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GB/T 18604-2014 English PDF (GBT18604-2014)

GB/T 18604-2014 English PDF (GBT18604-2014)

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GB/T 18604-2014: Measurement of natural gas flow by gas ultrasonic flow meters

This Standard specifies measurement performance requirements of gas ultrasonic flow meters, flow meter body requirements, installation and maintenance, field verification test requirements, and flow calculation methods and measurement uncertainty estimates.
GB/T 18604-2014
NATIONAL STANDARD OF THE
PEOPLE REPUBLIC OF CHINA
ICS 75.180.30
E 98
Replacing GB/T 18604-2001
Measurement of natural gas flow by gas ultrasonic
flow meters
ISSUED ON: FEBRUARY 19, 2014
IMPLEMENTED ON: JUNE 01, 2014
Issued by: General Administration of Quality Supervision, Inspection and Quarantine;
Standardization Administration of the People's Republic of
China.
Table of Contents
Foreword ... 4
1 Scope ... 6
2 Normative references ... 6
3 Measurements, terms and definitions ... 7
4 Measurement principle ... 10
4.1 Fundamental principle ... 10
4.2 Influencing factors of accuracy measurement ... 11
5 Working conditions ... 11
5.1 Natural gas quality ... 11
5.2 Pressure ... 12
5.3 Temperature ... 12
5.4 Flow range and flow direction ... 12
5.5 Velocity distribution ... 12
6 Measurement performance requirements ... 13
6.1 Measurement performance requirements for multi-path gas ultrasonic flow meter ... 13 6.2 Measurement performance requirements for single-path gas ultrasonic flow meter ... 16 6.3 Influence of working conditions on measurement performance ... 16
7 Flow meter requirements ... 16
7.1 Composition and basic provisions ... 16
7.2 Meter body ... 17
7.3 Ultrasonic transducer ... 19
7.4 Electronic components ... 20
7.5 Flow computer ... 22
8 Installation requirements and maintenance ... 24
8.1 Installation influencing factors ... 24
8.2 Pipe configuration ... 25
8.3 Maintenance ... 27
9 Testing requirements for on-site verification ... 28
9.1 Testing contents and steps ... 28
9.2 Testing report ... 28
10 Flow calculation method and estimation of measurement uncertainty ... 29 10.1 Flow calculation under standard reference conditions ... 29
10.2 Determination of measured flow value under standard reference conditions... 31 10.3 Flow calculation under working conditions ... 31
10.4 Estimation of flow measurement uncertainty ... 31
Annex A (informative) Fundamental principles ... 35
Annex B (normative) Flow calibration of flow meter components ... 46
Annex C (normative) Exit-factory testing requirements ... 53
Annex D (informative) Documents available ... 56
Annex E (informative) Generation and prevention measures of acoustic noise ... 59
Annex F (informative) Performance verification tests of flow meter and flow conditioner ... 65
Annex G (informative) Monitoring and guarantee of on-site measurement
performance of flow meter ... 67
Foreword
This Standard was drafted in accordance with the rules given in GB/T 1.1-2009. This Standard replaces GB/T 18604-2001 ?€?Measurement of natural gas flow by ultrasonic flow meter?€?. Compared with GB/T 18604-2001, in addition to editorial modifications, main technical changes as follows:
- added three terms: maximum error shift with one path failed, speed of sound (SOS) deviation and metering package (see 3.2.17, 3.2.18 and
3.2.19);
- modified influencing factors of measurement accuracy; divided the
influencing factors into two categories: internal factors and external factors (see Clause 4);
- further specified the range of working temperature as medium temperature and ambient temperature (see 5.3);
- improved the requirements for zero-flow reading of multi-path gas ultrasonic flow meter; added two technical requirements of sound velocity deviation and maximum sound velocity difference; modified the maximum peak-to-
peak error requirement above the demarcation flow (see 6.1);
- added that according to the ambient conditions and working conditions, taking necessary thermal insulation, anti-freeze measures, and related
requirements for acoustic noise and pulsation to flow meter components
(including upstream and downstream straight pipe sections, flow meters
and flow conditioners, temperature tapping holes and sampling holes)
(see 8.1.1, 8.1.4, 8.1.5 and Annex E);
- modified relevant requirements for pipe installation upstream straight pipe section and flow conditioner installation position, temperature
measurement hole and sampling hole insertion depth, flow conditioner
(see 8.2.2, 8.2.5 and 8.2.7 and Annex F);
- added the requirements for on-site measurement performance of ultrasonic flow meters in routine maintenance (see 8.3.1 and Annex G);
- added the requirements that theoretical sound velocity is calculated
according to the method provided by AGA Report No.10 ?€?Speed of sound
in natural gas and other related hydrocarbon gases?€? and other methods
that are same as the calculation (see 9.1.3);
- added the calculation method and uncertainty estimation for mass flow and energy flow (see Clause 10);
- modified flow calibration to flow calibration of metering package; modified stability requirements for temperature and pressure, test traffic point (see B.2.2 and B.3.3);
- deleted the original Annex E ?€?Upper and lower pipe length requirements?€?; - added technical requirements of ?€?acoustic noise generation and prevention measures?€? (see Annex E);
- added technical requirements of ?€?flow meter and flow conditioner
performance verification test?€? (see Annex F);
- added technical requirements of ?€?monitoring and guarantee of flow meter on-site measurement performance?€? (see Annex G).
