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PNNL Hoisting and Rigging Manual

| Scope | General |

| Guidelines | Figure 1: Sling Stresses at Various Sling Angles | Alloy Steel Chain Slings | Figure 2: Chain Sling Major Components | Table 1: Rated Load for Alloy Steel Chain Slings ASTM A391 | Table 2: Typical Reduction of Chain Sling Working Load According to Temperature(a) | Table 3: Frequent and Periodic Inspection of Chain Slings | Table 4: Maximum Allowable Wear at any Point of Link | Wire Rope Slings | Figure 3: Typical Wire Rope Slings | Figure 4: Nominal End Attachment Efficiency | Table 5: Wire Rope Slings in Choker Hitch | Figure 5: Wire Rope Efficiencies for Various D/d Ratios | Figure 6: Rigging Tackle and Equipment Identification Tag Example | Table 6: Allowable Broken Wires in Braided and Cable-Laid Slings | Table 5: Wire Rope Slings in Choker Hitch | Figure 7: Correct and Incorrect Ways to Use Wire Rope Clips (Clamps) | Synthetic Web Slings | Figure 8: Synthetic Web Slings | Figure 9: Web Sling With Loop Eyes or End Fittings |

Slings

Scope

This section addresses the requirements for lifting slings manufactured from the following materials:

  • alloy steel chain
  • wire rope
  • metal mesh
  • sewn synthetic web.

General

Guidelines

Slings, other than those described in this section, such as polyester round slings and Kevlar1 fiber (yarn) slings shall be used in accordance with recommendations of the sling manufacturer.  Slings manufactured from conventional three-strand natural or synthetic fiber rope are not recommended for use in lifting service.  Natural or synthetic fiber rope slings shall be used only if other sling types are not suitable for the unique application.  For natural or synthetic rope slings, the requirements of ASME B30.9, and OSHA 1910.184(h) shall be followed.  All types of slings shall have, as a minimum, the rated capacity clearly and permanently marked on each sling.  Each sling shall receive a documented inspection at least annually, more frequently if recommended by the manufacturer or made necessary by service conditions.

Defective Slings

Slings to be repaired and recertified shall be stored in a secure manner that renders them inaccessible for use while repair is pending.  Unless defective slings are to be repaired and recertified, they shall be destroyed to prevent future use.

Multiple Leg Slings

When lifting rigid objects with multiple-leg slings (three or four legs), two of the legs should be capable of supporting the total load.  Multiple-leg slings shall be selected to suit the most heavily loaded leg rather than the total weight.

Sling Angles

A key factor in determining sling stress is sling angles (Figure 1).

Periodic Load Tests

Periodic load testing of slings is not recommended.

Figure 1. Sling Stresses at Various Sling Angles
(Sling Angles Less than 30º Not Recommended)

Sling Stresses at Various Sling Angles

Alloy Steel Chain Slings

Design Factors and Chain Properties

Chain for alloy steel chain slings shall conform to the requirements of ASTM A391/A 391M, Standard Specification for Grade 80 Alloy Steel Chain.  Rated loads for alloy steel chain slings shall be based on a minimum design factor of 4.

The general configuration of a chain sling is shown in Figure 2.

Rated Loads

The rated loads for alloy steel chain slings are presented in Table 1.

Sling Identification

Alloy steel chain slings shall be labeled by the manufacturer with permanently affixed durable identification stating the following:

  • chain size
  • manufacturer's grade (only ASTM A391 is allowed for lifting purposes)
  • rated load and angle upon which the rating is based
  • reach
  • number of legs
  • manufacturer's name or trademark.
  • An additional tag, sticker, or other identifier shall be added by the user to indicate when the next periodic inspection is required.

Effects of Environment

Environmental limits for alloy steel chain slings are listed in Table 2 and are presented below:

  • If the chain sling becomes heated to a temperature of 400°F (204°C), rated loads shall be reduced in accordance with the chain manufacturer's recommendations regarding usage both while heated and after being heated.
  • If the chain slings are to be used in temperatures of -40°F (-40°C) or less, the manufacturer should be consulted.

