 1 2360.30 I 996.04 1 0.9972424 I 998.79 I 996.60

3 100 NA O. 9973979 NA NA

4 200 76.3 2360.90 996.64 O. 9977083 998.93 996.74

5 300 NA O. 9980181 NA NA

6 400 NA O. 9983273 NA NA

7 500 NA O. 9986357 NA NA

Figure 30-Continued



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A P I M P M S * l 4 * b 91 W 0732290 0095895 T

SECTION GCONTINUOUS DENSITY MEASUREMENT 43

PYCNOMETER CERTIFICATE Page 5 of 8 ~ ~~~~

Date: February 24, 1986 Serial No.: 206

Water-Weigh Calibration Method-Test A Data (Continued)

I I I I i i i

31 2900 NA 1.0058509 NA NA

Comments:

Water-Weigh Calibration Method-Test B Data

Wk1365.35 q I w,: 1366.48 q Water Data 1 Dry Air Data

Average 7;: 77. OF (25.27O c) I 7;: 77.0°F (25.OO0C)

pwt: O. 9969742 g/cm3 I PA: 0.00118 g/cm3

K,,: 3.12 X I cBw: 1.001037 Weigh

No.

1

2

3

4

5

6

7

8

9

10

11

O. 9987811

700 NA O. 9990878 NA NA

800 77.5 2363.46 999.15 O. 9993937 999.76 997.53

900 NA O. 9996992 NA NA ..

Figure 30-Continued



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_ _ _ -. -_ - - -

A P I M P M S * l 4 - b 91 0732290 0 0 9 5 8 9 b L


PYCNOMETER CERTIFICATE Page 6 of 8 ~~ ~ ~ ~

Date: F e b r u a r y 24, 1986 Serial No.: 206

Water-Weigh Calibration Method-Test B Data (Continued)

13 1 1100 1 I I NA 1 1.0003079 1 NA 1 NA

14 1200 NA 1.0006111 NA NA

15 1300 NA 1.0009140 NA NA

16 1400 NA 1.0012163 NA NA __ ~ ~ _ _ ~ ~ ~

17 1500 77.4 2366.45 1002.14 1.0015179 1000.62 998.39

18 1600 NA 1.0018185 NA NA

19 I 1700 I I I NA I 1.0021189 I NA I NA ~ 1 NA I 1.0024187 I NA NA

21 I 1900 I I I NA I 1.0027178 I NA I NA 22 2000 NA 1.0030163 NA NA

23 2100 NA 1.0033143 NA NA

24 I 2200 I I I NA I 1.0036115 I NA I NA 25 2300 NA 1.0039082 NA NA

26 2400 NA 1.0042050 NA NA

27 2500 NA 1.0045004 NA NA

28 2600 NA 1.0047953 NA NA

29 2700 NA 1.0050895 NA NA

30 2800 NA 1.0053839 NA NA

31 2900 NA 1.0056769 NA NA

Comments:

Figure 30-Continued



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A P I MPMS*LV.b 91 = 0732290 0095897 3 W



Definitions of Symbols

C,, = correction for air buoyancy on weighings

- - - o‘oo12/PTWr)(1 - PA’PTWf) (1 - 0.0012/PTw,)(1 - PA’PFtp) *

C,,, = correction for expansion due to temperature on steel pycnometer

E,, = coefficient of expansion due to internal pressure on pycnometer.

E, = coefficient of cubical expansion due to temperature on steel pycnometer

= 2.88 x 1 O” for Type 304 stainless steel (nominal) = 2.65 x for Type 31 6 stainless steel (nominal) = 1.86 x 1 O” for carbon steel (nominal).

h = elevation of weigh scale above sea level

= 1 + (T, - Td)(Et).

K, = isothermal compressibility of water at 74.696 psia and T,, in degrees Celsius

= [50.88496 + (6.163813 x lO-’)(q) + (1.459187 x IO“)(T,‘)

+ (20.08438 x IO“)(T3) - (58.4772 x 10”)(T,4) + (410.411 x 10-”)(T,5)]

x {[I + (19.67348 x lO”)(T,)](14.50377 x IO‘)}. KIP = average isothermal compressibility of water at pt and T,

= Kt{1.00033 - [(0.217656 x Io4)(Pf f Pd)/2] f (0.8546265 x iO”)[(e + pd)/2]‘}.

