Derating-Crane

16 tons.

The static test load should have been 22.5=1.25*Rated load according to your data.

Apply same equation for derating considering the static test load as 16 Tons. Due to uncertainties about loads the rated load has to be always so chosen that the lifting can be done thus the 25% margin.

You should not just derate the crane. Please check its condition, why it is not lifting designed 22.5 Tonne test load?. Is there any major problem it its drives,brakes etc. If everything is o.k then derated capacity should be 12 Tonne. Suresh Sharma.

You should refer to the manufacturer's specifications and limitations applicable to the operation of crane. If manufacturer's specifications are not available, a qualified engineer competent in this field can determine depending how old of the crane and on its condition and as such should be appropriately documented and recorded. Some countries will base on how long the crane in operation, and in most of the time I had encoutered pro engr in this field derates to 80-50 percent of the crane.