In this kind of flow meter straight pipe section of the configuration length, AGA.NO.9 number of the report: Although the manufacturers recommended installation practices are not consistent, but generally require the upstream of the flow at least 5~10D of the straight pipe section, downstream at least 3D straight section."
In order to reflect the standards with the characteristics of the operation, according to the standard or the report's recommendations, combined with the actual situation of the production site, also made reference to the views of the ultrasonic flowmeter manufacturers, in the standard try to give the a of ultrasonic flowmeter downstream straight pipe length configuration technical regulations or requirements, namely: in the need to install the rectifier, multi-channel ultrasonic flowmeter in the upper reaches of the shortest straight pipe length should is 10d downstream the shortest straight pipe length should be as 5D; if you use a rectifier, rectifier installation position and the corresponding pipe length should consult the manufacturer.
(3) quality requirements for straight pipe sections
Steps and convex objects: any step of the shortest length of straight pipe (measuring tube) and other convex objects in the lower section of the ultrasonic flow meter will cause the change of the flow pattern of the measured medium, thus increasing the uncertainty of flow measurement. But in fact, as long as the piping used careful selection or take appropriate boring of the inner wall of pipeline, or according to the site of the pipeline conditions for manufacturers to put forward the ultrasonic flowmeter must reach the inner requirement and other means, you can avoid the connection step, in order to achieve between the straight pipe and ultrasonic flowmeter diameter connected or good matching; in addition, in the construction and assembly process, take will be connected to the inner wall of the weld polished smooth or appropriate to expand the flange gasket inner diameter measures can also avoid bumping into objects and other disturbance debris barrier. Therefore, it is necessary and feasible to restrict the steps and the convex. II inner surface: if in internal and measurement of the meter body on the inner wall of the tube there is a rust, oil or sulphur powder and other appendages. On the one hand may will change the actual diameter of pipeline measurement, on the other hand may will increase the measuring pipe inner wall roughness average, second may also lead to acoustic wave (pulse signals in the reflection of the inner wall of the meter body appear divergence and attenuation. All of these factors may result in severe impact (ISO/WD17089 think on the measurement results and measurement error of the resulting may exceed 1%), so in the meter and the measuring tube surface is proposed requirements and restrictions is to achieve accurate measurement is one of the basic premise.
(4) thermometer installation
The installation of the thermometer should be mainly considered the following three points:
Temperature sensing element should have sufficient length to ensure that there is sufficient contact area between the measured medium and the temperature measuring element, and the influence of the flow pattern is as small as possible.
(5) acoustic noise
Ultrasonic flowmeter is a kind of measuring instrument based on the principle of acoustics. So the existing ultrasonic flowmeter is sensitive to the noise, especially for the high speed, large pressure and so on. So it can affect the normal operation of the flowmeter.
(6) the role of the rectifier
Generally speaking, the installation of the rectifier can improve the measurement conditions of the ultrasonic flow meter to a certain extent, so it can also improve the accuracy of the measurement results, especially for single channel ultrasonic flow meter, the effect may be more obvious. But if improper modeling of rectifier, processing quality is not high or installation and use of improper maintenance, and may increase the measurement error caused by backfire consequences. Therefore, in the design and installation process of ultrasonic flowmeter application, it is necessary to analyze the specific problems. That is to say, it should be for the type of the selected flow meter, the flow pattern of the distortion of the form, the severity and the accuracy of the flow measurement to determine whether to install the form of the rectifier.
(7) the installation method of the flow meter
Theoretically speaking, gas ultrasonic flowmeter can use horizontal, vertical and inclined arbitrary installation, and along the edges of the meter body pipeline axis rotated. However, in the actual installation process should take into account the following 3 aspects: the flow meter (especially in which the ultrasonic transducer) is easy to detect and repair; second ultrasonic transducer is easy to be affected by air flow in impurities and effusion.
Therefore, the GB/T18604-2001 uses a gas ultrasonic flowmeter to measure the natural gas flow standard recommended by the horizontal installation of this conventional way.
3 use, maintenance and management
(1) periodic inspection
Regular inspection is an effective method to prevent and eliminate the instrument failure in advance. If the periodic detection is too long, some problems may not be found in time and processing; if the period is too short, the workload may also destroy the original performance of the mechanical and electronic components (such as sealing), therefore, should be based on the situation to determine the reasonable periodic detection cycle.
As for the content and method of the periodic inspection, according to the GB/T18604-2001 gas flow ultrasonic flowmeter to measure the natural gas flow rate of this standard in accordance with the requirements of section 8.3~9.2. Part of the production site because it is difficult to remove the flow meter from the process line, the installation of the zero flow test in this case, can be completely shut down in the case of the downstream valve. But it must also be guaranteed: the use of the valve must have a flexible opening and closing characteristics and good off performance. Turn off the rear of upstream and downstream valve may not appear any internal leakage and external leakage phenomenon; II to avoid meter and pipeline internal fluid convection, media and ambient temperature difference shoulds not be too big. Otherwise, it shall be taken insulation measures; (3) in the renovation in the process of testing, pressure and temperature should remain stable and measure the relative uncertainty degree should be controlled in the urel (P) is less than or equal to 0.1%, urel (T) less than or equal to 0.2 percent; (4) near the pipe due to the negative effects brought by the gas flow or other mechanical vibration to zero flow test should be as far as possible to control in the smaller range.
(2) test report
The ultimate goal of on-site inspection or testing is to allow the management of ultrasonic flowmeter or user of the equipment operation and performance of a whole process, a full range of understanding and understanding. Therefore, according to the specific situation of on-site inspection and testing of a formal written report is also very necessary. Specific format and contents of the report, on the one hand can be reference GB/T18604-2001 gas ultrasonic flowmeter measurement of natural gas flow the standard paragraph 9.2 requirements. On the other hand can also be according to the actual situation of their own design or appropriate additions and deletions.