This Standard uses redrafting method to modify and adopt AGA Report No.10 ?€?Speed of sound in natural gas and other related hydrocarbon gases?€?.
This Standard was proposed by and shall be under the jurisdiction of National Technical Committee on Petroleum Gas of Standardization Administration of China (SAC/TC 355).
The drafting organizations of this Standard: National Oil and Gas Large Flow Metering Station Chengdu Sub-Station, PetroChina Southwest Oil and Gas
Field Branch, PetroChina Group Engineering Design Co., Ltd. Southwest
Branch.
Main drafters of this Standard: Duan Jiqin, He Min, Wen Dailong, Ren Gui, Huang He, Liu Yongming, Chen Huiyu, Wang Qiang, Chen Qi, Ni Rui.
Measurement of natural gas flow by gas ultrasonic
flow meters
1 Scope
This Standard specifies measurement performance requirements of gas
ultrasonic flow meters, meter body requirements, installation and maintenance, field verification test requirements, and flow calculation methods and
measurement uncertainty estimates.
This Standard is applicable to gas ultrasonic flow meters of plug-in transit-time difference method (hereinafter referred to as the flow meter), which are generally used for natural gas flow measurement in gathering devices, gas pipelines, storage facilities, gas distribution systems and customer metering systems. The use of external clamp-on gas ultrasonic flow meter can refer to this Standard.
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.
GB 3836.1, Explosive atmospheres - Part 1: Equipment - General
requirements
GB 3836.2, Explosive atmospheres - Part 2: Equipment protection by
flameproof enclosures ?€?d?€?
GB 3836.4, Explosive atmospheres - Part 4: Equipment protection by
intrinsic safety ?€?i?€?
GB/T 4208, Degrees of protection provided by enclosure (IP code) (IEC
60529)
GB/T 11062-1998, Natural gas - Calculation of calorific values, density, relative density and Wobbe index from composition
GB/T 13610, Analysis of natural gas by gas chromatography
GB/T 17747 (all parts), Natural gas - Calculation of compression factor GB/T 21446-2008, Measurement of natural gas flow by means of standard
orifice meter
SY/T 0599-2006, Metallic material requirements - Resistance to sulfide
stress cracking and stress corrosion cracking for gas surface equipment JJG 1030-2007, Verification Regulation of Ultrasonic Flowmeters
ISO 5167-1:2003, Measurement of fluid flow by means of pressure
differential devices inserted in circular cross-section conduits running full - Part 1: General principles and requirements
AGA Report No.10, Speed of sound in natural gas and other related
hydrocarbon gases
3 Measurements, terms and definitions
3.1 Measurements
See Table 1 for the measurements, names and symbols of unit used in this Standard.
Table 1 -- Measurements and names as well as symbols of unit
Symbol of
measurement Name of measurement
Measurement
dimension Symbol of unit
D Inner diameter of flow meter L m
kc Velocity distribution correction 1
L Path length L m
P Static pressure ML-1T-2 Pa
qv Volumetric flowrate L3T-1 m3/s
qm Mass flowrate MT-1 Kg/s
qe Energy flowrate L3T-1 J/s
qt Transition flowrate L3T-1 m3/h
Qn
Volume accumulation over a period
of time under standard reference
conditions
L3 M3
T Airflow thermodynamic temperature K
t Time T s
V Mean axial fluid velocity LT-1 m/s
Average flow velocity along acoustic
path LT
-1 m/s
X Axial distance L m
Z Compression factor 1
?? Path angle 1 rad
NOTE 1: In the measurement dimension, symbol L refers to length, symbol T refers to time, symbol M refers to mass and symbol refers to thermodynamic temperature.
