Feasibility Study of S-Lay Installation for Deepwater SCRs and Pipelines

Abstract

The J-lay and S-lay are two common methods for SCR and pipeline installations. When using the S-lay installation method, onboard welded pipe joints leave the vessel horizontally and are guided to the seabed over a stinger structure. The pipe is lowered using tensioners. With the advantage of high production rate, Slay can be a cost-effective solution for deepwater riser and pipeline installation. Based on HYSY201 installation vessel, this paper investigates the feasibility of S-lay installation for deepwater SCRs and pipelines to be used in South China Sea. It first introduces the SCRs and pipelines to be used for a deep draft semi-submersible for the Lingshui 17-2 project. It then presents the S-lay installation vessel HYSY201 and S-lay configuration. The hydrodynamic motion analysis for a Response Amplitude Operator (RAO) was computered for HYSY201 in different environmental headings. With the site-specific metocean design basis, this paper presents an installation procedure, analysis methodology, and acceptance criteria. The study covers different sizes of SCRs and pipelines to investigate the feasibility of S-lay installation. The study starts from the static installation analysis of SCRs and pipelines and includes different installation steps. The acceptance criteria are examined for the pipes at over bend and sag bend regions. The support reactions load on the stinger structure are reported at each step. The dynamic analysis is selectively performed to evaluate Dynamic Amplification Factors (DAFs) of support reaction loads especially for roller box supports on the stinger structure. The sensitivity of DAFs to wave parameters such as wave height and peak period is analyzed as well. The extreme support reaction loads are computed for evaluating the strength performance of the stinger structure. The feasibility of S-lay installation for deepwater SCRs and pipelines is determined by the global performance of SCRs and pipelines, installation vessel hold back tension and A&R winch load capacity, and performance of the stinger structure. Based on the study work, this paper finds the feasibility of S-lay installation of deepwater SCRs and pipelines for Lingshui 17-2 project using the installation vessel of HYSY201.