Comparisons study of S-Lay and J-Lay methods for pipeline installation in ultra deep water
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The pipeline industry has developed its technical capabilities to enable operations in deeper water. In ultra deepwater developments, the offshore industry has been challenged to solve demanding tasks, to develop new and reliable installation technologies for deepwater and uneven seafloor conditions, and to discover technology to deal with harsh environmental conditions. Pipeline installation in deeper water area needs special considerations regarding the lay vessel capabilities. These capabilities are that the vessel should have enough tension capacity for the deeper water and good dynamic positioning system restricted to small movements only. Two common methods used to install pipeline are the S-Lay and J-Lay methods. Some parameters need to be considered when choosing the appropriate installation method, therefore limitations for each methods are investigated. For the S-Lay method, these important parameters Include vessel tension capacity, stinger length, stinger curvature, strain in the overbend region and bending moment in the sagbend region. The maximum depth at which a given pipeline can be laid could be increased with a longer stinger of the lay barge and bigger vessel tension capacity. However, choosing these options may require clamping to pull the pipeline that can cause a heavy mooring system and high risk associated with a very long stinger subject to hydrodynamic forces. In addition, these options also could destroy the pipe coating. On the contrary with the S-Lay method, the J-Lay method reduces any horizontal reaction on the vessel’s equipment, and because of this, the J-Lay technology might be used to meet project requirements in deeper water. However, the capability of the J-Lay method in deep and very deep waters requires barges with dynamic positioning capabilities. This is because positioning by spread mooring with anchors would always be worthless and often unfeasible due to the safety of operations. Under extreme conditions, the loading process induced by the lay barge response to wave actions in deep waters is less severe for J-lay method compared to other methods. However, special attention has to be paid to the complex nature of vortex shedding induced oscillations along the suspended pipeline span. Considering the aspects mentioned above, studies will be carried out in this master thesis. The thesis will expose two pipeline installation methods, i.e. S-Lay and J-Lay methods for various water depths and pipe sizes. Starting from 800 m to 4000 m water depth, pipe sizes more than 24 inch will be investigated. The effect of increasing strain in the overbend region and effect of reducing the stinger length will be studied to meet these challenges and to improve the laying efficiency especially using the S-lay method. Plot for various water depths and pipeline properties will be presented as the results of this master thesis. The installation analysis will be performed by using computer program SIMLA.
Master's thesis in Offshore technology