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GB/T 18604-2014 (GB/T 18604-2023 Newer Version) PDF English


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GB/T 18604-2014: PDF in English (GBT 18604-2014)

GB/T 18604-2014 NATIONAL STANDARD OF THE PEOPLE’S 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 φ 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; φ 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%; f) Maximum speed of sound (SOS) difference between each acoustic path: 0.5m/s. 6.1.2 Accuracy of large-diameter flow meter Before any adjustment of flow calibration factor, the multi-path gas ultrasonic flow meter of which the diameter is equal to or greater than 300mm shall meet the following requirements for measurement accuracy (see Figure 2): a) Maximum error: ±0.7%, qt ≤ q ≤ qmax; ±1.4%, qmin ≤ q < qt; b) Maximum peak-to-peak error: 0.7%, qt ≤ q ≤ qmax; 1.4%, qmin ≤ q < qt. 6.1.3 Accuracy of small-diameter flow meter Before any adjustment of flow calibration factor, the multi-path gas ultrasonic flow meter of which the diameter is less than 300mm shall meet the following requirements for measurement accuracy (see Figure 2): a) Maximum error: ±1.0%, qt ≤ q ≤ qmax; ±1.4%, qmin ≤ q < qt; b) Maximum peak-to-peak error: 1.0%, qt ≤ q ≤ qmax; 1.4%, qmin ≤ q < qt. NOTE: When the path length is short, it is difficult to measure the transit-time of acoustic wave in turbulent gas. Therefore, the requirements for the small-diameter flow meter are low. Figure 2 -- Summary of measurement performance requirements for multi-path gas ultrasonic flow meter Zero-flow reading < 6mm/s (for each acoustic path) Uncorrected calibration curve of flow meter Repeatability Large-diameter flow meter (≥12’’) Maximum peak-to-peak error=0.7% (qj≥qt) Small-diameter flow meter (< 12’’) Maximum peak-to-peak error=1.0% (qj≥qt) Maximum peak-to-peak error=1.4% (qj< qt) Repeatability Extended error limit Error limit of small- diameter flow meter Error limit of large- diameter flow meter Error limit of large- diameter flow meter Error limit of small- diameter flow meter Extended error limit Flow / qi 6.2 Measurement performance requirements for single-path gas ultrasonic flow meter The measurement performance requirements for single-path gas ultrasonic flow meter may be lower than the measurement performance requirements for multi-path gas ultrasonic flow meter. The specific indicators are provided by the manufacturer. 6.3 Influence of working conditions on measurement performance Under the working conditions specified in Clause 5, the flow meter shall meet the measurement performance requirements specified in 6.1 and 6.2 without any manual adjustment. If the manual input of physical parameters is required to determine the physical parameters (such as density and viscosity) under natural gas flow conditions, the manufacturer shall give the sensitivity degree that the flow meter is affected by those parameters, so that when the working conditions are changed, the user can determine whether the influence brought by those changes is acceptable. 7 Flow meter requirements 7.1 Composition and basic provisions 7.1.1 Composition The flow meter mainly consists of the following two parts: a) meter body, ultrasonic transducer and its mounting parts; b) signal processing unit (SPU) that is composed of electronic components and microprocessor system. It receives ultrasonic transducer signals and has functions such as processing measurement signals and displaying, outputting and recording measurement results. The electrical signal processing and conversing part located in the field is installed in the converter. 7.1.2 Basic provisions Use the materials that are suitable for working conditions of the flow meter to design and manufacture the meter body and all other parts, including pressure members and external electronic components, in accordance with the process requirements for the metering system where they are. If the user has special requirements, it shall comply with the appropriate specifications or regulations applicable to each specific installation condition specified by the user. Before the flow meter exits the factory, the manufacturer shall conduct exit- factory testing and provide the exit-factory testing report to the user. See Annex C for the exit-factory testing requirements. There shall be corresponding documents, see Annex D. 7.2 Meter body 7.2.1 Maximum working pressure The maximum designed working pressure of the flow meter shall be the minimum among the maximum working pressures of the following components: meter body, flange, ultrasonic transducer components and their mounting connectors. The connecting flange of the meter body shall comply with general industrial standards, national or international standards. 7.2.2 Corrosion resistance requirements All components of the flow meter that are in contact with the medium shall be made of the materials that are suitable for natural gas. The materials used for the flow mater that contains corrosive mediums such as H2S and CO2 shall comply with the provisions of SY/T 0599. All external parts of the flow meter shall be made of corrosion resistant materials. Or use corrosion resistant coating that is suitable to use in a typical atmospheric environment of the natural gas industry. 7.2.3 Ability of adapting to environment The shell, nameplate of the flow meter and each component shall comply with the provisions of GB/T 4208, at least meeting the level requirements of IP65. 7.2.4 Length and nominal diameter The manufacturer shall give the standard length of the meter body of each pressure level and nominal diameter. In order to match existing pipes, the user can specify different lengths and nominal diameters. 7.2.5 Ultrasonic transducer port Natural gas may contain impurities (such as condensate or dust). The designed ultrasonic transducer port shall minimize the possibility of liquids or solids staying on them. According to user’s requirements, a valve may be provided so that the ultrasonic transducer can be replaced with internal pressure in the meter body. 7.2.6 Pressure obtaining hole There shall be at least one pressure obtaining hole on the meter body to measure the static pressure. The nominal diameter of each pressure obtaining hole shall be within 4mm~10mm. If the wall thickness of meter body is less than 20mm, the nominal diameter of the pressure obtaining hole shall be 4mm. And from the inner wall of meter body, at least within the length 2.5 times the diameter of pressure obtaining hole, it is cylindrical; and the axis of the pressure obtaining hole shall be perpendicular to the measuring tube axis. The edges of pressure obtaining hole of inner wall of meter body shall be right angle, without burrs and curls. Each pressure obtaining hole shall have internal thread that can be equipped with isolation valve and swing space where it can directly mount the isolation valve on the pressure obtaining hole. The specification of the internal thread is better to be 1/4" NPTF or 1/2" NPTF. The pressure obtaining hole shall be set at the top, left or right of meter body. When necessary, the pressure obtaining hole can be added, so as to provide the flexibility to install pressure transmitter to the user, be conducive to maintenance and discharge the condensate in the pressure transmitter pressure tube back into the meter body. 7.2.7 Flow meter markings A nameplate that contains the following information shall be set on the flow meter: a) Manufacturer’s name, flow meter model, serial number and date of manufacture; b) Nominal pressure and total mass; c) Nominal diameter and inner diameter; d) Highest and lowest storage temperature; e) Working pressure and temperature range; f) Maximum and minimum hourly flow under working state; g) Positive direction of gas flow; h) Explosion-proof level. For easy identification, each ultrasonic transducer port shall be marked with a permanent unique mark. If a stamp mark on the meter body, it shall use low stress stamping form, i.e., round bottom print. 7....... ......
 
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