Repairing Clad Pipelines: The First-Of-Its-Kind Metal-Seal Connector
Authors: Cavallini F. , Lazzarin D. , Mattarucco R. , Michelazzo L. , Quick A. 
Published: October 2023

The paper provides an overview on the key features of the first-of-its-kind, metal-seal repair connector for metallurgically clad and mechanically lined pipelines designed and built to ensure continuity of internal cladding without reduction of internal diameter. A discussion on the advantages of such a connector for sour service and/or clad pipelines, and an update on the DnV qualification program is provided together with application cases focusing on how to effectively deploy the connector in an emergency scenario.

Having identified the need for a Corrosion Resistant Alloy (CRA) compliant repair solution which doesn't reduce the internal diameter of the pipeline, a bespoke design has been developed and prototyped. The following major phases of development have been undertaken: 1) A review of the issues and limitations associated with using current connector technology, especially in relation to CRA clad or lined pipelines in sour service, 2) A solution for the issue of pipeline fluids being in contact with the Carbon Steel (CS) pipe was identified together with related functional requirements, and 3) A comprehensive DnV technology qualification testing program was carried out on a full-scale 26″ prototype connector. At the time of writing, a type-approval certificate to cover the various pipeline sizes will be granted within 2023.

Subsea pipeline connectors are a consolidated solution for emergency/planned pipeline repairs and for tie-ins to existing pipelines (field reconfiguration and extension). Currently these solutions are largely used in the industry for CS pipelines, with an extensive track record of successful installations. Nowadays, however, the need to develop more complex reservoirs, particularly sour gas, in an effective manner, requires offshore operators to adopt internally clad or lined CRA pipelines, which consequently opens the dilemma of how to repair them in case of need, exclusively maintaining the uninterrupted and contiguous CRA pressure containment envelope, so that the pipeline fluid does not come into contact with the CS carrier pipe. Key features of the presented metal-seal connector include: l) DnV Technology Qualification (TQ) for small to large pipelines (from 6″ to 38″), unique in the industry and tailored to the Middle East region, 2) Metal-to-metal sealing technology granting permanent repair, 3) Capability to support the same design loads and conditions of the original pipeline, 4) No reduction of the internal diameter (ID) of the pipe, 5) Capability to compensate misalignments of the pipe cut-end, and 6) A versatile diver-assisted or diverless setup for deep water applications. Furthermore, the subject solution can also manage pipelines with multiple wall thicknesses and it's ideal for integration into an EPRS club or other situation where there may be multiple pipelines of the same diameter but differing wall thicknesses.

Internally clad or lined CRA pipelines are widely used, and their planned utilization is forecasted to increase, thus unlocking the exploitation of challenging reservoirs. A repair connector purposely conceived for such pipelines will offer to offshore operators an innovative and robust solution to face emergencies or, on existing pipelines, for tie-ins to allow fields reconfiguration.