1、Manual of PetroleumMeasurement StandardsChapter 6Metering AssembliesSection 7Metering Viscous HydrocarbonsSECOND EDITION, MAY 1991REAFFIRMED, MAY 2012Manual of PetroleumMeasurement StandardsChapter 6Metering AssembliesSection 7Metering Viscous HydrocarbonsMeasurement CoordinationSECOND EDITION, MAY
2、1991REAFFIRMED, MAY 2012SPECIAL 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, MANUFACTURERS, OR SUPPLI
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7、ORING DEPARTMENT TELEPHONE (202) ANNUALLY AND UPDATED QUARTERLY BY API, 1220 L STREET, N.W., WASHINGTON, D.C. 20005. ONE-TIME EXTENSION OF UP TO TWO YEARS WILL BE ADDED TO THIS 682-8000. A CATALOG OF API PUBLICATIONS AND MATERIALS IS PUBLISHED Copyright 1991, American Petroleum Institute This public
8、ation is intended as a guide for the design, installation, operation, and proving of meters and their auxiliary equipment used in metering viscous hydrocarbons. API publications may be used by anyone desiring to do so. Every effort has been made by the Institute to assure the accuracy and reliabilit
9、y of the data contained in them; however, the Institute makes no representation, warranty, or guarantee in connection with this publication and hereby expressly disclaims any liability or responsibility for loss or damage resulting from its use or for the violation of any federal, state, or municipa
10、l 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., Washington, D.C. 20005. CONTENTS Page SECTION 7-METERING VISCOUS HYDROCARBON
11、S 6.7.1 Introduction . 1 6.7.2 Scope and Field of Application 1 6.7.3 Referenced Publications . 1 6.7.4 Definitions 1 6.7.5 Installation and Selection of Meters and Auxiliary Equipment . 1 6.7.5.1 Installation 1 6.7.5.2 Special Meter Construction 1 6.7.5.3 Displacement Meters . 2 6.7.5.4 Turbine Met
12、ers 2 6.7.5.5 Method of Heating . 2 6.7.5.6 Air Remover or Eliminator . 3 6.7.6 Meter Proving . 4 6.7.6.1 Conventional Pipe Provers . 5 6.7.6.2 Tank Provers 5 6.7.6.3 Gravimetric Proving 5 6.7.6.4 Master-Meter Proving . 5 6.7.6.5 Small-Volume Provers 5 6.7.7 Meter Operation . 6 Figures I-Meter Insta
13、llation With Return Line for Maintaining Heat at the Meter 3 4 4 2-Truck Meter Installation With Block-Valve System 3-Line Meter Installation With Block-Valve System . V CHAPTER 6-Metering Assemblies SECTION 7-METERING VISCOUS HYDROCARBONS 6.7.1 Introduction This publication is intended as a guide f
14、or the design, installation, operation, and proving of meters and their auxiliary equipment used in metering viscous hydrocarbons. The objective of this publication is to stress the differences between metering high-viscosity hydrocarbons and the nor- mal application of metering less viscous hydroca
15、rbon liquids. In general, the contents of Chapter 4, Chapter 5, and Chapter 12.2 of this manual apply. This publication supple- ments Chapters 4 and 5 and Chapter 12.2, in the field of metering viscous hydrocarbons. For example, some opera- tions require purging the viscous liquids from the lines to
16、 prevent congealing during idle periods or to prevent con- tamination. If the air or gas used to displace the liquid is pumped through the meter when the lines are being refilled, the meter may operate at excessively high rates. This misoperation can damage the moving parts of the meter and will cau
17、se erroneous meter registration. The recommenda- tions in this chapter should help to avoid misoperation, and if followed, the recommendations should protect the meter from damage and inaccurate measurement because of entrapment of air or gas. When alternative procedures are given, the recommendatio
18、ns of the meter manufacturer should be followed. 6.7.2 Scope and Field of Application This chapter defines viscous hydrocarbons and describes the difficulties that arise when viscous hydrocarbons are raised to high temperatures. The effects of such temperatures on meters, auxiliary equipment, and fi
19、ttings are discussed, and advice and warnings to overcome or mitigate difficulties are included. 6.7.3 Referenced Publications API Manual of Petroleum Measurement Standards Chapter 1-“Vocabulary Chapter WProving Systems” Chapter 4.2, “Conventional Pipe Provers” Chapter 4.3, “Small-Volume Provers” Ch
