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  1. ~ ~ STD.API/PETRO MPMS 14.b-ENGL 19’13 IBI 0732270 U L Z 2 1 8 3 075 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 beenfound in API MPMS Chapter 14.6 “ C O ~ ~ ~ ~ U O U Measure- Density S 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 thejìrst equationfor variable C,, is only for evacuated weight pycnometers. The C,equation found on page 45 is onlyfor 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 conver- sionfactors with more signifcant digits, refer to thefollowing docwnent (or its successor): “Standadfor Use o the International System of Units (SI):The Modem f Memk System” (IEWASTM SI-IO;1997). IEEE SrandantF Coodimthg Committee I and ASTM Committee E-43, published by Institute of Electrical and Electronics 4 Engineers, Inc.. 345 h t 47th St., New Y & NY 10017. This document has replaced o 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 atmosphericpressure. 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 InstituteLicensed by Information Handling Services
  2. Pages 42,43, and 44. On page 42, C,, was incorrectlycalculated using the air-filled weight calculations,as described in section 14.6.6.4.3.It was not calculated using the 14.6.6.6.2 evacuated weight method. Aditiornliy, the valuesfor 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 Weighsare of little use. See thefollowing two tablesfor corrected values: Test B Data _. . I 2 50 77.5 2360.26 994.76 0.9970810 997.67 995.45 4 200 77.5 2360.89 995.39 0.9975464 997.84 995.62 10 800 77.5 2363.46 997.96 0.9993975 998.56 996.34 12 1000 77.5 2364.30 998.80 1.0000108 998.79 996.57 17 1500 77.4 2366.45 1000.95 1.0015514 999.40 997. i8 In the above Test A and Test B tables, thefollowing values also apply: Pd = 14.696 psia datum pressure, E, = 2.88E-5 per degree Fahrenheit, pA= 0.001I75 g / c d for Test A calculated by using the air density equation on page 45 at 79"E pA= 0.001I79 g/cmfor Test B calculated by using the air density equation on page 45 at 77"E C,, = 0.99985for both Test A and Test B. Page 45. ïñe equationfor 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 multiplicationsign. 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 l W ) ( T f ) (1.459187 x lP3)(Tf2) + (20.08438 x lW)(T3)- (58.47727 x lW)(Tp)+ (410.411 x 10-lz)(T:)] i- { [ 1 + (19.67348 x 10-3)(Tf)]( 14.50377 x l W ) }COPYRIGHT American Petroleum InstituteLicensed by Information Handling Services
  3. 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 Kipequation 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 MPMS 14.6 pia bar "C "F Iob/bar i/pSi R, (i/psi> Pw,(g/cm3) pw, wem, 77 5.31 0.00 32.0 50.8850 35084x I 0 4 3.5061 x 104 0.999840 1.oooO58 77 5.31 20.00 68.0 45.8914 3.1641 x I 0 4 3.1620~ 104 0.998202 0.9983% 77 5.31 50.00 122.0 44.1727 3.0456~ 0 4 I 3.0436~104 0.988058 0.988245 611 42.13 0.00 32.0 50.8850 3.5084~ 0 4 3.4860~ I 104 0.999840 I .O01 922 611 42.13 20.00 68.0 45.8914 3.1641 x I 0 4 3.1439~I 0 4 0.998202 I .oooOn 611 42.13 50.00 122.0 44.1727 3.0456~104 3.û261 x 1 0 1 0.988058 0.989844 1465 101.01 0.00 32.0 50.8850 3.5084~ IO+3.4547~104 0.999840 1.o04874 1465 101.01 20.00 68.0 45.8914 3.1641 xl043.1157~I 0 4 0.998202 I .o02733 1465 101.01 50.00 122.0 44.1727 3.0456~104 29990x104 0.988058 0.992374 3050 210.29 0.00 32.0 50.8850 35084x104 3.3996~106 0.999840 1.010264 3050 210.29 20.00 68.0 45.8914 3.1641 x I 0 4 3.0660~I 0 4 0.998202 I .o07579 3050 210.29 50.00 122.0 44.1727 3.0456~ 0 4 I 2.9511 x 104 0.988058 0.996988COPYRIGHT American Petroleum InstituteLicensed by Information Handling Services
  4. ~~ 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. 20005COPYRIGHT American Petroleum InstituteLicensed by Information Handling Services
  5. A P I MPMS*14.6 91 0732290 O095848 1 -Manualof 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 InstituteCOPYRIGHT American Petroleum InstituteLicensed by Information Handling Services
  6. 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 PRECAUTIONS WITH RESPECT TO PARTICULAR MATERIALS AND CONDI- 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 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 THE PUBLICATION BE CONSTRUED AS INSURING ANYONE AGAINST LIABIL- ITY FOR INFRINGEMENT OF LEITERS PATENT. 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 CYCLE. THIS PUBLICATION W L L NO LONGER BE IN EFFECT FIVE YEARS AF- TER ITS PUBLICATION DATE AS AN OPERATIVE API STANDARD OR, WHERE AN EXTENSION HAS BEEN GRANTED, UPON REPUBLICATION. STATUS OF THE 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 InstituteCOPYRIGHT American Petroleum InstituteLicensed by Information Handling Services
  7. FOREWORD This standard provides design and operating procedures for continuous density measure- ment 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 measure- ment 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 in- clude 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 pub- lication and hereby expressly disclaims any liability or responsibility for loss or damage re- sulting 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. iiiCOPYRIGHT American Petroleum InstituteLicensed by Information Handling Services
  8. CONTENTS Page SECTION 6-CONTINUOUS DENSITY MEASUREMENT 14.6.1 Scope and Field of Application ................................................................ 1 14.6.2 Safety ........................................................................................................ 1 14.6.3 Referenced Publications ........................................................................... 1 14.6.4 Measurement Applications ....................................................................... 2 14.6.5 Nomenclature ........................................................................................... 3 14.6.6 Mass and Apparent Mass Values .............................................................. 3 14.6.7 General Design Considerations .............................................. .................. 10 14.6.8 Density Meters ......................................................................................... 14 14.6.9 Pycnometers ............................................................................................. 15 14.6.10 Density Sampling Systems ....................................................................... 17 14.6.11 Proving Systems ....................................................................................... 21 14.6.12 Proving of Density Meters ....................................................................... 22 14.6.13 Proving Procedures .................................................................................. 23 14.6.14 Calculation Procedures .................................................................. ........... 24 14.6.15 Field Verification Procedures for Pycnometers ........................................ 26 14.6.16 Laboratory Calibration Procedures for Pycnometers ............................... 32 14.6.17 Density of Water ....................................................................................... 47 14.6.18 Density of Air ........................................................................................... 48 14.6.19 Bibliography ............................................................................................. 50 APPENDIX-PRECAUTZONARY INFORMATION ........................................... 51 Figures 1-Typical Measurement System ........................................................................ 2 2-Typical Primary Apparent Mass Standards Certificate .................................. 5 3-Typical Secondary Apparent Mass Standards Certificate .............................. 6 4-Net Forces on Pycnometer ............................................................................ 8 5-Typical Ethylene Density Envelope ............................................................... 11 6-Density Changes due to Pressure Deviations ................................................ 12 7-Density Changes due to Temperature Deviations ......................................... 13 8-Temperature and Pressure Points for Inferring Density Deviation ................ 14 9-Single-Sphere Pycnometer ............................................................................ 17 10-Double-Wall Vacuum Sphere Pycnometer .................................................. 18 11-Single-Cylinder Pycnometer ........................................................................ 19 12-Classification of Density Sampling Systems ............................................... 19 13-Insertion-Type Continuous Density Sampling Systems .............................. 20 14-Slipstream-Type Continuous Density Sampling Systems: Pump Devices . 20 15-Slipstream-Type Continuous Density Sampling Systems: Restriction Devices ..................................................................................... 21 16-Slipstream-Type Continuous Density Sampling Systems: Velocity Head Devices ................................................................................ 22- 17-Typical Proving Report: Example 1 ............................................................. 27 18-Typical Proving Report: Example 2 ............................................................ 28 19-Vacuum Filling the Water Reservoir (Field Verification) ............................ 29 20-Deaerating the Water Reservoir (Field Verification) ................................... 30 21-Evacuating the Air-Filled Pycnometer ........................................................ 31 22-Vacuum Filling the Pycnometer .................................................................. 31 23-Vacuum Emptying the Pycnometer .............................................................. 32 24-Field Verification Form ............................................................................... 34 25-Vacuum Filling the Water Reservoir (Laboratory Calibration) ................... 35 VCOPYRIGHT American Petroleum InstituteLicensed by Information Handling Services
  9. API M P M S * 1 4 . b 91 0732290 0095852 3 Page 26-Deaerating the Water Reservoir (Laboratov Calibration) .......................... 36 27-Vacuum Emptying the Pycnometer ............................................................. 37 28-Pycnometer Calibration Test Apparatus ...................................................... 37 29-Reinstallation of Test Tubing ...................................................................... 38 30-Typical Pycnometer Certificate and Calibration Calculations ..................... 39 3 1-Optional E, Test Apparatus .......................................................................... 47 Tables 1-List of Symbols .............................................................................................. 4 2-Classification of Density Meters ................................................................... 15 3-Classification of Density Provers .................................................................. 15 4-Test Equipment Required for Field Verification of Pycnometers .................. 29 5 -Atmospheric Water Density as a Function of Temperature .......................... 33 6-Test Equipment for Laboratory Calibration of Pycnometers ......................... 35 7-Predicted Water Density ................................................................................ 48 8-Experimental Versus Predicted Water Density .............................................. 49 viCOPYRIGHT American Petroleum InstituteLicensed by Information Handling Services
  10. 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 rupture disk to burst. g. As soon as possible after weighing, the pycnometer This standard provides criteria and procedures for design- should be emptied in a safe location. (Temperature rise may ing, installing, and operating continuous density measure- cause excessive pressure in a filled prover, resulting in pos- ment systems for newtonian fluids in the petroleum, sible release of product.) chemical, and natural gas industries. The intent of this stan- h. The pycnometer and associated equipment should be reg- dard is to provide the user with a density accuracy of 0.10 ularly inspected and properly maintained by competent per- percent for most applications. sonnel. The application of this standard is limited to clean, homo- i. The pycnometer shall be stored and transported empty to geneous, single-phase liquids or supercritical fluids. The pro- prevent damage to the pycnometer, bursting of the rupture cedures and criteria contained in this standard have been disk, and other hazardous conditions. successfully applied to fluids whose flowing density is j. Cleaning and drying of the pycnometer should conform greater than 0.3 gram per cubic centimeter at operating con- to established safety procedures and accepted methods of ditions above 60°F (15.6”C) and saturation pressure. handling compressed gas. This standard does not advocate the preferential use of k. Personnel should be familiar with the fluid’s properties any particular type of equipment, Neither is it the intent of and hazards. this standard to restrict the future development or improve- ment of density measuring equipment. The contracting par- 14.6.3 Referenced Publications ties should mutually agree on equipment selection, design, and operating procedures prior to custody transfer. The following publications are cited in this chapter: ACGI“ 14.6.2 Safety Threshold Limit Valuesfor Chemical Substances and Personnel involved in the handling of petroleum products Physical Agents in the Work Environment and related fluids are exposed to hazards that demand con- API stant attention to many precautions peculiar to the type of Publ 2026 Safe Descent Onto Floating Roofs of Tanks measurement equipment and commodities handled. Follow- irr Petroleirm Service ing are some reminders for both designers and operating per- Publ 2217 Guidelines for Conjìned Space Work in the sonnel for density metering systems. This section does not Petroleum Industiy attempt to take the place of individual company safety in- Manual of Petroleum Measiiremenf Standards structions. Chapter 9, “Density Determination,” Section The following precautions should be considered: 1, “Hydrometer Test Method for Density, Relative Density (Specific Gravity), or API a. All electrical components shall be designed i accordance n Gravity of Crude Petroleum and Liquid Pe- with the appropriate electrical hazardous area classification. troleum Products,’’ and Section 2, ‘LPressure b. All equipment shall be designed to withstand the maxi- Hydrometer Test Method for Density or Rel- mum operating pressure to which it can be exposed. ative Density” c. All materials used shall be resistant to corrosive attack by Chapter 11, “Physical Properties Data,” Sec- the fluids with which they come in contact and shall be com- tion 2.3, “Water Calibration of Volumetric patible with cryogenic temperatures that may occur as a re- Provers’’ sult of autorefrigeration. GPA2 d. Adequate facilities shall be provided for isolating, depres- Std 2145 Table of Physical Constants for the P a r e n surizing, venting, flaring, and draining. Hydrocarbons and Other Components of e. When highly volatile fluids are vented, appropriate pro- Natural Gas tective clothing should be worn to prevent cold bums due to autorefrigeration of the fluid. f. After filling, the pycnometer should be weighed as soon IAmerican Conference of Governmental Industrial Hygienists, 6500 Glen- way Avenue, Building D-5, Cincinnati, Ohio 45211. as is practical to minimize any rise in temperature of the con- *Gas Processors Association, 6526 East 60th Street, Tulsa, Oklahoma tents, resulting in increased pressures that could cause the 74145. 1COPYRIGHT American Petroleum InstituteLicensed by Information Handling Services
