Break opening times for axial rupture of a gas-pressurised pipe

The consequences of a major rupture of a pressurised pipe are strongly influenced by the break characteristics (i.e. fracture orientation, opening time and final breah area). For example, the amplitude of the blast wave generated in the external atmosphere is dictated by the rate at which energy is released through the developing breach and hence is a function of opening time. A pipe is assumed to be fully open when the breach area is twice the cross-sectional area of the pipe, thus allowing full flow from each leg of the pipe.This paper describes experiments where the development of an axial rupture in large gas-pressurised steel pipes was observed by high speed photography. The tests were performed on 610 mm diameter pipes, with wall thicknesses of either 6.2 mm or 9.3 mm, apart from the final test where a 915 mm diameter, 12.5 mm wall thickness pipe was ruptured. Rupture pressures ranged from 19 bar to 40 bar.Measured breach opening times are compared with data from earlier small scale tests (102 mm diameter pipes with 1.6 mm wall thickness) where rupture pressure ranged from 50 bar to 120 bar. Both sets of data are shown to be in general agreement with a theoretical model which combines an upper limit ductile fracture propagation velocity with a simple inertia model for the displacement of the free edges of the breach. For large pipes the measured and predicted opening times are significantly longer than the maximum of 1 ms specified in the current US design codes.