A Novel Subsea Connector for Repairing Clad Pipelines

Abstract

Subsea pipeline repair connectors have been used in the oil & gas industry for many years and are considered a valid and safe way of repairing major damages and restoring the original pipeline condition in case of an emergency repair; they can also be used for tie-ins to allow extensions by connection of new pipeline sections to an existing one and they have an extensive track record mainly on carbon steel pipelines but are fit also for stainless steel and duplex pipelines. The increasing number of subsea pipelines with internal CRA cladding which have been deployed in recent years and are foreseen in the future poses new technological challenges since conventional sealing solutions are not suitable for or have limitations in this specific application: in this case the repair connector not only needs to be designed to be compliant with the sour product but it also needs to protect the pipeline carbon steel wall from coming into contact with the internal fluid. This paper presents a new concept of a pipeline repair connector that has been developed from the beginning specifically to target repairs on sour service lines and in particular on clad lines. This innovative repair connector is based on a metal to metal sealing technology that offers permanent repair without any reduction of the pipeline's internal diameter, provides a versatile diver/diver-less solution, can deal with multiple wall thicknesses and can also be applied to other types of pipelines, such as those for sour service with internal corrosion allowance since it can manage pipe wall thickness reduction over time. The design of the mechanical connector has been carried out in compliance with DNV pipeline codes after a comprehensive technology qualification testing campaign under DNV certification and focused on medium size pipes. A full-scale 26″ prototype connector has been designed and fabricated for completing the qualification testing program including all required pressure and loading conditions. FEM analyses of the testing configurations have been carried out for comparison with test data so to validate the FEM models and extend results to other sizes within a predefined range. The matching between the experimental data and FEM calculations has allowed setting up a Type Approval process with DNV and, after a design effort covering various pipeline sizes and types, the connector will be certified for a wide range of large bore pipelines and design conditions and be ready for release to the market.