The Comparison of Acoustic Emission Activities between Material Integrity and Leakage during CNG Cylinder Testing

Abstract

The objective of this paper is to study the different acoustic emission (AE) activities from material integrity and leakage which were obtained from CNG steel cylinder during pressurization. CNG type I cylinders were employed to test by hydrostatic stressing. The pressure was continuously increased to over 1.1 time of operating pressure or leakage occurrences. AE sensors, resonance frequency of 150 kHz, were mounted on the outside cylinder wall to detect the AE activities throughout the testing. AE activities were compared between AE of material expansion and leakage by amount of AE signals detected then analyzed by AE parameters. AE parameters including Amplitude, Count, Energy (MARSE), Duration and Rise time were analyzed to distinguish the AE data. The AE wave form in time and frequency domain were also considered in analysis process. The location of AE sources were located by the calculation the arriving differenced time of 2 or more sensors to indicate the position of cylinder faults. The results showed the AE signals of material expansion were randomly detected throughout the pressurization until the Enegy and Amplitude of detected signals were increased by high incresing rate where was leakage occurrences. AE parameters of Amplitude and Energy can be significantly represented the difference between material expansion and leakage. Addition, the Hit rate monitoring cloud be a notice activity before cylinder leaks. The benefits of this work are the AE characterization of the material expansion, leakage and noise for improvement of Type-1 CNG cylinder tests.