1、BRITISH STANDARD BS 7702:1993 ISO 9200:1993 Guide to Volumetric metering of viscous hydrocarbons UDC 665.73/.74-404.2:531.732BS7702:1993 This British Standard, having been prepared under the directionof the Petroleum Standards Policy Committee, waspublished under the authorityof the Standards Boarda
2、nd comes into effect on 15October 1993 BSI 07-1999 The following BSI references relate to the work on this standard: Committee reference PTC/12 Special announcement in BSI News, August 1993 ISBN 0 580 22287 X Committees responsible for this British Standard The preparation of this British Standard w
3、as entrusted by the Petroleum Standards Policy Committee (PTC/-) to Technical Committee PTC/12, upon which the following bodies were represented: Department of Trade and Industry (Gas and Oil Measurement Branch) Department of Trade and Industry (National Engineering Laboratory) Institute of Petroleu
4、m Royal Institution of Naval Architects Salvage Association The following body was also represented in the drafting of the standard, through subcommittees and panels: GAMBICA (BEAMA Ltd.) Amendments issued since publication Amd. No. Date CommentsBS7703:1993 BSI 07-1999 i Contents Page Committees res
5、ponsible Inside front cover National foreword ii Introduction 1 1 Scope 1 2 Definition 1 3 Description of metering system 1 4 Meter proving 5 5 Meter operation 7 Annex A (informative) Sample gravimetric meter proving report form 8 Figure 1 Single-case meter installation with return line 4 Figure 2 T
6、ruck meter installation with control valve system 4 Figure 3 Line meter installation with control valve system 5 List of references Inside back coverBS7702:1993 ii BSI 07-1999 National foreword This British Standard has been prepared under the direction of the Petroleum Standards Policy Committee, I
7、t is identical with ISO 9200:1993 Crude petroleum and liquid petroleum products Volumetric metering of viscous hydrocarbons, published by the International Organization for Standardization (ISO). ISO 9200 was prepared by Subcommittee 2, Dynamic petroleum measurement, of Technical Committee 28, Petro
8、leum products and lubricants, in which the United Kingdom participated. CAUTION. Attention is drawn to the Health and Safety at Work etc. Act 1974 and the need for ensuring that the guidance given in this British Standard is carried out with suitable precautions. The guidance given in this British S
9、tandard is intended to be carried out by appropriately qualified and experienced persons and/or other suitably trained and/or supervised personnel. Normal safety precautions should be used throughout the use of this guide. Additional information. In the case of gravimetric meter proving (4.3 and Ann
10、ex A), care should be exercised to ensure calculations adjust between apparent mass in air, as recorded by a weighing scale and true mass as indicated by density instruments. The buoyancy factors are given in API Table 56 in AnnexA of BS 6441:1993. It should also be noted that for LPG containers, we
11、ighing scales record a value nearer to true mass than apparent mass in air andtherefore, no adjustment is needed for this product. A British Standard does not purport to include all the necessary provisions of a contract. Users of British Standards are responsible for their correct application. Comp
12、liance with a British Standard does not of itself confer immunity from legal obligations. Summary of pages This document comprises a front cover, an inside front cover, pages i and ii, pages1 to 10, an inside back cover and a back cover. This standard has been updated (see copyright date) and may ha
13、ve had amendments incorporated. This will be indicated in the amendment table on the inside front cover.BS7702:1993 BSI 07-1999 1 Introduction This International Standard is intended as a guide to the design, installation, operation and proving of meters and their auxiliary equipment used in meterin
14、g viscous hydrocarbons. The objective of this International Standard is to stress the differences between metering high viscosity hydrocarbons and the normal application of metering to less viscous hydrocarbon liquids. Some operations require purging the viscous liquids from the lines to prevent con
15、gealing during idle periods or to prevent contamination. If the air or gas used to displace the liquid is pumped through the meter when refilling the lines, the meter may operate at excessively high rates. This can cause damage to the moving parts of the meter and may result in erroneous meter regis
16、tration. The recommendations in this International Standard should assist in avoiding misoperation, and the recommendations, if followed, should protect the meter from damage and inaccurate measurement due to entrapment of air or gas. Where alternative procedures are given, the recommendations of th
17、e meter manufacturer should be followed. 1 Scope This International Standard defines viscous hydrocarbons and describes the difficulties that arise when viscous hydrocarbons are raised to high temperatures. The effects of such temperatures upon meters, auxiliary equipment and fittings are discussed,
