Scope
This procedure defines the process required to properly perform proving
using tank prover. This procedure covers:
1. Truck Loading/Unloading Meters
2. Refueler / Defueler / Dispensing Meter
PROVING PROCEDURE BY TANK PROVER
Procedure
GENERAL GUIDELINES:
1. A meter should be proved in its normal installation, and at the expected flow rate. The meter should be proved under the pressure and temperature conditions at which it will operate, with the liquid that it will measure and with the accessory components it will run. Conditions should be the same before and after each proving run.
2. Provision in the metering circuit must be made to accurately measure product temperature and pressure in the meter. Any necessary corrective actions to the metering skid must be performed prior to proving.
3. Operational flow rate must be constant and free from surges and pulsation; it must stay within ±10% of its nominal value and should neither exceed 2411 L/min. (in 4-inch lines) nor 85% of the manufacturer’s meter rated capacity. The flow rate must be measured and all corrective actions must be made to meet these conditions prior to proving operations.
4. Prove meters whenever any of the following occurs:
o Four months has elapsed since the last proving operation or after delivery of 2 million liters by the meter, whichever occurs first.
o Operational flow rate has changed by more than Δ 10 % since last proof.
o Significant change in system pressure has occurred such as after pumping equipment upgrade.
o Change in product, or density.
o Meter has been opened for inspection or repaired.
o Meter head accessories have been changed, repaired, or removed.
5. Re-calibrate and re-certify prover tank every five-years or whenever it is suspected that the volume of the tank has been affected for any reason such as by modification or damage.
6. Weather conditions must be suitable during all proving runs. Proving runs must not be performed during bad weather such as heavy rain or strong winds. Ambient temperature need to be fairly constant, proving runs that are performed during changes in ambient temperature of more than 5 °C shall be voided. Product temperature shall not differ from ambient temperature by more than 10 °C unless the prover tank is well insulated. Tank prover shall be shielded from direct sun light.
PREPARATION:
Obtain previous proving certificate.
Check validity of all certification.
Schedule proving date with operation to spare the bay during proving operation.
Secure necessary equipment for the proving period.
Identify and schedule necessary witnessing personnel.
Obtain necessary work permits.
Check the condition and the operation of the metering circuit at the bay and assure that all components are up to standards and in perfect working conditions. Check for leaks.
Check the condition of proving equipment, hoses, couplers, and adapters; inspect for any damage. Check the integrity of equipment security seals; reject equipment if any seal is broken. Ensure that tank prover is clear of product, the interior is free from any debris or corrosion, and all prover valves turn freely; lubricate if necessary.
PRE-PROVING OPERATIONS:
1. Move the proving equipment to the bay including the tank truck, where applicable, and place “BAY CLOSED” sign into position.
2. Position the prover in a location to properly connect and interface to the loading/unloading arm or coupler. Assure that all the weight is on the jacks and off the tiers; level the prover.
3. Connect the electrical grounding device clamp and all necessary safety interlocks to assure that product is permitted to flow.
4. Assure that all 4 thermowells (3 in the prover tank and 1 next to the meter) are filled with Ethylene Glycol. Place mercury in glass thermometer into each thermowell.
5. Verify that all prover valves move freely and are closed.
6. Connect, as appropriate, the prover “Outlet” connection to either the product return line (“from prover” meter connection) or the dump truck using a proper adapter and hose. Open the “from prover” meter connection valve or the dump truck loading valve.
Top loading of prover tank:
Open the upper neck cover and close the vapor recovery connection valve. Lower the drop pipe of the loading arm into the proving tank carefully. The drop pipe should reach the bottom of the proving tank as close as possible and the loading arm should be sloped downward;
avoid hitting the internals of the prover tank. Re-adjust the position of the prover if necessary. Withdraw the loading arm to the normal stow away position.
Bottom loading of prover tank:
Close the upper neck using the cover and by latching all four lock hasps; open the vapor recovery connection valve. Connect the vapor recovery hose where applicable. Connect the API loading coupler to the prover “Inlet” connection.
Meters in unloading stations:
Close the upper neck using the cover and by latching all four lock hasps; open the vapor recovery connection valve. Connect the prover “Inlet” connection to the “to prover” meter connection and the prover “Outlet” connection to the “from prover” meter connection using appropriate adapters and hoses. Close the double block and bleed valve (an isolation valve) associated with the meter. Open both the “from prover” and the “to prover” meter connection valves.
