Three firms have joined forces to lighten the load of offshore heavy lifting game. Elaine Maslin found out more.
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DeepTek drum winch, with 150m test length of LankoDeep AHC rope, installed on Jebsen and Jessen 110-tonne knuckle boom crane. |
Fiber rope has been around for quite some time in the offshore industry. It’s been used in mooring applications, by tugs and for towing seismic arrays.
The first 100% Dyneema ropes were used in 1996, the 2001 initiated deepwater installation of subsea hardware (DISH) joint industry project took the technology further, and more recently fiber rope cranes have been developed.
At the time of the DISH JIP launch, fiber rope was billed as “the future,” however, take up has been slow in the deepwater offshore construction sector. This is mostly attributed to perceived cost, risk and “paralysis by analysis,” according to a presentation at IMCA’s Fibre and Hybrid Ropes for Subsea workshop in Amsterdam in late 2014.
A consortium of three businesses is hoping to change the game.
DSM Dyneema, Deep Tek and Lankhorst Ropes teamed up to create a soft rope system that is already making industry headway.
Its first two, 110-tonne, 3000m water depth-rated systems are currently being installed on the 88m-long vessels MMA Prestige and MMA Pinnacle, owned by the Australia-headquartered Mermaid Group. The so-called soft tope system is the first system to adhere to DNV-OS-E407 (Underwater Deployment and Recovery Systems), which looks at the complete lift system rather than just the individual elements. The system’s development was partially influenced and enabled by the standard, which was set out in 2013, says Moya Crawford, managing director of Deep Tek, based in Fife, Scotland.
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LankoDeep AHC 12x3 strand rope, made from DM20 XBO fiber by DSM Dyneema during rope spooling trials. |
“We saw a potential in the market and to meet DNV GL’s new standard we needed to work together, but the new standard also enabled us to innovate and to give confidence to the customer,” Crawford says.
“It is a significant achievement to have the world’s first, that breakthrough. We think it will completely alter the way subsea infrastructure is designed and installed.”
The system is a multi-layer, soft rope, active heave compensated (AHC), drum-winch system that can be installed in offshore cranes and certified by DNV GL. It uses a drum winch, with Deep Tek chevron winch spooling (the rope is laid in a chevron pattern), which eases pressure and strain on the rope and prevents burying in of the rope, and 3km of 76mm, 12x3 strand LankoDeep AHC rope, made from DM20 XBO fiber with an IcoDyn 10 coating. Each system for Mermaid will also use a 110-tonne capacity knuckle boom crane from Jebsen and Jessen Offshore.
While there’s been concern about understanding the behavior of fiber rope, Rigo Bosman, an application development technician at Dutch company DSM Dyneema, says the DM20 XBO fiber is fully understood.
Dyneema DM20 XBO fiber has been developed to be used in ropes that combine high creep resistance with high bending performance, making it possible to use very high line tensions. At the rope’s performance point (maximum rope tension of 110-tonne and maximum rope temperature of 50°C) the rope has a margin of creep time to failure of more than three, in continuous use, during its lifetime.
The XBO is added to the HMPE fiber through a proprietary process developed by DSM Dyneema and lessens the internal abrasion in the rope as it is pulled back and forth over sheaves during active heave compensation operations, known as cyclic bending over sheave (CBOS).
The LankoDeep AHC 12x3 rope construction helps reduce the tension required to bed-in the rope, as well as reducing internal heating and abrasion in active heave compensation. Next to that, a new splice has been designed and certified to ensure that end connections are secure.
The soft rope system also comes with a monitoring system, which records all the operational data to model how the rope is performing and predict its remaining life. “That’s a real breakthrough,” Bosman says. “It requires that we have a logging system where we very accurately monitor, along the length of the rope, the energy input that DSM can translate into the remaining life, which helps maximize the value and benefit to the end user.” To do this, a DM20 XBO lifeTIME model is used to model and predict the rope’s status.
Heat generation can be an issue, so rope temperature management is performed via a pre-warning and alarms system to trigger water cooling. It has been shown that in realistic AHC operation conditions, the rope temperature will stay below 50°C when sprayed. In extreme conditions (high loads in a storm) the rope can be paid out to work on a new part of the rope, or AHC can be switched off.
The crane for the first system for Mermaid is to be supplied in June with testing through summer. The vessel is expected to be going to the market by yearend.
Also, higher capacity systems are under development. A 165-tonne at 3000m water depth has been proposed, and 275-tonne, 440-tonne and 825-tonne systems at 3000m are being developed.
“This is a project I don’t think any of the three companies could have done individually,” says Chris Ayers, president and CEO of WireCo WorldGroup, which owns Netherlands-based Lankhorst Ropes. “From the beginning, this made a lot of sense to us. We got the rope produced, and got a customer, and hope there are many more to come.”
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