Manual of Petroleum Measurement Standards Chapter 10 - Sediment and Water Section 11 - Continuous On-line Measurement of Water Content in Petroleum and Petroleum Products FIRST EDITION, JULY 2000

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TABLE OF CONTENTS Section Page 0 Introduction ............................................................................................................................................................2 1 Scope........................................................................................................................................................................3 2 References ...............................................................................................................................................................3 3 Definitions...............................................................................................................................................................3 4 Significance and Use.............................................................................................................................................5 5 OWD Operating Criteria ........................................................................................................................................5 6 Stream Conditioning ..............................................................................................................................................6

6.1 General ...........................................................................................................................................................6 6.2 Velocities and Mixing Elements.................................................................................................................6

7 Installation...............................................................................................................................................................7 8 Pacing On-line Water in Petroleum Device .......................................................................................................8

8.1 Flow Proportional Pacing ............................................................................................................................8 8.2 Time Proportional Pacing ...........................................................................................................................9

9 Auxiliary Instrumentation .....................................................................................................................................9 10 Applications .....................................................................................................................................................27

10.1 Pipeline .........................................................................................................................................................27 10.2 Marine...........................................................................................................................................................27 10.3 Process .........................................................................................................................................................27 10.3.1 Refining ...................................................................................................................................................27 10.3.2 Production ...............................................................................................................................................27 10.3.2.1 Allocation Measurement ..................................................................................................................27 10.3.2.2 Well Test.............................................................................................................................................27 10.3.2.3 Water Separator Facilities ..............................................................................................................28 10.3.2.4 Crude Oil Gathered by Tank Truck...............................................................................................28 10.3.3 Marketing................................................................................................................................................28

11 Initial Acceptance Testing of OWD Systems ...............................................................................................9 11.1 Baseline Water Plus Injected Water Volume Method (Method 1)....................................................10 11.1.1 Test Preparation (Method 1)................................................................................................................10 11.1.2 Test Procedure (Method 1)...................................................................................................................10 11.1.3 Acceptance Criteria (Method 1)..........................................................................................................14 11.2 Proven Sampling System Method (Method 2)........................................................................................17 11.3 Average of Instantaneous Sample Method (Method 3).........................................................................17

12 Calibration Verification....................................................................................................................................19 12.1 Calibration of OWD System Components..............................................................................................19 12.2 On-line Spot Sample Verification Testing Procedure (Method 3)....................................................20 12.3 Off-line OWD Verification Testing Procedure ....................................................................................20

13 Auditing and Reporting Requirements For Custody Transfer: ................................................................21 0 Introduction The purpose of this draft standard is to provide guidance for the continuous on-line measurement of real-time water content in petroleum and petroleum products using an On-line Water in petroleum and petroleum products measurement Device (OWD) and to collect consistent data. Such measurements are of benefit in both custody transfer and process control applications. When real-time percent water measurements are made for custody transfers and some other applications (e.g. allocation measurement), there must also be a flow measurement to provide a flow-weighted average water content value.

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This methodology can be used in conjunction with other methods of water determination or as a stand-alone method. However, automatic sampling is essential for the following custody transfer applications: § If the on-line water measurement device used cannot effectively derive the overall integrated

average water content to the required accuracy. § If other properties are require (e.g. API gravity, sediment content). § If retention samples are required. This technology should be viewed as one of several methods to determine the water in petroleum and petroleum products. The method for measuring water in petroleum and petroleum products should be selected with consideration given to installation, application, and properties of the product being measured. 1 Scope This draft standard describes methods for the continuous on-line real time measurement of free and entrained water quantities in petroleum and petroleum products (OWD). The procedures for the proper installation, operation and calibration of on-line water in petroleum measurement devices are also described. This standard only addresses the measurement of water in petroleum liquids. This standard does not address the measurement of any solid and/or gaseous phases that may also be present. The term petroleum will be used throughout this standard to describe petroleum and petroleum products normally associated with the petroleum industry. This standard applies to water concentrations from 0.02% to 100%. In the event that there is an issue with the results of this standard and API MPMS Chapter 8.2, the referee method is API MPMS Chapter 8.2. 2 References API Manual of Petroleum Measurement Standards Chapter 3

Chapter 4 Chapter 5 Chapter 6 Chapter 8, Sampling (all sections)

Chapter 10, Sediment and Water (all sections) Chapter 20.1 Allocation Measurement Chapter 21.2.10 Flow Measurement Using Electronic Metering Systems 3 Definitions

