A Pipeline Dent Assessment Model Considering Localised Effects

The Canadian Pipeline Design Standard (CSA Z662) [1] requires the repair of smooth dents with depths exceeding 6% of the pipeline’s outside diameter. This limit on dent depth is reduced in the presence of additional localised effects such as pipe wall gouges, corrosion or planar flaws. Furthermore, it has been observed that pipe wall metal loss, planar flaws and weld seam interaction with dents can significantly reduce the service life of a dented pipe segment. A previously developed pipeline dent assessment model, based on the actual dent profile and in-service pressure history applied to non-linear pipe finite element model with a fracture mechanics crack growth algorithm, has been used to explore the consequences of these localised effects. The effects of corrosion (uniform or local pitting), weld seams (including their weld toe stress concentration effects and residual stress fields), planar flaws (cracks) and gouges on the service life of a dent are reviewed in this investigation. The performance of the model is demonstrated based on its agreement with field observations. The dent assessment model application and validation processes has indicated that the model presented here can be reliably used to predict the service life of dented pipelines in the presence of various localised effects.