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INTRODUCTION

During the preparation of the first edition of API Standard 1101: Measurement of Petroleum Liquid Hydrocarbons by Positive Displacement Meter (formerly API Code 1101), general developments were being made in the techniques of proving meters by mechanical displacement provers. These developments are now sufficiently advanced to warrant standardization and are covered in this standard.

Improvement in the techniques of meter proving has progressed to the extent that mechanical displacement provers reduce the expense and difficulty of proving meters of large capacity and makes more practical the application of these meters in large pipeline, tanker, and barge metering operations. Yet these techniques apply equally well to smaller size meters; for example, those being used in lease automatic custody transfer operations.

Brief descriptions of some of the mechanical displacement provers are included in Par. 2026 and Par. 2027 of API Standard 1101. It is in this field that most of the new developments have occurred and with which this standard is chiefly concerned. Mechanical displacement provers have been developed for pipeline use which utilize a calibrated portion of the pipeline itself, either straight, U-shaped, or ''folded,'' as the prover. Auxiliary .sections of piping, constructed specifically as prover sections, are also widely used and these may be straight sections of pipe or folded pipe laid in the form of a loop. Both portable and stationary provers may be constructed on these principles. Some provers are so arranged that liquid can be displaced in either direction, viz., the reciprocating or bidirectional types.

The chief advantage of most of these mechanical. displacement provers is that, during proving, the flow of liquid through a meter being proved is not interrupted. This permits the meter to be proved on a continuous flow without starting or stopping the meter.

When a meter is thus being proved while it is running under normal operating conditions, the volume required to be displaced from the prover by the displacing device is dependent upon: 1, repeatability required; 2, the resolution with which the meter register can be read; and, 3, the resolution with which the position of the displacing device can be located at the extremities of the prover section. The application of high-rate pulse generators on the meters and precision displacer detectors in the prover section, combined with the elimination of errors arising from the start-stop method, have enabled the use of considerably smaller prover volumes than previously described in Par. 2004 of API Standard 1101, and at the same time have provided a high order of proving repeatability.