1、A BRITISH STANDARD Liquid hydrocarbons - Dynamic measurement - Proving systems for volumetric meters Part 1. General principles * * rn The European Standard EN IS0 72781 : 1995 has the status of a British standard ICs 75.m BS EN IS0 7278-1 :1996 Inco?-pomti?q Amendment No. 1 BS6866:PartI :I990 renll
2、mbered Committees responsible for this British Standard 8895 The following l3SI references relate to the work on this mdad committee reference pTc/lP haft for comment 8461863 DC ISBN O M10 18712 8 The preparation of this British Standard was enmted by the Petroleum Standards Policy Committee (PRY-)
3、to khnicai CommiW PTC/12, upon which the foiiowing bodies were represented: 4d 1996 Department of Energy (Gas and oil Measurement Branch) Deparbinent of kade and Industry (National Engineering Laboratory) Department of ?kansport (Marine Directorate) General Council of British Shipping instituk of Pe
4、troleum Royal institution of Naval Architects Salvage Association The following bodies were also represented in the draftkg of the standard, through subcommittees and panels GAMBICA (BEAMA La) institute of Measurement and Control United Kingdom fkhore Operatois Association This British Standard, hav
5、ing been prepared under the directcm of the Pemoleum standards Policy committee, was pubiished under the authority of the Board of BSI and comes into effect on 31 July 1990 O BSI l99 Amendments issued since publication Indicated by a sideline in the margin S-hc.-F- - t; - CEN EN*ISO 7278-1 95 m 3404
6、549 0323787 59T m Issue 1, April 1996 BS EN IS0 7278-1 : 1996 Summary of pages The following table identifies the current issue of each page. issue 1 indicates that a page has been introduced for the first time by amendment. Subsequent issue numbem indicate an updated page. Verticai sidelining on re
7、placement pages indicates the most recent changes (amendment, addition, deletion). I issue II Page I Issue bnt cover Inside front cover a b i ii EN cover page iib 2 2 1 blank Original 2 1 1 1 2 3 back cover 1 Back cover Original original original Original Original blank 2 2 Change of identifier Wher
8、ever BS 6866 : Part 1 : 1990 appears in this standard, it should be read as BS EN IS0 7278-1 : 1996. A Contents page Committees responsible Inside fmnt cover National foreword ii Introduction O Introduction 1 1 Scope and field of application 1 2 Reference 1 3 Typesof prover 1 4 General consideration
9、s 1 5 Pankproversystems 3 6 On-he pipe prover systems 3 7 Centralized prover systems 4 8 Master meter systems 4 9 Bibliography 5 CEN ENUISO 7278-3 95 H 3404589 8323789 362 / these parts are in preparation. Parts covering other aspects or types of proving systems may be added as the need arises. The
10、purpose of proving a meter is to determine its relative error or its meter factor as a function of flow rate and other parameters such as temperature, pressure and viscosity. The purpose of determining the relative error is to find out whether the meter is working within prescribed or specially ac-
11、cepted limits of error, whereas the meter factor is used to cor- rect any error in the indication of a meter by calculation. 1 Scope and field of application This part of IS0 7278 provides general principles for proving systems for meters used in dynamic measurement of liquid hydrocarbons. 2 Referen
12、ce IS0 4124, Liquid hydrocarbons - Dynamic msurement - Statistical control of voumetric metering systems. 1 3 Types of prover 3.1 The following types of proving systems are in use: ai tank prover systems; b) pipe provers, bidirectional and unidirectional. Pipe provers with precision tubes as describ
13、ed in 6.7 are available for special applications; ci master meters. Indirect procedure of volume com- paricon which causes additional uncertainties can be used for all liquids and flow rates, provided that the master meter is proved against acceptable proving systems under condi- tions which simulat
14、e those under which it will operate. Sometimes, a meter is used as a means of standardization of transfer; this equipment is generally known as a “master meter“. 3.2 Provers can be used either connected (fixed or mobile) to the metering station or in a central proving station to which the meters or
15、the measures can be taken to be proved. 3.3 In order to limit the maximum uncertainty to f 0.01 % when using a pulse generator for proving, at least 10 o00 pulses shall be obtained from the meter per proving run. This number of pulses can be reduced by pulse-interpolation techniques which allow eith
16、er the use of meters with fewer pulses per unit volume or reduction of the prover volume. 4 General considerations 4.1 A meter should be proved at the expected operating or prescribed or agreed rates of flow, under the pressure and temperature at which it will operate and on the liquid which it will
17、 measure. In situations where it is not feasible to prove the meter on the liquid to be metered, the meter should be proved on a liquid having a density, viscosity and, if possible, temperature as close as possible to those of the liquid to be measured. A meter that is used to measure several differ
