Inspection before use
A sling will eventually deteriorate as a result of abrasive wear, wire breaks, loss of lubrication, corrosion and consolidation of the core and rope strands. Damage is not always readily evident. The normal types of damage are described in this section.
The pre-use inspection for wire rope slings shall give particular emphasis to:
Check the identification stamp or tag and ensure the WLL of the sling is clearly legible.
Check load-bearing points for excessive wear, kinking, broken wires and corrosion.
Check each strand along its length, opening the rope as much as practicable to enable examination of the surfaces of the strands towards the inside of the rope.
Check end fittings and attachments for any signs of deformation, excessive wear or corrosion.
Check the sling for heat damage. This is usually obvious through the discolouration of the wires.
Types of Damage
Wire rope can be damaged in different ways and the resulting damage can take the forms of external wear, local abrasion, broken wires, internal wear, physical deterioration, corrosion, kinking and flattening of eyes.
Severe overloading of wire ropes is evidenced by an increasing rate of fracture of the wires and excessive stretch under load accompanied by marked reduction in diameter.
External wear can be caused by dragging the sling over rough surfaces and is the most readily noticeable cause of weakness, particularly if a new sling is available for comparison. In the extreme, the outer strands become worn as the outer wires within the strands are flattened and worn.
Local abrasion, as distinct from external wear, can be caused by the passage of the sling over sharp edges whilst under tension and can cause a serious loss of strength. It is good economy to protect slings at points where excessive local abrasion can occur. Cuts, bruises and similar damage can be internal as well as external. This type of damage is indicated by local rupturing or loosening of wires or strands. It is caused by lack of care in use such as hammering of the slings and careless placement of the load. Internal wear is caused by repeated flexing of the sling and by particles of grit picked up in service. Internal wear is accelerated by lack of lubrication and by corrosion.
Corrosion is caused by dampness and exposure to acids, alkalis, other chemicals, flue gases, industrial dusts, ashes and similar substances.
High temperatures, such as those found in foundries, steel works and like applications, reduce both the strength and the safety of a sling.
Distortion, permanent set or any physical deformation of end fittings, particularly at load bearing points should be regarded as dangerous and the sling should not be used.
The decision whether or not to withdraw a sling from use shall be based on an assessment of the general condition of the sling. After examination, if any doubt exists about the safety of a sling, it shall be withdrawn from service.
Slight damage to the outer wires of a wire rope sling may be disregarded. Serious damage of one strand or somewhat less serious damage to more than one stand however, merits rejection of the sling.
Slings that have been subjected to impact loads, overloaded or loaded in a kinked condition shall be destroyed and discarded.
Where kinking is such that it creates a hazard in taking up loads through hand injuries or causing unevenness or jerking during loading, the kinked slings shall be discarded.