Examination and Generation Condition of Screech Tone Detected during Gas Leakage on Pipe Using Acoustic Emission Technology

Acoustic emission (AE) technology has been applied in monitoring and inspection of flaws specifically on gas leakage from pipeline installations th rough research in the field and laboratory. We have chosen four types of artificial defe cts such as straight-, stepwise-, truncated cone- and slit-type pinholes to quantify the smallest po ssible defect from the material flaw that could be emanated in actual pipe installations. One of the a dvantages in this research study is the possibility to characterize the different AE signals generated during gas leakage and eventually enhance the accuracy in the analysis of defect development during actual monitoring and inspection of pipelines. The purpose of this study is to char acterize and analyze the generated AE signals during gas leakage on pipe with these artificial def ects. The main objective is to examine and make clear the generation condition of the screech tone that is characterized as the feedback loops driven by large-scale instability of waves of gas fl ow near the outlet. When this gas pressure is reached at the critical level of 220 kPa based on the assumption that the gas flow velocity reached to its sound velocity, the shock cell is developed in which the screech tone simultaneously takes place. In the case of the only str aight- and slit-type pinholes, the AE signals showed a decreasing peak frequency after reaching the critica l gas pressure. The pressure where the screech tone occurred depended on the pinhole shapes. In t he case of the truncated cone-type pinhole, the screech tone did not occur because of stabi lity of gas flow through the defect. The characteristics of the screech tone have been discu ssed in detail.