Safe Working Load Vs Working Load Limit

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Chris Achilles
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Safe Working Load Vs Working Load Limit

Post by Chris Achilles » Thu Jul 02, 2009 12:56 pm

I don't know how many designers are aware of this but there seems to be an increase in the number of suppliers quoting Working Load Limits for Bow Shackles and other lifting items instead of the usual Safe Working Load. Recently I specified 4T SWL bow shackles on a modular lift and received a complaint from site that the lugs where too big for 4T shackles. It transpired that the crane company had sent 4T WLL (Working Load Limit) shackles not 4T SWL which are much bigger. When comparing the 2 catalogues it turns out that a 4T SWL shackle is the same size as an 8T WLL shackle which would suggest that the safety factor on a SWL is twice that of a WLL unless steel has got twice as strong overnight!

Has anyone got any guidance on specifying WLL shackles in lieu of SWL shackles. My current thoughts are to get some benefit from the new system and apply a factor of 1.5 not 2.

This is a useful description of WLL I found on the web:-

The Working Load Limit (WLL) is the maximum load which should ever be applied to the product under any condition. The Working Load Limit is based on a load being uniformly applied in a straight line pull.

It is the responsibility of the ultimate user to determine a Working Load Limit for each application. Many factors should be considered: included among, but not limited to, loads applied, speed of operation, acceleration or deceleration, length of rope or cable, shock loads, abrasion, corrosion, number, size, condition and location of drums and sheaves, facilities for inspections, and the danger to life and property should a rope or cable break.

Any ideas or opinions?

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