Scope
This procedure defines the process required to properly perform proving using a small volume prover. This procedure covers:
1. Pipeline Meters
2. Truck Loading/Unloading Meters
3. Refueler / Defueler / Dispensing Meter
PROVING PROCEDURE BY SMALL VOLUME PROVER
Frequency As indicated
Procedure The meter may be proved by one of the following methods:
Method 1
Turbine meters and displacement meters whose pulse generation is
directly from, or very close to, the measuring elements can be proved with
the same methods used for conventional displacement provers. This
normally consists of five consecutive passes or round trips that repeat
within 0.05 percent (± 0.025 percent of the average).
The average of the results from these passes or prover round trips then
becomes the meter factor to be used in subsequent operations.
Method 2
Meters that have a non-uniform pulse output (that is, turbine and
displacement meters with gear trains, shaft couplings, and shaft-driven
accessories) may be proved by increasing the number of passes or prover
round trips or by increasing the repeatability tolerance. For example, 10
passes or prover round trips that repeats within 0.10 percent (±0.05
percent of the average).
The average of the prover-pass results becomes the meter factor to be
used in subsequent operations. Additional passes or prover round trips
may be added as required to accommodate meters that repeat beyond
0.10 percent (20.05 percent of the average) because of the non-uniform
pulse characteristics. For example, 15 prover passes or prover round trips
that repeat within 0.15 percent (±0.075 percent of the average) would be
the next level of consideration. The rationale for this procedure is that as
the number of passes or prover round trips is increased, the repeatability
performance of the meter usually increases and at the same time the
quality of the average improves.
Method 3
A meter that has more severe non uniform pulse output or a prover that is
minimal in size may necessitate using the following method. The concept
is to accumulate individual prover passes or prover round trips to form
groups and then to average each group. The ranges of these groups
should fall within tolerances that are consistent with the first and second
methods. The average of the group averages then becomes the meter
factor to be used in subsequent operations.
Increasing the number of passes or prover round trips in each group will
improve the quality of the intergroup repeatability. Twenty passes or prover
round trips per group is considered a practical limit; more will not improve
the quality. If an acceptable repeatability is not obtained in 20 or fewer
passes or prover round trips, the meter manufacturer should be consulted.
Operation
Proving with small volume provers requires the same good practices
commonly associated with pipe provers. All valves in the flow path
between the meter and the small volume prover must be positioned so that
fluid cannot be diverted from or added to the stream. All valves associated
with the proving system must include a method for detecting leaks and
must be free from leaks.
The proving system shall include at least one temperature indicator in the
flow line adjacent to the meter and at least one indicator adjacent to the
prover.
Venting should be performed on the small volume prover and at other
appropriate locations to ensure that air or gas is not trapped in the flow
system before proving.
Steady flow should be established in the system to ensure stable
temperature and pressure before proving. The need for maintaining back
pressure on the meter/ prover system depends on various factors such as
fluid velocity, fluid vapor pressure, and operating pressure and
temperature.
Meter pulse output should be checked to ensure pulse integrity.
Mechanical or electrical meter register tests should be conducted before
proving. The displacer seals of small volume provers should be checked
for sealing integrity in accordance with the manufacturer’s recommended
procedure.
Pulse-interpolation or other types of counters used in conjunction with
small volume provers shall be verified for correct operation before proof
runs are conducted.
Automated small volume provers that incorporate microprocessor
computer sequence control, pulse interpolation, data acquisition, and data
reduction shall be tested for functional operation before meter proofs are
conducted. Such systems should contain self-test features to verify the
operation of computer software and hardware. Manufacturer’s procedures
and recommendations should be followed in accordance with the
appropriate sections of the Manual of Petroleum Measurement Standards.
In unidirectional small volume provers, a proving run consists of one trip of
the displacer through the calibrated section.
In bidirectional small volume provers, a proving run consists of a round trip
of the displacer (that is, the sum of two consecutive trips in opposite
directions through the calibrated section).