Metal Compatibility

[Archena]

Thanks!!!! I really appreciate it!

[christo]

Could there be any chance the nut was pot metal or zinc?

- that would explain a lot to me - I've seen a lot of cast metal nuts as well as sheet metal

[Archena]

I don't know what pot metal is. I've never seen zinc take a polish (dunno if it can) so I really doubt zinc. I wouldn't have thought it was sheet metal - it had an interior concave which I wouldn't expect from a punch. I remember it being steel. I'll check when I go back to the hardware store - they still carry that brand...

Or, I might still have the 2 inch nut I bought in the package. I'll check.

[fortran]

If you connect dissimilar materials in the presence of an electrolyte, corrosion can always happen. Pure water at pH 7 isn't a very good electrolyte, but most water has dissolved salts in it of some kind. Even heat treating a metal can cause it to become different enough from an un-heat treated version of the same metal, to make it look different. What is happening is an electric circuit is being set up, with some of the current traveling through the electrolyte and then returning through the dissimilar metals. Brass gets used in many kinds of plumbing, because it is lousy at conducting electricity. However, it is still better than things like plastic at conducting electricity.

The best thing to do, is use the same material. Next best, is if you have to use different materials, separate them with something like plastic which doesn't conduct electricity (is a dielectric).

[Xabia Jim]

This is a huge issue in the boating industry where you have salt water and metal thru-hulls, steel shafts, brass props, etc. If stuff corrodes, boat can sink... They attach the sacrificial zincs at various places around the boat to protect (slow down) this corrosion. These often need to be changed out more than once a year.

Years ago I worked for an acid distributor. They had one truck go out with a load of nitric acid, I think in a stainless steel tank truck but someone had put a brass plug somewhere....made quite a mess.

[fortran]

Corrosion is a big problem all over. Steel are useful materials, but they get over specified. I suppose familiarity is part of the problem, but the reason people aren't familiar with other materials, is that these other materials are never specified.

A good example I see every day, is a metal box in a ditch, something to do with underground pipe or cabling. The paint either wasn't applied perfectly (likely) or the paint got chipped. In any event, some of the underlying steel is exposed, and since ordinary steel will not form a dense adherent oxide (rust), the paint blister and falls off, exposing even more steel, and pretty soon it is just another rusty piece of junk in the ditch. Aluminum or fibreglass would probably both work better, and look nicer for a longer time.

[Archena]

Thanks, guys. I'm moving shortly so someone else (my landlords) can figure out the plumbing and I really appreciate the help with the other project.

I knew that nut was steel!

[CajunKnight]

check with a local hardware and look in the cabinet making area, you can get copper plated screws. They are a bit higher in cost but will handle the job quite well.

[Archena]

Thanks! I appreciate it!