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Shock absorbers help improve subsea riser safety

13 November 2015

Shock absorbers play an important role in the operation of a new and innovative family of emergency release connectors for subsea risers developed by Aberdeen-based Subsea Technologies.

Subsea Technologies' Xtreme Release (XR) connector

Subsea Technologies' worldwide patented Xtreme Release (XR) connector was developed to remove the entire concept of 'maximum riser disconnect angle', a long standing challenge of subsea riser design.

The XR Connector differs fundamentally from all other subsea connectors because it is based on a face-to-face technology rather than a conventional male-into-female engagement. This key differentiator enables the XR Connector to release safely, reliably and repeatedly with up to 100 percent of maximum bending capacity applied.

By comparison, existing connectors - even those that claim to be capable of ‘high angle release' - cannot separate with high bending loads applied, so the maximum disconnect angle (and therefore the maximum applied bending load) has to be limited to prevent lock-up.

Any floating vessel connected by a riser pipe to a wellhead on the seabed must be able to disconnect rapidly from the wellhead in the event of a position-keeping emergency. If it can't, there is a high risk of severe damage to the vessel (potentially causing injuries and fatalities), catastrophic failure of the riser pipe, severe damage to the wellhead and possibly loss of well containment.

Existing Emergency Disconnect Packages (EDPs) have to limit the maximum disconnect angle to prevent the EDP from ‘locking up'. To maintain this small angle, the distance the vessel can move from the nominal centre position is limited and therefore the crew has only a small window of reaction time to identify a position-keeping failure, close in the well and disconnect from the wellhead.

If the crew reacts too slowly, or problems occur too quickly for the crew to react, the vessel and its crew can rapidly reach the point beyond which the riser will not disconnect - not a position any vessel crew, operator or owner would want to encounter.

Because the XR Connector has no maximum disconnect angle and can release at up to 100 percent of maximum bending capacity, there is no risk of it locking up when released under load. This means that vessels can move much further away from the wellhead before disconnecting from the subsea wellhead, and when they do release, the vessel crew can be confident that there is no risk of finding the riser stuck.

This capability means that the XR Connector offers greatly improved vessel safety, improved asset protection and improved productivity. The XR Connector also enables vessels to continue operations through more severe weather than previously possible, subject to other components in the riser system having sufficient bending capacity.

Integral with the face-to-face seal technology are clamping dogs and, in a controlled or emergency release, significant kinetic energy can be imparted into the dogs. Ace Controls subsea shock absorbers were designed into the assembly to safely absorb this kinetic energy and thus ensure that no damage occurs to the dogs or other equipment during the release.

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