In order to perform pipeline maintenance it is often necessary to excavate the pipeline. To ensure this is conducted safely, the expected condition of the pipeline and possible failure scenarios are considered in order to establish a safe operating pressure during the excavation and subsequent work. For pipelines that are laid in rocky terrain, consideration must be given to the possibility of a large rock impacting the pipeline. The purpose of this work is to describe the application of a numerical procedure to establish the safe working pressure during the excavation of a pipeline in a rocky terrain. A numerical procedure, developed previously [1] was shown to conservatively estimate a safe working pressure for the case of a rock falling on the pipeline. FEA was used to determine the relationship between the available kinetic energy of a falling rock and the energy to puncture the pipeline (as a function of internal pressure). The resulting puncture dimensions were then compared to the critical-crack-length to cause rupture. The safe pressure was obtained from the pressure where rupture first occurs, reduced by an appropriate safety factor. This paper describes the application of the numerical procedure described to cover a large range of pipe toughnesses and internal pressures.

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