I can never remember which metals shouldn’t coexist. I just added a galvanized coupling to an otherwise brass section of compressed air line. Am I asking for trouble?
Thx,
Scott.
Always remember those first immortal words that Adam said to Eve, “You’d better stand back, I don’t know how big this thing’s going to get.â€
Replies
Scott,
Won't be a problem .
if it's a cheap china coupling... it will rust from the inside... at least in my experience
p
I was always told that using a brass nipple to go from copper to steel was OK. Never understood the logic of it but that's what I was told.
Is that an "old plumber's tale"?
"Let's get crack-a-lackin" --- Adam Carolla
Brass nipple atleast 6" in length is code acceptable for transitions from ferros to non ferros.“It so happens that everything that is stupid is not unconstitutional.” —Supreme Court Justice Antonin Scalia
Is bronze better?
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Code accepts it, but it's not the best practice for water. The OP may well be OK if his air is dry enough. For W/H's, I've had much longer lasting results using galv in the heater to stainless braid to brass to copper. Stainless seems to be the best for coexistence.
-- J.S.
What about gas lines? Aren't most shut off valves brass that are threaded onto black pipe?
Yes brass / bronze.
But not a problem, copper to ferros metals will harm the copper if there is enough moisture“It so happens that everything that is stupid is not unconstitutional.” —Supreme Court Justice Antonin Scalia
Sure, but gas isn't an electrolyte. Basically, water is the only electrolyte we have to worry about in our plumbing. The OP was concerned about compressed air, in that case, condensation is the only consideration.
-- J.S.
WH's since they are equipment & require a union of some sort, I usually use a die-electric union or a flex insulating connector---- 2 birds with one stone.“It so happens that everything that is stupid is not unconstitutional.” —Supreme Court Justice Antonin Scalia
I've tried dielectric unions, IIRC they failed in under five years. Maybe I just got bad ones. The stainless braid flexes are still looking like new. I wish I'd thought to write the date on them when I put them in.
-- J.S.
Those stainless braided ones should be insulating as well IIRC“It so happens that everything that is stupid is not unconstitutional.” —Supreme Court Justice Antonin Scalia
Any two disimilar metals and moisture can cause galvanic corrosion. Your local natural gas utility will have a technician that is usually very knowledgable in the field. Probably a free phone call to sleep easy.'
Have a good day
CLiffy
If it's brass no problem, if it's copper then you will have a problem, but only if moisture is present.
“It so happens that everything that is stupid is not unconstitutional.” —Supreme Court Justice Antonin Scalia
Mixed metals are only a problem in the presence of an electrolyte (water), so if the air is reasonably dry you should be OK. And brass/bronze is supposedly a "safe" metal -- can coexist with either copper or iron.
Worst case it would take 20-30 years to corrode through. Bigger danger is causing loose bits of rust in air, but only if the air's pretty wet.
Brass is not really a "safe metal"- it can cause galvanic problems with galvanized and steel components in the presence of an electrolyte, but to a considerably lower extent than would be experienced with a direct transition between steel or galv and pure copper. Brass is far less electrically conductive than copper, so a long enough piece of it moderates the galvanic currents when you do a copper to galv or steel transition, reducing the rate of corrosion very considerably. Stainless works the same way: although there's a galvanic series difference between galv or steel and stainless, and similarly between stainless and copper, in practice the transitions are not attacked except in very corrosive services with strong electrolytes.
Unless an air line is mounted in a wet location, or left to fill with condensate, there won't be any significant galvanic corrosion worries.
Since this is a compressor line, it seems that there will always be moisture present inside this coupling and line.
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Yeah, but enough to serve as an electrolyte? That would basically require standing water in the joint.
People never lie so much as before an election, during a war, or after a hunt. --Otto von Bismarck
Maybe so, but I've seen the problem on roof flashings that only had water flushing over them, not standing around.In any case, since this is an accessable line in shop or job space, there is no problem, just change it someday, if the compressor itself lasts that long.
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Don't worry about it, there's got to be millions of brass nipples connected to galve. with no problems; it use to be commonn to connect the two together,[Old days]. Lots of luck. ...................................................... "If all else fails, read the directions"
Probably not a problem in an air line but not good in a water line.