Remote Connection of Deepwater Pipelines Using Standard Bolted Flanges
Authors: Frazer Ian , Monnot Frederic , Fletcher John 
Published: October 2008

Standard bolted flanges are the most commonly used and cost effective method for connecting pipelines both on shore and offshore in conventional water depth. This paper will address the advantages bolted flanges can offer in deep water pipelines where expansion of pipes may be a critical issue. A field proven system, which can be used to remotely connect bolted flanges subsea, will be presented. Lessons learned from the remote connection of over 100 flanges in deep water operations in West Africa will be presented. This has included disconnection and reconnection operations, as well as the remote tie-in of deep water flowlines in both horizontal and vertical orientations. Other applications for bolted flanges, such as the repair of deep water pipelines, will be discussed together with ways in which several pipeline operators can benefit simultaneously from the advantages offered by flanges.

Introduction

The past 15 years has seen a fundamental change in subsea construction technology, from being a diver dominated activity to the remote systems used for the construction of today's deep water field developments. The need to work in water depths beyond the capability of divers has driven this change to remote technology leading to the development of reliable Remotely Operated Vehicles (ROV) and a collectionof tools capable of performing a wide range of tasks. The remote connection of flowlines and pipelines in particular has been the subject of significant development activity over this period, resulting in the development of a number of proprietyconnectors and connection systems /1/. The majority of these connection systems are based upon mechanical connectors, which have been developed specifically for the remote connection of pipelines; many based upon connectors used for drilling applications. Consequently the connectors andresulting tie-in spools can be relatively large and complex (Figure 1).

Figure 1 : Tie-In Spool with Remote Mechanical Connectors (available in full paper)

For pipeline connections installed by divers the use of standard bolted flanges became and still are the connector of choice both from a reliability and an economic point of view. As a result, back in 1996, the challenge of enabling the use of bolted flanges for deep water pipeline connections was taken up by the Acergy engineering team. The resulting connection and alignment system known as MATIS (Modular Advanced Tie-In System) was first used on a deep water project in 2000 for the flowline and riser connections at the Girassol development offshore Angola /2/. Since then over 100 flangeshave been successfully connected in deep water. The use of standard bolted flanges for the connection of deep water pipelines may provide some significant advantages over the mechanical connectors more commonly used in deep water today, these include :-Bolted flanges are field proven and have been extensively used in subsea applications throughout the offshore industry for high pressure gas/oil pipeline for many yearsFlange material and design can be easily customized to fit the fluid and flow characteristics (CRA, HP/HT, etc.)Bolted flanges offer the most tolerant connection with regards to stress in the system and long term reliability. In addition they are least subject to damage in case of future disconnection and reconnection.