Attachments

Requirements for attachments to alloy steel chain slings follow:

  • Hooks, rings, oblong links, pear-shaped links, mechanical coupling links, or other attachments shall have a rated load at least equal to that of the alloy steel chain with which they are used.  In cases where the particular use makes this impractical, the sling shall be marked with a rated load (working load limit) that is consistent with the least working load rating of any component.
  • Standard attachments should be of a size recommended by the sling manufacturer.
  • All welded components in the sling assembly shall be proof-load tested as components or as part of the sling assembly.
  • Makeshift fasteners, hooks, or links formed from bolts or rods shall not be used. Nonstandard end fittings designed by a qualified engineer may be used.
  • Where used, handles shall be welded to the master link or hook before heat treating.  (This prohibits welding on chain slings during field operations.)

Figure 2. Chain Sling Major Components

Chain Sling Major Components

Table 1: Rated Load for Alloy Steel Chain Slings ASTM A391

Rated Load for Alloy Steel Chain Slings ASTM A391

Table 2: Typical Reduction of Chain Sling Working Load According to Temperature(a)


Temperature of chain (°F)

Reduction in working load (%)
While heated
After cooling
400
10
10
500
10
10
600
20
10
700
25
10
800
45
10
900
55
15
1,000
60
20

(a) This table is provided for information and may not reflect specific chain sling manufacturer's recommendations.  It is important that the manufacturer be contacted if a chain sling will be used at temperatures of 40°F or more.

Chain Sling Inspection

Initial Inspection

Before use, all new, altered, modified, or repaired slings shall be inspected by a designated person to ensure compliance with the requirements of Design Factors and Chain Properties above.

Frequent and Periodic Inspection

Inspection of chain slings in regular service is divided into two general classifications based on the interval at which inspection should be performed. The intervals, in turn, are dependent on the degree of exposure of the sling components to wear and deterioration.  The two general classifications are designated as "frequent" and "periodic," with respective intervals between inspections as defined in Table 3.

  • Frequent Inspection.  Slings shall be inspected for defects and damage at intervals as defined in Table 3.  In addition, the following visual observations should be conducted during regular service to ensure that no damage or evidence of malfunction appears between regular inspections.  Any such deficiencies shall cause the sling to be set aside for periodic inspection.

    Table 3: Frequent and Periodic Inspection of Chain Slings
    Service level
    Sling service
    Frequent inspection(a)
    Periodic inspection(b)
    Normal Service that involves use of loads within the rated load Monthly Yearly
    Severe Service that involves normal service coupled with abnormal operating conditions Daily to weekly Monthly to quarterly
    Special or infrequent Service that involves operation, other than normal or severe, which is recommended by a qualified individual Before and after each occurrence Before each occurrence or sequence of occurrences within a 30-day period
    (a)  Visual examinations by the user with records not required.
    (b)  Visual inspection by a qualified inspector making a record of the inspection or of apparent conditions to provide the basis for a continuing evaluation.
    • Chain and attachments should display no wear, nicks, cracks, breaks, gouges, stretch, bends, weld splatter, discoloration from excessive temperature, or excessive throat opening of hooks.  Chain links and attachments shall hinge freely with adjacent links. Latches on hooks, if present, should hinge freely and seat properly without evidence of permanent distortion.
    • The tag or other marking should be examined to verify periodic inspection is current.
  • Periodic Inspection.  Complete link-by-link inspections of the slings shall be performed at the intervals defined in Table 3.  Any deficiencies shall be examined and a determination made as to whether they constitute a hazard.  These inspections shall include chain sling frequent inspection, as specified above, in addition to the following:
    • Each link and attachment shall be individually examined, taking care to expose inner- link surfaces of the chain and chain attachments to inspect for those items defined for frequent inspection.
    • Worn links shall not exceed the values in Table 4 or the values that are specifically recommended by the manufacturer.
    • Sharp transverse nicks and gouges shall be rounded by grinding,2  and the depth of the gouge or rounded portion shall not exceed values provided in Table 4.
    • Hooks shall be inspected.
    • If present, latches on hooks should seat properly, rotate freely, and show no permanent distortion.

Table 4: Maximum Allowable Wear at any Point of Link

Nominal chain or coupling size (in.)(a)
Maximum allowable wear of cross-sectional diameter (in.)
9/32
3/64
3/8
5/64
1/2
7/64
5/8
9/64
3/4
10/64
7/8
11/64
1
12/64
1-1/4
16/64
(a)  For other sizes, consult chain or sling manufacturer.
  • Documentation.  The periodic inspection shall be documented by any one of the following methods:
    • Mark a serial number on the sling and maintain inspection records by serial numbers.
    • Institute a comprehensive marking program (such as color coding) to indicate when the next inspection is required.
    • Mark each sling with a tag that indicates when the next periodic inspection is required.  This tag becomes the record.

