Galvanic corrosion of nickle copper alloys (nicopp, cunifer)

[Tim?]

what I'm doing. I'm trying to install copper-nickle brake lines but I'm trying to figure out what fitting to use. options are brass, steel, or stainless(which would fluctuate between active and passive given road salts, etc). I'm joining with aluminium and carbon steel and obviously copper-nickle line. Right now, i don't really have any data as for how the lines react with the steel nuts, and it seems stainless is a fairly safe bet, but, runs risks given metallurgy of the aluminium in question and the stainless in question. So, I'm hoping someone can help me sort out some of these unknowns.

i've been doing a lot of reading, and, can't really come to any certain conclusions because it seems there are some base elements to consider, and then, the environmental situation seems to play a huge role. For example, high alloy stainless and cupronickle under theoretical situations react and the copper-nickle alloy should become and anode and corrode heavily. However, http://www.copper.org/applications/marine/cuni/pdf/124_schleich.pdf provided a situation where there was a biofilm over the high alloy stainless and essentially there was no reaction. this is to say, in a normal atmosphere the materials should react, so, this is essentially my point.. I'm not sure where to go with any conclusion.

a major point in this discussion seems to be this "as long as the cathodic surface area(the more noble metal of the galvanic couple) is very small in comparison to the anodic surface area(the less noble metal) no change in corrosion behaviour is observed)" via http://www.euro-inox.org/pdf/map/Contact_with_Other_EN.pdf

However, that reality isn't so well met. The 'nut' in question will be fairly small relative to whatever its being connected to. a nut relative to a small aluminium master cylinder, or even smaller wheel cylinder. However, size ratio to a caliper is probably a 'safe' size difference. There is also the nut itself to the line, which would be about relative to the master cylinder situation, as the line is so small relatively.

A:so, here is my issue consider nuts on the line, brass is essentially out as it will be heavily cathodic relative to aluminium and steel, but, is non reactive to the copper-nickle line. B:stainless is a big mystery, it has little to no reaction with steel, but, potentially is either mildly reactive or non reactive with copper-nickle as well as aluminium. C:steel nuts will be an anode on the line, also potentially taking the line with them, also are corroded easily in oxygen(normal atmosphere) as well as their zinc coating being heavily anodic with copper-nicklehttps://[URL='http://www.fastenal.com/content/feds/pdf/Article%20-%20Corrosion.pdf']www.fastenal.com/content/feds/pdf/Article%20-%20Corrosion.pdf[/URL], however, no reaction with aluminium or steel, yet, everybody seems to use steel nuts..

lastly, there is considerations for the actual connections to the material. the flared end of the copper-nickle hose will be in direct contact with whatever material its being mated to. i guess in europe this stuff is more common and used with success, but, it seems like it should be reacted with any aluminium is contacts??

http://www.npl.co.uk/upload/pdf/bimetallic_20071105114556.pdf (other considerations)

---edit
i apologize, this probably should have been in the materials section

 

[SteamKing]

Why copper nickel brake lines? Why not use stainless steel if you are worried about corrosion? It seems to me that stainless would be less expensive than Cu-Ni and be easier to obtain/have fabricated for your vehicle. Using SS, that's a couple fewer dissimilar metals to put into the corrosion chain of your brake system. It's also not clear if Cu-Ni alloys are compatible with the hydraulic fluids used to fill the braking systems of most vehicles.

With Cu-Ni piping systems in the marine environment, usually there is an upper limit to the salinity of the seawater to which these systems are exposed. For use in road conditions, these salinity limits may be exceeded. Also, Cu-Ni is susceptible to attack when sulfides or ammonia are present. It's also not clear if Cu-Ni is an approved substitute material to use for fabricating brake lines according to standards organizations like the SAE (Society of Automotive Engineers). If your retrofitted vehicle should suffer a mishap, using unapproved materials in the braking system would just make the situation all that much worse for you.

 

[Tim?]

stainless lines actually present their own issues, being more cathodic, they'll eat aluminium and steel fitting alike. I'm not so worried about sulfur, mostly would be dealing with sodium chloride(as road salt), copper-nickle shows superior corrosion resistance in 'salt sprays' over everything else, is cheaper than stainless, and margins easy to work that steel, and stainless lines are essentially out of the question as far as forming/flaring. specialty tools because stainless work-hardens so readily, flaring stainless lines is next to impossible. there are a few companies selling nickle-copper lines on the market, aside from ordering something from a foreign market(say china), it will be DOT approved. not to mention its used in many european markets as an OE solution.

alright ssooo, i actually was talking with someone on another forum, and, came to the conclusion there that there essentially won't be any issue. looked at the conductivity rates, apparently being within 0.15mv is ideal, 0.30 is an upper limit, copper-nickle and aluminium aren't a huge deal, also, it seems in practice, environmental factors always work out different than theory/lab results. ssoo, vian http://www.ssina.com/corrosion/galvanic.html http://www.bssa.org.uk/topics.php?article=89 what i found is that the stainless nuts and copper-nickle lines should be perfect, same for into the steel areas, the copper-nickle flare against the aluminium should also be fine. However, there is some 'unknown' relative to what takes place with the steel fittings normally used on the copper-nickle. if they are zinc chromate plated, the chromate should provide a good barrier until the zinc is used up, but, the steel nuts will be fairly anodic in this case, not sure why its not seen or reported. that being said, stainless into aluminum given any electrode(water/salt/etc) should case fairly adverse reactions, unless its 430 stainless. sssoo, my final solutions here was to use a brass adapter for connecting to aluminium bits as a sort of 'insulator' between the stainless nuts, however, if I'm honest, using a steel adapter would be better as it would react less with the aluminium, but, obviously would corrode most easily. ssoo, I'm pretty much figured out at this point.

"Clips do not suffer accelerated corrosion as might have been anticipated probably because they in turn are connected to larger steel members. An advantage has been found in that it is easier to disconnect copper-nickel tube from brake cylinders. Naturally, some corrosion of the steel nut occurs but it appears there is less tendency for the nut to bind onto a copper-nickel than a steel tube" - http://copperalliance.org.uk/docs/librariesprovider5/resources/is49-copper-nickel-brake-tubing.pdf

as it turns out, the area of the anode plays a large role in determining how reactive the connection will be. this is to say, a small master cylinder could be an issue, however, as its bolted to the car itself, there is a very large surface area to deal with.