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analyzer loop: A low volume stream diverted from the main pipeline. Also known as a sample loop, slip stream or fast loop. controller: A tertiary device (e.g. PLC, Flow Computer, etc.) that accepts inputs from an OWD, flow meter, and other necessary sensors. dissolved water: Water in solution in petroleum and petroleum products. emulsion: An oil/water mixture that does not readily separate. entrained water: Water suspended in oil. Entrained water includes emulsions but does not include dissolved water. flow proportional water measurement: A measurement of the water flow rate calculated from the on-line water fraction determined from the OWD measurement and the liquid flow rate through the pipe. free water: Water that exists in a separate phase. homogenous : Composition of a liquid is the same at all points in a vessel, container or pipeline cross section. measurement location: Point where OWD measures the water content of the petroleum stream. OWD: On-line Water in petroleum and petroleum product measuring Device (referred to as a water cut monitor in other API Measurement Standards). OWD System - An OWD system consists of one or more OWD’s, stream conditioning, other measurement devices (e.g. temperature, pressure, density, flow, etc.), and a controller. pacing: Setting the measurement reporting period proportional to flowrate or time. range: The maximum and minimum values attainable from a measurement device. When applied to an OWD, the units will be percent water by volume (e.g. 0-5% or 0-100%). representative sample: A portion extracted from a total volume that contains the constituents in the same proportions that are present in that total volume. sample: A portion extracted from a total volume that may or may not contain the constituents in the same proportions that are present in that total volume. static mixer: A device that utilizes the kinetic energy of the flowing stream to achieve stream conditioning.

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stream condition: The distribution and dispersion of the pipeline contents at the measurement location. stream conditioning: The mixing of a flowing stream so that fluid constituents are homogeneously distributed and dispersed across the pipe at the measurement location. weighted average water content: The average water content at the measurement location for the measurement period. For volumetric methods, the weighted average water content is the average of the water values measured at uniform volume intervals and is representative of the water content for the entire measurement period. 4 Significance and Use Measuring the quantity of water in petroleum liquids is critical for quantity and quality measurement. An OWD System can provide the user with information about net oil and water amounts or timely information about high levels of water that can cause process problems. The performance specification given for custody transfer applications will not normally be required for process monitoring, alarm, and control applications. 5 OWD Operating Criteria The following custody transfer criteria must be satisfied to obtain a representative measurement from a flowing stream, otherwise the performance of the OWD may be affected: a. For non-homogeneous mixtures such as crude oil and water, free and entrained water must

be uniformly dispersed at the measurement point. b. On-line water in oil measurements must be flow proportional and provide a representative

measurement of the entire parcel volume. The on-line water measurement is monitored continuously and integrated with the flow signal to calculate water content for the entire parcel.

c. OWD measurements that are affected by fluid properties and operating conditions (e.g.

density, temperature, pressure, salinity, viscosity, etc.) require those parameters to be measured and corrections made. Some OWD’s will automatically compensate for changes in these properties and conditions.

d. The fluid must be gas free. Water content is generally within a range from 0.02% to 5 percent. If the water content occasionally exceeds the 5 percent range, use an OWD system with wide-range capability. If the OWD system is not capable of the required accuracy over the expected range (for custody transfer measurement), the system must have a multiple range capability.

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Most OWD’s only detect water, not sediment. If necessary a separate representative sample must be taken and a test conducted to obtain the sediment value. The Karl Fischer coulometric titration is the recommended method for the analysis of samples taken in the calibration and verification of OWD’s that are used for custody transfer applications, because the test is best suited for field application and detects water only. 6 Stream Conditioning 6.1 General The OWD must be located at a point where the flowing stream is adequately mixed. The mixing may be accomplished by the flowing velocity of the fluid through the piping system and/or by adding mixing elements. Petroleum that contains free or entrained water requires sufficient mixing energy to create a representative stream at the measurement point. 6.2 Velocities and Mixing Elements Table 1, from MPMS Chapter 8.2 based on statistical data, provides a guideline for minimum velocities versus mixing elements for pipes 5 centimeters (2 inches) in diameter and larger. Stream conditioning can be accomplished with pressure reducing valves, metering manifolds, lengths of reduced diameter piping, pumps, or piping elements ( valves, elbows, tees, piping, or expansion loops). If the flow velocity at the OWD location falls below the minimum levels in Table 1, additional means, such as static mixers or power mixers, may be required. The relative position of the mixing elements and the OWD must be considered.

