Abstract This paper aims to compare the different sealing methods that are typically used in the subsea mechanical connectors, such as elastomeric, graphite and the frontal metal-to-metal sealing system implemented in the novel subsea connectors purposely developed for CRA clad and lined pipelines. The frontal metallic sealing has been conceived to cope with the inner layer with the same material of the CRA, thus avoiding material heterogeneity and perfectly reinstating the original containment. Repair connectors for CRA clad and lined pipelines follow the main installation steps, diver or diverless, of the more conventional elastomeric connector and of the graphite seal connector, which rely on the pipe's outer surface for sealing. However, the peculiarity of the CRA pipeline layering calls for a new sealing method to the pipe frontal cut end to reinstate the original fluid containment and prevent to be in contact with the pipe carbon steel wall. This needs different pipe preparation to remove all flaws up to required tolerances from the pipe cut end frontal surface. The different seal materials can be seen as an evolution to respond to the increasing repair needs: The elastomeric seal represents the largely used solution for non-sour service pipeline, the sealing is on the pipe's outer surface and requires the removal of the pipe coating and the weld seam, thanks to the polymer adaptability once energized. The repair with elastomeric seal is regarded as a non-permanent solution due to the aging of the polymer, potentially no compliant with the residual pipeline lifetime. The graphite seal is considered an evolution of elastomeric seal, replaced by metallic material making the repair permanent. Likewise for the elastomeric connector the sealing is on the outer surface, however the installation tolerances are more stringent due to the limited capability of the graphite to radially expand when energized, making the intervention more complex. The frontal metal sealing, conceived for the CRA pipelines, mates the inner CRA layer with the same noble material preventing the corrosive fluid to contact the carbon steel pipe wall, therefore reinstating the original containment differently from the outer surface sealing. The installation requires preparation of the pipe cut-end surface to the required tolerances with limited complexity compared to the elastomeric connector. The Saipem Grip & Metal Seal Connector (GMSC), specifically designed for application to sour-service pipelines and in particular to CRA clad or lined lines, to overcome the limitations of the conventional connectors that rely on sealing on the pipe's outer surface, thus exposing the pipe wall to corrosive fluid. The frontal metal seal in fact reinstates the original pipe containment without narrowing down the internal diameter keeping the same pigging capability.
Girello et al. (Mon,) studied this question.