  11. A P I MPMS*L4.b 91 = 0732290 0095854 7 = 2 CHAPTER 14-NATURAL MEASUREMENT GASFLUIDS OSHA3 14.6.4.2 MASS FLOW MEASUREMENT Occupational Safety and Health Standards (29 Code of Mass flow measurement techniques are used on Federal Regulations Sections 1910.1000 and compressible fluids with varying compositions and poorly following) defined properties of thermal expansion, compressibility, and admixture shrinkage. The criteria given in this standard have 14.6.4 Measurement Applications been successfully applied to the following fluids: 14.6.4.1 GENERAL The following are the two most common applications for a. Polymer-grade ethylene. b. Ethane mixtures or raw make. continuous density measurement of hydrocarbons and other related fluids in custody transfer service: c. Pure CO2and CO;, mixtures. d. Liquefied petroleum gas mixtures. a. Mass flow measurement. e. Natural gas liquids. b. Volume measurement at standard conditions for fluids of varying composition. Mass flow measurement requires the continuous integra- As shown in Figure 1, both applications share the same basic tion of flowing volume times flowing density over a time pe- components: riod to obtain total mass and mass flow rate. a. Density meter. b. Continuous density sampling system. 14.6.4.3 VOLUMETRIC MEASUREMENT c. Volume meter. Volumetric measurement at standard conditions is used on fluids with variable compositions and well-defined pres- 30ccupationalSafety and Health Administration, US.Department of Labor. The Code of Federal Regularions is available from the U.S. Government sure-volume- temperature relationships, such as the follow- Printing Office! Washington, D.C. 20001. ing: LEGEND a Strainer 7 Straightening vanes 1 1I 8 Turbine meter @ Therrnowell Pressure indicator Density meter Figure i-Typical Measurement SystemCOPYRIGHT American Petroleum InstituteLicensed by Information Handling Services
  12. A P I MPMS*I<L+*b 91 m 0732290 0095855 9 m S C I N 6-CONTINUOUS E TO DENSITY MEASUREMENT 3 a. Propane mixes. Mass is defined in terms of a standard mass, and therefore b. Butane mixes. the mass of an object is simply a multiple of the mass stan- . dard. The mass of an object remains constant regardless of Volumetric measurement at standard conditions requires its location. Thus, the mass of an object does not vary as it is the correction of density measured at flowing conditions to moved from one part of the earth to another, although the net the equivalent value at standard conditions of temperature forces acting on the mass may change. If the net forces and pressure (or equilibrium pressure). A weighted volume- change, the weight of the object will vary from location to averaged density or the continuous calculation of net stan- location. dard volume and an API gravity at 60°F (or density at 60F) Apparent mass is defined as the weight of an object in air, can be used for custody transfer applications. compared with a mass standard. A mass measurement by Corrections for the effect of temperature and pressure on weighing is performed in air, as are virtually all mass refer- the flowing density, commonly referred to as C,,and C are , ence standards calibrations. Thus, when two objects are required to arrive at an API gravity at 60°F and equilibrium compared in mass, each object is subjected to two principal pressure. Additional corrections for the effect of pressure opposing forces: and temperature on the density meter may be required to measure the flowing density accurately. a. A lifting force equal to the mass of air displaced by the object times the force of gravity, 14.6.4.4 REFERENCE AND DATUM CONDITIONS b. A downward force equal to the mass of the object times the force of gravity, The reference conditions of pressure and temperature for custody transfer of hydrocarbons and other petroleum-re- Since all mass reference standards calibrations are made lated fluids are as follows: in air and are performed by comparing an unknown standard with a known primary standard, the mass of the unknown a. The reference pressure is atmospheric pressure (14.696 standard is frequently reported as the mass the standard pounds per square inch absolute). For fluids whose vapor would appear to have when compared with a reference stan- pressure at the reference temperature is greater than atmo- dard at 20°C in air with a density of 0.0012 gram per cubic spheric, the reference pressure shall be the equilibrium vapor centimeter. Whenever apparent mass is used, it is necessary pressure at the reference temperature. to specify the density of the (normally hypothetical) refer- b. The reference temperature is 60.0"F (156°C). ence standard against which the unknown standard is being The datum conditions for pycnometers calibrated in accor- compared. This statement of the density of the reference dance with 14.6.16 are as follows: standard, called reference density, is necessary because the apparent mass value depends in part on the volume of the a. For U.S. units, a pressure of 14.696 pounds per square reference standard. A reference density of 8.0 grams per cu- inch absolute and a temperature of O.O°F. bic centimeter is normally used to report the apparent mass b. For SI units, a pressure of 101,325kilopascals and a tem- of a standard or object. This is referred to as the apparent perature of -17.8"C. mass versus 8.0 grams per cubic centimeter at 20°C in nor- mal air (0.0012 gram per cubic centimeter), In the past, the 14.6.5 Nomenclature apparent mass was reported against the density of normal The symbols used for mathematical variables in this stan- brass at 20OC. This is referred to as the apparent mass versus dard are listed in Table 1. 8.3909 grams per cubic centimeter at 20°C in normal air. 14.6.6 Mass and Apparent Mass Values 14.6.6.2 MASS AND APPARENT MASS STANDARDS 14.6.6.1 DEFINITIONS By international agreement, the international mass stan- In the field of measurement, considerable ambiguity exists dard is the International Prototype Kilogram, a platinum- with respect to the definitions of mass, apparent mass, and iridium standard (90 percent platinum. and 10 percent weight. The following definitions are presented to enable the iridium) that is kept at the International Bureau of Weights user of this standard to understand more clearly the relation- and Measures i Sèvres, France. The primary mass standard n ship of these terms. for the United States, which has been compared with the In- Weight is defined as the net force exerted on an objects ternational Prototype Kilogram, is the U.S. Prototype Kilo- mass, compared with a reference standard, In most situa- gram 20, a platinum-iridium standard kept at the National tions, the net force is a combination of the earths gravity and Institute of Standards and Technology (NIST) in Gaithers- the buoyancy of the A uid surrounding the object. Weighing is burg, Maryland. defined as measuring the net force acting on an objects Mass standards are precise standards whose volume, den- mass. sity, cubical coefficient of thermal expansion, and mass haveCOPYRIGHT American Petroleum InstituteLicensed by Information Handling Services
  13. API MPMS*L4.6 91 M 0732290 0095856 O M 4 CHAPTER 14-NATURAL GASFLUIDS MEASUREMENT Table 1-List of Symbols Units Symbol Meaning U.S. SI , Apparent mass of fluid 7 .t g Apparent mass of test weights g E Correction for air buoyancy on weighing - - I Correction for effect of temperature on steel pycnometer - - Density meter factor - - Coefficient of expansion due to pressure on pycnometer cm3/psi cm’k~a Coefficient of cubical expansion due to temperature on pycnometer I/OF ipc Buoyancy force on fluid Ibf N Buoyancy force on steel of pycnometer Ibf N Buoyancy force on test weights Ibf N Buoyancy force on evacuated pycnometer volume lbf N Gravitational force on fluid Ibf N Gravitational force on steel of pycnometer Ibf N Gravitational force on test weights i bf N Total forces on steel of pycnometer when fluid filled Ibf N Total forces on steel of pycnometer when evacuated” Ibf N Total forces on steel of pycnometer when air-filled Ibf N Dimensional conversion constant, - - 32. 17405(lbm-ft)/(lbf-s2) or l.O(kg.m)/(N.s’) Local gravitational constant ft/s2 m/s2 Elevation of weigh scale above sea level ft m Isothermal compressibility of water at 14.696 psia and a temperature I/psi IkPa Average isothermal compressibility of water at a pressure and a temperature I/psi 1kPa Mass of any object g g Mass of fluid g g Mass of test weights g g Datum pressure of pycnometer, psi Wa 14.696 psia or 101.325 E a or O psig Test pressure psi !‘ &a Pycnometer base volume, cm3 cm3 pycnometer volume at damm pressure and datum temperature Pycnometer volume at datum temperature and test pressure cm3 cm3 Pycnometer volume at test temperature and 0.0 psia cm3 cm’ Pycnometer volume at test temperature and test pressure cm3 cm3 Datum temperature, O F “C O.O°F or -17.8OC Test temperature O F “C Volume of any object cm3 cm3 Volume of test weights cm3 cm3 Weight of air-filled pycnometer g g Weight of fluid-filled pycnometer g g Weight of pycnometer with all air evacuated g g Density of any object g/cm3 g/cm3 Density of dry air g/cm’ g/cm’ Density of fluid at test temperature and test pressure g/cm3 g/cm’ Density of field test weights g/cm3 g/cmJ Density of reference test weights g/cm3 g/cm’ Density of water at test temperature and 14.696 psia g/cm3 g/cmJ Density of water at test temperature and test pressure g/cm3 g/cm3 ‘includes buoyancy force associated with the internal volume. been determined by NIST. Mass standards are used for primary mass or primary apparent mass standards, which in highly accurate measurements in scientific research labora- turn have been certified by NIST. Apparent mass standards tories but are impractical for precise commercial measure- are used by all states and by commercial laboratories as their ments. primary standards for precise weighings. A typical commer- Apparent mass standards are precise standards whose den- cial laboratory’s certificate for a set of primary standards is sity and apparent mass have been determined by a high- shown in Figure 2. precision commercial laboratory, as compared with their pri- The NIST Classification of Mass and Laboratory Weights mary standards. Apparent mass standards are calibrated by (mass and apparent mass standards) is based on tolerancesCOPYRIGHT American Petroleum InstituteLicensed by Information Handling Services
  14. A P I MPPlS*i<LLi-b 91 0732290 0095857 12 I 1 SECTION 6-CONTINUOUS MEASUREMENT DENSITY 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 Analytical balances, or weigh scales, are vertical force set of apparent mass standards is shown in Figure 3. 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 1O g x 1 mg- Revised June 8,1983 0 Corrections (mg) Nominal Brass Stainless Value 8.3909 g/cm3 8.000 g/cm3 Uncertainty (mg) -25.13 114.66 43.89 -4.34 65.56 21.84 8.30 43.24 10.44 14.15 35.12 6.83 2.79 16.77 4.99 4.27 11.26 0.041 1.62 5.11 0.027 1.72 3.82 0.026 0.15 1.55 0.021 -0.48 1 0.218 0.034 0.110 0.459 0.016 O. 103 0.312 0.014 0.033 O. 173 0.012 0.014 0.084 0.0 14 -0.026 0.009 0.007 -0.0036 0.0173 0.0049 0.0208 0.0348 0.0035 -0.0381 -0.0311 0.0030 -0.0201 -0.0166 0.0016 -0.0171 -0.0150 0.0012 -0.0193 -0.0179 0.0009 -0.0232 -0.0226 0.0009 -0.0006 -0.0002 0.0007 -0.0115 -0.0112 0.0008 -0.0252 -0.0251 0.0007 -0.0135 -0.0135 0.0009 -0.0042 -0.0041 0.0007 -0.0034 -0.0033 0.0008 -0.00 19 -0.0019 0.0007 0.0011 0.0011 0.0009 Figure 2-Typical Primary Apparent Mass Sfandards CertificateCOPYRIGHT American Petroleum InstituteLicensed by Information Handling Services
  15. A P I MPMS*14.b 71 0732270 8875858 4 M 6 1&NATURAL GASFLUIDS CHAPTER MEASUREMENT Mass and Laboratory Weight Manufacturer Certificate No. 112543-86 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) ( mg) I ( Yo) I 2 kg +27.5 40.0 0.0020 1 kg +13.0 20.0 0.0020 500 g +3.7 10.0 0.0020 200 g +2.8 4.0 0.0020 100 g +1.1 2.0 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 pri- mary 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: = (Apparent mass) 1 - (0.0012/8.0) 1 - (0.0012/7.84) 1 Figure 3-Typical Secondary Apparent Mass Standards Certificate ing on an unknown object, compared with the net force act- apparent mass standard’s density is greater than the object’s ing on a known object (an apparent mass standard). By density, the buoyancy correction must be greater than 1. If definition, they are influenced by external vertical forces. the apparent mass standard’s density is less than the object’s The principal vertical forces that influence the weighing density, the buoyancy correction must be less than 1. The instrument’s performance are local gravity, air buoyancy, air buoyancy correction equation is given in 14.6.6.5. currents, vibration, and attitude. Lesser forces, such as elec- trostatic and magnetic forces, are beyond practical field and 14.6.6.4 APPARENT MASS TO MASS VALUES laboratory accuracy levels. The influence of air currents on the analytical balance can All hydrocarbon and other petroleum-related fluid densi- be controlled by the use of a draft shield. ties are based on mass or weight in a vacuum. Air buoyancy The influence of vibration and attitude can be controlled corrections are therefore required for all calibrations of den- by mounting the analytical balance on a level, stable surface sity meters, laboratory calibrations of pycnometers, and field that is free from vibration. verification of pycnometers. By calibrating in air an analytical balance to a known ap- In practical field and laboratory weighings, the mass of an parent mass standard, the balance is prepared to read the ap- object shall be calculated from its apparent mass by the fol- parent mass of any object whose density is equal to the lowing equation: apparent mass standard’s reference density. This calibration Mass = Apparent mass x Air buoyancy correction method also corrects for the effect of local gravitational forces as long as the balance is not moved to a different io- Although it is recognized that a more explicit treatment may cation. be performed, the precision of this equation is sufficient for The influence of air buoyancy forces on an object can be the limits of practical field and commercial laboratory deter- calculated if the object’s density or volume is known. If the minations.COPYRIGHT American Petroleum InstituteLicensed by Information Handling Services
