Synthetic web slings offer a number of advantages for rigging purposes. The most commonly used synthetic web slings are made of nylon- or polyester-type yarns (Fig. 7). They have the following properties in common:
- Strength,
- Convenience,
- Load protection, and
- Economy.
Each synthetic material has its own unique properties.
Certain synthetic materials perform better than others in specific applications and environments. Consult the sling manufacturer or a qualified person for a specific application or before using in and around chemical environments.
Synthetic webbing materials other than nylon and polyester are also used and the manufacturer should be consulted for specific data for proper use.
Identification:
New slings are marked by the manufacture to show:
- The rated load for each type of hitch, and
- The type of synthetic web material.
In addition, slings may be marked to show:
- The manufacturer’s code or stock number, and
- The name or trademark of the manufacturer.
Fig-7
GENERAL NOTE: Ensure that fittings designed for synthetic slings are used.
Rated loads:
Rated loads (capacities) for single-leg vertical, choker, basket hitches, and two-leg bridle slings are as shown in Tables 21 through 25.
For angles not shown, use the next lower angle or a qualified person to calculate the rated load. Rated loads are based on:
- Material strength,
- Design factor,
- Type of hitch,
- Angle of loading (see Fig. 3),
- Diameter of curvature over which the sling is used, and
- Fabrication efficiency.
Do not use horizontal angles less than 30 degrees except as recommended by the sling manufacturer or a qualified person.
The rated load for a sling in a choker hitch is the value in Tables 21 through 25, provided that the angle of the choke is 120 degrees or more (see Fig. 2). For angles of choke less than 120 degrees, use the reduced rated load values provided by the sling manufacturer or a qualified person. For other synthetic webbing materials and for configurations not shown, use the rated loads provided by the sling manufacturer or a qualified person.
Fittings:
Ensure that mechanical fittings used as part of a synthetic web sling meet the following:
- Materials are compatible with the mechanical and environmental requirements of the sling,
- Fittings have a rated load at least the same as the synthetic webbing sling,
- Fittings have sufficient strength to sustain twice the rated load of the sling without visible permanent deformation, and
- Surfaces are clean, and sharp edges are removed.
Table 21
Rated Load for One-ply, Class 5 Synthetic Webbing Slings
Expressed in Pounds
GENERAL NOTES:
(a) The rated loads are based on stuffer weave construction webbing with a minimum certified tensile strength of 6,800 pounds per inch of width of the webbing.
(b) Rated loads for Types III and IV slings apply to both tapered and non tapered eye constructions. Rated loads for Type V slings are based on non tapered webbing.
(c) For Type VI slings, consult the manufacturer for rated loads.
(d) For choker hitch, the angle of choke is 120 deg or greater.
Fig-2
Table 22
Rated Load for Two-Ply, Class 5 Synthetic Webbing Slings
Expressed in Pounds
GENERAL NOTES:
(a) The rated loads are based on stuffer weave construction webbing with a minimum certified tensile strength of 6,800 pounds per inch of width of the webbing.
(b) Rated loads for Types III and IV slings apply to both tapered and non tapered eye constructions. Rated loads for Type V slings are based on non tapered webbing.
(c) For Type VI slings, consult the manufacturer for rated loads.
(d) For choker hitch, the angle of choke is 120 deg or greater.
Inspections:
Designate a qualified person to inspect slings each day before use for damage or defects.
This qualified person also performs additional periodic inspections where service conditions warrant, as determined on the basis of:
- Frequency of sling use,
- Severity of service conditions,
- Nature of lifts being made, and
- Experience gained during the service life of slings used in similar circumstances.
Make periodic inspections of synthetic web slings at intervals no greater than 12 months. A good guide to follow includes:
- Yearly for normal service use,
- Monthly to quarterly for severe service use, and
- As recommended by a qualified person for special and infrequent service use.
Although OSHA’s sling standard does not require you to make and maintain records of inspections, the ASME standard contains provisions on inspection records.
Make a thorough inspection of slings and attachments. Items to look for include:
- Missing or illegible sling identification,
- Acid or caustic burns,
- Melting or charring of any part of the sling,
- Holes, tears, cuts, or snags,
- Broken or worn stitching in load bearing splices,
- Excessive abrasive wear,
- Knots in any part of the sling,
- Discoloration and brittle or stiff areas on any part of the sling,
- Pitted, corroded, cracked, bent, twisted, gouged, or broken fittings, and
- Other conditions that cause doubt as to continued use of a sling.
Where any such damage or deterioration is present, remove the sling or attachment from service immediately.
Table 23
Rated Load for One-Ply,Class 7
Synthetic Webbing Slings
Expressed in Pounds
GENERAL NOTES:
(a) The rated loads are based on stuffer weave construction webbing with a minimum certified tensile strength of 9,800 pounds per inch of width of the webbing.
(b) Rated loads for Types III and IV slings apply to both tapered and non tapered eye constructions. Rated loads for Type V slings are based on non tapered webbing.
(c) For Type VI slings, consult the manufacturer for rated loads.
(d) For choker hitch, the angle of choke is 120 deg or greater.
