4 9 1 fm rs Manual of Petroleum Measurement Standards Chapter 4—Proving Systems Section 9—Methods of Calibration for Displacement and Volumetric Tank Provers Part 1—Introduction to the Determination o[.]
INTRODUCTION
Provers are precision devices that serve as volumetric standards to verify the accuracy of liquid volumetric meters used in custody transfer measurement Both displacement and tank provers are employed to establish a meter's factor, which corrects for discrepancies between the metered volume and the true volume Calibration determines the base volume of a displacement or tank prover, which is crucial for calculating these meter factors However, the accuracy of a meter factor is constrained by various considerations.
All prover volumes for meter calibration must be established through calibration rather than theoretical calculations Volumetric provers possess a precise reference volume determined by recognized calibration methods, including waterdraw, master meter, and gravimetric techniques The ongoing development of Parts 2, 3, and 4 of API MPMS Chapter 4, Section 9, aims to ensure accurate determination of the calibrated volume of meter provers.
U.S Customary and Metric (SI) Units
This standard accommodates both International System (SI) and U.S Customary (USC) units, allowing implementation in either system The choice of units is generally dictated by contracts, regulatory requirements, manufacturers, or users' calibration programs Once a specific system of units is selected for an application, this standard does not permit arbitrary changes between units.
National Weights and Measures Agencies
Throughout this document issues of traceability are addressed by references to NIST (National Institute of Standards and Tech- nology) However, other appropriate national metrology institutes can be referenced.
Safety Considerations
This standard does not address safety considerations related to the described work, placing the responsibility on the user to understand and implement all relevant safe work practices Users must also adhere to all applicable federal, state, and local regulations, such as those set by the Occupational Safety and Health Administration, and stay informed about safety and health regulations pertinent to the activities outlined in this standard.
SCOPE
Chapter 4, Section 9 outlines the essential procedures for gathering field data to calculate the Base Prover Volume (BPV) for both Displacement Provers and Volumetric Tank Provers This section guides users through the preparation of the prover, execution of calibration runs, and documentation of the necessary data for determining the base volumes Additionally, it addresses the evaluation of results and troubleshooting common calibration issues.
Chapter 4, Section 9, Part 1 serves as the Introduction, outlining essential general aspects applicable to all calibration methods Each subsequent section detailing specific prover calibration methods should be used in conjunction with Part 1 Together, these sections provide comprehensive information necessary for completing the required calibration methods.
This standard does not provide detailed calculation procedures For comprehensive calculation details related to each calibration method, please consult the latest edition of the API Manual of Petroleum Measurement Standards, Chapter 12, Section 2.
TERMS, SYMBOLS AND APPLICATIONS
This document does not contain unique definitions; however, section 3.0 includes selected publications that provide definitions related to the calibration of displacement and tank provers The terms and symbols outlined are widely accepted for meter prover calibration If a term is defined in another API MPMS Standard, that definition will take precedence over the broader definition provided here.
Terms
The Base Prover Volume (BPV) refers to the prover's volume under standard conditions, as indicated on the calibration certificate It is calculated by taking the arithmetic average of a sufficient number of consecutive Calibrated Prover Volume (CPV) measurements.
The Calibrated Prover Volume (CPV) refers to the volume measured at base conditions between the detector switches of a unidirectional prover, or the volume within a prover tank between designated "empty" and "full" levels, established through a single calibration run For a bi-directional prover, the calibrated volume is the total of the two volumes displaced between detectors during a calibration round-trip.
The calibration certificate package is a comprehensive document that details the Base Prover Volume (BPV) along with the physical data utilized in its calculation It encompasses witnessed field data, summary calculations, and essential traceability documentation.
4.1.4 double block and bleed valve: A high-integrity valve with double seals that has provision for determining whether either seal is leaking.
4.1.5 prover calibration pass: A single movement of the displacer between two predetermined detectors.
A prover calibration run involves a single pass of a unidirectional prover, a round trip of a bi-directional prover, or the filling or emptying of a volumetric tank prover This process yields the necessary data to calculate the Calibrated Prover Volume (CPV).
1National Institute of Standards and Technology, 1655 N Ft Myer Drive, Suite 700, Arlington, Virginia, 22209 www.nist.gov.
S ECTION 9—P ART 1—M ETHODS OF C ALIBRATION FOR D ISPLACEMENT AND V OLUMETRIC T ANK P ROVERS 3
A round trip in a bi-directional meter prover consists of an OUT pass and a BACK pass of the displacer The OUT pass indicates the flow of liquid in the FORWARD direction as the displacer moves away from the HOME position, while the BACK pass signifies the flow in the REVERSE direction as the displacer returns to HOME The terms "Left to Right" and "Right to Left" are used to describe these flow directions, which are determined by facing the 4-way valve from a position away from the prover skid For a visual reference, see Figure 1, which illustrates the "Left" and "Right" sides of the bi-directional meter prover.
4.1.8 targeted BPV: A term associated with atmospheric tank prover calibration, and refers to adjusting the scales to an even nominal value, such as 500 gallons or 1000 gallons.
