Case Study

14-inch 2500# Subsea Mechanical Connector Contingency - North Sea UKCS

Tool - Mechanical Pipe Connector

Location - North Sea - UK

Operating Environment - Offshore Subsea

Pipeline Medium - Ambient

Activity - Pipeline Repair

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14" Subsea Mechanical Connector

STATS Group provided two class 2500 subsea mechanical connectors as part of a subsea flange repair project in the North Sea, UKCS.

A Problem Discovered at the Worst Possible Time

During the offshore installation phase of a new field development in the North Sea UKCS, spool pieces were installed and the pipeline subjected to leak-testing. It was at this stage that an integrity issue emerged - damage to the sealing face of the platform riser base flange, the precise connection point allocated for tie-in of the new pipeline.

With a commissioning schedule at stake, the operator needed to act.

Repair First - But Plan for Failure

The preferred course of action was an in-situ repair of the damaged flange. However, in case the repair was unsuccessful, a contingency solution was developed - one that would allow the damaged flange to be cut and removed and replaced with a 14" class 2500 mechanical connector, installed directly onto the bare pipe end. This would ensure the schedule for commissioning the new pipeline would not be jeopardised if the subsea flange repair failed.

STATS Group was contracted to engineer and supply the solution.

Highlights

Contingency solution engineered and delivered to protect the commissioning schedule during active field development
14" class 2500 rating - high-pressure subsea specification met in full
Two connectors manufactured - one subject to destructive bend fatigue testing for technical assurance, primary connector preserved for deployment
Full witnessing by independent verification body and client at every stage of manufacture, assembly and testing
Primary repair successful - connector not deployed, now stored for the client in a state of readiness for future planned or emergency repair
Connector designed for installation onto plain pipe end following removal of the damaged flange

14in Subsea Mechanical Connector Close Up

Built to a Standard That Left Nothing to Chance

Two 14" class 2500 subsea mechanical connectors were manufactured - two, for a deliberate reason. For technical assurance, one connector was subject to bend fatigue testing, and as the fatigue test was a test to destruction, the primary connector could not be used. A factory acceptance test was carried out on both connectors before they were shipped to a third party for the bend testing. All stages of manufacture, assembly and testing were witnessed by an independent verification body and the client.

The connector is designed for deployment onto a plain pipe end following removal of the damaged flange. A seal compression flange is actuated to set the seals, which are then pressure tested to prove the integrity of both seals prior to setting the locks. The lock bowl is actuated by torquing a separate array of bolts to set the locks onto the pipe. Each lock segment is individually torqued to ensure even circumferential grip load around the host pipe, eliminating excessive stress and unacceptable strain of the pipeline.

A final localised code-compliant strength test and seal leak test verifies that the connector is structurally secured and the seals are leak tight. An environmental seal in the compression flange allows the lock cavity to be flushed with an inert fluid.

Ready When Needed

The in-situ repair of the platform riser base flange was successful. The contingency connector was not required and installation was not needed.

The connector is stored for the client in a state of readiness for any future planned or emergency repair scenarios.

The project ensured the schedule for commissioning the new pipeline was protected - with a fully engineered, manufactured, and verified contingency solution in place throughout the repair process.