Ropes can be soft to the touch and flexible in compression, but incredibly tough and strong under tension.
Modern-day heavy lifts increasingly use ropes made from synthetic materials, rather than steel wire ropes, which had been the standard alternative to natural fiber for more than a century in hoisting and pulling applications.
The challenge when lifting objects as diverse as wind turbine transition pieces, blades and towers, oil and gas structures for deployment subsea, or massive mining and drilling equipment, is in rope, materials and assembly selection.
There’s never a one-size-fits all option so the success of a high-risk project, when expensive or irreplaceable items are lifted, depends on correct choices. These decisions can become harder when objects have irregular shapes or abrasive surfaces.
Strength properties remain the top consideration when selecting a suitable rope for a lifting sling assembly; however lightweight and low-stretch products also provide advantages for teams involved in handling the equipment.
This is why specialist advice is often needed to assure certainty. Cortland has provided its lifting expertise to clients for more than 30 years and can accurately calculate weight and strength limitations, providing sound advice to customers.
When a synthetic rope is bent around a sheave or pin, as is commonly the case, it experiences a loss in strength due to bending. A rope when loaded in a straight pull only has to handle axial stress, but when bent around an object, the total stress becomes a function of tension and bending combined.
The effect of this bending is dependent on the overall sling configuration. At the planning stages of any lift expert knowledge is required. This includes the ability to calculate D:d ratio, which refers to the sling’s diameter (d) and the diameter of the object it interfaces (D).
For wide, heavy equipment such as crane decks, mining components or large diameter pipelines, a ‘basket’ of slings can be an appropriate solution. Basketing means that slings will share the load between multiple connection points, and this requires additional calculations.
In these projects, high performance fiber can be used as a direct replacement for steel. Advantages include lightweight, easy to handle materials with high resistance to water and chemicals. When it comes to the effects of impact loading, compression points on synthetics can be teased out, whereas steel versions will permanently deform once bent and compressed, affecting their future use. Fiber models are also compatible with all rigging hardware associated with steel, unlike more traditional ropes, which are often larger in diameter.
Ropes made from synthetic materials act in the same way as traditional fiber or steel, but there is now greater understanding that they can do so much more over and above the obvious. They are multi-functional products that can take the manpower effort and tension out of high-stakes heavy lifts. More than this, they have become increasingly proven as superior alternatives in comprehensive testing and in practice. This is why it is worth exploring high performance ropes more closely.