The Fusion Bonded Joint: A New Way of Joining HDPE Lined Pipes for Reeling and Fatigue Sensitive Applications

Abstract

Corrosion protection is a key aspect of all subsea developments. Indeed the complexity of subsea pipe maintenance and repair makes it necessary to provide solutions suitable for the full life time of the field. Though sensitive applications such as production lines transporting corrosive compounds, CO2 and H2S for instance, immediately comes to mind when mentioning corrosion, other applications, though seemingly less demanding, also require to be properly addressed from a corrosion perspective. One of these applications is water injection lines. Corrosion in these lines is usually tackled with using a wide range of approaches depending on operation philosophy: topside treatment, corrosion allowance, cladding or plastic liners. A balance usually has to be found between how extensively the injected water is processed topsides and what other corrosion mitigations methods are deployed. This assessment should be carefully conducted the selected approach will impact procurement and installation costs. For instance, increasing the pipe wall thickness to cope with corrosion would results in higher lay vessel installation capabilities as well as longer welding time while relying on clad pipes would negatively impact procurement costs and require more complex NDT methods to be implemented. Plastic liners offer a relevant alternative though their implementation has to be carefully assessed so as to ensure it remains cost competitive. To that extent, the Fusion Bonded Joint has been developed and qualified. This system ensures the continuity of the plastic layer at carbon steel weld locations while limiting the offshore cycle time thus preserving lay rates of the installation vessel. This paper includes an overview the technology itself as well as a summary of the extensive qualification campaign that has been carried out. A global overview of the testing campaign will be provided from the early stages of the development to the full scale testing of the technology in an environment representative of its actual operating conditions. Topics discussed will include: prototyping of the system and associated tools, qualification of the electro-fusion welding process as well as its control and qualification of the carbon steel welding process. The main challenges and outcomes of tests performed will be presented and discussed. A focus on the specificities of the fatigue testing campaign will be presented including fatigue string design as well as fatigue performance of plastic electro-fusion weld. Eventually, the applicability of the FBJ to reeling will be discussed.