Connect power cables. Assure prover discharge pump is operational.
Check the integrity of metering circuit security seals; assure that all are intact and traceable. Halt proving till further investigation if any seal is broken or un-traceable. Record the metering circuit seals serial numbers in the remarks section of the proving form; item D1.
PROVING OPERATIONS:
In proving meters by tank prover method, proving operations consists of a set of similar procedures and steps that are repeated several times. The common and similar steps are detailed separately at the beginning of this section.
Common Operations:
Filling and emptying of the prover tank are common procedures. Each is described separately below. They are referenced in the proving procedure by name only.
Filling the Prover Tank:
The filling procedure described below is the same for all runs and applies to both top and bottom loading of the prover tank. It also provides for meters used in unloading stations.
The filling flow rate during all proving runs must remain as constant as possible and equal to the normal operational flow rate. For meters fitted with electronic preset devices, ramping up and down of the flow rate is allowed at the beginning and end of the run, respectively.
Preparation:
Assure that the prover “Isolation”, “Filling”, “Drain”, “Drip”, and “Drip-tank-drain” valves are closed.
Reset the stop watch to zero.
For mechanical preset devices, disable all ramping up or down functions if possible and preset a volume that is equal to the nominal volume of the prover of 5000 Liters.
Otherwise, preset a volume that is 30 Liters more than the sum of nominal volume of the prover tank plus the volume registered during ramping down (normally 100 Liters). This assures that the preset valve does not go to low flow at the end of filling of the proving tank; the volume to preset is 5130 Liters.
Filling procedure:
Since there are two possible ways to load the tank prover tank (top loading and bottom loading), two procedures are needed.
Top loading:
Assure that the loading arm dead man valve is open (if installed), and that the prover “Isolation” valve is closed.
Lower the drop pipe of the loading arm into the proving tank carefully, noting the position and inclination as this should be reproduced for each run. The drop pipe should reach the bottom of the proving tank as close as possible to minimize product splashing. Avoid hitting the internals of the prover tank.
Push the “start” button, or pull the “start” arm, opening the control valve; start the stop watch simultaneously. The product should start flowing into the tank. Continue filling the tank until the product is seen in the upper gauge glass and the level is within the graduated scale of the upper neck. When this level is reached, push the “stop” button on the meter preset device; stop the stop watch simultaneously.
Withdraw the loading arm slowly till the tip is just below the liquid level. Keep the loading arm at this position for 10 seconds, then raise the loading arm slightly above the liquid level and keep it in this position for a 10-second drip period. Finally, withdraw the loading arm completely from the prover tank upper neck.
Bottom loading:
Disconnect the prover “Outlet” coupler; keep coupler at a higher level than that of prover discharge pump. Observe for leaks throughout the filling operation.
Open the prover tank “Isolation” valve.
Push the “start” button, or pull the “start” arm, opening the control valve. The product should start pressurizing the associated hoses and connections; wait 5 seconds. Check for leaks constantly and especially during this pressurization period.
Open the prover “Filling” valve quickly but smoothly and allow the product to flow into the tank, start the stop watch simultaneously. The operating flow rate should be reached as quickly as possible and maintained for as long as possible but without over-filling the tank. Continue filling the tank until the product is just seen in the upper gauge glass and the level is within the graduated scale of the upper neck. When this level is reached, close the prover “Filling” valve immediately but without introducing any hammering to the line. Stop the stop watch. Close the prover tank “Isolation” valve. Push the “stop” button on the preset device.
Connect back the prover “Outlet” coupler.
Emptying the Prover Tank:
The emptying procedure described below is the same for all runs and applies to both top and bottom loading of the prover tank. It also provides for meters used in unloading stations.
Bottom loading (only): Disconnect the vapor recovery connection, where applicable.
Open the prover tank “Isolation” valve.
Start the discharge pump and immediately open the prover “Drain” valve.
Continue draining the prover tank using the discharge pump until the level is just seen at the top of the bottom gauge glass. Close the prover “Drain” valve and immediately stop the discharge pump.
Close the prover tank “Isolation” valve.
