A new model of unstable ductile crack propagation and arrest of pressurized gas pipeline is presented. The model couples pipe deformation and fracture with gas decompression. The model also takes account of backfill effect. Pipe deformation and pressure changes are obtained by solving one-dimensional differential equations. Validity of the model was checked by comparing with published full-scale burst test data. The model can predict history of crack velocity and arrest crack length with fairly good accuracy. The model can be applied to wide ranges of gases, pipe grades and pipe sizes because it does not rely on parameter adjustment by experimental data sets but is based on physical assumptions.

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Burst tests of line pipes containing high-pressure hydrogen and methane gas were conducted. The pipes tested were X65 ERW pipes with 267mm outer diameter and 6mm wall thickness. Applied pressures were 12 and 15MPa. A 300mm long crack was initiated by a shaped charge. Unstable shear fracture propagated at velocity of approximately 200m/s and then arrested. It was demonstrated that the arrested crack lengths were shorter in the hydrogen gas burst tests than methane gas burst tests. Pressure measurement indicated that decompression wave in hydrogen gas propagated faster than that in methane gas. This is the primary reason to the shorter arrested crack lengths for the hydrogen gas burst tests. The test results are discussed based on numerical analyses of gas decompression behaviors.

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Full-scale burst test of X65 UOE linepipe, with 559mm outer diameter and 13.5mm wall thickness, pressurized at 16MPa by hydrogen gas was conducted. A 735mm long crack was introduced by explosive shaped charge over circumferential weld. The cracks were initiated and propagated in the both directions. The propagated crack lengths were 600mm and 270mm. J integral resistance curves were obtained from drop-weight as well as quasi static tests for the tested pipe material which was subjected to hydrogen charging. The tested steel showed little change in the resistance curves under realistic charging condition. Numerical simulation model of dynamic crack propagation, coupled with gas decompression behavior considering gas escape from opened crack, showed that an initiated crack was arrested at shorter distance in hydrogen gas pipelines than in methane gas pipelines, primarily due to earlier gas decompression in the former. The present results, together with the earlier full-scale burst tests conducted by the authors, demonstrated that hydrogen gas pipelines can be operated safely by using modern high-strength and high-toughness steel linepipes.