20、apter 4.5, “Master-Meter Provers” Chapter 4.4, “Tank Provers” Chapter 5-“Metering” Chapter 5.2, “Measurement of Liquid Hydrocarbons by Displacement Meters” Chapter 5.3, “Measurement of Liquid Hydrocarbons by Turbine Meters” Chapter 7.2, “Dynamic Temperature Deter- mination” Chapter 12.2, “Calculatio
21、n of Liquid Petroleum Quantities Measured by Turbine or Displacement Meters” 6.7.4 Definitions A viscous hydrocarbon is any liquid hydrocarbon that requires special treatment or equipment when it is handled or stored because of its resistance to flow. Another liquid that does not need these precauti
22、ons might have some of the characteristics or present some of the measurement problems characteristic of viscous liquids. Examples of liquid hydrocarbons that are generally considered as viscous are those with viscosities greater than 100-400 centipoise (cP) milliPascal-seconds (mPa-sec), such as No
23、. 5 and No. 6 bunker fuels, asphalts (both penetration grades and cutbacks), most lubricating oils and grease components, and some crude oils. Definitions of other terms can be found in Chapter 1 of this manual. 6.7.5 Installation and Selection of Meters and Auxiliary Equipment 6.7.5.1 INSTALLATION
24、The provisions of Chapter 5 should be followed in select- ing and installing meters and auxiliary equipment. The selec- tion of air removers (eliminators) is of particular importance when they are used in viscous liquid service, and their selec- tion is discussed separately in this publication. If t
25、he meter is to be installed in a vertical line, special consideration should be given to equipment design. Some types of meters are not designed for vertical installation, and the performance of these types could be affected. Because of the various types of meters available and the wide differences
26、in liquid and measurement conditions, it is important that the meter manufacturer be given complete information on the proposed application. The information to be provided is listed in 6.7.5.2. 6.7.5.2 SPECIAL METER CONSTRUCTION Many viscous liquids are heated to reduce viscosity and facilitate hand
27、ling. 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 excess stressing of internal 1 2 CHAPTER however, there will be some reduction in the accuracy. 6.7.5.4 TURB
28、INE METERS The performance characteristics of turbine meters are altered considerably by changes in liquid viscosity. The varia- tions in the meter factor because of viscosity change is most noticeable when viscous fluids are metered. Turbine meters will also exhibit changes in the meter factor as t
29、he flow rate changes. These effects are most significant when viscous fluids are metered. However, when larger turbine meters will be operating over narrow flow ranges and when viscosity is not likely to vary either because of changes in temperature or changes in the liquid characteristics, acceptab
30、le accuracy may be obtained. The use of turbine meters on viscous hydrocarbons is generally considered impractical because normal changes in flow rate or viscosity would warrant re-proving the meter to achieve acceptable accuracies. 6.7.5.5 METHOD OF HEATING If the liquid needs to be heated for ordi
31、nary pumping and handling, the liquid in the meter should be kept heated to reduce the viscosity to a practical flow condition and prevent solidification during idle periods. Accessory equipment, such as valves, strainers, and air eliminators, must be heated and insulated. This requirement is partic
32、ularly necessary for air eliminator venting mechanisms and control valve pilots. For services in which the liquid is heated while in storage, the liquid may be kept in the line to the meter and the accessories may be heated by circulating the liquid through a return line. This method is of particula
33、r value for tank trucks when auxiliary heating methods are difficult to provide. 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, a means must be provided
34、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. Solenoid-or SECTION 7-METERI
35、NG VISCOUS HYDROCARBONS 3 Return line to storage Thermometer Pressure gauge Pump Strainer Meter Figure 1-Meter Installation With Return Line for Maintaining Heat at the Meter motor-operated valves-permit control of the circulation from a remote control point. Heating will reduce the viscosity of mos