M = mass of fluid in pycnometer

Pd = datum pressure of pycnometer (14.696 psia).

pt = test pressure.

= (W - ~ o ) ( c B w ) *

PBV = pycnometer base volume.

PVp = pycnometer volume at datum temperature and test pressure

PVw = pycnometer volume at test temperature and test pressure

= PV~/CTS,.

= M/PWip.

Td = datum temperature of pycnometer.

T, = test temperature.

W, = weight of fluid- filled pycnometer.

Wo = weight of pycnometer with all air evacuated

pA = density of dry air = 0.00122[1 - 0.032(h/l000)][520/(T, + 460)].

Figure 30-Continued



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~ . . _. -

A P I MPMS*14.b 91 0732270 0095878 5

46 CHAPTER 1 &NATURAL GAS FLUIDS MEASUREMENT


Definitions of Symbols

pmt = density of field or scale test weights from test weights' certificate = 7.84 g / cm3 for stainless steel test weights (nominal) = 8.3909 g/cm3 for brass test weights (nominal).

pTWr = density of reference test weights from test weights' certificate = 8.00 g / cm3 for reference test weights (nominal) = 8.3909 g/cm3 for brass test weights (nominal).

pw, = density of water at test temperature (in degrees Celsius) and standard atmospheric pressure, as determined from Chapter 1 1.2.3 (Wagenbreth water equation)

- 0.000001 12671 3526T4 + 0.000000006591 795606T5) / 1000.

pwlp = density of water inside pycnometer at test temperature and test pressure

= (999.8395639 + 0.06798299989T - 0.0091 O6025564Tf2 + 0.0001 005272999T3

= Pwt 111 - [(i7,,)(p, - P,)ll.

Comments:

Figure 30-Continued



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API MPMS*K14.b 91 0732290 0095879 7


nominal Et cannot be substantiated by the manufacturer, tests may be conducted to determine the thermal expansion of the pycnometer (see Figure 3 1). A minimum of two temperature tests shall be conducted at least 40°F apart.

Calibration and calculation procedures are purposely not included for the Et determination test. The E, for each manufacturer's pycnometers should not change as long as the materials used remain consistent in their thermal expansion properties.

14.6.17 Density of Water 14.6.17.1 GENERAL

The density of a liquid decreases with increasing temperature and, to a much lesser degree, increases with increasing pressure. The density of deaerated, distilled water can therefore be expressed as a function of temperature and pressure.

14.6.17.2 WATER DENSITY AT TEST TEMPERATURE AND PRESSURE

Assuming that the change in density is small compared with the original density, the following equation can be used to calculate water density at the test pressure and temperature. The application of the equation is limited to a temperature range of 32OF-125"F and a pressure range of 14.696- 3000 pounds per square inch absolute.

Pd = datumpressure = 14.696 pounds per square inch absolute.

The accuracy associated with this equation is limited by the following factors:

a. The accuracy of the reference water density, pwt, over the test conditions. b. The accuracy associated with calculating the average isothermal compressibility of water, z,, at the test conditions. c. The use of only distilled, deaerated water.

14.6.17.3 REFERENCE WATER DENSITY (pwt)

In Chapter 11, Section 2.3, the Wagenbreth water density equation is used to determine the water density at the test temperature and standard atmospheric pressure. The Wagen- breth equation expresses the mass density, in grams per cubic centimeter, as a function of temperature at 14.696 pounds per square inch absolute as follows:

pwt = r(9.998395639 x lo2) + (6.798299989 x lO")(T,)

- (9.106025564 x

+ (1.005272999 x IO")(T:)

- (1.126713526 x lO")(Tp)

+ (6.591795606 x i04)(q5)]/ 1000

P W , , = Pw, /[i - q p , - 411 Where:

Where: = test temperature, in degrees Celsius.

pWrp = water density at the test temperature and pressure. fiv, = water density at the test temperature and Pa KIP = average isothermal compressibility of water at the

Several water density equations exist, but only slightly different values are obtained from them. Using the Wagen- breth equation, at 60°F (15.6"C) and 14.696 pounds per square inch absolute (101.325 kilopascals), the density of water is as follows:

test conditions. Pf = test pressure.

18 Temperature bath with coiled tubing

I

Pycnometer

Note: All flowing tubing, all valves, and the pycnometer shall be insulated to maintain a stable temperature.