Table 1 - General Guidelines for Minimum Velocities Versus Mixing Elements

(From API MPMS Chapter 8.2-95) Minimum Pipeline Velocity, meters per second

Mixing Element

Piping

0

0.305

0.61

0.91

1.22

1.52

1.83

2.13

2.44

Power Mixing Horizontal or vertical

Adequate at any velocity

Static Mixing Vertical Stratified Not Predictable

Adequately dispersed

Static Mixing Horizontal Stratified Not predictable Adequately dispersed Piping elements

Vertical Strat ified Not predictable Adequately dispersed

Piping elements

Horizontal Stratified Not predictable Adequately dispersed

None Horizontal or vertical

Stratified or not predictable

0 1 2 3 4 5 6 7 8

Minimum Pipeline Velocity, feet per second

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7 Installation Follow the manufacturer’s recommended installation guidelines. The OWD should be located where there is adequate stream conditioning. When mixers are used, the manufacturer of the mixer should be consulted for the optimum location of the OWD relative to the mixer. The OWD shall be located such that accumulation of water and/or gas will not affect the measurement. See Figure 1 for recommended location of OWD in a pipeline application. For an OWD installed on an analyzer loop, the stream through the loop should be representative of the main line and should be homogenous. See Figure 1 item B2. A flow indicator must also be installed in the analyzer loop.

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Figure 1: Recommended Location of OWD in a Pipeline Application

The verification of OWD’s shall require a sample probe for drawing spot samples from the pipe for analysis. The sample withdrawn from the pipe must be representative of the flowing stream being measured for water content. For the sampling probe location position, and size, follow the guidelines for manual sampling of pipeline streams in MPMS Chapter 8. 8 Pacing On-line Water in Petroleum Device 8.1 Flow Proportional Pacing

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The preferred method for pacing an OWD is by flow meter. When flow is measured by multiple meters, the OWD should be paced by the combined total flow signal. Alternately, a separate OWD may be installed in each meter run. When transfer is by tank measurement, a flow signal must be provided to the OWD controller. This signal may be provided by an Automatic Tank Gauging system (ATG) or by an add-on flow-metering device. These devices should have a flow measurement accuracy of ± 10 percent or better, over the range of flow rates that will be experienced during the transfer. 8.2 Time Proportional Pacing Flow proportional pacing may not be necessary for process control/alarm applications. For custody transfer applications, an OWD should operate proportionally to flow. However, time proportional pacing for custody transfer applications may be acceptable when the flow rate variation is less than ±10 percent of the average rate. 9 Auxiliary Instrumentation Some OWD’s may use an input from one or more auxiliary measurement devices (e.g., for measuring temperature, pressure, density, salinity, viscosity, etc.) to improve water measurement accuracy. The accuracy of these auxiliary measurement devices must be verified regularly. The required frequency of these verifications (and recalibrations as necessary) is dependent upon the application and the OWD manufacturer’s recommendations. 10 Initial Acceptance Testing of OWD Systems This section describes methods for the initial acceptance testing of OWD systems through the use of various techniques for establishing the reference water content of the stream, which is then compared to the results from the OWD. (Note: All components of the OWD system must be calibrated prior to initial acceptance testing.) It is important that all parties agree to the method used. The following three methods are described herein: Method 1: Establish the reference water volume percent using baseline water and the injected water volume measurements. (This is the preferred method for custody transfer facilities.) Method 2: Establish the reference water volume percent using a proven sampling system. (This can result in twice the tolerance range of Method 1 depending on the original deviation for the sample system proving. Therefore, this method may not be acceptable for custody transfer facilities.)

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Method 3: Establish the reference water volume percent for several instantaneous samples. (This method relies exclusively on a limited number of instantaneous samples. This method is applicable to process or production OWD installations, but may not be acceptable for custody transfer facilities.)

10.1 Baseline Water Plus Injected Water Volume Method (Method 1) Water volume injection tests are designed to prove the entire OWD system. In each test a known amount of water is injected into a known volume of petroleum of a known baseline water content. Water volume percent measured by the OWD are compared with water volume percent calculated from the injected water volume plus baseline water volume percent. 10.1.1 Test Preparation (Method 1) Preparation prior to the acceptance test should include the following procedures: 1. Determine the method and accuracy by which the water and petroleum volumes will be

measured. The meter used to measure the injected water shall be calibrated. Petroleum volumes should be measured by tank gauge or meter(s) in accordance with applicable API MPMS Chapters 3,4,5, and 6 guidelines.

