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Technical innovation in offshore heavy lifting systems

CO-AUTHORS: Sara Fletcher, Technical Development Manager, Bridon International; Jurgen de Jong, Senior Technical Superintendent, Heerema Marine Contractors

When undertaking surface-based heavy lifting operations such as transferring nine thousand tonne topsides between vessels, marine contractors must be assured they can rely on their crane ropes. With daunting costs associated with every day of project downtime, operators simply cannot afford an unanticipated failure that could put their work on hold during rectification or until a new rope is delivered. Furthermore, crane ropes used in such operations are not simple consumable products that can be straightforwardly slotted into independently designed lifting systems. They are highly engineered pieces of machinery that must lift thousands of tonnes of valuable equipment under challenging environmental conditions, and as such are an integral part of the lifting systems themselves. With this in mind, contractors must be assured of rope integrity and reliability, and plan advance replacement accordingly.

Close collaboration between operators and their equipment suppliers is crucial to the creation of effective heavy lifting systems. Such collaboration is exemplified by the long-term partnership between marine contractors Heerema Marine Contractors and rope manufacturers Bridon International, who on vessels like the DCV Balder operate highly optimised lifting systems that truly make the most of state of the art rope technology.

Built in 1978, the DCV Balder was originally equipped with 2 heavy lift cranes. In 2002 the DCV Balder underwent a major upgrade to a multipurpose deepwater construction vessel with the addition of a DP system, Mooring Line Deployment System and a 1050 tonnes top tension J Lay Tower. Heerema recognised that to harness the full potential of these state-of-the-art lifting systems, they would need to be equipped with equally advanced rope technology. It was at this point that the company turned to Bridon.

Heerema’s first priority was ensuring that the vessel’s new J-Lay system had sufficient handling capacity to deploy huge loads under challenging conditions. With this in mind, its Abandonment and Recovery (A&R) winch would require a single deployment rope of unprecedented strength and complexity. First of all, to guarantee safety in operation the rope was required to provide a massive 1500 tonne breaking load In addition to the immense loads the rope would have to carry, the nature of the single line load handling arrangement required it to exhibit limited rotation under load; necessitating a multistrand wire rope construction which had never before been produced in such large diameters and lengths.

To identify practical solutions to these significant technical challenges, Bridon embarked upon an extensive development program. The Bridon Technical Team began by designing a rope that could theoretically attain the required properties, manufacturing a small scale trial model to confirm design assumptions and assess manufacturing process methodology. When this trial demonstrated a successful outcome, Bridon commenced building of the full scale rope.

At a number of points over the following years, the Balder has taken on operational challenges that required longer and stronger A&R ropes, and Bridon has consistently worked with Heerema to supply these. Having replaced the original 3150 metre rope supplied in 2000 with a 3400 metre length, in 2007 Bridon was commissioned to construct a new rope to enable the Balder to make 4000 metre deployments in the Gulf of Mexico on behalf of BP. The scale of this superlative rope was so significant that Bridon had to invest in new handling equipment to enable its construction.

As contractors like Heerema continue to explore greater depths in challenging environments, Bridon is actively expanding its manufacturing capabilities so as to anticipate and accommodate their needs. The company is currently constructing a £30 million factory that by early 2013 will produce multi-strand ropes in lengths of over 7000 metres and gross package weights of up to 650 tonnes - making them by far the largest and most complex in the world. These ropes will dramatically expand the scope of the possible for operators working in deeper waters and more challenging environments.

In addition to its J Lay Tower, Heerema’s DCV Balder was equipped with 2 heavy lift cranes, both of which have a lifting capacity in excess of 3000 tonnes. As part of the upgrade of one of these cranes, Heerema turned to Bridon to supply a matched pair of two 19,000 metre long wire ropes. The production of ropes suitable for such complex, multi-reeved heavy lift cranes required both significant technical expertise and manufacturing consistency. Heerema again turned to Bridon to develop, test and deliver the ropes, and their performance was such that equivalent arrangements and specialist equipment are used across Heerema’s unique fleet of the Hermod, Thialf and Balder.

The technical horizons of offshore construction applications and the ropes which work within them are expanding at a rate of knots. Whilst the historical challenge of deep water deployment was to deploy 300 tonnes in 3000 metres water depths, boundary-pushing operators are now looking to achieve deployment of 400 tonnes at 4000 metres depths. Such demands are increasing the performance characteristics required of heavy lifting ropes. From ensuring optimised bend fatigue performance and effective lubrication, to enhancing crush performance and achieving specific engineered stiffness characteristics, developing the next generation of offshore ropes is a complex and varied challenge.

A key front in the technical development of heavy lifting wire ropes is the use of specialist polymers to boost rope reliability and performance. Bridon‘s technical division boasts a team of dedicated polymer experts who identify, select and process novel polymer materials to optimise the performance of ropes in the most onerous of applications. This work has led to the development of Bridon’s patented manufacturing process that applies a plastic jacket around the core of a wire rope in an exact profile to support and follow the helix of the rope’s strands. This cushion supports the geometry of the wire rope and limits the impact of interwire contact to enhance the work life of the rope. New materials are being trialled to allow the application of this technology to even more critical applications in deep waters, under high pressures and in heat sensitive applications such as heave compensation.

In addition to steel wire ropes, Bridon is also working to develop synthetic fibre solutions which trials indicate can be highly suited to next generation offshore operations. The use of fully synthetic ropes can offer the highest strength to weight ratio for subsea handling, extending the depth range of existing equipment without any detrimental impact on static load capacity. Crucially, tailoring extension characteristics of synthetic products can also negate the need for additional load displacement compensation. Bridon has completed detailed data development for its product range to be able to demonstrate performance in extension, and its in-house testing facilities can model individual client requirements to optimise rope design for a specific load case.

In the development of optimised heavy lifting systems for offshore applications, collaboration is key to technical innovation. Bridon and Heerema’s relationship clearly demonstrates what can be achieved in this area when suppliers and operators work together in a sustained and supportive way. The two companies’ collaboration has allowed Bridon to gain the most rounded possible understanding of the complex challenges Heerema faces. This understanding has allowed Bridon to develop highly unique rope applications that are uniquely designed to overcome Heerema’s challenges.

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