  16. A P I MPMS*1LI-b 91 W 0732290 0095859 b W SECTION 6-CONTINUOUS MEASUREMENT DENSITY 7 14.6.6.5 CORRECTION FOR AIR BUOYANCY ON (Net force), = Net force of fluid-filled pycnometer WEIGHINGS (Cew) - Net force of evacuated pycnometer The mass of a test fluid shall be calculated using a pyc- or, nometer by the following equation: (Net force), = (4 + epyC)Fzp,c - Mfl = (wf- wo><cBW) Where: The following formula shall be used for laboratory cali- + = FR Flpsc total forces exerted on the fluid-filled pyc- bration of pycnometers: nometer. Fzpyc total forces exerted on an evacuated pycnom- = eter. The forces on the fluid combined with the forces exerted Keeping in mind the practicality of field conditions, the for- on the steel shell of the pycnometer are expressed as folIows: mula becomes the following for proving and verification tests: F, + epsc (F, = - 4,) + (E - es) W B = - (PA /PTWí) Although the pycnometer is evacuated, the internal volume is displacing air and therefore has a buoyancy force for the For field weighings, the value of pAis calculated as a evacuated volume. The forces on the steel shell of the pyc- function of elevation only (see 14.6.14.2). To simplify field nometer and the buoyancy force exerted on the evacuated calculations, the value for ,C can be constant for each bal- , volume are expressed as follows: ance location using a specified set of weights. FZpyc = 4 - (Fbs + Fbv) 14.6.6.6 DERIVATION OF EQUATION FOR CBw Substituting, 14.6.6.6.1 General (Netforce), = [(F, - Fbn) + (e - The derivation of the ,C equation has been written for , - [E - (Fbs + Fbv)l qualified technical personnel with a background in physics. To derive the equation to correct for the air buoyancy on Reducing the equation yields the following: all weighings, the use of a perfect electronic balance is as- (Netforce), = (F, - ,+ 6 ) Fbv sumed. The balance has been calibrated with the apparent mass standards shown in Figure 3, in an air densify of And, 0.00118 gram per cubic centimeter. When a fluid-filled pyc- Fbfl = @ApYp )(gr / 8,) nometer is placed on the balance, it indicates a scale reading And, of 2000 grams, The evacuated weight of the pycnometer in- dicates a scale reading of 1000.0 grams. The air-filled weight Fbv = (pAp~)(gl/gc) of the pycnometer indicates a scale reading of 1001.18 Assuming that the pycnometer volume does not change grams. The Pvpvalue for the pycnometer is 1000.00 cubic significantly between an evacuated and a fluid-filled state, centimeters. As shown in Figure 4, the net forces may be calculated as Pl$) = Pv, follows: By definition, And, = PFtpPVlp &I = Fbv PYP = M/PF,, Reducing the net force equation yields the following: For both the apparent mass standard and the fluid, (Net force), = F, Net force = Force due to gravity - Buoyan€force of air Remembering that the scale is perfect, Since the electronic balance is perfect, no corrections are (Net force),, = (Net force), needed for the balance: Since the test weights have both gravitational and buoy- (Net force), = (Net force), ancy forces exerted on them, 14.6.6.6.2 Using the Pycnometers Evacuated - wlb = Ffl Weight (Wo) For the mass standard, the gravitational forces are expressed The fluids net force is calculated as follows: as follows:COPYRIGHT American Petroleum InstituteLicensed by Information Handling Services
  17. 8 CHAPTER 14-NATURAL GASFLUIDSMEASUREMENT Volume of steel Volume of steel 1 5" 5 s + Volume of evacuated fluid pycnometer F, F,+E USING EVACUATED WEIGHT Wo Volume of steel 5s 5, 5 s + 4 Volume of fluid Volume of steel 1 I F, F,+< USING AIR-FILLED WEIGHT W, Figure 4-Net Forces on Pycnometer 6, = (PTWrv,, )(ål/ g,) Again substituting into the equation for net force and then re- ducing, For the fluid, the gravitational forces are expressed as fol- lows: Mfl = MI, - (P, IPnvr 11 Ffl = (PFtppvp )(8l 1g ) c The mass value of the apparent mass standard can be cal- culated by the following equation (in accordance with NIST The air buoyancy forces are expressed as follows: procedures): FbiW = @*Yw)(å, 1å, 1 Substituting into the equation for net force, Substituting, (å, / å, )(PnvrYw - P A K ) = (åi 1å ) ( ~ , t p P V , p ) c By definition, From the previous section, Mass = Apparent mass x Air buoyancy correctionCOPYRIGHT American Petroleum InstituteLicensed by Information Handling Services
  18. API M P M S * L Y - b 91 m 0732290 0 0 9 5 8 b L Y m SECTION MEASUREMENT C CONTINUOUS DENSITY 9 Solving for the mass of the fluid, Substituting into the equation for net force, Mfl = 1000 - (o’oo12/8’o) 1 - (0.0012/7.84) = 999.85 grams [i - (0.00118/7.84)] I 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-throughpycnometers 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 Solving for the mass of the fluid, r The net force of the fluid-filled pycnometer is expressed as follows: (Net force), = (Ffl + KpJ - Kpyc The mass value of the apparent mass standard can be cal- The net force of the air-filled pycnometer is expressed as fol- culated as follows: lows: Ffl + Kpyc = (& - &fl) + (Fs - Fbn) Since the pycnometer is air filled, the internal volume is not Substituting, displacing air and therefore has no bouyancy force: Kpyc = - Fbs Substituting, From the previous section, (Net force), = [(F,- Fb,) + (F, - &)I - (F, - Fbs) Mass = Apparent mass x Air buoyancy correction Reducing the equation yields the following: Therefore, (Net force), = F, - Fb, And, Fbfl = (PApyp )(gl / gc And, Remembering that the scale is perfect, Pr = Fp (K - wa)/pyp (Net force),, = (Net force), Solving for the mass of the fluid, &w - ‘biw = Ffl - 6l For the mass standard, the gravitational forces are expressed as follows: f M , = 998.82 1 - (0.0012/8.0) 1 - (0.0012/7.84) 1 - (0.00118/7.84) 1 K v = (P,vfv,w)(gl /gc) { 1 - [0.00118/(998.82/1000.0)] = 999.85 grams And the air buoyancy forces are expressed as follows: %w = (PAYw)(gl / gc) 14.6.6.6.4 Summary of C,, Equation For the fluid, the gravitational forces are expressed as fol- For the Woapplication, the CBw equation corrects only for lows: the buoyancy of the additional test weights required to deter- Ffl = (PFtppyp )(gl 1gc) mine the difference between the Wf and Wovalues. In both the Wo and W, derivations, the simplified CBw And the air buoyancy forces are expressed as follows: equation was not used to accurately reflect the results. The Fbfl = (PApyp )(8, /gc) simplified CBw equations are as follows: When using Wo,COPYRIGHT American Petroleum InstituteLicensed by Information Handling Services
  19. API MPMS*L4.b 91 E 0732290 0075862 b 10 CHAPTER 1&NATURALGASFLUIDS MEASUREMENT 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 me- 14.6.6.6.5 Mass and the C,, Equation ter, pycnometer, and volume meter should coincide as closely as possible, such that the following criteria are met: Since the laboratory-determined pycnometer volume and evacuated weight are considered more accurate than the a. During normal operation, the density deviation between field-determined W, values, the Womethod shall be used for the density meter, pycnometer, and volumetric meter shall all flow-through pycnometers. not exceed 0.05 percent. The mass density of the fluid contained in a flow-through b. Error resulting from pressure differences shall not exceed pycnometer shall be calculated using the following equation: 0.01 percent or 1 pound per square inch gauge, whichever is greater. PFIP = [(Wf - W o ~ / ~ Y p 1 C , , c. Error resulting from temperature differences shall not ex- The mass of the fluid contained in a flow-through pyc- ceed 0.04 percent or 0.2"F, whichever is greater. nometer shall be calculated using the following equation: Figure 8 is a piping schematic that shows the temperature Mfl = cWf - wo)cBV and pressure points. For some fluids, the deviation criteria above are not prac- 14.6.7 General Design Considerations tical (for example, applications in which operation is close to 14.6.7.1 GENERAL the critical point). For these applications, the density meter shall be installed so that the following criteria are met: Before a density measurement system is designed, a thor- ough understanding of the fluid and the measuring equip- a. During proving, the density deviation between the sample ment is necessary to achieve a density accuracy of 0.10 point, the density meter, and the pycnometer shall not exceed percent. A systematic approach to the design should include 0.05 percent (see Figure 8, Points 1, 2, and 3). close attention to the following areas: b. To minimize any density deviation due to pressure, the density meter shall be located as close as is practical to the a. Fluid properties and behavior. volume meter. b. Density meter. c. To minimize any density deviation due to temperature, c. Pycnometer (flow-through design). the main line piping between the volume meter and the sam- d. Density sampling system. ple point shall be fully insulated. e. Density proving system. f. Volumetric meter influence. Density variation of the fluid with respect to composi- tional changes should be evaluated to determine its effect on Accurate continuous density measurement requires ther- the density meter and the volume meter. mal insulation of the volume meter, density meter, pycnom- eter, and all interconnecting piping to minimize density 14.6.7.2.3 Other Properties and Behavior deviations due to temperature differences. General areas of importance are presented below. De- Other process fluid properties and behavior should be re- tailed criteria are presented throughout this publication. viewed to assess the possible impact on the safety, accuracy, and reliability of the system. The following areas should be 14.6.7.2 FLUID PROPERTIES AND BEHAVIOR considered: 14.6.7.2.1 - General a. Cleanliness. The properties and behavior of the fluid being measured, b. Homogeneity. as well as their impact on the measuring equipment, must be c. Corrosiveness. fully understood. The areas described in 14.6.7.2.2 and d. Polymerization. 14.6.7.2.3 should be considered. e. Viscosity. f. Autorefrigeration. 14.6.7.2.2 Fluid Density g. Solids precipitation. Assuming a constant fluid composition, the fluid density Fluid separation behavior should be assessed to prevent liq- can be inferred by measuring the fluid temperature and pres- uid-liquid separation, hydrate formation, or dry ice forma- sure. Therefore, temperature and pressure differences be- tion (for CO2 service).COPYRIGHT American Petroleum InstituteLicensed by Information Handling Services
  20. A P I MPMS*lJLl-b 91 W 0732290 00958b3 8 W SECTION 6-CONTINUOUS DENSITYMEASUREMENT 11 14.6.7.3 DENSITY METER 14.6.7.4 PYCNOMETER The selected density meter should be evaluated for sensi- Only pycnometers with a flow-through design shall be tivity to the sample system’s flow rate, attitude, velocity of used, The selected pycnometer should be evaluated for sen- sound in a flowing fluid, temperature and pressure variations, sitivity to the sample system’s flow rate, attitude, liquid and dirt and pipe rouge, accumulation of liquids (for example, particulate accumulation, and atmospheric water condensa- glycols, oils) or particulates, mechanical vibration, and fluid tion. pulsations and pressure surges. 2200 2000 1800 1600 Q> c 5 1400 2 m c o .- C 1200 5 m v> 8 Q l n 1000 3 O a gj 2 800 2 a 600 400 1 pound per cubic foot 200 - O I I I I I I I I I I 35 40 60 80 1O0 120 140 160 180 200 220 Temperature, degrees Fahrenheit Figure 5-Typical Ethylene Density EnvelopeCOPYRIGHT American Petroleum InstituteLicensed by Information Handling Services
  21. A P I MPMSU/4.6 91 0732270 0075864 T 12 CHAPTER 14-NATURAL GASFLUIDS MEASUREMENT 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 crit- ical 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 e. Be installed to minimize fluid pulsation and pressure surges. The density meter and pycnometer can only measure the f. Be installed so that associated pipeline facilities can be fluid passing through them. As a result, the density sampling cleaned without an impact on density measurement. system shall meet the following criteria: g. Provide connections for one or more pycnometers. a. Be installed in a location where the fluid is homogeneous. Since the density sampling system requires a continuous b. Not induce separation of the process fluid. slipstream sample, it is time dependent and may not pre- c. Provide the necessary test points for determining temper- cisely correspond to rapid variations in density. This is com- ature and pressure at each device. monly referred to as densify lagging. d. Provide sufficient flow to minimize response delays be- Density determination errors normally result from the fol- tween the density meter and the pycnometer. lowing:COPYRIGHT American Petroleum InstituteLicensed by Information Handling Services
  22. A P I M P M S * 1 4 * b 91 = 0732290 00958b5 1 CONTINUOUS DENSITY SECTION MEASUREMENT 13 - ~ a. Process temperature and/or pressure changes. a. Average the results of several provings. b. Ambient temperature differences. b. Increase the repeatability tolerance. c. Fluid compositional changes. The accuracy of the measurement may suffer as a result of To minimize the effect of temperature differences, thermal this practical approach. bonding of the density sampling system is necessary for all installations, The sampling system must be installed in close 14.6.7.6 DENSITY PROVING SYSTEM thermal contact with the main pipeline, and the entire system The density proving system determines the density meter (density meter and sampling system) must be thermally insu- correction factor and consists of the following equipment: lated against ambient conditions. a. Pycnometer. If the density varies by more than 0.05 percent over the b. Weigh scale and test weights. period of time needed to fully stabilize the pycnometer, it is c. Temperature instrument. not likely that a prover repeatability of 0.05 percent will be d. Pressure instrument. obtained for two consecutive proving runs. For this situation, the parties may agree to take one or both of the following ap- To assure that the density deviation meets the criteria proaches: called for in 14.6.7.2, temperature and pressure measure- 0.06 (0.033"C) + ! O 2 e 3 0.075 O (0.042"C) 8 $ 8 ô Y- C .- c O 0.1 .- m > (0.056"C) a> U ? ! 3 c $. 9 E z c 0.15 (0.083"C) 8 H 0.2 (0.1 1°C) 0.5 (0.28"C) I I I I 0.30 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 DeviationsCOPYRIGHT American Petroleum InstituteLicensed by Information Handling Services
  23. A P I MPMSUL4.b 91 0732290 0 0 9 5 8 b b 3 14 CHAPTER 1‘&NATURAL GASFLUIDS MEASUREMENT Point 1 n TW 111 PI 1 I Flow W Density meter location (see Detail A) Point 3 n- - SVen d 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 a. Discrete, or noncontinuous, density meters. proving. b. Continuous density meters. Table 2 illustrates the classification of density meters. 14.6.7.7 INFLUENCE OF VOLUMETRIC METER Density meters may be installed upstream or downstream 14.6.8.2 DISCRETE DENSITY METERS from the flowmeter, as near as is practical to the primary Discrete density meters, which rely on a discrete represen- measuring device to minimize density errors. tative sample, consist of the following instruments: Care shall be taken not to disturb the velocity profile for turbine, vortex, and orifice meters. Flow shall not be by- a. A hydrometer or thermohydrometer. passed around the flowmeter. b. A Westphal balance. Restriction devices installed between the flowmeter and c. A pycnometer, which may be of the glass or the flow- the prover (if applicable) may create flowmeter proving er- through type. rors if they create a density difference between the prover The Westphal balance, glass pycnometer, and atmospheric and the flowmeter. hydrometer are limited to density determination for atmo- spherically stable, well-defined fluids. The method for deter- 14.6.8 Density Meters mining density using an atmospheric hydrometer is 14.6.8.1 GENERAL described in Chapter 9, Section 1. Insh-uments used to measure fluid density are divided into The pressure hydrometer is limited to density determina- two groups: tion for well-defined fluids that are stable at operating pres-COPYRIGHT American Petroleum InstituteLicensed by Information Handling Services
