This study investigates the effect of wrapping carbon fiber reinforced polymer (CFRP) over conventional steel offshore pipelines on improving their capacity under external hydrostatic pressure. Buckling performance of bare steel pipelines (conventional) and composite pipes (CFRP-strengthened) subjected to external pressure are examined analytically and numerically. In composite pipelines, the cylindrical steel tubes are wrapped with CFRP in 0/90° and ±45° fiber orientations. The finite element analysis (FEA) results are validated against analytical solutions on buckling of bare and composite pipelines. A parametric study is also carried out to investigate the effect of D/t ratio, the ratio of the thickness of the FRP to the steel-wall thickness, and the fiber orientation on the buckling capacity of composite pipelines. A good agreement between the current FEA and theoretical results are observed for pipelines with D/t > 30. Results also show that wrapping 0/90° cross-ply CFRP on the conventional steel pipes is more efficient in bucking resistance than the ±45° one. Using 0/90° orientation wrapping, the collapse pressure of a thin pipelines (D/t=100) can be enhanced by a factor of 15.
Exploration of hydrocarbons has shifted to deep and ultra-deep waters due to the scarcity of near-shore resources and recent advancements in deep water drilling technologies. Pipelines are long tubular structures used to transport hydrocarbons over long distances, and are designed to resist installation, operation and environment loads safely during their design lives. During installation and shutdown, an empty pipeline undergoes large external pressure due to the hydrostatic load, which may cause collapse in the tube wall. In addition, high-pressure and high-temperature (HP/HT) pipelines may collapse under combined loading due to the interaction between external pressure and thermal loads (Karampour et al., 2015; Karampour, 2018) or seismic loads (Mina et al., 2020).
Subsea pipelines are slender structures that can experience several structural instabilities. Global buckling can occur through lateral or upheaval buckling modes, however, these two buckling modes are not essentially failure modes (Karampour et al., 2013). Propagation buckling is the most critical one that increases the chance of pipeline failure, especially in the ultra-deep waters (Albermani et al., 2011; Karampour et al., 2017; Stephan et al., 2016; Alrsai et al., 2018a; Alrsai et al., 2018b). Hence, in deep waters, the failure mode associated with the buckle initiation and its propagation is the main consideration in the pipeline design.
