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Patrick Cotnoir Sep 9, 2013 6:15:00 AM 4 min read

Synthetic Web Slings

A question that has been asked of me many times over the last 20 years is; "Do I have to wait until I see the red fiber yarn to take my sling out of service?"

Well the quick answer to that is NO. The red tracer is merely an aid as to let you know that some scrubbing (abrasion) or cutting has occurred! We never want to get into that mind set of having to wait to see red yarns before we take our slings out of service.

The WSTDA-WB-1  (Web Sling and Tie Down Association) is the standard for the manufacturing of nylon and polyester web slings, and it only gives a passing mention of red tracer yarn as a possible indicator of wear or cutting. The red yarn is merely something the manufacturers of the material insert to try and help us have indicators as to the amount of abuse the sling may have seen.

In North America, the general practice is to refer to the ASME Standard (American Society of Mechanical Engineers) B30.9 Slings rejection criteria when looking for the most comprehensive and up-to-date information, as developed by a full industry consensus body. The ASME B30.9-5.9.4 states the following:

A synthetic webbing sling shall be removed from service if any of the following conditions are present:

(a) missing or illegible sling identification

(b) acid or caustic burns

(c) melting or charring of any part of the sling

(d) holes, tears, cuts, or snags

(e) broken or worn stitching in load bearing splices

(f) excessive abrasive wear

(g) knots in any part of the sling

(h) discoloration and brittle or stiff areas on any part of the sling, which may mean chemical or ultraviolet/sunlight damage

(i) fittings that are pitted, corroded, cracked, bent, twisted, gouged, or broken

(j) for hooks, removal criteria as stated in ASME B30.10

(k) for rigging hardware, removal criteria as stated in ASME B30.26

(l) other conditions, including visible damage, that cause doubt as to the continued use of the sling

Notice letter (d) Holes, tears, cuts, or snagsโ€ฆ there is no mention anywhere of the red tracer yarn. 

In certain parts of Canada, the tolerance is a little more unique, and yet they still quote the ASME B30.9 standard. They allow for a certain length of edge cut and percentage of abrasion to be displayed on the sling before taking it out of service. They also allow a certain percentage of the WARP and WEFT (sets of yarns in the material to give the material its strength) threads to have damage.  ITI has performed hundreds of tests involving flat web sling tears, cuts and snags over the last 25+ years. A simple edge cut to a 2โ€ double ply sling, produces an average loss of strength of 25% vs. a new sling. I truly respect the potential damage from cutting or abrading load bearing yarns in a web sling, and am always ready to enforce letter (l) above, โ€œwhen in doubtโ€ฆ throw it outโ€!

The real underlying issue for these slings is the lack of protection they get. ITI has officially investigated nearly 100 rigging accidents over the last 20 years and our findings showed that 87% of the incidents involved synthetic slings. The majority of the cases are not because a sling did not have the capacity for the job, but because it was not sufficiently protected from either cutting or friction damage. Cutting and friction are the primary causes for web sling failures. The p.s.i. experienced by the sling at the sling-to-load bearing points of a choker or basket hitch can be extreme, often severing wear material like rubber pads or fire hose used as a โ€œsoftenerโ€. If the sling slides along the load surface while tensioned it can fail quickly due to the heat generated against the sling webbing โ€ฆ like a hot knife through butter. There are many great options out there for sling protection, and the cost is negligible considering some of the outcomes. I conducted an accident investigation this year where $300 worth of proper sling protection would have saved an employeeโ€™s life. (See the listing below for a variety of sling protection options available for the marketplace.)

Figure 1 - Interfron Wire Rope Protector
Figure 2 - Meshguard Protector    
Figure 3 - Linton Corner Protector   


interfron wire rope protector

 meshguard protector  linton corner protector


So, is the red tracer yarn a value? To some maybe, and to others not at all. These Slings that we are speaking of are somewhat considered consumable items. The cost for a 2โ€ x 10โ€™ double ply Type 3 nylon sling is roughly in the price range of $20.00 dollars.  However, the cost for not protecting them can run into the millions.

So letโ€™s protect our slings, thereby protecting the lives of those who work near them.