FRACTURE OF DUCTILE PIPELINES SUBJECTED TO BENDING AND REVERSE BENDING LOADS

Closed-form solutions for the elastic-plastic deformation and fracture responses of an offshore pipeline during reeling and unreeling operat ions are derived. As an example, an API 5L X52 pipeline of thickness 2 5.4 mm (I in.) and outer diameter 406 mm (16 in.) bent over a drum rad ius of 16.5 m (54 ft) and then straightened back to its original confi guration is considered it was found that the pipeline underwent signif icant plastic deformation during bending and reverse bending. The plas tic zone extended from the top (bottom) of the pipe to 16.46 mm above (below) the neutral axis during bending. Modified J-integral and J(R) resistance curves were compared to evaluate through-thickness crack gr owth and stability. The difference between predicted crack growth and experimental results varied from 30 to 140 percent. J-integral-based c rack growth predictions were significantly lower and much closer to ex perimental results than previous predictions based on crack tip openin g displacement. Finally, a failure assessment diagram (FAD)for the pip eline was presented. The FAD would enable one to assess the propensity to fracture in pipelines.