Important. This is an explanation of the general engineering theory of slings, not an occupational safety instruction and not a regulatory document. Our TU-001 (class 3) and TU-002 (class 8, T8) do not provide for the use of our chains as slings: a sling chain is a separate product (a certified class 8 sling assembly to GOST/EN 818-2 with its own standard sling coefficients). We do not publish standard sling coefficients: the calculation is approximate, and the final decision is confirmed by a specialist of your organisation.

From load mass to leg load

The tension of one leg of a symmetrical sling is calculated by the formula:

S = Q / (n · cos α)

Q — the weight of the load, kN. If the mass is known in tonnes, Q = m × 9.81;
n — the number of load-bearing legs. For a 4-leg sling with uniform loading the calculation uses 3 legs — standard practice;
α — the angle of each leg from the vertical. The larger the angle, the higher the tension: at 60° it is twice as high as for a vertical leg.

Standard practice limits the angle from the vertical to 60°: beyond that the tension grows too quickly, and the growing horizontal component compresses the load.

Example 1: load 5 t, 4 legs, angle 30°

Q = 5 × 9.81 ≈ 49.0 kN; S = 49.0 / (3 × 0.866) ≈ 18.9 kN per leg.

With a ×4 safety factor the required breaking load is BL ≥ 75.5 kN — the level of the 8×24 class 8 size (BL = 80.6 kN). For the sling itself such a chain is taken as a certified sling assembly of class 8 (to GOST/EN 818-2), not as a chain from our TU-002 line.

Example 2: the same load, angle 60°

S = 49.0 / (3 × 0.5) ≈ 32.7 kN; BL ≥ 130.8 kN — for class 8 this is the level of the 11×33 size (BL = 154 kN).

The angle grew from 30° to 60° — and a chain several sizes larger was required. That is why the legs are kept as close to vertical as possible.

Safety factor

The examples use a ×4 factor — the “lifting” option in our Selection by load; the Chain sling calculator offers ×4, ×5 and ×6. This is an approximate engineering factor on the breaking load (BL), and not standard sling coefficients: the standardised coefficients for sling assemblies are set by GOST/EN 818-2 and the occupational safety rules. Our TU-001/TU-002 do not define sling coefficients — the application and the final choice are confirmed by a specialist.

Where the chain for a sling comes from

A sling chain is not the same product as a lifting chain for hoists and mechanisms. Slings are assembled from certified sling assemblies of class 8 with standard sling coefficients (to GOST/EN 818-2 and the occupational safety rules); the assembly is confirmed as a whole product — with a data sheet, marking and periodic testing.

Our lines TU-001 (class 3) and TU-002 (class 8, T8) do not provide for this: our chains are not sling material. The difference is explained in the article Chain slings and class 8 lifting chains.

Calculator

The Chain sling calculator calculates the leg tension and the required BL for your conditions, and shows the selection of class 8 sizes for reference — by breaking load (the examples above can be reproduced in it in a minute). Our TUs do not provide for the use of our chains as slings, so the calculator's result is a guide, not a ready sling solution.

Do not confuse a cargo sling with the galvanized chain sling product for restraint systems: their purpose and requirements are different.

Chain sling calculation: legs, angles, tension