  24. A P I MPMS*i<14.6 71 0732270 0075867 5 SECTION C CONTINUOUS DENSITY MEASUREMENT 15 Table 2 Classification of Density Meters - tube) of known volume. The vessel is continuously weighed, and the result is divided by the volume to determine density. Discrete Continuous Depending on the required accuracy, corrections for the fluid Atmospheric hydromefer Vibrating element temperature and pressure are applied to the results. Pressure hydrometer Buoyancy Meters that use the continuous weighing technique are Westphai balance Continuous weighing Pycnometer [glass or flow through) Consfant head sensitive to vibration and horizontal position, Application is Acoustic limited to ñuids of low or moderate viscosity. Nuclear Capacitance 14.6.8.4 ACCURACY The selected density meter shall have a minimum overall sures below 203 pounds per square inch absolute (14 bar). accuracy of 0.001 gram per cubic centimeter and a repeata- The method for determining density using a pressure hy- bility of 0.0005 gram per cubic centimeter over the range of drometer is described in Chapter 9, Section 2. design operating conditions. Depending on the density me- ter, compensation may be required for the effects of operat- 14.6.8.3 CONTINUOUS DENSITY METERS ing temperature and pressure on the meter’s performance. 14.6.8.3.1 General To ensure accuracy, the meter shall be installed in accor- dance with the criteria given in 14.6.7 and 14.6.10, as well as Continuous density meters, which require a continuous the manufacturer’s recommendations. representative sample from a homogeneous process stream, Proving of the density meter (or determination of its oper- use a variety of measurement principles to hfer density. The ating accuracy) shall be performed in accordance with the most common instruments currently used in custody transfer criteria and procedures given in 14.6.11 and 14.6.12. applications use the vibrating-element (natural-resonance), buoyancy, or continuous weighing technique. The descrip- 14.6.9 Pycnometers 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. 14.6.9.1 GENERAL A flow-through pycnometer is the most accurate device 14.6.8.3.2 Vibrating- Element Technique for calibrating a density meter under flowing conditions. Dis- The vibrating-element, or natural-resonance, method is crete density meters, which require a grab sample, can also based on the principle that frequency is inversely propor- be used as density proving devices. Table 3 illustrates the tional to density. A continuous sample of the fluid is passed classiücation of density provers. through or around a body vibrating at its natural frequency. The vibrating body can be a tube, cylinder, or flat plate. 14.6.9.2 DEFINITION Meters that use the vibrating-element technique are sensi- The term pycnometer refers to both glass and flow- tive to velocity-of-sound effects and dirty fluids. Protection through pycnometers. This standard only covers the use of from rouge buildup, oil films, and particulates that might flow-through pycnometers. In the remaining sections of this scratch the element is necessary. standard, pycnometer refers to a flow-through pycnometer. Pycnometers are defined by the following criteria: 14.6.8.3.3 Buoyancy Technique a. They are vessels with a flow-through design that traps a The buoyancy technique is based on Archimedes’ princi- representative sample of the test fluid at operating condi- ple, which states that an immersed body is buoyed up by a tions. force equal to the weight of the fluid it displaces. A contín- b. They permit safe handling of high-pressure fluids during uous sample is passed through a chamber that maintains a sampling and transport. float in a balanced position. The electric force needed to c. Their volume and evacuated weight are known to a preci- maintain the balanced position is directly proportional to sion of 0.02 percent over the operating pressure and temper- density. ature range. Meters that use the buoyancy technique are sensitive to vi- bration, horizontal position, and dirt buildup. Application is Table 3-Classification of Density Provers limited to fluids of low or moderate viscosity. Flow-Through Pycnometers Discrete Density Meters 14.6.8.3.4 Continuous Weighing Technique Single sphere Atmospheric hydrometer Doubie-wall vacuum sphere Pressure hydrometer The continuous weighing technique is carried out by con- Single cylinder Westphal balance tinuously passing the fluid through a vessel (a bulb or U Glass pycnometerCOPYRIGHT American Petroleum InstituteLicensed by Information Handling Services
  25. A P I MPMS*14.b 71 H 0732270 0095868 7 H 16 NATURAL GASFLUIDS CHAPTER MEASUREMENT The pycnometer’s volume and evacuated weight shall be The volume temperature and pressure corrections have based on its unique values, as determined by the procedures been determined to be linear. described in 14.6.16. Those values are as follows: 14.6.9.4.3 Double-Wall Vacuum Sphere a. Pycnometer base volume (PBV). b. Coefficient of expansion due to internal pressure ( E J . A double-wall vacuum sphere pycnometer consists of two c. Coefficient of expansion due to test fluid temperature (E,). stainless steel spheres (one inside the other, with a vacuum d. Evacuated weight of the pycnometer (Wo>. pulled on the annulus) with an internal capacity of approxi- mately 1000 cubic centimeters. It is designed and con- 14.6.9.3 DESIGN CRITERIA structed for a maximum allowable working pressure specified by the user. The following criteria should be considered when the size, The vacuum minimizes thermal exchange between the test design, and construction of pycnometers are determined: fluid and the ambient air. For test fluids that operate at tem- a. To minimize weighing errors, the ratio of the pycnome- peratures below ambient, this eliminates the possibility of ter’s evacuated weight to the weight of the fluid should be water condensing on the outside of the pycnometer. kept low. Figure 10 shows the double-wall vacuum sphere design. b. Because of current scale limitations, the mass of a water- The fluid flows through the inlet valve into the sphere and filled pycnometer shall not exceed 5000 grams. then up through the siphon tube. The gas vent and siphon c. Considering balance capabilities, the pycnometer’s vol- tube minimize the possibility of gases being trapped and as- ume shall not be less than 500 cubic centimeters. For most sist in removing deposition. applications a volume of approximately 1O00 cubic centime- The volume temperature and pressure corrections have ters is recommended. been determined to be linear. d. The pycnometer’s shape and materials of construction shall provide a safe, precise, easy-to-clean device. All sur- 14.6.9.4.4 Single Cylinder faces shall be smooth and polished to facilitate cleaning. The pycnometer’s flow pattern shall be designed to eliminate de- A single-cylinder pycnometer consists of a stainless steel position and gas entrapment, ensure proper purging, and al- cylinder with a capacity of approximately 500 cubic cen- low temperature stabilization. timeters, fitted with integral valves at each end, that is de- e. Precision shutoff valves shall be fitted at each end of the signed and constructed for a maximum allowable working pycnometer. The valves shall either be welded or form an in- pressure specified by the user. tegral part of the pycnometer. The valves shall provide a fast, Figure 11 shows the single-cylinder design. The fluid positive, zero-leakage shutoff and shall be resistant to abra- flows from bottom to top, minimizing the possibility of gases sive material. being trapped. f. A full-flow rupture disk shall be installed to prevent over- The volume temperature and pressure corrections have pressure due to thermal expansion of the test fluid. been determined to be linear. g. A serial number shall be permanently affixed to the ves- sel. 14.6.9.5 CERTIFICATION Certification of flow-through pycnometers shall be in ac- 14.6.9.4 CLASSIFICATION cordance with 14.6.16. Certification shall be performed 14.6.9.4.1 General when any of the following occurs: There are three types of flow-through pycnometers-sin- a. Original construction is completed. gle sphere, double-wall vacuum sphere, and single cylinder. b. Two years have elapsed since the last certification. c. The vessel has been damaged. 14.6.9.4.2 Single Sphere d. The vessel has been disassembled. e. The valve parts have been replaced. A single-sphere pycnometer consists of a stainless steel f. The rupture disk has been replaced. sphere with a capacity of approximately 1000 cubic centime- ters that is designed and constructed for a maximum allow- If the valve manufacturer can substantiate claims that re- able working pressure specified by the user. placement of the welded valve parts will not change the pyc- Figure 9 shows the single-sphere design. The fluid flows nometer volume or its evacuated weight by more than 0.02 through the inlet valve into the sphere and then up through percent, then recertification is not required. A similar veri- the siphon tube. The gas vent and siphon tube minimize the fication is required for replacement of the rupture disk. An possibility of gases being trapped and assist in removing de- evaluation should be performed to assure that the E,, value is position. not altered when these parts are replaced.COPYRIGHT American Petroleum InstituteLicensed by Information Handling Services
  26. A P I M P M S * 1 4 - b 91 = 0732290 0095869 9 SECTION 6-CONTINUOUS DENSITYMEASUREMENT 17 14.6.9.6 VERIFICATION b. The system shall include a sample probe in the center third of the pipe for slipstream flow. Verification of the pycnometer’s base volume (PBV) and c. The system shall not induce separation of the process its evacuated weight (Wo) be performed in accordance may fluid. with the procedures described in 14.6.15. It is important to d. The system shall provide sufficient flow to minimize den- note that the prover’s Epand E, values can only be confirmed by performing the tests called for in 14.6.16. sity lags between the density meter and the pycnometer. The results of the verification test shall not be used to e. The system shall not cause cavitation or flashing of the redefine the PBV and W,values, fluid. The results of the verification test can be used to confirm f. The installation shall permit the escape of any air or gas that a replacement valve or rupture disk has not changed the bubbles. PBV and Wovalues by more than 0.02 percent. g. The installation shall minimize fluid pulsation and pres- sure surges. h. The installation shall permit cleaning of associated pipe- 14.6.1 O Density Sampling Systems line facilities without an impact on density measurement. 14.6.10.1 DESIGN CRITERIA i. The entire sampling system, including the density metes and pycnometer, shall be thermally bonded in accordance The density meter measures only the fluid passing through with the requirements in 14.6.7.5. the density sampling system. The density sampling system j. The system shall include vertically mounted thermowells shall meet the following criteria: for temperature instruments, to relate density deviation to a. The system shall be installed in a location where the fluid temperature differences. is homogeneous and within the density deviation criteria of k. The system shall include taps for pressure instruments, to 14.6.7.2.2. relate density deviation to pressure differences.COPYRIGHT American Petroleum InstituteLicensed by Information Handling Services
  27. A P I MPMSUL4.b 91 0732290 0095870 5 18 CHAPTER 14-NATURAL GASFLUIDS MEASUREMENT 1. The system shall provide adequate filtration and condi- As an option, the system may include a flow indicator to tioning to prevent particulates from damaging the density assure adequate flow through the sampling system at all meter or pycnometer. times. m. The system shall include connections to permit conve- nient installation and removal of the pycnometer. 14.6.10.2 TYPES n. The system shall include a means of venting or flaring 14.6.10.2.1 General fluid when the pycnometer is installed. Density sampling systems are divided into two major o. The system shall not affect the velocity profile for turbine, groups: grab-sample and continuous-sample systems. Figure vortex, or orifice meters. 12 summarizes the classification system. p. The system shall not bypass flow around the volume me- ter. 14.6.10.2.2 Grab-Sample Systems q. The pycnometer installation shall take into account flow rate, mounting attitude, and thermal bonding. Grab-sample systems take a spot sample of the fluid at the r. The density meter installation shall take into account flow sampling point. Discrete density meters normally use these rate, mounting attitude, thermal bonding, and maintenance. systems. The user assumes that a representative sample of s. Any pumps associated with the sample system shall be the fluid has been provided. Grab-sample systems are not installed downstream from the pycnometer and density me- covered by this standard. ter to preclude errors caused by pump-induced pressure or temperature increases. 14.6.10.2.3 Continuous-Sample Systems t. The installation of restriction devices between the flow- Continuous-sample systems constantly pass a representa- meter, the density meter, the pycnometer, and the prover, tive sample of the fluid through or around the density instru- which could result in density differences, shall be avoided. ments. Continuous-sample systems are classified in two Figure 1O-Double-Wall Vacuum Sphere PycnometerCOPYRIGHT American Petroleum InstituteLicensed by Information Handling Services
  28. A P I M P M S * L 4 - b 91 m 0732290 009547L 7 m Plug valve SECTION &CONTINUOUS - DENSITYMEASUREMENT Insertion Direct In line I Density sampling systems Slipstream Pump devices Restriction devices Orifice plates S bends Control valves Reduced pipe Velocity head devices 19 I Grab Scoop tubes Pitot tubes Figure 12-Classification of Density Sampling Systems Vessel I pipe, the pycnometer and its associated sampling system still constitute a slipstream design. 14.6.10.4 SLIPSTREAM SYSTEMS ü Slipstream continuous-sample systems are the most com- monly used. As shown in Figure 12, there are three types of I slipstream systems, based on flow inducement: I a. Pumps. b. Restriction devices. c. Velocity head devices. Pumps can provide the energy needed to maintain flow Rupture disk 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 Plug valve through the use of orifice plates, S bends, control valves, and reduced pipe diameters. Figure 15 shows two typical instal- lations. Velocity head devices provide the energy needed to main- tain 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 in- Note: The vaive body is an integral part of the vessel. stalling the pycnometer in series may stop flow through the density sampling system. An alternative method is to install Figure 1I-Single-Cylinder Pycnometer the pycnometer sampling system in parallel with the density meter sampling system. groups, based on the mounting of the density meter: inser- tion and slipstream. 14.6.10.5 THERMAL BONDING 14.6.10.3 INSERTION SYSTEMS Thermal bonding is required on all installations to mini- Figure 13 shows a typical insertion continuous-sample mize density errors due to temperature differences. Various system. Even though the density meter is installed in the levels of thermal bonding, based on the fluid’s sensitivity toCOPYRIGHT American Petroleum InstituteLicensed by Information Handling Services
  29. 20 CHAPTER 14-NATURAL GASFLUIDSMEASUREMENT FI Pycnometer I v o DIRECT INSERTION Flow - Flow 6 - II II IN-LINE INSERTION I 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. ditions. Insulation is installed between the volume meter and Two types of thermal bonding systems have been successful: the sampling system. b. The sampling system is installed externally to the main a. The sampling system is installed in close thermal contact pipeline, and the entire system is insulated against ambient with the main pipeline, and the entire system (density meter conditions by being installed in an insulated housing. In and sampling system) is insulated against ambient con- 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 DevicesCOPYRIGHT American Petroleum InstituteLicensed by Information Handling Services
