Failures of Welding Repaired Pipeline

Enormous attention has been attracted to the safety issues regarding numerous pipelines that have had to be repaired by welding. The present paper describes experimental and numerical research conducted to assess the structural condition of welding-repaired pipeline, subjected to internal pressure including cyclic load. Six full-scale pipe specimens are tested under pressure to determine their structural capacity. Their stress distributions are measured, and their stress concentrations and yield and burst limit load are analyzed. The results of the present study demonstrate that on the pipelines with a single drilled hole the burst occurred far from the welding sites, whereas on the pipelines with several holes drilled 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. It is also found that the burst pressure may not be affected by welding either tube-cap or patch and cyclic loading, but the yield 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. In addition, using nonlinear finite element tools, stresses state in welding repaired pipeline is calculated. It is showed that bulging occurs in long and narrow area along longitudinal direction, addressing where burst rupture occur.