Synthetic sling inspection is the most skipped step on most job sites. Synthetic slings are the most-used and least-inspected rigging on most job sites. They are cheap enough to treat as consumable, soft enough to look undamaged when they are not, and easy enough to replace that nobody builds a program around them. Then one gets cut on a sharp edge nobody dressed, and the investigation asks who inspected it and when.
The rejection criteria in ASME B30.9 are not subtle. What makes synthetic sling inspection difficult is that the damage modes are mostly invisible from three feet away, and the single most important check takes two seconds and is skipped constantly.
The tag is the first test, and most slings fail it
Before any condition assessment, read the tag. Under B30.9 a synthetic sling must carry a legible identification showing the manufacturer’s name or trademark, the manufacturer’s code or stock number, the rated loads for the hitch types used, and the type of synthetic material. Missing or illegible identification is, on its own, a removal-from-service condition.
This is not a technicality. A sling without a legible tag has no defensible capacity, and the crew will assign it one from memory — always generously. On a first rigging inspection, tag failures alone routinely account for a quarter of the inventory being pulled, and the replacement cost is consistently smaller than the owner feared.
Removal criteria for web slings
B30.9-5 sets the conditions requiring immediate removal. A web sling comes out of service for any of the following:
- Missing or illegible sling identification.
- Acid or caustic burns — discoloration, stiffening, or a powdery surface.
- Melting or charring of any part of the sling.
- Holes, tears, cuts, or snags in the webbing.
- Broken or worn stitching in load-bearing splices.
- Excessive abrasive wear.
- Knots in any part of the sling.
- Discoloration, brittleness, or other evidence of UV degradation.
- Fittings that are pitted, corroded, cracked, bent, twisted, gouged, or broken.
- Any other condition, including visible damage, that causes doubt as to continued use.
That last one is deliberately broad and it is the inspector’s actual authority. Doubt is enough grounds. A sling that makes an experienced person hesitate does not need to match a listed category to come out of service.
Round slings hide their damage by design
A round sling is a bundle of load-bearing core yarns inside a protective cover, and the cover is not the sling. That construction is excellent for protecting the fibers and terrible for inspection, because the part carrying the load is the part you cannot see.
The governing rule is straightforward: if the cover is damaged such that the core is exposed, the sling is removed from service. No exceptions, no assessment of how much core is showing. Beyond that, look for cover cuts and snags, hardness or stiffness indicating heat or chemical exposure, inconsistent diameter along the length — which suggests core damage or bunching — and any area where the sling will not lie flat.
Squeeze along the length with both hands. Core damage often presents as a soft spot or a lump where the yarns have shifted or broken. It is the only practical field method for finding something the eye cannot reach.
Cuts, abrasion, and telling them apart
| Damage type | What it looks like | Usual cause |
|---|---|---|
| Cut | Clean-edged severance of fibers, often across the weave | Sharp edge with no protection |
| Snag / pull | Loops of yarn pulled proud of the surface | Burrs, weld spatter, rough castings |
| Abrasion | Fuzzy, thinned surface over a broad area | Dragging, repeated contact, gritty loads |
| Crushing | Flattened, glazed webbing with fiber breakdown | Pinched under a load or in a hitch |
| Heat damage | Glazing, hardening, melted or fused fibers | Welding, hot work, friction |
| Chemical attack | Discoloration, powdery surface, local stiffening | Acids, caustics, solvents |
Surface fuzzing from normal abrasion is expected and is not by itself a removal condition — that is what the wear surface is for. What matters is whether load-bearing fibers have been severed. Fuzz that wipes away and leaves intact weave is wear. Fuzz that reveals cut yarns underneath is damage.
Chemicals matter more than people think
Nylon and polyester are the two common synthetics and they fail under opposite chemistry, which is why substituting one for the other without checking is a real hazard. Nylon is degraded by acids. Polyester is degraded by alkalis and caustics. Both are damaged by some solvents and by prolonged elevated temperature.
The problem is that chemical degradation frequently produces no visible change until the sling is loaded. Where slings work around plating lines, batteries, concrete, cleaning chemicals, or process piping, the exposure history matters as much as the visual condition — and the correct response to a known exposure is removal, not inspection. In petrochemical environments, chemical exposure is the dominant removal cause and it rarely announces itself.
Sunlight is a slow chemical attack
Ultraviolet degradation is the most underrated failure mode in synthetic rigging, because the storage that causes it looks like reasonable housekeeping. A sling hung on the outside of a job box, on a fence, or in the back of an open truck is being degraded continuously.
The visible indicators are fading, a chalky or powdery surface, and stiffness. Strength loss can be major before any of those appear clearly. This is one of the strongest arguments for indoor, shaded, dry storage — the subject of how slings get ruined between lifts, which is where most of the damage in a typical inventory actually originates.
Repairs, proof testing, and what the field may not do
Synthetic slings may only be repaired by the manufacturer or a qualified person equivalent to the manufacturer, and repaired slings must be proof tested and permanently marked to identify the repairing agent. In practice this means the field does not repair synthetic slings. Sewing a sling on site, taping a cut, or tying a knot to shorten it are all removal conditions rather than fixes.
Knots deserve a specific mention because they look like a solution. A knot in a synthetic sling can reduce capacity dramatically and creates a stress concentration exactly where the fibers are already bent. B30.9 lists knots as a removal condition without qualification.
Synthetic sling inspection: who inspects, and how often
Two intervals apply. Before each use, the sling is inspected by the user or another designated person — this is a condition check, not a documented event. Periodically, at intervals determined by service severity, a documented inspection is performed by a designated person; B30.9 sets the outside interval at one year for normal service, with more frequent intervals for severe and special service.