  30. API M P t l S * l 1 4 - 6 91 0732290 0095873 O i SECTION 6-CONTINUOUS DENSITY MEASUREMENT 21 protection from the elements when the density meter is 14.6.11.2.3 Weigh Scale proved. Insulation is installed between the volume meter and the sampling system. A weigh scale, or analytical balance, of sufficient preci- sion to obtain measurement accuracy of 0.02 percent of the 14.6.11 Proving Systems test fluid’s weight or the air-filled pycnometer’s weight, whichever is less, shall be used. Weigh scales are classified 14.6.11.1 GENERAL in two groups: The accuracy of the proving system is vitally important in a. Electronic scales. obtaining a successful pycnometer proving. One of the most b. Mechanical scales (triple beam and hanging basket). important pieces of equipment is the weigh scale or analyti- cal balance, Both types of scales have been successfully used, but a higher degree of success has been achieved with electronic 14.6.11.2 APPARATUS scales. 14.6.11.2.1 General Scales shall be calibrated at the time of proving with certi- fied apparent mass standards (test weights) to assure accu- Five pieces of equipment are needed to perform an accu- racy and to avoid weighing errors due to local gravitional rate pycnometer calibration of a density meter. This equip- forces. ment is described in 14.6.11.2.2 through 14.6.11.2.6. Selection of the type of weigh scale should take into ac- count the fluid- or air-filled mass of the pycnometer, the pre- 14.6.11.2.2 Pycnometer cision of the scale, and environmental conditions. A pycnometer is a vessel whose volume (PQ and evac- The scale shall be mounted on a level, stable, vibration- uated weight (Wo) known within 0.02 percent. Thepyc- are free surface. If the scale is not equipped with an internal nometer shall be calibrated in accordance with the criteria level, an appropriate level shall be used to verify that the and procedures described in 14.6.16. scale pan is horizontal. I+ 30 maximum +I ORIFICE Pc o e r yn m t , e O( - I I I CONTROL VALVE Figure 15-Slipstream-Type Continuous Density Sampling Systems: Restriction DevicesCOPYRIGHT American Petroleum InstituteLicensed by Information Handling Services
  31. A P I MPMS*L4.b 9L W 0732290 0095874 2 = 22 CHAPTER I &NATURAL GASFLUIDS MEASUREMENT Flow __* PYCNOMETER IN SERIES WITH DENSITY METER I PYCNOMETER IN PARALLEL WITH DENSITY METER -Flow Note: When the pycnometer is connected in series with the density meter, the pressure drop caused by the pyc- nometer 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 14.6.11.2.6 Pressure Instrument currents on the scales measurements. Pressures shall be measured with a device accurate to 1 A pycnometer holding tray is recommended for centering pound per square inch (6.90 kilopascals) and traceable to and stabilizing the pycnometer during weighing. NIST. Electronic devices are preferred because of their read- ability. 14.6.11.2.4 Certified Test Weights In some situations, a differential pressure device may be required to assure that the density deviation due to pressure Certified apparent mass standards (test weights) that con- is within the design criteria given in 14.6.7.2.2 and depicted form to NIST Class S or P shall be used to calibrate the in Figure 8. weigh scale. Figure 3 shows a certificate for typical sec- ondary apparent mass standards traceable to NIST. 14.6.12 Proving of Density Meters The test weights shall be recertified if they have been damaged or are suspected of being in error. 14.6.12.1 METHOD Proving a density meter at actual operating conditions (at 14.6.11.2.5 Temperature Instrument elevated pressures) and with a precision of 0.05 percent shall be accomplished by using a flow-through pycnometer. The Temperatures shall be measured with a portable device ac- pycnometer method consists of four discrete steps: curate to 0.2"F (O. 1OC) and traceable to NIST. Electronic de- vices are preferred because of their readability. a. Entrapping a homogeneous, representative sample of To eliminate possible errors, the same device shall be used fluid at the density meters operating conditions in a pyc- at all three points (the thermowells shown in Figure 8). nometer of precisely known volume and evacuated weight.COPYRIGHT American Petroleum InstituteLicensed by Information Handling Services
  32. A P I MPMS*L4*b 9L m 0732290 0095875 4 m I SECTION &CONTINUOUS MEASUREMENT DENSITY 23 I b. Accurately determining the fluid-filled weight of the pyc- a. Wash the inside of the pycnometer with solvent and then nometer. with acetone to remove any residual solvent. c. Correcting the pycnometer volume for the effects of fluid b. Dry the inside of the pycnometer thoroughly by purging temperature and pressure. with clean, dry air or clean, dry nitrogen for several minutes d. Correcting for the effect of air buoyancy. to evaporate the remaining acetone. c. Wash the outside of the pycnometer with distilled water. Successful proving criteria require that the density meter Rinse with acetone. Blow dry the outside of the pycnometer. factors (DMFs) for two consecutive proving runs have a re- peatability tolerance not greater than 0.05 percent. 14.6.13.3 CALIBRATING AND CHECKING THE For most applications, the pycnometer is installed in series TEST EQUIPMENT with the density meter. For some applications, the pycnom- eter is installed in parallel with the density meter. Caution The following procedure shall be performed to calibrate must be observed to assure that the density meter and pyc- and check the test equipment: nometer are experiencing the same homogeneous fluid at the a. Calibrate the weigh scale using the certified test weights. same density conditions. b. Verify the operation of the temperature and pressure de- vices. 14.6.12.2 DENSITY STABILITY Unless otherwise agreed upon by the two parties, provings 14.6.13.4 VERIFYING THE PYCNOMETER’S should be conducted when fluid conditions approach steady EVACUATED WEIGHT state. If the density varies more than 0.05 percent over ape- The following procedure shall be performed to verify the riod of time required to fully stabilize the pycnometer, the re- pycnometer’s evacuated weight (Wo): quired repeatability of 0.05 percent is likely to be unobtainable. a. Place the air-filled pycnometer on the weigh scale and record the scale’s reading. 14.6.12.3 FLUID BEHAVIOR b. Calculate the field Woand verify that it does not differ from the certificate value by more than 0.02 percent. If the Fluid behavior, along with its impact on the performance pycnometer has been weighed with the field fittings attached, of the pycnometer, should be evaluated. Errors may be in- add the fittings’ weight to the certificate Wobefore compar- troduced as a result of the following factors: ing the Wovalues. a. Polymerization-Will polymerization occur during fil- c. If the field Wodiffers from the certificate value by more ling, operation, or emptying of the pycnometer? than 0.02 percent, verify the calculations, recheck the scale b. Liquid-liquid separation-Will liquid-liquid separation calibration, or both. occur during filling, operation, or emptying of the pycnom- d. If the field Wohas increased more than 0.02 percent from eter? Will lubricating oil or glycol adhere to the inside of the the certificate Wo,either the pycnometer has been insuf- pycnometer? ficiently cleaned and driedor the fittings’ weight is incorrect. c. Autorefrigeration-Will autorefrigeration occur? If so, Continue to clean the pycnometer or remove the fittings until will hydrates form? For CO,, will dry ice form? What im- the Wovariance is less than or equal to 0.02 percent. pact will autorefrigeration have on the time required to reach e. If the field Wohas decreased by more than 0.02 percent temperature stability? from the certificate Wo,either the pycnometer has been dam- aged or the fittings’ weight is incorrect. Remove the fittings To eliminate autorefrigeration, the pycnometer and its piping to verify possible damage. If the pycnometer is damaged, it may be preloaded with an inert gas at a pressure sufficient to shall not be used. prevent the phenomenon. 14.6.13.5 INSTALLING THE PYCNOMETER 14.6.1 3 Proving Procedures The following procedure shall be performed to install the 14.6.13.1 GENERAL pycnometer or pycnometers: Before a proving run can be performed, all test equipment a. Install the pycnometer in series with the density mefer or shall be calibrated or checked. Refer to Figure 8 in following in a parallel slipstream. Allow product to enter the upstream the proving procedures. pycnometer valves first. Then vent or flare any gases or va- pors from the pycnometer and its piping through the vent 14.6.13.2 CLEANING THE PYCNOMETER valve. The following procedure shall be performed to clean the b. When the pycnometer is filled with fluid, fully or partially pycnometer: close the bypass valve to initiate flow.COPYRIGHT American Petroleum InstituteLicensed by Information Handling Services
  33. A P I MPMS*14-b 91 E 0732270 0 0 7 5 8 7 6 b 24 NATURAL GASFLUIDSMEASUREMENT CHAPTER c. Install an insulation blanket on the pycnometer. Except c. Calculate the repeatability. A successful proving requires when a double-wall vacuum sphere pycnometer is used, the that the DMFs for two consecutive proving runs not differ by pycnometer shall be insulated to speed temperature stabiliza- more than 0.05 percent. tion and prevent water condensation. d. When two successful consecutive provings have been performed, calculate the average DMF. 14.6.13.6 VERIFYING DENSITY DEVIATION AND e. For applications in which the density meter’s output is ad- STABILITY justed, an additional proving run shall be performed to con- The following procedure shall be performed to verify den- firm that the adjusted density meter’s output does not differ sity deviation and stability: from the new test’s result by more than 0.05 percent. a. Observe the output of the density meter for several min- 14.6.13.9 EMPTYING THE PYCNOMETER utes to verify steady-state density conditions. b. When temperature and pressure differences between the The following procedure shall be performed to empty the density meter and the pycnometer or pycnometers have pycnometer or pycnometers: stayed within the criteria given in 14.6.7 for a sufficient pe- Note: For some applications, the steps described in Items b and c below may riod of time, record the following field data: be waived if agreed upon by the two parties. 1. Observed density (density meter output). a. Empty the pycnometer in a safe location by either venting 2. Density meter temperature. or flaring the contents. 3. Pycnometer temperature. b. Clean the pycnometer in accordance with 14.6.13.2. 4. Density meter pressure. c. Verify the pycnometer’s evacuated weight (Wo)using the 5. Pycnometer pressure. procedures described in 14.6.13.4. If the pycnometer’s evac- c. Partially open the pycnometer bypass valve and then im- uated weight differs from the certificate value by more than mediately close the pycnometer’s inlet and outlet valves. Be 0.02 percent, the test results are voided. 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 14.6.14 Calculation Procedures void the test. 14.6.14.1 GENERAL 14.6.13.7 DETERMINING THE FLUID-FILLED The steps described in this subsection outline the appro- WEIGHT priate calculation procedures for proving density meters by The following procedure shall be performed to determine the use of pycnometers. the pycnometer’s fluid-filled weight (W,): From the pycnometer’s certificate, obtain the following Note: To prevent operation of the rupture disk, the time required to remove data: the pycnometer, weigh it, and empty it in a safe location shall kept to a min- imum. a. The pycnometer’s air-filled weight (W,). b. The pycnometer’s evacuated weight (Wo). a. Remove the insulation blanket from the pycnometer or c. The pycnometer’s base volume (PBV). pycnometers. d. The coefficient of cubical expansion due to temperature b. If necessary, wash both valve openings and the outside of on the pycnometer (Et). the pycnometer. Blow dry with dry air or nitrogen. Repeat if e. The coefficient of cubical expansion due to pressure on necessary. the pycnometer ( E J . c. Place the pycnometer on the weigh scale and record the f. The datum pressure of the pycnometer (P,). weight. g. The datum temperature (&). 14.6.13.8 CALCULATING THE DENSITY METER If the pycnometer’s fluid-filled weight (W,) was determined CORRECTION FACTOR with the fittings attached, add the weight of the field fittings to the certificate W, and W, values before proceeding. The following procedure shall be performed to calculate In addition, obtain the following data: the density meter correction factor: a. The elevation of the facility above sea level (h). a. Calculate the density meter correction factor ( D M F ) in b. The density of the reference test weights (pnv,). accordance with the instructions given in 14.6.14. c. The density of the field test weights (pnvf). b. Repeat the steps described in 14.6.13.5 through 14.6.13.7 d. The existing density meter factor (DMF). and Item a above to obtain the second consecutive DMF. (When using two pycnometers in series, two consecutive From the proving procedures, obtain the following data DMF values have already been obtained from Item a above.) for each of a minimum of two consecutive proving runs:COPYRIGHT American Petroleum InstituteLicensed by Information Handling Services
  34. A P I M P M S x L 4 - 6 91 m 0732290 0095877 8 m SECTION 6-CONTINUOUS DENSITY MEASUREMENT 25 a. The meter reading. 14.6.14.7 DETERMINE THE MASS OF THE b. The pycnometer’s air-filled weight OY,). FLUID (M‘J c. The pycnometer’s fluid-filled weight (Wf). The mass of the fluid (M,) shall be calculated using the d. The test pressure (PJ. following equation: e. The test temperature (Tf). Mfl = (w,- Wo>C,,v 14.6.14.2 CALCULATE THE AIR DENSITY 14.6.14.8 DETERMINE THE DENSITY AT TEST For calibration of density meters by pycnometers, the dry CONDITIONS (pFip) air density shall be calculated using the following equation (ü.S. Units): The value for pFlp shall be calculated using the following equation: pA = 0.0012[1 - (0.032h 1lOOO)] PFip = lpvv Where: If necessary, convert the density to the appropriate units. The ti = elevation above sea level, in feet. conversion factors are as follows: For a given proving location, the air density is constant. As a. To convert from grams per cubic centimeter to kilograms a result, the air density need only be calculated once. per cubic meter, multiply by 1000. b. To convert from grams per cubic centimeter to specific 14.6.14.3 VERIFY THE PYCNOMETER’S gravity, divide by 0.999012. EVACUATED WEIGHT (Wo) c. To convert from grams per cubic centimeter to pounds per The field Woshall be calculated using the following equa- cubic foot, multiply by 62.428. tion: d. To convert from grams per cubic centimeter to pounds per gallon, multiply by 8.3454. Field Wo = Field W, - pAPBV e. To convert from grams per cubic centimeter to pounds per barrel, multiply by 350.51. Compare the field Wowith the certificate Wo.If the differ- ence exceeds 0.02 percent, the pycnometer shall not be used. 14.6.14.9 DETERMINE THE DENSITY METER FACTOR (DMF) 14.6.14.4 CALCULATE THE PYCNOMETER’S FLOWING VOLUME (PV;,) The DMF shall be calculated using the following equa- tion, with pFtp the same units as the density meter’s read- in The PK, shall be calculated using one the following equa- ing: tions: When Pf is in pounds per square inch absolute, DMF = pFiP /(Density meter reading) Pyp = [PBV + Ep(P, - Pd)][l + Et(Tf - Td)] When Pf is in pounds per square inch gauge, 14.6.14.10 DETERMINE THE RESULTS OF THE SECOND PROVING RUN Pyp = [PBV + EpP,][l + Et(T, - T,)] Repeat the calculations described in 14.6.14.2 through 14.6.14.5 CALCULATE THE APPARENT 14.6.14.9 for the second proving run. MASS OF THE FLUID 14.6.1 4.11 DETERMINE THE REPEATABILITY OF The apparent mass of the fluid (AM,) shall be calculated THE RESULTS using the following equation: The repeatability of the results can be calculated using the AMfl = W, - r-V, following equation: Maximum DMF - Minimum DMF 14.6.14.6 CORRECT FOR AIR BUOYANCY ON % = x 100 TEST WEIGHTS (&) Minimum DMF The CBw field provings shall be cakulated using the for For a successful test, the DMFs for two successive proving following equation: runs shall not differ by more than 0.05 percent. ‘BW = - (pA/pT!Vf) 14.6.14.12 CALCULATE THE NEW DMF A constant value for CBwmay be used for a specific site and The average DMF value shall be calculated using the fol- test equipment. lowing equation:COPYRIGHT American Petroleum InstituteLicensed by Information Handling Services
