High-performance steel wire ropes for offshore cranes

21st February 2013

High-performance steel wire ropes can make a big difference especially in offshore applications. Gerald Neuwirth explains why

Cranes on offshore-platforms need to perform in the best possible way without the risk of failure in critical moments. Demanding the highest and permanent use in extreme environment conditions is characteristic for offshore cranes. High device availability is very important far away from the coast, while safety and reliability are crucial factors for both the cranes and the steel wire ropes in use.

Teufelberger, as a manufacturer of high performance steel wire ropes with a strong presence in the offshore industry, says these ropes make a big difference, especially in offshore applications.

Wire rope basics

The main difference between a standard wire rope and a high-performance wire rope can be found in the following features. In general, ropes for offshore applications should only be used with galvanised wires. Only this ensures a long service life. Galvanised wires have a far better base in quality as ungalvanised ropes.

- Compaction of the wires. Compacted ropes reach significantly higher breaking forces than non-compacted ropes (up to 30 per cent). This makes a big difference as a compacted rope allows crane producers to use a smaller rope diameter to reach the same breaking load. On the other hand, compacted ropes offer a smooth rope surface, resulting in reduced abrasion on rope, sheaves and drums. Compacted ropes also work perfectly in multi-layer spooling, as they offer a high form stability against lateral pressure. Important is also what kind of compaction technology is being used to ensure a perfect result.

- Plastification of the rope core. In order to ensure permanent lubrication and less friction between core and outerstrands, the core should be plasticised. Here it is important to use a plastic which does not absorb water. The rope strands are embedded in a synthetic coat during the stranding process. This offers an additional protection of the rope core against external influences, increases the lifetime of the rope due to permanent lubrication and the rope also reaches higher breaking forces through reduced friction in the rope.

- Significantly higher service life of the ropes in use. Especially on offshore cranes this is a very important issue to be considered. To change a crane rope - especially under harsh conditions - is not an easy task. Therefore it makes sense to extend the use of a crane rope to the maximum possible period. Furthermore, it is crucial to avoid unplanned downtimes of the crane in use - due to problems with a rope - as this can cause significant costs due to high day rates. By considering the total cost of ownership (TCO), a high performance steel wire rope pays off in a short periode, especially on offshore applications.

- Langs lay ropes for multi-layer spooling. For cranes using ropes in multi-layer spooling ropes in langs lay are recommended. These ropes normally will reach a higher lifetime than ropes with ordinary lay and are more flexible which gives a bether performance on the drum and a higher crush resistance.

As a summary, the initial investment in a high-performance wire rope is higher of course, but the performance and the overall costs over the lifetime period of the rope gives a better return on that investment.

Specific applications

Depending on the application it is important to select the proper rope type. Non-rotating, high performance ropes - like the TK 16 Evolution from Teufelberger - are used as main and auxiliary hoist ropes in single or multi-layer spooling.

The fact that the rope is non-rotating is of crucial importance especially in offshore crane applications, (as the rope is 'rotation resistant itself' due to the construction parameters of the rope).

This helps to avoid uncontrolled movements of load which can be a risk for person and goods and - as a consequence - to the overall security of a platform. Best spooling properties for fast winch speeds are another benefit when using a high-performance wire rope.

For boom hoist applications (multi-layer spooling) an 8 strand, compacted rope, preferable langs lay for multi-layer spooling - eg, the QS 816 V (G) - will be recommended. High resistance against radial deformation and high flexibility will definitely increase lifetime and safety.

Teufelberger ropes are designed for demands in the offshore industry and are very specific for an individual crane producer. Other special areas where high performance steel wire ropes are used are for example riser tensioner ropes. Especially on riser tensioner ropes long fatigue life time in relation to bendings is a merit for the customer. With the QS814VG (8 strand and high number of wires) these criteria will be fulfilled.

As a summary, there is a broad range of different rope types and in any case it is very important to select the right rope type for a specific application. Industry experts - either from the rope manufacturer or from the rope supplier - are the right source of information before purchasing a rope. They can make an evaluation of the conditions under which a specific rope needs to operate on a specific crane.

For international clients, as this is primarily the case in the offshore industry, the rope-availability on every major offshore hotspot on earth is also a very important factor. Teufelberger, for example, has a global distribution network with ropes in stock in every major part of the world. A team of service engineers with a broad experience in the offshore industry ensures a quick response and action in case of troubles or if just help is needed. This is a very important backup function and a key criteria when selecting a rope supplier.

For example, the customer base of Teufelberger includes crane producers (eg, Liebherr or Seatrax), drilling companies (Transocean, Diamond Offshore) and production companies (Shell, BP, Petrobras) which have international activities in every part of the world.

Gerald Neuwirth is with Teufelberger Seil GmbH, Wels Austria.

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