PIPE PROVER CALIBRATION BY WATERDRAW METHOD

This procedure provides guidelines to determine the volume of unidirectional and bi-directional conventional pipe provers at base conditions of temperature and pressure by the waterdraw method.

Frequency

As indicated in Procedure No. 049

Procedure Pipe provers shall be calibrated by the waterdraw method when newly
installed or any one of the following conditions exists

 Alterations or repairs are made to the prover that may
affect the certified base volume.
 A meter control chart indicates that there has been a
change in prover base volume.
 Expiration of the validity of the base prover volume. The
base volume is valid for 5 (five) years or 3 (three) years if it
is obtained by waterdraw or Master Meter method,
respectively.

PROVER CLEANING PROCEDURE

Prover cleaning shall be performed in accordance with Procedure No. 51

TEST SETUP

The test set-up and piping installation for the calibration of the prover is
shown in Attachment I. The distances between the calibration
equipment and the prover under test should be as short as possible, to
assist temperature stability.

WATERDRAW METHOD

EQUIPMENT

a) Field Standard Test Measures:

Field Standard Test Measures to be used for the
calibration must meet the design and construction
requirements as identified in MPMS Chapter 4 Section
4.7.4. The calibrating agency shall be the U.S. National

Institute of Standards and Technology (NIST) or another
competent laboratory that is consistent with user
requirements and certified by NIST or the UK National
Weights and Measures Laboratory (NWML). Calibration
certificates must have been issued in the last 5 years.
CMU or the calibration Agency will supply the field
standard test measures.

b) Control Box:

One 120-volt a/c. supply control box comprising; 24-volt
D.C. output (to solenoid valve), on-off switch, main
power supply indicator light, detector switch trip
indicator light, buzzer and buzzer reset switch. CMU
will supply the control box.

c) Water Reservoir:

The proponent or CMU should provide a water storage
tank, of a capacity of 2-3 times of the total volume of the
test measures. A larger reservoir is preferred for more
stable temperature and to ensure the Net Positive
Suction Head pressure (NPSH) required for the pump is
always present.

d) Water Pump:

The proponent or CMU should provide a non-fluctuating,
centrifugal pump, with a minimum capacity of 150 US
gallons per minute, a minimum discharge pressure of 40
psig and a maximum discharge pressure of 100 psig.

e) Spare sphere and detector switches:

The proponent should arrange to have a spare sphere
and two new detector switches (or four if four switches
are installed) available at the job site prior to the start of
the calibration.

f) Sphere removal, sizing and inflation equipment:

The proponent should provide the sphere removal tools –
usually a hand operated vacuum pump and suction cup;
a sphere sizing device – a sizing ring or certified diameter
tape; and the sphere inflation pump and fittings.

g) Thermometers:

Two thermometers, of maximum range 150 F are
required. They must have calibration certificates
traceable to a working standard issued in the last 5 years,
be graduated in single degrees or less and be readable
to, and have accuracy of, 0.1F. These will be supplied
by the calibration Agency.

h) Pressure Gauges:

Two pressure gauges of maximum range 100 psig are
required. They must have calibration certificates
traceable to a working standard issued in the last 12
months and be readable to, and have accuracy of, 1 psig.
These will be supplied by the calibration Agency.

i) Platform:

A platform must be erected above the reservoir to
safely accommodate the test measures and the
calibration engineer representing the calibration
Agency. This will be provided by the proponent or
CMU.

Water Discharge Header (Manifold):

A manifold, for discharging water into the test
measures must be fabricated. This will vary with the
number of test measures used for the calibration.
Appendix C shows a configuration with four test
measures. In this case there will be a rigid manifold

with off takes to each test measure consisting of the
following:

i) One quarter-turn, tight seating, shut off ball valve for
each test measure-filling pipe. In parallel with;
ii) A 24 volt D.C. normally open tight seating solenoid
valve in series with a quarter turn tight seating shut off
ball valve and a flexible tube.

j) Miscellaneous hoses and piping.

The proponent will provide assorted hoses and piping.
This includes 3 inch hard piped connection between
pump and inlet of prover under test and flexible hose
or hard piped connection from prover under test to
water discharge header (manifold).

PROCEDURE

In the case of royalty transfer provers, an in-house test shall be
conducted to confirm acceptable repeatability of the prover volume. The
test procedure shall be the same as the official test. Once the
preliminary test is successful, the official test will be conducted in the
presence of MINPET representative(s).

1. Drain the prover and isolate from the meter streams by fitting
blind flanges on inlet and outlet pipe work.

2. Open the prover closure and remove the sphere from the
interchange valve.

3. Wipe clean and inspect the entire surface of the sphere for
signs of damage e.g. miss-shape, cuts, wear, blistering,
score marks etc. Replace if damaged.

4. Measure the prover sphere around the equator and pole
planes using a diameter tape or sizing ring. Record the
smaller of the two dimensions. The correct inflation size is

taken from the previous calibration certificate. Inflate or
deflate as necessary.

