Knut Buschmann is a busy man. He was elected president of OIPEEC, the international organisation for the study of the endurance of ropes, at the organisation’s conference in Stuttgart in March. He is a former president of Associated Wire Rope Fabricators, and continues to serve as a member of its technical committee where he is working on developing test method procedures for the rigging industry. He has worked on the development of a number of industry standards, including the high performance round sling standard with the Cordage Institute’s technical committee and the Canadian tower crane standard with the CSA Z-248 committee.
He is also president and general manager of Canada’s Unirope, which specialises in high performance wire rope, standard wire rope and non-rotating wire rope for tower cranes, mobiles and truck cranes, overhead cranes and gantry cranes.
During his time, much has changed in the rope industry, not least for OIPEEC, which has seen its role change as a research coordinator.
“The OIPEEC organisation was formed in 1963 and one of the initial tasks was to coordinate research and testing between European universities and rope research institutes, such as Stuttgart, Dortmund, Delft, Zurich, Grenoble, Paris, Florence, Katowice and Reading,” he says.
“This is all gone today. With the enlargement of the EU, research funding for ropes was halted and withdrawn.
“The respective rope research institutes were phased out or were closed when their professors either retired or moved on to different subjects.”
Buschmann says the only institute left standing with substantial equipment, funding and research staff is the Institute of Mechanical Handling and Logistics at the University of Stuttgart.
“As an organisation, OIPEEC does not perform wire rope science research itself but rather tries to coordinate international research through active working groups. Moreover, OIPEEC meetings usually foster ‘research exchange’ between individuals involved in rope science. As such, OIPEEC fulfils the role of providing an international meeting place of rope scientist engineers and researchers from around the globe.”
This exchange of ideas has nurtured the latest development in wire rope inspection, an automated visual system (see page 29). The technology is designed to ease the job of inspection staff, Buschmann says, as the current procedure puts a “tremendous strain” on them and “may even put in question the validity of such visual inspections.
“Everyone who has ever done this knows that by looking at a running rope which is twisted, your eyes start to loose control to a point that when the rope movement stops the inspector has the impression that the rope is still moving in front of his eyes.
“This is on top of sometimes severe weather and poor lighting conditions.
“Over the years, the hardware and software for the automated visual inspection method has been developed. The hardware is equipped with four digital cameras and a special light system that produces a ‘movie’, which can then be analysed in an office. Sophisticated software detects variations in the rope diameter, the lay length, and detects flaws, like deformations and wire breaks.”
Another development in the wire rope industry, although not as positive as that of a new inspection technique, is a reduction in teaching on wire rope in engineering classes. Buschmann says this has led to the old guard of wire rope knowledge “fading away” and a younger generation of engineers emerging who do not understand the properties of wire rope.
“Young engineers who are confronted with wire ropes are at times completely overwhelmed as to the characteristics of wire rope. It is not uncommon that we get questions like ‘what is the elongation at 2% offset?’, or ‘why is it that wire rope still has elastic elongation although you pre-stretched it?’ Or it is not understood why wire rope should not be used, neither be proof loaded or pre-stretched, to beyond 50% of breaking strength because that is where wire rope enters plastic elongation. It is also not understood or realised that, except for one, no standard describes the true rope performance in terms of lifetime expectancy but that wire rope standards simply state breaking strength.
“No wonder that design engineers get the idea that the rope with the highest breaking strength must also be the best, as that the breaking strength is the engineering yardstick of overall rope quality.
“That leads to a situation today that some more recent crane designs completely focus on rope breaking strength rather than on rope performance. The concept that a high ratio of a design factor does not necessarily result in a greater operational safety is completely lost at times. And then there is the increasing request for information on the e-modulus. Upon questioning the design engineer what exactly they want to try to determine, nearly all of them have no clear answer; they just want the information ‘because it’s available’.
“This is where the OIPEEC organisation may have an increasing role in the future. OIPEEC is the only international body which is able to fill the gap left open by most universities and engineering colleges today.”
Another change has been the increased use of multilayer spooling systems on cranes, particularly those that are traditionally fitted with a single layer drum system.
Buschmann says it is a well-known fact in the crane industry that multilayer spooling systems reduce the lifespan of wire rope, but it is only a recent study by the University of Stuttgart that revealed this reduction can be as much as 88% to 97%. “Or wire rope on a single layer drum will last between 8 and 33 times longer than on multilayer drums,” says Buschmann.
“The operators of such cranes are completely unaware of the greatly reduced lifetime expectancy of their ropes and, furthermore, are unaware of the rope maintenance that is required. For the most part this includes that the ropes must be regularly re-spooled with applicable pre-tension to even mitigate the problem, not to speak of making the problem go away.
“To make matters worse, there are some construction crane types which, when in service, do not permit to re-spool their multilayer ropes to set the correct pre-tension. There is nothing a rope manufacturer can do to correct this problem.”
In the future, Buschmann says the main change in the wire rope will be the growth in use of synthetic ropes to replace steel counterparts.
This is already taking place, Buschmann says, with steel rope anchor lines being swapped out for fibre alternatives in offshore installations.
“The deeper offshore oil platforms are drilling for oil, the more of a problem a heavy steel wire rope becomes. Fibre ropes have near neutral buoyancy and have a very favourable stretch and rotation characteristic. Hurricane Katrina showed that installations which were anchored with fibre ropes held much better than the ones anchored with steel wire ropes.
“The offshore industry follows a rapid increase in water depth to develop oil and gas fields, from around 500m in 1996 to around 2,000m in 2000. New fields under development are found at water depths up to 3,500m.
“The need to install increasingly large and complex equipment on the sea bed will present major challenges at these depths because the self-weight of a steel wire rope will make current systems increasingly insufficient. For example, if a steel wire rope has a lifting capacity of 100% at sea level the capacity due to its own weight drops to about 50% at 3,000m depth.
“Modern fibre rope with neutral buoyancy will still have 100% payload capacity at such depths.”
Research is now taking place so synthetic ropes can be introduced to running applications where the rope runs over sheaves and is spooled onto a drum system; predominantly the crane sector, Buschmann says.
“Currently, there is a research project underway between DSM, Cortland and Liebherr to replace a steel wire rope with a fibre rope on a tower crane. Other projects involve so called ‘hybrid’ rope types in which the rope steel core is being replaced with high performance fibres.
“The advantage is that the effect of abrasion is still controlled by outside steel wires, while a large portion of the weight is replaced with synthetic fibres. Such developments are specifically designed for ultra deep mine applications; South African gold mines in particular.”
