National Association of Chain Manufacturers (NACM), representing domestic manufacturers of welded and weldless chain since 1933, has conducted D/d testing on alloy chain. D/d is the ratio between the curvature taken by the sling D, and the diameter of the component chain d. NACM alloy chain manufacturers supplied Grade 100: 9/32”, 3/8” and ½” and Grade 80: 3/8” for testing. Until this point, no published information was available for chain regarding D/d. NACM wanted to publish information to make recommendations on the minimum pin diameter for proof testing basket chain slings based on link deformation and rating/ derating of baskets and endless slings vs D/d ratio.
NACM testing results are shared below.
1) Effect of D/d is the same for all sizes and grades of alloy steel chain.
2) Strength loss is highly consistent with D/d ratio.
3) No damage to chain at WLL (working load limit) with a D/d as low as 2.
4) Minimum D/d pin diameter of 5 recommended for proof testing basket slings.
5) Strength loss is 10% or less once D/d is 5 or greater.
The chart below shows reductions in working load limit of an endless alloy sling based on D/d ratio. Consult the manufacturer for any D/d below 2.