Overturning a heavy object onto cribbing, using one lift hook and chain block. To upend the object, chain block “A” and the sling “B” should exchange points.
Doglegs, Sets & Kinks
When a loop is “pulled through,” it forms a kink, which permanently deforms a wire rope by freezing or locking wires and strands. This prevents them from sliding and adjusting, and reduces rope strength. The damage is irreparable and the sling should be taken out of service.
A dogleg is a “set,” which occurs when a wire rope sling is pulled down snug against a load. A dogleg usually can be “rolled back” or turned inside out, and usefulness of the sling restored, since strands can still adjust. If the dogleg is severe, the sling must be removed from service. If the dogleg is minor, (exhibiting no strand distortion) and cannot be observed when the rope is under tension, the area of the minor dogleg should be marked for observation and the sling can remain in service.
Eye deformation is ordinarily not detrimental to sling strength, as long as there are no broken wires or gross distortion of the lay of strands. An eye has two legs, so it has adequate strength for the load the body can carry. A sling should be retired when distortion locks the strands or flattens the rope in the eye so strands cannot move and adjust.
Care of Wire Rope Slings
The amount of care and proper maintenance a sling receives will go a long way in determining its service life. Following are guidelines which experience has shown helpful.
Storage: Proper storage requires that slings be kept in an area where they will not be exposed to water, extreme heat, or corrosive fumes, liquids, sprays, of being run over or kinked.
Slings should never be left beneath loads or lying wound where they may be damaged. All slings, when not in use, should be kept on a rack. Use of a rack minimizes accidental damage and allows easier monitoring of condition between regular inspections. A rack will also save time by allowing larger slings to be picked up and returned by crane, thereby reducing manhandling.
Rigger’s Check List
- Analyze and Measure—Determine the total change weight to be moved, as well as exactly how far it is to move and how high it must be lifted.
- Determine the Hitch—Decide how the load is to be connected to the lifting hook, and how the sling will grip or be attached to the load.
- Select the Sling—In addition to adequate Rated Capacity for the angles involved, the sling body should be of the type and style best suited to handling this specific load. Select a sling with proper end attachments or eye protection, as well as attachment hardware, such as clevises.
- Inspect the Sling—Make a good visual check of the sling you select to determine if it is in good condition and capable of making the lift. Refer to prevailing OSHA and ASME regulations for inspection criteria.
- Rig Up, Not Down—Always attach the sling to the load first, then attach it to the hook.
- Check Everything—Before attempting a lift, take a light strain on the rigging, checking to see that blocking, sling and load protection and all safety devices are in place.
- Stand Clear and Lift—Let the lifting device and rigging do the job—don’t use brute strength to prevent swinging or movement. Use a tagline or tether to control any movement. Keep all hands and toes out from under the load when it is suspended.
- Don’t Jerk—Lift slowly and with a steady application of power.
- Put It Away—After you’ve completed the job, check the sling for any damage (if it’s damaged, red tag it immediately or advise the sling inspector), then return it to the sling storage rack for safekeeping until next usage.
Steel core slings should never be used at temperatures above 400°F, or below minus 40°F.
Wire rope with a steel core should be selected if there is any evidence to suggest that a fiber core will not provide adequate support to the outer strands, and/or if the temperature of the working environment may be expected to exceed 180°F.
For operating temperatures above 200°F, de-rating of the minimum breaking force of the rope is necessary (e.g. between 200°F and 400°F reduce by 10%; between 400°F and 600°F reduce by 25%; between 600°F and 800°F reduce by 35%).
Do not use ropes with high carbon wires above 800°F.
Failure to observe this general guidance could result in failure of the ropes to support the load.
For temperatures over 800°F, other materials, such as stainless steel or other special alloys, should be considered.
Rope lubricants and any synthetic filling and/or covering materials may become ineffective at certain low or high operating temperature levels.
Certain types of rope end terminations also have limiting operating temperatures, and the manufacturer should be consulted where there is any doubt. Ropes with aluminium ferrules must not be used at temperatures in excess of 300°F.