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No crane necessary

1 May 2011

Twaron and FibreMax lighten the load for offshore rig-builders

In harsh conditions and offshore applications, drilling companies have historically relied on steel cables. But steel cables are often heavy and bulky – requiring cranes to use them. However, when you’re out at sea, you can’t always get your hands on the equipment you need. Cable manufacturer FibreMax has developed a strong yet lightweight Twaron cable that just two people can manage – without the need for a crane. Designed for a customer of the Nederlandse Aardolie Maatschappij (NAM), this cable will soon be in action on rigs in the North Sea.

Swapping heavy steel for Twaron fibers

In 2010, NAM approached FibreMax with a unique request, says Wilco van Zonneveld, Sales Engineer at FibreMax. “It’s for Swift Drilling, one of their downstream customers,” he says. “They need specialized lifting slings for use on a new drilling rig they’re building in the North Sea. The slings will be used to lower sections of the new well onto the seabed. But the tricky thing is that the crane on the drilling rig will not be available when Swift Drilling needs to lower the well. So each individual section has to be lowered by hand.” Had the crane been available, Swift Drilling would have used steel cables for this application. But in this case, steel cables of the appropriate strength and length would be far too awkward and heavy, with each one weighing as much as 400kg and requiring as many as 15 people to deploy. FibreMax’s Twaron cables, on the other hand, weigh only 40kg each and can be managed by just two people. “Twaron has a number of properties essential for this application,” says Wilco. “It has an excellent strength-to-weight ratio and is highly resistant to corrosion. It also has very low ‘creep’, which means it does not stretch and weaken with use as other synthetic fibers do. It’s basically a very stable and strong fiber. Plus, Teijin Aramid’s support is very good. If you’re working on a unique application like this one, they think with you and are always available to help.”

Stronger, lighter construction

Finding the right fiber was only half of the formula for FibreMax. Its “endless winding” method of construction was also essential in producing lifting slings with the right strength-to-weight ratio. In this method, fibers aren’t twisted or braided (as in most ropes or cables), but instead lie parallel to one another. “We wind all the fibers continuously around two end fittings, and keep winding until we reach the cable’s exact required strength.” The core fibers are then tightly wrapped in tape and over-braided with protective fibers to preserve them from environmental conditions and abrasion.

Updating an old technology

Endless winding is used today by a number of other manufacturers, but FibreMax has redesigned the technology to produce cables that truly standout for their quality and reliability. “We’ve developed a special machine – the only one of its kind in the world – capable of keeping the tension in each single strand of fiber precisely the same at all times,” says Wilco. “This is essential because, otherwise, you need to wind on far more fiber to achieve the same break strength as we do. If the tension in each fiber is different, then when you put a load on the cable, first one fiber will stretch, then another, then another – leading to an uneven distribution of force. When you pull on one of our cables, all the fibers are immediately loaded to the same level and can work together. This also means that the particular characteristics of a high-performance fiber such as Twaron – with its high strength, light weight and very low stretch – are translated directly into the cable. Thanks to the combination of Twaron fibers and FibreMax’s endless winding technology, Swift Drilling has the tailor-made cables it needs – and while they’re just as strong, they’re 90% lighter than steel cables. So while cranes certainly haven’t been rendered obsolete, they are no longer essential in this particular application. Another advantage of using Twaron in this application is that it minimizes the risk of injury for the people handling the cables: when steel cables are damaged, broken wires form “fishhooks” that can tear the hands of deckhands. Read about another cable that solves this issue on page 8 in the article “No fishhooks in this firewire”. On page 9, you can read about more of FibreMax’s Twaron-reinforced cables – ones that are being used by Dutch fair-ride manufacturer KMG to build the world’s tallest mobile fair attraction ever.