# SIST EN ISO 4267-2:1998

(Main)## Petroleum and liquid petroleum products - Calculation of oil quantities - Part 2: Dynamic measurement (ISO 4267-2:1988)

## Petroleum and liquid petroleum products - Calculation of oil quantities - Part 2: Dynamic measurement (ISO 4267-2:1988)

Defines the various terms employed in the calculation of metered petroleum quantities. Also specifies the equations which allow the values of correction factors to be computed. Also gives rules for the sequence, rounding and significant figures to be employed in a calculation. Provides tables which may be used to look up specific correction factors should it not be desired to calculate them by manual as well as computer methods. The field of application is the volumetric measurement of liquid hydrocarbons, including liquefied petroleum gases, by meter and prover. It does not include two-phase fluids.

## Mineralöl und flüssige Mineralölerzeugnisse - Berechnung von Ölmengen - Teil 2: Dynamische Messung (ISO 4267-2:1988)

Diese Internationale Norm definiert unterschiedliche Begriffe (Wörter oder Symbole), die zur Berechnung von gemessenen Mineralölmengen eingesetzt werden. Hat die Mineralölindustrie gewöhnlich für ein und dieselbe Menge zwei oder mehrere Begriffe benutzt, so hat man nun einen bevorzugten Begriff ausgewählt.

## Pétrole et produits pétroliers liquides - Calcul des quantités de pétrole - Partie 2: Mesurage dynamique (ISO 4267-2:1988)

La présente Norme internationale définit les différents termes (qu'il s'agisse de mots ou de symboles) employés dans les calculs des quantités de pétrole. Lorsque deux ou plusieurs termes sont utilisés dans l'industrie pétrolière pour désigner la même chose dans des transactions commerciales, un seul terme a été choisi. La présente Norme internationale spécifie également les équations permettant le calcul des facteurs de correction. Elle formule également des règles concernant l'ordre des opérations, les arrondis et les chiffres significatifs à utiliser dans les calculs. Elle fournit des tables qui peuvent être utilisées pour obtenir des facteurs de correction spécifiques lorqu'on ne souhaite pas effectuer des calculs manuels ou informatiques. Sont également inclus dans cette norme, le calcul des volumes de référence des étalons, les coefficients des compteurs et les tickets de comptage. Le domaine d'application de la présente Norme internationale concerne le mesurage volum

## Nafta in tekoči naftni proizvodi - Izračun količin olja - 2. del: Dinamična meritev (ISO 4267-2:1988)

### General Information

### Standards Content (Sample)

2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.Mineralöl und flüssige Mineralölerzeugnisse - Berechnung von Ölmengen - Teil 2: Dynamische Messung (ISO 4267-2:1988)Pétrole et produits pétroliers liquides - Calcul des quantités de pétrole - Partie 2: Mesurage dynamique (ISO 4267-2:1988)Petroleum and liquid petroleum products - Calculation of oil quantities - Part 2: Dynamic measurement (ISO 4267-2:1988)75.180.30Oprema za merjenje prostornine in merjenjeVolumetric equipment and measurementsICS:Ta slovenski standard je istoveten z:EN ISO 4267-2:1995SIST EN ISO 4267-2:1998en01-maj-1998SIST EN ISO 4267-2:1998SLOVENSKI

STANDARDSIST EN ISO 4267-2:1998

SIST EN ISO 4267-2:1998

SIST EN ISO 4267-2:1998

SIST EN ISO 4267-2:1998

SIST EN ISO 4267-2:1998

ISO INTERNATIONAL STANDARD INTERNATIONAL ORGANIZATION FOR STANDARDIZATION ORGANISATION INTERNATIONALE DE NORMALISATION MEXflYHAPOflHAR OPf-AHM3A~MR fl0 CTAHflAPTM3A~MM Petroleum and liquid Petroleum products - Calculation of oil quantities - Part 2: Dynamit measurement Mrole et produits p&roliers liquides - Calcul des quantittk de phrole - Partie 2 : Mesurage dynamique 4267-2 First edition 1988-12-01 Reference number ISO 4267-2 : 1988 (E) SIST EN ISO 4267-2:1998

