Calculating Wear of Steel Wire Rope

PNNL: Hoisting and Rigging Manual - Wire Rope

What is exactly "birdcaging"? I've got an idea but, guess I didn't work with the cranes enough to see that.

I sure did enjoy my time with cranes and boomtrucks.

It was right damned dangerous.

The fact that wire rope is classified as a "machine" has long fascinated me.

For me it is fascinating since for me it is the simplest machine, and right old.

"Transfers energy to accomplish a task." is what I remember as the definition of a machine that makes wire rope a machine unto itself.

I do wonder what the most perfect lubricants are for the wire rope.

Now I wonder what the most advanced Cranes are?

Over the past few years some cranes have fallen over which makes me think there is a gap in institutional memory in their operational staffing. I spoke to a Crane operator about this who said that was a significant factor and he had had trouble with young bucks, bullheads, that hardly knew what they were doing.

I've worked stages and seen people get hurt when ropes broke.

Time to failure is pretty much known, though hemp rope had better not be lubricated since sulfur in the oil causes premature failure of a hemp rope.

-at least as far as I remember.

"birdcaging" happens when a cable(wire rope) gets kinked.

The outer strands are stretched so that they no longer conform to the OD of the wire rope. It looks like a bird cage in that area.

Not good.

or when the outplay of cable is slower than that of the drum feeding it and it unravel and bunches up. Like a birds nest. Think of the spool on a fishing rod and reel that spins faster or longer than the line plays out.

NO!

Only inspection can determine whether and when wire rope [or any rope] should be replaced.

Please tell me that you are NOT responsible for safety or operations wherever wire rope is used. This is basic stuff that you learn the first day on the job - or hopefully before you even get to the job site. And when you get there you have to know what to look for.

Lynlynch put up a fine link I read with interest.

Certainly inspection is bottom line. The link Lyn put up did seem at some point to call for regular change out of the Wire Rope regardless of appearance, which makes sense to me.

I myself am more familiar with aircraft where propellers and bolts even are changed after specific hours of duty regardless of what they look like.

At least in that arena, they have very good ideas about when things will wear out.

Hell you can buy a lightbulb that says right on it how many hours to expect out of it.

Guy I worked with was a real seat of the pants sort.

It was an adventure working with him.

I know with climbing ropes you are supposed to get another after so many jerk stops, or whatever they call it.

While for normal construction operations smooth operations are possible so as to make time before failure more consistent. I have seen some struggles. The time we pulled a Windless out of a ship was dramatic. Ship cranes and cranes and wire rope used near or on the seas, I would expect to fail sooner than inland operated machines, making the numbers shorter from my experience.

So when you take into account environment and application of course realistically inspection is the way to know.

An aviation story illustrating downward service time before overhaul was when the aircraft fuselage cracked open in Hawaiian Island service because of much higher takeoff and landing rates than normally anticipated.

Think it was a 737.

Point is there is known time to failure for most anything, but the numbers are not the reality.

Transcendian:

Don't confuse yourself. Mean Time to Failure [MTF] is a statistically derived estimate based on an extensive set physical and material assumptions. Of course rotating parts of aircraft are among the most closely watched for failure and those service intervals are adjusted based on particular environmental factors and service SOPs. Air Carriers for example, have Service Life Extension Programs that are principally applied to turbine engines.

However, wire rope, particularly when used in hoisting operations out doors, is subject to uncontrolled or uncontrollable wear from air borne grit and lubrication failure.

In short, although wire rope of a particular size, and spec in a specific application may have an expected life, and there are procedures for insuring that that useful life expectancy is reached, there is no MTF for wire rope.

I have a hard time believing that there is no Mean Time to Failure for any machine.

I've worked with this stuff and accept that it is very strong, and even see why it may well be different from a propeller on an Electra that will fail after so many hours.

Just because the variable life span of wire rope is long, does not mean that it will never fail as long as it looks good.

If I was the Chief Mechanic and had to sign off on some Service Life Extension, I'd sweat doing that, and need some really compelling reason to do so knowing that if I am wrong, people may die.

Like I said my experiences with wire rope are limited.

Still I've worked with it and other machines enough to know I'm not at all confused about the fact that things break.

Yes - things break. The point is that some things are not susceptible to quantitative determinations. Especially when environmental factors are highly variable and operating conditions are not controllable.

