Acoustic emission for periodic inspection of composite wrapped pressure vessels

Type 3 composite cylinders are used by the U.S. Navy to store compressed gases. The recertification procedure for these cylinders requires a hydrostatic test and an internal visual inspection every five years. Physical Acoustics Corporation has developed an AE based test method for the periodic inspection of these cylinders. AE baseline tests were performed on over fifty "good" cylinders and damage and/or fatigue cycling was introduced in fourteen cylinders. After damage and cycling the cylinders were tested again, which resulted in a dramatic increase in AE activity compared to that prior to the damage. The most active cylinders were also hydrostatically tested. No cylinders failed this test. However, a subsequent burst test showed a substantially decreased burst pressure for the AE active cylinders. A consistent correlation between burst pressure and AE activity was observed. An accept/reject criterion was developed to differentiate those cylinders with acceptable burst strength from those with unacceptable burst strength.