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Slings and rigging: the soft revolution

19 July 2017
Fibre rope slings offer a number of advantages over steel wire for heavy lift projects. Easier handling and weight savings, to name but two. Research by Lankhorst Ropes into heavy lift slings is set to broaden the scope for high performance synthetic slings in maritime applications.

At the recent IMCA Rope Forum 2017, Slings and rigging: ‘The soft revolution’ session, in Amsterdam, Lankhorst Ropes presented a paper entitled: Realistic testing and development of high performance slings. “We have chosen to look at the complete lifting system, recognising that the slings are part of a complex system where interfaces between the sling, sling arrangement, crane, hook block, spreader bar, other connecting hardware and lifted mass need to be understood and managed,” says Rui Pedro Faria, Project Manager, Lankhorst Ropes.

Realistic Testing

Lankhorst fibre slings are designed for engineered lifts. These are project specific, non-routine lifts and specially prepared and documented by industry procedures such as DNVGL-RP-N201. The Lankhorst Heavy Lift development program is designed to: improve knowledge on sling behaviour under different and realistic load scenarios allowing better characterisation of sling capacity, better use of sling intrinsic capacity and more accurate calculation of design/safety factors.    

The testing program aims to simulate realistic load conditions during all offshore lifting phases. The more complex lifting scenario, ship to seabed and reverse, was selected to provide a meaningful understanding of the operation, encompassing: lift in air, splash zone and underwater lift. It is while passing through the splash zone that the lifting slings experience the greatest efforts. In this phase, the lifting arrangement experiences oscillating stochastic forces as a result of buoyancy effects, sea waves and wind interaction.

Throughout the test program, Lankhorst is developing understanding of sling behaviour, interfaces and boundary conditions. This will help to determine the sling’s service life and operational limits, as well as to define relevant rope failure modes and ways to prevent them.

Consistent with its commitment to realistic testing, the Lankhorst R&D program is a joint effort with installation companies, incorporating input received from them to create accurate lifting simulations based on real lift operations, and so develop full understanding of rope performance under relevant usage scenarios.

Certification and Re-certification

A key objective of this Lankhorst research is the development of heavy lift slings that are provided in a certification readiness level, in accordance to DNVGL-OS-E303. To achieve this objective, the ‘Qualification of New Technology framework’ (TQ) as proposed by DNV-GL is implemented. With the TQ approach, existing standards can be applied, when relevant, and remaining unknowns can be addressed through a claim-argument-evidence structure to provide the fundamentals of safe use. “Overall, the Lankhorst research will increase confidence in using fibre rope slings in engineered lifting operations, by providing a safe, reliable and “fit for purpose” product, which are certified by DNV-GL. With this approach, less conservative design/safety factors can be validated”, notes Rui Pedro Faria.

For more information on Lankhorst Heavy Lift Slings, email: heavylift@lankhorstropes.com.