Figure 31-Optional Et Test Apparatus



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A P I MPMS*KLg-b 7 1 0732270 0075900 T m

48 CHAPTER NATURAL GAS FLUIDS MEASUREMENT

pw, = 62.3660 pounds per cubic foot = O. 9990 12 1 gram per cubic centimeter

At 68°F (20.0"C) and 14.696 pounds per square inch absolute (101.325 kilopascals), the density of water is as follows:

pw, = 62.31572 pounds per cubic foot = 0.9982019 gram per cubic centimeter

14.6.17.4 AVERAGE ISOTHERMAL COMPRESSIBILITY OF WATER (K,)

Although liquids are not normally considered to be compressible, a correction for water compressibility as a function of pressure and temperature must be applied to achieve an acceptable accuracy. Enough data exist to determine the average isothermal compressibility of water. This standard uses the following equation:

iTiP = K,(1.00033 - [(2.17656 x 10-5)(Pf - Pd)/2]

+ ((8.546265 x 10-'o)[(Pf + Pd)/2I2))

Pf = test pressure, in pounds per square inch absolute. Pd = datum pressure

K, = isothermal compressibility of water at a pressure of 14.696 pounds per square inch absolute and the test temperature.

The effect of pressure on the isothermal compressibility of water has been calculated by curve-fitting the compressibility of water as a function of pressure at 68°F (20°C). To calculate the isothermal compressibility of water at 14.696 pounds per square inch absolute and the test temperature, K,, Kell's equation was adopted:

Where:

= 14.696 pounds per square inch absolute.

K, = [50.88496 + (6.163813 x 10-')(Tf)

+ (1.459187 x 10-3)(Tf) + (20.08438 x lO")(T:)

- (58.4772 x 10-9)(Tp) + (410.41 1 x lO-'*)(T;5)]

+ {[i + (19.67348 x 10-3)(Tf)](14.50377 x lo6))

Where:

Tf = test temperature, in degrees Celsius.

Several calculated values for KI and K,, are given in Table 7.

14.6.17.5 UNCERTAINTY ANALYSIS

Within the temperature and pressure limitations defined in 14.6.17.2, the predicted water density is estimated to be within kO.01 percent of the true value. A comparison of Kell's experimental water densities with the predicted values confirms the stated uncertainty (see Table 8).

14.6.1 8 Density of Air 14.6.18.1 GENERAL

The density of air is a term in the equation for the correction for air buoyancy on weighings (Csw; see 14.6.6.5) and is also used to verify the field Wo. Although the density of moist air is less than that of dry air (see GPA 2143, all calculations shall use dry air density. As shown below, a sensitivity analysis indicates that the error resulting from the use of dry air density is well within the accuracy of this standard.

14.6.18.2 DRY AIR DENSITY

14.6.1 8.2.1 For laboratory calibrations of pycnometers, dry air density shall be calculated using the following equations. In U.S. units,

Table 7-Predicted Water Density

George S. Kell Isothermal

Compressibility of Water Water at 14.696 psia

Pressure Temperature (K,) Wagenbreth MPMS 14.6

psia bar OC "F 106/bar I/psi Ktp (lípsi) PW, (dcm3) pWip (g/cm3)

77 5.30 0.00 20.00 50.00

611 42.11 0.00 20.00 50.00

1465 101.01 0.00 20.00 50.00

3050 210.28 0.00 20.00 50.00

32.0 68.0

122.0

32.0 68.0

122.0

32.0 68.0

122.0

32.0 68.0

122.0

50.8850 45.8918 44.1732

50.8850 45.8918 44.1732

50.8850 45.89 18 44.1732

50.8850 45.8918 44.1715

3.5084 x 3.1641 x 3.0456 x

3.5084 x 3.1641 x 3.0456 x

3.5084 x 3.1641 x 3.0456 x

3.5084 x 3.1641 x 3.0455 x

3.5061 x 10" 3 . 1 6 2 0 ~ 3.0436 x

3.4860 x 3.1439 x l u 6 3.0262 x 3.4548 x 3.1 158 x 2.9991 x

3.4000 x 3.0663 x 2.95 14 x

0.999840 0.998202 0.988058

0.999840 0.998202 0.988058

0.999840 0.998202 0.988058

0.999840 0.998202 0.988060

1 .O00058 0.998398 0.988245

1.0019 17 1 .O00072 0.989840

1.004849 1.0027 13 0.992355

1 .O 10 157 1.007492 0.9969 1 I



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A P I f lPMS*L4*b 9 3 m 0732290 0095903 L W