Proof Test

New, repaired, or reconditioned chain slings, including welded components, shall be proof tested by the sling manufacturer or repair agency to twice the rated capacity.  The sling custodian shall retain a certificate of the proof test and shall make it available to authorized personnel for examination.

The proof load for multiple-leg slings shall be applied to the individual legs and shall be twice the rated capacity of a single-leg sling.

Mechanically assembled slings need not be proof tested provided all components have been proof tested.

Repairs

Repairs are typically not allowed at PNNL. Any hazardous condition disclosed during inspection or operation shall be corrected before the chain is used again.  Chain repairs shall be made only by the chain manufacturer or qualified personnel vendor and reviewed by a qualified engineer.

When repairs are made, the following criteria shall be followed:

  • Alloy steel chain, attachments, and coupling links used for repair shall conform to the strength requirements and other requirements of the original sling.  Cracked, broken, or bent links and attachments shall not be repaired; they shall be replaced.
  • When repaired, a sling shall be permanently marked to identify the repairing agency.
  • Mechanical coupling links or carbon steel repair links shall not be used to repair broken lengths of alloy chain.

Operating Practices

Operating practices and guidelines for the use of alloy steel chains are as follows:

  • Slings having suitable characteristics for the type of load, hitch, and environment shall be selected.
  • The weight of the load shall be within the rated load (working load limit) of the sling.
  • Chain slings shall not be shortened or lengthened by knotting, twisting, or other methods not approved by the sling manufacturer.
  • Slings that appear to be damaged shall not be used unless they are inspected and accepted as usable in accordance with the periodic inspection requirements stated above.
  • The sling shall be hitched or rigged in a manner providing control of the load.
  • Sharp corners in contact with the chain sling should be padded with material of sufficient strength to minimize damage to the sling.
  • Portions of the human body should be kept from between the sling and the load and from between the sling and the crane/hoist hook.
  • Personnel should stand clear of the suspended load.
  • Personnel shall not ride the sling.
  • Shock loading is prohibited.
  • Slings should not be pulled from under a load when the load is resting on the sling.
  • Slings should be stored in an area where they will not be subjected to mechanical damage, corrosive action, moisture, extreme heat, or kinking.
  • Twisting and kinking the legs (branches) shall be avoided.
  • The load applied to the hook should be centered in the bowl of hooks to prevent point loading on the hook, unless the hook is designed for point loading.
  • During lifting, with or without load, personnel shall be alert for possible snagging.
  • In basket hitch, the load should be balanced to prevent slippage.
  • The sling's legs (branches) should contain or support the load so that the load remains under control.
  • Multiple-leg (branch) chain slings shall be selected according to Table 1 when used at the specific angles given in the table.  Operation at other angles shall be limited to rated loads of the next lower angle given in the table or calculated trigonometrically so as to not introduce into the leg (branch) itself a working load in direct tension greater than that permitted.
  • Slings should be long enough so that the rated load is adequate when the angle of the legs (branches) is taken into consideration.
  • Slings should not be dragged on the floor or over an abrasive surface.
  • When used in a choker hitch arrangement, slings shall be selected to prevent the load developed on any portion of the sling from exceeding the rated load of the chain sling components.
  • Before using a chain sling outside the temperature range of -40°F to 400°F (-40°C to 204°C), contact the sling manufacturer.

Wire Rope Slings

Wire Rope Grades

Wire rope slings are fabricated from various grades and types of wire rope. The manufacturer of the sling shall be consulted for specific data on the grade and type of rope used.  The general configuration of the wire rope sling is shown in Figure 3.

Wire Rope Sling Properties

Rated loads of wire rope slings shall be specified by the manufacturer, using a design factor of at least 5.  Rated loads are based on the following factors:

  • Nominal wire rope strength.
  • Nominal splicing and end attachment efficiency (see Figure 4).
  • Angle of loading (see Figure 1).  The rated load (load-carrying ability required) is based on sling angles.  If slings are not vertical, the load carrying ability is reduced:

    Rated load = vertical capacity X sine of minimum horizontal angle

Angles – Sine
30E    – 0.500
45E    – 0.707
60E    – 0.866

  • If two or more slings are used, the least horizontal angle (greatest vertical angle) shall be considered.
  • Horizontal sling angles less than 30E (vertical angle more than 60E) should not be used.
  • Type of hitch (e.g., straight pull, choker hitch, or basket hitch).
  • D/d ratio (see Figure 5):
    D = diameter of curvature around which rope is bent
    d = diameter of rope.

