Failure analysis of beta-C titanium alloy high-pressure vessels

An attempt has been made to apply the linear elastic fracture mechanics concept to Beta-C titanium alloy pressure vessels that exhibited brittle fractures during hydrotesting. Based on the results of stress analysis on the real structures and fracture surface examinations, a stress-intensity factor, K[sub IC], was estimated. The K[sub IC] value of the material in the cracking direction was measured by a surface semi-elliptical crack method. It was found that the K[sub IC] value of the material is very close to the estimated stress-intensity factor K[sub I] during failure, which places the pressure vessels in a critical condition in that a small variation in flaw size may cause a catastrophic failure. A compromise must be made between K[sub IC] and the required yield strength. In this restricted case, the yield strength of the material should be controlled in the range of 1,150 to 1,200 MPa to avoid brittle fracture and the possible occurrence of yield during hydrotesting. Control of microstructure and other mechanical properties is also discussed in this investigation.