ISO 18081:2016 pdf free
ISO 18081:2016 pdf free.Non-destructive testing一Acoustic emission testing (AT)一Leak detection by means of acoustic emission
The pressure difference is the primary factor affecting leak rate. However, the presence of leak paths may depend on a threshold value of fluid temperature or pressure. Pressure dependent leaks and temperature dependent leaks have been observed, but in extremely limited number. Pressure-dependent or temperature-dependent leaks denote a condition where no leakage exists until threshold pressure or temperature is reached. At this point, the leakage appears suddenly and may be detectable.
When the pressure or temperature is reversed, the leakage follows the prescribed course to the critical point at which leakage drops to zero. Temperature and pressure are not normally applied in the course of leak testing for the purpose of locating such leaks. Instead, they are used to force existing discontinuities to open, so as to start or increase the leakage rate to point of detection.
An example of this effect is the reversible leakages at seals below the service temperature and/or service pressure.
AE waves emitted by a leak will normally have a characteristic frequency spectrum depending on the pressure difference and shape of the leak path. Therefore the detectability of the leak depends on the frequency response of the sensor and this shall be taken into account when selecting the instrumentation.
The AE intensity from a natural complex leak path (e.g. pinhole corrosion, fatigue or stress corrosion cracks) is generally greater than that produced by leakage from a standard artificial source, such as a drilled hole used for verification. The main parameters defining the complexity are the cross section,length and surface roughness of the leak path.
Acoustic emission signals are the response of a sensor to sound waves generated in solid media. These waves are similar to the sound waves propagated in air and other fluids but are more complex because solid media are also capable of resisting shear force.
Waves that encounter a change in media in which they are propagating may change directions or reflect. In additions to reflection, the interface causes the wave to diverge from its original line of flight or refract in the second medium. Also the mode of the wave may be changed in the reflection and/or refraction process.ISO 18081 pdf download.
