RACTURE MECHANICS. METHODOLOGY TO ASSESS THE INTEGRITY OF REELED PIPES

The reeling process is one of the most important methods for offshore installations of linepipes. Pipe segments are welded onshore and subsequently bent over a cylindrical rigid surface (reel) in a laying vessel. The pipe is significantly cyclically strained. Due to the severe loading cycles suffered by the pipes, it is necessary an adequate methodology to assess the integrity of these components. Current recommended methodologies were not specifically developed for reeling situations, If are straightforward applied unreliable results can be obtained. In the current work, the points that need to be resolved before extending the methods for assessing reeling situations are clearly identified. Theoretical models to describe the crack driving force evolution and the material fracture resistance behavior through strain cycles are proposed. As a result a methodology to assess the integrity of pipes subjected to a single reeling cycle is developed. The case where several reeling cycles are applied is considered. In addition to the fracture mechanics methodology, a fatigue crack growth formulation controlled by ∆J parameter is proposed. This formulation accounts for the crack growth produced during subsequent reeling cycles. In addition, a probabilistic fracture mechanics approach is included. This procedure takes into account the statistical distributions of the material properties and pipe geometry, using the Monte Carlo method. Two-parameter Weibull distributions were used to model the variability of the input parameters. Fatigue and fracture experimental programs were developed. Monotonic and cyclic fracture mechanic tests were performed on single edge notch in tension (SENT) specimens. As result, a general methodology for assessing the integrity of pipes under reeling condition was proposed