  35. A P I M P M S * 1 4 - 6 91 0732290 0095878 T 26 CHAPTER 14-NATURAL GASFLUIDS MEASUREMENT Average DMF = ( D M F for Run 1 + D M F for Run 2) 1 2 for 10 minutes. Close the inlet valve. (The pycnometer is probably not yet fully evacuated.) The method of applying the average D M F to the custody d. Wash the outside of the pycnometer with distilled water, transfer quantities depends on the secondary equipment that and then rinse with acetone. Blow dry the outside of the pyc- converts the density meter’s raw output to engineering units, nometer. the mass flow integrating equipment, and the accounting e. Conduct all weigh tests without field or laboratory fit- policies of the operator. The equipment manufacturers tings. Conduct weigh tests on pycnometers equipped only should be consulted to assure the correct application of the with valves. The removal of all fittings accomplishes two proving results. goals: Both parties should agree on the method by which the av- 1. The pycnometer’s base volume is verified as it was de- erage DMF is to be applied to the custody transfer quantities teimined in the calibration (without any fittings). prior to commencement of movements. 2. Entrapment of air and water by the fittings is elimi- Figures 17 and 18 show examples of density meter prov- nated. ing reports that use the data for the pycnometer. f. Calibrate the weigh scale with the apparent mass stan- dards. 14.6.15 Field Verification Procedures for Pycnometers 14.6.15.4 VACUUM FILL AND DEAERATE THE 14.6.15.1 OBJECTIVE OF TEST WATER RESERVOIR The objective of the field verification test is to determine The water reservoir shall be vacuum filled and deaerated whether the pycnometer’s base volume (PBV) and evacuated in accordance with the following procedure: weight (Wo)have changed since the last calibration. An ac- a. Set up the test apparatus as shown in Figure 19. ceptable verification is determined by the repeatability of the b. Close Valve A and pull a vacuum on the system. The wa- test results for two consecutive runs. ter will be displaced from the 1-gallon container to the water A repeatability of at least 0.02 percent for each of the fol- reservoir. lowing values for two consecutive runs is needed to provide c. When enough water has been displaced, turn off the vac- an acceptable test: uum pump. d. Set up the test apparatus as shown in Figure 20. a. The pycnometer’s evacuated weight (Wo). e. Close Valve A. Deaerate the distilled water by pulling a b. The pycnometer’s air-filled weight (W,). vacuum on the water reservoir, as shown in Figure 20, until c. The pycnometer’s base volume (PBV) at 14.696 pounds all air bubbles have ceased. Close Valve F, and disconnect per square inch absolute. the Tygon tubing from Valve E If the field-determined PBV and Wodo not differ from the certificate values by more than 0.02 percent, then the pyc- 14.6.15.5 DETERMINE THE EVACUATED AND nometer does not require recertification. The field verifica- AIR-FILLED WEIGHT tion test does not confirm the Ep and E, values. The pycnometer’s evacuated weight (Wo)and air-filled weight (W,) shall be determined in accordance with the fol- 14.6.15.2 TEST EQUIPMENT lowing procedure: The test equipment required for field verification of pyc- a. Connect the pycnometer to the Tygon tubing, as shown in nometers is listed in Table 4. Figure 2 1. b. Evacuate the pycnometer with the vacuum pump to at 14.6.15.3 CLEAN THE PYCNOMETER AND least 29.0 inches of mercury for 2 minutes. Shut the outlet CHECK THE TEST EQUIPMENT valve. Before a pycnometer can be verified, it must be thor- c. Disconnect the pycnometer from the Tygon tubing, place oughly cleaned, and all test equipment must be calibrated or the evacuated pycnometer on the weigh scale, and record the checked, in accordance with the following procedure: evacuated weight (Wo)to the nearest O. 1 gram. d. Repeat the steps described in Items a-c above until two a. Wash the inside of the pycnometer with a petroleum- successive weighings for Wodo not differ by more than 0.02 based solvent, such as kerosene, and then with acetone to re- percent. Record the last Woreading. move any residual solvent. e. Open the inlet valve. After 30 seconds, weigh the pyc- b. Rinse the pycnometer with distilled water, and then wash nometer and record the air-filled weight (W,) to the nearest with acetone to remove any residual water. 0.1 gram. c. Dry the inside of the pycnometer thoroughly by purging with dry nitrogen, and then evacuate it with a vacuum pump (text ronrinued on page 29)COPYRIGHT American Petroleum InstituteLicensed by Information Handling Services
  36. A P I MPMS*II.b 9% 0732290 0095879 I SECTION 6-CONTINUOUS MEASUREMENT DENSITY 27 DENSITY METER PROVING REPORT Pipeline: CO^ Pipeline Date: 6/18/87 Location: Meter station Report:I 8 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 PB 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 Ib/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 €,XE 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 Ib/ft3 45.778 45.760 ~ 17 DMF = line 16 i line í 1.0035 1.0030 ResuIts 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 1COPYRIGHT American Petroleum InstituteLicensed by Information Handling Services
  37. A P I MPMS*14.b 91 W 0 7 3 2 2 9 0 0095880 8 = 28 CHAPTER 14-NATURAL GASFLUIDS MEASUREMENT DENSITY METER PROVING REPORT PiDeline: CO-, P i D e l i n e I Date: 6/18/86 I ~ ~ ~ Location: Meter s t a t i o n 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: Vibratins W": 1355.57 i w,: Existing DMF i. 0002 I En: O. 00132 I €0: CW B : 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 IPressure I psig I 1200 1200 / Ambient temperature I "F 62 62 Volume i I Prover serial no. I I 501 i 501 l 5 IProver base volume I cm3 I 992.39 I 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(seenote) 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 13 Test density = line 12 x 62.428 Ib/ft3 I 45.778 45.759 14 Density factor = line 13 t line 1 1.0035 1.0030 15 Average density factor 1.0032 Note: ,C = 1 - í ~ d o ~ ~ ~ ) . , Comments: Company: Witness : Figure 18-Typical Proving Report: Example 2COPYRIGHT American Petroleum InstituteLicensed by Information Handling Services
  38. API MPMS*14mb 91 œ 0732290 0095881 T œ SECTION 6 ~ O N T i N U O U S MEASUREMENT DENSITY 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 0.1 g Test weights NíST Class P or S Glass thermometer As needed 0.2”F Vacuum manometer 0-120 tiìm Hg 1% Distilled water in glass container 7000 cm’ Glass-beaker water trap 250 cm’ Vacuum pump 0-30 in Hg O. 1 pm Hg” Stainless steel tubing 20.250 in Clear vacuum tubing 20.250 in “Ultimatevacuum. 14.6.15.6 DETERMINE THE WATER-FILLED served entering the water trap, close the pycnometer’s outlet WEIGHT valve and then its inlet valve, followed by Valve A. e. Remove the pycnometer, and using a syringe, wash both The pycnometer’s evacuated weight and air-filled weight valve openings with acetone to remove excess water. Blow shall be verified using the water-weigh method in accor- dry the pycnometer with dry nitrogen. Repeat if necessary. dance with the following procedure: f. Place the water-filled pycnometer on the weigh scale and a. Assure that the water reservoir and the pycnometer are record the fluid-filled weight (W,) to the nearest O. 1 gram. stabilized at room temperature before proceeding with the g. Place the pycnometer on the vacuum-emptying apparatus verification. and empty the water from the pycnometer using the vacuum- b. Install the pycnometer on the test apparatus, as shown in emptying method shown in Figure 23, Figure 22. Verify that Valve F is closed and Valve A is open. h. Remove the clear vacuum tubing and flush it with acetone c. Evacuate air from the pycnometer and all vacuum tubing to remove excess water. Blow dry the tubing with dry nitro- through Valve A and the inlet and outlet valves for 10 min- gen. Repeat if necessary. utes. i. Repeat the steps described in 14.6.15.3, Items a-d; d. Open Valve F. Fill the pycnometer with distilled water 14.6.15.5; and 14.6.15.6, Items a-g. from the water reservoir. When a full flow of water is ob- j. Repeat the steps described in 14.6.15.3, Items a-d. Bennert-type vacuum mercury manometer 1 7fL Clear Tygon tubing ’/-inch stainless steel tubingCOPYRIGHT American Petroleum InstituteLicensed by Information Handling Services
  39. A P I MPMSxL4.b 9 1 0732290 0095882 1 30 CHAPTER 14-NATURAL GASFLUIDSMEASUREMENT 1- 7fL Clear Tygon tubing %-inch stainless steel tubing Bennert-type vacuum mercury manometer i Vacuum pump Water reservoir (7000-cm3glass container of distilled water) Figure 20-Deaerating the Water Reservoir (Field Verification) 14.6.15.7 VERIFY THE PYCNOMETER’S BASE pA = 0.0012[1 - (0.032h/1000)] VOLUME c,,v = 1 - (P, /Pnvr) 14.6.15.7.1 General 14.6.15.7.3 Determine the Mass of the Water This subsection describes the calculation method that shall The mass of the water (M,) shall be determined using the be used to verify the pycnometer’s base volume (PBV). following equation: From the procedures described in 14.6.15.1 through 14.6.15.6, the following data were obtained for each of two Mfl cwf - wo)cBV water-weigh verification runs: 14.6.15.7.4 Determine the Volume of the a. The pycnometer’s evacuated weight (Wo). Pvcnometer at the Test Conditions b. The pycnometer’s air-filled weight (W,). The volume of the prover at the test conditions (PV,,) shall c. The pycnometer’s fluid-filled weight (W,). be determined using the following equation: d. The test temperature (Tf). PYp = Mfl 1 W t p P The following data must also be known: Where: a. The elevation of the facility above sea level (h), in feet. b. The density of the test weights from the test weights’ pwlp density of distilled, deaerated water at T, and atmo- = certificate (pTWf), grams per cubic centimeter. in spheric pressure, in grams per cubic centimeter. c. The coefficient of cubical expansion due to temperature (pwtp be obtained from Table 5.) can (El),as shown on the certificate. d. The coefficient of expansion due to pressure on the pyc- 14.6.15.7.5 Determine the Pycnometer’s Base nometer (Ep), shown on the certificate. as Volume e. The datum temperature (&), in degrees Fahrenheit, as The pycnometer’s base volume ( P B V )shall be determined shown on the certificate. 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.COPYRIGHT American Petroleum InstituteLicensed by Information Handling Services
  40. A P I MPMS*14.b 91 = 0732290 0095883 3 W SECTION &CONTINUOUS DENSITY MEASUREMENT 31 / Water trap Bennert-typevacuum mercury manometer I f Vacuum pump Figure 21-Evacuating the Air-Filled Pycnometer Water beaker with Bennert-typevacuum mercury manometer Water reservoir I Vacuum pump Figure 22-Vacuum Filling the PycnometerCOPYRIGHT American Petroleum InstituteLicensed by Information Handling Services
  41. A P I MPMS*<L4.b 91 W 0 7 3 2 2 9 0 0095884 5 W 32 CHAPTER 14-NATURAL GASFLUIDS MEASUREMENT - Outlet I lo Bennert-typevacuum mercury manometer / I i r ?rtrap Vacuum pump Figure 23-Vacuum Emptying the Pycnometer 14.6.15.7.6 Determine the Repeatability of the eter’s volume at a datum temperature and separate test pres- Verification Test sures (PV,). One test pressure shall be 100 pounds per square inch ab- A repeatability of at least 0.02 percent for the following solute or less to assure adequate deaeration. A second test values for two consecutive runs is needed to provide an ac- ceptable verification test: pressure shall be above the pycnometer’s normal operating pressure so that the prover will not be operated outside of its a. The pycnometer’s evacuated weight (Wo). calibration data base. The third pressure shall be approxi- b. The pycnometer’s air-filled weight (W,). mately halfway between the other two pressures. c. The pycnometer’s base volume (PBV). A repeatability of at least 0.02 percent for the following values for two consecutive runs is needed to provide an ac- 14.6.15.7.7 Compare Test Results With ceptable test: Certificate Values a. The pycnometer’s evacuated weight (Wo). If any of the values specified in 14.6.15.7.6 differ from the b. The pycnometer’s air-filled weight (W,). certificate values by more than 0.02 percent, the pycnometer c. The pycnometer’s volume (PV,) at the datum temperature shall be calibrated in accordance with 14.6.16. Figure 24 and a pressure of 100 pounds per square inch absolute or shows a sample calculation worksheet for field verification less. of a pycnometer. d. The pycnometer’s volume (PV,) at the datum temperature and the maximum operating pressure. 14.6.16 Laboratory Calibration e. The pycnometer’s volume ( P h )at the datum temperature Procedures for Pycnometers and a pressure midway beteen the two pressures specified in Items c and d. 14.6.16.1 OBJECTIVE OF TESTS Based on the empirical data, the pycnometer’s volume at The objective of the pycnometer calibration is to deter- the test temperature and pressure (PV,,) shall be calculated mine the following unique values: using the following equation: a. The pycnometer’s air-filled weight (W,). b. The pycnometer’s evacuated weight (Wo). Pyp = [PBV + Ep(P, - p,)][1 + E,(T, - T,)] c. The pycnometer’s base volume (PBV). The nominal E, values may be used for calibrations, pro- d. The coefficient of cubical expansion due to temperature vided that the manufacturer has confirmed a linear relation- on the pycnometer (E,). ship for thermal expansion of the pycnometer. If the parties e. The coefficient of cubical expansion due to internal pres- wish to confirm the nominal E, value, the test method dis- sure on the pycnometer (Ep). cussed in 14.6.16.9 is recommended. An acceptable test is determined by the repeatability of the 14.6.16.2 TEST EQUIPMENT test results for two consecutive runs. A run consists of one evacuated weigh (Wo), air-filled one The test equipment required for laboratory calibration of weigh (Wa), and at least three determinations of the pycnom- pycnometers is listed in Table 6.COPYRIGHT American Petroleum InstituteLicensed by Information Handling Services