Table 8-Experimental Versus Predicted Water Density

Water Pressure Temperature Predicted Experimental

MPMS 14.6 George S. Kell Residual, e (e/Kell) x 100 psia bar O C "F p\vtvlp ( d c d pWlp ( d d Well -MI) (%)

77 5.30 0.00 32.0 1.000058 1.000118 0.000060 0.006 20.00 68.0 0.998398 O. 9 9 8 4 O 6 0.000008 0.001 50.00 122.0 0.988245 0.988223 -0.000022 -0.002

611 42.11 0.00 32.0 1.001917 1.001979 0.000062 0.006 20.00 68.0 1.000072 1 .oooO83 o.oo0011 0.001 50.00 122.0 0.989840 0.989822 -0.oooO18 -0.002

1465 101.01 0.00 32.0 1.004849 1.004936 0.000087 0.009 20.00 68.0 1.002713 1 .O02742 0.000029 0.003 50.00 122.0 0.992355 0.99235 1 -0.000004 -0.000

3050 210.28 0.00 32.0 1.010157 1.010323 0.000166 0.016 20.00 68.0 1.007492 1.007606 0.000114 0.01 1 50.00 122.0 0.996911 0.996976 0.000065 0.007

pA = 0.0012[1 - (0.032h/1000)][520/(Tf + 460)] 14.6.18.4 SENSITIVITY ANALYSIS In SI units, 14.6.1 8.4.1 General

Although the density of moist air is slightly less than that of dry air, a sensitvity analysis indicates that the amount of pA = 0.0012[1 - (0.105h/1000)][520/(1.8T, + 492)]

Where: errorresulting from the use-of the dry air value is beyond the attainable accuracy.

14.6.1 8.4.2 Example

given:

pA = dry air density, in grams per cubic centimeter. h = elevation above sea level, in feet (meters). TI = dry air temperature, in degrees Fahrenheit (degrees

Celsius). Consider the following example. The following data are

14.6.1 8.2.2 For density meter provings and field verification tests, dry air density shall be calculated using the following eauations. In U.S. units.

pFlp = 0.3000 gram per cubic centimeter. h = 50feet. T, = 68°F.

U I

pA = 0.0012[1 - (0.032h/1000)]

In SI units,

pA = 0,0012[1 - (0.105h / lOOO)]

B = 750 millimeters. pnvr = 8.00 grams per cubic centimeter (reference test

pnvf = 7.84 grams per cubic centimeter (stainless steel weights).

test weights). Where: Dewpoint = 50'F.

The dry air density is calculated as follows: pA = dry air density, in grams per cubic centimeter. ti = elevation above sea level, in feet (meters). pA = 0.0012(1 - [(0.032)(50)/ 1000])(0.984849)

= 0.001 18 gram per cubic centimeter

14.6.18.3 MOIST AIR DENSITY The moist air density is calculated as follows: Converting the air temperature from degrees Fahrenheit to degrees Cel- sius, Moist air density can be calculated using the following

equation:

PA = [0.0012929(273.13 / T,)][(B - 0.3783e) / 7601

Where:

T, = (5/9)(Tf - 32) = (5/9)(68 - 32) = 20

pA = moist air density, in grams per cubic centimeter. Tf = air temperature, in kelvins. B = barometric pressure, in millimeters of mercury. e = moist air vapor pressure, in millimeters of mercury.

Where:

T, = air temperature, in degrees Celsius. Tf = air temperature, in degrees Fahrenheit.



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_ _ A P I M P M S * 1 4 - b 91 0732290 0095902 3


Converting the air temperature from degrees Celsius to kelvins,

Tk = T, + 273.15 = 20 + 273.15 = 293.15

Where:

Tk = air temperature, in kelvins. T, = air temperature, in degrees Celsius.

