The most critical financial decision regarding cranes is selection of an appropriate classification or duty for its intended use. Not only does this impact initial capital cost but more importantly downstream costs such as maintenance, repair, major inspection and ultimately replacement.
We commonly find crane owners who have implemented robust crane management processes but struggle with the concept of crane classification and usage. This is reinforced by many crane service providers who pay limited attention to it and rather take a generic calendar based approach.
This is important as every crane is designed for a finite life. In Australia nominally 10 years for mechanical components and 25 years for structural components when designed in accordance with AS1418.
Note the word ‘nominally’ – the actual life is dependent upon the classification and usage. To illustrate this: take an overhead crane with a MRC of 5 tonne. If it has a typical C3 M3 classification, then it is designed to lift the crane’s maximum rated capacity (MRC) 32,000 times over it’s life, and the hoist is designed to lift and lower 5 t for 400 hours. For a structural life of 25 years this equates to 3.5 lifts per day (note that the mechanical classification is based on running time under load rather than cycles, but the concept is similar).
However if the load lifted, crane classification or usage varies we can get interesting outcomes as crane life does not have a linear relationship with load lifted or classification. The Australian Standard classifications range from C1 to C9 and M1 to M8 with each increase in class doubling the life of the crane or mechanism. Therefore a C9 crane is designed for 256 times the life of a C1 crane.
Also all loads lifted are not equal. A lift of 50% of the crane’s rated capacity only uses 12.5% of the crane life of a max capacity lift*. For example if we take that same 5 t C3 crane but the majority of lifts are all at 1 t, the life increases by a factor >100 from 32,000 lifts to 4,000,000 lifts.
Consider the following two examples of use for this same crane:
Example 1: Production facility
Lifts 4.8 t twice an hour (16 times per day)
Crane life: 6.2 years
Example 2: Workshop
Lifts 5 t once per month and 1 t every twice an hour (16 times per day)
Crane life: 545 years
When selecting a crane don’t rely on the manufacturer to select an appropriate crane classification. Consider a range of crane capacities and classifications then compare total life cycle cost based on capital cost, estimated design life and projected maintenance costs. This is not always straight forward so consider using a suitably qualified independent 3rd party provider. A relatively small upfront cost could have major savings over the life of the crane.
* The equivalent full load cycle is equal to P/MRC³, where P = load lifted and MRC = maximum rated capacity