Safe slinging

D errick Bailes first encountered wire rope slings many years ago. “I recall many years ago visiting the rigging stores of our then nationalised power generator and seeing a jungle of wire rope slings hanging from their racks, each with their own distinctive bends and kinks which outlined the shape of the load they had been used with,” says Bailes. “The riggers knew what each was for and they generally avoided re-using them on any load other than that they were shaped for. There wasn’t a chain sling or textile sling in sight – they were never used.

“Since then attitudes have changed considerably, as have the products on the market. Higher grade mechanically assembled chain slings have removed much of the weight advantage of wire rope and offer far greater versatility and durability. Textile webbing slings and roundslings offer considerable reductions in weight and more flexibility than wire rope slings,”Bailes says.

“As a consequence the market is more evenly divided between the various types and we encourage the selection of the most appropriate type of sling for the application. This often involves using slings in combination to get the best attributes of each. For example lifting a machined shaft using roundslings in choke hitch, which then engage with a chain sling suspended from the crane hook. The roundslings provide lifting points without damaging the finished surface of the shaft, whilst the chain sling provides easy length adjustment,” Bailes says.

Howard Kaplan agrees that, given the variety on the market, a wire rope sling might not be the best. “I, too, thought like that when I was teaching full time. In our perfect world of the classroom we can create scenario after scenario about how we would rig a load, and when lifting million-dollar MRI magnets my company will purchase whatever is required or the customer supplies the appropriate rigging,” he says.

“But my problem is the every day lifting that goes on in every construction site across America. If we send a taxi crane to a job site that crane is outfitted with the best general rigging we can think to outfit it with considering the size of the crane, its capacity, and the amount of room the crane has for rigging. This is compounded by America’s highly faulty oversized weight and width permitting practices. It is very difficult for us to travel our large cranes as opposed to the way I often see them travelling abroad.

“So we use the best rigging we can and we often make do, sometimes at the cost of the rigging. As the safety and training manager, I often go to jobs and bring out rigging for a specific
task, but it’s difficult to anticipate every lift and every load. We do the best we can with continued education for our crane operators, crane oilers, millwrights and helpers.”

Point by point

In the USA, there are two Federal OSHA standards for rigging – general industry standard 1910.184 and construction standard 1926.251. Both standards rely heavily on manufacturer specifications, Kaplan says.

In the general industry standards for slings 1910.184 starts with safe operating practices. Over the page, we summarise the standards and offer comments from both men.

1910.184(c)

Safe operating practices. Whenever any sling is used, the following practices shall be observed:

1910.184(c)(1)

Slings that are damaged or defective shall not be used.

Under each specific sling type there is inspection and rejection criteria. The rejection criteria for a wire rope sling are:

1910.184(f)(5)

Removal from service. Wire rope slings shall be immediately removed from service if any of the following conditions are present:

1910.184(f)(5)(i)

Ten randomly distributed broken wires in one rope lay, or five broken wires in one strand in one rope lay.

Howard Kaplan: “Does this apply to standard six, seven or eight-strand rope, or cable-laid ropes, or both? How many riggers know the difference between a wire and a strand? Ask your riggers what a strand is, how many will tell you, you can have a few broken strands?

“This is no simple worry about semantics. Our industry has relied on such a large design factor that riggers will overload slings, use them when they are clearly damaged, and when asked why they simply reply, ‘It was fine last time’ or ‘They are not as bad as you think’. The thought process that damaged slings can still be used is where real training comes in. Once identified, broken wires are a very good indicator for the user. The rigger can look at the sling, see a bad spot, look for broken wires, and either reject it or use it.

“What is a rope lay and how is it measured? A lay length is the linear measurement; it’s the distance it takes one strand to revolve around the core of the rope one time.

