Artikel 11 Pipa Bawah Laut

SUBSEA TIE-IN METHODS

 

Unlike onshore tie-ins, it is difficult to make subsea tie-ins in terms of material handling, pipe cutting, welding, etc. Subsea tie-in is typically made by diver-assisted flange connectors for shallow water pipelines and diverless remotely operated vehicle (ROV) connectors for deepwater pipelines.

There are three types of connectors available: flange, clamp (Graylok type), and collet connectors. Clamp or collet connector is more favorable over the flange connector due to ROV operability, offshore connection time, and available tie-in tools from contractors. Flange connector is industry proven technology and can be easily procured from vendors’ shelf. However, due to lengthy subsea connection time, unfriendly ROV operation, and limited availability of connection tools/systems, the flange connector is not recommended for deepwater application.

Clamp connector is compact and widely used for deepwater tie-ins. A single bolt with hinge system clamp connector is preferable for the diverless ROV connection. The seal ring between two hubs provides very secure mechanical sealing as the internal pressure is energized.

Collet connector is more expensive and complicated than any other connectors. Hydraulic pressure is used to close the fingers of collets and set the drive ring which locks the collets. There are two types of collet connectors; integral and non-integral.

• An integral collet connector has a self-contained actuator and is much larger and more expensive than a non-integral collet connector.

• A non-integral collet connector requires an external, reusable actuator that is deployed and retrieved by a running tool. Nonintegral collet connector is more compact than integral collet connector and economical when more than three collet connectors are required (if only one running tool is required).

Figures 1 and 2 show each connector components and collet connector assembly sequence, respectively.

 Figure 1. Connector Types

 Figure 2. Collet Connector Assembly Sequence

Table 1 shows each connector type’s advantages, disadvantages, and available vendors.

Table 1 Pros and Cons of Each Connector

 

Generally, three diverless subsea pipeline connection methods have been used in the offshore industry. These methods are:

• Pull-in Connection
• Vertical or Horizontal Jumper Connection
• Stab and Hinge-over (S&HO) Connection

The pull-in connection is a cost-effective method for both 1st end and 2nd end connections. However, this method is known to take more offshore time than jumper connection due to subsea pull-in operation. Both vertical and horizontal jumper connections have been widely used for 2nd end connection. The vertical jumper connection is more attractive than the horizontal jumper connection because of easy installation and competitive hardware tool cost. However, the abrupt vertical elevation difference by the vertical bends may cause a hydrate formation (slug). The disadvantages of the horizontal jumper are difficulty in adjusting misalignment and possible residual tension on the pipe due to horizontal stroking. The stab and hinge-over connection is ideal for 1st end connection because of easy and simple installation without any other pipe lay initiation support. The material and fabrication cost may be higher but its offshore installation time is less than the jumper connection.

Figures 3 through 6 illustrate each tie-in method.

 

Figure 3. Pull-in Connection Method (by Aker Kvaener)

 

 

Figure 4 Vertical Jumper Connection Method (by FMC (top) and Aker Kvaner(bottom))

 

 Figure 5 Horizontal Jumper Connection Method

 

Figure 6 Stab and Hinge-over Connection Method (by OSI)

Table 2 summarizes the advantages and disadvantages of each tie-in system.

 

Table 2 Pros and Cons of Each Connection Method

To make deepwater connections, several tools and systems are required in addition to connectors. Followings are typical tie-in tools required for deepwater diverless tie-ins:

• ROV
• ROV running tool, seal replacement tool, actuator, etc.
• Pull-in skid with winch (for pull-in connection)
• Alignment funnel & sleeve (for jumper connection)
• ROV control panel (for Collet connector)
• Stab pin unit & receptacle base (for stab & hinge-over)

Many connector manufacturers and installation contractors offer their connection tools and systems. The tie-in systems available for pull-in connection include:

• DMaC (Diverless Maintained Cluster) by Subsea Offshore
• UTIS (Universal Tie-in System) and ROVCON (ROV Connection) by FMC
• DFCS (Diverless Flowline Connection System) by Sonsub
• McPAC (McEvoy Pull-in And Connection) by Cameron
• ICARUS by ABB
• RTS (Remote Tie-in System) and BBRTS (Big Brother RTS) by Aker Kvaener
• Flexconnect II by Technip, and many others

All systems above can make connections using either clamp or collet connectors, except

McPAC and ICARUS which only can use clamp connectors.

Figure 7 shows the pull-in connection systems offered by industry.

Figure 7 Pull-in Connection Systems

There exist many tie-in systems available for jumper connection and S&HO connection as listed below.

• BRUTUS by Sonsub for horizontal jumper connection
• VCS (Vertical Connection System) and GHO (Guide and Hinge-over) system by Aker Kvaener
• STABCON (Stab and Connect) connection system by FMC for horizontal jumper connection
• S&HO system by OSI, and many others 

Source:

Lee, Jaeyoung. 2007. Introduction to Offshore Pipeline and Risers.