Figure 3. Typical Wire Rope Slings

Typical Wire Rope Slings

Figure 4.  Nominal End Attachment Efficiency

Nominal End Attachment Efficiency
  • When a sling is used in a choker hitch, the angle formed in the rope body as it passed through the choking eye (the choke angle) should be 120 degrees or greater.  For smaller angles, the rated load shall be reduced as shown in Table 5:

Table 5:  Wire Rope Slings in Choker Hitch

Angle of choke (degrees)

Percentage of choker-rated load

120 to 180

100

90 to 119

87

60 to 89

74

30 to 59

62

0 to 29

49
Nominal End Attachment Efficiency

Figure 5. Wire Rope Efficiencies for Various D/d Ratios

Wire Rope Efficiencies for Various D/d Ratios

The strength reduction (efficiency) is based on the D/d ratio.  For example, a rope bent around a pin of equal diameter will have a D/d ratio of 1.  The efficiency will be 50%.  The rope will have only 50% of the nominal strength attributed to it.

Proof Test

Wire rope sling assemblies shall be proof tested using the following criteria:

  • Hand Tucked.  The proof load for hand-tucked slings shall be a minimum of the rated load and shall not exceed 1.25 times the rated load.
  • Wire Rope Clips.  The proof load for wire rope clip slings shall be a minimum of the rated load and shall not exceed two times the rated load.
  • Others.  The proof load for other types of slings including mechanical splice, zinc-poured, resin poured, and swagged socket shall be two times the vertical rated load.
  • Multiple Leg Slings.  The proof load for multiple-leg bridle slings shall be applied to the individual legs.  The proof load for the individual legs shall be consistent with the particular single-leg assembly stated above.  Any master link to which multiple legs are connected shall be proof loaded to two times the force applied by the combined legs.

Sling Identification

Wire rope slings shall be labeled with a tag or other identification methods similar to that shown in Figure 6.  Other identification methods that provide the same information are acceptable.  The tag, or other identification method, shall state the following:

  • manufacturer's name
  • rated load (rated capacity)
  • load test date
  • periodic inspection due date.

Figure 6.  Rigging Tackle and Equipment Identification Tag Example

Rigging Tackle and Equipment Identification Tag Example

Effects of Environment

Damage from caustic or acid substances or fumes can affect wire rope sling length.  A strongly oxidizing environment attacks common sling materials.  The manufacturer, therefore, should be consulted before slings are used in chemically active environments.  Specific environmental limits are as follows:

  • Fiber core wire rope slings of all grades shall not be exposed to temperatures in excess of 180°F (82°C) or less than -40°F (-40°C).
  • Wire rope slings of any grade shall be used only between 400°F (204°C) and -60°F (-51°C) unless written approval is obtained from the wire rope manufacturer.

Minimum Sling Lengths

Slings made of rope with a 6 x 19 and 6 x 37 construction, and cable-laid slings, shall have a minimum clear length of rope 10 times the rope diameter between splices, sleeves, or end fittings.

Braided slings shall have a minimum clear length of rope 40 times the component (individual) rope diameter between the loops or end fittings.

Grommets and endless slings shall have a minimum circumferential length of 96 times the body diameter of the grommet or endless sling.

End Attachments

Requirements for attachments to wire rope slings are presented below:

  • All welded load-bearing components (welded before or after assembly) in the sling shall have a design factor of 5:1 and shall be proof tested by the manufacturer or the manufacturer's agent to twice their rated load.  The sling custodian shall retain proof test reports and shall make them available to authorized personnel for examination.
  • Welding of handles or any other accessories to end attachments, except covers to thimbles, shall be performed before assembling the sling.
  • Eyes in wire rope slings shall not be formed using knots.

Inspection and Replacement

Frequent Inspection

Users shall visually inspect slings each day of use for gross damage, such as listed below, which may be an immediate hazard:

  • Distortion of rope in the sling such as kinking, crushing, unstranding, birdcaging, main strand displacement, or core protrusion.  Loss of rope diameter in short rope lengths or unevenness of other strands should provide evidence the sling or slings should be replaced.
  • General corrosion.
  • Broken or cut strands.
  • Number, destruction, and type of visible broken wires (ten randomly distributed broken wires in one rope lay or five broken wires in one strand in one rope lay).

