Abstract

Flexible reinforced thermoplastic pipes (RTPs) have been increasingly accepted as an important alternative to conventional metallic offshore pipes for oil and gas applications. Mechanical behaviour of flexible RTPs subjected to typical installation and operational loads is analysed in this paper. Results of finite-element simulations are presented for the RTPs with different material characteristics. Strength and buckling analyses have been performed considering a non-linear behaviour of the material. The minimum allowable bend radii of RTPs are determined. The effects of material nonlinearity, loading paths and diameter-to-thickness ratios on the performance of the RTP are investigated. It has been shown that the buckling mode of failure becomes more critical for RTPs with larger diameter-to-thickness ratios and adopting conventional approach based on the maximum allowable strain of the cover used in industry to predict the minimum allowable bend radii could lead to inaccurate results. It is found that the spoolability assessment and estimation of the minimum allowable bend radius of the RTP can be substantially improved by using the FEA approach presented in this work.

In the case of combined external pressure and bending, the corresponding critical loads and buckling mechanisms are shown to be dependent on the loading paths. The values of the critical external pressure are decreased with the decrease in the applied rotations, showing that the resistance to buckling of the RTP with larger initial curvatures is reduced. Also it is demonstrated that modes of collapse depend on the extent of initially applied bending. It is shown that significant difference (up to 17%) in terms of the critical loads can be caused by loading paths for a curved RTP.

The axial tension is found to have significant effect on the buckling behaviour and the corresponding critical load of the RTP. These effects should be taken into account in the design and analysis of the RTPs. The results obtained in this study will help understand the mechanical behaviour of RTPs during installation and improve their design characteristics.

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