Utilising Clever Composite

Online Editor

Subsea maintenance? Use composite, advises Jean-François Ribet

In 2022, most of the oil & gas offshore infrastructures in Northern Europe are ageing and facing harsh conditions. At the same time, we need to continue to operate them without shutting down.

Composite has become a key solution for years now to keep platforms in good shape and maintain their topside and subsea networks with lower restrictions than traditional solutions, no shutdown and no fire permits in most cases.

When dealing with subsea pipelines and caissons, the situation becomes more critical. The maintenance is more challenging and it mobilises more resources. How can operators maintain and efficiently repair the subsea part of an offshore platform?

Case Study: Maintenance Of Subsea Caissons

This is the main topic of a project in Northern Europe that 3X Engineering was requested to tackle. The major challenge was to seal many holes on subsea caissons, considering the cold temperatures and the harsh weather conditions during application in the North Sea, its specific salinity rate, the steel grade and more.

After years of development and testing within its R&D department, 3X Engineering developed the proper composite to ensure a successful repair.

One of the key aspects was to get a resin used as a primer and able to cure at cold temperature while ensuring a good bonding. The requested adhesion standard was to get a minimum of 5 MPa. Finally, 3X was able to achieve an average of 10 MPa.

This first step validated, the second challenging part was the field application. To overcome it, an automatic wrapping machine using a wrapping patent developed by 3X was installed around the caissons. It made it possible to wrap hundreds of composite layers in a few hours while minimising the use of divers and so having a better safety during the application process.

The holes were sealed using specific filler and plates, subsea primer and a certain number of layers of subsea composite made of epoxy resin and Kevlar tape. The number of layers was calculated according to the standard ISO24817 combined with finite element analysis. The preparation of the composite was done on the platform and then the latter was given to the divers to install the composite bobbin on the automatic wrapping machine.

Next Steps

Thanks to many years of experience on onshore offshore and subsea installations, 3X Engineering is continuing to work closely with the main operators in the oil & gas sector. One of the future needs will be to find solutions to maintain and repair the subsea networks in deep water areas, up to 3,000m deep, which means to consider harsher constraints never met until now by exploring new paths in technology for the application process.

Jean-François Ribet is with 3X Engineering