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Joining steel pipe to galvanized pipe
Q. Is it ok to join galvanized pipe to steel pipe? I was told this should not be done due to galvanic corrosion. Dissimilar metals? Zinc coating and steel? I know about joining copper to steel, but have never heard it applied to galvanize and steel.
Thank You,
Supervisor - Palo Alto, California, USA
2004
Galvanized pipe is steel pipe with a zinc coating on it to serve as galvanic protection. As a thought experiment, recognize that even if all of the pipe were galvanized, the time will come when the zinc coating will be worn away in areas and you would have a mix of galvanized pipe and steel pipe -- so I foresee no calamity. But what is going to happen in your situation is that the zinc coating will (to a very limited extent) protect the plain steel pipe as well as the galvanized pipe. In so doing, the zinc will be less able to protect the pipe that it was coated onto because it will be eaten away faster, perhaps much faster.
If the zinc coating is important to one portion of the pipe, you need a dielectric union; if the zinc is unimportant and just happens to be there, without a fuller understanding the installation I see no problem. Good luck.
Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
2004
Using zinc plated threaded rods and hardware on plain steel beams
Q. I am installing two steel channel beams on an existing main center beam of a house so that two lally columns may be removed. The new steel beams will sandwich the existing wood beam and then be through bolted. My question is: will there be corrosion if I use zinc plated threaded rod with, washers and nuts or should I use steel components to avoid dissimilar metal contact between the beam and the bolts? Thank you.
Anthony PisaniRemodeling contractor - Franklin, Massachusetts, Norfolk County
April 23, 2014
A. Hi Anthony. The interior of homes is usually a pretty good environment where corrosion issues aren't severe, and therefore the zinc plating on the rods and fasteners may in fact last a very long time, especially if this is the living space rather than the basement. The situation is that the zinc plating won't hurt anything, it just wouldn't help much if there was a corrosive situation because the large surface area of the beams would sacrificially consume the zinc plating on the small surface area components very quickly. Then you'd have steel beams and steel hardware, which is probably still fine.
Regards,
Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
May 2014
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