2. Locate the water injection point upstream of the elements expected to produce the stream

conditioning for the OWD system. Be aware of potential traps in the piping that may prevent all of the injected water from passing the measurement point. Care should be taken to ensure that the location and manner in which water is injected does not contribute additional mixing energy, which could distort the test results. Equipment or facilities used to inject water should be in accordance with local safety practices.

3. Review the normal operating conditions of the pipeline in terms of flowrates and petroleum

types. Select the most common, worst-case conditions to test the OWD. The worst case is usually the lowest normal flow rate and the lowest viscosity (lowest density or highest API gravity) petroleum normally received or delivered. However, a very high viscosity oil may be the “worst case”.

4. Determine a point where samples can be drawn downstream of the stream conditioning.

Samples must be homogeneous and representative of the flowing stream. These samples will be used for baseline water determination and possibly for spot samples during the test period. Sample probe should meet the requirements described for the probe design in API MPMS Chapter 8.1 or 8.2.

10.1.2 Test Procedure (Method 1) Typical timing for Method 1 is shown on Figure 2. A flowchart for the test procedure is shown on Figure 3 and the details follow the figure.

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PURGE

BASELINE SAMPLE

WATER INJECTION

WATER ARRIVES

BASELINE SAMPLE

AC

TIV

ITY

TIME

Note - Times are calculated based on minimum oil flow rate and distance between the injection and the sample point.

TO ALLOW FOR LAGAND SPREADING

TEST PERIOD

Figure 2: Typical Timing Diagram For OWD System Test.

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Purge System AtHigh Flowrate

Adjust FlowrateFor Test

DetermineBaseline Water

Content

Draw Sample

Determine OWDReading At TimeOf Sample Draw

Determine WaterContent Of

Sample

Is AvgOWD Equal To

AvgSample?

Adjust OWD ToMatch SampleAnalysis (to bedone on initialseries only)

Completed5 SeparateSamples?

No

No

Average Thesample analysis

To Determine TheBaseline WaterVolume Percent

No

Yes

Record InitialPetroleum

Volumes (TankGauge Or Meter

Reading)

Record InitialWater

Flow MeterReading.

Turn Water OnAnd Adjust

Injection Rate.

Perform WaterInjection

Vary waterinjection rates to

simulate thevarious

percentages ofwater to beexpected.

Turn Water OffAnd Record Water

Flow Reading.Allow time for

injected water topass the OWD.Simultaniously

stop/record testdata

FinalBaseline ForThis Test?

Confirm BaselineStability By

Determining AFinal Baseline And

Comparing It ToInitial Baseline.

Is BaselineStable?

CalculateDeviation Between

OWD MeasuredAnd Calculated

Actual.

TwoConsecutive

Tests MeetingCriteria?

No

Yes

Yes

No

Test Is Complete

Yes

If Baseline Continues ToFluctuate, Stop Test And

Correct.No

Baseline Is NotStable. StabilizeThe System And

Try Again.

Range Of Sample

Values within0.1% ?

Yes

Yes

Run one more pass to confirm clibration

Figure 3: Flowchart of Procedure for OWD System Initial Acceptance Testing Using Method 1.

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Test Procedure Details (Method 1) Note: Following method is described for Custody Transfer with water volume percents up to 5% 1. Purge the system at a high flow rate to displace free water that may be lying in the pipeline

system upstream of the OWD. 2. Adjust the flow rate for the test. BASELINE STEPS 3. Determine the baseline water content per API MPMS Chapter 10 (Karl Fisher coulimetric

titration or Dean & Stark distillation) and calibrate the OWD as listed in the steps that follow. (a) Draw a sample from sample point. (b) Determine and record the OWD reading at the time the sample is drawn (c) Determine and record the water volume percent of the sample

(d) Repeat steps a thru c for 4 more samples, using even time intervals between samples (e) Average the 5 OWD readings (f) Average the 5 sample analysis results (g) Compare average of sample analysis results to average of OWD readings (h) Adjust the current OWD reading by the difference between the averages (i) Repeat steps a thru c one time to verify the OWD has been calibrated properly. (j) Average the 6 sample analysis results to determine the baseline water volume percent.

Note: § The range (highest value versus lowest value) of the sample water volume percent

should be within 0.1% to have a stable baseline. § The variation in the difference between the paired results (sample n – OWD n) must

be within a tolerance of +/- 0.05 water volume % .