Derrick Bailes: “Herein lies a difference in the practice we encourage in Europe. Wires breaks occur in slings for different reasons to those in running ropes. In running ropes on conventional metal sheaves, wear occurs on the outer wires where they contact the sheaves and this initiates fatigue cracks in the wire. Hence the practice of counting visible broken wires, our guide being a maximum of 5% of the total wires in any length of 10 rope diameters.

“In slings the damage arises from kinks and notching on sharp edges and corrosion if neglected. It can be much more localised and go deeper into the rope affecting several wires at the same point. Also these days we are much more cautious about injury to the rigger’s hands. Our guidance for slings is therefore to reject them when only a single wire is broken. Similarly we reject terminal fittings which are visibly distorted indicating misuse or overload.”

1910.184(f)(5)(ii)

Wear or scraping of one-third the original diameter of outside individual wires.

Howard Kaplan: “One wire, wear or damage to one wire. A 6×19 piece of wire rope can have 156 individual wires. The standard is not clear how many wires are too many.”

1910.184(f)(5)(iii)

Kinking, crushing, bird caging or any other damage resulting in distortion of the wire rope structure.

Derrick Bailes: “Wire rope slings are great in straight pull and basket hitch around large diameter items such as pipes. Interestingly the one sector of UK industry where wire rope slings still dominate is the offshore oil industry, reflecting the US practices introduced in the early days.

“Most offshore applications, particularly container lifting sets, use the rope in straight pull. Wire rope is not so good around anything with small radius corners that cause permanent kinks unless it is always used for the same load.

“Using a kinked rope back in straight pull will frequently cause wire failure at the kink, so is not a good idea. If a rope has a permanent set it should be discarded.” He also adds that any rope with wires whose positions in the strands have been disturbed, or any protrusion of the core, should be discarded.

Howard Kaplan: “Kinking is a matter of definition. If someone says, ‘Picture a car in your head,’ what kind of car do you picture? A Ford, Chevy, or even a Yugo? I was always taught a kink is damage to the wire rope that causes permanent rope distortion.

“The analogy I use in my classes is a forklift sling. If you have ever seen someone slip the eye of a wire rope sling over the tine of a fork lift and apply a load to it you know what I mean by a fork lift sling. The bent corners of the forklift sling are kinks. You can have kinks in slings from normal use too. But it is not clear when it is too much.”

1910.184(f)(5)(iv)

Evidence of heat damage.

Howard Kaplan: “This is one standard I have no problem with at all. Heat comes from many sources and there does need to be a visual inspection.”

Derrick Bailes: “One of my rejection criteria is evidence of heat damage, eg melted lubricant, blueing of wires, contamination by weld splatter, or evidence of arcing.”

1910.184(f)(5)(v)

End attachments that are cracked, deformed or worn.

Howard Kaplan: “As with heat damage inspectors or users need to be aware of the weak link scenario and where to look for absolute rejection criteria. “

Derrick Bailes also includes damage to protective thimbles, hand splices, ferrules, including cracking or slippage.

1910.184(f)(5)(vi)

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.

Howard Kaplan: “This is if you have a hook on the sling and then you need to know what the hook looked like when it was new. Without an initial inspection or manufacturer specifications there is no way of knowing if your hook is opening until maybe it’s too late.”

Derrick Bailes says that ineffective safety catches on hooks are also grounds for discard.

1910.184(f)(5)(vii)

Corrosion of the rope or end attachments.

Howard Kaplan: “Corrosion is another point of contention. Light rust or corrosion can be easily cleaned off with a light penetrating lube. How many slings do you see lubricated in the field? Very rarely do I see this.”

Derrick Bailes also adds that he would discard a rope with illegible markings, such as the sling identification mark and the safe working load including the range of angles for which the sling is rated.

Howard Kaplan concludes that training, and the judgements of expert trainers, can help riggers make the right choices.

“With good training, riggers can work out the best answers. You must ask questions of your instructors. I used to work for one of the best in the country. They are not the cheapest but you are going to get what you pay for.”