1、BRITISH STANDARD BS ISO 7278-4:1999 ISO 7278-4: 1999 Liquid hydrocarbons Dynamic measurement Proving systems for Volumetric meters Part 4: Guide for operators of pipe provers ICS 75.180.30BSISO7278-4:1999 This British Standard, having been prepared under the directionof the Sector Committeefor Mater
2、ials and Chemicals, was published underthe authority of the Standards Committee and comesinto effect on 15August1999 BSI 03-2000 ISBN 0 580 32797 3 National foreword This British Standard reproduces verbatim ISO7278-4:1999 and implements it as the UK national standard. The UK participation in its pr
3、eparation was entrusted by Technical Committee PTI/12, Petroleum measurement and sampling, to Subcommittee PTI/12/1, Static and dynamic measurement, which has the responsibility to: aid enquirers to understand the text; present to the responsible international/European committee any enquiries on the
4、 interpretation, or proposals for change, and keep the UK interests informed; monitor related international and European developments and promulgate them in the UK. A list of organizations represented on this subcommittee can be obtained on request to its secretary. Cross-references The British Stan
5、dards which implement international or European publications referred to in this document may be found in the BSI Standards Catalogue under the section entitled “International Standards Correspondence Index”, or by using the “Find” facility of the BSI Standards Electronic Catalogue. A British Standa
6、rd does not purport to include all the necessary provisions of a contract. Users of British Standards are responsible for their correct application. Compliance with a British Standard does not of itself confer immunity from legal obligations. Summary of pages This document comprises a front cover, a
7、n inside front cover, pagesi andii, theISO title page, pagesii toiv, pages1 to25 and a back cover. This standard has been updated (see copyright date) and may have had amendments incorporated. This will be indicated in the amendment table on the inside front cover. Amendments issued since publicatio
8、n Amd. No. Date CommentsBSISO7278-4:1999 BSI 03-2000 i Contents Page National foreword Inside front cover Foreword iii Text of ISO 7278-4 1ii blankBSISO7278-4:1999 ii BSI 03-2000 Contents Page Foreword iii Introduction 1 1 Scope 1 2 Normative references 1 3 Principles 2 3.1 Ways of expressing a mete
9、rs performance 2 3.2 How meter performance varies 3 3.3 Correction factors 4 4 Meters and provers 4 4.1 Pulse-generating meters 4 4.2 Sources of error in operating meters 5 4.3 Pulse interpolators 6 4.4 Conventional pipe provers 6 4.5 Small volume pipe provers 10 4.6 Methods of installing pipe prove
10、rs 11 4.7 Sources of error in operating pipe provers 12 4.8 Prover calibration and recalibration 14 4.9 Meter installations 14 5 Safety requirements 14 5.1 General 14 5.2 Permits 14 5.3 Mechanical safety 14 5.4 Electrical safety 18 5.5 Fire precautions 19 5.6 Miscellaneous safety precautions 19 5.7
11、Records 19 6 Operating a pipe prover 19 6.1 Setting up a portable prover 19 6.2 Warming up provers 20 6.3 Periodical checks of factors affecting accuracy 20 6.4 The actual proving operation 20 6.5 Assessment of the results 21 6.6 Fault finding 21 Annex A (informative) Bibliography 25 Figure 1 Princi
12、ple of operation of pipe prover 7 Figure 2 Arrangement of a typical unidirectional prover 8 Figure 3 Arrangement of a conventional sphere type bidirectional prover 9 Figure 4 Example of a unidirectional small volume prover with internal valve 12 Figure 5 Example of a unidirectional small volume prov
13、er with external valve 13 Figure 6 A simple turbine flowmeter installation with bidirectional prover 15 Figure 7 A typical multi-stream metering installation 16 Figure 8 Example of control chart 22 Table 1 Trouble-shooting guide for pipe prover operators 23BSISO7278-4:1999 BSI 03-2000 iii Foreword I
14、SO (the International Organization for Standardization) is a worldwide federation of national standards bodies (ISO member bodies). The work of preparing International Standards is normally carried out through ISO technical committees. Each member body interested in a subject for which a technical c
15、ommittee has been established has the right to be represented on that committee. International organizations, governmental 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 electr
16、otechnical standardization. Draft International Standards adopted by the technical committees are circulated to the member bodies for voting. Publication as an International Standard requires approval by at least75% of the member bodies casting a vote. International Standard ISO7278-4 was prepared b
17、y Technical Committee ISO/TC28, Petroleum products and lubricants, Subcommittee SC2, Dynamic petroleum measurement. ISO 7278 consists of the following parts, under the general title Liquid hydrocarbons Dynamic measurement Proving systems for volumetric meters: Part 1: General principles; Part 2: Pip