ISO 4267-2 : 1988 EI Foreword ISO (the International Organization for Standardization) is a worldwide federation of national Standards bodies (ISO member bedies). The work of preparing International Standards is normally carried out through ISO technical committees. Esch member body interested in a subject for which a technical committee has been established has the right to be represented on that committee. International organizations, govern- mental and non-governmental, in liaison with ISO, also take part in the work. ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of electrotechnical standardization. Draft International Standards adopted by the technical committees are circulated to the member bodies for approval before their acceptance as International Standards by the ISO Council. They are approved in accordance with ISO procedures requiring at least 75 % approval by the member bodies voting. International Standard ISO 4267-2 was prepared by Technical Committee ISO/TC 28, Petroleum products and lubricants. Users should note that all International Standards undergo revision from time to time and that any reference made herein to any other International Standard implies its latest edition, unless otherwise stated. 0 International Organkation for Standardization, 1988 0 Printed in Switzerland ii SIST EN ISO 4267-2:1998

Contents Page 0 Introduction ......................................................... 1 1 Scope and field of application .......................................... 1 2 References .......................................................... 1 3 Definitions.. ........................................................ 2 4 Hierarchy of accuracies ............................................... 2 4.1 Purpose and implications .......................................... 2 4.2 Hierarchy ....................................................... 2 5 Principal correction factors ............................................ 2 5.1 Purpose and implications .......................................... 2 5.2 c,, ............................................................. 3 5.3 cps ............................................................. 4 5.4 CP, ............................................................. 4 5.5 c,, ............................................................. 5 6 Calculation of prover volume ........................................... 5 6.1 6.2 6.3 6.4 6.5 6.6 6.7 6.8 6.9 Purpose and implications .......................................... 5 Volume Standard measures ........................................ 5 Rulefor rounding - Provers ....................................... 5 Temperature and pressure ......................................... 6 Calculation of base volumes ........................................ 6 Corrections applied to measured-volume water draw method ........... 6 Example of calculation - Calibration of pipe prover by water draw method using field Standards ....................................... 6 Example of calculation - Calibration of tank prover by water draw method using field Standards ....................................... 8 Example of calculation - Calibration of pipe prover by master meter method ......................................................... 9 . . . Ill SIST EN ISO 4267-2:1998

ISO 4267-2 : 1988 (El 7 Calculation of meter factor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 7.1 Purpose and implications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 7.2 Temperature and pressure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13 7.3 Rule for rounding - Meter factors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13 7.4 Calculation of Standard meter factor for a displacement meter, using a prover tank . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13 7.5 Calculation of Standard meter factor for a turbine meter, usingapipeprover . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 7.6 Calculation of meter factor at Standard conditions for a displacement meter, using a master meter . . . . . . . . . . . . . . . . . . . . . . . . . . 17 8 Calculation of K-factor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19 8.1 Purpose and implications .......................................... 19 8.2 Temperature and pressure ......................................... 19 8.3 Rule for rounding - K-factors. ..................................... 19 8.4 Calculation of K-factor for a turbine meter, using a pipe prover .......... 19 9 Calculation of measurement tickets ..................................... 20 9.1 Purpose and implications .......................................... 20 9.2 Rule for rounding - Measurement tickets. ........................... 20 9.3 Correction factors and accuracy .................................... 20 Annex A Correction factors for the effect of temperature and pressure on steel . . 22 iv SIST EN ISO 4267-2:1998

