A synthetic revolution
By Laura Hatton28 September 2015
With increased usage of ropes made from synthetics, replacement criteria for ropes are a key topic of concern in the lifting industry. Laura Hatton reports
In 2014 EN 13001-3-2 was published by the European crane standards committee CEN/TC 147. A technical paper critiquing the EN 13001-3-2 rope selection methodology, raising safety issues, has since been published by the Technical University at Dresden, in Germany raising concerns over the approach to rope selection. The paper recommends the use of ISO 16625 (replaced ISO 4308) instead and has gained support from European Federation of Wire Rope Industries (EWRIS) and Drahtseilvereinigung (Association of German Steel Wire Rope Makers, DSV), members of which include Bridon, Casar, Diepa and Teufelberger.
For synthetic ropes there are general ISO standards. The crane industry, however, is still working on adapting current steel wire crane rope standards to the use of high performance synthetic ropes. A spokesperson from synthetic fibre manufacturer DSM Dyneema, a supplier of the High Modulus Polyethylene (HMPE) fibre that is used to construct some synthetic fibre ropes, explains, “Within the EU region applications can be covered by the European Machinery Directive – within this are guidelines for the safe usage of machinery and auxiliaries. Crane manufacturers have also initiated work on adapting EN 13000 and relevant ISO standards. In the USA, for example, there is a draft ASME standard B30.30 that, once approved, will specifically cover synthetic ropes.”
As Michael Quinn, at synthetic fibre rope manufacturer Samson, director of new business development points out, the development of these standards is needed to support the use of this technology in the marketplace. Until such a regulation is in place, Samson, like many rope manufacturers of synthetic rope, has developed inspection and retirement criteria for its KZTM100 rope, which was developed in collaboration with crane manufacturer Manitowoc for hoist lines in mobile crane applications. The KZTM100 was the first synthetic rope designed specifically for mobile cranes (see IC March 2014, page 13).
Marcus Klink at Casar, originally a manufacturer of only steel ropes but now part of the WireCo World Group, adds, which includes manufacturers of synthetic rope, “For synthetic ropes, the whole development has just started and the lifting industry must adapt clear and easy-to-use standards for discarding. Steel cables have been used in many industries for more than a century and are recognised in the market for providing a higher breaking force compared to a same diameter synthetic rope at a two or three times lower price level. In addition, they provide a sense of security by clearly defined discard criteria according to ISO 4309. These discard criteria have been reviewed, revised and improved many times and are well established.
“High quality steel wire ropes are designed in a way that the rope clearly shows its criteria for withdrawal from service (for example by a certain number of wire breaks on the surface). Compared to synthetic ropes, which is measured in millions of filaments, the counting of broken fibres is impractical. Furthermore, these very small filaments are vulnerable to damage and have a highly anisotropic nature. This means that the strength of the material acts axially down the length of the rope, but it also results in a material that is weaker off axis and resulting in more sensitive to harm from external contact than a steel wire. If the filaments of a synthetic rope indeed break, the frayed fibre will tend to stay attached to the rope body or even increase the volume between adjacent filaments. Consequently, a simple diameter measuring will not show the loss of material in the same way as in the case of an abraded steel rope.”
Compared to steel ropes, the material properties of synthetic rope provide some significant advantages, including weight reduction. Michael Quinn at Samson says, “With an 85 % reduction in weight, the hoist line below the boom tip is much lighter. This can allow OEMs to improve load charts, particularly on long boom applications. In addition, most high performance fibres are resistant to chemical degradation, which make synthetic ropes an excellent choice in corrosive environments.”
The benefits of synthetic fibre are noted by many industries, including the marine industry, as Andy Ash Vie, Harken Industrial, CEO adds, “With fibre rope there is a reduction in maintenance, replacement costs and shipping costs, as the sheer bulk of moving a replacement steel cable compared to replacement fibre cable is enormous, so everything is a lot easier.
“There are, however, some problems with using synthetic ropes, one of which is spooling. For example, with a low load the first layer of rope being wound onto the winch is in a pliable state. Then as the load is lifted up the fibre rope on the winch becomes stiffer and risks ‘sinking’ into the layer below it. The result is that the rope will ‘jam up’ when you try to release it. The problem can be solved by either designing the rope and its weave to be compact, so when the load is off it remains stiff. The second approach is to separate the pulling function from the spooling function.
“The idea comes from marine applications, where sailors use a sailing winch to pull the rope in using only three, maybe four, wraps of the rope. The remaining rope is then left on deck,” Ash-Vie explains. “In the crane industry this is obviously not ideal, so the solution would be to have a capstan winch to pull the load and then have a separate storage reel for the remaining rope. By separating the two functions it could be possible to have a high load operating winch and a low load spooling winch. Of course, putting this idea into practice would need to be considered at design stage, and not at retrofit stage.
“Other areas that need attention are pulleys and hook blocks. We’ve noticed that companies are starting to use synthetic ropes and are feeding it into the same set up as for steel ropes. The pulley blocks or the sheaves are all heavy steel blocks and, because the new synthetic rope is so much lighter, in cases where you have a big heavy block with a light load, the block will not align to the load. This results in chafing and could cause damage.
“We are just seeing the first flickering flames of a synthetic revolution in cranes and we are seeing various different companies starting to pick it up,” Andy Ash-Vie adds. “What we need to look at is how do you get the best out of using synthetic rope and how do you avoid its pitfalls? In addition, what are the consequences if we move away from steel wire technology and what is the impact on a crane, or other lifting equipment, throughout the chain of lifting operations?”
For the offshore industry, synthetic ropes have a number of advantages and can handle heavy loads at increasing depths. Lankhorst Ropes, for example, has supplied two 3,100 metre long LankoDeep AHC ropes for a pair of 110 tonne Jebsen and Jessen knuckle boom crane systems.
The cranes are being installed on the MMA Prestige and MMA Pinnacle, two 88 m long vessels owned by the Australia-headquartered Mermaid Group. The LankoDeep AHC rope forms part of a new Soft Rope system that is capable of handling heavy loads at depths of more than three kilometres.
“The Soft Rope system comprises Lankhorst Ropes’ LankoDeep rope, DSM Dyneema and an Active Heave Compensation (AHC) drum winch system from Deep Tek,” a company spokesperson says. “The drum winch design ensures a spooling pattern that allows multiple layers of fibre rope to be spooled onto a load bearing winch drum with no risk of cutting in. It is certified by DNV-GL at 110 tonnes in the air and 110 tonnes at 3,000 m water depth.”
LankoDeep AHC is based on Dyneema DM20 XBO synthetic filament. “The new rope has 12 stranded braids where each strand is a three-strand rope,” Sérgio Leite, Lankhorst Ropes sales director of heavy lift explains. “This construction, combined with the DM20’s XBO coating, helps reduce the tension required to bed-in the rope, as well as reducing internal heating and abrasion. In addition, the rope can be inspected and is also repairable. Larger Soft Rope systems capable of handling 165 and 275 tonnes are in also development.”