Wire rope is a machine.
It’s a rather complex machine, actually. Its primary function is to move, which in turn is where it obtains its source of strength. And because it is such a complex piece of machinery, no precise rules have been given to determine exactly when a wire rope sling has passed it’s service or expiration date. There are guidelines, though, one should follow to know whether the sling they possess is suitable for continued use or needs replacement.
The reason we should inspect wire rope slings prior to use is to identify potential hazards or damage that may be present and if it’s suitable for continued use. The Occupational Safety and Health Administration (OSHA) and ASME B30.9 standards also dictate that inspection intervals and procedures must be performed and that the inspections are executed by the sling user. Since all wire rope that has been fabricated into slings applies to the same work practices as all “working” wire rope, it’s essential that the sling inspector has a good working knowledge of wire rope design and construction before conducting an inspection of the wire rope sling.
In this in-depth article, we will cover the different types of wire rope, splicing methods, basic inspection criteria, storage procedures, and more.
Wire Rope Types
As with most types of wire rope, a number of multi-wired strands are laid or helically bent around what is essentially called a core member. Typically, there are two types of cores that are used in the process of manufacturing wire rope: fiber cores and IWRC cores (nonfiber). IWRC is a steel core whilst a fiber core is comprised of synthetic fibers. For this particular article, we will be focusing mainly on IWRC cores, which is the more commonly-used type of wire rope cores. (Klinke, 24)
Hand Vs Mechanical Splicing
When it comes to how the eye of a wire rope sling is spliced, there are again two preferred methods: Hand and Mechanical. A hand splicing method offers a narrower profile and therefore can fit through tighter spaces. Because no metal sleeve is required to secure the eye in a hand-sliced sling, it offers more flexibility to the user, but less in carrying capacity. A mechanical splicing is fabricated by unlaying the rope body into two parts, one containing half the number of strands and the other having the remaining strands and core. The rope is then unlayed far enough back to allow the eye to be formed by looping one part in one direction and the other part in the opposite direction and laying the rope back together. The strands are rolled back around the rope body and a metal sleeve is slipped over the ends and pressed to secure the ends to the sling body. This option is more economical, offers the highest of rated capacities, and is the most preferred option amongst wire rope users. (Klinke, 24)
Basic Inspection Criteria
According to the Wire Rope Technical Board, a proper inspection should follow a systemic procedure. The following numerical list below was provided by the Wire Rope Technical Board’s Wire Rope Sling Users Manual, 3rd Edition and as it stands the most up-to-date and current method of inspecting wire rope slings.
- First, it is necessary that all parts of the sling are readily visible. The sling should be laid out so every part is accessible.
- Next, the sling should be sufficiently cleaned of dirt and grease so wires and fittings are easily seen. This can usually be accompanied with a wire brush or rags.
- The sling should then be given a thorough, systematic examination throughout its entire length, paying particular attention to sections showing the most wear.
- Special attention should also be paid to fittings and end attachments, and areas of the sling adjacent of these fittings.
- When the worst section of a sling or the weakest link has been located, this area should then be carefully checked against the criteria.
- Label or identify slings that are inspected.
- Keep records of inspections that include dates and corresponding conditions of slings.
- Dispose immediately of slings that are rejected. (Wire Rope Sling Users Manual, 136)
Ideally, other systems of ensuring the quality of your slings should be installed in your warehouse or facility’s inspection procedures. For example, Lifting Gear Hire is completing the final stages of adopting a brand new, streamlined RFID tracking system to record when equipment was inspected, who inspected it, if and when the equipment was damaged, as well. This new system will help speed up LGH’s intensive testing and inspecting processes.
It’s also advisable to find quality training resources or learning institutes that teach courses on how to properly inspect wire rope slings; preferably ones that can teach you how and also provide you a Rigging Gear Inspector certification, too.
A sling’s service life can be extended substantially should it receive a fair amount of care and maintenance. This includes the type of storage its housed within, the temperature in which its kept at, and how often/well it’s lubricated on a consistent basis. Proper storage commands that slings be housed in an environment free of exposure to water, extreme heat, corrosion, liquids, sprays, kinks, etc.
Slings should never be left beneath loads or lying around where they can be susceptible to damage. So basically, don’t leave it outside so it may get run over by a crane. Steel is not impervious to destruction. A rack is permissible to house your slings when not in use. Custom racks can also be constructed to accommodate slings of any size should a sling not adhere to typical rack sizes.
As with most machines, wire rope is lubricated at the time of its own manufacture. No supplementary lubrication is generally required if the sling has been used under typical conditions, but if a sling was stored outside or in any environment that could cause corrosion, it is advisable to apply additional lubrication to prevent the onset of rusting or corroding. If in the event the wire rope needs to be re-lubricated, the same type of lubrication during manufacture must be applied.
The temperature of its storage also plays an important role in preserving the lifespan of a sling. It’s generally accepted and agreed that steel cored slings shouldn’t be used at temperatures above 400 deg. F or below minus 40 deg. F. Although it’s not always easy to see when a sling has been damaged by temperature-related causes, a general rule of thumb is that if there are any suspicions that a sling’s integrity may have been compromised, it should be taken out of service right away or at the very least the manufacturer should be consulted. (Wire Rope Sling Users Manual, 134)
Minimum Sling Lengths
Cable laid and 6x19 and 6x37 slings shall have a minimum clear length of wire rope 10 times the component rope diameter between splices, sleeves, and end fittings. If you have a one-inch sling, then you have to have 10 diameter lengths in between the splices so you have to have a minimum 10 inches between the knuckles.
