Enormous attention has been attracted to the safety issues regarding numerous pipelines that have had to be repaired by such local reinforce as welding a tube-cap or patch. The present paper provides a detail description of experimental and numerical research conducted to evaluate the structural condition of locally reinforced pipelines, subjected to internal pressure including cyclic load. Six full-scale pipe specimens are tested under pressure to determine their loading capacity. Their stress distributions are measured, and their stress concentrations and plastic limit loads are analyzed. The result of the present study demonstrates that the burst pressure may not be affected by welding either a tube-cap or patch and cyclic loading, but the plastic limit loads of the repaired pipelines decreased respect to undamaged pipeline, among which the lowest one decreased up to 85% of that of the undamaged pipeline. It is also found that on the pipeline repaired by a single tube-cap or patch the burst occurred away from the welding sites, whereas on the pipeline included several tube-caps in short span the burst took place between the two adjacent tube caps, suggesting that multi-cap repair is disadvantageous to the loading capability of the pipelines. In addition, using nonlinear finite element tools, stresses state in locally reinforced pipeline is calculated. It is showed that bulging occurs in long and narrow area in the pipe along longitudinal direction, addressing where burst rupture occur.

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