scope:

The effect of flaws with and without cyclic loading was investigated on a composite overwrapped pressure vessel with a non-load sharing polymer liner. Flaws were machined in the structure to four depths and then were cycled for 0, I 0,000 and 20,000 cycles. Finally, the cylinders were hydrostatically burst. These data were compared to a reference burst value of a cylinder without flaws or cycles. The cylinder was 406 mm (16 in.) in diameter by 1020 mm ( 40 in.) long with a service pressure rating of 24.8 MPa (3600 psi).

The lowest burst-to-operating pressure ratio was 2.13, which occurred with the flaws cut 40% into the structure and no cycles. Even with the deepest flaw and cycling, the resulting burst pressure margin would allow safe operation of the pressure vessel over a period of time. The lack of significant additional strength loss with cycling gives a degree of confidence that even if flaws are not found immediately, the risk of a fai lure due to the flaw is low.