1. The influence of magnetic field
During on-site inspection, it often occurs that when the on-site conditions meet the inspection requirements, no matter which installation method is used or how to adjust the position of the transducer, the acoustic signal cannot be received, Situations that ultimately lead to detection failure. At this time, the operator needs to check whether there are large electrical appliances or rows of electrical appliances in the surrounding environment.
High voltage cables. These large electrical appliances and cables will generate strong electromagnetic fields, which have a great impact on the ability of the transducer to send and receive signals, resulting in the transducer not working properly. In this case, the only choice is to select a location on the pipeline far away from these strong magnetic field generators for detection.
2. The influence of incorrect input of the outer diameter value and wall thickness value of the pipeline
The ultrasonic flowmeter usually calculates the inner diameter of the pipeline under the condition of inputting the outer diameter of the pipeline and the wall thickness of the pipeline, then calculates the distance between the transducers, and finally calculates the pipeline through the relationship between the transducer distance and the sound wave propagation time. The average axial velocity of the fluid inside. If the outer diameter and wall thickness of the pipeline are input inaccurately, the obtained measurement results are also inaccurate, and even the transducer cannot receive the signal, resulting in the detection failure.
During the actual inspection on site, the pipeline under test will be more or less fouled, which will thicken the wall thickness of the pipeline, but the specific thickness of the thickened wall can only be known through several methods.
(1) Disassemble the pipeline that can stop the operation, and directly measure the wall thickness of the pipeline. This is the easiest and hardest way to do it
(2) Use a thickness gauge to measure the wall thickness of the pipeline with thin scaling. Thickness gauges may also be powerless for thickly fouled pipelines.
3) Human estimation. According to the service life of the pipeline, the fluid condition in the pipeline, and the previous experience of cleaning the pipeline fouling layer, the fouling thickness of the pipeline is estimated, and the current wall thickness of the pipeline is obtained.
3. The effect of temperature
Different transducers have different temperature ranges. Too high or too low temperatures can result in inaccurate measurements or detection failures. Therefore, it is very necessary to ask the actual situation of the pipeline under test before testing, and then select a suitable transducer.
Some brands of portable ultrasonic flowmeters can correct the test results by setting the appropriate temperature parameters (such as the fluid temperature option under the measured fluid menu). This correction affects the measurement results and should not be ignored in actual operation.
When the surface temperature of the pipeline exceeds 80℃, the couplant will evaporate in a very short time, and it will not be able to isolate the air and reduce the energy loss of the sound wave. At this time, other methods should be used to ensure that the transducer can be close to the tube wall, and the energy loss of the sound wave should be minimized.