NOTE 2: The symbols not listed in the table are explained in the text.
3.2 Terms and definitions
The following terms and definitions apply to this document.
3.2.1 transit-time difference method
A gas flow measurement method that within the same stroke in the flowing gas, using the transit-time difference of two ultrasonic signals of downstream and upstream transits to determine the average flow velocity along acoustic path. 3.2.2 ultrasonic transducer
A component that converts acoustic energy to electrical signal and vice versa. Generally, it is installed in a pair and the pair work simultaneously.
3.2.3 signal processing unit
A part of flow meter, consisting of electronic components and microprocessor system.
3.2.4 meter body
A pipe section where the gas to be tested passes, where components such as ultrasonic transducer and pressure measuring connector are installed, that is manufactured in a special way to comply with relevant regulations in any aspect. 3.2.5 acoustic path
The actual path of the ultrasound signal between a pair of transmitting and receiving ultrasound transducers.
3.2.6 path length; L
The distance between the end faces of a pair of ultrasonic transducers (see Figure 1).
3.2.7 axial distance; X
The projection length of path length on the parallel line of pipe axis (see Figure 1).
Figure 1 -- Simplified geometric relationship diagram of plug-in gas
ultrasonic flow measurement
3.2.8 path angle; ??
The angle between acoustic path and pipe axis (see Figure 1).
3.2.9 average flow velocity along acoustic path;
Gas flow velocity in a plane that is determined by acoustic path and flow direction.
3.2.10 mean axial fluid velocity; V
Ratio of flowrate to measured cross-sectional area.
3.2.11 velocity distribution correction; kc
Ratio of mean axial fluid velocity to average flow velocity along acoustic path. 3.2.12 velocity sampling interval
Time interval between two adjacent gas flow measurements by a pair of
ultrasonic transducers or acoustic paths.
3.2.13 zero-flow reading
The reading of the maximum permissible flow rate when gas is in a state of rest. 3.2.14 transition flow rate; qt
The flow value between the maximum flow and the minimum flow. It divides the flow range into two zones with different tolerances, that is, ?€?high zone?€? and ?€?low zone?€? (see Figure 2).
3.2.15 maximum peak-to-peak error
The difference between the upper limit maximum error point and the lower limit maximum error point (see Figure 2).
3.2.16 flow calibration factor
Flow meter coefficient that to conduct flow calibration on the flow meter and correct the test results according to a certain correction method, hereinafter referred to as the calibration factor.
3.2.17 maximum error shift with one path failed
At the same flow, the maximum difference BETWEEN the measurement error
when all acoustic paths work AND the measurement error when one acoustic path fails.
3.2.18 speed of sound (SOS) deviation
The maximum relative deviation between average sound velocity obtained by the measurement of flow meter and theoretical sound velocity in the gas. 3.2.19 metering package
The component that consists of a flow meter, supporting upstream and
downstream straight pipe sections, temperature measuring hole, pressure obtaining hole as well as flow conditioner.
4 Measurement principle
4.1 Fundamental principle
The gas ultrasonic flow meter of transit-time difference method is a velocity flow meter that measures high frequency sound pulse transit-time to obtain gas flow. The transit time is measured by the acoustic pulses that are transmitted and received between pairs of transducers outside the pipe or within the pipe. The acoustic pulse transits along the diagonal direction (see Figure 1). Acoustic pulses transmitted downstream are accelerated by airflow while acoustic pulses transmitted in reverse flow shall be decelerated. The transit-time difference is related to the mean axial fluid velocity. Use numerical calculation technique to calculate the mean axial fluid velocity and the flow that pass through the gas ultrasonic flow meter under working conditions. The flow meter that only has one acoustic path is called single-path gas ultrasonic flow meter. The flow meter that has two or more acoustic paths is called multi-path gas ultrasonic flow meter. When the ultrasonic transducer is in direct contact with the gas, it is called plug-in. When the ultrasonic transducer is not in direct contact with the gas, it is called external clamp-on.
See Annex A for more details.