INTERNATIONAL STANDARD ISO 4267-2 : 1988 (EI Petroleum and liquid Petroleum products - Calculation of oil quantities - Part 2: Dynamit measurement 0 Introduction Before the compilation of this publication, words and expres- sions employed in dynamic measurement calculations were in- terpreted slightly differently by different People, and there was a lack of coherence in their use. In addition, because data were spread over so many Standards, there was difficulty in readily comparing the finer Points. of calculations. Rules for rounding, and the choice of how many significant figures entered each calculation, were open to a variety of inter- pretations. For different Operators to obtain identical results from the same data, the rules for sequence, rounding and significant figures have to be defined. This International Stan- dard aims, among other things, at defining the minimum set of rules required. Nothing in this International Standard precludes the use of more precise determinations of temperature, pressure and density or the use of more significant digits, by mutual agreement among the Parties involved. This International Standard aims at consolidating and standar- dizing calculations pertaining to the metering of Petroleum li- quids, and at clarifying terms and expressions by eliminating local variations of such terms. The purpose of standardizing calculations is to produce the same answer from the same data regardless of the computing System used. Although ISO/TC 28 Standards use 15 OC as a Standard reference temperature, it is recognized that individual countries may use other reference temperatures, for example 20 OC, 12 OC or 60 OF. This Standard sets minimum levels of accuracy for industrial calculations, but, if Parties consider agreeing to set tighter re- quirements, it is important to demonstrate whether such re- quirements tan be met. Future technological progress in meter proving and Operation may justify a tighter specification for calculation procedures. 1 Scope and field of application This International Standard defines the various terms (be they words or Symbols) employed in the calculation of metered Petroleum quantities. Where two or more terms are customarily employed in the oil industry for the same quantity, a preferred term is selected. This International Standard also specifies the equations which allow the values of correction factors to be computed. lt also gives rules for the sequence, rounding and significant figures to be employed in a calculation. lt provides tables which may be used to look up specific correction factors should it not be . desired to calculate them by manual as well as Computer methods. The calculation of prover base volumes, meter fac- tors and measurement tickets is also covered. The field of application of this International Standard is the volumetric measurement of liquid hydrocarbons, including li- quefied Petroleum gases, by meter and prover. lt does not in- clude two-Phase fluids (though it may be found useful in such situations) except in so far as Sediment and water may be mixed in with crude Oil. 2 References ISO 91-1, Petroleum measurement tables - Part 7: Tables based on reference temperatures of 75 OC and 60 OF. ISO 2715, Liquid h ydrocarbons - Volumetric measurement b y turbine meter Systems. ISO 5024, Petroleum liquids and gases - Measuremen t - Standard reference conditions. ISO 7278-2, Liquid hydrocarbons - Dynamit measurement - Proving Systems for volumetric meters - Part 2: Pipe pro Vers. 1 ) ISO 8222, Petroleum measuremen t s ystems - Calibration - Temperature corrections for use with volumetric reference measuring s ystems. ISO 9770, Petroleum products - Compressibility factors for hydrocarbons in the range &S kg/m3 to 7 074 kg/m3. 1 1 1) At the Stage of draft. SIST EN ISO 4267-2:1998

