S-lay installation of a 6-inch small-sized SCR with flexible joint assembly in the 2nd end is investigated in this paper. Due to the huge difference in external dimensions, weights and bend stiffnesses between the riser pipe and the flexible joint, passing through the S-lay vessel stinger of the flexible joint assembly poses a big challenge to the strength integrity of the overbend section of the SCR, especially the steel pipe at the connection with the flexible joint body. This paper summarizes the engineering approach and FEA analysis work that were carried out in order to reduce the maximum strain in the critical riser overbend section. These engineering approach options include design of a long tapered stress joint type shroud, an extended upper shroud, to facilitate installation of flexible joint assembly travelling along the stinger. The latter approach is selected for detailed design which lays the engineering groundwork for successful pre-laid operation of the 6-inch SCR with flexible joint.
There are several methods to lay pipeline offshore in deep water region, which includes S-Lay, J-Lay, Reel-Lay etc. Reel-lay is an extremely efficient method for the installation of small to middle size rigid pipelines, with advantages gained by the high production rate as well as the controlled welding and inspection conditions onshore. However, to achieve its efficiency, a spool base is required nearby to reduce transit time to and from the pipe installation location. For S-lay installation method, onboard welded pipe joints leave the installation vessel horizontally and are guided over the "stinger" in order to control the deflection of the pipe in the over-bend region above the pipeline inflection point. The S-lay installation is a conventional pipelay method for rigid pipes, which is suitable for large pipe sizes and can be a cost-effective of higher pipelay rate solution in comparison with J-lay method for deepwater riser and pipeline installations.