18、 and advice and warnings to overcome or mitigate difficulties are included. 2 Definition For the purposes of this International Standard, a viscous hydrocarbon is defined as any liquid hydrocarbon that requires special treatment or equipment in its handling or storage because of its resistance to fl
19、ow. Examples of liquid hydrocarbons which are generally considered as viscous are residual fuels with a viscosity greater than 750 m 2 /s at 50 C, bitumens (both penetration grades and cutbacks), most lubricating oils and grease components, as well as some crude oils. Note that viscosity is a parame
20、ter in its own right, regardless of temperature. NOTE 1It is possible that another liquid not needing these precautions might have some of the characteristics or present some of the measurement problems characteristic of viscous hydrocarbons. 3 Description of metering systems 3.1 Selection and insta
21、llation of meters and auxiliary equipment 3.1.1 General Care should be taken in the selection and installation of meters and auxiliary equipment. Theselection of air removers (eliminators) is of particular importance when used in viscous liquid service and is discussed separately in 3.1.6. If the me
22、ter is to be installed in a vertical line, special consideration should be given to equipment design. Some types of meters are not designed for such an installation, and the performance of these types could be affected. Because of the various types of meters available and the wide differences in liq
23、uids and measurement conditions, it is important that the meter manufacturer be given complete information on the proposed application. The information that should be provided is listed in 3.1.2. 3.1.2 Special meter construction Many viscous liquids are heated in order to reduce viscosity and facili
24、tate handling. If the viscous liquids are to be heated, certain special details in the meters construction and manufacture are required. Extra clearance between moving parts may be provided to prevent interference, to reduce the work load required, and to compensate for the higher temperature and al
25、tered viscosity. Certain viscous liquids can contain corrosive materials, and this corrosivity can increase as the liquid temperature increases. Where significant, the metallurgy of the meter, its trim and auxiliary equipment shall be capable of resisting this corrosion. At elevated temperatures, sp
26、ecial meter construction materials may be required. Where dissimilar metals are used, the high temperature can result in mechanical interference caused by differences in metal expansion. This is particularly true where liners or lining sleeves are used. The use of devices such as ventilated counter
27、extensions may be necessary to separate the counter and the meter adjuster from the heat source.BS7702:1993 2 BSI 07-1999 Meters used in the transfer of liquids at elevated temperatures are often fitted with automatic temperature compensators that automatically adjust the counter registration to 15
28、C. These compensators are designed to cover a certain rangeof operating temperatures. If a registration adjusted to 15 C is desired, the range of operating temperatures shall be accurately specified, as well as the density of the liquid or its coefficient of expansion. Operating a temperature compen
29、sator at temperatures above its design range will result in inaccurate registration and can damage the device. Standby temperature during idle periods can exceed the design temperature rating and result in damage to the automatic temperature compensator or to the moving parts of the meter. The meter
30、 manufacturer can make recommendations specific for the intended operating conditions to minimize possible problems. The manufacturer should be provided with the following information: flow rate range at maximum and minimum viscosities; maximum and minimum operating pressures; maximum and minimum te
31、mperatures; anticipated standby (or off-duty) temperature; viscosity of fluid at maximum and minimum temperatures (pascal-second, centipoise or any other recognized viscosity indication); specific gravity of fluid at maximum and minimum temperatures; type of proving equipment under consideration; na
32、ture and amount of any corrosive elements present; nature and amount of any abrasive elements present; compatibility (or noncompatibility) of construction material with the fluid. 3.1.3 Displacement meters Displacement meters have performance characteristics on viscous fluids different from inferent
33、ial and turbine meters. Performance in a displacement meter is affected by meter slippage. Slippage is the unmetered flow passing through the mechanical clearance between the moving parts of the meter, and is caused by the differential pressure across a heated meter resulting from mechanical and flu
