Autumn 2018

Safely tethered mooring in the Barents Sea

Monitoring the safe mooring of the world's largest floating offshore oil and gas project in the arctic waters of Norway

In the summer issue of Pelican we revealed that Strainstall has secured a £1.1m chain tension monitoring project for the world’s largest floating production storage and offloading (FPSO) facility which will be stationed in the Arctic Circle.

The Johan Castberg FPSO is owned by oil major Equinor and, on its completion in 2022, will be installed at an oil and gas field offshore of Hammerfest in the Barents Sea. Once in operation, the vessel will tap into an estimated 450 – 650m barrels of oil extracted over a 30-year period. This requires all components used in the build to have exceptional resilience and longevity.

The Strainstall team is working closely with the FPSO turret designer, SBM Offshore (SBM) which has been tasked with supplying the turret mooring system. This sophisticated system is integrated into the vessel, keeping everything permanently fixed to the seabed while allowing the vessel to freely ‘weathervane’ around its moored position. Crucial subsea pipelines are connected to the vessel through ‘risers’ which pass from the sea bed through this turret.

The extreme conditions in northern Norway mean the Johan Castberg requires a specially designed turret and unique chain tension monitoring system to keep the ‘risers’ free from stress even in the face of rough seas, extreme winds and icebergs.

Strainstall’s world leading specialist experience and expertise in designing load cells and systems for offshore mooring applications was used to optimise the turret design to achieve exceptional performance and reliability while being cost-effective. The team was able to build on its existing strong and trusted relationship with SBM, with both parties collaborating on every stage of the project, from initial design to building and comprehensively testing the proposed solution and then successfully validating the design before the full system was put into production.

This collaboration has led to the development of a reliable technical solution that will operate throughout the extensive processing window and will also withstanding the harsh conditions at the site.

‘By working together, we were able to strengthen the specification in some key areas to ensure reliability and relax the spec in other, less critical areas to achieve a better design at a lower cost,’says Strainstall’s business development manager, Frank Rose.

‘A key factor in securing this contract was our ability to work in collaboration with SBM to focus on truly minimising life cycle cost through appropriate design,’ he adds.

The team was also able to build on experience gained through designing the load-monitoring equipment used to help relocate the Halley Research Station in Antarctica last year, which had necessitated the building of a special environmental chamber designed to test equipment at -40c.

As part of this project, Strainstall has also provided an evaluation piece for SBM’s research and development facility. It will be subjected to further testing, with a view to being used on similarly challenging projects in the future.

The Johan Castberg mooring system secures 15 chains to the turret using a specialist connector assembly unit, and Strainstall is supplying a Chain Tension Monitoring System (CTMS) that includes 60 compression load cells plus cables and instrumentation to provide critical real time mooring information to operators onboard.

Frank adds: ‘This close working relationship is indicative of the mutually successful partnerships we are increasingly building with our customers to meet the on-going pressure to reduce costs in the oil and gas industry.’


 Johan Castberg in numbers  
$7bn                                                          Cost of FPSO design and build
116km Total length of pipelines and umbilicals from seabed to surface
295.2km Length of topside structure
30,000m3 Daily oil production capacity
40,000m3 Daily liquid production
31 Number of wells
21 Number of risers



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