Session: 04-04-04 Lateral Buckling and Reeling

Paper Number: 125900

125900 - Reeling and Unreeling a Pipeline With Lüders Bands on a Reel 

Experiments and analyses have demonstrated that under bending tubes with Lüders bands develop localized diamond-shaped patterns of inclined bands of higher strain on both the tensioned and compressed sides. When the pipe is wound onto a large diameter reel, in order for the line to conform to its curvature the bands form clusters separated by elastic zones. The present study uses large-scale finite element analysis to study the evolution of these events under repeated reeling/unreeling of pipelines. The analysis is coupled to a custom combined isotropic-kinematic hardening constitutive model. Localization associated with Lüders banding is reproduced by partial softening that covers the extent of the instability, and the Bauschinger rounding of unloading/reverse loading by nonlinear kinematic hardening. The analysis demonstrates that the band clustering initiates close to the point of first contact with the reel and leads to localized curvature, wrinkling of the top and bottom surfaces of the pipe, and ovalization. Close to first contact with the reel, the section moment reaches a local maximum and drops to a lower level as it moves further down the reel. During unwinding, the line straightens without sharp changes in curvature, the strain in the clusters is reduced, but new localization patterns nucleate in the elastic zones between the initial clusters. The straightened line ends with residual ovality, axial surface undulations, and residual stresses. During subsequent cycles, the line continues to bend in a smooth manner, but the clusters of bands reappear during winding and the secondary patterns during unwinding. The ovalization accumulates with every cycle, the undulations due to wrinkling remain, and so do the residual stress and strain fields. The accumulated ovality degrades the pipeline and the wrinkles induced by Lüders banding further aggravate this degradation. It will be demonstrated that for unfavorable combination of pipeline diameter-to-thickness and back tension, the pipeline can buckle and collapse during reeling.

 

Presenting Author: Stelios Kyriakides University of Texas

Presenting Author Biography: Decades long researcher in mechanical behavior of offshore structures

Authors:

Stelios Kyriakides University of Texas
Weihan Zhang University of Texas at Austin