Methods of deep buried pipeline leak detection

In order to reduce the leakage rate of water supply network, most Chinese urban water supply companies have carried out water supply network leakage monitoring and leakage detection, and some water departments have also set up professional leakage detection teams or professional leakage detection companies, which will play a positive role in controlling the leakage of China's pipeline network. The law of underground pipeline leakage is from dark leakage to bright leakage, sometimes the water from dark leakage flows into rivers, sewers or cable trenches without becoming bright leakage, so how to quickly detect dark leakage is an urgent task for China's urban water supply companies, especially water supply pipe network leakage detection.

Over the years, due to the consensus on water supply pipeline leaks, a variety of leak detection methods and leak detection equipment are used, commonly used leak detection methods include: listening to sound leak detection method, correlation analysis leak detection method, borehole listening to sound leak detection method, etc. These leak detection methods rely on the sound generated by the leak to detect and locate the leak, which has been proven to be an effective leak detection method.

Generation and types of water supply pipe leakage sounds

The task of water supply pipes is to deliver potable water to customers to meet the most basic needs of people's lives. However, water supply pipes can also leak, and when friction occurs between water jetting out of the pipe and the edge of the leak, as well as impact or flow with the surrounding medium, vibrations of different frequencies and amplitudes are generated, resulting in leak sound waves. The type of leak sound can usually be divided into three types.

1. Leak friction sound

Is the water ejected from the pipe and by the leakage of water sound waves generated by the leakage edge friction, its frequency is usually 100 ~ 2500Hz, and along the pipe to the far side of the exponential law decay (I = I0e_ax, I0 indicates the leakage point sound intensity, I indicates the sound intensity at the leakage point X, a indicates the attenuation coefficient), the propagation distance is usually related to the water pressure, pipe, pipe diameter, interface, leak size, etc., in a certain Range, can be in the gate ﹑ hydrant and other exposure points, in order to hear and measure the sound waves of leakage.

2. Water head impact sound

Is the impact of the water ejected from the pipeline and the surrounding medium generated by the sound wave leakage, as well as the funnel-shaped wave that spreads through the soil to the ground, or the spherical wave that propagates to the ground, can be heard on the ground with a leak detector, its frequency is usually between 100 ~ 800Hz.

3. Water flow and medium friction sound

It refers to the water ejected from the pipe, driving the flow of surrounding particles (such as soil particles, sand grains, etc.) and the collision friction generated by the leakage sound waves, whose frequency is low and usually cannot be heard on the ground, and can only be heard and measured when the listening stick is inserted near the underground leak, which provides the means to finally confirm the leak.

In short, the three types of leak sound waves mentioned above are detected by different instruments and equipment, and a pipe leak detector is used to detect the frictional sound at the edge of the leak.

Technicians use the pipeline leak detector, along the pipeline above the interval of 0.5 meters to select points, vertical pipeline parallel displacement of three points, large pipelines using the "S" shaped selection of points, point by point to listen, through the ground sound intensity, audio detection analysis, to pinpoint the location. The key is to choose different frequency bands for different leakage points, such as the correct choice, can improve the accuracy of leakage point positioning, reduce the error. Leakage point to produce the frequency of the leak sound and pipe network rupture size, pipe diameter, pipe related. Usually, the leakage sound of plastic pipe is a low frequency signal, while the leakage sound of steel or cast iron pipe is a high frequency signal. When the technician locates the leak point, he must master the diameter of the pipe line where the leak point is located, pipe and other parameters in order to correctly select the filter band, so that the main frequency of the leak noise can be highlighted, the purpose of which is to amplify the leak noise signal and suppress the interference noise signal, so that the technician can quickly and precisely locate the leak point.