Traceability refers to the ability to relate the results of a measurement or the value of a standard to established references, typically National or International Reference Standards This relationship is maintained through a continuous, unbroken chain of controlled comparisons, each accompanied by specified uncertainties It is essential to emphasize that traceability is only valid when scientifically rigorous evidence is consistently gathered, demonstrating that the measurement yields documented results with quantified total measurement uncertainty.
Symbols
This publication employs a combination of upper and lower case notation for symbols and formulas For instance, the symbol T represents the Temperature of the Liquid To enhance clarity, additional letters are appended to symbols, with specific meanings: “m” denotes a meter (Tm), “p” indicates the meter prover (Pp), and “tm” refers to the test measure (Ttm).
SI International System of Units (e.g bars, cubic meters, kilograms, degrees C) USC US Customary Units (e.g psig, cubic feet, pounds, degrees F)
ID Inside Diameter of the prover pipe
OD Outside Diameter of the prover pipe
WT Wall Thickness of the prover pipe Liquid Density
The density of the liquid is measured in kilograms per cubic meter (kg/m³), referred to as DEN The base density of the liquid, also expressed in kg/m³, is denoted as DENb Additionally, the observed density of the liquid at base pressure is indicated by DENobs, which is also measured in kilograms per cubic meter Furthermore, RHOb represents the base density of the liquid used for prover calibrations.
The RHOp represents the density of the liquid in the prover, which is essential for prover calibrations RHOtm indicates the density of water in the test measure, crucial for waterdraw calibrations RHOmp refers to the density of the liquid in the master prover, used for master meter calibrations, while RHOmm denotes the density of the liquid in the master meter, also for master meter calibrations Additionally, temperature plays a significant role in these measurements.
Deg C Celsius temperature scale Deg F Fahrenheit temperature scale
T Temperature in deg F or deg C units
Td Temperature of detector mounting shaft or displacer shaft on displacement prover with external detectors and a captive displacer.
Ttm Temperature of water in test measure, in deg F or deg C units
Tp Temperature of liquid in Prover in deg F or deg C units
The Tm temperature refers to the liquid temperature measured in meters, expressed in either degrees Fahrenheit or degrees Celsius Similarly, Tmm indicates the temperature of the liquid in the Master Meter, while Tmp represents the temperature in the Master Prover, both also in degrees Fahrenheit or degrees Celsius Pressure measurements are provided in kilopascals (kPa), with absolute pressure represented as kPag and gauge pressure as psi (pounds per square inch) Additionally, psia denotes pounds per square inch in absolute pressure, while psig indicates pounds per square inch in gauge pressure.
P Operating pressure in gauge pressure units
Pb Base pressure, in psi or kPa pressure units
The pressure of the liquid in the prover is measured in gauge pressure units (Pp), while the pressure in the master prover is also expressed in gauge pressure units (Pmp) Additionally, the pressure of the liquid in the master meter is represented in gauge pressure units (Pmm) It is essential to consider correction factors for accurate measurements.
E Modulus of Elasticity of the steel prover
F Compressibility factor of the liquid
Fp Compressibility factor of the water in the prover Fmp Compressibility factor of the water in the master prover Fmm Compressibility factor of the water in the master meter
Gl Linear coefficient of thermal expansion
Ga Area coefficient of thermal expansion
Gc Cubical coefficient of thermal expansion of the prover Gcm Cubical coefficient of thermal expansion of the test measure Volumes
The BMV Field Standard Test measures the base volume as indicated on the calibration certificate The BMVa Field Standard Test adjusts this base volume according to the scale reading Additionally, BPV refers to the Base Volume of the Prover under standard conditions.
CPV Calibrated Prover Volume as determined by a single calibration run
SR Scale Reading of the Field Standard Test MeasureSRu Upper Scale Reading of Atmospheric Tank ProverSRl Lower Scale Reading of Atmospheric Tank Prover
S ECTION 9—P ART 1—M ETHODS OF C ALIBRATION FOR D ISPLACEMENT AND V OLUMETRIC T ANK P ROVERS 5
Applications
Prover calibration is first conducted at the manufacturing plant where the prover is constructed and is typically repeated after installation at the operational site Following this initial calibration, regular calibrations are scheduled to ensure ongoing accuracy and reliability.
There are many reasons to account for the necessity of frequent and regular recalibration of a prover, some of these, but not all, are as follows:
• Frequency of use and general wear
• Detector maintenance, wear, adjustment or replacement
• Deposit build-up on the prover walls (e.g wax, paraffin, etc.)
• Loss of, or damage to, the internal coating of the prover walls
• Physical damage to the prover
• Maintenance on the calibrated section of the prover
• Over-pressurization of the prover
• Constructional changes to the prover
Prover calibrations are often witnessed by the interested parties See Appendix A for information on calibration witnesses.
Regular re-calibration of all provers is essential to minimize measurement errors and reduce overall uncertainty in prover volume The frequency of re-calibration varies based on the prover's usage and the volume throughput at the facility For detailed guidance, refer to API MPMS Chapter 4.8, “Guide to the Operation of Provers.”