18、e provers; Part 3: Pulse interpolation techniques; Part 4: Guide for operators of pipe provers; Part 5: Small volume provers. Annex A of this part of ISO7278 is for information only.iv blankBSISO7278-4:1999 BSI 03-2000 1 Introduction All measuring instruments which have to meet a standard of accurac
19、y need periodic calibration that is to say, a test or series of tests has to be performed in which readings obtained from the instrument are compared with independent measurements of higher accuracy. Petroleum meters are no exception. Nearly all those used for the purpose of selling or assessing tax
20、es, by national laws, need proving at intervals, and when there is a large amount of money at stake they are likely to be calibrated quite frequently. In the petroleum industry the term “proving” is used to describe the procedure of calibrating volume meters on crude oil and petroleum products. The
21、most usual way to prove a meter is to pass a quantity of liquid through it into an accurate device for measuring volume, known as a prover. With very small meters the proving device may be a volumetric flask or similarly shaped vessel of metal with an accurately known volume. There are, for instance
22、, standard measuring vessels which can be used to prove the meters incorporated in gasoline dispensing pumps at roadside filling stations. If the pump dial registers10,2 litres when enough gasoline has been delivered to fill a10 litre vessel, it is evident that the meter is over-reading by2%. In a l
23、arge metering installation, where a single meter can be passing thousands of litres per second, the situation is much more complicated. The measuring elements of the meters generally do not drive mechanical dials graduated in units of volume like a gasoline dispenser, but instead cause a series of e
24、lectrical pulses to be generated which are registered by electrical counters. With meters of this type the purpose of proving is to determine the relationship between the number of pulses generated/counted and the volume passed through the meter a relationship which varies with the design and size o
25、f the meter and can be affected by flowrate and liquid properties. Another difficulty is that where the meters are in a pipeline the flow through these large meters usually cannot be stopped and started at will. Consequently, both the meters and the prover have to be capable of being read simultaneo
26、usly and “on the fly”, that is, while liquid is passing through them at a full flowrate. The proving is complicated still further by the effects of thermal expansion and compressibility on the oil, and that of thermal expansion and elastic distortion under pressure on the steel body of the prover. T
27、his part of ISO7278 is concerned with only one class of provers, known as pipe provers, which are used very widely where meters for crude oil and petroleum products have to be proved to the highest possible standards of accuracy. In principle, a pipe prover is only a length of pipe or a cylinder who
28、se internal volume has been measured very accurately and having a well-fitted piston (or a tightly-fitted sphere acting like a piston) inside it, so that the volume swept out by the piston or sphere can be compared with the meter readout while a steady flow of liquid is passing through the meter and
29、 prover in series. In practice, however, various accessories must be added to the simple pipe-and-piston arrangement to produce a prover that will work effectively. 1 Scope This part of ISO7278 provides guidance on operating pipe provers to prove turbine meters and displacement meters. It applies bo
30、th to the types of pipe prover specified in ISO7278-2, which are referred to here as “conventional pipe provers”, and to other types referred to here as “compact pipe provers” or “small volume provers”. It is intended for use as a reference manual for the operation of pipe provers, and also for use
31、in staff training. It does not cover the detailed differences between provers of broadly similar types made by different manufacturers. 2 Normative references The following standards contain provisions which, through reference in this text, constitute provisions of this part of ISO7278. At the time
32、of publication, the editions indicated were valid. All standards are subject to revision, and parties to agreements based on this part of ISO7278 are encouraged to investigate the possibility of applying the most recent editions of the International Standards indicated below. Members of IECandISO ma
33、intain registers of currently valid International Standards. ISO 2714:1980, Liquid hydrocarbons Volumetric measurement by displacement meter systems other than dispensing pumps. ISO 2715:1981, Liquid hydrocarbons Volumetric measurement by turbine meter systems. ISO 4124:1994, Liquid hydrocarbons Dyn