Periodic Inspection

A wire rope sling periodic inspection shall be performed by a qualified inspector on a regular basis (at least annually).

  • Inspection frequency shall be based on the following criteria:
    • Frequency of sling use.
    • Severity of service conditions.
    • Nature of lifts being made.
    • Experience gained on the service life of slings used in similar circumstances.
  • The periodic inspection shall be documented by any one of the following methods:
    • Mark a serial number on the sling and maintaining inspection records by serial numbers.
    • Institute a comprehensive marking program (such as color coding) to indicate when the next periodic inspection is required.
    • Mark each sling with a tag that indicates when the next periodic inspection is required.  This tag becomes the record.

The periodic inspection shall be performed by a qualified person.  Inspection shall be conducted on the entire length of each sling including splices, end attachments, and fittings.  Deterioration that would result in loss of original strength shall be observed and determination made whether further use of the sling would constitute a hazard.

Replacement

Wire rope slings shall be immediately removed from service if any of the following conditions are present:

  • For strand-laid and single-part slings, ten randomly distributed broken wires in one rope lay or five broken wires in one strand in one rope lay.
  • Broken wires in braided and cable-laid slings (Table 6).
  • Severe localized abrasion or scraping of one-third the original diameter of outside individual wires
  • Kinking, crushing, birdcaging, or any other damage resulting in distortion of the rope structure.
  • Evidence of heat damage.
  • End attachments that are cracked, deformed, or worn to the extent that the strength of the sling is substantially affected.
  • Severe corrosion of the rope or end attachments.
  • Hooks that have been opened more than 15% of the normal throat opening measured at the narrowest point or twisted more than 10° from the plane of the unbent hook.

Table 6:  Allowable Broken Wires in Braided and Cable-Laid Slings

Sling body
Allowable broken wired per lay or one braid
Allowable broken strands per sling length
Less than eight-part braid
20
1
Cable laid
20
1
Eight-part braid and more
40
1

Because many variable factors are involved, no precise inspection criteria can be given for determining the exact time for replacement of a sling.  In this respect, safety depends largely on the use of good judgment by a qualified person in evaluating the remaining strength in a used sling after allowing for deterioration disclosed by inspection.  Safety of sling operation depends on this remaining strength.

Operating Practices

Operating practices and guidelines for the use of wire rope slings are as follows:

  • Slings having suitable characteristics for the type of load, hitch, and environment shall be selected.
  • The weight of load shall be within the rated capacity of the sling.
  • Wire rope slings shall not be shortened or lengthened by knotting or twisting or with wire rope clips or other methods not approved by the sling manufacturer.
  • Slings that appear to be damaged shall not be used unless they are inspected and accepted as usable in accordance with the periodic inspection requirements stated above.
  • The sling shall be hitched in a manner providing control of the load.
  • Sharp corners in contact with the wire rope sling should be padded to minimize damage to the sling.
  • Portions of the human body should be kept from between the sling and the load and from between the sling and the crane hook or hoist hook.
  • Personnel should stand clear of the suspended load.
  • Personnel shall not ride the sling.
  • Shock loading is prohibited.
  • Slings should not be pulled from under a load when the load is resting on the sling.
  • Wire rope slings should be stored in an area where they will not be subjected to mechanical damage, corrosive action, moisture, extreme heat, or kinking.
  • Twisting and kinking the legs shall be avoided.
  • The load applied to the hook should be centered in the base (bowl) of the hook to prevent point loading of the hook, unless the hook is designed for point loading.
  • During lifting, with or without load, personnel shall be alert for possible snagging.
  • In a basket hitch, the load should be balanced to prevent slippage.
  • The sling's legs should contain or support the load so that the load remains under control.
  • Multiple-leg slings shall be selected so as not to introduce a working load in direct tension in any leg greater than that permitted.  Triple- and quadruple-leg sling ratings should be considered the same as a double-sling rating because in normal lifting practice the load will not be uniformly distributed on all legs, leaving only two legs to carry the load.  If rigging techniques—verified by a qualified rigger or rigging specialist—ensure the load is evenly distributed, then full use of three legs is allowed.  Special rigging techniques verified by a qualified engineer shall be required to prove a load is evenly distributed over four or more sling legs.
  • Slings should be long enough so that the rated load is adequate when the angle of the legs is taken into consideration.
  • Slings should not be dragged on the floor or over an abrasive surface.
  • In a choker hitch, slings shall be long enough so that the choker fitting chokes on the wire rope body and never on the fitting.
  • Slings shall not be inspected by passing bare hands over the wire rope body.  Broken wires, if present, may injure the hands.
  • Fiber core wire rope should not be subjected to degreasing or a solvent because it will damage the core.
  • Single-leg slings with hand-tucked splices can be unlaid by rotation.  Care should be taken to minimize rotation.
  • An object engaging the eye of a loop eye sling should not be greater in width than one-half the length of the loop eye.