Consideration of the following items will help to establish the possible loss exposure and measurement risk, and will help to determine a required frequency of calibration for all provers:
• Volume through the metering system associated with the prover between prover calibrations
• Number of meters regularly proved by the prover and their frequency of proving
• The total yearly value of each product metered
• Service conditions and properties of products being metered and proved
• Whether the prover is portable or stationary
• The different types products being metered
• The range of properties of liquids being metered
• The required yearly maintenance and repair
• The total overall condition, including detectors and sphere displacer
Portable provers often operate under harsher conditions, making it essential to consider their total annual road usage when determining recalibration frequency It is important to closely monitor and assess whether portable provers require more frequent recalibration compared to stationary provers.
Current industry standards dictate that prover recalibration should occur every one to five years, depending on factors such as wear and tear, measurement risk management, and volume of loss exposure In certain extreme situations, recalibrations may be required as frequently as every three to six months For more details on calibration frequency, refer to Appendix B and API MPMS Chapter 4.8.
TYPES OF PROVERS
The following describes the most common types of provers See other sections of API MPMS Chapter 4 for additional detail on prover design.
Displacement Type Unidirectional Provers With Free Displacers
• Unidirectional—Sphere Provers with Mechanical Detectors
Unidirectional provers can be categorized into two main types based on how the displacer is managed The first type, the manual-return unidirectional prover, utilizes a section of pipeline as the prover section, with detector switches placed at specific points to define the calibrated volume A displacer-launching device is positioned upstream, and receiving facilities are located downstream, typically using conventional scraper traps During a proving run, a displacer is launched to displace the reference volume and is then manually returned to the launch site, though this method is now less common The second type, the circulating-return unidirectional prover, also known as the endless loop, features a piping arrangement where the downstream end crosses over the upstream end This design allows the displacer to be transferred from the downstream to the upstream end without removal from the prover, with detectors positioned within the looped section Endless prover loops can be operated either manually or automatically.
Displacement Type Bi-directional Provers with Free Displacers
• Bi-directional—Sphere Provers with Mechanical Detectors
• Bi-directional—Piston Provers with Magnetic Detectors and Check Valves
• Bi-directional—Piston Provers with Mechanical Detectors and Check Valves
Bi-directional provers come in three types: the sphere prover with mechanical detectors, the piston prover with magnetic detectors and check valves, and the piston prover with mechanical detectors and check valves These provers feature a pipe length that allows a displacer to move back and forth, triggering a detector switch at each end of the calibrated section To enable flow reversal through the prover, suitable supplementary pipe-work and a reversing valve assembly, which can be manually or automatically operated, are utilized While the main body of the prover is typically a straight pipe, it can also be contoured or folded for space efficiency or mobility In the contoured design, a sphere serves as the displacer, whereas a piston or sphere can be used in the straight-pipe configuration.
Displacement Type Meter Provers With Captive Displacers
• Unidirectional Piston Provers with Optical (external) Detectors
A prover with a captive displacer features an attached shaft or rod that moves in unison with the displacer, maintaining a constant displacement except during calibration runs when it enters and exits the calibrated section This design results in equal upstream and downstream volumes when a shaft is connected to both sides of the displacer with equal area displacement Additionally, the system may include one or two other detector or guide rods linked to the captive displacer.
Provers with externally mounted optical detectors may experience differing thermal effects on steel, depending on the area and linear aspects If the prover chamber and the mounting defining the linear distance between the detectors are identical, the thermal effects would align However, often the prover chamber is constructed from stainless steel, while the mounting may utilize a special alloy with a different thermal expansion coefficient Consequently, for accurate prover calibration, it is essential to measure both the prover barrel temperature and the detector temperature.
Displacement Type Meter Provers with Multiple Volumes
In the case of a displacement prover with multiple volumes, each volume is treated as an independent prover unit, requiring individual calibration Each calibration must adhere to the same standards outlined in the detailed calibration procedures For reference, Figure 2 illustrates the different detector switch configurations applicable to multiple volume provers.
S ECTION 9—P ART 1—M ETHODS OF C ALIBRATION FOR D ISPLACEMENT AND V OLUMETRIC T ANK P ROVERS 7
Atmospheric Tank Provers
An atmospheric tank prover is a volumetric vessel featuring an upper neck, sight glass, scale, and conical sections, typically divided by a cylindrical section Various types of atmospheric tank provers are distinguished by the method used to define their bottom "zero."
The bottom-weir type prover features a bottom neck located beneath the lower cone, which may include a sight glass and scale Regardless of these additions, it is characterized by a fixed bottom "zero" established by the weir.
The dry-bottom type prover is characterized by the absence of a bottom neck beneath the lower cone In this design, the closed bottom drain valve establishes the bottom "zero," similar to the functionality of a field standard test measure.
The wet-bottom type prover features a bottom neck located beneath the lower cone, equipped with a sight glass and scale The "zero" point is established by the scale's "zero," allowing for practical readings that may occur both above and below this reference point in the lower neck.
EQUIPMENT
Changes in fluid properties, operating conditions and equipment components may affect the uncertainty of the volume relative to the volume obtained at calibration conditions.
