Recent years have seen fibre rope steadily displace steel wire for offshore lifts, but there is a need for greater standardisation, harmonised testing and certification and in-depth understanding of reuse and retirement
Eighty-five members and guests attended the International Marine Contractors Association’s (IMCA’s) lifting and rigging seminar, an event that, like earlier workshops, focused on defining the issues related to high-value subsea construction ropes and on the performance slings and grommets used for subsea construction. The title – ‘Slings and rigging – the soft revolution’ – indicated strongly the steady move over the last four to five years from wire to high-performance fibre-based rigging. After a welcome and introduction from the seminar chairman, there followed a number of presentations and workshops designed to review the status and issues surrounding the use of fibre rope technology.
Seaway Heavy Lifting’s principal engineer Dirk-Jan Mattaar provided a presentation on the company’s experience in moving from steel to synthetic fibre slings. “Why do we use them?” he asked. “Because manual operation with fibre rope slings is safer, faster and requires fewer riggers. It only takes a few seconds to attach. It saves an awful lot of time when it comes to connection slings to hooks,” he explained. However, the company hasn’t stopped using steel slings altogether, primarily because of damage on fibre slings, even though they are highly cut-resistant.
“Proper sling protection is essential,” he said, noting that the cost for fibre was still higher than steel. Another concern about fibre ropes is high-temperature operations. When used in high temperatures in some parts of the world, strength loss due to high temperatures need to be borne in mind, he said. Over time, in high temperatures, the safety factor of fibre rope can reduce. Other issues that need to be addressed include the fact that certification of fibre ropes has not yet been standardised, guidance on inspection and when to discard is not clear cut and connection of steel slings to fibre slings should not be undertaken due to internal torques and twists.
IMCA Lifting and Rigging Committee member Caspar Berends, who works for TechnipFMC, gave a presentation on engineering with fibre slings and the challenges this can bring. This included bending effects over crane hooks (especially DIN hooks, which could damage both fibre and wire slings), reuse of slings, load test requirements and how to determine correct skew factors.
Reuse of fibre slings had been undertaken, he explained. However, the company thought it wise to involve the manufacturer for inspection before reuse, especially after reconfiguration or resplicing. Damage to protective jackets can easily happen. This leads to questions about whether it is possible or advisable to undertake repairs on a vessel. “Clients could be concerned with damage to protective jackets. We needed guidance on how to deal with this,” he said.
Mr Berends said fibre slings can be beneficial for deck handling. Technically, they are fit for purpose, but if they pick up a lot of sand and grit when ashore at a storage yard, damage could occur and fibre rope could be deemed too high risk to use. “We really want to use them, but this is a challenge,” he said.
Jumbo’s project engineer Sita Verburg and senior port engineer Dries Stommen gave a presentation on issues involved with complex rigging work during the lifting and transportation of two 1,000 tonne pile clusters. This required an asymmetrical lift under different lifting configurations. Another difficulty was that the single hook became completely filled with rope. It was important to ensure that the ropes did not become crossed whilst on the hook.
Saipem UK’s chief operating officer Vince McCarthy gave a presentation on the use of fibre rope on Statoil’s Hywind floating offshore wind project. This involved lifting the upper structure of a wind turbine (complete with blades attached) and mounting it on a floating spar-type foundation. The upper structures were lifted from the bottom, so the lift was potentially very unstable. He explained that contractor Franklin Offshore had to manufacture the slings to particularly tight tolerances, and the slings were pre-stretched to bed in splices against the actual load that they would see. This was to ensure that the variation in the lifting slings was acceptable. This was important because, when the turbine was lowered onto the spar, it would sink by approximately 11 m.
Samson’s application engineering manager Justin Smoak noted that standards for steel wire had evolved over many years. Fibre rope has only been around and in regular use for a few years. Fibre ropes behave in the same way as steel, but there are significant differences between fibre ropes due to the use of differing materials and weave. Under IMCA guidelines, manufacturers are required to guarantee the maximum breaking load (MBL) of a sling, but Samson believes that the whole rope needs to be broken, not just strands. Mr Smoak discussed retirement considerations and demonstrated Samson’s visual retirement guide, which has been developed as a result of many tests. Data-driven strength models for fibre rope are important, he said, and can provide assurance that they can be used at the designed factor of safety and satisfy end-user risk tolerance requirements.
Cortland’s business unit leader Luis Padilla said it was important that the industry work together to create standards to help the end user. He noted that industry recertification guidelines were weak. “Nothing beats a well informed customer,” he told delegates. “There is a need to build trust with the customers, and customers need to know what to ask for and define. Standardisation can help with this,” Mr Padilla said.
Lankhorst’s project manager Rui Pedro Faria said realistic load testing that looked at each part of a subsea lift was important. Realistic testing could help justify the use of lower safety factors, he said, noting that the company is working with DNV GL on technology qualification for both new and used slings.
Bridon-Bekaert’s fibre technology manager Tim Hunter said that, for use and reuse of fibre slings, it was important to get the original specification right. “Knowing the retirement point is critical,” he said, “[but] some users give it a lot of attention in the specification, others very little.” The lack of standardisation described by other speakers is apparent in testing, which means that interpretation of results is being performed in different ways – even down to MBL and how it is defined. “The biggest challenge in the industry is certification,” he said. “Standardisation is not a set of laws, it’s about consensus in the industry,” he concluded.
Rolls-Royce to deliver world’s first hybrid subsea crane
Rolls-Royce has been contracted by Brazilian shipowner CBO to equip a platform supply vessel with the first example of its patented dual draglink subsea crane. The crane will be the first subsea crane designed to use either fibre or steel wire rope.
The hybrid dual draglink crane will be installed on CBO Manoella, which is currently being modified from a platform supply vessel (PSV) to a remotely operated vehicle (ROV) support vessel. The active heave compensated crane is designed for continuous operation in a tough and corrosive offshore environment with a focus on efficient and safe load handling.
The crane to be installed on CBO Manoella is a hybrid dual draglink crane with a lifting capacity of up to 50 tonnes and an operating depth of up to 3,000 m. It will be equipped with wire rope when it embarks on its first subsea assignment off the coast of Brazil. However, the possibility of changing to fibre rope provides flexibility in a challenging market.
Because of the low weight of the fibre rope, the vessel’s deck load capacity can be increased by approximately 100 tonnes. Another benefit of using a low-weight fibre rope instead of steel wire is increased lifting capacity at large depths. The cable traction control unit (CTCU) forms the crane winch and is located at the main boom. This solution saves space compared to a solution where the CTCU is mounted below deck and also makes it a better choice for retrofits. The horizontal elbow derrick movements provide active heave compensation. This significantly reduces wear and build-up of heat in the lifting line compared to when the active heave compensation system is part of the winch.
Delivery of the crane was due to take place in Q3 this year. The scope of supply includes a complete dual draglink crane system including the CTCU, cabin and control system.