Subsea Connection System: Jumper Tie-in Spool, Either Vertical or Horizontal?

A subsea connection system, often referred to as a subsea tie-in spool, is a critical component used in offshore oil and gas production to connect and interface various subsea equipment and infrastructure. It plays a crucial role in the installation, maintenance, and repair of subsea pipelines and subsea wellheads, which are typically located on the seabed.

Key Features

  • Key features and functions of a subsea connection system include:

  • Connection Interface: Subsea tie-in spools provide a means to connect different subsea elements, such as pipelines, flowlines, control umbilicals, or jumpers. They have flanges or connectors at each end to facilitate secure connections.

  • Versatility: These systems are highly adaptable and versatile, allowing for connections between various subsea components with different sizes, specifications, and configurations.

  • Pressure Integrity: Subsea tie-in spools are designed to maintain pressure integrity, ensuring that the subsea infrastructure can transport fluids (oil, gas, or water) without leaks.

  • Sealing Mechanisms: To prevent the ingress of seawater and maintain the integrity of the system, subsea tie-in spools often incorporate sealing mechanisms, such as gaskets or metal-to-metal seals.

  • Material and Corrosion Resistance: These components are typically made from materials that can withstand the harsh underwater environment and resist corrosion, such as corrosion-resistant alloys (CRA) or stainless steel.

  • Installation and Retrieval: Subsea tie-in spools can be installed during the initial construction of subsea infrastructure or retrieved and replaced during maintenance or repair operations. This flexibility is essential for maintaining and upgrading underwater production systems.

  • Rigless Operations: Some tie-in spool systems are designed to enable rigless (without a drilling rig) connections and interventions, reducing costs and operational complexity.

Vertical Connection System

Vertical connection systems typically consist of a downward facing funnel which aligns with an upward facing hub, mounted on the host structure. The final connection, delivering the full preload, is either via a hydraulic or manual connector.

The main benefit of a vertical connection system is that the jumper can be installed in a single trip. The system uses gravity to assist in guiding and landing the structure onto the mating hub, resulting in a saving of approximately 8 hours of offshore construction vessel time per spool/jumper.

Vertical connection systems do not require large, operation specific installation tooling, saving on both tool rental and installation costs.

Lastly, maintenance activities for vertical systems, for example seal change out, can be performed without crane assistance. Lifting and change out can all be performed via ROV tooling which can typically be offered on a rental basis.

One of the disadvantages of a vertical system is that the connection tends to be larger and heavier than horizontal connection systems. That said, the difference is marginal over as a percentage over the host structure and is therefore not a significant decision factor.

Horizontal Connection System

Horizontal connection systems can be assembled to either a flexible or rigid spool system. There are various designs of this type of connection system but they all work on similar principles. 

The jumper connector is landed either on a porch or on the sea bed and is pulled into the mating half, located on the host structure. Pull in is achieved using a crane deployed tooling or ROV attached tooling (winch). 

The primary difference between a vertical and horizontal connection system is the two-stage installation process required for a horizontal connection system.

Another key benefit of horizontal connection systems is that the spool has a relatively low profile unlike the high “M-shaped” profile required for vertical connection systems. This is particularly beneficial where damage from fishing vessels or VIV damage is a concern.


Subsea connection systems, or tie-in spools, are critical components in offshore oil and gas operations. They facilitate the connection of various subsea elements and ensure the integrity of the subsea infrastructure, enabling the efficient extraction of hydrocarbons from beneath the seabed while also allowing for maintenance and repairs as needed.

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