Prover Detector Switches
A detector switch is a high precision device mounted on a prover, which is used to detect the passage of a displacer The calibrated volume of a prover is the amount of fluid that is displaced between two detector switch positions Additional detector switches may be used if more than one calibrated volume is required on the same prover, or they can also be used to signal the entrance of a displacer into the sphere resting chamber Several types of detector switches are described below.
The mechanical detector switch is mainly utilized with an elastomeric sphere displacer, although it can also be applied with piston displacers It activates when the displacer makes contact with a rod or ball extending into the prover pipe, resulting in the opening or closing of a switch through mechanically or magnetically driven contacts.
Mechanically actuated detectors can be either pressure balanced or not Pressure balanced detectors feature ports or passages that ensure equal pressure distribution on the switch rod, effectively counteracting the influence of pressure on the detector's activation.
6.1.2 Proximity-Type Magnetically Actuated Detector Switches
This detector switch is specifically designed for use with piston displacers and is externally mounted, ensuring that no components extend into the prover pipe The mechanism of the detector switch is activated by an excitor ring on the non-magnetic piston displacer as it moves beneath the proximity-type detector switch.
The traditional design of an optical detector features a light source and a photoelectric detector cell positioned directly opposite each other on a compact metal base plate During standard operation, the light source emits a beam that directly illuminates the photoelectric cell This beam is interrupted by a lever or plate attached to a moving rod on the displacer, which triggers the detector switch when the light beam is broken.
Launching Chambers and Transfer Chambers
In both unidirectional and bi-directional meter provers, a designated area is necessary for the displacer to rest when not in use In bi-directional meter provers, this area is known as a launching chamber, and sphere displacers require launch chambers at both ends of the prover pipe However, piston type bi-directional provers do not need expanded launch chambers since the flowing stream is diverted upstream of the launch chambers using check valves Conversely, unidirectional meter provers utilize a transfer chamber along with valves to store the sphere away from the flowing stream and facilitate the re-launching of the displacer when needed.
Sphere Interchanges
Unidirectional provers utilize a sphere interchange to transfer the sphere from the downstream to the upstream end of the proving section This transfer can be achieved through various combinations of valves and devices designed to minimize bypass flow It is crucial to ensure a leak-tight seal between the upstream and downstream sides, which must be verified prior to the sphere reaching the first detector switch in the proving section.
Four-Way Valves
The four-way diverter valve is essential for bi-directional provers, enabling the change of flow direction while managing low-pressure differentials It features a double block and bleed mechanism to ensure the valve's sealing integrity, which must be confirmed before the sphere triggers the first detector To facilitate the sphere's movement during valve operation and guarantee that the valve is completely closed before contacting the first detector switch, a pre-run section of pipe is incorporated into the prover design, tailored to the specified flow rate.
Displacers
In a displacement prover, the displacer creates a seal that ensures the flow moves through the measuring section without bypassing it, which is essential for accurate calibration This displacer also activates detector switches that determine the prover's volume There are three main types of displacers used in this process.
The most common sphere displacer is the inflatable type It has a hollow center with one or more valves used to inflate the sphere
A common practice for filling the sphere involves using a 50/50 mixture of glycol and water, although water or glycol can be utilized individually for specific applications The sphere is generally inflated to about 2% to 5% larger than the internal diameter of the calibrated section of the prover.
The primary elastomers utilized in sphere displacers are neoprene, urethane, and nitrile, each serving distinct applications It's important to note that no single material is universally suitable for every use Additionally, the displacer composition employed during factory calibration may differ from that of the displacer calibrated for regular field operation.
In some cases, usually in displacement provers below 6" in size, sphere displacers are made of solid nitrile, urethane or neoprene rubber, manufactured to a predetermined oversize and cannot be inflated.
Piston displacers, typically crafted from lightweight aluminum or non-magnetic stainless steel, are integral components in bi-directional provers These cylindrical pistons feature seals and wear-rings at both ends, along with an exciter ring that activates a proximity detector switch as the piston moves beneath it The construction of piston seals commonly utilizes Teflon and polyurethane elastomers for optimal performance.
6.5.3 Captive Displacers—Piston with Shaft (Rod)
Certain provers use a captive displacer piston, which is usually made from aluminum or stainless steel These captive displacers feature Teflon-based elastomeric seals that make contact with the inner walls of the prover's measuring section.
The displacer is typically connected to a shaft or rod that extends outside the prover, facilitating its movement to the upstream end of the measuring section This shaft not only aids in positioning the displacer but also activates the detector switches Certain captive displacers feature dual self-checking seals, similar to block and bleed valves Additionally, some models incorporate an internal valve within the piston, equipped with elastomeric seals to prevent flow through the piston during operation.
S ECTION 9—P ART 1—M ETHODS OF C ALIBRATION FOR D ISPLACEMENT AND V OLUMETRIC T ANK P ROVERS 9
Valves, Relief Valves, Drains and Vents
The unidirectional prover sphere handling interchange, the bi-directional prover four-way valve, and all valves located between the calibrated section of the prover and the calibration unit, shall seal without any visible internal or external leakage when in a closed position
In a unidirectional prover, it is crucial for the sphere handling interchange to ensure that the four-way valve, or the older four-valve systems in a bi-directional prover, along with any valve bypassing the prover, seals completely when closed Incomplete closure of a prover valve can lead to significant measurement errors.
