Within Sakhalin II Phase 2 Development Project - Offshore Pipelines and Cables EPIC contract, it was required to design the expansion spools at PA-B offshore platform for the connection of the 14" gas & oil pipelines to the relevant risers. This paper describes the technical and schedule issues associated with the design, fabrication and installation of these spools together with the adopted and successfully implemented solution. The area is characterised by extreme environmental conditions like pack and heavy ice transported by wind and currents and earthquakes that could affect the expansion spools integrity. The 70m long expansion spools were designed to cope with the following requirements:
to withstand vertical and horizontal high loads (1000 KN) due to iceberg impact;
to be able to accommodate differential displacement between pipeline and platform due to earthquakes and platform settlement;
the riser stubs, exiting the platform wall, has to be protected from ice impact;
no dredging is allowed closer than 15m from platform wall due to platform stability and safety reason;
very tight schedule for design, material procurement, fabrication and installation;
installation constraints imposed by the selected installation vessel already planned.
An innovative solution was conceived using standard materials and components to develop an original concept and foresees the design, procurement, fabrication and installation activities performed in two stages, namely:
First year installation campaign (2005):
preparation of the area to locate the spools leaving opened a corridor in the platform scour protection gravel berm using temporary items;
installation of the base protection structure for the riser stubs;
installation of the entire scour protection around the platform.
Second year installation campaign (2006 now moved to 2007):
removal of the temporary items and opening of a 6 m wide corridor between the risers and the edge of the platform scour protection;
performance of all the dredging work to prepare the trench to bury the spools;
installation of the spools, of the risers stub protection cover roof and reinstatement of the gravel berm and trench backfilling.
To cope with the design requirements and mainly with the tight project schedule the conceived solution consisted in:
steel frame to protect the riser stubs in the first winter before final installation of the spools and of the relevant protection system;
standard reinforced containers, to maintain a free corridor in the platform scour protection gravel berm until the spool is deployed;
spool protection system composed by a "pipe in pipe", where the inner 14" is the process pipe and the 36" steel outer casing constituted the protection system;
the process pipe inside the outer casing is free to move in order to avoid overstress on the spool / riser stub flange