Deep Water Tie-In

Abstract

This paper, named “Deep Water Tie-In”, describes a tie-in concept for large diameter pipelines. The concept is developed for use at large water depths where diving is both costly and dangerous.

The concept is developed for a typical Gravity Base (GBS) platform situated in 300 metres water depth.

The tie-in of pipelines with a diameter of up to 40” is achieved through a tie-in arrangement system pre-installed in the platform substructure. The main components are an atmospheric tie-in tunnel, seal tube and J-tube for pipeline pull cable. The paper describes each of these components in more detail before it embarks on a step by step account of the pipeline tie-in procedure.

In order to establish design loads on the sealtube and identify the optimum pipeline approach, computer analyses have been carried out. It is shown that a curved pipeline approach or a dogleg are both feasible from a load on anchor or stress in pipeline point of view. However, a straight pipeline approach causes loads and stresses too high for practical design purposes.

In order to evaluate the advantages of the proposed tie-in arrangement, the paper ends with an outline of alternative tie- in concepts.