14.5.1 Working Load Limit/SWL

Consideration must be given to the working load limit of the sling and the SWL with which it is then attributed for the particular service conditions so as to ensure that no part of the sling is overloaded by the method of use. The working load limit of a sling depends upon the following three factors:

  1. The size and grade of chain selected. It will be noted that as the grade of chain sling selected increases from 4 (or M) to 6 (or S) to 8 (or T) progressively smaller chain slings can be used to achieve equivalent strength, e.g. a Grade 8 (or T) sling will have twice the lifting capacity of a Grade 4 (or M) sling of the same size.

  2. The geometry of the sling: i.e. the number of chain legs and, in the case of multi-leg slings, the angle of the legs to the vertical and the disposition of the legs in plan. Angles should be assessed as shown in figures 14.13 to 14.15 inclusive. The angle to the vertical = β (‘included angle’ = 2β).

  3. The method of rating, this may be either the uniform load method or the trigonometric method, dependent on the application. It should be noted that the uniform load method is the only method of rating multipurpose slings used in Harmonised European standards. For an explanation of these two methods, refer to section 1 1.A5.4.3 Methods of Rating Lifting Slings.

Note

The maximum angle of inclination at which the sling may be rated is 60° (120° included angle) but it may only be rated for use at 45° (90° included angle)

Figure 14.5.1-1 A. Two leg sling. B. Three leg sling. C. Four leg sling.

The SWL to be marked on the sling should be assessed by a Competent Person and will be the same as the working load limit in normal conditions or less than the working load limit under special conditions. The SWL of the sling selected must be at least equal to the maximum load to be lifted. The maximum load that can be lifted by a sling may also vary from the marked SWL depending upon the method of use. The most commonly used methods are dealt with in section 14.5.2 Method of Use below. Where it is proposed to use slings in some other way the operative should consult a Competent Person.