Bolting unit allows flange tie-in of deepwater pipelines

Ian Frazer
Stolt Comex Seaway

Bolted flanges are by far the most widely used and cost effective method of connecting subsea pipelines. As a result, there is considerable experience and confidence with the long term performance of subsea flanges.

The installation of bolted flanges subsea has been performed exclusively by divers.

As a result, the use of this important connection method has been precluded from deep water ap plica tions, where diverless methods are essential.

To meet this challenge, Stolt Comex Seaway (SCS) has designed and successfully tested a system, christened MATIS, which enables standard API and ANSI flanges to be aligned and connected subsea without the need for divers. This provides the opportunity of utilizing proven technology from shallow water into deepwater applications, with the benefits of reduced costs and lead times and an overall increase in system reliability.

The MATIS system, which was developed as part of an extensive four-year research and development program, consists of a set of equipment comprising pipe handling frames, a flange alignment frame, and the flange connection tool, which includes the bolt tensioning equipment.

The system has been designed to allow the utilization of standard flanges for various deepwater pipeline tie-in scenarios, such as a spool piece connection and flowline-tree connections. MATIS is suitable for use in connecting pipelines diameters ranging from 6 in. to 36 in., and the water depth is limited only by the length of umbilical available. The flange connection sequence is a two-stage process, the first to get the flange faces into alignment using the handling frames, and the second to install the bolting equipment on to the flange and complete the connection.

The system can be deployed from a standard dynamically positioned diving support vessel (DSV), equipped with a 50-ton bottom-reaching crane. The tie-in operation is monitored and controlled from the DSV via an umbilical connected to the subsea equipment. The unit is fitted with an emergency disconnection system which incorporates complete system redundancy such that no single point of failure can prevent disconnection of components of the overall system.

Each component within MATIS is equipped with an ROV over-ride which can be used in the event of a disruption to the control system. It is estimated that a complete tie-in operation can be performed in 10 hours with the MATIS system. It is currently planned to utilize the MATIS on a subsea project in the North Sea later in 1998. A 10-in. gas pipeline will be connected to a riser base using a flanged spool piece. The work, which is within diver depths, will be performed remotely and marks a further step in the overall development of this new deep water tie-in system.