GB/T 21446-2008 in English

《GB/T 21446-2008用标准孔板流量计测量天然气流量》由TC355（全国石油天然气标准化技术委员会）归口，TC355SC10（全国石油天然气标准化技术委员会油气计量及分析方法分会）执行，主管部门为国家标准化管理委员会。
本标准规定了标准孔板的结构形式、技术要求；节流装置的取压方式、使用方法、安装和操作条件、检验要求；天然气在标准参比条件下体积流量和能量流量、质量流量以及测量不确定度的计算方法。同时还给出了计算流量及其有关不确定度等方面的必需资料。
本标准适用于取压方式为法兰取压和角接取压的节流装置，用标准孔板对气田或油田采出的以甲烷为主要成分的混合气体的流量测量。
本标准不适用于孔板开孔直径小于１２．５ｍｍ，测量管内径小于５０ｍｍ 和大于１０００ｍｍ，直径比小于０．１和大于０．７５，管径雷诺数小于５０００的场合。

This standard specifies the structure form and technical requirements of standard orifice; the pressure tapping mode, usage method, installation and operation condition and inspection requirements of throttle device; the calculation method of the volume flow and ernery flow, quality flow and the uncertainty measurement of natural gas under the standard reference condition. The required data such as calculated flow and relevant uncertainlty are also supplied meanwhile.
This Standard is universal for the throttle device with flange pressure tapping and corner pressure tapping as the pressure tapping mode: standard orifice has been employed for the measurement of the mixed gas flow with the methane as the substantial ingredient produced from gas or oil fields.
This standard is not applicable to occasion with the opeing diameter of orifice less than 12.5mm, the inner diameter of measurement tube less than 50mm and greater than 1000mm, the diameter ratio less than 0.1 and greater than 0.75, the Reynolds number of caliber less than 5000.
The metering system rebuilt or newly built shall meet the requirements of this Standard. This Standard does not emphasize the updating of the existing metering system. If the metering system doesn't meet the requirements of this Standard, there may be additional errors of metering system due to the inadaption between the flow condition and the upstream straight pipe segment.

Foreword I
1 Scope 1
2. Normative References 1
3 Quantity, Terms and Definitions 2
3.1 Quantity 2
3.2 Terms and Definitions 3
4 General Requirements for Measurement 5
4.1 Throttling Device 5
4.2 Gas Flow Conditions 5
4.3 Standard Reference Condition 6
5 Instalaltion Requirements 6
5.1 General Principles 6
5.2 Straight Pipe Segment Conditions 7
5.3 Layout Requirements Of Straight Pipe Length 9
5.4 Flow Conditioner 14
5.5 Installation of Orifice Plate Holder 20
5.6 Assembling and Gasket 21
5.7 Parameter Measurement And Signal Lead 21
6 Structure Form and Technical Requirements of Orifice Plate 21
6.1 Orifice Plate 21
6.2 Orifice Plate Holder 24
Figure 10 Orifice Plate Holder Of Angle Joint Pressure Tap 27
7 Inspection Requirements 28
7.1 Geometric Inspection of Throttling Device 28
7.2 Coefficient Detection and On-Line Calibration 29
8 Gas Discharge Measuring Principle And Calculation Method 29
8.1 Measuring Principle 29
8.2 Application Scope of Measurement 30
8.3 Calculation Method of Gas Discharge 31
8.4 Calculation of Gas Discharge and Determination of Coefficient Parameter 33
8.5 Value Method and Data Rounding 36
8.6 Orifice Flowmeter'measuring System 36
9 Uncertainty Estimation of Gas Discharge Measurements 37
9.1 Uncertainty Definition 37
9.2 Actual Estimation of Uncertainty 37
Appendix A (Normative) Table of Major Physical Parameter Determination and Flow Calculation of Natural Gas 43
A.1 Determination of Major Physical Parameter 43
A.2 Common Table for The Calculation of Natural Gas Flow 49
Appendix B (Informative) Performance Test for Flow Conditioner 85
B.1 Explanation 85
B.2 Requirement of Assessment Test for Standard Device 85
B.3 Performance Test and Evaluation for Flow Conditioner 85
Appendix C (Informative) Parameter Measurement and Signal Lead 89
C.1 Requirements of Selecting Measuring Instruments 89
C.2 Installation Provisions of Temperature Measurement 89
C.3 Requirements of Measuring Pressure and Differential Pressure 90
C.4 Requirements of the Setting of Pressure Tap 90
C.5 Requirements of Connecting Pipe 91
C.6 Installation of Differential Pressure Signal Pipeline 91
Appendix D (Informative) Processing Where Throttling Device Is Partially Deviated from Standard Code in Service 94
D.1 Illustration 94
D.2 Processing upon Acuity of Rectangular- entrance-edge of Orifice Plate's Opening Being Corrosive 94
D.3 Processing upon Meter tube's Inwall Roughness Being Corrosive 95
D.4 Fluid Test of Determining Pipeline Inwall 's Roughness 96
Appendix E (Informative) On-line Calibration of Orifice Meter's Measuring System of Natural Gas 98
E.1 Online Calibration 98
E.2 Standard-flowmeter-device for On-line Calibration 98
E.3 Coefficient of On-line Calibration, Mf 99
E.4 Estimation for Uncertainty of On-line Calibration 100
Appendix F (Informative) Example of Natural -gas -flow -calculation and Design Calculation 101
F.1 Example of Calculation of Natural GasFlow 101
F.2 Example of Design Calculation of Orifice plate’s Opening Diameter 104
F.3 Calculation Example of Differential Pressure's Measuring Range 107
F.4 Estimation of Uncertainty 110
Appendix G (Informative) Flow chart of Gas Flow Calculation and Design Calculation 112
G.1 Explanation 112
G.2 Iterative-Computation Format 112
G.3 Flow Chart of Computer Calculation 114
Appendix H (Informative) Basic Technique Requirements for Gas Flow Computer System 118
H.1 General Rules of Flow Computer System's Application 118
H.2 Composition of Flow Computer System 118
H.3 Basic Technique Requirements for Flow Computer System 118
H.4 Uncertainty of Measurement Computer System 121