WATER INJECTION STEPS Note: Approximately one hour is required for the water injection 4. Record the initial petroleum volume by tank gauge or flow meter reading and initialize the

flow weighted calculation device (e.g. flow computer), i.e. open the ticket. 5. Record the initial water flow meter reading; turn the water on and adjust the injection rate. § During the test period, adjust the injection rate to simulate the various percentages of

water to be expected, as agreed between parties. (Note: Ensure the percent water injected is within the capabilities of the OWD.)

6 Turn the water off and record the water flow meter reading. 7 Continue taking readings from the OWD until the injected water is calculated to have

passed the measurement device. 8 Stop the collection of the test data, simultaneously record the final petroleum volume by

tank gauge or meter reading and finalize the flow weighted calculation device (e.g. flow computer), i.e. close the ticket.

9 Confirm Baseline stability by repeating Step 3 (excluding 3.h).

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§ The difference in the percent water in the initial and final baseline shall be less than or equal to 0.1 % ( %1.0±≤− ineFinalBaselelineInitialBas )

Note: For a water content >5%, the difference in the percent water in the initial and final baseline shall be less than or equal to 4% of water reading (e.g., if baseline water is 10% the allowable difference is (10% x 4% = 0.4%), which is maximum baseline deviation.)

§ If the difference between initial and final baseline results is greater than 0.1 percent (or 4.0 percent of reading for a water content in the range of >5%) return to step 4. If the baseline continues to fluctuate, stop test and take corrective action.

10 Using the following equation, calculate the deviation between the water in the test readings minus the readings in the baseline compared to the amount of water injected.

DEV = (Wtest – Wbaseline) – Winjected Where: DEV = deviation (volume %)

Wtest = water in test readings (OWD value in volume %). Wbaseline = baseline water adjusted to test conditions (volume %) = Wavg x (TOV-V)/TOV

Wavg = average of all OWD measured baseline results, water in (volume %) TOV = total observed volume (test oil plus injected water) that passes the measurement probe (barrels) V = volume of injected water in barrels Winj = water injected during test (volume %) = V/TOV x 100 11 Repeat steps 3 through 14 until two consecutive tests are within the acceptable deviation

limits (e.g. see Table 2). 10.1.3 Typical Acceptance Criteria (Method 1) Baseline Acceptance a. Custody Transfer Applications: The difference in the percent water in the initial and final

baseline shall be 0.1 percent or less for a water content range of 0.02% to 5%. (The difference in the percent water in the initial and final baseline shall be 4 percent of reading or less for a water content range of >5% to 100%.)

b. Non-Custody Transfer Applications: The acceptable difference in the percent water in the

initial and final baseline should be agreed by all the parties. Typically the differences should be 2 percent or less for a water content range of 0% to 100%.

System Acceptance

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a. OWD System Acceptance Custody Transfer: The deviation between the water content from the OWD and the known baseline plus injected water is within the allowable deviation limits (e.g. see Table 2), for two consecutive tests.

b. OWD System Acceptance Non-Custody Transfer: The deviation between the water

content from the OWD and the known baseline plus injected water should be agreed by all the parties, for two consecutive tests

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Table 2 - Typical Deviations for the OWD System Acceptance Tests for Custody Transfer

(Volume Percent)

Typical Deviation Total Water (Wbl+Winj) Using Tank Gauges Using Meters % of

Reading 0.5 0.13 0.09 1.0 0.15 0.11 1.5 0.16 0.12 2.0 0.17 0.13 2.5 0.18 0.14 3.0 0.19 0.15 3.5 0.20 0.16 4.0 0.21 0.17 4.5 0.22 0.18 5.0 0.23 0.19 3.8

>5.0 to 100

10 25 50 75 100

0.40 1.00 2.00 3.00 4.00

0.40 1.00 2.00 3.00 4.00

4.0

4.0 4.0 4.0 4.0 4.0

Notes:

1. Basis for the above Table 2 and the following notes is API MPMS 8.2.A Table 1. 2. The reference to tanks or meters refers to the method used to determine the volume of crude oil or

petroleum in the test. 3. Deviations shown reflect use of the Karl Fischer test method described in MPMS Chapter 10.9 for

water. 4. Interpolation is acceptable for water concentrations between values shown in the table. For example, if

the total water is 2.25 percent, the allowable deviation using tank gauges would be 0.175 percent, and 0.135 percent if using meters.