18、ent liquids shall be proved on each such liquid. Similar liquids may be used if a simple, known relationship exists between the relative error, flow rate and viscosity, provided that the uncer- tainty of measurement remains within acceptable limits. In any event, calibration should take place at a f
19、low rate equivalent to that at which the meter will be used. A meter shall be proved in different circumstances as follows: a) Initial proving. This shall be carried out on the perma- nent location or in a central station where the expected con- ditions of operation can be reproduced. The initial pr
20、oving makes it possible to determine the relationship between the relative error (or meter factor) and different parameters such as viscosity or temperature. 1) At present at ti,C stage of draft. 1 IS0 7278-1 : 1987 (E) b) Occasional or periodical proving. If a simple relationship between the relati
21、ve error (or meter factor) and influencing parameters can be determined, the meters shall be reproved periodically using a prover either on the site or in a central- ked station. Otherwise, the meter shall be reproved on the site whenever significant changes in the influencing par- ameters, such as
22、viscosity or temperature, occur. Regular provings are also needed to follow effects of mechanical changes. 4.2 Many petroleum liquids of high vapour pressures are measured by meter. If liquid evaporation during normal opera- tion or proving could occur and affect measurement, the prov- ing system sh
23、ould provide means to avoid evaporation. 4.3 The proving of a meter is like a laboratory test: when properly done, it provides a high degree of repeatability, which is necessary for measurement accuracy. There are as many details of the meter, its piping and the proving systems, which can contribute
24、 to measurement uncertainty, as there are in determining physical properties of the measured liquid. Fur- thermore, the proving system shall be maintained in good oper- ating condition. Thorough inspection of provers and their ancillary equipment should be made with sufficient frequency to ensure re
25、producibility of proving results. It is essential that meter performance data be observed, recorded and studied and that calculations be correct (see IS0 4124). The accuracy and repeatability of the proving can be affected by observation errors in determining the opening meter reading or the closing
26、 meter reading, the test volume passing through or delivered to the prover and in reading temperature and pressure, and by implicit errors in computation in the process of correcting a measurement to standard conditions. 4.4 as described below. Meter proving can be classified according to procedure,
27、 a) The stantiing start-and-stop procedure uses registers (counters) from which the opening and closing readings are obtained at no-flow conditions. Opening and closing of valves shall be performed rapidly. b) The running start-and-stop procedure involves obtain- ing the opening and closing meter re
28、adings of the proof while the meter is in operation. This is accomplished by the use of auxiliary or secondary registers of high discrimination which can be started and stopped while the meter and primary register continue to operate. 4.5 Every meter proof shall be made with the same register equipm
29、ent as is used in regular operation or with additional synchronised auxiliary registers for the running start-and-stop procedure 4.4 b)l. Inclusion of special auxiliary equipment such as the following is permitted: density selector, temperature compensator, and quantity-predetermining register. If e
30、mployed, the auxiliary equipment shall be set and operative when making the proof runs. Time between proving runs shall be kept to a minimum. 4.6 usually depend on the type of service. There are two general objectives to meter proving which In the first, a meter can be proved to establish its perfor
31、mance by adjustment of its registration, if necessary, to give a meter factor of 1 ,o00 O so that its indicated volume will be the volume of liquid actually delivered (gross volume within desired tolerances). This is the normal practice for a meter operating on intermittent deliveries, such as a tan
32、k truck meter or a loading rack meter at a teminal or bulk plant. In the second, a meter can be proved to determine its meter factor or, if possible, a simple relationship between its meter factor and influencing parameters such as viscosity or temperature so that this factor or this relationship ca
33、n be applied to the indicated volume to compute the gross volume delivered through the meter. This is the normal practice in the case of continuous or long-duration measurement. 4.7 When a meter is being proved for adjustment, a preliminary unrecorded run shall be made, as necessary, to equalise tem
