2008 Volume 49 Issue 10 Pages 2341-2346
A unique behavior of acoustic signals occurred for each type of defect as evident in their respective time and frequency domains. Straight pinhole shows that the faster the gas leakage passes through the defect the greater the magnitude of amplitude of the generated AE signals was recorded. Scattered AE signals took place above the critical pressure due to large scale flow instability. For stepwise pinhole, the magnitude of amplitude is higher for a thicker wall dimension and has a common characteristics with a sudden dropped of amplitude over the transition of flow. In a similar manner, the cone-type pinhole shows other distinct characteristics for two different dimensions. When pressure is over 370 kPa unusual sound is generated for 1.0 mm wall thickness. On the other hand, only straight pinhole shows a decreasing peak frequency after reaching the critical pressure, which is attributed to screech tone characteristics. While for stepwise pinhole with 1.0 mm wall thickness, the peak frequency is generally higher compared with 2.0 mm wall thickness. The cone-type orifice have similar pattern with stepwise pinhole in terms of peak frequency. Generally, the dissimilarity of AE generated signals revealed a distinct characteristic for every type of pipe defect. And the effect of stepwise deviation is extremely obvious in various depths.