API MPMS 4.2-2003 pdf download.Manual of Petroleum Measurement Standards Chapter 4—Proving Systems Section 2—Displacement Provers.
2.7 PRESSURE DROP ACROSS THE PROVER In determining the size of the piping and openings to be used in the manifold and the prover, the pressure loss through the displacement prover system should be compatible with the acceptable pressure loss in the metering installation. Excessive pressure drop may prevent the meter from being proved at its normal flow rate(s) and/or minimum backpres- sure required for the meter. 2.8 METER PULSE TRAIN The electrical pulse output from the meter can exhibit vari- ations even though the flow rate through the meter is con- stant. These variations may be caused by mechanical and electrical imperfections of the meter, pulse generator, and in signal processing technique. Ideally, under stable flow condi- tions, the meter pulse train should be uniform. However, mechanical gears, bearing wear, blade imperfections, cou- plings, adjusting devices, counters, mechanical temperature correction devices, and other accessories reduce the unifor- mity of the meter pulses. For meters installed with a gear- stack, the further the pulse generator is from the meter, the more erratic the pulse train becomes. Variations in the meter pulse output may result in unac- ceptable proving performance. Appendix E discusses the evaluation of pulse variations of meters. 2.9 DETECTORS Detectors must indicate the position of the displacer within ± 0.005% of the linear distance between switches (a range of 0.01%). The repeatability with which a prover’s detector can signal the position of the displacer (which is one of the gov- erning factors in determining the length of the calibrated prover section) must be ascertained as accurately as possible. Appendix A discusses this in more detail. For prover with external detectors, care must be taken to correct detector posi- tions that are subject to temperature changes throughout the proving operation. 3.2 INTERNAL AND EXTERNAL COATINGS Internally coating the prover with a material that provides a hard, smooth, long-lasting finish will reduce corrosion, pro- long the life of the displacer and the prover. This will improve the meter repeatability when proving at low flow rates. Expe- rience has shown that internal coatings are particularly useful when the prover is used with liquids that have poor lubricat- ing properties, such as gasoline or liquefied petroleum gas; however, in certain cases, satisfactory results and displacer longevity may be achieved when uncoated pipe is used. The materials selected for the internal coating application should be compatible with the liquid types expected. The coatings should be applied according to the manufacturer’s recom- mendations. Extreme caution should be exercised in the sur- face preparation so that the coating is applied over a clean white-blasted metal with a minimum anchor pattern as speci- fied by the manufacturer. Externally coating the prover section and associated piping will reduce corrosion and will prolong the life of the prover, especially for installations where the prover is buried. 3.3 TEMPERATURE MEASUREMENT Temperature sensors shall be of suitable range, resolution, and accuracy, and should indicate the temperature within the meter and the temperature within the calibrated section of the prover. A means shall be provided to measure temperature at the inlet and outlet of the prover (see API MPMS Ch. 7 for detail requirements). If it can be determined that the tempera- ture of the flowing fluid at the meter and the prover does not vary by an amount that will result in a Ctl factor change of 0.0001 or less, one temperature probe may be used between the prover and the meter being proved. One temperature device is allowed on the outlet of a prover if the prover is upstream of the meter or on the inlet of the prover if the meter is upstream of the prover. Caution must be exercised to ensure that the temperature sensors are