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API STD 2534

1st Edition, March 1970

Complete Document

Measurement of Liquid Hydrocarbons by Turbine Meter Systems



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Superseded By: API MPMS 4.1

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Description / Abstract:

INTRODUCTION

This standard has been prepared as a guide for design, installation, and operation of turbine meter systems in liquid hydrocarbon service. Primary emphasis is placed on the turbine meter and its accessories, but many of the concepts and innovations described are adaptable to other devices concerned with the volumetric measurement of liquid hydrocarbons. For details of specific equipment previously documented by the American Petroleum Institute, refer to API Standard 1101: Measurement of Petroleum Liquid Hydrocarbons by Positive Displacement Meter (ANSI Z11.170-1965). API Standard 2531: Mechanical Displacement Meter Provers (ANSI Z11.171-1965), and API RP 2533: Metering Viscous Hydrocarbons.

The turbine meter has been recognized as an acceptable quantity measuring device for many years; however, its usefulness to the oil industry has become apparent only during the past decade. Improvements to the measuring element and the ever-increasing rates of flow jointly account for vigorous interest in a compact, mechanically simply, long-lived liquid meter.

The turbine meter consists of a rotor or propeller which senses the linear velocity of a flowing stream. The moving liquid imparts a rational or tangential velocity to the rotor which is proportional to rate of flow. The movement of the rotor is detected by mechanical, optical, or electrical means and is recorded on an appropriate readout device.

Turbine meters have typical performance characteristics that are best described by meter performance curves (see Appendix A, Fig. A-1). Principal parameters, such as flow rangeability within tolerable limits of linearity and repeatability, are related to fluid properties (i.e., density, viscosity, and vapor pressure) and to mechanical meter characteristics (i.e., rotor mass, bearing friction, magnetic drag, and wetted area relating to fluid imposed drag on the turbine or rotor).

The combination of fluid properties and mechanical meter characteristics produces a deviation from an ideal of meter linearity. Accordingly, turbine meter selection should be governed by an assessment of the characteristic curves of the proposed turbine meter.

Turbine meters selected for the noted operating criteria, when properly installed and carefully proved, will perform continuous measurement with a minimum of inaccuracy.

Mechanically, turbine meters are well able to withstand the rigors imposed by severe flow overranging accompanied by extreme flow pulsations. However, they are susceptible to damage from extraneous solids entrained in the liquid, particularly if these are of significant size, but finely divided solid particles generally pass through the meter without causing damage. In rare cases where large objects become lodged in the meter, even to the point of stalling a rotor, fluid blockages with resultant overpressurization of the system is not likely to occur.

The turbine meter system effectively measures liquid volume, but it does not offer a universal solution to every flow measurement problem – at least not at this time. This standard describes how a turbine meter system works and endeavors to give the reader a technical background to better understand the details of its operation. The descriptive material is incorporated in the appendixes of the standard. A major effort has been made to describe techniques and effects that contribute to the successful attainment of a high degree of metering accuracy and reliability within a demonstrated turbine meter system capability. Achievement of this goal is the responsibility of the equipment manufacturer; but to an even greater degree, it becomes the responsibility of the ultimate user. Should the highest level of precision be unnecessary or unjustifiable, a number of the recommendations in this standard may be compromised. Certain of the recommendations should never be ignored. Therefore, those which, if not followed, would adversely influence the satisfactory performance of a turbine meter system have included the compulsary verb from shall. The word should indicates provisions which are advisory but not required in every instance. The word may indicates provisions which are optional and, consequently, are at the discretion of the user.

The intent of this standard is to give the reader the most complete and comprehensive information currently available. Because of the lack of experience in a number of operational areas, revisions to this standard will be required at some time in the future.

Sufficient leeway has been incorporated into this text so that experimentation and equipment improvements may be encouraged without creating undue hardship, while at the same time a procedure may be implemented to satisfactorily deal with each new application.