I never said that wire rope will never fail. In fact the point is the opposite. You have to inspect it continuously to insure that you will not experience an unexpected failure. You really should learn to read English a bit more closely.{:>)

btw - experience is what you get when you don't get what you expect to get.

I reject your point. All machines are susceptible to quantitative determinations.

You in fact contradict yourself.

Do not lecture me as if you are in any position of right to do so.

I can read and write English as well, if not better than you.

I am experienced enough to know you're the one who needs to read more closely what I wrote, in this case, than I am.

For one thing I agree that inspection on the day is the bottom line, and say that the variables may lengthen or shorten service life.

You remind me in your post of the time I said back to some fundamentalist Christian exactly what they said to me in more secular language, and then they told me I was going to be certain to go to Hell.

Experience is experience.

I've had plenty enough to not put up with some snotty intonations from you, or anybody else.

You condemn yourself out of your own mouth. - Or is it fingers? If you think that you can read + write submit your posts to an 8th Grade English teacher and see what grade you get.

What I have tried to explain is not my opinion but industry standard practice. C.f., link you claim to have read. In any event you clearly do not understand the issue and your attempt to define the universe by your own experience only puts you deeper in the hole. Remember Mark Twain's advice, "When you find yourself in a hole, stop digging."

I understand the issues.

8th Grade English Teachers are not competent to judge me when it comes to this sort of work experience.

Some industries are more advanced than others. Aviation practices from the tool room to the ramp and off to the air, are superior to whatever other slapdash and grandfathered slop allowed in other industries.

You explained your opinion, and I said I didn't agree fully with it.

Get that through your head.

If Milo, and C_Warner_711, Del, or Lynlynch come around and tell me I need a ladder on this one, I might concede, but you so far have no great status with me enough that I will put up with insults.

We all know that just because the regs allow for slop on the ground, not everything is written down.

Sure enough while wire rope is long lived and strong, every machine has limits that are quantifiable and known or knowable.

Steel is not excepted from these facts.

Far as I am concerned you are the one digging a hole you'll have to leap further to get out of than I will.

Further I spoke with a crane operator who allowed that though he did not ever retire wire rope before a braid split, he did not allow more than one, and that in his experience of running these things 48, or four thousand and eight hundred hours was about the service life of wire rope.

"I know with climbing ropes you are supposed to get another after so many jerk stops, or whatever they call it."

They call it falls.

6 falls and the rope is to be retired.

If this rope is part of certified lifting equipment, then the engineer/surveyor responsible for the company providing the facility's indemnity insurance will carry out the inspection. Certified lifting equipment must never be used for purposes other than lifting, and its use must be carefully controlled. The identification number of certified lifting equipment must be kept in a general register for the facility, together with this engineer/surveyor's periodical reports on its condition.

If the rope is part of non-certified pulling equipment, where the load itself is supported on the ground or on other structures, then it will have a tensile limit, which could in principle be established by local testing. Be aware though that the fracture of a steel rope this thick will release a lot of energy, which is disspated readily into structures both mechanical and human that may be present. So there is a risk. The testing facility needs careful design so that human structures are not put at risk by this testing.

Those ID numbers and records are important according to the crane operator I spoke with last night.

He had to get home to his wife and so while I was able to get from him the average time of service for wire rope in normal operating circumstances from his experience he had mentioned a boom failure briefly on equipment that was supplied to him to operate that was missing these ID numbers.

Next time I see him I'll see what more details on this interesting subject I can collect.

While I can see that in the case of wire rope, it is not mandated by time of service for retirement, it apparently does have a typical service life. For a company this would seem to me to be practical knowledge allowing for preparatory purchase of replacement wire rope so that when the time came for replacement, the material was on hand.

As I said in the prior post, the operator I spoke with said from his experience you were looking at 3 years, or 48 hundred hours, average. I shall seek further details of interest, such as exact crane etc.

I did participate in a Crane Test at sea once, and it was a fine, interesting, and dangerous fun, beautiful thing to do.

Put a 5,000 pound weight on a flatbed, took that to Morehead City, put the weight in a Twin Cat Water taxi, backed that up to the John C Pope tanker ship with engines roaring and hung the weight off the ships supply crane, backed off and watched the weight hang for about 15 minutes, and then put it back on the deck, and went back to shore.

I regret not having a camera with me that day.