5. This table is based, in part, on statistical analysis of a database consisting of 36 test runs from 19 installations. Due to the number of data, it was not possible to create separate databases for the method of petroleum volume determination using tank gauges and using meters. Therefore, it was necessary to treat the data as a whole for analysis. The database is valid for the water range 0.5 percent to 2.0 percent. The reproducibility standard deviation calculated based on the data, at a 95 percent confidence level, has been used for the values “Using Meters” shown in the table in the water range 0.5 percent to 2.0 percent. Assigning these values to the meter is based on a model that was developed to predict standard deviations for volume determinations by tanks and meters. Values shown in the table “Using Tank Gauging” in the range 0.5 percent to 2.0 percent were obtained by adding 0.04 percent to the values “Using Meters” in this water range. The value of 0.04 percent was derived from the aforementioned model as the average bias between tank and meter volume determinations.

As there is insufficient test data for water levels over 2.0 percent, values shown in the table

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above 2.0 percent have been extrapolated on a straight-line basis using the data in the 0.5 percent to 2.0 percent range. 10.2 Proven Sampling System Method (Method 2) Compare the OWD System results to an existing sampling system results in normal operations, proven for the typical grades of petroleum and the conditions to be encountered. (If the conditions have changed since the last proving of the sampling system, the existing system may no longer meet the requirements of API MPMS Chapter 8.2 and any comparison to an OWD could introduce a bias.) The number of measurement periods should be agreed upon between the parties involved, with a minimum of five measurement periods. Acceptability is checked by comparing the flow weighted average of the OWD measurements to the proven sampling system test results over the same measurement period. Deviation between the OWD and the proven sampling system results must be within the deviation limits agreed to by all parties, e.g. see Table 2, based on the original sample system acceptance test (tank gauge or meter). An optional consideration would be to inject water at various rates (one rate per measurement period) to verify the OWD system performance over a range of water contents expected during normal operation. 10.3 Average of Instantaneous Sample Method (Method 3) This method is an example of an alternate means to test an OWD. It can be used when a certified automatic sampling system is not available, flowrate is unknown, and/or baseline water content may vary widely (e.g., well test environments or high water content). This test method shall not be used when test methods 10.1(water injection test method) or 10.2 (direct comparison with an existing certified sampling system) can be utilized. The intent of this test method is to accomplish the following: 1) To evaluate if the average of the OWD instantaneous readings are reflective of the average

of the instantaneous samples, within the allowable deviation limits of Table 3. 2) To evaluate how well the OWD accurately reflects the variations in water content when

compared to actual sample results during the water injection period. If the water content normally varies it may not be necessary to inject additional water.

10.3.1 Test Preparation (Method 3) Preparation prior to the acceptance test should include the following procedures: 1. Locate the water injection point upstream of the elements expected to produce the stream

conditioning for the OWD system. Be aware of potential traps in the piping that may prevent all of the injected water from passing the measurement point. Care should be taken to ensure that the location and manner in which water is injected does not contribute additional mixing energy, which would distort the test results. Equipment or facilities used to inject water should be in accordance with local safety practices.

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2. Review the normal operating conditions of the pipeline in terms of flowrates and crude

types. Select the most common, worst case conditions to test the OWD. The worst case is commonly the lowest normal flow rate and the lowest relative density (highest API gravity) petroleum normally received or delivered.

3. Care should be taken in selecting a sample draw location, at a point where the flow is a

homogeneous mixture and representative of the flowing stream. Additionally this location should be in close proximity to the OWD. Whenever possible the sample should be taken from a sample draw probe.

10.3.2 Test Procedure (Method 3) The purpose of the Baseline test is to establish initial accuracy and repeatability of the OWD. 1. Purge the system at a sufficiently high flow rate to displace free water that may be lying in

the pipeline system upstream of the OWD. 2. Draw-off an initial baseline sample and compare with the OWD instantaneous reading when

the sample was drawn. 3. Determine the baseline water volume percent and calibrate the OWD per the Baseline

Steps in Method 1 (Section 10.1.2.3). 4. Average the OWD readings and sample results to define the deviation of the Baseline. 5. The difference between the average OWD and the average sample results must be within

the tolerances agreed to by the parties, e.g. see Table 3. 6. Record the initial water flow meter reading; start the water injection and adjust the injection

rate. A water flow meter allows the operator to verify the water volume, injection flow rate and evaluate the corresponding OWD deviations.

The purpose of the injection portion of this test is to prove the accuracy and repeatability of the OWD during varying water conditions. 7. Approximately one hour is required for the water injection.

• During the injection period draw off 12 samples at equal time intervals (approximately 5-minute intervals) recording the OWD instantaneous reading at the same time (as in Step 3).

