By Dean McDonald, founder, Crane Rope Solutions
What should end a kelly rope’s life?
A kelly rope should be replaced because of crown wire breaks, and nothing else. Crown wire breaks are fatigue breaks on the tops of the outer strands, where the rope bends over the sheaves. They are the normal way for a kelly rope to wear out.
If your kelly ropes are coming off for any other reason, it points to one of two things:
- The wrong rope construction for the rig.
- A fault in the rope system: a bad sheave, a bent kelly bar, or something else on the rig that is damaging the rope.
Either way, a new rope of the same type will fail the same way. Find the cause first. Send us photos of the damage and the rope specification, and we’ll tell you which one it is.
How long should a kelly rope last?
About 2,000 operating hours is a typical life for a kelly rope that suits the rig and is retired for crown wire breaks. If yours are coming off much sooner, look for one of the problems below.
Why do kelly bars get dropped?
Usually because the wrong rope was selected and nobody caught the warning signs. The two cases I see most:
- A rope without plastic. Without a plastic layer the rope has much less protection against internal wear and crushing.
- A cheap three-layer rope with plastic that wasn’t inspected for a change in lay length. These ropes can deteriorate inside, where you can’t see it. A lengthening or shortening of the lay is the warning sign. Measure the lay length when the rope is new and check it at every inspection.
Why do crowd ropes fail?
Crowd ropes usually fail from crushing. The crowd system pushes and pulls the kelly bar under high load, and the rope is crushed on the drum.
This can often be fixed with the right rope: one built to resist crushing, for example with compacted strands and a plastic-protected core.
Which rope is best for a drilling rig?
My first choice for deep foundation rigs is Teufelberger-Redaelli TK16. A good alternative is any two-layer rotation-resistant rope with plastic, such as Verotop S+ or Python DynamiQ.
Why rotation resistant: the kelly rope is attached to a swivel on top of the kelly bar. Rotation-resistant ropes can work with a swivel; ordinary six- or eight-strand ropes should not be used with one, because the swivel lets them unlay under load.
Why plastic: the plastic layer keeps the strands from rubbing on each other, holds lubricant in and keeps dirt out, and helps the rope resist crushing on the drum.
Galvanized or bright for a kelly rope?
Galvanized is often the better choice. The kelly rope runs on a single part over only one or two sheaves, so the small loss in bending efficiency from galvanizing doesn’t matter. Dirt and aggregate are a bigger threat than humidity, and a galvanized rope with less grease picks up less dust.
What end fitting does a kelly rope need?
A thimble eye sized to the swivel on the kelly bar, secured with a single aluminium sleeve (ferrule) of the European type. Check the pin hole (bore) diameter of the thimble on your old rope or in the rig manual; European specifications often list it as “Bohrungs-Ø”.
Don’t order a kelly rope with two stainless duplex sleeves instead. With two sleeves the eye doesn’t sit directly in line with the rope. Everything hanging below the eye then sits crooked, and drilling becomes much harder.
Find the ropes for your rig
Kelly, crowd and auxiliary rope sizes, lengths and part numbers for every rig we have data on:
Frequently asked questions
Should a kelly rope be the same as a crane hoist rope?
No. A kelly rope takes constant shock loads but relatively few bending cycles, and it works with a swivel. The right construction is different.
My kelly rope birdcaged. Is it the rope?
Possibly, but check the sheaves and the kelly bar too. A kelly rope that is right for the rig, on a rig in good condition, should wear out with crown wire breaks.
How many hours should a kelly rope last?
About 2,000 hours, if it is the right rope for the rig and the rig is in good condition.
Why does my kelly hang crooked after a rope change?
Check the eye. A kelly rope made with two stainless duplex sleeves instead of a single aluminium sleeve holds the eye out of line with the rope.
Can a crowd rope be made to last longer?
Usually. Crushing is the most common cause, and it can often be fixed by choosing a more crush-resistant rope.
From our inspections
Case study: Damage at the dead end of a drilling rig rope: shorten or replace?