Recently the pre-salt development is a great challenge for Petrobras regarding the offshore exploration and production activities. The pre-salt area comprises several ultra-deepwater fields located far off the Brazilian coast.

In order to flow the produced gas of these pre-salt fields, Petrobras has planned to install large diameter gas export pipelines as trunklines. The design of large diameter gas pipelines in ultra-deepwater of about 2200m has hydrostatic collapse and installation loadings being the major issues to be faced by the technical team. Reduction of pipeline wall thicknesses may improve the technical and economic feasibility of its installation in ultra-deepwater and sometimes can also increase the number of laying barges / vessels able to perform the installation. However, reduction in wall thickness is only feasible if the pipeline integrity under external pressure as well as under combined loadings is ensured in accordance with the applicable design code and the engineering best practices.

This paper presents the assessment of some design parameters able to reduce the wall thicknesses along the pipeline length, while keeping the commitment to the engineering good practices and complying with all requirements of the DNV-OS-F101 design code. In order to illustrate the assessment, this paper presents results of two gas pipelines designed in accordance with DNV standards, one of them being optimized. The benefits of this optimization are emphasized in this work.

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