ISO 4267-2 : 1988 (El 3 Definitions 4 Hierarchy of accuracies following For the pu rposes of this International Standard, the definitions apply to the terms used herein: 4.1 Purpose and implications 3.1 base volume: The volume of a prover under Standard conditions. 3.2 indicated volume: The Change in meter reading that occurs during a transfer through the meter. 4.1.1 There is an inevitable, or natural, hierarchy of ac- curacies in Petroleum measurement. At the top are volume Standard measures which are cettified by a government agency or laboratory traceable to the appropriate national Standard. From this level downwards, any uncertainty at a higher level must be reflected in all the lower levels as a systematic error. 3.3 K-factor: The number of pulses generated by a meter for a unit of volume delivered. Whether such systematic error will be positive or negative is unknown; either is possible. pulses generated by meter 4.1.2 To expect equal or less uncet-tainty at a lower level of 1 K-factor = the hierarchy than exists in a higher level is unrealistic. The only / volume delivered by meter I way to decrease the random component of uncertainty in a / / 3.4 measurement ticket: A generalized term for the writ- ten acknowledgment of the receipt or delivery of a quantity of crude oil or Petroleum product, including a record of the measurement data (see clause 9). lt may be a form to be com- pleted, a data print-out or a data display depending on the degree of automation, remote control, or computerization. Previously described as “run ticket” and “receipt and delivery ticket”. number of determinations, and calculate the mean value. The number of significant digits in intermediate calculations of a value tan be larger in the upper levels of the hierarchy than in the lower levels. 4.2 Hierarchy given measurement System or method is to increase the 3.5 meter factor: The ratio of the actual volume of liquid passed through a meter to the volume indicated by the meter. 4.2.1 The hierarchy of accuracies in this Standard is struc- tured, in general, as shown in table 1. volume passed through a meter 4.2.2 This Standard gives rules for rounding, truncating and Meter factor = volume indicated by the meter reporting final values for each level of the hierarchy. 3.6 net Standard volume: The total Standard volume (sec 3.9) minus the volume of water and Sediment transferred through the meter. 5 Principal correction factors NOTE - For clean, refined products, the total Standard volume and net Standard volume are usually equal. 37 . reading; meter reading: The meter volume (sec indicated vohme). instantaneous display of 3.8 Standard (reference) conditions: For the measure- ment of Petroleum and its products, these are a pressure of 101,325 kPa (1,013 25 bar) and a temperature 15 OC, with the exception of liquids having a vapour pressure greater than at- mospheric pressure at 15 OC, in which case the Standard pressure is the equilibrium vapour pressure at 15 OC (sec ISO 5024). 3.9 total Standard volume : The total volume temperature, also corrected to Standard pressure. at Standard 3.10 total volume: The indicated volume multiplied by the appropriate meter factor for the liquid and flow rate concerned, without correction for temperature and pressure. lt includes all water and Sediment transferred through the meter. 5.1 Purpose and implications 5.1.1 Designation of correction factors by Symbol rather than by words is recommended because, first, it abbreviates their expression; second, it allows algebraic manipulations; third, it indicates their similarity subject only to the particular liquid or metal involved; and fourth, it tan more readily eliminate confu- sion, as for example the differente between the compressibility factor F of a liquid and the correction factor CP,, which is a function of F. There are six principal correction tions of liquid quantities. factors employed in calcula- 5.1.2 The first of these six correction factors is the meter fac- tor MF, a non-dimensional value which corrects the volume in- dicated on a meter or meter accessory to the actual volume, be that volume a raw or corrected volume (sec clause 7). In some instances, the K-factor is used in place of or along with the meter factor (sec clause 8). 2 SIST EN ISO 4267-2:1998

