This procedure provides guidelines to determine the volume of piston type Small Volume Provers (SVP) at base conditions of temperature and pressure using the waterdraw method.
SMALL VOLUME PROVER CALIBRATION BY WATERDRAW METHOD
Frequency: As indicated in Procedure No. 049
Procedure SVP Cleaning Procedure
If SVP is used for refined products, such as motor spirit, diesel and kerosene, Cleaning will not be necessary, but the unit should be flushed with fresh clean water prior to the calibration.
If the SVP is installed in fuel or crude oil service then it should be cleaned from any oil, scale or hydrocarbon products according to the following procedure:
1. The SVP must be connected to power and nitrogen supplies as used to perform and control a normal meter proving operation.
2. In addition, ensure the following items are available prior to commencement of the cleaning exercise:
a. Sufficient quantity of diesel to fill the SVP and 50% of the reservoir.
b. Clean, fresh water supply.
c. A reservoir and pump with electrical isolator/starter.
d. Suitable hoses to circulate the system.
e. A non-foaming de-greasing detergent. Example, Sotin 2000, Perolin PK800, or equivalent.
3. Install the pump to the reservoir outlet and a hose from the pump discharge to the inlet of the SVP and connect the return hose from the outlet of the SVP to the reservoir.
4. Fill the system with diesel by starting the pump and venting at the SVP high point vent valves.
5. With the SVP and associated pipe work full and the reservoir approximately half full, start the pump. Circulate the diesel by initiating a prove command to the SVP, to move the
piston up and down the prover barrel, a minimum of twenty trips, venting at the high point vent valves after every five trips.
6. Leave the SVP full of diesel for twelve hours.
7. Circulate the diesel by initiating a prove command to the SVP, to move the piston up and down the prover barrel, a minimum of ten trips, venting at the high point vent valves every five trips.
8. Drain the diesel from the system and fill the prover with fresh water from the reservoir.
9. After filling the system with fresh water, ensure that the reservoir is approximately half full. Add the correct quantity of de-greasing detergent, according to the detergent manufacturer’s instructions.
10. Circulate the water and detergent solution, by initiating a prove command to the SVP, to move the piston up and down the prover barrel, a minimum of twenty trips, venting at the high point vent valves every five trips.
11. Leave the SVP for twelve hours with the water and detergent solution in the system.
12. Circulate the water and detergent solution, by initiating a prove command to the SVP, to move the piston up and down the prover barrel, a minimum of ten trips, venting at the high point vent valves every five trips.
13. Drain the system and re-fill with fresh water, venting at the high point vent valves.
14. Circulate the fresh water, by initiating a prove command to
the SVP, to move the piston up and down the prover barrel,
until, by observation, the discharged water is clean.
15. If traces of the detergent solution remain it may be necessary to re-fill the system once or twice to achieve clean discharged water.
16. The SVP is now ready for calibration. Leave full of clean
water if there is a delay.
Test Set-Up
A different test set-up is required for the calibration of downstream and
upstream volumes. The piping installation shown in Attachment I of this
Procedure is for downstream volume calibration. It is necessary to change
the inlet and outlet connections at the SVP when calibrating the upstream
volume and to provide additional pipe and valves to return the piston to
the start position. Details can be found in the vendor documentation. The
distances between the calibration equipment and the prover under test
should be as short as possible, to assist temperature stability.
Procedure
In the case of royalty transfer SVP’s, an in-house test shall be conducted to
confirm acceptable repeatability of the SVP volumes. 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). Saudi Aramco safety procedures and work permit
requirements must be observed at all times.
1. The calibration of SVP’s by the waterdraw method may
be simplified by placing the SVP, test measure and reservoir
with test liquid in a stable temperature environment, shaded
from direct sunshine, to allow the equipment and liquid to
reach an equilibrium temperature. It is important that
temperature be maintained as stable as possible throughout
the operation.
