Subsea Connections and Tie-in Methods 

The following chart depicts the main interfaces of a tie-in operation, which are then further explained in the following sub-sections.

This clearly shows the importance of an early integration of the tie-in method/connector system selection into the overall Project Plan as they impact and interfere with the subsea architecture (e.g. wells, manifolds) and flow-line designs and tie-in vessel selection.

Figure 2.1 - Tie-In Method main interfaces

A subsea structure has to be designed and equipped with due consideration of the following additional mechanical aspects:

Figure 2.2 - Example of vertical tree (Aker Solutions – KAOMBO PVXT)

The flow-line termination must be designed and equipped with the following considerations:

Figure 2.3 - Universal Tie-In System (UTIS) termination heads (courtesy of TechnipFMC)

Figure 2.4 - TOTAL’s KAOMBO Manifold

One or several vessel/ships of the following types could be involved in a tie-in operation:

The vessel and tie-in method choices are intimately related. Some tie-in methods would require the presence of two vessels (e.g. the Lay-away tie-in method, see "5.6. Surface tie-in, lay-away and lay-to", which requires the simultaneous presence of the laying ship and the drilling rig), this interface can have a costly repercussion on the project.

Launching and recovery of both the ROVs and the ROTs can also be defined as an interface item as its performance have a direct impact on the time (hence the cost) of a tie-in operation.

A set of tools exist per connector type to perform several functions (connection/disconnection, hubs cleaning, seal change out, acid injection, torqueing, etc.).

The connection tools set design is based on:

The connection tool design depends on the connector type (which determines the required functions: hydraulic supply, torque tool, integrated seal plate handling and replacement tool, etc.) and varies with each manufacturers. Some tools are proprietary (developed by SPS manufacturers or other manufacturers) and some are more common on the market (torque tool, hot stab, etc.).

The connector and connector selection is made and/or validated by the Project team.

Today tie-in techniques are mainly based on ROV light tie-in tools deployed on the seabed via a dedicated deployment basket.

Figure 2.5 - UCON-H tie-tools secured into purpose-built deployment basket (TechnipFMC)

A subsea intervention around a connection can be considered heavy; it involves the mobilisation and preparation on deck of a set of tools + set of contingency tools (in case something goes wrong). Instead of lifting one by one all tools on seabed, a dedicated tooling basket is utilised, as shown on picture above.

For the ROT/tie-in method, the ROV is used primarily as a visual control during the ROT landing and recovery, and to connect the pull-in wire (see chapter Section 5.3, “Flexible Spools, Jumpers, Spur Lines” "Lay-down and pull-in"). Its secondary function is to override some of the ROT main functions in case of an ROT mechanical failure.

In this case the main interfaces are related to:

With regard to the ROV mounted pull-in and connection tool, the interface requirements are much more stringent and could referred to "Interface Engineering" encompassing the full scheme, such as the designs of:

Figure 2.6 - DMAC / ROV based Pull-in and Connection Tool (courtesy of Subsea 7)

For modern tie-in systems, the tooling must be as light as possible, easy to manipulate, robust and ROV friendly (see UCON-H ROV tooling shown below).

Figure 2.7 - TechnipFMC – UCON-H connection system with associated tie-in tools

However the tooling could become heavier and more complex when connector sizes increase (42in tooling on Ichthys).