The Use of Acoustic Emission for Leak Detection in Steel Pipes

摘要

Acoustic emission (AE) energy is present due to sudden release of energy when materials experience deformation, crack, or fault. The same situation also occurs for leakage on pipe where acoustic emission exists excited by the turbulence in the fluids around the leak. For the development of leak detection system, it is instructive to investigate further the relation between leak properties and acoustic emission signal. For this, an experimental rig to detect leak was built using 8 inch galvanized steel pipe. The length of the pipe was 2 meters. A leak was made with 5 mm diameter and located in 1 meter from the end pipe. The pipe was filled with water and compressed until certain pressure reached. An acoustic emission transducer, Bruel and Kjaer type 8313, was mounted on the pipe wall and connected to digital oscilloscope to detect AE signal. The experiment was conducted by placing a sensor at a distance of 15 cm, 30 cm, 45 cm, 60 cm, and 75 cm from the position of the leak. Measurements were also performed with the variation of the pressure 3 bar, 4 bars, 5 bars, 6 bars, and 7 bar for those points. Considering acoustic emission wave travelling on pipe is plane wave, leak detection energy attenuation based is potential to use. Wave attenuation constant β is thus required and obtained based on experimental result where the amplitude varies with the spatial and inside pressure of pipe. It is found that β=0.024 for the case considered here. Subsequently, the distance of leak location from the sensor position can be determined by the attenuation constant and the ratio of energy. Using this method, the error of prediction is expected about 15.8%.