[RIGGER’S CORNER]
SYNTHETIC WEB SLINGS – UV Degradation
CONTRIBUTED BY MIKE RIGGS, RIGGING INSTITUTE,
WWW.RIGGINGINSTITUTE.COM W
hen a load is small, light, polished, fragile or delicate, polyester and nylon web slings are one of the most common synthetic
slings used because web slings are less likely to damage the surface of the load then other styles.
Web slings are quite fl exible and provide a secure grip around the lifted load. T ese slings also have the added benefi t of being lightweight, making them easier to handle than a steel sling. Severe environments that contain chemicals, high operating temperatures, damaging edges, protrusions or roughness will aff ect the performance of polyester or web slings. Synthetic web slings must always be protected from protrusions and edges of loads. Most accidents that occur with synthetic web slings are the result of damage caused by either cutting or ultra-violet (UV) light degradation. ASME B30.9-5.9.4 Removal Criteria states: “A synthetic webbing sling shall
be removed from service if conditions such as the following are present… (h) discoloration and brittle or stiff area on any part of the sling, which may mean chemical or ultraviolet/sunlight damage…”.
Ultraviolet Light (UV) Ultraviolet light mainly comes from the sun, although other sources include fl uorescent lighting, black light, welder arcs, and Xenon light (used in automobile headlights). A human who is exposed to ultraviolet light will develop sunburn if protection is not used. Likewise, synthetic materials used for tension members that are exposed to the elements will eventually show signs of deterioration if not properly protected. All synthetics need protection if the user desires to have its full strength
remain over a long period of time. Ropes and cordage slings that are made from aramid material are generally sheathed in polyester in order to maintain the veracity of the fi nished product when exposed to sunlight on a regular basis. T e polyester acts as a sacrifi cial component while the aramid is the strength bearing member.
UV light degrades synthetic materials by transferring energy into the fi bers often causing damage by breaking down the molecular bonds in the fi ber structure. Darker colors provide better UV resistance than lighter colors and thicker materials resist UV light better than thinner materials.
Testing T e WSTDA (Web Sling & Tie Down Association) conducted UV testing on polyester and nylon web slings in 2006. T e testing showed that polyester webbing held up to UV better than nylon webbing. After a twelve month period UV degradation leveled off at a 30% loss of sling strength. However, the slings made from nylon webbing lost strength of 50% to 60% over a thirty-six month period with no signs of leveling off .
20% 10% 0%
-10% -20% -30% -40% -50%
5 X WLL
CTRL 6 12 16 20
MONTHS OF EXPOSURE AVERAGE OF 4 TESTS
WLL = Working Load Limit = Rated Capacity
UNTREATED TREATED
Polyester web slings lost up to 30% of their strength during the fi rst 12 months, and then leveled off .
WIRE ROPE EXCHANGE JULY-AUGUST 2012 83 24 28 32 36
ALL UV TESTS OF 2” NYLON 66 CLASS 5 AND 7 - 1 AND 2 PLY - TYPE 5 ENDLESS SLINGS
40% 30% 20% 10% 0%
-10% -20% -30% -40% -50%
5 X WLL
CTRL 6 12 16 20
MONTHS OF EXPOSURE AVERAGE OF 4 TESTS
WLL = Working Load Limit = Rated Capacity
UNTREATED TREATED
Nylon web slings lost 50% - 60% of their strength after 36 months, with NO indication of leveling off .
24 28 32 36
DESIGN FACTOR 7 : 1
6 : 1
5 : 1
4 : 1
3 : 1
ALL UV TESTS OF 2” POLYESTER CLASS 5 AND 7 - 1 AND 2 PLY - TYPE 5 ENDLESS SLINGS
DESIGN FACTOR 6 : 1
5 : 1
4 : 1
3 : 1
PERCENT LOSS FROM 5 X WLL
PERCENT LOSS FROM 5 X WLL
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