Cautions and Prohibitions

The sling's intended use shall determine the type of rope and termination.  The following cautions and restrictions apply to this determination:

  • Rotation-resistant wire rope shall not be used for slings.
  • Wire rope clamps (clips) shall not be used to fabricate wire rope slings except when the application of the sling prevents the use of a prefabricated sling or when the specific application is designed by a qualified person (see Figure 7).  When used, slings fabricated using wire rope clamps shall be de-rated to 80% of the rated wire rope load capacity to account for the efficiency of the clamps.  Wire rope clamps must be installed in accordance with the manufacturer's recommendations.  The nuts on the clamps must be checked periodically and retorqued to the recommended value to maintain the efficiency rating. Slings made with wire rope clips should not be used as a choker hitch.
  • Wire rope wedge sockets shall not be used to fabricate wire rope slings.
  • Slings with eyes formed by folding back the rope (not a Flemish eye loop) and secured with one or more metal sleeves pressed (not forging) over the wire rope junction are prohibited for lifting service.

Onsite Sling Fabrication

Slings for lifting service may be fabricated onsite by a knowledgeable craftsperson using one of the following methods:

  • Wire rope clips. This method shall be used only in special cases.
  • Hand tucked. The terminal efficiency is reduced (see Figure 4).  This sling type is usually more expensive than most commercially made slings.
  • Flemish eye with swaged socket. This is the best selection for general purposes and shall be used except when use is impractical.
  • Slings shall be made only from new wire rope.  When swaged fittings are used, they shall be used as recommended by the fitting manufacturer and the swaging machine manufacturer. Thimbles should be used unless their use makes the sling impractical.

Figure 7.  Correct and Incorrect Ways to Use Wire Rope Clips (Clamps)

Note:  Number of clamps varies with rope size and construction.

Correct and Incorrect Ways to Use Wire Rope Clips (Clamps)

Synthetic Web Slings

Construction

Webbing

Synthetic web slings fabricated by sewing woven synthetic webbing of nylon or polyester yarns form the basic sling types shown in Figures 8 and 9.  Webbing shall have the following characteristics:

  • Sufficient certified tensile strength to meet the sling manufacturer's requirements.
  • Uniform thickness and width.
  • Full woven width, including selvage edges.
  • Webbing ends sealed by heat, or other suitable means, to prevent raveling.
  • Stitching shall be the only method used to attach end fittings to webbing and to form eyes.

Fittings

If synthetic web slings incorporate metal fittings, the fittings shall have the following properties:

  • Fittings shall have sufficient strength to sustain twice the rated load of the sling without permanent deformation and a minimum breaking strength equal to five times the rated capacity of the sling.
  • Surfaces shall be cleanly finished and sharp edges removed to prevent damage to the webbing.
  • Slings incorporating reused or welded fittings shall be proof tested to two times the rated load of the sling.
  • Slings incorporating aluminum fittings shall not be used where fumes, vapors, sprays, mists or liquids of caustics, or acids are present.
  • The eye opening in the fitting shall be the proper shape and size to ensure that the fitting will seat properly in the hook or other attachment.

Coatings

Synthetic web slings may be coated with suitable material that will impart the following desirable characteristics:

  • abrasion resistance
  • sealing to prevent penetration of foreign particles and matter
  • increased coefficient of friction
  • protection from sunlight or ultraviolet degradation.

Figure 8. Synthetic Web Slings

Synthetic Web Slings

Figure 9.  Web Sling With Loop Eyes or End Fittings

Web Sling With Loop Eyes or End Fittings

Marking (Sling Identification)

Synthetic web slings shall be labeled (a sewn-on leather tag is recommended).  The label shall state the following:

  • Manufacturer's name or trademark.
  • Manufacturer's code or stock number.
  • Rated loads for the types of hitches used.
  • Type of synthetic web material.
  • An additional tag, sticker, or other identifier shall be added by the user to indicate when the next periodic inspection is required.
  • If the synthetic web sling is to be used for critical lifts, the tag or other identification means shall be used to indicate that a proof test has been performed.

