ABSTRACT

In recent decades, global economic growth has increased the demand for more energy and natural resources, leading to the exploration of oil and gas in deep and ultra-deep water. In this context, pipelines, as major components of oil and gas production facility, faces new challenges both in terms of design and installation.

A thick-walled pipeline is required to withstand buckling during the installation process due to the combination of high external hydrostatic pressure and overbend/sagbend bending during the pipe-laying process in deep water. Given that existing lay vessels have limited tension capacities to reduce the bending radius, measures must be implemented in both pipeline design and lay vessel configurations, to allow for ultra-deep-water installation.

The two most common methods used to install large diameter pipelines in deep water are with S-Lay or J-Lay vessels. Some parameters need to be considered when choosing the appropriate installation method, therefore limitations for each method are investigated.

Regarding the wall thickness design requirement, several research and collapse testing program have been performed to investigate potential improvement of allowable strain level that can influence ovality/OOR.

Recent research and project experience show that as-manufactured ovality/OOR as low as 0.5% or even less can be achieved compared to the conventional OOR of 1.5%. In addition, the tests also document the potential for improving the important linepipe fabrication factor (αfab) from 0.85 to 1.0 for UOE/JCOC pipe. If such improvements are applied, significant reduction in linepipe procurement and construction cost can be achieved. In some cases, such optimization is required for enabling project feasibility, e.g. in pipeline projects pushing the industry limits wrt water depth and diameter.

Considering the aspects mentioned above, studies will be carried out in this paper. The paper will focus on S-Lay and J-Lay methods for various water depths, steel grades and pipe sizes. Starting from 0 to 4 000 m water depth, steel grades of X65, X70, X80, X100 and pipe sizes from 18 inch and larger including the effect of OOR are investigated.

The paper will illustrate with practical applications of two installation methods with each their own domain of excellence and also overview of installation vessel available in nowadays pipeline industry.

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