A Complete Guide to Wire Rope
What is wire rope?
Wire rope is a type of cable which is made up of several strands of metal wire laid or twisted into a braid or helix. Do you know how often your wire rope needs to be inspected? Wire rope inspections are vital to industries that use wire rope.
One of the most important purposes of carrying out wire rope inspections or testing is to oversee the process of depreciation in the wire rope. When any depreciation or deterioration is identified these wire ropes can cease to be used immediately before it becomes a hazard. A great advantage of conducting these examinations is to analyse and identify if there is unexpected corrosion and destruction.
Wire rope inspection and testing
Commonly, there is a constant increase rate in the amount of wire rope breaks, during the lifespan of that wire rope. Wire ropes need to be inspected and tested as they have a limited life, like all consumable products. Early in the life of the wire rope (when it is starting to be used), the wires and strands of the rope settle into position and the breaking strength increases. Once it has hit its maximum, the breaking strength then decreases rapidly.
Wire rope inspections should only be carried out by highly trained professionals. There are 2 ways that these inspections are carried out on crane wire rope: Visual and Non-Destructive. Visual and no-destructive examinations are equally as important but a non-destructive wire rope test is a lot less frequent than a visual wire rope inspection. Destructive testing only takes place when specifically required by a company to find out what type of wire rope something is that has not been labelled and is not common practice in the general testing/inspections.
Visual inspection of wire rope
The visual method is a simple yet effective method to check for external damage to a crane wire rope. Visually inspecting the entire length of rope is very important. The rope should be inspected 2 to 3 feet at a time and examined carefully at each stop. Whilst inspecting the wire rope it also cleaned with Lanotec and a wire brush.
Although tedious, it can determine many visual signs of wire rope damage, such as; kinks, bird caging, cutting, knots, flattening, crushing & heat damage (burn marks, discolouration of the metal). Wearing heavy duty gloves, an inspector will grab the rope and lightly move a rag slowly along the length of rope. Broken wires will often stick out (porcupine) and will therefore snag on the rag. Should the rag snag on a wire, the inspector should the stop and visually assess the rope condition. Broken wires do not always ‘porcupine’. Visual inspections should not be the only method relied on for inspecting crane wire ropes.
Due to the composition of a wire rope, the outer layer only represents approximately 40% of the metallic cross section of the rope and only approximately half of this is visible due to the strand twisting inside and out. That means you are only able to visually examine approximately 20% of the entire rope composition. You can only assume that the other 80% is in good condition.
Internal wire rope damage
Although the external 20% may look in good condition it may be concealing a great number of wire breaks and internal damage. Wire ropes with internal damage that have no signs of external damage can be extremely dangerous. This is why an internal wire rope inspection should also be completed. Internal deterioration is the primary cause of many rope failures, mainly due to corrosion and the normal progress of fatigue. Single-layer stranded ropes may be opened up slightly to allow an assessment of their internal condition, provided that they are at zero tension; though, some restrictions occur with large rope sizes. Permanent damage can be caused to multi-layer wire ropes if they are opened.
Internal wire rope inspection
Internal inspection should always be carried out by a capable person. The method of inspection consists of firmly attaching two clamping jaws of appropriate size at a suitable distance apart to the rope. During the inspection of sections of rope adjacent to terminations, it is adequate to use a single clamping jaw, since the end anchorage system, or a bar suitably located through the end portion of the termination, may be used as the second clamp.
By the application of a force to the clamping jaws in the opposite direction to the rope lay, the outer strands separate and move away from the core. Care should be taken during the opening process to ensure that the clamping jaws do not slip about the outside of the rope. The strands should not be displaced excessively. When a limited opening is achieved, a small probe, such as a screwdriver, may be used to remove grease or debris that could obstruct observation of the interior of the rope. The crucial points that should be observed are as follows:
State of the internal lubrication
Degree of corrosion
Indentation of wires caused by pressure or wear
Existence of wire breaks (these are not necessarily visible)
After inspection, a service dressing should be introduced into the opened part and the clamping jaws rotated with moderate force to ensure correct replacement of the strands around the core. After removal of the jaws, the outer surface of the rope should be greased. Since it is impossible to inspect the interior of the wire rope over the whole of its length, suitable sections shall be selected.
For wire ropes that wind onto a drum, or pass over pulleys or rollers, it is recommended that the lengths that engage the pulley grooves when the appliance is in a loaded condition be inspected. Those localised lengths in which shock forces are arrested (i.e., adjacent to drum and jib head pulleys) and those lengths that are particularly exposed to the weather for long periods should be inspected. Attention should be given to the length of rope close to its termination, and this is particularly important for fixed ropes, such as stays or pendants. This is where a visual inspection is complimented by a non-destructive test. .