The last inspection of lifting equipment shows when the equipment was last inspected by a competent person, but does not show what may have happened to the equipment between inspections. An overloaded chain, a shackle dropped to the ground, or a sling in contact with acid at work would all show the same tag date and would no longer be the same equipment that the examiner signed off on.
Equipment is removed from service due to what is observed about the equipment during inspection, rather than the length of time since the last inspection. The inspection date verifies the condition at the time of inspection. The condition beyond the inspection will continue to change.
Overloading a chain causes it to stretch. The stretching is real and measurable. A chain that has been overloaded will be longer than the desired length when spanned across a given space. When a chain stretches, it is permanently longer and is no longer safe for use. Wear at the bearing points needs to be checked. The retiring diameter of a chain is a 10% reduction in diameter at the bearing points, which are the contact points between the links in a chain. This amount of wear occurs quickly for a chain in heavy use. Any bent or twisted link means the chain needs to be retired. A chain link that has permanently stretched beyond its original position where it is straight will permanently deform how the chain links carry a load.
Shackles indicate their failures at the pin and at the bow. A pin that has become slightly bent is removed from service, because screw threads require an alignment and an uneven load causes changes in design intent. Wear at the bow follows a similar rule as wear on a chain; a shackle is retired at ten percent wear. A shackle that has been subject to a side load clearly displays it in its shape and in its cross-section before it does in a measurement. Corrosion that has pitted the surface causing a reduction in cross-section is a retirement reason. Surface rust that has not corroded through the steel is not a retirement reason, but can appear to be the same on a cursory inspection. Because of that, anything that looks like more than light surface rust should be examined rather than just wiped clean and put away.
Webbing slings have greater specificity in retirement criteria than do chain or steel slings. Sling webbing fails if any load-bearing fibers are cut, regardless of the size of the cut. There is no passing cut-length threshold. A webbing cut equates to retirement of the sling. The same applies to abrasion which removes the webbing cover to expose the core fibers. Breaking of any stitch anywhere on the sling body results in retirement. Exposure of fibers to chemicals results in the fibers losing strength or becoming too soft and brittle. Any of these conditions, acting alone, may result in retirement of the sling. A webbing sling that has ever been knotted is retired no matter the condition of the sling. A knot in a webbing sling reduces the load capacity that cannot be restored by removing the knot.
Sling end fittings and the master link in a chain sling are part of the integrated system and therefore retirement is not limited to the master link, if there is a broken or cracked master link.
The retirement date is a fact of time. Retirement is a condition decision, and the condition of lifting equipment is not static and will not wait for the next scheduled examination.