Scope
This procedure defines the process required to properly perform proving using
a pipe prover. This procedure covers:
1. Pipeline Meters
2. Truck Loading/Unloading Meters
3. Refueler / Defueler / Dispensing Meter
PROVING BY PIPE PROVER | PROCESS & CONTROL SYSTEM
Frequency As indicated
Procedure
INSPECTION
Prior to the meter-proving operation the pipe 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 pipe prover with no
leakage or diversion between the meter being proved and the pipe
prover.
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) 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.
4) Periodically, the displacer should be removed from the prover and
examined as prescribed by the manufacturer. The sphere or seals
should be replaced if there is any sign of mechanical damage or
softening by chemical action. Spheres should also be inspected for
roundness and proper inflation using either a sizing ring supplied
by the manufacturer or a tape measure. A piston prover displacer
may be subject to a leak test as prescribed by the manufacturer.
PREPARATION
The pipe prover should be installed as close as possible to the line meter to
minimize temperature and pressure differences between the meters The pipe
prover normally is installed downstream of the line meter. The following steps
should be taken:
1) Check that the end closures and any fittings are properly fastened
and that all vent and drain valves on the prover are closed.
2) Proceed with filling the prover as follows:
a) Partially open the prover inlet valve to fill the prover slowly.
b) Observe the system for leaks. Wait until the system is
completely filled and the connections have been shown to be
leak-tight before fully opening the prover inlet valve.
c) Open vents to allow discharge of air or vapor when fluid is
admitted into the prover.
d) At this point the prover outlet valves may be safely opened.
e) After all the connecting valves are fully opened, the meter divert
valve between the prover inlet and outlet valves may then be
closed.
f) Operate the prover displacer at least one proving cycle and vent
the high points. The vents should be checked repeatedly until it
is certain that no vapor remains in the prover.
g) Verify the seal integrity of all vents, drains, relief valves, and
double block-and-bleed valves between the meter and the outlet
of the prover.
OPERATING PROCEDURES
Each proving run shall be of sufficient volume to discriminate volume units to 1
part in 10,000. In the case of loading rack meters, each proving run should be
conducted at the normal loading flow rate. 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. Maintain the flow through the proving system until stable conditions of
pressure, temperature, and flow rate exist. Once stability is achieved,
proving operations may proceed.
b. Determine the actual flow rate on the first pass of the displacer and
make spot checks thereafter.
c. Determine the meter temperature and pressure during each pass of
the displacer. When using a bi-directional prover, record the meter
temperature and pressure, using the average of readings taken for
each pass of any given round trip.
d. Using both inlet and outlet thermometers and pressure gauges,
determine the average prover temperature and pressure during each
pass. The average prover temperature and pressure recorded on a
round trip basis in the case of a bi-directional prover.
e. If using a bi-directional prover, record the reading of the prover counter
at the end of each round trip of the displacer. For a unidirectional
prover, record the reading of the prover counter at the end of each
[ass of the displacer.
f. Repeat the proving operation until the required minimum number of
proving runs is attained.
ASSESSMENT OF RESULTS
A common practice is to require a minimum of five 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 a second set of proving runs. If the repeatability of the second set
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.
A common practice is to limit the change in consecutive meter factors of proving periods to
+/-0.25% or less. This is a measure of reproducibility and is determined as follows:
Range of Reproducibility = New Meter Factor – Old Meter Factor / Old Meter Factor x 100
Changes in the linearity of the historical meter factors over time are also a good check for
prover functioning. Historical meter factor data should be maintained and is best assessed
by keeping a control chart which is a graph of meter factor plotting against the dates of the
tests.