Controlled buckles in subsea pipelines exposed to expansion forces canbe triggered by various methods such as snake-lay, installing sleepers/berms, or the residual curvature method (Statoil patent, 2002). Thelatter (RCM) is relatively new but is gaining popularity and has now beensuccessfully applied to four pipeline projects. During installation, shortsections of residual curvature in the vertical direction are introducedto the pipeline, and these introduce a rotationally destabilising eect.Dierent as-installed configurations may result: the residual curvaturesection may rotate over into the horizontal plane on the seabed; or it mayremain vertical. If it remains vertical, self-weight can cause the pipe toslump down onto the seabed and become straightened.When applying the RCM, it is preferable for the pipeline to rotate approximately90 during installation, for the purposes of reducing the criticalbuckling force and avoiding the introduction of artificial free-spansat the residual curvature sections. Therefore it is important to analysethe rotation behaviour at the design stage. Rotational fixedness at thelay-vessel and resistance from soil friction act to restrain the pipe, butexperience from, for example Statoil’s Skuld Pipeline Project, indicatesthat the residual curvature sections tend to rotate. Recent analysis workon rotation during installation of the Johan Sverdrup in-field pipelines ispresented. The shallower depth reduced the tendency to rotation comparedto reference projects, and the analysis results were used to guideinstallation settings to assure a robust rotation response during lay.
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