2. Connect pump, hoses, valves and fittings as shown in
Attachment C of this Procedure to calibrate the downstream
volume of the SVP.
3. Start the pump and slowly fill the system with fresh,
clean, deaerated water by opening valves in sequence from
pump discharge to the return to the reservoir. Check for leaks
at hoses, fittings and critical valves – they must be bubble
tight.
4. Confirm functionality of hand valves, pump start / stop
control and the water draw kit.
5. The SVP piston seal integrity should be verified
according to the manufacturers recommended procedure. For
example, this may involve carefully filling and applying water
pressure to both sides of the piston, and then increasing
pressure on the upstream side and monitoring movement of
the piston shaft with a dial test indicator.
6. The water quality must be checked. This is achieved by
filling the test measure 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.
7. 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.
8. Valve V1 is a pump by-pass valve, used to control
pump discharge pressure and prevent overheating of the
pump. Valves V2 and V5 are isolation valves and are open for
the test. Set the flow rate by minor adjustment to V1 and V2 or
V5 – use a stop watch to time the piston between optical
switches and calculate the flow rate.
9. Open valve V6 and circulate the water to and from the reservoir through the flexible pipe downstream of the waterdraw piping assembly.
10. Utilizing the toggle switch on the interface board, move
the piston through the SVP enough times to flush and
eliminate air that may have been caught in parts of the
system. Vent the air at the SVP high point vent valves V3 and
V4. Continue to move the piston to allow the water and metal
of the SVP system to reach a common and steady
temperature.
11. Fill the test measure through the flexible pipe. Leave
valve V6 open.
12. The SVP piston/detector ‘flag’ must be driven to the
start position upstream of the 1st optical switch.
13. Close valve V6 and, utilizing the toggle switch on the
interface board, drive the piston/detector ‘flag’ back to the 1st optical switch by flowing through the solenoid valve to the
reservoir. Record the SVP outlet pressure immediately prior
to the ‘flag’ hitting the 1st optical switch. When the ‘flag’ hits the
optical switch the flow will stop.
14. Drain the 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.
15. Vent at the SVP high point vent valves and initiate the calibration run by operating the toggle switch on the interface
board.
16. Fill the test measure, through the flexible pipe, by opening quarter turn valve V6. Once the ‘flag’ passes the 1st optical switch flow will also be through the solenoid valve.
17. Obtain SVP inlet and outlet temperature readings (T1 & T2) and ambient temperature in the immediate vicinity of the optical switches (Td), and record on the calibration sheet.
18. Knowing the manufacturer’s nominal volume between
the optical switches, the last cubic inches can be anticipated.
Close valve V6 and leave the solenoid valve open. Water will
flow into the test measure until the ‘flag’ hits the 2nd optical
switch at which time the solenoid valve closes and stops the
flow to the test measure.
19. Record the test measure scale reading to the nearest
cubic inch and the temperature to 0.1F.
Note: If thermowells are not installed it may be
necessary to record the water temperature when
draining the test measure. In this case drain
immediately after recording the scale reading and place
the temperature device in the immediate vicinity of the
drain outlet.
20. Repeat steps 14 through 19 until two consecutive runs
agree within 0.020%.
21. When conditions of 20, above, are achieved, repeat
steps 14 through 19 at a 25% (minimum) changed flow rate.
The result of this confirming run and the two initial runs shall
fall within a spread of not more than 0.020%.
22. If the confirming run is successful the calculations to
determine the SVP downstream volume at base conditions
must be performed.
23. The new downstream base volume of the SVP will be
the average of all three runs.
24. Exchange inlet for outlet connections etc. at the SVP
and, using the same procedure as described above, calibrate
the SVP upstream volume. The interface board provides the
control signals that enable the piston to seal when traveling in
the reverse direction and to trip the solenoid valve on the trailing edge of the optical switch signal.
25. Disconnect all the calibration equipment following
confirmation that the calibration has been successful.
26. Drain, de-isolate and return the SVP to service.