Service severity drives everything. A sling used weekly in a clean shop is in normal service. The same sling used daily around sharp edges, chemicals, or heat is severe service, and annual is nowhere near enough. This mirrors how duty cycle changes the inspection clock for the crane itself.
Building an inventory that can actually be inspected
The practical obstacle is not knowing what to look for. It is knowing what you own. Rigging inventories accumulate. Slings arrive with equipment, get borrowed between crews, and end up in trucks with no record connecting them to anything.
A workable system needs three things: a unique identifier on each sling that survives the environment, a register listing every identifier with its capacity and in-service date, and a documented periodic inspection recorded against the identifier. Colour-coded quarterly tags are a common and effective addition — they make an overdue sling visible from across the yard rather than requiring a file lookup. A structured sling inspection sheet keeps the criteria consistent between inspectors, which matters more than any individual inspector’s judgment.
Edge protection is an inspection finding, not an accessory
Nearly every cut synthetic sling was cut by an edge someone decided was not sharp enough to matter. Steel plate, structural shapes, precast concrete, pipe ends, and machined castings all cut webbing under load, and the load is what makes the difference — an edge that feels harmless by hand becomes a blade at tension.
Corner protectors, wear pads, and sleeves are the control, and their absence in a rigging inventory is itself a finding. When an inspection turns up several slings with cuts in similar positions, the slings are the symptom. The missing edge protection is the cause, and replacing the slings without addressing it just resets the clock. Look at what the crew is actually lifting, and ask whether the protection on the truck matches it.
The same reasoning applies to hitch practice. Choker hitches concentrate wear at the choke point, basket hitches bear on the load’s corners, and both produce predictable damage patterns that tell you how the sling has been used. Reading those patterns turns a sling inspection into information about the rigging program rather than a pass/fail on hardware.
Synthetics are one part of a mixed inventory
Most rigging lockers hold synthetics alongside chain, wire rope, and hardware, and each has entirely separate removal criteria. Applying the wrong ones is common — particularly the assumption that a visual check enough for webbing is enough for everything else.
It is not. Chain slings under B30.9 require link-by-link examination and measured stretch against a recorded baseline. Wire rope slings follow different broken-wire criteria than the running rope on the crane, which is a distinction that trips up experienced people. Shackles have their own pin, wear, and marking requirements, and counterfeit hardware is a live problem. Spreader beams and lifting devices fall under B30.20 and need their own documented inspections entirely.
A rigging program that inspects everything to the synthetic criteria will pass gear it should not. The efficient fix is a single inspection routine that branches by material type, run by someone who knows which branch applies — which is exactly what first-visit findings tend to expose when a locker has been self-inspected for years.
Common questions
Who should inspect rigging equipment and document its condition periodically, at intervals of a year or less — competent people, crane operators, lift directors, or manufacturers?
Competent people. ASME B30.9 assigns the documented periodic inspection to a designated person, and OSHA requires that inspections of rigging be performed by a competent person. Operators perform the before-each-use check. The documented periodic inspection belongs to the designated competent person, at intervals not exceeding one year and more frequently under severe service.
According to federal OSHA safety standards, how often must rigging equipment be inspected?
Before each use and at intervals determined by service conditions, with documented periodic inspections at least annually. 1926.251(a)(1) requires inspection each day before use and as necessary during use; B30.9 supplies the periodic documented interval.
Can a synthetic sling with a small cut stay in service?
No. Holes, tears, cuts, and snags are listed removal conditions with no size threshold. The absence of a tolerance is intentional — a cut is a stress concentration regardless of length.
Does a faded sling have to be removed?
Discoloration is a listed indicator of UV degradation and warrants removal when accompanied by stiffness, a chalky surface, or other evidence. Fading alone on an otherwise sound sling calls for judgment, and doubt resolves toward removal.
Can we repair a synthetic sling in our shop?
No, unless your shop is the manufacturer or a qualified person equivalent to it, with proof testing and permanent marking. Field repairs are removal conditions.
How long does a synthetic sling last?
There is no expiration date in the standard. Condition and service history govern. A sling stored properly and used lightly may last years. One stored outdoors can be unfit within a season without ever lifting anything.
Removing gear is the cheapest part of the program
The resistance to condemning slings is almost always financial, and it is almost always misplaced. Synthetic slings are among the least expensive items in the lifting chain, and the cost of replacing an entire questionable inventory is typically a fraction of a single day of crane time.
What actually makes removal hard is the absence of a disposal habit. A sling pulled from service and left in the locker returns to service, reliably, within weeks — because someone needs a sling and there is one right there. Cut condemned slings before they leave your hand. Cut the eyes, not just the body, so the remains cannot be repurposed. It takes five seconds and it is the only removal method that survives contact with a crew that is in a hurry.
Build the replacement cost into the operating budget rather than treating each removal as an unplanned expense, and the argument disappears. Programs that budget for rigging attrition inspect honestly. Programs that do not develop a quiet incentive to find everything acceptable.
Inspect the inventory once and the problem becomes manageable
Synthetic sling programs fail from accumulation, not from ignorance. Nobody knows what is in the inventory, so nobody can inspect it, so the tag check never happens and the storage never improves.
A single documented baseline — every sling identified, capacities recorded, unfit gear removed — converts that into an ordinary maintenance task. Talk to us about a rigging inspection and you will get the inventory, the removals, and the register to keep it current.
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