ISO 4267-2 : 1988 (El Table 1 - Hierarchy of accuracies I I Hierarchy I factors ai malrccb ;N%+ChWmd!SA: I I I Correction Temperature and nd Number of pressure I W.YI”” significant level IIILGt ,,,,,,ate digits in determination. -- --___-_- -~---__. calculations for entering to volume calculations, to 6 7 Prover calibration Meter factor 6 decimal I I 0,05 OC 50 kPa2) 4 025 OC3) decimal places 5 50 kPa2) 8 I K-factor 4 decimal places 5 0,25 OC3) 50 kPa2) 9 Measurement tickets 4 decimal places 5 0,50 OC3) ~ 50 kPa2) 1) When water is used as the calibration liquid, correction factors for the effect of temperature and pressure on the calibrating liquid to 6 decimal places are used. When a hydrocarbon is used as the calibrating liquid, correction factors for the effect of temperature and pressure on the calibrating liquid shall be calculated using the procedures referred to in ISO 91-1. Factors calculated using ISO 91-1 will be limited to 5 significant figures (4 or 5 decimal places). Cases may arise where calibration Personne1 do not have the capability to calculate ISO 91-1 values but do have access to the printed tables referred to in ISO 91-1. Under these conditions, linear interpolation of the tables over a limited span is ac- ceptable for use in correcting for the temperature differente between master meter and prover during calibra- tion. 2) In all hierarchies above, pressures shall be read, recorded and rounded to the nearest 50 kPa (0,5 bar). Where the gauge scale permits a closer tolerante, readings should be read, recorded and rounded to the nearest gauge scale division. 3) The use of a temperature determination device that tan perform to a more stringent determination level than outlined in table 1 is acceptable provided that the installation, maintenance, Operation and calibration practices are adequate to ensure Performance to the level Chosen. 5.1.3 The next four correction factors employed in calcula- tions of liquid quantities are needed because of changes in volume from the effects of temperature and pressure upon both the containing vessel (usually made of mild steel) and upon the liquid involved. These four correction factors are: C,, (or CTS) . . . the correction factor for the effect of temperature on steel (sec 5.2) Cps (or CPS) . . . the correction -factor for the effect of pressure on steel (sec 5.3) CP, (or CPL) . . . the correction factor for the effect of pressure on liquid (sec 5.4) C,I (or CTL) . . . the correction factor for the effect of temperature on liquid (see 5.5) 5.1.4 Finally, there is a correction factor Csw (or CSW) for ac- counting for the presence of Sediment and water in crude oil (sec 9.3.1). 5.1.5 Additional subscripts may be added to the symbolic notations above to make it clear to what part of the measuring apparatus they apply, namely p for prover, m for meter and M for a volume Standard measure. While the customary subscript notation is used in this Standard, the allowed upper case notation is needed for Computer pro- gramming and is convenient in typing. In such cases, M for measure shall be SM while m for meter shall be M. 5.1.6 The method for correcting volumes by 2 or more factors is to first obtain a CCF (combined correction factor) by multiplying the individual correction factors together in a set se- quence, rounding at each Step. Only then multiply the volume by the CCF. The set sequence is MF, C,,, Cps, CP& Ct, and Csw, omitting any factors that may not be required in the calculation. NOTE - This is considered the theoretically correct sequence for ap- plying the six correction factors. However, it is acknowledged that, in some cases where mechanical or electronie devices are used to apply one or more of these factors, the Order may be changed. This is especially true of temperature-compensated meters. However, if the correction factors are determined using the correct basis of temperature, pressure and density, the numerical value of the com- bined correction factor (CCF) will not be significantly different from the theoretical value. 5.1.7 All multiplication within a Single Operation shall be com- pleted before the division is started. 5.2 C, 5.2.1 The volume of a metal Container, such as a pipe prover, tank prover or volume Standard measure, will Change when subjected to a Change in temperature. The volume Change, regardless of shape, is directly proportional to the temperature 3 SIST EN ISO 4267-2:1998

so 4267-2 : 1988 (El Change of the material of which the Container is made. The cor- rection factor for the effect of temperature on steel (C,) shall be calculated from the equation E is the modulus of elasticity of the Container material (2,l x lO* kPa for mild steel and 1,9 x lO* kPa to 2,0 x lO* kPa for stainless steels); T is the wall thickness of the Container in millimetres. cts = 1 + (t - 15) y . . . (1) where 5.3.2 Cps values for specific sizes and wall thicknesses of mild-steel pipe provers and pressures may be found in tables 6 and 7 of annex A of this International Standard. When the volume of the Container at atmospheric pressure &,.,os (i.e. zero gauge pressure) is known, the Container volume at any other pressure VP tan be calculated from the equation t is the Walls; temperature, in degrees Celsius, of the Container Y is the coefficient of cubical expansion per deg of the material of which the Container is made. ree Celsius vp = Gmos x Cps . . . (5) Thus, Cts will be greater than 1 when the temperature t is greater than 15 OC, and less than 1 when the temperature t is less than 15 OC. 5.3.3 When the Container volume at any gauge pressure P is known, the equivalent Container volume at atmospheric pressure Vatmos tan be calculated from the equation 5.2.2 The value of y is 3,3 x 10D5 (or 0,000 033) per degree Celsius for mild or low-carbon steels, and has a range of 4,30 x 10m5 to 540 x 10B5 per degree Celsius for Series 300 stainless steels. The value used in the calculations shall be that given on the certificate from the calibrating agency for a volume Standard measure or from the manufacturer of a pro- ver. Tables of Ct, values against observed temperature will be found in annex A of this Standard, the table for stainless steels being based upon a typical value of y of 5,lO x los5 for Series 300 stainless steels. V atmos = VplCps 5.4 cp, 5.4.1 The volume of a liquid is inversely proportional to the pressure acting on that liquid. The correction factor CP, for the effect of pressure on a volume of liquid tan be calculated from the equation 5.2.3 When the volume of the Container at Standard temperature (15 OC) is known, the volume at any other temperature t tan be calculated from the equation vt = 45 x cts . . . (2) P is the gauge pressure in kilopascals; p’ is the equilibrium vapour pressure of the liquid at the measurement temperature, in kilopascals gauge pressure [P, is taken as zero gauge pressure for liquids which have an equilibrium vapour pressure less than atmospheric pressure (101,325 kPa absolute pressure) at the measurement temperaturel; 65 = vcts 5.3 cps F is the compressibility factor for hydrocarbons from ISO 9770 (this is determined at the meter operating temperature and the oil density at 15 OC; for water, the compressibility factors at various water temperatures are listed in table 2 below). 5.3.1 If a metal Container such as a tank prover, pipe prover or volume Standard measure is subjected to an internal pressure, the Walls of the Container will stretch elastically and the volume of the Container will Change accordingly. Table 2 - Isothermal compressibility factor for water While it is recognized that simplifying assumptions enter the equations below, for practical purposes the correction factor Cps for the effect of internal pressure on the volume of a cylin- drical Container shall be calculated from the equation C PS = 1 + PDIET . . . (4) Temperature Compressibility factor OC kPa-1 5 4,9 x IO-7 IO 4,8 x IO-7 15 4,7 x IO-7 20 4,6 x IO-7 25 4,5 x IO-7 30 4,5 x IO-' 35 4,4 x IO-7 40 4,4 x IO-7 45 4,4 x IO-7 50 4,4 x IO-7 where P is the internal gauge pressure in kilopascals; D is the internal diameter in millimetres; 4 SIST EN ISO 4267-2:1998