  42. A P I MPMS*14.b 91 m 0732290 O095885 7 = SECTIONCONTINUOUS DENSITY MEASUREMENT 33 14.6.16.3 CLEAN THE PYCNOMETER AND a. Wash the inside of the pycnometer with solvent and then CHECK THE TEST EQUIPMENT with acetone to remove any residual solvent. b. Rinse the pycnometer with distilled water, and then wash Before a pycnometer can be certified, it must be thor- with acetone to remove any residual water. oughly cleaned, and all test equipment must be calibrated or c. Dry the inside of the pycnometer thoroughly by purging checked, in accordance with the following procedure: with dry nitrogen, and then evacuate it with a vacuum pump Table 5-Atmospheric Water Density as a Function of Temperature Water Water Water Temperature Temperature Temperature Density Density Density OF "C ídem) "F OC ídcm3) O F "C ídcm3) 70.00 21.11 0.9979661 75.00 23.89 0.9973218 80.00 26.67 0.9966025 70.10 21.17 0.9979539 75.10 23.94 0.9973082 80.10 26.72 0.9965874 70.20 21.22 0.9979418 75.20 24.00 0.9972945 80.20 26.78 0.9965723 70.30 21.28 0.9979296 75.30 24.06 0.9972807 80.30 26.83 0.9965571 70.40 21.33 0.9979174 75.40 24.11 0.9972670 80.40 26.89 0.9965419 70.50 21.39 0.997905 1 75.50 24.17 0.9972532 80.50 26.94 0.9965266 70.60 21.44 0.9978929 75.60 24.22 0.9972394 80.60 27.00 0.9965 114 70.70 21.50 0.9978805 75.70 24.28 0.9972256 80.70 27.06 0.9964961 70.80 21.56 0.9978682 75.80 24.33 0.9972117 80.80 27.11 0.9964808 70.90 21.61 0.9978558 75.90 24.39 0.9971978 80.90 27.17 0.9964654 71.00 21.67 0.9978434 76.0iJ 24.44 0.9971838 81.00 27.22 0.9964500 71.10 2 1.72 0.9978310 76.10 24.50 0.9971699 81.10 27.28 0.9964346 7 1.20 21.78 0.9978185 76.20 24.56 0.9971559 8 1.20 27.33 0.9964192 71.30 21.83 0.9978060 76.30 24.61 0.9971419 8 1.30 27.39 0.9964037 71.40 21.89 0.9977935 76.40 24.67 0.9971278 8 1.40 27.44 0.9963882 71.50 21.94 0.9977809 76.50 24.72 0.9971í37 81.50 27.50 0.9963727 71.60 22.00 0.9977683 76.60 24.78 0.9970996 81.60 27.56 0.9963571 71.70 22.06 0.9977557 76.70 24.83 0.9970855 81.70 27.61 0.9963416 71.80 22.11 0.9977430 76.80 24.89 0.9970713 81.80 27.67 0.9963260 71.90 22.17 0.9977303 76.90 24.94 0.9970571 81.90 27.72 0.9963103 72.00 22.22 0.9977 176 77.00 25.00 0.9970429 82.00 27.76 0.9962947 72.10 22.28 0.9977049 77.10 25.06 0.9970286 82.10 27.83 0.9962790 72.20 22.33 0.9976921 77.20 25.11 0.9970144 82.20 27.89 0.9962633 72.30 22.39 0.9976793 77.30 25.17 0.9970000 82.30 27.94 0.9962475 72.40 22.44 0.9976664 77.40 25.22 0.9969857 82.40 28.00 0.99623 17 72.50 22.50 0.9976536 77.50 25.28 0.9969713 82.50 28.06 0.9962159 72.60 22.56 0.9976407 77.60 25.33 0.9969569 82.60 28.11 0.9962001 72.70 22.61 0.9976277 77.70 25.39 0.9969425 82.70 28.17 0.9961843 72.80 22.67 0.9976148 77.80 25.44 0.9969280 82.80 28.22 0.9961684 72.90 22.72 0.9976018 77.90 25.50 0.9969135 82.90 28.28 0.9961525 73.00 22.78 0.9975887 78.00 25.56 0.9968990 83.00 28.33 0.9961365 73.10 22.83 0.9975757 78.10 25.61 0.9968845 83.10 28.39 0.9961206 73.20 22.89 0.9975626 78.20 25.67 0.9968699 83.20 28.44 0.9961046 73.30 22.94 0.9975495 78.30 25.72 0.9968553 83.30 28.58 0.9960885 73.40 23.00 0.9975363 78.40 25.78 0.9968406 83.40 28.56 0.9960725 73.50 23.06 0.9975232 78.50 25.83 0.9968260 83.50 28.61 0.9960564 73.60 23.11 0.9975099 78.60 25.89 0.9968113 83.60 28.67 0.9960403 73.70 23.17 0.9974967 78.70 25.94 0.9967966 83.70 28.72 0.9960242 73.80 23.22 0.9974834 78.80 26.00 0.9967818 83.80 28.78 0.9960080 73.90 23.28 0.9974701 78.90 26.06 0.9967670 83.90 28.83 0.9959918 74.00 23.33 0.9974568 79.00 26.11 0.9967522 84.00 28.89 0.9959756 74.10 23.39 0.9974434 79.10 26.17 0.9967374 84.10 28.94 0.9959594 74.20 23.44 0.9974300 79.20 26.22 0.9967225 84.20 29.00 0.9959431 74.30 23.50 0.9974166 79.30 26.28 0.9967076 84.30 29.06 0.9959268 74.40 23.56 0.9974032 79.40 26-33 0.9966927 84.40 29.11 0.9959105 74.50 23.61 0.9973897 79.50 26.39 0.9966777 84.50 29.17 0.9958941 74.60 23.67 0.9973762 79.60 26.44 0.9966628 84.60 29.22 0.9958777 74.70 23.72 0.9973626 79.70 26.50 0.9966477 84.70 29.28 0.9958613 74.80 23.78 0.9973491 79.80 26.56 0.9966327 84.80 29.33 0.9958449 74.90 23.83 0.9973355 79.90 26.61 0.9966176 84.90 29.39 0.9958284 75.00 23.89 0.9973218 80.00 26.67 0.9966025 85.00 29.44 0.9958119COPYRIGHT American Petroleum InstituteLicensed by Information Handling Services
  43. API MPMS*LY*b 71 0732270 0075886 7 34 CHAPTER 14-NATURAL GASFLUIDS MEASUREMENT CALCULATION WORKSHEET 13 Test vs. Certificate No. 702C W O 1350.85 1350.83 o. 001% w, 1352.05 1351.97 O. 006% PBV 995.43 , 995.44 o. 001% I Figure 24-Field Verification Form for 10 minutes. Close the inlet valve. (The pycnometer is 2. Entrapment of air and water by the fittings is elimi- probably not yet fully evacuated.) nated. d. Wash the outside of the pycnometer with distilled water, f. Calibrate the weigh scale with the NIST Class P or S ap- and then rinse with acetone. Blow dry the outside of the pyc- parent mass standards. nometer. e. Verify the calibration of the pressure transmitters with a deadweight tester. 14.6.16.4 VACUUM FILL AND DEAERATE THE f. Verify the calibration of the digital thermometer with a WATER RESERVOIR certified thermometer by placing both in a beaker of water to The water reservoir shall be vacuum filled and deaerated assure agreement within 0.2"F. in accordance with the following procedure: g. Conduct all weigh tests without field or laboratory fittings. Conduct weigh tests on pycnometers equipped only with a. Set up the test apparatus as shown in Figure 25. valves. The removal of all fittings accomplishes two goals: b. Close Valve A and pull a vacuum on the system. The wa- 1. The pycnometers base volume is established without ter will be displaced from the 1-gallon container to the water any fittings. reservoir.COPYRIGHT American Petroleum InstituteLicensed by Information Handling Services
  44. l SECTION 6-CONTINUOUS DENSITY MEASUREMENT 35 Table 6-Test Equipment for Laboratory Calibration of Pycnometers Specifications Instrument Range Accuracy Volume Size Required Equipment Analytical balance with air shield 0-5000 g fO.O1 g Stainless steel fest weights 50-5000 g NIST Class P or S Digital thermometer As needed fO.l°F Glass thermometer As needed M.I°F Bennert-type vacuum manometer 0-120 mm 1% Pressure transmitter 1 0-500 psig 0.25%" Pressure transmitter 2 0-3000 psig 0.25C/o3 LED display 1 15-515 psia LED display 2 15-3015 psia Deadweight tester 0-3000 psig 0.101 Distilled water reservoir 5 gal (clear glass container) Water trap (clear glass beaker) 7000 cm3 Water cushion cylindefl 250 cm3 Vacuum pump O. 1 p n HgC 90 Ilmin Stainless steel tubing 20.250 in Clear vacuum tubing 20.250 in Optional Equipment (for Determinations of E,) Temperature bathd f58T 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 9 7 Digital thermometer Clear Tygon tubing %-inch stainless steel tubing 5-gallon container of Water reservoir Figure 25-Vacuum Filling the Water Reservoir (Laboratory Calibration)COPYRIGHT American Petroleum InstituteLicensed by Information Handling Services
  45. A P I M P M S * l 4 - b 91 œ 0732290 0095888 2 œ 36 14-NATURAL GASFLUIDSMEASUREMENT CHAPTER c. When enough water has been displaced, turn off the vac- 14.6.16.6 VACUUM FILL THE PYCNOMETER uum pump. The pycnometer shall be vacuum filled in accordance with d. Set up the test apparatus as shown in Figure 26. the following procedure: e. Close Valve A. Deaerate the distilled water by pulling a a. Install the pycnometer on the test apparatus, as shown in vacuum on the water reservoir, as shown in Figure 26, until Figure 28. all air bubbles have ceased. Close Valve E b. Evacuate air from the pycnometer and all stainless steel f. Before proceeding with the calibration, assure that the and vacuum tubing through Valves A and D for 10 minutes. temperature of the water reservoir and the pycnometer has Make sure that Valve B is closed. stabilized. The water reservoir need not be stabilized at room c. Open Valve F and fill the pycnometer with distilled water temperature, but the water temperature should approximate from the water reservoir. When a full flow of water is ob- room temperature. served entering the water trap, close the pycnometer’s outlet valve and Valve A. Open Valve B. 14.6.16.5 DETERMINE THE EVACUATED AND d. Pressure the system to 100 pounds per square inch abso- AIR-FILLED WEIGHT lute below the set point of the rupture disk. Check for leak- The pycnometer’s evacuated weight (Wo)and air-filled age. weight (W,) shall be determined in accordance with the fol- lowing procedure: 14.6.16.7 CALIBRATE USING THE WATER- WEIGH METHOD a. Evacuate the pycnometer with the vacuum pump to at least 29.0 inches of mercury for 2 minutes, as shown in Fig- The pycnometer’s water-filled weight shall be verified us- ure 27. ing the water-weigh method in accordance with the follow- b. Place the evacuated pycnometer on the weigh scale and ing procedure: record the evacuated weight (Wo)to the nearest 0.01 gram. a. Adjust the pressure to the desired setting. Close the pyc- c. Repeat the steps described in Items a and b above until nometer’s inlet valve and ensure that the pressure has not two successive weighings for Woagree within 0.02 percent. risen. If it has risen, open the pycnometer’s inlet valve, ad- Record the last Woreading. just the pressure accordingly, and then close the valve. d. Open the inlet valve and allow air to enter. After 30 sec- b. When the pressure is correct, close Valve D. onds, weigh the pycnometer and record the air-filled weight c. Record the water reservoir’s temperature, as indicated by (W,) to the nearest 0.01 gram. the digital thermometer, to the nearest O. 1°F. Bennert-type vacuum mercury manometer n (glass container of distilled water) 7fL Clear Tygon tubing %-inch stainless steel tubing Figure 26-Deaerating the Water Reservoir (Laboratory Calibration)COPYRIGHT American Petroleum InstituteLicensed by Information Handling Services
  46. A P I MPMS*i(/4.b 91 9 0732290 0095889 4 9 SECTION&CONTINUOUS DENSITYMEASUREMENT 37 /-inch stainless steel tubing i Figure 27-Vacuum Emptying the Pycnometer manometer U Point 1 Valve 0 Valve C Valve D thermometer 9 Valve F * O Valve A U Water trap (4000 cm3) 7- Vacuum pump Weigh scale with air shield Water reservoir 7fL Clear Tygon tubing íalass container of /-inch stainless steel tubing Figure 28-Pycnometer Calibration Test ApparatusCOPYRIGHT American Petroleum InstituteLicensed by Information Handling Services
  47. A P I MPMS*14-b 9 1 0732290 0095890 O W 38 CHAPTER 14-NATURAL GASFLUIDS MEASUREMENT - d. Remove the pycnometer, and using a syringe, wash both Note: A successful calibration run requires that the temperature of the water reservoir not vary by more than 1.O”F during the run. the inlet and outlet valve openings with acetone to remove excess water. Blow dry the openings with nitrogen. k. Place the pycnometer on the vacuum-emptying apparatus, e. Place the water-filled pycnometer on the weigh scale and and empty the water from the pycnometer using the vacuum record the fluid-filled weight (W,) to the nearest 0.01 gram. empyting method, as shown in Figure 27. f. Remove the section of test tubing and flush it with ace- 1. Repeat the steps described in 14.6.16.3, Items b and c; tone to remove excess water. Blow dry the tubing with nitro- 14.6.16.5; 14.6.16.6; and 14.6.16.7, Items a-j. (This com- gen. Wash the exposed portion of Valve D with acetone. pletes the second run.) Blow dry the valve with nitrogen. Repeat if necessary. g. Reinstall the test tubing and the pycnometer on the test 14.6.16.8 CALCULATE THE TEST RESULTS apparatus as shown in Figure 29. Open Valve G. The test results shall be calculated in accordance with the h. Evacuate air between Valve D and the pycnometer’s inlet tolerances given in the example shown in Figure 30. Because valve through Valve G for 5 minutes. Close Valve B. Open of the complexity of the equations, all calculations should be Valves A and D. After a full flow of water enters the water performed with the aid of a personal computer. trap, close Valves G and A. Open Valve B. i. Open the pycnometer’s inlet valve. 14.6.16.9 DETERMINE THE PYCNOMETER’S Et j. Repeat the steps described in 14.6.16.6 and 14.6.16.7, The pycnometer’s thermal expansion factor (E,)should be Items a-i, until at least three test weights have been recorded supplied by the manufacturer. However, if the pycnometer’s at three different pressures. Record the room air temperature to the nearest O. 1°F. (This completes the first run.) (text continued on page 47) Vacuum manometer Point h 7 I I Valve E Valve C Valve A Water trap (4000 cm3) 7 r l Vacuum pump Weigh scale with air shield d Water reservoir (glass container of distilled, deaerated water) l- 7fL Clear Tygon tubing %-inch stainless steel tubing Figure 29-Reinstallation of Test TubingCOPYRIGHT American Petroleum InstituteLicensed by Information Handling Services
  48. API M P M S * 1 4 . 6 71 m 0732290 0075891 2 m SECTION 6-CONTINUOUS MEASUREMENT DENSITY 39 PYCNOMETER CERTIFICATE Page 1 of 8 Date: F e b r u a r y 24, 1986 Certificate No.: wErGH1 Ownership: MPMS C h a p t e r 1 4 . 6 Pvcnometer Data Serial no.: 2 O 6 Prover type: S i n g l e s p h e r e Manufacturer: Maximum allowable working pressure: 1 9 0 0 p s i g Steel type: S t a i n l e s s , Type 304 Rupture disk pressure: 1800 p s i g Thermal coefficient (€J: 2 . 8 8 x 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 Range: 0-5500 g Accuracy: O . lo F Accuracy: o . o 1 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 Elevation: 50 ft Range 2: 0-3000 p s i g NIST Class: P Accuracy: O . 2 5 % Deadweight Tester Manufacturer: Model: Range: 0-3500 p s i g Accuracy: o . 1 0 % Comments: Figure 30-Typical Pycnometer Certificate and Calibration CalculationsCOPYRIGHT American Petroleum InstituteLicensed by Information Handling Services
  49. A P I MPMS*14.b 71 0732290 0075892 4 = 40 CHAPTER 14-NATURAL GASFLUIDS MEASUREMENT PYCNOMETER CERTIFICATE Page 2 of 8 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) 25 Test A NA 1- Test B NA Test A vs. Test B Repeatability (%) NA Pressure (Psi4 25 I PV, (cm3) NA 50 996.60 996.63 O. 003 50 I 996.62 1 5 100 200 300 400 NA 996.74 NA NA NA 996.80 NA I NA 0.006 NA + 100 400 I I I NA 996.77 NA p 500 NA NA NA 500 NA 600 NA NA NA 600 1 NA 13 700 800 900 1000 1100 NA 997.47 NA 997.75 NA 997.53 NA 997.76 NA I 0.006 NA o. 001 NA + 700 1000 1 I NA 997.50 997.76 1200 NA NA NA 19 1300 1400 1500 1600 1700 NA NA 998.36 NA NA NA 998.39 NA O. 003 + 1300 1600 I I NA 998.38 NA 1800 NA 1900 NA NA NA 1900 I NA 2000 NA NA NA 2100 NA NA I 2200 NA NA I 2200 I NA 2300 NA NA I 2300 1 NA ~~ Figure 30-ContinuedCOPYRIGHT American Petroleum InstituteLicensed by Information Handling Services
  50. A P I M P M S * l i 4 - b 91 0 7 3 2 2 9 0 0095893 b W SECTION 6-CONTINUOUS DENSITY MEASUREMENT 41 PYCNOMETER CERTIFICATE Page 3 of 8 Date: F e b r u a r y 24, 1986 _ _ _ _ _ _ ~ I Seriai NO.: 206 Pycnometer Calibration Summary (Continued) PV, (cm3) Weigh Pressure Test A vs. Test B Pressure No. (Psial Test A Test B Repeatability (%) (PW PV, (cm3) 26 2400 NA NA NA 2400 NA 27 I 2500 I NA I NA I NA 2500 NA 28 2600 NA NA NA 2600 NA 29 2700 NA NA NA 2700 NA 30 I 2800 ~~ I NA I ~ NA I NA 2800 NA 31 2900 NA NA NA 2900 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, - - O.O00028S(T, - Td)] Pd)][l i Comments: Name I Name Company Company ~ Figure 30- ContinuedCOPYRIGHT American Petroleum InstituteLicensed by Information Handling Services
  51. .. - - A P I MPMS*14.6 9 1 W 0732290 0 0 9 5 8 9 4 8 42 CHAPTER 14-NATURAL GASFLUIDS MEASUREMENT I ~ Date: February 24, 1986 ~~ ~ PYCNOMETER CERTIFICATE ~ Serial No.: 206 ~~ ~~ Page 4 of 8 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 PA: 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-ContinuedCOPYRIGHT American Petroleum InstituteLicensed by Information Handling Services
