Bursting Analysis of Compound Circular Gas Cylinder

During water pressure testing, the compound circular gas cylinder burst when the water pressure rose to 58 MPa. The designed pressure is 60MPa. Beforethe water pressure testing, strength testing, air tightness testing and fatigue testinghad beencarried out. The lining of the cylinder is TC4 titanium alloy by superplastic forming and laser welding, and the outer wrapping is aramid fiber. In order to find out the failure cause, macro and micro observation, chemical composition analysis and metallographic structure examination were carried out. The results show that the crack originated from the weld toe of the inside weld of the lining, and there are several small brittle quasi cleavage planes slightly oxidized at the source zone. Fatigue striations can be seen at the transition zone between the source zone and fast fracture zone. The analysis shows that the crack initiated during the welding and propagated during the fatigue testing. Then during water pressure testing, the stress intensity factor reached the critical value, resulting in bursting. The crack is hydrogen embrittlement crack. Environment absorbing hydrogen occurred during welding due to poor gas protection.