5. Apply a thin coating of silicone grease to the sphere and
return it to the prover. Secure the closure.

6. Remove and service or replace detector switches. This
depends on prover performance records. If undecided,
always replace detector switches with new ones.

7. Connect pump, hoses, valves and fittings as shown in
Attachment C of this Procedure. Start the pump and slowly
fill the system with fresh, clean water, by opening valves in
sequence from the pump discharge to the return to the
reservoir. Check for leaks at hoses, fittings and critical
valves – they must be bubble tight.

8. Connect detector switch signal cables to the control box and
24-volt solenoid valve signal.

9. Confirm functionality of hand valves, signal cables, solenoid
valve, control box and pump start / stop control.

10. The water quality must be checked. This is achieved by
filling one of the test measures to the top of the gauge glass.
If the observed water level changes due to bubbles being
present then the water cannot be used and it will be
necessary to drain all water from the system and replace
with fresh, clean, deaerated water.

11. Perform function test of the pressure instruments by
substitution method to confirm agreement within 1 psig. I.e.
observe the indication of each pressure instrument at a
single location where the pressure remains constant.
Compare temperature instrument readings to confirm
agreement within 0.1ºF. Fill each thermowell to be used with
a temperature transmission liquid such as Glycol.

12. Once the above preparations have been made refer to
Attachment I of this Procedure. Valve V1 is a pump by-pass valve, used to control pump discharge pressure and prevent
overheating of the pump. Valves V2 and V3 are isolation
valves and can be considered open for the test. Set the flow
rate by minor adjustment to valves V1 and V2 or V3 – use a
stopwatch to time the sphere between detector switches and
calculate the flow rate.

13. Open valves V4 to V8, and the test measure drain valves.
Operate the sphere interchange valve to move the sphere
through the prover enough times to flush and eliminate air
that may have been caught in parts of the prover system.
Vent the air at the prover high point vent valves. Continue to
move the sphere to allow the water and metal of the prover
system to reach a common and steady temperature.

14. Use this time to establish the sequence of test measure
filling to be adopted during the calibration. The sequence
should provide uninterrupted flow into the test measures, if
possible

15. Fill each test measure by closing the test measure drain
valves and then closing valves V5, V6, V7 and V8 as the
water level reaches the gauge scale. Leave valve V4 open.

16. The sphere must be driven to a start position at the inlet of
the interchange valve.

17. Vent at the prover high point vent valves, operate the
interchange valve, close valve V4 and drive the sphere to the
1
st
detector switch by flowing through the solenoid valve on
the discharge header to the reservoir.

18. Record the prover inlet and outlet pressures immediately
prior to the sphere hitting the 1
detector switch. When the
sphere hits the detector switch the flow will stop.
st

19. Check the bleed valve associated with the interchange valve
to confirm seal integrity. A differential pressure gauge that
monitors the valve seal cavity verses the line pressure may
be installed to enable this check.

20. Drain each test measure into the water reservoir, allowing
the drain time shown on the test measure calibration
certificate. This is called a wetting run and establishes the
‘clingage’, which must be present whenever the test
measure is used.

21. Fill test measures through valves V5, V6, V7 and V8.

22. Obtain prover average outlet temperature readings when the
sphere is between detector switches and record on the
calibration sheet.

23. Knowing the manufacturer’s nominal volume between the
detector switches, the last few gallons can be anticipated.
Valves V5, V6, V7 and V8 shall be closed and the solenoid
valve open, thus allowing flow of water into a chosen test
measure through the flexible pipe downstream of the
solenoid valve. Water will flow into the test measure until the
sphere hits the 2nd detector switch at which time the
indicator lamp and buzzer turn on and the solenoid valve
closes, thus stopping the flow to the test measure.

24. Record the test measure scale readings to the nearest cubic
inch and the temperatures to 0.1F.

Note: If thermowells are not installed it may be
necessary to record the water temperature when
draining the test measures. In this case drain
immediately after recording the scale reading and
place the temperature device in the immediate vicinity
of the drain outlet.

25. Repeat steps 17 through 24 until two consecutive run
volumes agree within 0.020% for Uni-Directional Pipe
Prover.

Note: for Bi-Directional Pipe Prover, volumes must
agree as follows:

a) First and second forward half trip volumes
within 0.020%.
b) First and second reverse half trip volumes
within 0.020%.
c) Total of the first round trip volume versus total
of the second round trip volume, within
0.020%.

26. When conditions of 25, above, are achieved, adjust valves
V1 and V2 or V3 and repeat steps 17 through 24 at a 25%
(minimum) changed flow rate. The result of this confirming
run shall not vary from the first two run volumes by more
than 0.020%.

27.
If the confirming run is successful the calculations to
determine prover volumes at base conditions must be
performed.

28. The new base volume of the prover will be the average of all
three run base volumes.

29. Disconnect all the calibration equipment following
confirmation that the calibration has been successful.

30. Drain, de-isolate and return the prover to service.

ATTACHMENT I