  52. 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 (25.27Oc ) 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 O. 9987811 9 700 NA O. 9990878 NA NA 10 800 77.5 2363.46 999.15 O. 9993937 999.76 997.53 11 900 NA O. 9996992 NA NA . . Figure 30-ContinuedCOPYRIGHT American Petroleum InstituteLicensed by Information Handling Services
  53. ___ -. -_ - - - A P I M P M S * l 4 - b 91 0732290 0 0 9 5 8 9 b L 44 CHAPTER 14-NATURAL GASFLUIDS MEASUREMENT 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-ContinuedCOPYRIGHT American Petroleum InstituteLicensed by Information Handling Services
  54. A P I MPMS*LV.b 91 = 0732290 0095897 3 W SECTION 6-CONTINUOUS MEASUREMENT DENSITY 45 PYCNOMETER CERTIFICATE Page 7 of 8 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 = 1 + (T, - Td)(Et). E,, = coefficient of expansion due to internal pressure on pycnometer. E, = coefficient of cubical expansion due to temperature on steel pycnometer = 2.88 x 1O” for Type 304 stainless steel (nominal) = 2.65 x for Type 316 stainless steel (nominal) = 1.86 x 1O” for carbon steel (nominal). h = elevation of weigh scale above sea level K, = isothermalcompressibility 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 = (W - ~o)(cBw)* Pd = datum pressure of pycnometer (14.696 psia). pt = test pressure. PBV = pycnometer base volume. PVp = pycnometer volume at datum temperature and test pressure = PV~/CTS,. PVw = pycnometer volume at test temperature and test pressure = 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-ContinuedCOPYRIGHT American Petroleum InstituteLicensed by Information Handling Services
  55. ~ .. _. - A P I MPMS*14.b 91 0732270 0095878 5 46 CHAPTER 1&NATURAL GASFLUIDSMEASUREMENT PYCNOMETER CERTIFICATE Page 8 of 8 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 11.2.3 (Wagenbreth water equation) = (999.8395639 + 0.06798299989T - 0.0091O6025564Tf2+ 0.0001005272999T3 - 0.000001 126713526T4 + 0.000000006591795606T5)/ 1000. pwlp= density of water inside pycnometer at test temperature and test pressure = Pwt 111 - [(i7,,)(p, - P,)ll. Comments: Figure 30-ContinuedCOPYRIGHT American Petroleum InstituteLicensed by Information Handling Services
  56. API MPMS*K14.b 91 0732290 0095879 7 SECTION 6-CONTINUOUS DENSITY MEASUREMENT 47 nominal Et cannot be substantiated by the manufacturer, tests Pd = datumpressure may be conducted to determine the thermal expansion of the = 14.696 pounds per square inch absolute. pycnometer (see Figure 3 1). A minimum of two temperature The accuracy associated with this equation is limited by the tests shall be conducted at least 40°F apart. following factors: Calibration and calculation procedures are purposely not included for the Et determination test. The E, for each man- a. The accuracy of the reference water density, pwt, over the ufacturers pycnometers should not change as long as the test conditions. materials used remain consistent in their thermal expansion b. The accuracy associated with calculating the average iso- properties. thermal compressibility of water, z,, at the test conditions. c. The use of only distilled, deaerated water. 14.6.17 Density of Water 14.6.17.1 GENERAL 14.6.17.3 REFERENCE WATER DENSITY (pwt) The density of a liquid decreases with increasing temper- In Chapter 11, Section 2.3, the Wagenbreth water density ature and, to a much lesser degree, increases with increasing equation is used to determine the water density at the test pressure. The density of deaerated, distilled water can there- temperature and standard atmospheric pressure. The Wagen- fore be expressed as a function of temperature and pressure. breth equation expresses the mass density, in grams per cu- bic centimeter, as a function of temperature at 14.696 pounds 14.6.17.2 WATER DENSITY AT TEST per square inch absolute as follows: TEMPERATURE AND PRESSURE pwt= r(9.998395639 x lo2) + (6.798299989 x lO")(T,) Assuming that the change in density is small compared with the original density, the following equation can be used - (9.106025564 x to calculate water density at the test pressure and tempera- + (1.005272999 x IO")(T:) ture. The application of the equation is limited to a temper- ature range of 32OF-125"F and a pressure range of 14.696- - (1.126713526 x lO")(Tp) 3000 pounds per square inch absolute. + (6.591795606 x i04)(q5)]/1000 PW,, = Pw, /[i - q p , - 41 1 Where: Where: = test temperature, in degrees Celsius. pWrp water density at the test temperature and pressure. = Several water density equations exist, but only slightly fiv,= water density at the test temperature and Pa different values are obtained from them. Using the Wagen- KIP= average isothermal compressibility of water at the breth equation, at 60°F (15.6"C) and 14.696 pounds per test conditions. square inch absolute (101.325 kilopascals), the density of Pf= test pressure. water is as follows: Temperature bath with coiled tubing 18 I Pycnometer Note: All flowing tubing, all valves, and the pycnometer shall be insulated to maintain a stable temperature. Figure 31-Optional EtTest ApparatusCOPYRIGHT American Petroleum InstituteLicensed by Information Handling Services
  57. A P I MPMS*KLg-b 7 1 0732270 0075900 T m 48 NATURAL GASFLUIDS CHAPTER MEASUREMENT pw, = 62.3660 pounds per cubic foot K, = [50.88496 + (6.163813 x 10-)(Tf) = O. 9990 121 gram per cubic centimeter + (1.459187 x 10-3)(Tf)+ (20.08438 x lO")(T:) At 68°F (20.0"C) and 14.696 pounds per square inch abso- - (58.4772 x 10-9)(Tp) + (410.41 1 x lO-*)(T;5)] lute (101.325 kilopascals), the density of water is as follows: + + {[i (19.67348 x 10-3)(Tf)](14.50377 lo6)) x pw, = 62.31572 pounds per cubic foot Where: = 0.9982019 gram per cubic centimeter Tf = test temperature, in degrees Celsius. 14.6.17.4 AVERAGE ISOTHERMAL Several calculated values for KI and K,, given in Table 7. are COMPRESSIBILITY OF WATER (K,) Although liquids are not normally considered to be com- 14.6.17.5 UNCERTAINTY ANALYSIS pressible, a correction for water compressibility as a function Within the temperature and pressure limitations defined in of pressure and temperature must be applied to achieve an acceptable accuracy. Enough data exist to determine the av- 14.6.17.2, the predicted water density is estimated to be erage isothermal compressibility of water. This standard uses within kO.01 percent of the true value. A comparison of Kells experimental water densities with the predicted values the following equation: confirms the stated uncertainty (see Table 8). iTiP = K,(1.00033 - [(2.17656 x 10-5)(Pf - Pd)/2] + ((8.546265 x 10-o)[(Pf + Pd)/2I2)) 14.6.18 Density of Air Where: 14.6.18.1 GENERAL Pf = test pressure, in pounds per square inch absolute. The density of air is a term in the equation for the correc- Pd = datum pressure tion for air buoyancy on weighings (Csw;see 14.6.6.5) and is = 14.696 pounds per square inch absolute. also used to verify the field Wo.Although the density of moist K, = isothermal compressibility of water at a pressure of air is less than that of dry air (see GPA 2143, all calculations 14.696 pounds per square inch absolute and the test shall use dry air density. As shown below, a sensitivity anal- temperature. ysis indicates that the error resulting from the use of dry air density is well within the accuracy of this standard. The effect of pressure on the isothermal compressibility of water has been calculated by curve-fitting the compressibil- 14.6.18.2 DRY AIR DENSITY ity of water as a function of pressure at 68°F (20°C). To cal- culate the isothermal compressibility of water at 14.696 14.6.18.2.1 For laboratory calibrations of pycnometers, pounds per square inch absolute and the test temperature,K,, dry air density shall be calculated using the following equa- Kells equation was adopted: tions. 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 32.0 50.8850 3.5084 x 3.5061 x 10" 0.999840 1.O00058 20.00 68.0 45.8918 3.1641 x 3.1620~ 0.998202 0.998398 50.00 122.0 44.1732 3.0456 x 3.0436 x 0.988058 0.988245 611 42.11 0.00 32.0 50.8850 3.5084 x 3.4860 x 0.999840 1.0019 17 20.00 68.0 45.8918 3.1641 x 3.1439 x l u 6 0.998202 1.O00072 50.00 122.0 44.1732 3.0456 x 3.0262 x 0.988058 0.989840 1465 101.01 0.00 32.0 50.8850 3.5084 x 3.4548 x 0.999840 1.004849 20.00 68.0 45.89 18 3.1641 x 3.1 158 x 0.998202 1.0027 13 50.00 122.0 44.1732 3.0456 x 2.9991 x 0.988058 0.992355 3050 210.28 0.00 32.0 50.8850 3.5084 x 3.4000 x 0.999840 1.O 10157 20.00 68.0 45.8918 3.1641 x 3.0663 x 0.998202 1.007492 50.00 122.0 44.1715 3.0455 x 2.95 14 x 0.988060 0.9969 1 ICOPYRIGHT American Petroleum InstituteLicensed by Information Handling Services
  58. A P I flPMS*L4*b 9 3 m 0732290 0095903 L W SECTION 6-CONTINUOUS DENSITY MEASUREMENT 49 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 OC "F pvtvlp c d (d ( pWlp dd Well -MI) (%) 77 5.30 0.00 32.0 1.000058 1.000118 0.000060 0.006 20.00 68.0 0.998398 O.9984O6 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 0.992351 -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 0.011 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, 14.6.18.4.1 General Although the density of moist air is slightly less than that pA = 0.0012[1 - (0.105h/1000)][520/(1.8T, + 492)] of dry air, a sensitvity analysis indicates that the amount of Where: errorresulting from the use-of the dry air value is beyond the pA = dry air density, in grams per cubic centimeter. attainable accuracy. h = elevation above sea level, in feet (meters). 14.6.18.4.2 Example TI = dry air temperature, in degrees Fahrenheit (degrees Celsius). Consider the following example. The following data are given: 14.6.18.2.2 For density meter provings and field verifica- pFlp 0.3000 gram per cubic centimeter. = tion tests, dry air density shall be calculated using the follow- h = 50feet. ing eauations. In U.S. units. U I T,= 68°F. B = 750 millimeters. pA = 0.0012[1 - (0.032h/1000)] pnvr= 8.00 grams per cubic centimeter (reference test In SI units, weights). pnvf= 7.84 grams per cubic centimeter (stainless steel pA = 0,0012[1 - (0.105h / lOOO)] test weights). Where: Dewpoint = 50F. pA = dry air density, in grams per cubic centimeter. The dry air density is calculated as follows: 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- Moist air density can be calculated using the following sius, equation: T, = (5/9)(Tf - 32) PA = [0.0012929(273.13 / T,)][(B - 0.3783e) / 7601 = (5/9)(68 - 32) Where: = 20 pA = moist air density, in grams per cubic centimeter. Where: Tf = air temperature, in kelvins. B = barometric pressure, in millimeters of mercury. T, = air temperature, in degrees Celsius. e = moist air vapor pressure, in millimeters of mercury. Tf = air temperature, in degrees Fahrenheit.COPYRIGHT American Petroleum InstituteLicensed by Information Handling Services
  59. __ A P I MPMS*14-b 91 0732290 0095902 3 50 CHAPTER 14-NATURAL MEASUREMENT GASFLUIDS Converting the air temperature from degrees Celsius to kel- pA = [0.0012929(273.13/ 293.15)][(750 - 3.48) / 7601 vins, = 0.00118 Tk = T, + 273.15 Then for dry air, = 20 + 273.15 CBw = 1.003801 = 293.15 And for moist air, Where: C W = 1.003801 B Tk= air temperature, in kelvins. T, = air temperature, in degrees Celsius. Since the results are exactly the same when rounded to six decimal places, the error in using the dry air density is be- Converting the dewpoint from degrees Fahrenheit to de- yond the accuracy attainable by this standard. grees Celsius, T, = (5/9)(Tf - 32) 14.6.19 Bibliography = (5/9)(50 - 32) J. D. Parker, J. H. Boggs, and E. E Blick (Eds.), Introduction = 10 to Fluid Mechanics and Heat Transfer (3rd ed.), Addison- Wesley, Reading, Massachusetts, 1974. Using the appropriate value for 0.3783e from the CRC P. E. Pontius, Mass and Mass Values, National Bureau of Handbook of Chemistìy and Physics (3.48 at a dewpoint of Standards, Washington, D.C., January 1984. lO"C), the moist air density is calculated as follows: H. Colijn, Weighing and Proportioning of Bulk Solids (2nd ed.), Trans Tech Publications, Brookfield, Vermont, 1983. R. C . Weast (Ed.), CRC Handbook of Chemistry and Physics (69th ed.), Metals Handbook (Desk ed.), American Society for Metals, CRC Press, Boca Raton, Florida, 1988. Metals Park, Ohio, 1985.COPYRIGHT American Petroleum InstituteLicensed by Information Handling Services
  60. A P I MPMS*lYeb 91 H 0732290 0095903 5 APPENDIX-PRECAUTIONARY INFORMATION A.1 Physical Characteristics and Fire c. Keep containers closed when not in use. Considerations d. Keep work areas as clean as possible and well ventilated. e. Clean up spills promptly and in accordance with pertinent A.l . Personnel involved in the handling of petroleum-re- I safety, health, and environmental regulations. lated substances (and other chemical materials) should be fa- f. Observe established exposure limits and use proper pro- miliar with their physical and chemical characteristics, tective clothing and equipment. including potential for fire, explosion, and reactivity, and ap- propriate emergency procedures. These procedures should Information on exposure limits can be found by consulting comply with the individual companys safe operating prac- the most recent editions of the Occupational Safety and tices and local, state, and federal regulations, including those Health Standards, 29 Code of Federal Regidations Sections covering the use of proper protective clothing and equip- 1910.1000 and following and the ACGIH publication ment. Personnel should be alert to avoid potential sources of Threshold Limit Valuesfor Chemical Substances and Phys- ignition and should keep the materials containers cIosed ical Agents in the Work Environment. when not in use. A.2.1.2 INFORMATION CONCERNING SAFETY A.1.2 API Publication 2217 and Publication 2026 and any AND HEALTH RISKS AND PROPER PRECAUTIONS applicable regulations should be consulted when sampling WITH RESPECT TO PARTICULAR MATERIALS AND requires entry into confined spaces. CONDITIONS SHOULD BE OBTAINED FROM THE A.1.3 INFORMATION REGARDING PARTICULAR EMPLOYER, THE MANUFACTURER, OR THE MATERIALS AND CONDITIONS SHOULD BE OB- MATERIAL SAFETY DATA SHEET, TAINED FROM THE EMPLOYER, THE MANUFAC- TURER OR SUPPLIER OF THAT MATERIAL, OR THE A.2.2 ACETONE MATERIAL SAFETY DATA SHEET. Health effects can result from exposure to acetone via A.2 Safety and Health Considerations contact with fhe skin and eyes, breathing of vapors, or swal- A.2.1 GENERAL lowing. Acetone exhibits local irritant properties that may be manifested by dermatitis, stinging of the eyes, nose, or A.2.1.1 Potential health effects can result from exposure throat, or irritation of the respiratory system. Acute exposure to any chemical and are dependent on the toxicity of the to acetone above permissible exposure limits may result in chemical, concentration, and length of the exposure. Every- adverse systemic effects, including effects on the dermato- one should minimize his or her exposure to workplace chem- logical or central nervous system. Indications of a systemic icals. The following general precautions are suggested: effect may include skin irritation, headache, dizziness, a. Minimize skin and eye contact and breathing of vapors. drowsiness, loss of appetite, and nausea. There may also be b. Keep chemicals away from the mouth; they can be harm- long-term (chronic) health effects of varying severity from ful or fatal if swallowed or aspirated. exposure to acetone. 51COPYRIGHT American Petroleum InstituteLicensed by Information Handling Services
  61. Order No. 852-30346 1-1700-4/91-2.5G (9C)COPYRIGHT American Petroleum InstituteLicensed by Information Handling Services
  62. ~ A P I MPMS*L4.b 91 0732290 0095905 9 W American Petroleum Institute 1220 L Street, NorthwestCOPYRIGHT American Petroleum InstituteLicensed by Information Handling Services

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