Textile lifting slings, including flat webbing slings and round slings, are widely used in material handling and lifting operations. Although their construction is different, the testing principles, safety requirements, and inspection methods are highly similar.
This guide explains how lifting slings are tested, what standards apply, and what engineers should check before use.
Four Testing and Inspection Commonalities
Commonality 1: The absolute authority of tags
The identification tag affixed to a sling holds absolute authority, serving as its legal "identity card." For both flat webbing slings and round slings, the absence of the tag, its coverage by paint, or its fading to the extent that the Working Load Limit (WLL), material composition, or manufacturer information becomes illegible shall render the sling automatically disqualified. In such cases, no further tensile testing or supplementary inspection is warranted. The sole and correct course of action is to immediately reject the sling, remove it from service, and proceed with formal condemnation.
Commonality 2: Verification load and safety factor standards are consistent.
For non-destructive testing, the factory proof load test for both styles is typically 2 times the Work Load Limit (2 x WLL). In destructive break testing, mainstream standards dictate that both must satisfy a Design Factor (Safety Factor) of 6:1 or 7:1.
Commonality 3: The Hidden Dangers of Chemical and Photo-Chemical (UV) Aging
Synthetic materials have two worst enemies: sunlight and chemicals. Doesn't matter if it's polyester or nylon—leave them out in the sun too long or let them soak up too much chemicals, and the flat webbing will turn stiff and lose its color badly; the round sling's outer cover will get brittle and lose all its flexibility. When it comes time for tensile testing, these slings won't even make it to their rated load—they'll just snap right in the middle of the test. So during routine inspections, this is one thing you absolutely need to keep an eye on.
Commonality 4: Strict Requirements for Test Pin (Fixture) Radius
During pull testing, slings must never be rigged over sharp edges or hooks with inadequate radii. The radius of the testing machine's pin or end fitting must not be less than the compressed thickness of the sling at its point of contact. If the pin diameter is too small, excessive localized shear stress will render the test data inaccurate.
Structural Differences to Watch For During Testing
Flat Webbing Focus
Visual-First: Surface wear, torn stitches, and edge cuts are plain to see and judge with the naked eye.
Round Sling Focus
Tactile-First: Feeling along the body to detect internal hard lumps or bunching of broken core yarns.
Step-by-Step Tensile Testing Procedure for Slings
Measurement & Documentation. Lay the sling flat, measure its Effective Working Length (EWL), and record its initial visual state.
Mounting & Fixture Check. Fit the eyes (for flat webbing) or the loop body (for round slings) onto the testing machine pins that meet the radius specifications.
Constant-Rate Loading. Start the tensile machine; shock loading is strictly prohibited. For proof testing, load up to 2x WLL, hold, and observe. For destructive testing, pull at a constant rate until total structural failure occurs, and record the peak tonnage.
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