The Application of Wavelet in Petroleum Pipeline Detection

The leakage of petroleum can lead to serious economical loss. How to find out leakage spot is the key technology that we will discuss in the paper. In this paper, we apply wavelet transform to solving the problem. Because the audio signal from the leakage spot is very weak, when the sound spreads to the ends, the signal tested by sensor has been sinked down by other noise signals. It is difficult to get this signal with normal method. But we can amplify the low frequency filtering signal step by step in accordance to the micro-mirror character in wavelet transform. Then, apply correlation method to locate the leakage spot. Based on wavelet transform theory, we can effectively locate the leakage spot. We have put this technology into effect and benefit from the technology. Introduction: In recent years, the petrochemical industry is quickly developing, and the oil transmission. Pipelines pave wide geographic areas in china. The oil transmission pipelines extend in all directions, stagger in length and breadth and lay in the underground. Its distance is long. On the one hand, with using time increasing and the pipeline affected by the geography environment and transmission pipelines condition and so on, the underground oil pipeline happen the phenomena of the welding line rupture, inside and outside nature and the matter corrosion and perforation, which leads to leakage. On the other hand, some man in what are called third party damage want to obtain amazing profits, adopt non-law means frequently stealing oil by drilling hole in oil pipeline which leads to serious economical loss and is likely to cause a corrosion leak in the future on the same time. If we don’t find the leak place in the pipelines in time, it easily occurs to the tragedy accidents of the fire, the blast and the environment pollution. Once a leakage spot is established, at the instant of a breakdown of the pressure boundary (leak), the release of the elastic force couples with the system fluid to create a transient acoustic wave. This acoustic expansion wave travels outward in all directions from the source at the speed of sound for that fluid. In a pipeline, the expansion waves are guided through the fluid by the walls of the pipeline in either direction from the source of the break, to be detected by sensitive acoustic sensors placed at the ends of the pipeline. From times of arrival of the expansion waves at the sensor locations, the location of the leak is determined. The challenge of the technology is to pick up acoustic signal masked by the background noise. The figure 1: Wavelet transform is a new method of time-frequency analysis, which uses the scale operator replacing the transferable operator of the frequency and transforms the time-frequency plane into the time-scale plane. Its time windows function is changeably characteristic windows. When its frequency portion gets high, the time window is short, and vice versa. Because of its characteristic, wavelet can not only analyze high frequency elements, but also accurately estimate the low frequency elements of the signal. This paper briefly introduces the theory of wavelet transform and its application to detection and location of oil pipelines. Results: When the pipeline leaks, the acoustic signal travels in either directions from the source of the break. Figure 2 and Figure 3 is the acoustic signal detected by the sensors at the inlet of the pipeline and at the outlet of the pipeline respectively. Figure 2: The inlet original signal Figure 3: The outlet original signal After wavelet transform, apparent gorges can be seen, according to the distance between the two gorges, we obviously know the time interval that the acoustic signal arrives at the inlet and outlet. According to the figure 1 theory, we can locate the leak by the orientation formula what is as follow. t ∆