GB/T 17286 Liquid hydrocarbons dynamic measurement proving systems for volumetric meters is divided into four parts:
——Part 1: General principles;
——Part 2: Pipe provers;
——Part 3: Pulse interpolation techniques
——Part 4: Guide for operators of pipe provers
This is Part 1 of GB/T 17286.
This part is developed in accordance with the rules given in GB/T 1.1- 2009.
This part replaces GB/T 17286.1-1998 Liquid hydrocarbons - Dynamic measurement - Proving systems for volumetric meters - Part 1: General principles. The following main technical changes have been made with respect to GB/T 17286.1-1998:
——the Foreword in ISO standard is deleted;
——the standard structure is adjusted, the suspension sections in the original ISO standard are deleted, and some secondary title names are added;
—— the explanation of "tank prover systems" is given in 3.1 to unify the format;
—— the term "counting mechanism" in 4.6 and the subsequent paragraphs is changed to “tolerance modulator”；
——as for 4.9, the sentence “or if four individual unadjusted proving runs are made without any two successive runs checking within an acceptable repeatability” in the ISO standard is changed to “or if four individual unadjusted proving runs are made without any three successive runs checking within an acceptable repeatability”;
—— the titles of Clause 5, 6, 7 and 8 are modified;
——some inaccurate and irregular statements in the standard are modified.
This part, by translation, is identical to the international standard ISO 7278 - 1: 1987 Liquid hydrocarbons - Dynamic measurement - Proving systems for volumetric meters - Part 1 : General principles.
The Chinese document corresponding to the normative documents given in this part is as follows:
——GB/T 17287-1998 Liquid hydrocarbons - Dynamic measurement - Statistical control of volumetric metering systems (ISO 4124: 1994, IDT)
This part is under the jurisdiction of SAC/TC 355 National Technical Committee on Petroleum and Gas of Standardization Administration of China.
The previous edition replaced by this part is as follows:
——GB/T 17286.1-1998.
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Introduction
GB/T 17286.1-1998 is drafted according to Part 1 of ISO 7278 Liquid hydrocarbons - Dynamic measurement - Proving systems for volumetric meters, it is of significant guidance in the dynamic measurement of liquid hydrocarbons in China. It is necessary to revise GB/T 17286.1-1988 in order to meet the needs of the continuous development of China's petroleum industry and promote international trade and exchanges. ISO 7278 provides detailed descriptions of pipe provers, tank provers and pulse interpolation techniques. Parts covering other types of proving systems may be added as the need arises.
The purpose of proving a meter is to determine its relative error or its meter factor as a function of flow rate and other parameters such as temperature, pressure and viscosity.
The purpose of determining the relative error is to find out whether the meter is working within prescribed or specially accepted limits of error, whereas the meter factor is used to correct any error in the indication of a meter by calculation.
Liquid hydrocarbons - Dynamic measurement -
Proving systems for volumetric meters -
Part 1 : General principles
1 Scope
This part of GB/T 17286 provides general principles for proving systems for meters used in dynamic measurement of liquid hydrocarbons.
2 Normative references
The following referenced documents are indispensable for the application of this document. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies.
ISO 4124 Liquid hydrocarbons - Dynamic measurement - Statistical control of volumetric metering systems
3 Prover
3.1 Types of prover
The following types of proving systems are in use:
a) tank prover systems: made of metal (stainless steel, carbon steel, etc.), of the specified structure, with certain volume, and may be used as a means of standardization of transfer
b) pipe provers: bidirectional and unidirectional. Pipe provers with precision tubes as described in 6.7 are available for special applications.
c) master meters: a meter is used as a means of standardization of transfer. Master meters shall be verified as qualified under the condition close to the actual working condition, and then the working meter shall be verified by volume comparison method. This method may produce additional errors.
3.2 Setting of provers
Provers may be used either connected (fixed or mobile) to the metering station or in a central proving station to which the meters or the measures can be taken to be proved unconnected.
3.3 Minimum pulses
In order to limit the maximum error to ±0.01% when using a pulse generator for proving, at least 10000 pulses shall be obtained from the meter per proving run. This number of pulses may be reduced by pulse-interpolation techniques which allow either the use of meters with fewer pulses per unit volume or reduction of the prover volume.
4 General considerations
4.1 Proving requirements
A meter shall be proved at the expected operating or prescribed or agreed rates of flow, under the pressure and temperature at which it will operate and on the liquid which it will measure. In situations where it is not feasible to prove the meter on the liquid to be metered, the meter shall be proved on a liquid having a density, viscosity and, if possible, temperature as close as possible to those of the liquid to be measured. A meter that is used to measure several different liquids shall be proved on each such liquid. Similar liquids may be used if a simple, known relationship exists between the relative error, flow rate and viscosity, provided that the uncertainty of measurement remains within acceptable limits. Generally, calibration shall take place at a flow rate equivalent to that at which the meter will be used.
