What is a synthetic web sling and what damages it?

Synthetic web slings and round slings are fabricated from nylon or polyester yarns woven into flat webbing or enclosed in a round sleeve. They are widely used in applications where wire rope would damage finished surfaces, where lighter weight handling is required, or where the flexibility of a soft sling better conforms to the load shape. Like all rigging, synthetic slings have specific rated capacities for each hitch type and sling angle, and their condition degrades with use, chemical exposure, and UV exposure.

Nylon vs. Polyester

The two primary synthetic materials used in web slings are nylon and polyester. Nylon has slightly higher elongation under load, which provides a degree of shock load absorption. However, nylon loses a meaningful portion of its rated capacity when wet, because nylon absorbs water and the fiber strength decreases with moisture saturation. Polyester maintains its rated capacity when wet and has lower elongation than nylon, which makes it preferred for precision lifts where load stretch must be minimized. Polyester is also more resistant to most acids. Nylon is more resistant to alkaline chemicals. The sling's tag must identify the material so the rigger can evaluate chemical compatibility with the load and the work environment.

Removal-from-Service Criteria

ASME B30.9 and OSHA 1926.251 specify conditions that require immediate removal from service for synthetic slings. Any sling showing any of the following must be immediately retired: acid or caustic burns that have degraded the webbing; melted, charred, or heat-stiffened fibers; holes, tears, cuts, or abrasive wear that has reduced the webbing thickness; broken or worn stitching in the load-bearing splices; distorted or damaged hardware fittings; or UV degradation evidenced by surface powdering, brittleness, or discoloration. Color-coded labeling systems (WSTDA standard) assign specific colors to specific capacity ranges, but the label color alone is not sufficient to assess condition. A visually degraded sling with the correct color label is still a damaged sling that must be removed from service.

Sharp Edges and Storage

Synthetic slings have no tolerance for contact with sharp edges on loads without protection. A single pass over an unprotected structural steel edge can cut through the webbing completely, with no visible warning until the sling parts under load. Corner protectors or load-specific edge protection must be used whenever the sling contacts an edge with a radius of curvature less than the minimum specified by ASME B30.9 for the sling width. Storage must protect slings from sunlight, because UV radiation progressively degrades synthetic fibers even without mechanical use. Slings stored outdoors or in sun-exposed areas must be regularly inspected for UV degradation and replaced before the degradation reaches the removal threshold.