Open the prover “Drip” valve and finish draining the prover tank by gravity into the prover drip tank. When the entire product has been drained from the tank, wait an additional time (specified in the prover tank calibration plate) after cessation of flow. Close the prover “Drip” valve.
Open the “Drip-tank-drain” valve. Start the discharge pump and immediately open the prover drain valve to unload the drip tank. Once completely unloaded, close the prover “Drain” valve and immediately stop the discharge pump. Close the “Driptank-drain” valve.
Priming Run:
The purpose of this run is to eliminate any air and residual product, flush and prime the piping with the proving product. Only one priming run is required; no measurement is made nor is any data taken or recorded during this preliminary run.
Priming Run Procedure:
Partially fill the prover tank with product using 300 Liters as a preset volume and without using a stop watch.
Empty the prover tank
Wetting Run:
The purpose of this run is to equalize and stabilize the temperature and pressure of both the metering circuit and the prover, obtain product temperature and density, set the zero level in prover tank, and to determine the “as found” flow rate of the meter using a stop watch.
No other calculations are required during this run.
All pertinent data shall be entered under the “WETTING” run column.
Wetting Run Procedure:
Record the initial meter register reading.
Fill the tank with product
During the filling operation, measure and record the temperature and gauge pressure of the product during its passage through the meter;
After concluding the filling operation, and once the turbulence subsides take the reading of product level in the upper neck scale and the three thermometers in the prover tank and record them in the proving form. Make sure that the level reading is taken at the bottom of the meniscus.
Obtain a sample from the prover tank and determine its density and temperature (use a hydrometer and a thermometer). Record the results in the proving form.
Read and record the meter register after the filling operation.
Read the stop watch and record the elapsed time taken during the filling operation.
Empty the prover tank.
After completing the emptying procedure, read the zero level from the lower neck scale and record it on the proving form.
Pre-Calibration Runs:
The purpose of these runs is to determine the final repeatability of the meter under test, and it’s as-found accuracy prior to calibrator adjustment. The repeatability and accuracy figures obtained as a result of these runs determine the action to be taken on the meter under test. All pertinent data shall be entered under the “PRE CAL” columns, respectively.
Pre-Calibration Run Steps:
Record the initial meter reading.
Fill the tank with product.
During the filling operation, measure and record the temperature and gauge pressure of the product during its passage through the meter.
After concluding the filling operation, and once the turbulence subsides take the product level reading in the upper neck scale and the three thermometers in the prover tank and record them in the proving form. Make sure that the level reading is taken at the bottom of the meniscus.
Read and record the meter register after the filling operation.
Read the stop watch and record the elapsed time taken during the filling operation.
Empty the prover tank.
After completing the emptying procedure, read the zero level from the lower neck scale reading and record it in the proving form.
Post-Calibration Runs:
The purpose of these runs is to determine the final average % accuracy of the meter under test after adjustment of the mechanical calibrator. All pertinent data shall be entered under the “POST CAL”
columns, respectively.
Post-Calibration Run Steps:
Repeat the steps in the Pre-Calibration runs.
Proving Procedure:
The proving procedure outlined below consists of preliminary priming run, one wetting run, three pre-calibration runs, and two post calibration runs. The priming run is designed to flush out any air and residual product, prime the pump and fill the piping with the proving product. The wetting run is designed to establish the proper clingage inside the prover tank walls and to assure that the average flow rate is within the established operational flow rate. The pre-calibration runs are to determine the repeatability and accuracy of the meter under test. The post calibration runs are necessary to assure that the mechanical calibrator is set properly.
All proving runs and other steps must be performed in rapid succession to eliminate any possible effects of variations in operational and environmental conditions. Proving runs specified below are as named in the proving form.
Proving Steps:
Follow the instructions closely. Fill in preliminary information on the proving form.
A) Perform the priming run.
B) Perform one (1) wetting run.
C) Compute the product sample density at standard conditions and record it in the proving form.
D) Compute the average product temperature in the tank prover and record it in the proving form.
E) Compute the delivered volume to the tank, and the filling time in minutes and record them in the proving form.
F) Calculate the loading flow rate and record it in the proving form.