• Water injection rate can be varied to evaluate different levels of water content. 8. Stop the water injection and record the water flow meter reading. 9. Complete the worksheet. (See Appendix I)

• Calculate the average of the sample results. • Calculate the average of the OWD results. • Percent difference is (Average sample result – Average OWD result). • Refer to Table 3 for allowable deviation.

10. Repeat steps 3 through 9 until the results from two consecutive tests meet the deviation in Table 3.

11. If the system fails more than three times stop test and take corrective action.

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If the amount of oil available prevents tests of the above duration, the time period may be reduced as necessary. However, it is recommended that the number of samples in each test be maintained. Table 3 – Typical Deviations For The OWD Average Of Instantaneous Sample Method (Method 3)

Average (Instantaneous Sample) Typical Deviation 0.5 0.13 1.0 0.15 1.5 0.16 2.0 0.17 2.5 0.18 3.0 0.19 3.5 0.20 4.0 0.21 4.5 0.22 5.0 0.23

>5.0 to 100

10 25 50 75 100

0.40 1.00 2.00 3.00 4.00

Note: This Table is based on the values in Table 2 . 11 Calibration Verification An on-going OWD system calibration verification program shall be established . The calibration of all essential components of the OWD system shall be verified routinely. Initially, each OWD system shall be inspected and its calibration verified frequently. If operating experience confirms stable performance , the calibration verification schedule may be extended. 11.1 Calibration of OWD System Components Users should consult the manufacturers’ recommendation on calibration of the OWD system components. A representative tolerance for volume custody transfer applications is ±0.1 degrees F and ±0.5 degrees API or less. Generally, calibration is extremely important, since each measurement depends on another.

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(a) Calibrate all instruments used in the measurement calculation (b) Calibrate the OWD to the deviation agreed to by the parties, e.g. see Table 2.

All test equipment used in the calibration shall be traceable to NIST, or appropriate agency. All calibration records of test equipment should be maintained and available for review. (Examples are; date of last calibration, reagent change date, date any equipment was replaced.) All calibration records and performance records of the OWD system must be available for review by customers involved in measurement for the purposes of custody transfer. 11.2 On-line Spot Sample Verification Testing Procedure This testing procedure is used to regularly verify the OWD system calibration at the existing fluid/operating conditions. The flowing stream must be homogeneous at the test sample draw location. Draw a test sample, per API MPMS Chapter 8.1 and 8.3, from the location shown in 11.1.1 item 4 and simultaneously record the reading of the OWD (water content in volume percent). Analyze the test sample per API MPMS Chapter 10 and compare the results. Results must fall within the deviation agreed to by the parties, e.g. see Table 2. If results do not meet the agreed to tolerance, perform the calibration procedure below.

§ Record the OWD water volume percent reading at the time the sample is drawn § Determine the water volume percent of the sample analysis § Compare the OWD reading to the sample analysis § Adjust the OWD to match the sample analysis § Repeat steps to verify calibration

Record, sign and date the Calibration Worksheet. –(See example in Appendix II). Maintain a summary chart of test results to show repeatability and drift over time (See example in Appendix III) 11.3 Off-line OWD Verification Testing Procedure Periodically a closed loop system may be used to verify the OWD accuracy over a range of water/petroleum concentrations. Such a loop would have a known volume in which predetermined amounts of petroleum (or petroleum products) and water are mixed to create desired concentrations for testing. The closed loop can be any of the following: The manufacturer’s test loop, a portable system, or a permanent part of the OWD system installation. Having the loop at the OWD installation site makes it convenient to test using liquid from the flowing stream. Important Considerations:

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§ The closed loop must be well insulated to prevent internal condensation of water on the pipe wall.

§ The closed loop must have a temperature control (chiller/heat exchanger) to prevent temperature build up due to pumping the fluid in a small, closed loop.

12 Auditing and Reporting Requirements For Custody Transfer: The OWD System should indicate when it’s range is exceeded. When the OWD system is used in a custody transfer electronic measurement system, the user must comply with the standards as defined in API Chapter 21.2, Flow Measurement Using Electronic Metering Systems, Section 10, Auditing and Reporting Requirements.