A meter may be proved in different circumstances as follows:
a) Initial proving. This shall be carried out on the permanent location or in a central station where the expected conditions of operation can be reproduced. The initial proving shall make it possible to determine the relationship between the relative error (or meter factor) and different parameters such as viscosity or temperature.
b) Occasional or periodical proving. If a simple relationship between the relative error (or meter factor) and influencing parameters can be determined, the meters shall be reproved periodically using a prover either on the site or in a centralised station. Otherwise, the meter shall be reproved on the site whenever significant changes in the influencing parameters, such as viscosity or temperature, occur. Regular provings are also needed to follow effects of mechanical changes.
4.2 Evaporation of liquid
Many petroleum liquids of high vapour pressures are measured by meter. If liquid evaporation during normal operation or proving could occur and affect measurement, the proving system shall provide means to avoid evaporation.
4.3 Factors affecting proving results
The proving of a meter is like a laboratory test: when properly done, it provides a high degree of repeatability, which is necessary for measurement accuracy. Its piping and the proving systems, which can contribute to measurement uncertainty, as there are in determining physical properties of the measured liquid. Furthermore, the proving system shall be maintained in good operating condition. Thorough inspection of provers and their ancillary equipment shall be made with sufficient frequency to ensure reproducibility of proving results. It is essential that meter performance data be observed, recorded and studied and that calculations be correct (see ISO 4124).
The accuracy and repeatability of the proving can be affected by observation errors in determining the opening meter reading or the closing meter reading, the test volume passing through or delivered to the prover and in reading temperature and pressure, and by implicit errors in computation in the process of correcting a measurement to standard conditions.
4.4 Meter proving procedures
Meter proving procedures including:
a) Standing start-and-stop procedure. It uses registers from which the opening and closing readings are obtained at no-flow conditions. Opening and closing of valves shall be performed rapidly.
b) Running start-and-stop procedure. It involves obtaining the opening and closing meter readings of the proof while the meter is in operation. This is accomplished by the use of auxiliary or secondary registers of high discrimination which can be started and stopped while the meter and primary register continue to operate.
4.5 Register
Every meter proof shall be made with the same register as is used in regular operation or with additional synchronised auxiliary registers for the running start-and-stop procedure [4.4 b)]. Inclusion of special auxiliary equipment such as the following is permitted: density selector, temperature compensator, and quantity-predetermining register. If employed, the auxiliary equipment shall be set and operative when making the proof runs. Time between proving runs shall be kept to a minimum.
4.6 Objectives to meter proving
There are two general objectives to meter proving which usually depend on the type of service.
a) To determine the error characteristics of a meter. The relative error of a meter can be determined by adjustment of its meter tolerance regulator according to the proving result. To give a meter factor of 1.0000 so that its indicated volume will be the volume of liquid actually delivered. This is the normal practice for a meter operating on intermittent deliveries, such as a tank truck meter or a loading rack meter at a terminal or bulk plant.
b) To determine its meter factor. The relationship between its meter factor and influencing parameters such as viscosity or temperature so that this factor or this relationship can be applied to the indicated volume to compute the gross volume delivered through the meter. This is the normal practice in the case of continuous or long-duration measurement.
4.7 Test run
When a meter is being proved, a test run shall be made, to equalise temperatures, displace vapours or gases and wet the interior of the prover. Subsequent proving test runs shall be made in the required range of flow rates and the registration adjusted as necessary.
Each calibration point for the same flow shall be repeated at least three times. Further repeats may be necessary, if specified. See ISO 4124.
4.8 Prove flow rate
When a meter is being proved to determine the meter factor at one or several flow rates, the procedure shall be essentially as specified in 4.7, except that no changes shall be made to the meter registration adjusting device between runs. Proof runs shall be made and recorded until the specified number of consecutive runs at the same flow rate agree within an acceptable repeatability, at which point the average of these three runs shall be accepted as the established meter correction factor for this flow rate.
4.9 Data Analysis
If the registration of a meter, during proving, is not changing in accordance with adjustments made to the register adjusting device, or if four individual unadjusted proving runs are made without any three successive runs checking within an acceptable repeatability, all phases of the proving operation shall be examined for the cause of the discrepancy. If the cause is not found, the meter and its register mechanisms shall be inspected for electronic or mechanical defects, repaired and proved before being returned to service.
4.10 Rounding off for data
The practical limit of accuracy in any observed value such as the volume in the reference vessel during a meter proof is 0.01%. For this reason, meter factors shall be rounded to four decimal places, not more and not less, for example 1.001 6.
