Copper Wire Embrittlement

[SomeYahoo]

I was wondering if anyone had experienced copper wire embrittlement. Working on a generator, I noticed that some of the wires (near a connection point) were stiff. In addition to this, the silver coated stranded copper wire had darkened (indicating silver oxide formation).

I believe that this had caused a high-resistance connection. Data collected indicates that temperatures approached 300°F. I think that this covers all the symptoms that I know of, but if you need any additional information/clarification, I will do my best to oblige.

Does anyone have any insight on how this happened and/or the metallurgy involved? Any and all insight is appreciated.

 

[itsmoked]

further info please; what kind of facility? Any Hydrogen Sulfide (rotten eggs) around? Other gasses?

 

[SomeYahoo]

It is outside in the open air (actually above asphalt if it matters). I don't believe this is anything odd.

And no, no rotten eggs around. Could sulphur in diesel fuel (exhaust) cause this?

 

[itsmoked]

I doubt it but read on. HS will dissolve copper VERY quickly. And as with all chemical reactions the rule is the reaction rate of a chemical process doubles for every 10C in temperature rise. So if you had a little HS floating around and elevated temperatures I could image an installation that might last 5 years might last 8 months with HS around.

Okay so if you're not in some chemical plant or worse an oil field then HS probably isn't it.

However the rule mentioned above still applies. So if you have copper wires normally running around 300F then oxidation and chemical reactions between dissimular metals will speed (way) up. This is simular to your incandescent lamp holders puking-out after ten years and when you take them apart the copper wire is black and the screws are 'changed'.

Copper is embrittled by Hydrogen, Oxygen, Bismuth, Antimony and Mercury. Also apparently copper will become brittle due to inclusion of Sulfur molecules thru temperature cycling. You could find Sulphur in your diesel.

 

[IRstuff]

Perhaps there's a bit of work hardening. If the cables are being flexed from vibration or other motion, the copper could get work hardened.

Since work hardening changes the crystal structure, it would be possible to get a resistance change.

TTFN

 

[BrianR]

The silver plating is used on copper to extend its operating temperature range and is good to at least 200 degC. Silver is very sensitive to sulphur products too and goes black.

 

[electricpete]

Is it possible there is the other half of the chicken-or-the egg question? Embrittlement caused a high-resistance hot connection, or high-resistance or hot connection caused embrittlement. Original cause of high resistance hot connection could be varied... connections not properly torqued or crimped etc

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[BrianR]

I copied this text from a site for audiophobes who are seriously into copper:

"It is worthwhile to point out that the copper wire industry did not start making OFC wire for the needs of the audio industry! It was first made because the windings of large electrical generators, made from standard copper, would became brittle and fail due to their continuous exposure to high temperature, high g-forces and vibration. Generator windings made from OFC copper last longer. Apparently it is now routine for much, if not all, copper wire to be made under OFC conditions. Because of this, the difference in cost between ETP and OFC copper wire is small."

http://forums.audioholics.com/forums/archive/index.php/t-8852.html

 

[SomeYahoo]

Interesting thoughts folks. I was also concerned with the chicken/egg issue, but either way I believe there is a chemical reaction involved. If there was a poor connection, the heat there likely sped up the process.

IR - I don't believe it is work hardening as the wires are strain relieved fairly well. In addition, it only happened on some of the wires... likely the ones that got hottest.

Looks like I have some research to do with copper and silver reacting with sulphur. Thanks for the info!