Calculating the workload limit or working load limit (WLL) of a lifting sling is crucial to ensure safe lifting operations. The WLL represents the maximum load that a lifting sling is designed to handle under normal working conditions. To calculate the WLL of a lifting sling, you need to consider several factors and follow these steps:

Identify the Sling Type:

Determine the type of lifting sling you are using, such as wire rope, chain, synthetic web, round sling, or other specialized slings.

Determine the Sling Configuration:

Understand the configuration of the sling. Common configurations include single-leg, double-leg, triple-leg, and quadruple-leg slings. The configuration affects the sling's capacity.

Know the Angle of the Load:

Determine the angle at which the sling will be used to lift the load. The angle between the legs of the sling and the horizontal plane significantly impacts the WLL.

Common angles include 0° (vertical lift), 45°, and 60°. Note that as the angle decreases, the WLL increases.

Refer to the Manufacturer's Data:

Consult the manufacturer's documentation or markings on the sling for load capacity information. The manufacturer provides specific WLL values for different sling types, configurations, and angles.

Apply the Angle Correction Factor:

If the angle at which the sling will be used is different from the vertical (0°), apply the angle correction factor to adjust the WLL.

The angle correction factor depends on the sling configuration and the angle itself. Manufacturers typically provide tables or formulas to determine the correct factor.

Calculate the Adjusted WLL:

Multiply the manufacturer's rated WLL (for a vertical lift) by the angle correction factor to calculate the adjusted WLL for the specific lifting angle.

Example:

Manufacturer's WLL for a single-leg sling in a vertical lift = 10,000 pounds.

Angle correction factor for a 60° angle = 1.155 (as per manufacturer's data).

Adjusted WLL = 10,000 pounds (manufacturer's WLL) × 1.155 (angle correction factor) = 11,550 pounds.

Consider Additional Factors:

Depending on the specific lifting conditions, you may need to consider additional factors, such as the load's dynamic effects, shock loading, and environmental conditions.

Verify Compliance with Standards and Regulations:

Ensure that the calculated WLL complies with applicable industry standards, regulations, and safety guidelines. Different regions may have their own standards for safe lifting operations.

Label the Sling:

Clearly label the lifting sling with the calculated WLL, sling type, and other relevant information for easy identification and safe use.

Regularly Inspect and Maintain the Sling:

Perform regular inspections of the sling to detect signs of wear, damage, or deterioration. Remove damaged slings from service immediately and replace them as needed.