Wire rope slings are the most commonly used rigging hardware in major industries like, construction, marine, industrial and manufacturing. These are a prime component of all lifting and hoisting activities. Incorrect use of wire rope slings has resulted in many hazardous accidents in the past. Sling failures and incorrect rigging methods are one of the major reasons of these accidents. Common accidents that occur due to sling failure include imbalanced or loose loads slipping off the sling, or incorrect rigging causing the load to swing and rotate, which poses a danger to those standing near/under it.
The first step to avoid failure of slings is to make sure that it is purchased from a trusted high quality rigging manufacturer. Sales and safety go hand in hand. It is important that every supplier should provide quality slings to his customers to ensure their safety. Every user should look for rate capacity tags on the slings during purchase and discuss the needful with the manufacturer.
The following guidelines will ensure the safe use of wire rope slings:
1. How to follow safe lifting methods?
It is important to follow proper lifting methods in order to ensure safety. Firstly, make sure to calculate the weight of the load to be lifted. If the load already has hooks or lifting points make sure the sling legs are properly attached to these points. Also make sure the overhead lifting points are properly aligned to the load that is suspended. Location of the center of gravity of the load is another factor that should be determined to lift the material safely. If the load has harsh edges that can cause cuts or abrasion to the slings, protective padding or softeners should be used to protect the sling.
The number of sling legs and the angles also affect the sling capacity. As the angle between the sling legs decrease, load tension on sling legs will increase. The minimum angle between sling legs should be 30 degrees. In case the bridles are designed with different leg lengths it may result in different angles, causing imbalanced loading.
The rated capacity of the sling should never be exceeded. This includes rated capacity of the wire rope used, number of sling legs, and the other parts used in the sling. It also depends on the sling angles, the type of hitches etc. and following proper hitch methods to balance the load radius.
If you are using a single sling to load the material vertically, it can utilize the maximum capacity of the sling. But make sure you do not exceed the limit. If you are using two slings to load the material vertically, make sure leg angles are set appropriately. Divide the weight of your total load by the number of sling legs that are used. This will give you the load applied per leg in vertical lifting.
2. How to inspect wire rope slings?
Before using the slings make sure they are in good condition and are suitable for the given application. Clean the slings with a wire brush or rug to reveal the wire strands and fittings during inspection. Look for major damage or deterioration that can weaken the slings. Other obvious signs of damage include kinks, twists, crushing, broken wires or attachments and corrosion.
A designated person who is in-charge of the inspection should keep record of all inspections, repairs, changes and damage done on the slings. This will tell you when to discard or repair a particular sling. Also inspection should be conducted on the entire length of the wire sling and also the other fittings.
It is also important to conduct additional inspections along with daily inspections. Additional inspections include, test loading, lubrication and the regular tests. These inspections should be conducted by an expert who has proper knowledge of the wire rope slings.
3. When to discard a wire rope sling?
Consider following factors when discarding a wire rope sling from service:
- If you find the rate capacity tag missing from the sling, these should be removed from service immediately.
- If you find broken wires or strands, they should be discarded from service.
- Acidic or caustic burns can damage the slings.
- Look for wire strands that are pushing out from their positions. Such slings should not be used any further.
- Kinking, crushing, bird caging and corrosion are some common damages to look for.
- Cracked, bent or broken fittings should be removed immediately. If you find eye splices have slipped, or tucked strands have moved, these should be put into repair.
- If slings are over exposed to heat, they might result in discoloration or loss of internal lubricant, such slings should be repaired or replaced.
- Once you have identified the damaged slings, those which cannot be repaired should be removed from service and destroyed. Cutting the eye of the sling or removing other fittings will make sure that the sling is not accidentally reused again.
4. Safe Use of sling to ensure personal safety
Before you make the lift, perform a test lift to make sure the slings, blocking and sling protection are in place. Lift the load slightly off the ground and check the balance and leg angles. Make sure all the rigging parts are in place and correctly rigged to the load.
To prevent injuries stay clear off the area where the sling is loaded to the load and also where the sling is hooked to the crane or hoist hooks overhead. Do not by any chance stand under the overhead lifting devices.
In case of load slipping of the sling or sling rotation while the load is suspended, do not attempt to stop it physically immediately. Stay clear from the area, and approach only when the sling swings back in place.
Lift slowly and steadily without making sudden starts and stops when the load is being lifted. Make sure the breaking mechanism is working properly before performing any lift.
All said and done, these are just a few tips that will help you perform safe lifting practices. Lastly, make sure that the lift is conducted by a competent operator, who has sufficient knowledge and understanding of performing lift operations. A qualified operator can look for potential hazards and seek corrections wherever needed. Proper and safe use of rigging equipment will improve their service life and also ensure safety at the work place. And lastly, make sure you plan every lift to minimize any possible risks.