The lifting chains on the crane can become stretched by shock loading, lifting beyond the chains capacity and uneven weight distribution from load to chains causing overloading.
A bit of stretch in the chain is ok but once you get to 10% stretching in a single link the chains must be taken out of service and replaced.
For example if a link that is 30mm long when new and is now 33mm long or more that chains must be replaced, below 33mm is ok but keep on checking regularly especially if they have started to stretch.
You can see stretched chains straight away because 99% of the time they dont stretch evenly.
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