Double-block-and-bleed valves are essential for leak detection in provers, featuring a double-seated design with a space between the seats connected to a bleed valve By opening the bleed valve, operators can verify that the main valve is leak-free, as any leakage will be evident through the bleed In some systems, leakage is directed to a visible location, while in others, it is linked to a pressure gauge, indicating leakage through pressure changes.
During calibration, the prover and its associated piping may include relief, drain, and vent valves, which typically discharge into the drainage system, potentially concealing unknown leaks It is essential that all these valves provide a method for visual verification of leakage or be isolated during each calibration run.
Regular inspections of all valves in the prover system and in-line, up to the test measures, are essential to identify any external leakage while operating in an open position Detecting and addressing any leakage is crucial, as it can lead to inaccuracies in the certified volume.
Temperature and Pressure Indicators
Temperature measurement is essential at the point where the liquid exits the prover This is typically achieved using certified or calibrated mercury-in-glass thermometers or electronic temperature devices.
When there is a significant temperature difference between the ambient air and the calibration liquid, a thermometer stem correction may be necessary as per API MPMS Chapter 7 However, stem corrections are generally not required for prover calibrations, which typically occur close to ambient conditions The thermometer should have a scale with increments no greater than 0.2°F (0.1°C) and must maintain an accuracy of ±0.1°F (±0.05°C).
A certified thermometer with a calibration accuracy certificate traceable to NIST or another national metrology institute must be present on-site This certified thermometer is essential for verifying the accuracy of all working thermometers used in calibration procedures Both the certified and working thermometers should agree within ± 0.1°F (± 0.05°C) Alternatively, working thermometers that have been verified at three points within one year and a day of the prover calibration, using a thermometer with national standard traceability, may be utilized, provided they also agree within ± 0.1°F (± 0.05°C).
Electronic temperature measurement devices can be utilized for calibration when there is consensus among all parties involved It is essential to adhere to the guidelines specified in API MPMS Chapter 7 “Temperature Measurement” when using these devices Additionally, prior to each calibration, the device must be verified against a calibrated or certified thermometer with an accuracy of ± 0.1°F (0.05°C).
For accurate waterdraw calibrations, it is essential to measure pressure downstream of the displacer A connection for a pressure measuring device should be installed between the prover's water outlet and the pipework before the water enters the test measures Due to the low flow rate through the solenoid valve, which causes minimal pressure drop, it is permissible to place the pressure measuring device on the calibration unit.
Pressure measurements should be conducted using a calibrated dial type pressure gauge, accurate to one pound per square inch (1-psig) increments, accompanied by an on-site certificate of calibration accuracy This certificate must be traceable to NIST or a recognized national metrology institute and is valid for one year and a day from the calibration date Electronic or digital pressure gauges may also be utilized if all parties agree, but they must meet the same readability and accuracy standards as dial gauges, including the requirement for an on-site valid calibration certificate Additionally, all electronic pressure readings must be rounded to the nearest one pound per square inch (1-psig) for documentation purposes.
Hoses, Pumps and Connections
All hoses and connectors must operate without leaks and be compatible with the calibration liquid and expected maximum pressures For calibrations, wire-wound hoses are recommended to prevent collapse and minimize inflation due to pressure However, soft hoses may be permitted on the inlet side for water calibrations, as their inflation does not affect the calibration results Additionally, it is essential to keep the total length of hoses as short as possible to reduce the volume of liquid contained within them.
For effective calibration, it is essential that the pump used to circulate water is in optimal condition and free of leaks An electric motor-driven centrifugal pump is ideal, as it allows for easy adjustment of flow rates while maintaining low outlet pressure Typical pump capacities range from 20 to 100 gallons per minute (gpm), but larger pumps may be necessary for calibrating bigger provers A static head pressure of 30 to 50 pounds per square inch gauge (psig) is generally adequate, while higher pressures should be avoided to prevent issues such as hose swelling, leaking, or bursting, particularly at hose connectors.
Solenoid Valves and Logic Circuits
Solenoid valves and logic circuits may be used for any method of prover calibration The discussion below is a short introduction to the subject.
Solenoid valves play a crucial role in waterdraw calibrations by utilizing an electromagnetic plunger and an orifice, which can be adjusted with a disc or plug to control fluid flow The flow is restricted or completely shut off when the electromagnet activates the magnetic plunger These valves typically feature orifice sizes ranging from 3/32 to 1/4 inch and can function as either two-way or three-way valves.
Solenoid valves play a crucial role in controlling water flow during testing by stopping it to drain or redirecting it to the test measure Their use minimizes uncertainty in valve closure, ensuring that the test measure stops filling precisely when the displacer activates the second detector switch Additionally, solenoid valves facilitate consistent recording of the stop/start sequence during prover calibration, maintaining exact repeatable conditions They also ensure that the displacer reaches the same position each time it triggers the detector switch, enhancing the accuracy of the testing process.
