What is WLL, SWL, MBL, SF

WLL: Working load limit

The maximum load value or mass that a piece of lifting equipment is allowed to carry when lifting, lowering or suspending loads according to its designed use. This load requirement must be marked on the equipment used.

SWL: Safe working load

The maximum load value or mass that a piece of lifting equipment is allowed to carry when the load is lifted, lowered or suspended under specific operating conditions (should be recognized by a professional). The Lifting Operation and Lifting Equipment Management Regulations (LOLER) require that safe working loads must be marked on the equipment and this information should be reflected in the comprehensive inspection report.

MBL: Minimum breaking load

The minimum breaking load (MBL) is the load value obtained at the moment when the sample reaches fracture or failure, and the maximum working load (WLL) is obtained from this and according to a certain proportional relationship.

In order to obtain the minimum breaking load of some products, such as steel wire rope, we will conduct a destructive test on a sample steel wire rope and record the breaking load value reached at the time of breaking, or directly conduct a destructive test on the steel wire that constitutes the sample steel wire rope, and then deduce the breaking load of the entire steel wire rope according to the number of steel wire sections of the sample steel wire rope.

SF: safety factor, service factor or working factor

The meaning of these terms is actually the same, but the actual expression of the safety factor is probably better, so the term safety factor is now used in many standards and regulations. Under a certain minimum breaking load value (MBL), it is used to determine the maximum working load (WLL) of the equipment. Taking into account the different stress effects and safety risk factors that may be encountered during the use of the equipment, this factor is subject to change for insurance purposes. If the actual conditions of use are more severe than the conditions specified in the product standard, such as chemical corrosion environment, the user should increase the safety factor or reduce the safe working load (SWL) value according to the maximum working load (WLL).

Note: Maximum working load (WLL) and safe working load (SWL) can be confused. The former is determined by the equipment manufacturer according to the mechanical properties of the equipment, while the latter is prescribed by professionals, and its determination is based on the specific equipment use environment or conditions.

Generally, the safe working load (SWL) marked on the device is equal to the maximum working load (WLL), but sometimes it is slightly lower. For example, in coal mines and nuclear power plants, the maximum working load (WLL) is often greatly reduced for safety reasons, and the resulting safe load value is called safe working load (SWL), because some special risk factors associated with the operation of the equipment require a higher safety factor.