34、peratures, displace vapours or gases and wet the interior of the prover. Subsequent recorded proving test runs shall be made in the required range of flow rates and the registration adjusted as necessary. Each calibration point for the same flow should be repeated at least twice and preferably three
35、 times. Further repeats may be necessary, if specified. See IS0 4124. 4.8 When a meter is being proved to determine the meter factor at one or several flow rates, the procedure shall be essentially as specified in 4.7, except that no changes shall be made to the meter registration adjusting device b
36、etween runs. Proof runs shall be made and recorded until the specified number of consecutive runs at the same flow rate agree within an acceptable repeatability, at which point the average of these two runs shall be accepted as the established meter correction factor for this flow rate. 4.9 If the r
37、egistration of a meter, during proving, is not changing in accordance with adjustments made to the register adjusting device, or if four individual unadjusted proving runs are made without any two successive runs checking within an acceptable repeatability, all phases of the proving operation shall
38、be examined for the cause of the discrepancy. If the cause is not found, the meter and its register mechanisms shall be inspected for electronic or mechanical defects, repaired and proved before being returned to service. 4.10 The practical limit of accuracy in any observed value such as the volume
39、in the reference vessel during a meter proof is one part in 10 OOO. For this reason, meter factors shall be rounded to four decimal places, not more and not less, for example 1,001 6. 4.11 The results of calculation can be adversely affected by the use of abbreviated tables, the unstandardized round
40、ing of factors and/or intermediate calculations. The observed and computed data for all test runs made in obtaining a meter factor or other expression of meter performance shall be reported on a suitable meter proving report form. The completed form, when signed by the interested parties or by the l
41、egal authority, shall constitute approval, understanding and acceptance of the meter proof, unless otherwise limited to witnessing only by a notation on the report. 2 CEN ENJISO 7278-1 95 U 3404587 0323774 72“ !so 721 pipe circuit in which product flow is caused by a b) bench for setting up meters f
42、or calibration; c) pipe prover or tank prover; d) system for adjusting the static pressure of the circuit; e) storage tanks for draining and filling the circuits with products of different viscosities; b) Variations in pressure and temperature Mathematical corrections can be applied for changes in p
43、hysical dimensions of the meter, provided that the change due to other effects (mechanical tolerance, blade angle, etc.) is negligible at the operating and proving conditions. c) Curvedrift The overall reliability of the metering system shall not be af- fected between two consecutive provings, consi
44、dering : - long-term drift of the metering system; - metered liquid quality. 7.3 The central proving station need not be connected to the metering location and may be remote from it. Every care shall be taken during handling and transportation of the meter. 7.4 For turbine meters, special care shall
45、 be taken in the in- stallation to avoid misalignment. In any case, the straightener, or equivalent, should be kept attached to the meter for trans- portation and proving. 7.5 The results from a large number of tests on a range of meters of one tyoe can be used statistically to predict the overall r
46、eproducibility of the meter, taking into account all the parameters and the curve drift due to operation and transpor- tation. The statistical analysis of a sufficient number of tests will aid judgement in determining a) the optimum proving frequency; b) the need for maintenance. f) meters, such as
47、viscosity or temperature. instruments for the measurement of influencing para- 7.2 The meters shall be selected so that the influence of the following parameters is either negligible under operating condi- tions or accurately evaluated. a) Variations in flow rate and viscosity Several tests shall be
48、 carried out corresponding to different flow rates and viscocities covering the limits of operation. The resulting meter factors should be plotted in a three- dimensional space and smoothed with a mathematical func- tion. Other methods can be used, particularly the method based on the Reynolds numbe
49、r: the meter factors are associated with the corresponding value of the flow rate divided by the kinematic viscosity korrected at a given temperature: 15 OC is recommended). The resulting poins can be smoothed by a single curve. 8 Master meter systems 8.1 The master meter method of proving meters requires the selection of a meter with better performance characteristics than the meter to be proved. The master meter can be one of a battery of parallel meters, a mobile meter or a meter at a test station used specifically for proving meters. The master meter shall be r
