In-Depth Alloy Chain Sling Inspection Part 1: Twisting and Bending


by  on February 13, 2015

twisting and bending

Twisted and Bent Chain

twisting and bending

D/d is the ratio between the curvature taken by the sling ID and the diameter of the component chain D.










This article is Part 1 of a 5-part blog series that will cover what professional riggers should consider when performing an in-depth alloy chain sling inspection. Today, we’ll discuss the effect of twisting and bending.

Consider that chain is evaluated by applying loads in a pure tensile link end-to-link-end fashion and rated accordingly. Rigging chain around edges or corners alters the normal loading pattern significantly. A lack of proper padding or consideration of the D/d ratio (see above) for chain can result in twisted and bent links. Once a chain is twisted or bent it will alter inner link stresses which can result in failure. For this reason, all chain containing twisted or bent links must be removed from service immediately.

National Association of Chain Manufacturers (NACM), representing domestic manufacturers of welded and weldless chain since 1933, has conducted D/d testing on alloy chain. As a result of this testing, the NACM came out with the chart below which shows reductions in working load limits based on D/d ratio of alloy chain rigged around an edge or a corner. Consult the manufacturer for any D/d below 2. The latest revision ASME B30.9 2014 released for sale this month has adopted this chart into the new standard.

twisting and bending
Using proper sling protection, following the D/d capacity reductions and exercising proper rigging practices will eliminate damage to your alloy chain slings.

To learn more, view our Chain Sling Inspection Safety Webinar.
Want to get trained? Check out our Qualified Rigger 3 day Workshop.

{ 2 comments… read them below or add one }

Peter Cooke Peter Cooke March 11, 2015 at 10:00 am

Hello Joe,
Thanks for your comment. We would suggest protective padding anywhere the chain would make contact with an edge, since this is a D/d below 2 and is not recommended. Please let me know if you have any further questions.

Joseph S. Elliott March 10, 2015 at 5:55 pm

Peter – Regarding the above and D/d Ratio – Obviously above the Chain is shown going around a Round/Circular object that would be constant – In the case of picking up lets say a WF-Beam in the H position where you wrap the Leg of the Chain all the way around and hook it back into itself or to a Short Adjuster Leg Leg – IF available ? and you end up w/a 45 or 60 Deg. angle , which is usually acceptable – But, then you have the Links coming around the Flanges on the bottom where the Links are nearly always edge ways on the Flange – what kind of condition are you putting on the Sling Leg and the amount of de-rating should be considered ??? Hope I did not confuse you in trying to explain ? Thanks, Joe

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