The synthetic sling is an increasingly popular lifting tool. Euan Youdale speaks to Mike Riggs, director of training at US sling manufacturer Slingmax, about the safety issues surrounding the industry and its future.
There are solutions to protect synthetic slings from corners, protrusions and rough surfaces, using bulk nylon, rubber, and leather coverings or softeners. These materials, says Riggs, offer protection against abrasions, but have limitations.
"Exposure of a synthetic sling to load edges or corners requires a pad that is not susceptible to cutting, either because of toughness or separation."
An example is a tunnel-like product that separates and protects the sling from the load edge. Two such products, using the tunnel principle are the CornerMax Pad and the CornerMax Sleeve with Dyneema fibre. It was tested by Slingmax and found to have a cut resistance of 25,000 lbs (11.3 tonnes) per inch of sling.
Safety also remains a central concern when choosing which type of sling to use, says Riggs. "You must have the right type of sling for the job, it could be wire, but it must have the right radius and you must know the weight and forces to be placed on it. It must be in good working condition; there needs to be an understanding of the criteria for removing it from service and putting it in service. Often, people look at it and say ‘that's okay', but they don't actually know what they are looking at, or they play roulette with the design parameters."
For example, a 12,000 lb (5.4 tonne) capacity sling should be suitable to lift a 10,000 lb (4.5 tonne) load, Riggs explains. But if the synthetic web sling has some cuts and is faded out by UV degradation, its real lifting capacity can be drastically reduced.
This means that although the sling may come with a 5 to 1 designed capacity, its capabilities are much less.
This, however, does not stop some riggers from ignoring this fact by "cheating into the safety envelope. But that envelope is not there anymore when UV degradation happens, so you cannot rely on it," adds Riggs.
This, he says, lays the sling open to failure if there is an unexpected additional force. The correct course of action would be to put the sling out of service.
While training is crucial to safe sling use, it is the type and quality of the training that is paramount. Not only do personnel need to know the standards but they must know how to incorporate them into the rigging process.
While there are some good training companies, Riggs says the depth of training across the field is not adequate. "They get approached after there is an accident. But a lot of training testing is going to be incorporated because of the accidents that we have had. It's about a culture change, people hire someone who says they are a rigger, but they should have to verify who they say they are."
Another problem is that sling use, and rigging in general, can often be an afterthought in many training programmes. "Not all union programs cover that subject properly and will concentrate on their main subject, like welding, mechanics, fitting, wiring, etc, but miss out on rigging."
While most manufacturers provide training to customers for their own products, Slingmax says it offers schooling across all types of slings, even if they are not produced by the company. "We feel responsible whether we make it or not. There are real differences with different types of slings."
"One suggestion, that always comes up to improve sling safety, is to change the slings design factor from 5 to 7, as used in Europe. However, this will not change removal criteria for the slings and just gives a false sense of security to the user," says Riggs.
Round slings are taking over in popularity from web slings because they have a higher capacity and more companies are able to manufacture them worldwide, says Riggs. "I believe they are safer because on the double wall aspect you severely reduce UV degradation. And load core damage has a less accumulative affect on the ultimate strength, where as very miner damage will greatly reduce the ultimate strength of a web sling," adds Riggs.
High performance synthetic slings are becoming increasing popular throughout the lifting industry. "The industry in the US is booming and is very popular in the power, automotive, construction and shipbuilding industries," says Riggs. He explains that shipyards are increasingly able to build larger components which are suited to synthetic slings, meaning they are slowly taking over from metal slings. Another example is bridge building.
Synthetic slings now account for about 60% of all production at Slingmax. "Wire slings have not gone down but synthetic slings have gone way beyond them. They have better ergonomics and result in fewer back injuries and pinched fingers. The cost is less and they will sit in the back of a pickup and you do not need another crane to hook them up," says Riggs. "More and more people are making the fibre components, allowing them to be made," he adds.
As a result of recent hurricanes, including Katrina in 2005, offshore an example of one sector realising the advantages of synthetic slings, says Riggs. He explains how damaged drilling rigs, caused by the hurricanes, have left deep sea lifting requirements needing synthetic slings, because divers cannot cope with metal slings. "Using people to go down there meant the cost was getting ridiculous. So the industry took a fresh look at high performance fibre. It is proving to be working very well."
Slingmax's biggest capacity synthetic sling so far is a 600 tonne product, used for offshore and sub sea work. It has recently completed a year of use underwater in an oil-related project in the Gulf of Mexico. "The fibre is in excellent condition and so is the core. The company is planning on using it in other applications."
A shipbuilder in the Netherlands has also contacted Slingmax with regard to producing an 800 tonne capacity sling, and this has resulted in a number of enquiries from other companies interested in the same product.
Part of the attraction of synthetic slings, says Riggs, is the storage. "You can put three 250 tonne, 110 foot (34 m) long slings in a 4 x 4 x 8 foot crate."
"The industry has become much safer especially ergonomically. If you have a big wire rope sling and it slides off you can break a leg or a foot but a synthetic sling flops down on you and the injury is much less."
Another benefit is the almost limitless capacity of the synthetic sling, adds Riggs, as you can wrap as much fibre as you need to form the core of the sling.