Accidental Annealing of Wire Rope

[Flareman]

We use galvanized CS wire rope as Guy Ropes to support tall structural stacks. Typically the ropes we use are fully stranded with no core (such as 1 x 37) or may sometimes be fitted with a wire core (6 x 19 IWRC). The quality of the steel is "Improved plow" with a UTS in the region of 220,000 psi. Because of the manufacturing procedures, the steel has a high strength with no discernible yield so it can be used elastically up to about 50% of its UTS. Typical rope diameters range from 0.5" to 2".

I have a specific situation where some guy ropes (1.25" and 1.5") are located in the potential path of hot flue gases from a nearby combustion process. The hot stack is 9 ft diameter and the hot gas could emerge at temperatures up to 1800 degF. My calculations of the down wind plume conditions suggest that a momentary temperature as high as 1400 degF could occur at the guy ropes under certain conditions. Averaged over a longer period for wind variance the mean temperature might drop to perhaps 970 degF over 1 minute, 650 degF over 2 minutes.

My concern is that a period of high temperature exposure, albeit inadvertent, might begin to anneal some of the strands and soften the rope, significantly reducing its UTS and changing the important structural properties. I don't have a good feel for the TTT conditions, and am not well versed enough metallurgically to know the material properties from the crystalline structure. Hence my plea for informed opinions about how severe this concern may be.

Thanks for any input.

David

 

[metengr]

Flareman;
Not to throw water on your calculations, what I would suggest is to confirm actual wire rope metal temperatures using an infrared (thermal) gun or camera. We have these around our plants and they are very handy at determining surface metal temperatures of objects. Get this data and see what you really have in terms of a problem.

 

[ornerynorsk]

On smaller installations, I have seen deflectors used to protect temp sensitive equipment. Don't know if this would be practical or possible in your situation. Metengr is right, though, it should be verified. Could you install a recording pyrometer or other sensor to get a historical picture of it? Just my 2 cents.

 

[CoryPad]

Great advice from metengr and norsk. You may even consider a theromocouple attached to the wire to get highly accurate metal temperature measurement.

Regarding your actual question, if the steel is exposed to the temperatures you mention, it will lose strength. You may have problems with creep, reduced strength, or both.

 

[Flareman]

Gents, thanks for the initial input however I wasn't totally clear about this. The guys exist, the combustion unit is future.
I have to decide whether to
- tell the client there's a potential problem, and he has to move the planned combustion unit ($$ involved for re-engineering) or
- not raise the issue at all because it's not going to be a problem (because I can preclude my temperature ranges from the annealing range, or because my trusted eng-tips advisors don't think so!!)

Hence my need for a "primer" on the annealing temperatures and holding times for the high strength steel used for the ropes.

David

 

[MikeHalloran]

Stacks emit things other than hot air.
What could condense on a cold wire?
What could _that_ do to the wire?

Moving a stack before it exists is cheap.



Mike Halloran
Pembroke Pines, FL, USA

 

[Ron]

I would suggest you tell your client:

a. You have a potential problem (it would appear the potential is relatively high)
b. You can move the stack, or
c. Your firm can design a "work-around" that might include deflectors, diverters, etc.

If you know of other stacks within the property with similar conditions, do as Metengr suggested...get a thermogram of the plume and you'll have better data with which to decide.