Braided slings shall have a minimum clear length of wire rope 40 times the component rope diameter between the loops or end fittings. Cable laid grommets, strand laid grommets, and endless slings shall have a minimum circumferential length of 96 times their body diameter. (Rigging Gear Inspector Levels I & II, 42)
Safe Operating Temperatures
When steel-cored wire rope slings of any grade are used at temperatures above 400 deg. F or below minus 60 deg. F, recommendations of the sling manufacturer regarding use at that temperature shall be followed. This is because the metallurgy of the steel start to realign above those temperatures. If something has been used in or is planning to be used above those temperatures, consult the manufacturer of the sling to prevent degradation. (Rigging Gear Inspector Levels I & II, 42)
Removal From Service
OSHA specifics that wire rope slings must be removed from service should any of the following conditions become present or should occur:
- Ten randomly distributed broken wires in one rope lay, or five broken wires in one strand in one rope lay.
- Wear or scraping of one-third the original diameter of outside individual wires.
- Kinking, crushing, bird caging, or any other damage resulting in distortion of the wire rope structure.
- Evidence of heat damage, which is evident by wire discoloration, burn marks, weld splatter, etc.
- End attachments that are cracked, deformed, or worn.
- Hooks that have been opened more than 15 percent of the normal throat opening measured at the narrowest point or twisted more than 10 degrees from the plane of the unbent hook.
- Corrosion of the rope or end attachments. Only extreme corrosion is necessary to reject a sling. Light corrosion does not substantially affect the strength of a sling. (Rigging Gear Inspector Levels I & II, 42)
ASME B30.9 has similar standards to the terms stipulated above in addition to the following:
- Bent hooks can be no more than 5 percent over the normal throat openings, measured at the narrowest point from the plane of the unbent hook.
- Any evidence of eye splices that have slipped, tucked strands have moved, or pressed sleeves show serious damage may be sufficient cause to reject a sling.
- A very common cause of damage is the kink which results from pulling through a loop while using a sling, thus causing wires and strands to be deformed and pushed out of their original position. This unbalances the sling, reducing its strength.
Should a sling be determined as worn out or damaged beyond use because of any of the aforementioned reasons, the inspector should immediately tag the sling as Do Not Use. Afterwards, the sling should realistically be destroyed as soon as possible by cutting the eye and fittings from the rope with a torch. Cutting the body of the sling is also appropriate. This method of destruction should deter another employee from mistakenly using a sling that has been formally retired from service. Any inspection program, however thorough, is of no value if the slings that have been rejected or retired are not disposed of properly. (ASME B30.9-2014, 15)
According to ASME B30.9, should a sling become damaged and be eligible for repair, a restoration should only be conducted by the manufacturer itself or a qualifying individual with the appropriate experience and certifications. For example, if an end fitting such as a hook becomes bent beyond guidelines, you would need to send that back to the manufacturer regardless if the wire rope sling is in tact and undamaged.
All repairs conducted on wire rope slings will require marks, tags, or some kind of proof of its restoration and parts that need replacement can only be substituted for the same original parts that were used in its manufacturing.
Should the wire rope used to craft the sling itself become damaged, it is not to be repaired under any circumstances. For example, if one of the wires is damaged by weld splatter or heat damage, it is simply not possible to remove the one strand of wire and replace it. It’s also not necessarily cost-effective for that matter either. Repairs such as these could be more expensive than what the sling is even worth at that point. When a vehicle is involved in an accident, if the price of repair outweighs the total value of the vehicle, it’s considered totaled. Same principles apply to equipment such as wire rope slings. When repairs are worth more than the equipment itself, it’s time to scrap the wire rope sling. (ASME B30.9-2014, 15)
Moreover, if a repair is warranted and completed, a proof test of its structural integrity should be conducted. With wire rope slings, the proof test is a 200% load test.
When and how often you should inspect a wire rope sling are often the subjects of debate. The amount of usage the wire rope sling receives should equate to an appropriate number of inspections it receives every year. A wire rope sling that’s used a few times a year does not require the same number of inspections as a wire rope sling that’s used more frequently, for longer periods of time, and in compromising environments. A general rule of thumb when it comes to how often you should inspect a wire rope sling, at bare minimum, is once a year. However, if the wire rope sling is used frequently or in severe atmospheres where it could be exposed to extreme temperatures where the sling’s integrity can become challenged, then it’s advisable to inspect the wire rope every month or quarterly at least.
It’s also necessary to keep written records of when the wire rope was last inspected, so you can have proof of it’s inspection and rest assured when using it. If there was an accident or cause for concern, people will want to see those records. As long as those records match what you’ve been doing, you can protect yourself. It’ll also prevent someone from sending out a wire rope sling that’s unsafe or hasn’t been inspected. Because after all, the most important thing on a jobsite is maintaining safety. Safety must always come first.
- Klinke, Jerry. Rigging Handbook. 5th ed., ACRA Enterprises, Inc., 2016.
- Industrial Training International, Inc. Rigging Gear Inspector Levels I & II Resource Manual