36、t liquids, and the best transfer function may be effected by a variety of devices or methods. When steam is available, the lines may be steam- traced. Many recent installations use hot oil for tracing the lines. In either case, the meter and the accessories also can be heat-traced. When very viscous
37、 liquids are handled, steam- jacketed meters and accessory equipment may be needed. This equipment can also be used when hot oils are the tracing medium. When steam, hot-oil tracing, and jacketing are not possible, electric heating can be used as an alternative method. In smaller installations, the
38、use of electric-heating cable might be adequate and less costly. It is important that the temperature of the liquid be main- tained within a reasonably close limit because meter accuracy is affected by variations in meter temperature as well as by the resultant viscosity change. When the nature of t
39、he liquid requires a temperature higher than would be advisable for safety, the installation should provide a means to minimize the danger, such as adequate splash guards. If a displacement meter is provided with extra clearances for a high-operating temperature, that temperature should not be excee
40、ded, and the meter should be operated within a reasonable limit of this specified temperature. If the meter is operated at a higher temperature than that for which it is designed, interference between moving parts and excessive wear or damage may occur. The liquid temperature must be held below the
41、point that might cause vaporization and result in inaccurate meter registration. In some cases, care must be exercised to prevent overheating of the liquid to a point where it might ignite when exposed to the atmosphere. Overheating can also cause coking or chemical changes in some liquids. 6.7.5.6
42、AIR REMOVER OR ELIMINATOR It is difficult to separate entrained air or vapor from most viscous liquids. As viscosity increases, the time required for separating fine bubbles of air or vapor from the liquid in- creases. The removal of entrained bubbles requires a large air eliminator tank to effect s
43、eparation. In most instances, this approach is uneconomical in cost and required space con- siderations. The pumping of air or vapor should be prevented. A return line, as mentioned previously, permits the system to be purged by returning any air or vapor to the storage tank. In effect, this method
44、uses the storage tank as an air eliminator. When a return line can be used, circulation should be main- tained long enough to ensure that all air or vapor has been carried back to the storage tank. This need may be based on time, with liquid being pumped for a period more than suffi- cient to displa
45、ce the original contents of the line to the meter. A new installation must be started carefully. The entire metering system should be filled at a reduced rate until all air pockets have been eliminated from the equipment. An air pocket in a meter can result in damage if flow is stopped or started qu
46、ickly, creating a surge pressure. In some installations, the liquid in storage tanks may contain air or vapor bubbles. This situation could be caused by the method of heating or by pumping liquid into the storage at the same time that liquid is being pumped out. Some crude oils foam when heated, and
47、 the tank may need to settle before the product is withdrawn. A sampling device or method may be required with a testing system to determine when the air or vapor content is at an acceptable level. If this type of operation must be used without allowing sufficient time for separating the air or vapo
48、r, an air eliminator, designed for the particular operating conditions, is suggested. Therefore, the manufacturer should be consulted. When air or vapor must be pumped and cannot be removed with a circulating line or return line, a block valve may be used to stop flow when air vapor is detected. (Se
49、e Figures 2 and 3.) Several systems use valves that are operated electri- cally or hydraulically or by air. A means is provided for detecting the presence of air or vapor in the pump, in the line, or in the air eliminator. The detector then actuates the block valve. With these systems, the amount of air or vapor that must be eliminated is not large, and an air eliminator of 4 CHAPTER 6-METERING ASSEMBLIES Air diminatoi vent Truck tank P-1 I P - 11 II 4 Pressure therefore, a conventional pipe prover is recommended. (See Chapter 4.2.) However, in a dock installation, because space is
