Failure Analysis of Impact Damaged Pressure Vessels and Pipelines

The present paper is devoted to analysis of burst conditions of the pipeline-in-service and vessel under high pressure subjected to the debris impact due to accidental explosion. The central concern of this study is to determine the border between simple perforation and catastrophic fracture of impact damaged pressurized structure. Under certain conditions vessel perforation from the front side can lead to unstable, rapid crack growth (“unzipping”). The pressure vessel of the relatively small size can be damaged from the rear side as well. As a consequence, two main classes of catastrophic failure of such structures are likely to occur: structure fracture from the front side and failure from the rear side. Damage patterns and mechanisms leading to unstable crack growth are discussed. The impact holes in a wall of pressurized structure are considered as a crack-like defect. By the model suggested, the cracked area around the penetrated hole is simulated by two radial cracks emanating from the rim of a hole. So the diameter of the model hole is equal to the diameter of the front impact hole; the length of the crack is bounded by a damage zone, which is a zone of spall cracks adjacent to the perforated hole. In a gas-filled cylinder shell the stresses in the circumferential direction are twice the longitudinal stresses. Thus, in the process of fracturing the cracks tend to run longitudinally, perpendicular to the hoop stress. By this reason the hypothetical radial cracks are normal to the hoop stress. Nonlinear fracture mechanics techniques were used to analyze and predict whether a wall perforation will lead to mere leakage of gas, or whether an unstable crack will run and destroy the pressurized structure. The problem was solved by numerical method of singular integral equations in Chebyshev’s polynomials. A developed model was successfully applied to the simulation of experimental results.