ISO 4267-2 : 1988 EI 5.4.2 When pe is zero, equation (7) becomes: 5.5 Ctl CP1 1 =- . . . 1 - PF (8) 5.4.3 When Pe is greater than zero gauge pressure, equation (7) shall be used. NOTE - A convenient field method of determining Pe meter against a pipe prover is to proceed as follows: proving a a) On conclusion of the last proving round, stop the flow through the pipe prover and isolate it from the flowing Iines by shutting the ap- propriate valves. b) Reduce the pressure on the pipe prover by bleeding off liquid until the gauge pressure Stops falling. This will imply that a vapour space has been created, and that the liquid has reached its equilibrium vapour pressure. Shut the bleed valve, and read Pe on the gauge, making a record of the temperature at the time. The above procedure may be used for the determination of Pe for liquid mixtures that do not conform with published Charts showing Pe values plotted against temperature, or it may be used as a routine procedure. 5.4.4 When the volume of a low-vapour-pressure liquid is known at any pressure CV,), the equivalent liquid volume at Standard pressure (zero gauge pressure, or &tmos) tan be calculated from the equation 5.5.1 If a quantity of Petroleum liquid is subjected to a Change in temperature, its volume Change will be dependent upon the magnitude of the temperature Change, the location within a range of temperatures that this Change occurs at and the den- sity of the liquid. The values of C,, for the correction of volume to that at 15 OC shall be taken from tables referenced in ISO 91-1. 5.5.2 When the volume of a Petroleum liquid is known at any temperature t, the equivalent volume at Standard temperature (15 OC) tan be calculated from the equation b5 = vt x Ctl . . . (12) 5.5.3 When the volume of a Petroleum liquid is known at 15 OC, the equivalent volume at any temperature t tan be calculated from the equation &= 65Gl . . . (13) 6 Calculation of prover volume 6.1 Purpose and implications V atmos - - Vp x cpi . . . (9) 5.4.5 When the volume of a low-vapour-pressure liquid is known at zero gauge pressure, the equivalent volume at any other pressure VP tan be calculated from the equation vp = VatmosQl 5.4.6 When the volume of a high-vapour-pressure liquid is known at any measurement temperature t and pressure P, pressure correction is done in two Steps. The equivalent volume at such a liquid’s equilibrium vapour pressure & at the measurement temperature tan be calculated from the equation V pe = vp x CP, . . . (11) where CP, is calculated from equation (7). When this volume is in turn temperature-corrected to 15 OC using equation (121, the value of C,I taken from the appropriate table, or calculated, also corrects the volume for the Change in pressure from Pe at the measurement temperature to the equilibrium vapour pressure at the Standard temperature of 15 OC. lt should be noted that, while Pe at the measurement temperature t may be higher than atmospheric pressure (101,325 kPa absolute pressure), equilibrium vapour pressure at 15 OC may have fallen to atmospheric pressure or less. As noted under equation (7), the distinction between a low- vapour-pressure liquid and high-vapour-pressure liquid is based on whether its equilibrium vapour pressure is less than or greater than atmospheric pressure at the measurement temperature. 6.1.1 The purpc-; of calibrating a prover is to determine its base volume, that is, the volume of the prover under Standard conditions. The procedures to be used for a pipe prover are described in ISO 7278-2. 6.1.2 Base volume is expressed in cubic metres or Iitres. Whereas volumetric units (e.g. the litre) do not vary with temperature and pressure, the volume of a metal prover does. Therefore to define the base volume of a prover or volumetric Standard, it is necessary to specify Standard conditions, namely 15 OC and 101,325 kPa absolute pressure (atmospheric pressure). 62 . Volume Standard measures Volume Standards used to calibrate provers shall be certified by a government agency or by a laboratory traceable to the ap- propriate national Standard. Their certified volumes are given in measurement units at Standard conditions. The uncertainty figure of field Standards is usually the main component in the uncertainty figure of the prover calibration. 6.3 Rule for rounding - Provers When calculating a prover volume, determine individual correc- tion factors to 6 decimal places by using the appropriate for- mula (4 or 5 decimal places for C,I values when hydrocarbons are used). Record the combined correction factor (CCF) round- ed to 6 decimal places. When using the water draw method, each individual volume in a volume Standard sha 111 be corrected by Ctd,,,, [sec 6. 6.la)l and SIST EN ISO 4267-2:1998

