PSI - Issue 57

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Yann Chevalon et al. / Procedia Structural Integrity 57 (2024) 633–641 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

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Fig 2 Configuration of a floating production system

The riser parts of the flexibles are the focus point of that article; this is where dynamic loads apply on the flexibles. 2. Model description 2.1. Extruded polymer sheaths, and stress concentration factors As it has been described in the introduction, a flexible pipe is composed of different layers that can slide relatively between each other. This paper only focuses on the extruded polymeric layers material-: inner pressure sheath and outer sheath. These layers are extruded and the resulting geometry is a cylinder presenting irregularities on the inner surface after the polymer has been extruded on top of a wound layer with corrugations generated by gaps. In the case of an inner pressure sheath, irregularities are present on both inner and outer surface, and the outer surface irregularities come from creep of the polymer into the gaps.

Fig 3 (a)Sample of extruded outer sheath with an irregularity on the inner surface. (b) Sample of inner pressure sheath that creeped between PA gaps after being exposed to pressures and service temperatures for months.

Figure 3(a) provides an illustration of irregularities on the inner face, while Figure 4(b) provides a representation of irregularities on both the inner face and the outer face. The fatigue model, presented in the coming chapters, is intended to take into consideration the geometry defects of the material from manufacturing and service, but also the exposure to different temperatures. 2.2. Material of the polymer sheaths and temperature dependency The extruded layers are composed of thermoplastic polymeric materials. These materials exhibit a non-linear behavior and mechanical properties are heavily temperature and time dependent as illustrated in the figure 4(a) and 4(b) for a better understanding.