34、id friction. The magnitude of the slippage flow, which can be considered to have a laminar flow regime, is related to the meter flow rate, the size of the clearances, the viscosity and the fluid density. There is considerably less slippage through a meter as liquid viscosity increases. When a high d
35、egree of accuracy is required, re-proving is suggested with any viscosity change to re-establish accuracy. Some types of displacement meters can handle any viscous liquid that can be pumped, whereas others may be limited to handling liquids of specified maximum viscosities. All types, however, have
36、their maximum recommended flow rate reduced as the viscosity increases. The amount of flow rate reduction can vary with equipment from different manufacturers. A maximum limit on flow rate at high viscosity is necessary to maintain the meter pressure drop within the design limits, to prevent cavitat
37、ion and to reduce the viscous shear load on moving parts. 3.1.4 Inferential and turbine-type meters For turbine meters, changes in liquid viscosity result in a shift in the meter factor and a change in the range of flow rates over which the turbine meter will perform with close accuracy. A change in
38、 fluid viscosity requires re-proving of the meter for best accuracy. Turbine meters are available with viscosity-compensating devices or they can be designed to compensate for changes in viscosity, and are capable of operating over an acceptable flow range. In services where the turbine meter will b
39、e operating at flow rates which do not vary greatly, acceptable accuracy can be obtained if the meter is proved and if meter factors are established for the various expected viscosities and rates. These factors should be reproducible. Since the viscosity of a liquid may change considerably with a ch
40、ange in temperature, all meters should be re-proved for changes in temperature as well as changes in viscosity. Re-proving will establish a basis for determining the frequency of proving that may be required to achieve the desired accuracy of measurement. When the temperature of the metered liquid c
41、an vary by more than a few degrees during deliveries, a temperature recorder is recommended.BS7702:1993 BSI 07-1999 3 Because of these viscosity factors, inferential and turbine-type meters for use on viscous hydrocarbons can be limited in performance; however, they should not be ruled out. 3.1.5 He
42、ating methods If it is necessary to heat the liquid for ordinary pumping and handling, the liquid in the meter and the upstream piping should also be kept heated. The principal objective is to reduce the viscosity to a practical flow condition and prevent solidification during idle periods. Accessor
43、y equipment, such as valves, strainers and air eliminators, must be heated and insulated. This applies particularly to air eliminator venting mechanisms and control valve pilots. For services in which the liquid is heated while in storage, it is sometimes possible to keep the liquid in the line to t
44、he meter and the accessories heated by circulating the liquid through a return line. This method is of particular value on tank trucks where auxiliary heating methods are difficult to provide. Some double-case meters can be installed so that the meter housing is part of the circulating system. In th
45、is type of installation, the return line is connected to the meters outer housing. With single-case meters, the return line should tee off as close to the meter inlet as possible (see Figure 1). In some applications, circulating the liquid through the entire meter system might be advisable; however,
46、 a means is necessary to prevent registration on the meter counter during such periods of circulation. An automatic method of controlling circulation and counter registration is suggested in this type of installation. Valves should be located in the return line to permit easy control of flow. Soleno
47、id or motor-operated valves permit control of the circulation from a remote control point. Heating will reduce the viscosity of most liquids, and the best heat transfer function may be effected by a variety of devices or methods. Where steam is available, the lines may be steam-traced. Many recent i
48、nstallations use hot oil for tracing the lines. In either case, the meter and the accessories also can be heat-traced. In handling very viscous liquids, it may be necessary to use steam-jacketed meters and accessory equipment. This equipment can also be used where hot oils are the tracing medium. Wh
49、ere steam or hot-oil tracing or jacketing is not possible, electric heating can be used as an alternative method. In smaller installations, the use of electric heating cable may be adequate and less costly. It is important that the desired temperature of the liquid be maintained within reasonably close limits, not only for safety reasons, but also because meter accuracy is affected by variations in viscosity resulting from temperature fluctuations. If a displacement meter is provided with extra clearances for use at a high operating temperature,