34、amic measurement Statistical control of volumetric metering systems. ISO 4267-2:1988, Petroleum and liquid petroleum products Calculation of oil quantities Part2:Dynamic measurement. BSISO7278-4:1999 2 BSI 03-2000 ISO 7278-2:1988, Liquid hydrocarbons Dynamic measurement Proving systems for volumetri
35、c meters Part 2: Pipe provers. ISO 7278-3:1998, Liquid hydrocarbons Dynamic measurement Proving systems for volumetric meters Part 3: Pulse interpolation techniques. 3 Principles 3.1 Ways of expressing a meters performance The object of proving meters with a pipe prover is to provide a number with (
36、usually) four or five significant digits such as1,0029, 0,9998, or21586 which can afterwards be used to convert the readout of the meter into an accurate value of the volume passed through the meter. There are several different forms that this numerical expression of a meters performance can take, b
37、ut only three of them are of importance to the pipe prover operator. They are discussed below. 3.1.1 Meter factor The earliest petroleum meters were of the displacement type (see4.1) with dials reading directly in units of volume such as litres or cubic metres. Readings on the display are usually ap
38、proximate values. These values may be corrected to reflect a more accurate number by either changing the gear ratio in the display mechanism or through the use of a meter factor. Since difficulty can arise in attempting to achieve a given volume through changing the gears, the meter factor is more c
39、ommonly used. The meter factor, MF, is defined as the ratio of the actual volume of liquid passed through the meter(V) to the volume indicated on the dial of the meter (V m ). That is: In a proving operation the value of V is derived from the prover while V mis read directly from the meter. Afterwar
40、ds, when the meter is being used to measure throughput, readings can be multiplied by MF to give the corrected values of the volumes delivered. Meter factor is a non-dimensional quantity, a pure number. This means that its value does not vary with a change in units used to measure volume. 3.1.2 K fa
41、ctor During the past quarter of a century, turbine meters (see4.1) have come into widespread use in the petroleum industry. They do not usually have a dial reading in units of volume, because their primary readout is simply a train of electrical pulses. These are collected in an electronic counter,
42、and the number of pulses counted (n) is proportional to the volume passed by the meter. The object of proving such a meter is to establish the relationship between n and V. One way of expressing this relationship is through a quantity called K factor, which is defined as the number of pulses emitted
43、 by the meter while one unit volume is delivered. That is: When a meter is being proved it is necessary to obtain simultaneous values of n and V, with n coming from the meter and V from the prover. In subsequent use of the meter, the procedure is to divide the K factor into the number of pulses emit
44、ted by the meter in order to obtain the volume delivered. The K factor is not a pure number. It has the dimensions of reciprocal volume (1/V) and so its value depends upon the units used to measure volume. A value of K factor expressed as pulses per cubic metre, for instance, is a thousand times the
45、 value expressed as pulses per litre. 3.1.3 One pulse volume Because it is easier to multiply than to divide, the reciprocal of the K factor is a more useful quantity for field use when hand calculations are employed (but not when computers are used). This reciprocal is called the “one-pulse volume”
46、 (q) because it indicates the volume delivered by the meter (on average) while one pulse is emitted. It is defined by the equation: q has the dimensions of volume per pulse. When it is multiplied by the number of pulses emitted by the meter, the result is the volume delivered through the meter. 3.1.
47、4 Alternative uses of meter factor, K factor and one pulse volume It is shown in the previous subclauses how meter factor was originally used with displacement meters. With readout in units of volume, K factor and its reciprocal q are used with turbine meters, with the readout being a number indicat
48、ed on a pulse-counter. Nowadays however, this distinction has largely disappeared. On the one hand, displacement meters intended for use with pipe provers are always fitted with electrical pulse-generators, so that for the purposes of proving they behave like turbine meters and the results can be ex
49、pressed as a value of K factor or one pulse volume. On the other hand, some modern large-scale turbine metering systems incorporate a data processing module, sometimes known as a “scaler”, which converts the number of pulses emitted into a nominal value of the volume delivered; with such systems the earlier notion of meter factor again becomes useful in certain circumstances. MF = V/V m (1) K = n/V (2) q = 1/K = V/n (3)BSISO7278-4:1999 BSI 03-2000 3 Detailed instructions for the use of meter factor, K fac