ISO 4267-2 : 1988 EI C &M [see 6.6.1 b)]. This corrected volume is rounded to the same number of significant digits as the uncorrected volume. The corrected volumes are summed and then divided by Ctsp, CPsP and CPIP [see 6.6.1~11. This volume is then rounded to 5 significant digits. 6.4 Temperature and pressure During the calibration of a prover by the water draw method, the temperature and pressure of the water in the prover at the Start of calibration are observed and recorded. Likewise, the water temperatures of the individual withdrawals into volume Standards are observed and recorded at the time of recording the volume Standard volume. During the calibration of a prover by the master meter method, the temperature and pressure of the calibration liquid in the prover and meter are observed and recorded. The temperatures and pressures shall be read, recorded and rounded as specified in table 1. 6.5 Calculation of base volumes The procedure for calibrating pipe provers will be found in ISO 7278-2. The following sub-clauses specify the procedures for the calculation of the base volume of both pipe and tank provers calibrated by the water draw and the master meter method. 6.6 Corrections applied to measured-volume water draw method 6.6.1 In the water draw calibration procedure, the volume observed in the volume Standards must be subjected to certain corrections in Order to determine the base volume of the pro- ver. In the examples, the final subscripts p for prover, and M for measure, have been added to the correction factor desig- nations. Thus : a) The individual volume Standard water volumes shall be corrected for any differente in temperature between the A General information starting temperature of the water in the prover and the temperature of the water in the volume Standards when their volume was determined (6.4); this is done by multiply- ing the individual volume Standard volumes by C,,,. C,,, is defined as the correction for the temperature differente bet- ween the water in the test measure and in the prover; this is not the same as C,, which corrects to 15 OC rather than to prover temperature. The values of C,,, tan be determined by methods explained in ISO 8222. b) The individual volume Standard water volumes shall also be corrected for the effect of temperature on the volume Standard Shell. This is done by multiplying the in- dividual volume

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