6.9.2 For Waterdraw, Master Meter and Gravimetric Calibrations
A logic circuit is an electronic device that controls specific operational sequences within a system by managing signal transmission based on input signals These circuits are essential for calibration and play a crucial role in locating and tracking the position of a displacer When a detector switch is activated, the logic circuit alerts the operator through visible or audible signals regarding the position of the sphere displacer Additionally, solenoid valves positioned above the test measures operate in conjunction with the prover detector switches via the logic circuit.
• A single cable to both prover detector switches
In this configuration any time a detector switch is gated the logic circuit will NOT tell the operator specifically which detector switch was actuated.
• A separate cable to each prover detector switch.
In this configuration any time a detector switch is gated the logic circuit will tell the operator specifically which detector switch was actuated.
Prover calibrations can be conducted without logic circuits by directly wiring prover switches to solenoid valves Operators must closely monitor the activation of detector switches and solenoid valves to track the sphere displacer's location, as external signaling devices will be unavailable However, the general industry practice favors the use of logic circuits when they are accessible.
Field Standard Test Measures
Field standard test measures are essential for the waterdraw calibration method, providing accurate volume measurements Typically constructed from stainless steel, these measures serve as volumetric standards in the calibration of liquid provers.
Section 9, Part 1 discusses the calibration methods for displacement and volumetric tank provers, emphasizing the importance of using vessels that meet specific design criteria and are calibrated by recognized institutions like NIST Test measures typically range from one to 1000 gallons, with 500 gallons being the most commonly used size Detailed information regarding the calibration methods, frequency, and usage of these test measures is available through API.
MPMS Chapter 4.7 “Field Standard Test Measures.”
Test measures can have both "to contain" and "to deliver" volumes When utilizing the "to deliver" volume, these measures are filled, drained, and kept wetted prior to use For calibration purposes, only the "to deliver" volume is applicable, as "to contain" volumes are not suitable for prover calibrations This is due to the requirement for test measures to be completely clean and dry before each filling, which is often impractical in field operations.
Two adjustable spirit levels are typically mounted at right angles on the upper cone of a test measure, equipped with sealable adjusting screws and protective covers For calibration preparation, the test measure should be filled with water and leveled using its legs, followed by verification with a precision machinist's spirit level in two perpendicular directions If necessary, further adjustments to the leveling system may be made to ensure alignment with the machinist's level Once aligned, the spirit levels should be sealed and protected This verification and adjustment process is essential for all test measures before they are sent to standards agencies like NIST for calibration, ensuring consistency with the precision machinist's spirit level In smaller test measures, circular bubble levels may be utilized.
The NIST Report of Calibration for field standard test measures outlines the criteria for assessing the level state of any test measure filled with water In the event of a discrepancy between the permanently mounted levels and a precision machinist's spirit level used on the neck's top, the definition of the level position provided in the NIST Report shall take precedence.
Master Meter
A master meter is essential for calibrating master meter provers, utilizing highly accurate meters known for their excellent linearity and repeatability To maintain their integrity, these meters require annual inspections Regular reviews of the master meter calibration factors are necessary to ensure proper performance Installation and operation of the master meter must comply with API MPMS Chapter 5, and appropriate pressure and temperature instrumentation should be integrated into the meter run.
Master Prover
A master prover must be designed to operate alongside the master meter, adhering to the specifications outlined in API MPMS Chapter 4.2 It is important to note that the master prover should not be calibrated using the master meter method Additionally, the prover should include pressure and temperature instrumentation at both the inlet and outlet To ensure safety and reliability, all drain and vent valves on the master prover must be of the block and bleed type or equipped with alternative leakage detection methods.
Mobile Equipment
Prover calibration equipment is usually installed on a truck or trailer, and it is crucial for this equipment to be robustly built and securely fastened to avoid any deformation or damage during transport, use, or storage.
Gravimetric Equipment
Reference to the Gravimetric Method and Equipment can be found in Part 4 of this standard, which is currently under development.
DOCUMENTATION AND RECORD KEEPING
All observation data must be recorded in ink or automatically collected and reported by a flow computer with audit trail capabilities Prior to signing any documents, all observation data should be proofread against the input data used for calculations.
12 C HAPTER 4—P ROVING S YSTEMS ments In case of discrepancies or errors discovered at a later date the hand written observation data shall be used to correct the final volume
The Calibration Certificate Package must feature a Calibration Report that clearly displays the date of the prover calibration on its front Additionally, all relevant items related to the calibration should be documented within the Calibration Certificate Package.
For the Waterdraw, Master Meter and Gravimetric Methods:
• the location of the prover
• the serial number of the prover
• the serial number or seal number for each detector switch
• the owner or operator of the prover
• the material of construction of the prover
• the inside diameter of the prover
• the wall thickness of the prover
• the temperature indicators and pressure indicator used
• Calibration Certificates for all the temperature and pressure indicators used
• the displacer type, the size, and the durometer (if applicable)
• in the case of multi-volume displacement provers a a clear identification of the detectors used for this calibration b the physical location of each detector
• A copy of the handwritten observation documentation (signed by all parties as witness to the original observation data);
• A copy of the calculation and summary generated documentation
For the Waterdraw Calibration Method:
• the field standard test measures used
• copies of the NIST Reports of Calibration for all of the field standard test measures used.
