I forgot to mention another well-documented cause of copper tube failure; electrolysis. Same old electro-activity series stuff. Electrons and atoms jump where there is a shortage. I cannot recall the electrochemistry. With a sensitive DC meghommeter you can find the current. AC does not do it; the process reverses each cycle and nothing is moved to cause loss of metal. DC, even very small microamp currents of very low voltage will do it. This often occurs from electronics grounded into the electrical system that grounded to a water pipe, either by intent or by default. New electrical codes call for the entire reinforcing steel in the foundation to be used as a ground instead of the water pipe. Some EEs specialize in finding and correcting these faults. Gas piping systems routinely include sacrificial anodes (Magnesium, I think, because of its high electro voltage), to bleed of the current without causing corrosion to the ferrous gas piping. Another cause of electrolysis in metallic piping is induced currents. It is no longer allowable under many codes to place electrical power wiring and metallic gas piping within about two feet of one another because the field around the electrical cable can induce currents in the gas piping that will rapidly (a couple of years, perhaps in months) perforate the gas pipe, even if it is coated on the outside with a corrosion preventing plastic. The most pervasive and common cause of premature failure of copper piping systems is less esoteric; non-water soluble (grease-based paste) fluxes. The flux is used to make a optimal chemical environment for soldering, brazing, and welding. It is usually intentionally mildly corrosive to remove the film of oxide that forms instantly on the copper with exposure to air. This permits a better bond between the filler metal and the tube. The soldering paste will linger on the surface of the pipe even in the flow of water, and the part in contact with the metal will dissolve the pipe. New codes ban non-water soluble fluxes. The ASTM standard for copper tubing is 99.90 percent pure Cu. James-Osbourne: Holmes -----Original Message----- From: [email protected] [mailto:[email protected]] Sent: Saturday, October 20, 2001 1:49 PM To: [email protected] Subject: CS>On the Corrosion of Copper in DW In a message dated 10/20/2001 12:23:41 AM Eastern Daylight Time, [email protected] writes:
Subj:CS>RE: Stainless dangerous? Date:10/20/2001 12:23:41 AM Eastern Daylight Time From: [email protected] (Kevin Nolan) Reply-to: [email protected] <mailto:[email protected]> To: [email protected] In Digest #951, James-Osbourne: Holmes wrote: "I use stainless cookware, and do all of my cooking with the same distilled water with which I make silver. I think it depends on a whole bunch of factors. I doubt very much if the leaching in practice is of any consequence whatsoever. "Copper is another story. DW dissolves it quite rapidly; such that you cannot use ordinary copper water tube for DW distribution. It will both perforate quickly---exactly how fast I don’t know—and put a lot of copper in the water. I suspect--but do not know---that it will put a potentially toxic amount of Cu into the water, depending on how much you drink. If one had a sensitive scale, you could put a chunk into DW and weigh it after it had been in there a while, constantly changing the water so that the dissolved copper would not slow down the process. The “Waterwise” still manufacturer may offer solid information about the various grades of SS. This would still not duplicate the process of running continuously fresh DW through a pipe." Some worthwhile advice there, James. Reminds me of a story run a few months back on TV here in Oz, about the huge cost of corrosion in copper water pipe. It's locale dependent but occurs all over the world. Apparently no-one has an answer as to why it happens or how to cure it (apart from replacing the pipe). Interestingly, there seemed to be a correlation between higher levels of dissolved iron picked up from ground water, and copper corrosion levels JOH: The interesting thing here is that a copper pipe (which I'll assume is 99.9+% copper) should NOT dissolve in DW because (unlike zinc, for example), it is less reactive than hydrogen. The only thing I can think of is that perhaps there is another, even more noble, metal in the vicinity so that a corrosion cell is set up. What relatively common metal is more noble than copper? Beats me. Roger
