A numerical study of damage caused by combined pitting corrosion and axial stress in steel pipes

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A numerical study of damage caused by combined pitting corrosion and axial stress in steel pipes

Rajabipour, Ali / Melchers, Robert E.

Localized pipe wall damage accounts for many failures. Numerical modelling of pipes under increasing axial load and constant internal pressure when there is corrosion pits on the exterior surface of the pipe is reported herein. It is shown that for the assumed ideal elastic-plastic material the shape and volume of the plastic field depend on pit depth and its geometry. Initiation of plasticity commenced at the bottom of the pit but become more complex and spread into the adjacent regions at higher applied axial stress. It was found that the stress required for plasticity initiation depended on the aspect ratio of the pit mouth and that this also influences the amount of plastic volume that is formed. The loss of the pipe wall around the pit through plastic flow deformation can be estimated from the amount of plasticity that forms in the pipe wall under stresses. A critical minimum section of plasticity was associated with pipe wall failure leading to local pipe bursting and used to define a Damage Index. This is a function of pit depth, pit aspect ratio and applied axial stress. Polynomial of second and third order fit the development of the estimated opening area with R² > 0.9. This should be relevant to engineering applications, including estimation of the response of steel pipes under seismic loading that generates mainly axial stress in the pipe.