4.2 Influencing factors of accuracy measurement
4.2.1 Internal factors include:
a) Geometric size of meter body as well as accuracy and stability of
ultrasonic transducer?€?s position parameters;
b) Quality and accuracy of ultrasonic transducer and electronic components used for transit-time measurement (including electronic clock stability); c) Sampling period and integral calculation method used for transit-time testing and average flow rate calculation;
d) Calibration (including compensation for electronic component and
ultrasonic transducer signal lag).
4.2.2 External factors include:
a) Airflow velocity distribution;
b) Temperature gradient;
c) Airflow pulsation;
d) Acoustic and electromagnetic noise;
e) Solid and liquid depositions;
f) Geometric size changes over time.
5 Working conditions
5.1 Natural gas quality
The natural gas components measured by the flow meter are generally within the scope specified in GB/T 17747 (all parts). The relative density of the natural gas is 0.55~0.80.
In one of the following cases, it shall consult the manufacturer for the material of the flow meter, the type of the ultrasonic transducer as well as whether the measuring accuracy of the flow meter meets the requirements:
a) CO2 content exceeds 10%;
b) Work under conditions that are close to the critical density of natural gas mixture;
c) Total sulfur content exceeds 460mg/m3, including mercaptans, hydrogen sulfide and elemental sulfur.
Under normal gas delivery conditions, the attachments (such as condensate or oil residue with processing impurities, ash and sand, etc.) inside the meter body shall reduce the flow area of the flow meter, which shall affect the measurement accuracy. Meanwhile, the attachments shall also obstruct or attenuate the ultrasonic transducer to emit and receive ultrasonic signals OR affect the reflection of ultrasonic signals on the inner wall of the meter body. Therefore, it shall regularly check and clean the flow meter.
5.2 Pressure
The ultrasonic transducer has certain requirements for gas minimum density (it is the function of pressure). The minimum working pressure shall ensure that the acoustic pulse can transit normally in natural gas.
5.3 Temperature
The manufacturer shall, according to the actual working condition requirements of the user, provide a flow meter that meets temperature range requirements. The working medium temperature of the flow meter is -20??C~60??C; the working environment temperature range is -40??C~60??C.
5.4 Flow range and flow direction
The flow measurement range of the flow meter is determined by the actual flow rate of gas. The typical flow rate of the measured natural gas is generally 0.3m/s ~ 30m/s. The user shall verify that the measured gas flow rate is within the flow range specified by the manufacturer. The corresponding measurement
accuracy shall be in accordance with the provisions of Clause 6.
The flow meter has the ability to measure in both directions. The bidirectional measurements have the same accuracy. The user shall indicate if bidirectional measurement is required, so that the manufacturer can properly configure the signal processing unit parameters.
5.5 Velocity distribution
Under ideal conditions, the natural gas flow that goes into the flow meter shall be in symmetrically and fully-developed turbulent velocity distribution. The configuration of upstream pipe (i.e., various upstream pipe fitting, pressure regulator and length of straight section) shall influence the velocity profile of the gas that goes into the flow meter, so as to affect measurement accuracy. The size of the influence and whether the influence is positive or negative are related to the compensation capability of the flow meter to a certain extent.
6 Measurement performance requirements
This clause specifies that the flow meter shall meet a set of minimum
measurement performance requirements. Before the adjustment of flow
calibration factor, the flow meter shall meet the requirements for those performances, so as to ensure that the problems and defects of the flow meter are not covered due to the adjustment of flow calibration factor.
The user shall, according to the provisions of Clause 7 and Annex B, require inspection and flow calibration to the flow meter. It shall also follow the installation requirements in Clause 8 to ensure that the measurement accuracy of the flow meter is improved based on meeting the minimum performance
requirements.
For the flow meter of each size, the manufacturer shall specify the flow threshold, that is, minimum flowrate qmin, transition flowrate qt and maximum flowrate qmax. No matter whether it has been subject to flow calibration, within the flow range specified by the manufacturer, the flow meter shall meet the measurement performance requirements of this clause.
6.1 Measurement performance requirements for multi-path gas
ultrasonic flow meter
6.1.1 General
Before any adjustment of flow calibration factor, the general measurement performance of all multi-path gas ultrasonic flow meters shall be able to meet the following requirements:
a) Repeatability:
0.2%, qt ??? q ??? qmax;
0.4%, qmin ??? q < qt;
NOTE: q is the flow to be measured, same as follows.
b) Resolution: 0.001m/s;
c) Velocity sampling interval: ???1s;
d) Zero-flow reading: < 6mm/s for each acoustic path;
e) Speed of sound (SOS) deviation: ??0.2%;

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