Check if the pipe is full of fluid. Try the Z method for transducer installation （If the pipe is too close to a wall, or it is necessary to install the transducers on a vertical or inclined pipe with flow upwards instead of on a horizontal pipe).
Carefully select a good pipe section and fully clean it, apply a wide band of coupling compound on each transducer surface (bottom) and install the transducer properly. Slowly and slightly move each transducer with respect to each other around the installation point until the maximum signal is detected. Be careful that the new installation location is free of scale inside the pipe and that the pipe is concentric (not distorted) so that the sound waves do not bounce outside of the proposed area.
For pipe with thick scale inside or outside, try to clean the scale off, if it is accessible from the inside. （Note: Sometimes this method might not work and sound wave transmission is not possible because of the a layer of scale between the transducers and pipe inside wall）
Post time: Jan-26-2022