Repairing/Reconditioning:
Do not use worn or damaged slings or attachments. Discard or repair them. Use damaged slings only after they are repaired, reconditioned, and proof tested by the sling manufacturer or a qualified person using the following criteria:
- Ensure that the manufacturer or a qualified person performs repairs,
- Ensure that repairs of hooks and fittings meet ASME B30.10 and B30.26,
- Do not repair cracked, broken, melted, or damaged webbing material,
- Do not repair load-bearing splices,
- Do not make any temporary repairs of synthetic webbing or fittings, and
- Mark repaired slings to identify who made the repairs.
Retain the certificates of proof test and make them available for examination.
operating practices:
Do not use synthetic web slings with loads in excess of the rated load capacities described in the appropriate tables. Ensure that synthetic web slings have suitable characteristics for the type of load, hitch, and environment in which they will be used and that they are not used with loads in excess of the rated load capacities described in the appropriate tables. Consult the sling manufacturer or a qualified person for synthetic web slings not included in the tables. Follow other safe operating practices, including:
Sling Selection:
- For multiple-leg slings used with non symmetrical loads, ensure that an analysis by a qualified person is performed to prevent overloading of any leg,
- Ensure that multiple-leg slings are selected according to Tables 21 through 25 when used at the specific angles given in the table. Ensure that operations at other angles are limited to rated loads of the next lower angle given in the table or calculated by a qualified person, and
- Ensure that the fitting is the proper shape and size to ensure that it is seated properly in the hook or lifting device.
Table 25
Rated Load for Four-Ply, Class 7
Synthetic Webbing Slings
Expressed in Pounds
GENERAL NOTES:
(a) The rated loads are based on stiffer weave construction webbing with a minimum certified tensile strength of 9,800 pounds per inch of width of the webbing.
(b) Rated loads for Types III and IV slings apply to both tapered and non tapered eye constructions. Rated loads for Type V slings are based on non tapered webbing.
(c) For Type VI slings, consult the manufacturer for rated loads.
(d) For choker hitch, the angle of choke is 120 deg or greater.
Cautions to Personnel:
- Ensure that all portions of the human body are kept away from the areas between the sling and the load and between the sling and the crane or hoist hook,
- Ensure that personnel never stand in line with or next to the legs of a sling that is under tension,
- Ensure that personnel do not stand or pass under a suspended load,
- Ensure that personnel do not ride the sling or the load, unless the load is specifically designed and tested for carrying personnel, and
- Do not use synthetic webbing slings as bridles on suspended personnel platforms.
Effects of Environment:
- Store slings in an area where they will not be subjected to mechanical, chemical, or ultraviolet damage, or to extreme temperatures,
- When slings are exposed to extreme temperatures, follow the guidance provided by the sling manufacturer or qualified person.
- Consult the sling manufacturer for recommended inspection procedures when nylon or polyester webbing slings are extensively exposed to sunlight or ultraviolet light.
Rigging Practices:
- Ensure that slings are hitched in a manner providing control of the load,
- Ensure that sharp edges in contact with slings are padded with material of sufficient strength to protect the sling,
- Ensure that slings are shortened or adjusted only by methods approved by the sling manufacturer or a qualified person,
- Ensure that, during lifting with or without a load, personnel are alert for possible snagging,
- Ensure that, in a basket hitch, the load is balanced to prevent slippage,
- When using a basket hitch, ensure that the legs of the sling contain or support the load from the sides, above the center of gravity, so that the load remains under control,
- Do not drag slings on the floor or over abrasive surfaces,
- Ensure that, in a choker hitch, the choke point is only on the sling body, never on a splice or fitting,
- Ensure that, in a choker hitch, an angle of choke less than 120 degrees is not used without reducing the rated load,
- Ensure that slings are not constricted, bunched, or pinched by the load, hook, or any fitting,
- Ensure that the load applied to the hook is centered in the base (bowl) of the hook to prevent point loading on the hook, unless the hook is designed for point loading,
- Ensure that an object in the eye of a sling is not wider than one-third the length of the eye,
- Do not shorten or lengthen a sling by knotting or twisting,
- Do not rest loads on the sling,
- Do not pull a sling from under a load when the load is resting on the sling,
- Do not allow shock loading, and
- Avoid twisting and kinking.
Proof testing:
Before initial use, ensure that all synthetic webbing slings incorporating previously used or welded fittings and all repaired slings are proof tested by the manufacturer or a qualified person.
Other new synthetic webbing slings and fittings need not to be proof tested, although the employer may require proof testing in purchasing specifications.
Environmental effects:
Temperature
Do not allow nylon and polyester slings to be used in contact with objects or at temperatures in excess of 194 degrees F (90 degrees C), or below minus 40 degrees F (minus 40 degrees C).
Sunlight & Ultraviolet
Long-term exposure to sunlight or ultraviolet radiation can affect the strength of synthetic webbing slings. Consult the sling manufacturer for proper retirement criteria for synthetic webbing slings subjected to long-term storage or use in sunlight.
Chemical
The strength of synthetic webbing slings can be degraded by chemically active environments. This includes exposure to chemicals in the form of solids, liquids, vapors or fumes. Consult the sling manufacturer before using slings in chemically active environments.