G) Compare the computed flow rate with the average flow rate during the last meter calibration. Compute the percent change in the flow rate;
Δ flow rate = [(Current flow rate – Previous flow rate) / Previous flow rate] * 100.
i. If Δ flow rate is less than or equal Δ 10%, no flow adjustment is necessary. Proceed with the following steps.
ii. If Δ flow rate is greater than Δ 10%, adjust the flow rate to the nominal operating flow rate. Obtain another proving form and repeat the wetting run. Record the actions in the remarks section (item D1) of both proving forms accordingly. Proceed with the following steps.
H) Once the product temperature in the tank prover is determined, it shall be compared with the starting ambient temperature. Proceed to the next step only if the product temperature does not differ from ambient by 10 °C. If the difference is more than 10 °C, void the proving operation by writing the word void across the proving form. Document the voiding reason in the remarks section of the proving form. Reschedule another proving operation.
I) Perform three (3) consecutive Pre-Calibration runs.
J) After completing the above Pre-Calibration runs, compute or obtain and record the following for each of the three Pre Calibration runs:
Registration by meter.
Temperature factor for liquid in the meter.
Pressure factor for liquid inside the meter.
Registered volume by meter at standard conditions.
Average product temperature in prover tank.
Temperature correction factor for liquid in prover.
Temperature correction factor for steel of prover.
Gross delivered volume to prover.
Delivered volume to prover at standard conditions.
Elapsed time in minutes for the proving run.
Flow rate during proof.
Trial meter factor, or meter factor during this run.
INSPECTION
1) Inspect the prover tank for any dents that are not recorded on the calibration certificate, any foreign objects or clingage inside the tank, or failure of an internal coating that would have an effect on the calibrated volume of the prover tank.
2) Verify that the gauge scales are sealed.
3) Check for a current and valid calibration certificate.
4) Check that all connections are properly made and isolation/diverter valves are properly aligned.
5) Verify the integrity of all vents, drains, reliefs, and double block and-bleed valves between the meter and the prover.
OPERATING PROCEDURE
1) The initial step prior to the first proof run is to wet down the prover tank as follows:
a) Fill the tank with metered liquid.
b) Check the level indicators on the tank.
2) If the tank is equipped with a lower-gauge glass, close the main drain valve just prior to the liquid level reaching the zero mark.
3) Allow a minimum of 30 seconds drain down time (or that which is stated on the calibration report), then using the small drain valve, drain the liquid to the zero mark
4) If the tank is not equipped with a lower-gauge glass, leave the drain valve open until continuous flow ceases and dripping starts.
5) The drip should be allowed to continue for a minimum of 30 seconds (or that which is stated on the calibration report) before closing the drain valve.
Note: Whatever drip time is allowed between flow cessation and closing the drain valve must be used on all subsequent proof runs.
6) Using a tank prover report or worksheet record the appropriate meter, tank, and flow data as indicated in the meter factor calculation section of API MPMS, Chapter 12.2.
7) Record the following opening readings for the proving run on the prover report or worksheet:
a) Record the meter register, or zero the proving counter if one is being used.
b) Record the reading of the prover tank’s bottom gauge glass, if so equipped.
8) Start the flow through the meter into the tank.
9) While the tank is filling, record the average meter temperature and verify that the meter is operating at the desired proving rate.
10) Stop the meter flow when the liquid level is within the upper gauge scale range.
11) Record the prover tank temperature.
Note: If the tank has more than one thermometer, the recorded temperature is the average of all thermometer readings.
12) Record the following closing reading for the proving.
a) Record the meter register or the proving counter reading
b) Record the prover tank’s upper gauge glass reading.
13) Calculate the meter factor for this run as outlined in API MPMS, Chapter 12, 2. This completes one proving run.
14) Repeat until the required number of proof runs have been completed according to the following criteria;
a) Three consecutive proving runs in which the meter factors agree within a 0.05 percent range. The average of these meter factors is the final meter factor.
b) If an adjustment to the meter factor is made mechanically, that is, with a calibrator or mathematically, repeats Step 3a through Step 18 until three consecutive proving runs in which the meter factors agree within a 0.05 percent range. The average of these meter factors is the final meter factor.
15) Upon conclusion of the proving operation, if a prover tank is a portable unit isolates the prover from the flow stream, drain down; remove all connections made; and prepare the tank for removal from the site. If the tank is permanently located, isolate the prover from the flow stream; drain down; and place the tank in a protected idle mode.
ASSESSMENT OF RESULTS
Common practice is to require a minimum of three 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.