Loss of properties in Steel Wire Rope at 80 to 100'C 2

[BrianBT]

In a meeting to discuss discard criteria of Steel Wire Ropes a Rope Manufacturer suggested that the frictional heating effects of ropes formed from multiwire overlays subject to cyclical bending would lead to a reduction in service life due to other than fatigue.

Whilst aware that the wire rope can reach temperatures of 100+ 'C I was under the belief that this exceeded the pour point of the Grease, lubrication was lost and there follwed an increased wear mechanism which was the route cause.

But I was told this was not simply the case and if it were potentially an issue other lubricants could be used with substantially increased pour points. Instead I was told it was a metallurgical effect of the metal.

The rope are made for wires of typically a non-alloy carbon steel with a carbon content of 0.4 to 0.95% tensile strength 1760 to 2360 N/mm2. They may have been through a compacting process which involves crawing the wires through a shaped die.

Can anybody please suggest what mechanism could lead to loss of properties in the 80 to 100'C range. A subjective assessment on the effects of this mechanism.

 

[metengr]

The only advice I could give you is to discuss the above with another reputable wire rope manufacturer to sort out details. I really can't think of any other specific damage mechanism that could result in reduced service life other than wear/fatigue/corrosion damage mechanisms.

 

[FennLane]

I have been involved in the manufacture of a 1000 Tonne Wire Rope Testing machine used for testing and evaluation of wire ropes used in Mine Shaft Elevators and commssioned by a Bureau responsible for Safety in Mines.

Tensile testing of ropes was one step in the evalaution of ropes used in this environment but also much emphasis was placed on the detailed 'unwrapping' of test sections to examine the wear that had taken place, the amount of frteeing that had occured and the level of corrosion.

There were criteria established for all of these apsects of the rope and used in a decision matrix of when to replace cables due to risk assessment.

I could not accept a statement that suggested that transient tempertaures of 100 degC would be responsible for reduction in properties that shortened the life or ropes without significnt evidence as 100degC doesn't provide much in the way of an Activation energy for any damaging structural changes in this type of steel.


I would have to agree with metengr that wear/corrosion and fatigue are the real causes with damage due to fretting also an issue as lubrication breaks down. If you look at the inner structure of a 10 year old 70mm diameter locked core rope the level of corrosion and damage that can be found is staggering and it never failed to surprise me that ropes that looked dreadful and had several broken strands still generally met the required tensile strength criteria.


It must be worth a discussion with an organsiation responsible for Safety in Mines to see if they will provide copies of their inspection criteria. If they won't oblige then Insurance Companies such as Lloyds or DNV will have this type of document.

 

[BrianBT]

many thanks for your replies. These are in align with my own thoughts. I have contacted anouther major rope manufacturer and they are also in agreement with what you say. I have read several documents pertaining to Mine Lift Ropes which has recognised such as the importance of d/D ratios against bending fatigue and had not seen anything that suggested this.
There have been a couple of experiments recently considering the effects of heat generation in cyclical bending against the rope integrity and again I could not see that there results differed from our understanding.

I have requested the rope manufacturer to demonstrate the mechanism for this. I guess its should also be noted this company ( and their client who is a major Marine Contractor) do not recognise the significance of ageing ( loss of strength due to loss of ductillity thereby inability for individual wires to share the load) in the wire rope, something which has been universally accepted by everybody else which much evidence.

If the Rope manufactuere come back with an explanation I will post otherwise many thanks for your assistance