Abstract

This paper is based on the experience made during the engineering, fabrication and installation of rigid spools used to tie-in production lines (10”) to manifolds, in 650m max water depth, on a project recently completed in West Africa.

The design of tie-in spools needs to accommodate the operation and environmental loads, and the installation, fabrication, metrology and, if applicable, also stack up tolerances.

This may require spools of large sizes/weights and complex geometries, with associated fabrication and installation costs that significantly contribute to the overall costs of a project.

This paper is focused on the process that was followed during the execution of the RFI (Risers Flowlines Installation) EPCI (Engineering Procurement Construction Installation) contract.

To find workable configurations of the spools, such not to compromise the execution of the project, was a major challenge.

Horizontal connection systems were to be used.

Configurations of the spools, initially designed to be in contact with the seabed (“seabed-supported” design) turned to be by far more complex than the geometries estimated before the start of the detailed engineering, and which had been the basis for laying down the execution schedule of the project.

Spools suspended between the horizontal hubs (“free-spanning” design) were finally chosen, which significantly simplified the fabrication and the installation.

A key driver of the design was to keep the interface loads within the maximum permissible values specified for the connectors.

The feedbacks from the fabrication and the installation are included in the paper, and the lessons learned are provided.

Alternative solutions — based on use of flexible pipes — are also discussed.

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