Design Factor

The design factor for synthetic web slings shall be a minimum of 5.

Rated Load

A synthetic web sling shall not be used at a load greater than shown on its tag. Each manufacturer shall make available on request test data to justify the rated loads.

  • Bridle slings.  For rated loads of bridle slings, where both legs are not vertical and for consideration of the angle between basket hitch slings, the following equation shall be applicable.

    Rated load = vertical rated load x number of legs x sine of minimum horizontal angle

  • Choker hitch.  The rated load, in choker hitch, of single-leg slings shall be a maximum of 80% of the vertical rated load.

Proof Test

When specified by the purchaser, web slings of all types shall be proof loaded by the manufacturer.  Synthetic web slings used for a critical lift shall be proof loaded. 

Single-Leg and Endless Slings

The proof load for single-leg and endless slings shall be two times the vertical rated load.

Multiple-Leg Bridle Slings

The proof load for multiple leg bridle slings shall be applied to the individual legs and shall be two times the vertical rated load of a single-leg sling.

Effects of Environment

High radiation or chemically active environments can destroy the strength of synthetic web slings.  Sling materials can be susceptible to caustics and acids.  The manufacturer should be consulted before slings are used in chemically active environments.  Radiation degrades synthetic material.  Specific environmental limits are as follows:

  • Nylon and polyester slings shall not be used at temperatures in excess of 180°F.
  • Synthetic slings, including Kevlar,3 K-Spec,4 nylon, and polyester may be used in radiation areas only when the responsible person ensures that the absorbed dose shall not exceed 100,000 rad during the life of the sling.
  • Synthetic web slings that incorporate aluminum fittings shall not be used where fumes, vapors, sprays, mists, or liquids of caustics or acids are present.
  • Nylon web slings shall not be used where fumes, vapors, sprays, mists or liquids of acids or phenolics are present.
  • Polyester web slings shall not be used where fumes, vapors, sprays, mists, or liquids or caustics are present.
  • Synthetic web slings are not recommended where extensive exposure to sunlight or ultraviolet light is experienced.

Inspection

Initial inspection

Before any new or repaired synthetic web sling is used, it shall be inspected to ensure that the correct sling is being used as well as to determine that it has proper identification.

Frequent Inspection

This inspection should be made by the person handling the sling each day the sling is used.

Periodic Inspection

A periodic inspection shall be performed by a qualified inspector on a regular basis with frequency of inspection based on the following criteria:

  • frequency of sling use
  • severity of service conditions
  • nature of lifts being made
  • experience gained on the service life of slings used in similar circumstances.

The periodic inspection shall be made at least annually and shall be documented by any one of the following methods:

  • Marking a serial number on the sling and maintaining inspection records by serial numbers.
  • Instituting a comprehensive marking program (such as color coding) to indicate when the next periodic inspection is required.
  • Marking each sling with a tag that shows when the next periodic inspection is required. This tag becomes the record.

Removal Criteria

Synthetic web slings shall be removed from service if damage such as the following is visible:

  • acid, phenolic, or caustic attack
  • melting or charring on 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
  • excessive pitting or corrosion, or cracked, distorted or broken fittings
  • other visible indications that cause doubt as to the strength of the sling, such as loss of color that may indicate the potential for ultraviolet light damage.

If a synthetic sling located in a radiation area approaches its radiation exposure limit (100,000 rad during the life of the sling), it shall be removed from service.

Repairs

Synthetic web slings shall be repaired only by a sling manufacturer or a qualified repair agent.  When repaired, a sling shall be permanently marked to identify the repair agent.

Temporary repairs of either webbing, fittings, or stitching shall not be permitted.

A repaired sling shall be proof tested to two times its assigned rated load before being put back into service.

1Kevlar is a registered trademark of DuPont de Nemours and Company.

2Removal of sharp transverse nicks and gouges on chain slings, within the limits of this manual, is considered maintenance, not repair.

3Kevlar is a registered trademark of DuPont de Nemours and Company..

4K-Spec is a registered trademark of SlingMax.

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Hoisting & Rigging Manual

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