"INTRODUCTION This recommended practice has been prepared as a guide to assist in the design@ installation@ operation@ and proving of meters and meter accessories for the measurement of viscous hydrocarbons. The basic intent is to educate@ inform@ and warn prospective users??stressing the difference between this field of metering and the metering of less viscous hydrocarbons@ and giving them ing the benefit of the experience in this field of measurement to date. In general@ the procedures outlined in API Standard 1101 (USAS Zl I.l70)@* API Standard 2531 (USAS ZI1.l71)@' and a forthcoming publication@ API Standard 2534@' will apply. Viscous hydrocarbons have characteristics which can affect the various phases of meter installation@ operation@ and proving; therefore@ certain designs and procedures not provided in API Standard 1101 and API Standard 2534 are recognized and should be taken into consideration. This recommended practice should supplement all applicable API metering standards. A viscous hydrocarbon@ for the purpose of this publication@ will be any liquid hydrocarbon that requires special treatment in handling or storage@ such as heating@ or that requires special meter or special pump construction. It is possible that a fluid not requiring these precautions might have some of the characteristics or might present some of the measurement problems characteristic of viscous liquids. This publication also would apply to those liquidS. Exa!l1ples of liquids generally considered as viscous fluids in handling or metering are No. 5 and No. 6 bunker fuels; asphalts@ both penetration grades and cutbacks; most lubricating oils; and lubricating oil and grease components; as well as some crude oils. Positive displacement meters have different performance characteristics on viscous fluids than do the various inferential or turbine meters. Meter performance in the positive displacement meter is affected by meter slippage (see API Standard 1101@ Par. 4004 and 4005). There is considerably less slippage through the meter as the viscosity of the liquid increases. There is some change in slippage with change in viscosity. Where a high degree of accuracy is required@ proving is suggested with any viscosity change to reestablish the meter accuracy. Some types of positive displacement meters can handle any viscous liquid that can be pumped@ whereas others may be limited to handling liquids of specified maximum viscosity. All types@ however@ would have the maximum recommended flow rate@ which may vary with different manufacturers@ reduced as the viscosity increases. This limitation on flow rate at high viscosity is necessary to hold the meter pressure drop within the design limits@ prevent cavitation@ and reduce the viscous shear load on the moving members. The characteristics of inferential-type meters and turbine meters are altered by changes in liquid viscosity. A variation in viscosity results in a shift@ or change@ in the meter factor and a change in the range of flow rates over which the turbine meter will perform with close accuracy. Turbine meters are available with viscositycompensating devices@ or are designed to compensate for changes in viscosity@ and are capable of operating over an acceptable flow range. Where the turbine meter will be operating at flow rates which do not vary greatly@ acceptable accuracy can be obtained if the meter Ls proved and factors are established for the various viscosities and rates to be encountered. These factors would be reproducible. Since viscosity may change considerably with change in temperature@ all meters should be proved with a change in temperature as well as a change in viscosity. This will establish a basis for determining the frequency of proving that may be required to achieve the desired accuracy of measurement. Where the temperature of the metered liquid may vary by more than a few degrees during deliveries@ a temperature recorder is recommended. Because of the different types of meters available and the wide variation in liquid 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 under ""Special Meter Construction."" As mentioned in API Standard 1101@ the accuracy of measurement obtainable by compliance with the provisions of that standard may not be required in all applications. In the past@ the measurement of viscous liquids has often been far from precise. Many of these liquids have not been considered of great enough value per unit of measure to require any improvement of measuring methods. This situation is gradually changing. Procedures which were once acceptable in the handling and measurement of these liquids are becoming less acceptable. Where the value of the product warrants@ or where stock control is particularly important@ measurement of viscous liquids by meter may be as precise as the similar measurement of lighter@ less viscous liquids. This publication is intended as a guide to assist in the design and operation of metering installations based on current practices and procedures. Continued experience in the metering of these liquids may show that other practices and procedures can be used to accomplish tfie same results in a somewhat different manner. Certain alternate practices and recommendations are mentioned in connection with meters used on viscous liquids. These alternates exist because of the variety of measuring principles presently used in the design of meters. Some types of operation require purging the viscous liquids from the lines to prevent congealing dming 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 result in destructive forces on the moving parts of the meter and would certainly result in erroneous meter registration. Following these recommendations should assist in avoiding such types of misoperation and should protect the meter from damage and inaccuracies due to the measurement of air or gas. Where alternate procedures are given@ the recommendations of the manufacturer of the proposed meter should be determined and followed * REFERENCE on p.15."
API RP 2533-1969 history
1969API RP 2533-1969 Recommended Practice for Metering Viscous Hydrocarbons (First Edition)