4.11 Proving results
The results of proving can be adversely affected by the use of abbreviated tables, the unstandardized rounding of factors and/or intermediate calculations. The observed and computed data for all proving made in obtaining a meter factor or other expression of meter performance shall be reported on a suitable meter proving report form.
4.12 Proving of meter
Most of the procedures specified above have been for the proving of a single meter. If the meter to be proved is part of a battery of meters, it is necessary either to divert the stream from the selected meter to be proved through the prover or remove the meter to a central proving station.
5 Tank prover systems
5.1 As far as possible, the movement of all united supplementary bodies/matters inside the standard gauge shall be avoided, and in no case shall the gauge be adjusted to a given value by this means. The prover shall be recalibrated after any changes to components within the calibrated volume section such as gauge glasses, thermometer well or spray lines. The tank prover shall be designed in order to avoid any variation in its metrological characteristics and also to reduce clingage of liquid to the walls. The prover tank shall be inspected frequently for internal corrosion and for accumulation of sediment, rust, valve lubricant and other foreign material. Gauge scales shall be inspected frequently and the prover recalibrated if there is indication of gauge scale movements.
5.2 Proving with open prover tanks consists of a comparison of the change in volume of liquid indicated on the register and of the known volume in the tank prover. The liquid shall be passed through the meter under actual or simulated operating conditions of temperature, pressure, rate of flow, density and viscosity, into the prover, where its volume shall be determined from the gauge scales. The meter factor is the ratio between the actual volume measured with the prover converted to the conditions of temperature of the liquid during proving and the volume indicated on the meter register.
5.3 After a preliminary filling and draining of the prover tank, the lower level of the test liquid shall be determined. The meter to be proved shall then be stopped and the opening meter reading recorded. The proof run shall then be started by directing the liquid from the meter into the prover, maintaining the flow rate and meter pressure to simulate operating conditions. During the filling of the prover, the temperature of the metered stream near the meter shall be determined and recorded frequently enough to ensure art accurate average temperature of liquid as it passes through the meter. Flow shall be continued into the prover until the liquid reaches a suitable reading level. (Liquid levels in gauge glasses shall be determined by reading the bottom of the meniscus with transparent liquids, or the top of the meniscus with opaque liquids.) Flow shall then be stopped and stablized, the volume delivered to the prover promptly observed on the top gauge glass scale and recorded. Prover tank temperatures shall be taken, recorded and averaged, and the meter factor for the proof run calculated. The meter can be returned to service after proving.
5.4 Meter registration adjustments, if called for, can be made as required and subsequent proof runs can be made by repeating the proof run procedure just described.
5.5 In some types of open prover tanks, a top spray is used during the emptying of the prover to saturate the air drawn into the prover with the vapour of the test liquid to reduce evaporation of the test liquid during a subsequent proof run. Where this is done, the spray shall be turned on prior to each emptying of the prover and closed off prior to zeroing the liquid level.
5.6 There are certain variations inherent in the foregoing general procedure, arising primarily from design differences with respect to the method of establishing the starting liquid or zero level at the beginning of the proof run.
6 On-line pipe prover systems
6.1 In proving with pipe provers, checking of equipment prior to proving shall include inspection of all valves to ensure against internal leakage, and of the attachment of accessories used for proving and energizing electrical circuits. Thermometers and pressure gauges shall be checked periodically.
6.2 The entire liquid stream from the meter or battery of meters to be proved shall be diverted to flow through the pipe prover. In some permanently installed pipe proving systems, flow through the meter and the prover is continuous. Flow shall always be maintained through the meter and prover sections until stable conditions of temperature are reached. Vent connections shall be checked to ensure that the meter and prover sections are completely purged and that no pockets of air or vapour remain in the system.
6.3 A trial proving run is frequently conducted as a final check before starting the recorded meter proving. This is a good practice and is recommended for those provers where it can be readily accomplished. The trial run shall include checking of the electronic or other register. Observation of the readings from the trial run will often indicate equipment maladjustment not otherwise apparent.
6.4 Operations necessary to conduct proving runs will vary with the installations and can range from completely manual to fully automatic. The essential step will consist of operating a valve or combination of valves, which causes the metered stream to move the movable element (piston, sphere, etc.) through the calibrated section of the prover. The proving counter register shall be recorded prior to the start of every run or, if so equipped, it may be reset to zero. The switching operation shall be completed well before the movable element enters the calibrated section of the prover. In automatic systems, a pushbutton normally initiates a complete meter proof cycle and the timing of the operations is a matter of adjustment of the valve and the proper sequencing of the control system.
Foreword I
Introduction III
1 Scope
2 Normative references
3 Prover
4 General considerations
5 Tank prover systems
6 On-line pipe prover systems
7 Centralized prover systems
8 Master meter systems
