Scope
This procedure defines the process required to properly perform proving using
a master meter. This procedure covers:
1. Pipeline Meters
2. Truck Loading/Unloading Meters
3. Refueler / Defueler / Dispensing Meter
PROVING PROCEDURE BY MASTER METER
Procedure The calibration of the master meter shall be performed under conditions
similar to those expected during the line meter proving. A curve of master
meter factors should be established over the range of flow rates to be
encountered while proving a line meter. The meter factor applied to the master
meter shall be the average of proof runs on a similar liquid and within 10
percent of the flow rates expected during the proving of the line meter.
Either the standing start-and-stop or the running start-and-stop method of
proving may be used. With the standing start-and-stop method, the meter
registration is read before and after the proving run with flow stopped to
determine indicated volume. With the running start-and-stop method, the flow
is uninterrupted, and the proving counters must be simultaneously started and
stopped.
INSPECTION
Prior to the meter-proving operation the master meter prover and line meter to
be proved shall be inspected to ensure proper operation. This inspection shall
include, but not be limited to, the following steps:
1) Ensure that all liquid flowing through the line meter to be proved,
and only that liquid, passes through the master meter with no
leakage or diversion between meters.
2) Verify that all temperature, pressure, and density measurement
devices to be used during the proving operation are properly
installed, recently calibrated or verified, and operating within
acceptable tolerances as stated in API MPMS, Chapters 7 and 12.2.3)
3) All electronic instrumentation such as counters, switches, and interconnecting wiring shall be inspected for proper installation and operation. Care should be taken to ensure that all electrical pulse transmission cables are properly shielded and grounded.
PREPARATION
The master meter should be installed as close as possible to the line meter to minimize temperature and pressure differences between the meters The master meter normally is installed downstream of the line meter. The following steps should be taken:
If the master meter has an electrical output, care should be taken to ensure all electrical equipment is properly grounded to prevent errors from electrical noise.
1) The master meter output/registration must not be mechanically
temperature compensated. The master meter must not have a
mechanical adjustor or calibrator between the primary element
and the output/registration. When proving a meter with a master
meter, the same
2) If the master meter is permanently piped in a manifold with the
line meter to be proved, the isolation valves should be opened
and the flow directed through both meters.
3) Before the meter proving is made, the two meters shall be
operated at the desired flow rate for a period of time sufficient to
purge the system of vapor and to achieve steady temperature,
pressure, and flow rate.
OPERATING PROCEDURES
Each proving run shall be of sufficient volume to discriminate volume units to I
part in 10,000. In the case of loading rack meters, each proving run should
depict the start -up, shutdown, and interim flow patterns of a normal loading. If
electronic counters and high resolution meter transmitters are used to register
metered volume, at least 10,000 pulses must be collected during the proving
run.
Once the proving operation is started, it should be carried to conclusion in a
continuous process, without interruption or
delay. The following steps
should be taken:
a. Using a work sheet or master meter proving report (see Figure 6),
record the appropriate meter and flow data as indicated in the factor
calculations section of API MPMS, Chapter 12.2.
b. With flow through the meters, a proving run is initiated by
simultaneously gating both meter counters on. Meter temperature
and pressure are recorded for both meters during the proving run.
Flow rate through the meters during the proving operation should be
within 10 percent of the rate at which the line meter will operate. The
flow rate must remain relatively stable for all proving runs entered in
the meter factor calculation.
c. After sufficient volume has passed through the meters, the counters
arc simultaneously gated off. The indicated counter readings for the
run are recorded. This completes one run.
d. There are various ways of assessing whether the repeatability of a set
of readings is acceptable. The repeatability should not exceed the
limits agreed upon by all parties.
e. In some circumstances, statutory authorities or government
departments will set the limits for the range of a set of results.
f. One method of conducting a proving is to make five consecutive
meter proof runs within 0.05 percent. “Within a range of 0.05 percent”
is defined as a value that does not exceed 0.05 when applying the
following formula:
Maximum Value – Minimum Value / Minimum Value x 100
g. Checks should be made during the proving to ensure all equipment is
functioning properly and all test parameters are remaining within their
constraints.
h. Meter factor calculations shall be made as detailed in APT MPMS,
Chapter 12.2. An example “Meter Proving Report for the Master Meter
Method” was shown in Figure 14.
i. After completion of the proving operation, the master meter should be
isolated from the flow stream if the meter is permanently installed, or
disconnected if the meter is portable. A master meter should not be on
stream any longer than necessary for the proving operation. This
precaution is to limit meter wear and resulting factor shift.
j. Thermometers, pressure gauges, counters, and any other proving
equipment that is not a permanent part of the manifold should be
removed and stored until the next proving.
ASSESSMENT OF RESULTS
A common practice is to require a minimum of two consecutive runs that
agree within a range of 0.05 percent. If the repeatability of the meter factor is
unacceptable, it may be necessary to carry out additional proving runs. If the
repeatability is within the prescribed range, these results may be used. But if
the repeatability remains unacceptable, it is necessary to stop proving and
look for the cause of the problem.