Lifting Sling Breaking Force Test: Standards, Methods, and Technical Requirements

The lifting sling breaking force test is a destructive tensile test that determines the ultimate load at which a synthetic webbing sling or round sling ruptures, verifying compliance with the minimum breaking force required by standards such as EN 1492-1, EN 1492-2, corresponding GB standards, and ASME B30.9. This article explains the applicable standards, sample requirements, tested parameters, test procedures, acceptance criteria, and typical applications of breaking force testing for lifting slings.

Technical Overview

The lifting sling breaking force test, also known as the ultimate tensile strength test or minimum breaking load (MBL) test, is a destructive mechanical test performed on synthetic fiber slings to determine the maximum force the sling can withstand before rupture. The test verifies that the finished product achieves the minimum breaking force required by the applicable product standard, which is defined as a multiple of the working load limit (WLL).

For flat woven webbing slings and round slings made of man-made fibers, the principal reference standards include EN 1492-1 (flat woven webbing slings), EN 1492-2 (round slings), the corresponding Chinese national standards (GB) harmonized with the EN system, and, for the North American market, ASME B30.9 together with ASTM specifications such as ASTM D6771 for round slings. Under the EN and GB system, synthetic slings must achieve a breaking force of at least seven times the WLL (7:1), while ASME B30.9 specifies a minimum design factor of five (5:1) for synthetic web slings. Testing is carried out either by manufacturers as part of factory production control or by accredited third-party laboratories for type examination, certification, and independent verification.

Testing Samples

Flat Woven Webbing Slings

Single-ply, two-ply, and multi-ply flat slings woven from polyester (PES), polyamide (PA, nylon), or polypropylene (PP) multifilament yarns, with sewn eyes or endless construction, typically ranging from 1 t to more than 50 t WLL in straight pull. Finished slings are tested in the as-delivered configuration, including all stitching and eyes, at a representative free length, commonly 2 to 3 m between attachment points.

Round Slings

Endless round slings consisting of a load-bearing core of wound polyester yarns enclosed in a protective woven jacket. Both the complete sling and, where the verification plan requires, the core yarn bundle or jacket material can be submitted for testing.

Raw Webbing and Component Materials

Narrow-fabric webbing taken before sewing, core yarn lots, and sewing thread can be tested as full-width strip specimens to verify incoming material quality prior to conversion into finished slings.

Sample Condition and Conditioning

Samples must be unused and in as-manufactured condition, complete with labels and markings. Unless otherwise specified, specimens are conditioned in the standard textile atmosphere defined by ISO 139 (20 ± 2 °C and 65 ± 4 % relative humidity) for at least 24 hours before testing.

Testing Items

• Ultimate breaking force (maximum force at rupture) and verification against the required minimum breaking force
• Elongation at the working load limit and at the intermediate reference forces specified by the standard
• Elongation at break and full load-extension characteristics
• Residual (permanent) elongation after removal of a specified force
• Proof load verification by non-destructive loading, commonly to twice the WLL
• Effective length verification under reference tension
• Failure mode documentation, including yarn rupture in the body, eye or seam failure, and core failure in round slings

Testing Methods

Test Equipment and Calibration

A horizontal or vertical tensile test bed or universal testing machine with a capacity exceeding the expected breaking force is used; machines from 300 kN to more than 5,000 kN cover small to very large capacity slings. The force measuring system must be calibrated and traceable, generally to accuracy class 1 (±1 %) or better in accordance with ISO 7500-1. The rig is fitted with smooth pins, mandrels, or shackles of the diameter specified by the relevant standard so that the sling eyes are supported without edge cutting or abnormal abrasion. Because the rupture of a synthetic sling releases substantial stored energy, testing is conducted behind certified protective screens with remote load monitoring.

Test Procedure

• Record the sling identification, nominal width or diameter, effective length, color code, and label data before mounting.
• Mount the sling in a straight (vertical) pull configuration unless a basket or choked configuration is specifically required, terminating the eyes over the specified pins or mandrels.
• Apply a small initial reference force to remove slack and establish the datum for elongation measurement.
• Increase the force at a uniform, quasi-static rate, pausing at the specified intermediate forces, such as the WLL, to record elongation; the loading rate is controlled so that failure occurs in a controlled manner without dynamic effects.
• Continue loading until complete rupture, recording the maximum force, the force-elongation curve, and the location and mode of failure.
• Where required, remove the force at a specified level and measure the residual elongation after recovery.
• Test at least three specimens of the same type and batch; results are evaluated as specified by the standard, typically against the minimum value criterion.

Acceptance Criteria

The primary pass criterion is that the breaking force of every specimen is not less than the minimum breaking force stated by the standard, namely seven times the WLL under EN 1492-1, EN 1492-2, and the corresponding GB standards, and five times the rated capacity under ASME B30.9. Elongation at the WLL must fall within the limit declared by the manufacturer and marked on the label, and failure should occur in the load-bearing yarns rather than at the seams or eyes, unless the standard defines the stitched joint as the governing failure plane. Any specimen that breaks below the required force, or that fails prematurely at a stitch or eye, results in non-conformity of the type or batch.

Applications

• Type examination and conformity assessment of new sling designs, including CE marking support under the EU machinery framework
• Factory production control and statistical batch release testing during serial manufacture
• Supplier qualification and incoming inspection of webbing, core yarn, and finished slings
• Verification of slings after repair or modification, normally by proof loading rather than testing to destruction
• Technical investigation of sling failures, including expert reports for insurance and legal purposes
• Benchmark testing for product development and comparison of polyester, polyamide, and polypropylene constructions
• Compliance verification for import, export, tender, and customer audit documentation

FAQ

What is the difference between WLL and minimum breaking force?

The working load limit (WLL) is the maximum mass the sling is permitted to lift in a given configuration, while the minimum breaking force is the force the sling must achieve in a destructive tensile test. EN 1492 and the corresponding GB standards require a breaking force of at least 7 times the WLL, whereas ASME B30.9 requires a minimum design factor of 5.

Is the breaking force test destructive?

Yes. The specimen is loaded until it ruptures and can never be returned to service. For this reason, destructive testing is applied to type samples and statistical batches, while routine production relies on sampling plans combined with non-destructive proof loading where specified.

Can a used sling be retested to prove it is still safe?

A used sling cannot be re-certified by a breaking force test because the test destroys the specimen. Where standards permit, slings may undergo non-destructive proof loading, commonly to twice the WLL, after repair. In-service slings are otherwise assessed through periodic inspection by a competent person and retired when rejection criteria are met.

How many samples are required and in what length?

Typically at least three unused finished slings of the same type, color code, and WLL, each with an effective length of approximately 2 to 3 m, are submitted. For material-level verification, full-width webbing lengths or core yarn samples are provided as required by the applicable standard.

How long does the test take?

The machine time for an individual test is usually less than one hour. However, conditioning for at least 24 hours, testing of multiple specimens, and report preparation mean that final results are commonly issued within three to seven working days.

What is included in the test report?

An accredited test report states the standard applied, complete sample identification, equipment and calibration details, environmental conditions, force-elongation data, the breaking force of each specimen, elongation results, the pass or fail judgment against the required minimum, and photographs with a description of the failure mode.