Overview
ISO 7531:1987 - "Wire rope slings for general purposes - Characteristics and specifications" defines design, identification, manufacture and rating rules for general-purpose wire rope slings and sling assemblies. The standard covers single-leg and multilegged slings (two-, three- and four-legged), terminal eye formation (ferrule-secured or spliced), working load limit (WLL) calculation, permissible leg angles, length tolerances, marking and certification.
Key topics and technical requirements
- Scope: Specifies sling type, WLL and manufacture. Multilegged slings are normally built with legs of equal nominal length; unequal legs require special rating by a competent person.
- Types of single-leg slings: Spliced eyes or ferrule-secured eyes, with or without thimbles; soft eyes and terminal fittings described. Ferrule- and splice-related terminations must comply with ISO 8793 and ISO 8794 respectively.
- Rope types: Accepts ordinary-lay fibre- or steel-cored ropes referenced to ISO 2408. Mass factors are specified (examples in the standard: natural fibre core 0.36, polypropylene 0.35, steel core 0.4). Wire tensile grade is stated as 1 770 N/mm².
- Working load limit (WLL): Calculated using the formula given in the standard:
WLL = Fmin × ke / (km × ku)
- WLL expressed in tonnes; Fmin = minimum breaking force of the rope (kN).
- Default factor values are provided (as in the standard) - ke, km and ku - and national/customer-specific values may be used if specified.
- Multilegged slings: WLL = single-leg WLL × angle/leg-number factor (factors depend on included angles and are tabulated in the standard). Limits: angle to vertical β ≤ 60°; angle between opposite legs a ≤ 120°.
- Dimensions and tolerances: Nominal length tolerances (±2× rope diameter or ±0.5% of length, whichever greater). Tolerances between legs in multilegged slings also specified.
- Marking & certification: Durable tag, ferrule or master link must carry manufacturer ID, sling ID, WLL and applicable angles. Each batch must be supplied with a conformity certificate. Hooks/links must have ratings at least equal to the leg rating.
- Testing: Ropes, fittings and terminations must be tested per appropriate national standards and legislation (proof/loading cautions noted).
Applications and users
- Practical for lifting equipment manufacturers, sling fabricators, riggers, crane and lifting engineers, safety inspectors, procurement and compliance teams.
- Used to specify safe sling assemblies for construction, offshore, shipping, manufacturing and heavy-industry material handling where reliable WLL calculation, proper terminations and documented marking/certification are required.
Related standards
- ISO 2408 - Steel wire ropes for general purposes (characteristics)
- ISO 8793 - Ferrule-secured eye terminations for slings
- ISO 8794 - Spliced eye terminations for slings
Keywords: ISO 7531, wire rope slings, working load limit, multilegged slings, ferrule-secured, spliced eyes, sling assembly, lifting safety, sling marking.
