In the 1990′s an article was published stating that synthetic slings lose strength, strictly as a function of time. The article relayed the results of destruction testing performed on USED slings taken from power plants, line trucks, paper mills and other locations. A majority of the slings broke below a 5/1 design factor.
The less than scientific conclusion of the testing was that synthetic slings lose strength as a function of time and I was mentioned, possibly to add credence to the incorrect conclusion by making the point that if shelf life were not valid, “Gelskey would not put the date of manufacture on all slings made by his company”.
The logic was incorrect on many levels. The so called experiment lacked many basic elements necessary to prove the hypothesis under what is accepted as the scientific method, namely the independent variable, time was not isolated.
The sample slings pulled to destruction in this study had been subjected to use, weather and environmental factors. They could have been exposed to overloading, chemical and ultraviolet light degradation or perhaps were not manufactured properly.
All Lift-It slings are marked with date of manufacture and are individually serialized so that users and inspectors will have an exact idea of how long our slings have been in service. Our rationale was that despite appearances slings may be removed from service and destroyed as many are very inexpensive when compared to the cost of the items they handle. Simply stated, sling retirement may be an excellent form of cheap insurance. Another perspective may be to consider the cost of failure.
When slings are stored for extended periods in conditions that do not exactly duplicate optimum storage conditions, sling strength may be affected. An example would be when slings in Eastern Washington (desert conditions) are stored outside in metal containers. Those slings can take on spring steel qualities and recoil to assume their wrapped condition. After many years slings stored inside under conditions that DO NOT EXACTLY DUPLICATE optimal storage conditions, can begin to exhibit a gummy or sticky finish.
We have on a couple of occasions pulled slings to destruction that were kept in optimum storage conditions: dry, dark, cool and free of mechanical and environmental damage. In all instances the slings broke above the 5/1 design factor. Both slings were approximately eleven years old.
The salient difference in the destruction tests done by Lift-It and the testing done in the erroneous 1990’s article is that the Lift-It test slings were never used for lifting or subjected to any form of degradation.
Under these conditions, the independent variable, time was indeed isolated.
In the early nineties when the non-scientific study results were published I was assailed by webbing and yarn producers. I was informed on more than one occasion that synthetic fibers DO NOT lose strength strictly as a function of time. On one particular occasion, a fiber producer was extremely profane in making his point based upon extensive testing in oxidation chambers. Those results contradicted the incorrect conclusion made in the erroneous article.
Time, as independent variable, DOES NOT affect sling strength. Other variables such as storage and exposure to chemical, environmental and mechanical forms of damage do affect sling strength.
Always remember, sling design factors apply only to newly manufactured and unused slings.
Mike Gelskey, SR.
CEO-Lift-It Manufacturing Company, Inc.