Rigging hardware and its inspection

Rigging is everything between the crane hook and the load: slings, shackles, hooks, eyebolts, hoist rings, spreader beams and lifting beams. It is often the cheapest part of a lift and the part most likely to be damaged, misused or left in service after it should have been thrown away. A crane with a perfect inspection record will still drop a load if the sling under the hook is cut, kinked or overloaded.

This lesson describes the main types of rigging hardware, explains rated loads and design factors, and sets out what to look for during inspection and when to remove an item from service. It does not make anyone a qualified rigger, but it should allow a supervisor to recognize obviously defective gear and to ask the right questions of the people using it.

Rated load, design factor and the identification tag

Every piece of lifting hardware has a rated load, also called the working load limit: the maximum load the manufacturer allows in a stated configuration. The rated load is the minimum breaking strength divided by a design factor. The design factor gives a margin for wear, small shock loads and imperfect conditions; it is not extra capacity for the user.

Slings must carry a legible identification tag showing the manufacturer, the rated loads for the hitches the sling may be used in, and details such as the size, material or grade. ASME B30.9 requires slings to be removed from service when the tag is missing or unreadable, because without it nobody can know the sling's capacity. Shackles, hooks and hoist rings are marked by forging or stamping with their rated load and the manufacturer's name or mark.

Types of slings

Chain used for overhead lifting must be alloy steel chain of a grade intended for lifting, such as grade 80 or grade 100, and marked accordingly. Transport chain, such as grade 30, 43 or 70 used for tie-downs, is not suitable for overhead lifting and must never be used as a sling. Homemade slings, knotted ropes and chains joined with bolts are not acceptable rigging.

Nylon and polyester web slings behave differently. Nylon stretches more and is damaged by acids; polyester stretches less and is damaged by alkalis. Both lose strength at elevated temperatures, and manufacturers set maximum service temperatures, commonly around 90°C (194°F). Many web slings and round slings contain colored warning yarns or a red core cover that becomes visible when the outer layer is worn or cut through.

Shackles, hooks, eyebolts and other hardware

• Shackles connect slings to loads and to each other. Screw pin shackles are common for temporary connections; bolt type shackles with a nut and cotter pin are preferred where the pin could rotate or the shackle stays in place for long periods. A shackle pin must be the one supplied by the manufacturer for that shackle, never a bolt from the shelf.
• Hooks should have a latch that closes the throat, unless the application allows otherwise. A hook should carry the load in its bowl, not on its tip.
• Eyebolts and swivel hoist rings attach to threaded holes in the load. Shoulder eyebolts can be loaded at an angle only if fully seated with the shoulder flush, and their rated load drops sharply at angles; non-shoulder eyebolts are for vertical loading only. Swivel hoist rings rotate and pivot to align with the load and are preferred for angled lifts.
• Spreader beams and lifting beams are below-the-hook lifting devices. They must be designed for the purpose, marked with their rated load and weight, and inspected under ASME B30.20. A length of pipe or a piece of channel from the scrap pile is not a lifting beam.
• Wire rope clips, turnbuckles and master links all have their own ratings and installation rules. Wire rope clips, for example, must be installed with the saddle on the live, load-carrying part of the rope and torqued to the manufacturer's value.

Inspection: frequent and periodic

Rigging inspection happens at two levels. A frequent inspection is a visual check by a competent person before each use or each shift. A periodic inspection is a thorough, documented inspection of each item at least once a year, and more often when the rigging is used heavily, in harsh conditions or in critical service.

OSHA's 1910.184 requires slings and their fastenings and attachments to be inspected each day before use by a competent person, with additional inspections during use where service conditions warrant. Alloy steel chain slings also need a thorough periodic inspection at least every 12 months, with a record of the most recent one. In construction, 1926.251 requires rigging to be inspected before each shift and as needed during use.

Removal criteria

Removal criteria are the conditions that mean an item must be taken out of service. They come from the manufacturer and the applicable standard, and the inspector should have them on hand. The table below gives common examples.

Bending a sling: the D/d ratio

A wire rope sling bent around a small pin, a shackle or a sharp corner loses strength because the outer wires are stretched more than the inner ones. The effect depends on the D/d ratio: the diameter of the object the rope bends around, D, divided by the diameter of the rope, d. The smaller the ratio, the greater the loss. Manufacturers publish efficiency curves; typical values are shown below.

Removing, storing and caring for rigging

When an item fails inspection, tag it out of service and remove it from the work area so nobody picks it up by mistake. Damaged slings should be destroyed or cut so they cannot be used again, and a record kept. Rigging should be stored off the ground, in a dry place out of sunlight and away from chemicals and heat, and hung on racks so it can be seen and does not get kinked or crushed. A tidy rigging loft makes inspection easy and makes missing or damaged items obvious.