Converting the dewpoint from degrees Fahrenheit to degrees Celsius,

T, = (5/9)(Tf - 32)

= (5/9)(50 - 32) = 10

Using the appropriate value for 0.3783e from the CRC Handbook of Chemistìy and Physics' (3.48 at a dewpoint of lO"C), the moist air density is calculated as follows:

'R. C . Weast (Ed.), CRC Handbook of Chemistry and Physics (69th ed.), CRC Press, Boca Raton, Florida, 1988.

pA = [0.0012929(273.13 / 293.15)][(750 - 3.48) / 7601 = 0.00118

Then for dry air,

CBw = 1.003801

And for moist air,

CBW = 1.003801

Since the results are exactly the same when rounded to six decimal places, the error in using the dry air density is beyond the accuracy attainable by this standard.

14.6.19 Bibliography J. D. Parker, J. H. Boggs, and E. E Blick (Eds.), Introduction

to Fluid Mechanics and Heat Transfer (3rd ed.), Addison- Wesley, Reading, Massachusetts, 1974.

P. E. Pontius, Mass and Mass Values, National Bureau of Standards, Washington, D.C., January 1984.

H. Colijn, Weighing and Proportioning of Bulk Solids (2nd ed.), Trans Tech Publications, Brookfield, Vermont, 1983.

Metals Handbook (Desk ed.), American Society for Metals, Metals Park, Ohio, 1985.



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A P I M P M S * l Y e b 91 H 0732290 0095903 5

APPENDIX-PRECAUTIONARY INFORMATION

A.1 Physical Characteristics and Fire Considerations

A.l .I Personnel involved in the handling of petroleum-related substances (and other chemical materials) should be familiar with their physical and chemical characteristics, including potential for fire, explosion, and reactivity, and appropriate emergency procedures. These procedures should comply with the individual company's safe operating prac- tices and local, state, and federal regulations, including those covering the use of proper protective clothing and equipment. Personnel should be alert to avoid potential sources of ignition and should keep the materials' containers cIosed when not in use.

A.1.2 API Publication 2217 and Publication 2026 and any applicable regulations should be consulted when sampling requires entry into confined spaces.

A.1.3 INFORMATION REGARDING PARTICULAR MATERIALS AND CONDITIONS SHOULD BE OB- TAINED FROM THE EMPLOYER, THE MANUFAC- TURER OR SUPPLIER OF THAT MATERIAL, OR THE MATERIAL SAFETY DATA SHEET.

A.2 Safety and Health Considerations A.2.1 GENERAL A.2.1.1 Potential health effects can result from exposure to any chemical and are dependent on the toxicity of the chemical, concentration, and length of the exposure. Every- one should minimize his or her exposure to workplace chemicals. The following general precautions are suggested:

a. Minimize skin and eye contact and breathing of vapors. b. Keep chemicals away from the mouth; they can be harm- ful or fatal if swallowed or aspirated.

c. Keep containers closed when not in use. d. Keep work areas as clean as possible and well ventilated. e. Clean up spills promptly and in accordance with pertinent safety, health, and environmental regulations. f. Observe established exposure limits and use proper protective clothing and equipment.

Information on exposure limits can be found by consulting the most recent editions of the Occupational Safety and Health Standards, 29 Code of Federal Regidations Sections 1910.1000 and following and the ACGIH publication Threshold Limit Values for Chemical Substances and Phys- ical Agents in the Work Environment.

A.2.1.2 INFORMATION CONCERNING SAFETY AND HEALTH RISKS AND PROPER PRECAUTIONS WITH RESPECT TO PARTICULAR MATERIALS AND CONDITIONS SHOULD BE OBTAINED FROM THE EMPLOYER, THE MANUFACTURER, OR THE MATERIAL SAFETY DATA SHEET,

A.2.2 ACETONE

Health effects can result from exposure to acetone via contact with fhe skin and eyes, breathing of vapors, or swal- lowing. Acetone exhibits local irritant properties that may be manifested by dermatitis, stinging of the eyes, nose, or throat, or irritation of the respiratory system. Acute exposure to acetone above permissible exposure limits may result in adverse systemic effects, including effects on the dermato- logical or central nervous system. Indications of a systemic effect may include skin irritation, headache, dizziness, drowsiness, loss of appetite, and nausea. There may also be long-term (chronic) health effects of varying severity from exposure to acetone.

51



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Order No. 852-30346

1-1700-4/91-2.5G (9C)



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~

A P I MPMS*L4.b 91 0732290 0095905 9 W

American Petroleum Institute 1220 L Street, Northwest



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Documents

API Mpms Chapter 14.6 (1998)