Contributed by Bob Kozickie, Technical Sales Support Manager
Alloy Chain Slings are composed of a variety of components that work in conjunction with each other to perform the task of lifting heavy loads. The lifting system must be aligned properly in order to accomplish the slings’ objective. When the alignment is not correct, it can result in damage or catastrophic failure within the lifting system. The most common and preventable reason for the alignment not being correct is that the rigger had either tied the sling in a knot or twisted a leg of chain in order to shorten it.
When a chain is twisted or knotted, it puts the pulling stresses onto areas of each link that are not designed to withstand those forces. The pulling action will force the links to put a side torque onto the barrels or sides of the links. This torque then forces the weakest parts, the two radius areas, to allow the sides to move the steel in the direction the force is pushing onto the link. The result will be a twist in that chain link as well as the links adjacent to it.
We performed a test at our facility in Mount Pleasant, Pennsylvania. We made a chain sling which we heat treated and proof tested to twice its working load limit as is standard practice to certify a welded chain sling. The sling passed the proof test with no defects. We then introduced a severe twist into the leg of that same chain sling before we put it back into the test bed. We performed the same pull test but this time the test was stopped at the working load limit. After the chain was relaxed and removed from the test bed it was examined for any visual defects. The result was that a permanent helical twist was introduced into the chain. From top to bottom, the chain makes a turn from link to link in the areas that did not have bearing to bearing contact between the links.
The procedures for proof testing, minimum elongation, and break testing following the manufacturing process all state that the “load shall be applied in direct tension to an undamaged straight length of chain”. All the welds for each link must line up in the same plane during each testing process. These tests are all integrity test which verify that the chain was manufactured properly in compliance with all applicable standards. It is also the way that alloy chain is required to be aligned when used in rigging applications.
There are alternatives that the rigger can use to safely lift their loads. The first and most obvious is to have the sling manufacturer install chain shortening grab hooks at the top of the sling attached to the master link. These hooks can then be used to properly shorten each leg of chain to the desired length for a given load. The other option is to use a Chain Shortener Sling Assembly in line within the leg to reach the proper leg length. Either one of these options will work and are considered safe rigging practices.
Understanding that there are limitations as to what can and cannot be done with an alloy chain slings is beneficial to all involved with lifting and rigging. The strength and durability that each link of alloy chain possesses when it’s assembled into a chain sling is knowledge that will help the rigger to better perform their duties. This knowledge will help keep themselves and their coworkers safer when working in areas where loads need to be lifted and moved.