For the Master Meter Calibration Method:
• the serial number of the master prover
• the type of master prover
• the material of construction of the master prover
• the inside diameter of the master prover
• the wall thickness of the master prover
• Calibration Certificate Package for the Master Prover
• the type of master meter
• the size of master meter
For the Gravimetric Calibration Method:
• Calibration Certificates on the Standard Weights
• Calibration Certificate(s) on the Weigh Scale
• Note: This method under development so list is incomplete
CALIBRATION TROUBLESHOOTING GUIDE
Full records of the complete data collected during all the calibration runs, whether valid or invalid, should be recorded and kept in a systematic manner.
The primary source of a questionable measurement can normally be identified as one or more of the following as specific to the calibration method:
• Hydrocarbons in the system (when water is the calibrating medium)
S ECTION 9—P ART 1—M ETHODS OF C ALIBRATION FOR D ISPLACEMENT AND V OLUMETRIC T ANK P ROVERS 13
• Errors in determining test measure measurements
• Damaged or under-inflated sphere displacer
• Damaged or improperly fitting seals
• Wear in the piston displacer
• Contamination to the circulating (calibration) medium
• Damaged or contaminated field standard test measures (for the waterdraw method)
• Damaged master meter or master prover (for the master meter method)
• Damaged weighing device or weight standards (for the gravimetric method)
• Damaged temperature and pressure measuring devices
• Damaged or deteriorating internal surfaces of the prover
• Damaged or leaking sphere interchange
• Damaged or leaking four-way valve
Each of the above sources must be carefully examined until the cause of the abnormal measurements is found.
Calibration is typically conducted by one technician in the presence of several witnesses, who are often representatives from associated companies with vested interests in the custody transfer functions at the facility Involvement may also include company employees from various divisions and occasionally government officials at different levels All witnesses share equal responsibility for the calibration's success, emphasizing the importance of their active participation in all necessary calibration activities.
To ensure a swift and precise calibration process, all witnesses must be prepared to assist, advise, and engage in any necessary tasks.
• Validate the traceability of equipment by checking the calibration dates and the availability of valid calibration certificates and other records
• Witness the cleanliness and interior condition of the prover.
• Witness the inspection and sizing of the sphere displacers or pistons.
• Witness the inspection and all maintenance of the detector switches.
• Witness the verification of the temperature and pressure devices.
• Witness all general set-up activities including setting up the liquid circulation, venting of the air, and leak checking.
• Witness patrolling of the area for leaks during the calibration runs.
• Witness checking the integrity of block valves during runs.
• Witness checking the integrity of four-way valves during runs.
• Witness checking the integrity of sphere interchanges during runs.
• Witness the filling and general operation of the test measures (waterdraw) or the general operation of the master meter and master prover.
• Witness the filling and general operation of the prover being calibrated.
• Witness and check that the test measures are level when read (waterdraw).
• Witness test measure scale readings and interpolations (waterdraw).
• Witness temperature and pressure readings and interpolations.
• Witness the draining of test measures and the adherence to draining times (waterdraw).
• Witness the accurate determination of necessary temperatures and pressures.
• Keep or witness the recording (hand written) of all the calibration data as log entries.
• Where requested, offer advice in troubleshooting all problems and difficulties, and assist with the reading of thermometers and gauges.
• In general, witness the resolution of all the operations, processes and problems encountered.
A METHOD FOR DETERMINING THE FREQUENCY OF CALIBRATING PIPE PROVERS
This article presents a method for estimating the frequency of prover recalibration, offering a potential approach to determine suitable time intervals between calibrations Readers are encouraged to evaluate the applicability of this method in relation to their operational practices and the calibration intervals chosen for their pipe provers.
Each pipe prover operates as a distinct unit with unique usage patterns, varying conditions, and specific wear characteristics, leading to the necessity for individualized calibration frequencies The key consideration is the prover's ability to maintain its current calibrated volume If the prover volume remains within defined tolerances, recalibration is unnecessary until a significant change occurs.
The method establishes a threshold for allowable changes in prover volume at 0.050% It utilizes the actual volume change observed between successive calibrations, along with the time interval in months between these calibrations, to estimate the projected time frame in months for when a volume change of 0.050% is anticipated.
The debate centers on whether the allowable change in prover volume should be set at 0.050% or 0.020% While some argue for the stricter tolerance of 0.020% based on calibration standards, this could lead to unnecessary frequent calibrations of certain provers Therefore, a compromise of 0.050% is considered a more reasonable approach.
To ensure clarity, the example below utilizes a volume change of 0.050% If the operating company's policy specifies a different tolerance, such as 0.030%, this value should replace the 0.050% in the example It is important to note that no tolerance exceeding +0.05% should be applied, and this method is only valid after a baseline has been established.
To apply this method, first calculate the number of months since the last calibration compared to the previous prover calibration, along with the percentage of volume change between the two calibrations With this information and the permissible change of 0.050%, you can determine the estimated months until the next calibration is necessary.