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Appendix I Example Worksheet for OWD Acceptance Testing Using Average of Instantaneous Samples (Method 3) Date: Start time: End Time: _______ Avg. Temp. Avg. Gravity _____ Baseline Sample # Time

(hh:mm:ss) Sample Result (Vol % Water)

OWD Result (Vol % Water)

1 2 3 4 5 6

Baseline Average Water Injection Test: Sample # Time

(hh:mm:ss) Sample Result (Vol % Water)

OWD Result (Vol % Water)

1 2 3 4 5 6 7 8 9 10 11 12

Averages Results % Difference ___________ Acceptance: Pass/ Fail BY: DATE:

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Appendix II

Instrument: ________________________ Mfg: ____________________

S/N: ____________________ Model: __________________

Location: __________________________ Date: _______________________________________________________________________________________________________

I. Calibrate Densitometer (if used) before proceeding to the next step. (Use DensitometerCalibration Worksheet)

II. Temperature Adjust:

Test Equipment Used: __________________ Mfg: ______________________

S/N: ______________________ Date Calibrated: ____________

SampleID

Time DisplayedTemp

MeasuredTemp.

Temp.Deviation

CurrentTemp.Adjust

NewTemp.Adjust

III. OWD Calibration:

Test Method Used: __________________ Mfg: ______________________

Model & S/N: ______________________

Date Calibrated: ____________

SampleID

Time DisplayedContents

MeasuredContent

Deviation CurrentCal

Factor

New CalFactor

Index ReferenceVoltage

Calibrated By: _____________________ Date: _________ Agency: __________

Witness By: _______________________ Date: _________ Agency: __________

Company Name

OWD Calibration Worksheet

25

Instrument: ________________________ Mfg: ____________________

S/N: ____________________ Model: __________________

Location: __________________________ Date: _______________________________________________________________________________________________________

I. Temperature Adjust:Follow manufacturer's calibration procedures to calibrate temperature fordensitometer before proceeding to the next step.

II. Density Adjust:

Test Equipment Used: __________________ Mfg: ______________________

S/N: ______________________ Date Calibrated: ____________

SampleID

Time DisplayedTemp.

ObservedDensity

MeasuredDensity

Deviation CurrentCal

Factor A

New CalFactor A

Calibrated By: _____________________ Date: _________ Agency: __________

Witness By: _______________________ Date: _________ Agency: __________

Company Name

Densitometer Calibration Worksheet

26

Appendix III

Instrument: ________________________ Mfg: ____________________

S/N: ____________________ Model: __________________

Location: __________________________ Date: _________________

Enter final results of each calibration onto the Summary Page.This will help you spot trends

TestNumber

Test Date Test Time DisplayedContents

MeasuredContent

Deviation CurrentCal Factor

New CalFactor

Index ReferenceVoltage

Company Name

OWD Calibration Summary

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Appendix IV Applications OWD’s may be used in different custody and non-custody applications. Below are some examples of common applications 1 Pipeline Pipeline water content is generally within a range from 0.02% to 5 percent. If the water content occasionally exceeds the 5 percent range, use an OWD system with wide range capability. If the OWD system is not capable of required accuracy over the expected range (for custody transfer measurement), the system must have a multiple range capability. 2 Marine Applies to portable (shipboard) or stationary systems (refer to MPMS Chapter 8.2.9 for more detail). Installation requirements for shipboard OWD’s are the same as those discussed in MPMS Chapter 8.2.17. 3 Process Depending on the actual process application, the installation, calibration, and certification procedures for an OWD may be relaxed from the requirements for custody transfer. 3.1 Refining OWD’s can be used to monitor the water content of crude oil or other feedstocks to minimize process upsets, damage to equipment, and contamination of catalysts in refinery operations. The operation of equipment, like desalters, can be monitored and optimized with an OWD. 3.2 Production 3.2.1 Allocation Measurement OWD’s can be utilized to measure the total dry oil from various production facilities that would be used when the total production is allocated back to the individual wells and facilities. This application may also include the use of OWD’s on well test separators. 3.2.2 Well Test OWD’s can be utilized as part of well test facilities. After the gas is flashed in the separator, the total liquid can be measured and then the OWD used to quantify the amount of water in the stream. Often these streams will have high water content.

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3.2.3 Water Separator Facilities OWD’s can be used in production facilities to monitor the operation of the water separators to maximize separation while also maximizing throughput. 3.2.4 Crude Oil Gathered by Tank Truck OWD’s can be mounted on production gathering trucks to monitor the water content of crude oil loaded onto or discharged from the trucks. Alternatively, OWD’s can be ground mounted at the crude oil discharge metering points. The main concern with this application is the range of crude oil types encountered. 3.3 Marketing OWD’s can be utilized to monitor the water content of petroleum products in a marketing terminal to assure that water in excess of specifications is not shipped in or out of the facility. The OWD can be used to quantify the water transferred or as an indicator to stop a transfer if water above a specified level is detected.