The standard orifice is a circular perforated sheet obtained by machining.

The cylinder face of the throttle orifice is perpendicular to the upstream end face of the orifice plate, its edge is sharp, and the thickness of the orifice plate is smaller than the diameter of the orifice plate.

The part of the orifice plate in the measuring tube should be round and coaxial with the axis of the measuring tube, and the two ends of the orifice plate should always be flat and parallel

3.1 orifice eccentricity

According to gb2624-81, the orifice plate should be aligned with the straight pipe section in the throttling device.

Experiments show that the measurement error caused by the eccentricity of the orifice plate is generally less than 2%, and the higher the value of the apertures is, the greater the influence of the eccentricity.

3.2 bending of orifice plate

Improper installation or maintenance.

Bend or deform the orifice plate, resulting in large flow measurement error.

The maximum error caused by hole plate bending is about 3.5%.

3.3 edge acuity of orifice plate

Orifice inlet edge wear no sharp edge or corrosion occurs to gap, or orifice pipe inner weld or measuring flange gaskets, will make the actual flow coefficient increases and the differential pressure is reduced, cause small volume calculation.

Measures to improve measurement accuracy

1. Eliminate the pulsation flow in the air flow

Pipeline due to sudden changes in the velocity and pressure of the gas, cause the pulsating flow, it can lead to differential pressure fluctuation, and the throttle device of flow calculation formula is based on LanKong board of steady flow, when the measurement point has pulsation phenomenon, stable principle cannot be established, which may effect the precision of measurement, the measurement error.

The total uncertainty of the pulse flow is equal to the combination of the measurement error calculated in GB/ t2624-93 and the additional uncertainty added to the pulse.

Where: et-pulsation with additional uncertainty, dimensionless;

- axial average speed, m/s;

- mean square root value of velocity pulsation component, m/s.

(formula application condition is less than or equal to 0.32)

Therefore, in order to ensure the measurement accuracy of natural gas, the pulsation flow must be suppressed.

Common measures include:

(1) under the condition of meeting the measurement capacity, the measuring tube with a small inner diameter should be selected to improve the differential pressure and aperture ratio;

(2) the short voltage drawing pipeline is adopted to reduce the resistance parts in the pipeline and make the length of upstream and downstream pipelines equal, so as to reduce the resonance and pressure pulsation amplitude in the system.

(3) eliminate free liquid from the pipeline, and the pulsation caused by the accumulation of liquid in the pipeline can be handled by the automatic pigging system or the installation of a separator at a lower level.

2. The design and installation of the metering device shall comply with the platform SY/T 6143-1996

The fundamental reason that affects the measurement precision of orifice flowmeter is whether the geometric shape and flow dynamics of throttle device deviate from the design standard.

Therefore, it is necessary to check and maintain the system on a regular basis in the process of using the system. It is necessary to timely modify the changes of operating conditions such as pressure, temperature and flow in the actual use.

The product scheme of the fully compensated flow computer can be adopted to reduce the measurement error and ensure the measurement accuracy.

3. Avoid artificial measurement error

We will strengthen metrological management, improve the technical quality of operators, and actively introduce advanced natural gas metering technology from abroad.

The standard orifice is a circular perforated sheet obtained by machining.

The cylinder face of the throttle orifice is perpendicular to the upstream end face of the orifice plate, its edge is sharp, and the thickness of the orifice plate is smaller than the diameter of the orifice plate.

The part of the orifice plate in the measuring tube should be round and coaxial with the axis of the measuring tube, and the two ends of the orifice plate should always be flat and parallel

3.1 orifice eccentricity

According to gb2624-81, the orifice plate should be aligned with the straight pipe section in the throttling device.

Experiments show that the measurement error caused by the eccentricity of the orifice plate is generally less than 2%, and the higher the value of the apertures is, the greater the influence of the eccentricity.

3.2 bending of orifice plate

Improper installation or maintenance.

Bend or deform the orifice plate, resulting in large flow measurement error.

The maximum error caused by hole plate bending is about 3.5%.

3.3 edge acuity of orifice plate

Orifice inlet edge wear no sharp edge or corrosion occurs to gap, or orifice pipe inner weld or measuring flange gaskets, will make the actual flow coefficient increases and the differential pressure is reduced, cause small volume calculation.

Measures to improve measurement accuracy

1. Eliminate the pulsation flow in the air flow

Pipeline due to sudden changes in the velocity and pressure of the gas, cause the pulsating flow, it can lead to differential pressure fluctuation, and the throttle device of flow calculation formula is based on LanKong board of steady flow, when the measurement point has pulsation phenomenon, stable principle cannot be established, which may effect the precision of measurement, the measurement error.

The total uncertainty of the pulse flow is equal to the combination of the measurement error calculated in GB/ t2624-93 and the additional uncertainty added to the pulse.

Where: et-pulsation with additional uncertainty, dimensionless;

- axial average speed, m/s;

- mean square root value of velocity pulsation component, m/s.

(formula application condition is less than or equal to 0.32)

Therefore, in order to ensure the measurement accuracy of natural gas, the pulsation flow must be suppressed.

Common measures include:

(1) under the condition of meeting the measurement capacity, the measuring tube with a small inner diameter should be selected to improve the differential pressure and aperture ratio;

(2) the short voltage drawing pipeline is adopted to reduce the resistance parts in the pipeline and make the length of upstream and downstream pipelines equal, so as to reduce the resonance and pressure pulsation amplitude in the system.

(3) eliminate free liquid from the pipeline, and the pulsation caused by the accumulation of liquid in the pipeline can be handled by the automatic pigging system or the installation of a separator at a lower level.

2. The design and installation of the metering device shall comply with the platform SY/T 6143-1996

The fundamental reason that affects the measurement precision of orifice flowmeter is whether the geometric shape and flow dynamics of throttle device deviate from the design standard.

Therefore, it is necessary to check and maintain the system on a regular basis in the process of using the system. It is necessary to timely modify the changes of operating conditions such as pressure, temperature and flow in the actual use.

The product scheme of the fully compensated flow computer can be adopted to reduce the measurement error and ensure the measurement accuracy.

3. Avoid artificial measurement error

We will strengthen metrological management, improve the technical quality of operators, and actively introduce advanced natural gas metrology techniques from abroad.