Time to Next Calibration (months)
The prover is due for recalibration in 25 months, with the next projected calibration date estimated around 8/01/2006 This date can be determined by calculating the time and volume change from the calibration volume recorded on 7/02/2004 to the new volume at the time of the upcoming calibration.
The following guidelines should be adhered to with regard to the use of the above calculation:
• Under no circumstances should the projected time to the next calibration exceed 60 months 5 years
• If the allowable change in volume is less than absolute 0.02% (i.e – 0.02% or + 0.02%), then set the projected time to the next calibration at 12 months
If any mechanical repairs, alterations, or changes that impact the certified volume of the prover are performed, it is essential to calibrate the prover immediately after the work is completed Following this, schedule the next prover calibration for 12 months later.
Figure 1—Bi-directional Prover Orientation of “Left” and “Right”
Figure 2—Examples of Multi-volume Prover Detector Switch Configurations
$WRWDORIVL[YROXPHVPD\EH DYDLODEOHIRUFDOLEUDWLRQLQWKLV FRQILJXUDWLRQ
$)RXU'HWHFWRU6ZLWFK3URYHU ZKHUHWKHGHWHFWRUVZLWFKHV DUHDGMDFHQWWRHDFKRWKHU
$WRWDORIVL[YROXPHVVKRXOG EHDYDLODEOHIRUFDOLEUDWLRQEXW YROXPH$%DQGYROXPH&' DUHVRVPDOOWKDWWKH\DUH FRQVLGHUHGQHJOLJLEOH
Invoice To (❏ Check here if same as “Ship To”)
❏Payment Enclosed ❏P.O No.(Enclose Copy)
❏Charge My Global Account No.
❏VISA ❏MasterCard ❏American Express ❏Diners Club ❏Discover
Print Name (As It Appears on Card):
Quantity Product Number Title Total
Subtotal Applicable Sales Tax (see below) Rush Shipping Fee (see below) Shipping and Handling(see below)
★ To be placed on Standing Order for future editions of this publication, place a check mark in the SO column and sign here:
Pricing and availability subject to change without notice
❏API Member(Check if Yes)
Ship To (UPS will not deliver to a P.O Box) Name:
Mail orders must be paid by check or money order in U.S dollars, unless you have an established account Additional charges include state and local taxes, a $10 processing fee*, and 5% for shipping Please send your mail orders to API Publications, Global Engineering Documents, 15 Inverness Way East, M/S C303B, Englewood, CO 80112-5776, USA.
Purchase Orders – Purchase orders are accepted from established accounts Invoice will include actual freight cost, a $10 processing fee*, plus state and local taxes.
Telephone Orders – If ordering by telephone, a $10 processing fee* and actual freight costs will be added to the order.
All purchases in the U.S are subject to state and local sales tax, and customers seeking tax-exempt status must submit their exemption certificate to Global For U.S orders, shipping is conducted through traceable methods, with most orders dispatched on the same day Subscription updates are mailed via First-Class Mail, and additional shipping options, such as next-day service and air service, are available for an extra fee For further details, please contact 1-800-854-7179.
For international orders, we offer standard shipping via air express courier, with delivery typically taking 3-4 days from the shipping date If you need your order urgently, next day delivery is available for an additional $20, provided the order is placed by 2:00 p.m MST For returns, please contact Global’s Customer Service at 1-800-624-3974 to obtain pre-approval, as a 15% restocking fee may apply Please note that special order items, electronic documents, and age-dated materials cannot be returned.
All orders for hardcopy documents require a minimum total of $50, which includes the $10 processing fee but excludes taxes and shipping costs If the subtotal of the documents and the processing fee falls below $50, the processing fee will be adjusted to meet the minimum order requirement.
API Members receive a 30% discount where applicable.
The member discount does not apply to purchases made for the purpose of resale or for incorporation into commercial products, training courses, workshops, or other commercial enterprises.
Available through Global Engineering Documents:
Phone Orders: 1-800-854-7179(Toll-free in the U.S and Canada)
303-397-7956 (Local and International) Fax Orders: 303-397-2740
Online Orders: www.global.ihs.com
MPMS 4.1, Introduction MPMS 4.2, Displacement Provers MPMS 4.4, Tank Provers MPMS 4.5, Master-meter Provers MPMS 4.6, Pulse Interpolation MPMS 4.7, Field- Standard Test Measures MPMS 4.8, Operation of Proving Systems
There’s more where this came from.
The American Petroleum Institute provides additional resources and programs to the oil and natural gas industry which are based on API® Standards For more information, contact:
• API Monogram® Licensing Program Phone: 202-962-4791
• American Petroleum Institute Quality Registrar Phone: 202-962-4791
• API Perforator Design Registration Phone: 202-962-4791
• API ISO/TS 29001 Registration Phone: 202-962-4791
• API Training Provider Certification Program Phone: 202-682-8490
• Engine Oil Licensing and Certification System (EOLCS) Phone: 202-682-8516
• API PetroTEAM™ (Training, Education and Meetings) Phone: 202-682-8195
Check out the API Publications, Programs, and Services Catalog online at www.api.org