BI-DIRECTIONAL FLOW PROVERS TRUTH IN MEASUREMENT WITH DIRECT TRACEABILITY TO INTERNATIONALLY ACCEPTED STANDARDS
WHAT IS A PROVER? An open or closed vessel of known volume that is used as a volumetric reference standard for the calibration of meters in liquid petroleum service. – API Chapter 4 Section 1
WHAT IS ITS PURPOSE? In order to eliminate bias, the calibrated volume of a prover is used to determine a meter factor.
WHAT IS METER FACTOR? A meter factor is the ratio obtained by dividing the actual volume proven by the indicated volume registered by the meter. – API Chapter 4 Note: Factors that can influence the meter’s meter factor are flow rate, temperature, viscosity, wear, and contamination. Proving conditions should match operating conditions in order to maintain the most accurate results possible. Prover Volume _________________ Meter Factor = Meter’s Indicated Volume
BI-DIRECTIONAL PROVER Receiving Chamber Detector Switch Four-Way Valve Detector Switch Valve Actuator Sphere Displacer Launch Chamber
PROVER DESIGN REQUIREMENTS • Pipe Size, Schedule & Flange Rating • Sphere Displacer Velocity • Volume Between Detector Switches • Four-Way Valve Sizing • Four-Way Valve Actuator • Pre-Run Length
SPHERE DISPLACER VELOCITY ___________ BPH x 0.286 Max. V = = < 5.0 fps _ 2 (I.D. [in]) Note: Minimum Velocity to be no less than 0.5 fps Max. V = 3,960 x 0.286 = 4.42 fps 2 (16) Example: Max. Flow Rate = 3,960 BPH Pipe Diameter = 16”
PROVER VOLUME • Pre-run length • Distance (volume) between detector switches Distance between Detector Switches Pre-Run Length
LENGTH BETWEEN DETECTORS • In order to maintain an uncertainty of +0.01%, at least 10,000 meter pulses Distance between should be collected Detector Switches between detector switches. Example: Meter K-Factor = 2,000 pulses/bbl Min. volume to achieve 10,000 pulses (VBS) = 210 gallons Measuring section pipe inside diameter = 16” 2 Pipe cross sectional area (A) = 1.396 ft Distance between detector switches (VBS/A) = 20.11 ft.
FOUR-WAY VALVE SIZING
FOUR-WAY VALVE SIZING BPH x 0.286 < 15.0 fps Max. V = = _ 2 (I.D. [in]) Example: Max. Flow Rate = 3,960 BPH Pipe Diameter = 10” Max. V = 3,960 x 0.286 = 11.33 fps 2 (16)
FOUR-WAY VALVE ACTUATOR • Mechanical • Electrical • Hydraulic Note: The actuator is sized to maintain a reasonable Four-way valve cycle time, or Closed to Closed time (T c-c). This will be used to determine the required prover pre-run length.
LENGTH OF PRE-RUN (R P ) ( ) T 1 SEC x Max V ___ __ R P = C-‑C ¡ 2 + 2 Pre-Run Length
LENGTH OF PRE-RUN (R P ) ( ) T 1 SEC x Max V ___ __ R P = C-‑C ¡ 2 + 2 Example: Actuator Speed (T c-c) = 4.9 Seconds Sphere Velocity (Max V) = 4.42 fps ( ) 4.9 1 __ SEC x 4.42 ___ R P = = 13.03 ft + 2 2
LENGTH OF PRE-RUN (R P ) R P = 13.03 ft Pre-Run Length
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