Composite Pressure Vessel Testing using Acoustic Emission Testing
Acoustic emission (AE) technology has been applied to steel pressure vessels, including U.S. DOT and ASME high pressure cylinders, for over 40 years.Over the last few decades, the acoustic emission technology has also been applied to composite overwrapped pressure vessels (COPVs).Compared to other non-destructive testing (NDT) techniques, acoustic emission testing is unique because it detects active flaws in steel and composite pressure vessels.The concept is shown in Figure 1 for U.S. DOT steel cylinders. Two sensors are placed on both ends of the cylinder and connected to AE instrumentation using coaxial cable.The tube is pressurized from 50% to 110% of its maximum allowable working pressure (MAWP).If a fatigue crack, or corrosion related flaw, is present in the pressure vessel and grows during pressurization, it will emit a sound wave, or acoustic emission, which is detected by the sensors. The fatigue crack is located through analysis of the relative time-of-arrivals of the acoustic emission at each sensor.A cylinder passes or fails the test based on how much acoustic emission is detected over the course of the test. This is a summary of the basic procedure used in all U.S. DOT Special Permits that allow for acoustic emission testing in lieu of hydrostatic testing.